Processing and Fabrication of Advanced Materials VIII

The following sections are included:

• PREFACE

• ORGANIZERS

• CONTENTS

In this paper the cyclic fatigue and fracture characteristics of a spray atomized and deposition processed Al-Cu-Mg-Ag alloy are presented and discussed. Specimens of the alloy were cyclically deformed to failure at ambient temperature under stress amplitude-controlled conditions. The high-cycle fatigue and fracture characteristics of the alloy are compared with a conventional ingot metallurgy processed counterpart and discussed in light of intrinsic microstructural effects, nature and magnitude of cyclic stress, and ductility of the microstructure.

The precipitation sequence responsible for the age hardening behaviour of a cast Mg-5.1%Y-1.9%Nd-0.9%RE alloy (WE54) has been investigated over the temperature range of 150-300°C, using analytical electron microscopy. Plate-shaped precipitates of the β″ phase with an ordered DO₁₉ structure were observed to form at temperatures between 150-200°C. β′ were observed at temperatures between 175-300°C. Only β precipitates were observed when ageing was carried out at 300°C and above. Precipitates morphologies, composition, crystal structure and crystallographic orientation relationship were determined for the various types of precipitates formed when ageing at different temperatures.

The alloy WE54 initially in the standard T6 (solution treated at 525°C for 8 hours followed by ageing at 250°C for 16 hours) condition when exposed to temperatures below 200°C for 1000 hours and longer, suffered a reduction in ductility. The origin of the embrittlement was found to be due to the formation of G.P. zones from residual solute which is in equilibrium with the β phase.

Burnishing is a chipless cold working finishing process, by which smooth and workhardened metallic surfaces can be produced. In this paper, an attempt has been made to study the effect of the number of tool passes on surface characteristics and fatigue life of cast Al-Cu components. The conducted experimental work shows, that improvements in surface roughness and fatigue life can be achieved by the application of this process. The increase in the surface hardness and the depth of workhardened subsurface layers of the considered cast alloy were also studied.

Laser glazing of materials has grown significantly in recent decades due to its success at improving surface properties of both metals and ceramics. While applications are far ranging, and may include glazing of semiconductors in the microelectronics industry, benefits primarily stem from improved microstructure, i.e., reduction of porosity and creation of finegrained structure. Obtaining these results, however, requires understanding the relationship between input parameters such as laser intensity and scanning speed and outcome such as extent of melting.

A three-dimensional conduction model was formulated to predict the extent of melting. The model incorporates a unique variable-absorptivity function to account for absorptivity differences between solid and liquid phases, and also considers energy loss associated with phase change of melting. Predictions were compared to results from laser glazed type 304 stainless steel and to results from a constant-absorptivity model. The results were derived from experiments using a continuous-wave CO₂ laser over a range of power and scanning speed. Good agreement was found between the model and experimental results.

The Influence of humidity and chlorine on mechanical strength of fresh and reused tin–lead solder (solder dross) was investigated. Solidification rate and temperature profile was also discussed. Calculation showed that the solder solidified almost instantly.

Butt, simple lap and double lap joints of copper were prepared. No- clean flux rosin and solder mask with the thickness control of solder joint were implemented.

Salt spray fog test for sets of tin- lead joints was carried out. Samples exposed for different time was subjected to shear and tensile tests. The strength of the fresh and reused solder decreased with exposure time. White substances were found precipitated at the edges of the solder joint. X-ray diffraction analysis showed that these substances were PbCl₂ and PbCO₃. This result indicated that Cl^- ions attacked Pb in the solder and formed white porous substances that would weaken the strength of tin – lead solder.

In this study, Mg₂Si was synthesized from elemental powders of magnesium and silicon by mechanical alloying using a planetary ball mill. To study the influence of ball size, three different sizes of balls were employed. Although larger balls possess higher kinetic energy, experimental results showed that smaller balls may induce faster reactions between Mg and Si elements in comparison with that using bigger size balls if the angular speed of the ball mill was kept the same. Influence of kinetic and impact energies of ball milling on the formation of Mg₂Si has been studied. Mechanism of the fast reaction using smaller balls is discussed. Theoretical simulation showed that the total impact energy using small ball is higher than that using large balls even though the impact energy per hit using large ball is higher than that using small ball. This phenomenon is attributed to the difference in the amount of powder entrapped between two colliding bodies and the true speed of the balls.

A low-cost P/M processing route has been developed for the production of randomly packed hollow sphere structures (RHS). A fluidized-bed process allows mass production of iron-based green spheres with a large choice of possible sphere diameters and wall thicknesses. The individual sphere diameter may vary between 0.5 and 10 mm with wall thicknesses ranging from 20 to 1000 µm. From these green spheres, hollow sphere structures are formed in a special die. The subsequent consolidation and joining of the individual spheres is accomplished in one sintering step. Thus significant cost savings can be achieved over former approaches, where cellular metallic structures were obtained by brazing or sinter bonding of single metallic spheres.

With this method, test specimens from stainless steel 316L have been manufactured and their physical properties, i.e. density and compression strength, were measured.

In this paper, the microstructure, tensile response, cyclic stress amplitude-controlled fatigue response, damage tolerance and fracture characteristic of a copper-niobium microcomposite based on an oxide dispersion strengthened matrix are presented and discussed. The microcomposite samples were deformed in uniaxial tension and cyclically over a range of stress amplitudes, at both ambient and elevated temperatures, and at two different stress ratios. At a given stress ratio, an increase in test temperature was observed to have a detrimental influence on the cyclic fatigue life of the microcomposite. At given temperature the fatigue resistance. The influence of reinforcement on the mechanical response, damage tolerance and fracture behavior of the material is discussed in light of the specific roles of intrinsic microstructural effects, nature of loading, stress ratio, test temperature and macroscopic aspects of fracture.

This paper investigates the conditions for ductile-regime machining of (100) silicon wafers. Single crystalline diamond tools with 10-40 nm edge sharpness were used to machine the wafer at either a constant depth of cut, or in a taper mode to vary the depth of cut up to 1 µm. Feedrate was varied as a percentage of tool nose radius and the machining process was performed on an ultraprecision machining system. The surface and subsurface integrity were then characterized by atomic force microscopy, phase shift interferometry, and ion beam micromilling.

Ductile regime was achieved when machining along the <110> directions and the maximum chip thickness of less than 0.5 µm. Machining conditions that formed thicker chips lead to pitting, microcracks and slip lines. Such defects, could be more than 1 µm deep, were found along the <110> directions and occasionally along the <100> directions. Surface roughness below 10 nm was measured in a ductile regime area, but was as high as 170 nm in a fractured area. When cutting at a depth of cut in the magnitude of the tool edge sharpness, the surface finish was degraded due to radial cracks in the lateral plane due to rubbing between the tool and the workpiece.

A dual phase titanium alloy of the Ti-6Al-4V type was tested at a slow strain rate under uniaxial tension in ambient environment. The fracture was found to be largely transgranular, but the fracture initiation was observed to occur from grain boundary microcracks. A fracture model has been proposed to explain the interesting phenomenon. According to the model, the fracture begins with microcrack initiation at α grain boundaries (especially the triple points) or α/β interfaces. As the applied load increases, sliding occurs in those grain boundaries whose orientation coincides with that of the maximum shear stress. The titanium alloy has a very low work hardening rate; therefore, above a certain stress level, strain localisation occurs to form concentrated shear band at roughly 45 degrees to the loading axis, leading to the final transgranular fracture by shear.

Formation of the nickel-cadmium alloy in the negative electrode of nickel-cadmium cell subjected to continuous charging at elevated temperatures (40°C~45°C) is shown to be one of the causes of the "stepped" discharge curves. The alloy has been characterized by electrode potential measurement and X-ray diffraction method. The potential lowering during discharge is related to discharge of the alloy. X-ray diffraction suggests that the nickel-cadmium alloy can be formed during charge in negative electrode by interaction of the two metals. Addition of Ni (OH)₂ into Cd (OH)₂ active material is found to form the alloy more readily than sintered negative electrode alone.

Mo/Cu functionally graded material (FGM) was fabricated by explosive powder consolidation technique utilizing under-water shock pressure, and microstructural aspects and mechanical properties of as-consolidated and sintered Mo/Cu FGMs were investigated. There were no cracks and no tears in the resultant compact in which continuously compositional change was achieved. The full densification and homogeneous structure were obtained by sintering at 1273 K for 14.4 ks. From the results of thermal shock and cycling test, it is concluded that the Mo/Cu FGM produced in the present study has superior thermal shock resistance and relaxation ability of thermal stress.

In our previous work, we have developed bioactive components by coating a thin layer of hydroxyapatite (HA) onto the inner surfaces of pores in reticulated alumina. In this way, the basic requirements in bone implant are satisfied: (1) a high porosity level due to the nature of the reticulated alumina for an organization of vascular canals; (2) compatible mechanical properties with the bone structure, and (3) a high bioactivity induced by the thin layer of HA for bone ingrowth. In this study, we report the bioactivity behavior of synthesized HA. It has been found in this study that the in vitro bioactivity of the synthetic HA is strongly affected by the structural crystallinity. The bioactivity is found to be effectively reduced at a high degree of crystallinity, which is associated with the formation of a new phase on the HA surfaces. We discuss the underlying mechanisms for the observed bioactivity behavior.

The starting hydroxyapatite (HA) powders with different contents of water and lattice hydroxyls were used to investigate the influence of water on the conversion of the amorphous to crystalline apatite during plasma-spraying. The as-received HA coatings were post-heat-treated in different atmosphere to reveal the role of water molecules during the process of the phase transformation. The results show water plays an important role in the phase transformation. During the coating process, the absorbed water has the capacity of retention of hydroxyls on their position and so promotes the recrystallization of apatite crystallites in the melted HA particles. During the post-heat-treatment, the water molecules in the humid atmosphere not only enforce the conversion of amorphous to crystalline apatite but also promote the transformation of other HA-decomposed calcium phosphates such as tri- and tetra-calcium phosphates into HA. Water is also an important factor influencing the nucleation of cracks and the detachment of HA laminae in the plasma-sprayed HA coatings under ultrasonic treatment.

Hydroxyapatite (HA) powder was mixed with various particulate materials such as glass, α-TCP, TiO₂ and ZrO₂ in different weight percentages for producing functionally graded bioactive coatings on Ti-6Al-4V metal substrate. A functionally graded coating could be obtained by coating the substrate firstly glass (G) powders of known particle size as the bottom layer which was sintered at 900°C for a few minutes. Coating of subsequent layers of HA-G composites of different weight ratios (75%G and 25%HA, 50%G and 50%HA, 25%G and 75%HA) were performed in sequence and these layers were sintered again at 900°C for a few minutes in order to achieve good adhesion between the layers. The same technique was used to produce functionally graded HA-α-TCP, HA-TiO₂ and HA-ZrO₂ composite coatings. These coatings were subsequently subjected to various characterization techniques such as XRD, SEM, EDX, and hardness and modulus measurement by nano-indentation. The XRD results confirmed the presence of the corresponding components in HA composites. Under SEM, the surface morphology of different composite layers was observed and the presence of elements was shown by EDX analysis. Nano–indentation tests revealed that the HA-G functionally graded coating yielded the highest hardness and modulus values in comparison with other composite systems. It was shown that the coating technique adopted is versatile in producing various composite coatings.

The cytocompatibility of N⁺ ion implanted and shot peen surface amorphised Ni-Ti shape memory alloy has been evaluated using the MTT cytotoxicity assay over 48 hours of 3T3 fibroblast contact and growth. In addition, SEM morphological examination and wetting behaviour measurements with full culture media were made. The modified Ni-Ti surfaces did not induce a cytotoxic response over the examination period and the SEM direct observation showed normal morphologies of cells grown upon the Ni-Ti surfaces. These results indicate that the adherent Ti-O₂ rich surface film present on unmodified Ni-Ti is preserved during surface modification. Furthermore, the ion implanted surfaces showed enhanced cellular attachment, which is speculated to be a consequence of modified surface charge distribution.

A novel method of preparation of easily stripped off temporary wound dressing material is disclosed. A tri-layer membrane system for artificial skin is prepared in this study. In this process, the N-isopropyl acrylamide monomer is successfully grafted on the non-woven fabric by copolymerization. It is initiated by plasma to activate the surface of the non-woven cloth. N-isopropyl acrylamide is then grafted onto the surface of the non-woven cloth by γ-ray irradiation. The last layer but the most important of a bovine gelatin with glycosaminoglycans (chondroitin-6-sulfate) is grafted by UV light, which serves as a matrix for the infiltration of fibroblasts, macrophages, lymphocytes, and capillaries derived from the wound bed.

The goal in this work is to provide such a nonantigenic membrane closely resembling dermis in its anatomic structure and chemical composition, which would act as a scaffolding inducing the synthesis of a new dermis. The following describes the construction and animal testing of this artificial skin in extensively damage. In the experiment, the specimen are divided into 4 groups: (1) controlled group without dressing material, (2) non-woven fabric, (3) non-woven fabric grafted with NIPAAm, and (4) non-woven fabric grafted with NIPAAm, bovine gelatin, and glycosaminoglycans from bottom to top in sequence.

After operated for 6 weeks, both controlled group and non-woven fabric group stayed in the proliferative phase where no epidermis or dermis structure has been traced in the section. 6 weeks of postoperation, the third group has been healed completely in the maturation phase. The wound site has been totally recovery with normal dermis and epidermis structure around but the dressing material still stayed on the wound site. In the group of the non-woven fabric grafted with NIPAAm, geltain, and glycosaminoglycans, it has been recovery to the final stage of maturation phase. The wound site has been totally recovery at the 4^th week of postoperation. The dressing material of the group fall off automatically from the wound site without any damage to the skin after recovery. We believe the dressing material will have a great potential in medical application in the near future.

We have previously reported a blast coating method as a new coating method of titanium (Ti) with apatite (AP) at room temperature. The blast coating method gives much stronger AP coating on Ti surface when compared with those obtained by other coating methods at room temperature. As an initial step to evaluate the usefulness of the blast coating method, we evaluated tissue response and stability of AP coated Ti implant prepared with blast coating method using experimental animals. The AP coating stuck tightly on the Ti surface even after implant procedure. AP coated Ti implant showed excellent tissue response and much better osteoconductivity when compared with pure Ti implant. Therefore we concluded, AP coated Ti implant prepared with the blast coating method has a good potential value as osteoconductive implant material.

In reviewing the scientific literature of hard tissue repair/generation it can be concluded that it is worthwhile to evaluate the possibility of obtaining synergistic effects by combining bioresorbable scaffolds with other factors stimulatory to osteogenesis. Theoretically, this can occur at different principal levels. Cytokines, including growth factors such as BMP, the IGFs, TGF-b, PDGF, may be stimulatory to the differentiation of cells of the osteoblastic lineage, thus having the potential to promote an increased recruitment of osteogenic cells. The IGFs, TGF-b, PDGF are known to stimulate the synthetic capacity of mature osteoblasts. Finally, the FGFs are angiogenic and may thus improve nutrition in a healing bone defect by an early establishment of the vascular bed. Presently, the field of growth-stimulatory factors is strongly expanding. Even though the effects on bone of such factors are far from being completely elucidated, it may be expected that some of them will be of clinical relevance in the future. Future developments of de novo biodegradable and bioresorbable carrier and matrix materials treated with growth factors should have the objective to be: biointeractive and biomimetic devices/implants endowed with cell or cell-based signals; synthetic extracellular matrix for enhanced cell interaction, cell polarization, or remodeling; temporal and/or spatial delivery of bioactive agents over short and long time periods.

Medical porous implants have been shown to lead to higher bone/metal shear strength than other types of fixation. Medical implants coated with porous titanium were fabricated by cylindrical explosive compaction method. The central axis of the container has a titanium core with 5mm diameter. Three layers of titanium powders with sphere shape of 300µm to 1mm diameters were set up around the core. The obtained strength of bonding interface between the core and powders is high enough and the surface shows porous shape for favorable to bone tissue growth.

Self catalysed and latent acid poly(ortho esters) (POEs) with different compositions were used to fabricate the microspheres using a W/O/W double emulsion solvent extraction/evaporation method. The characteristics of POEs microspheres were analyzed by size distribution, surface morphology, protein encapsulation efficiency, initial burst and release profile. The results showed that protein-containing microspheres fabricated with different compositions of POEs had different release profiles. For instance, compared with the microspheres of POE prepared from 3, 9-diethylidene – 2, 4, 8, 10 – tetraoxaspiro [5, 5] undecane, a 89/10/1 mixture of cyclohexanedimethanol (CDM), triethyleneglycol (TEG) and cyclohexanedimethanol – monolactate (CDM-mLT) (POE4), the microspheres of POE prepared from a 75/20/5 mixture of CDM, TEG and CDM-mLT (POE3) has a more rapid release rate. It is due to this fact that TEG is more hydrophilic, compared with CDM. So a higher concentration of TEG dimer segments in the POE3 backbone can result in a faster water penetration rate. As a consequence, the degradation rate of POE3 is faster than that of POE4. However, the segments of hexanediol-diglycolate (HD-diGL) are more hydrophilic than CDM-mLT. So the release rate of the microspheres of POE prepared from 3, 9-diethylidene – 2, 4, 8, 10 – tetraoxaspiro [5, 5] undecane, a 75/20/5 mixture of CDM, TEG and HD-diGL (POE2) is faster than that of POE3. Moreover, POE microspheres at 37°C has a higher release rate than at 22°C. The SEM images of POE microspheres showed that all the POE microspheres have smooth and non-pores surface morphology, resulting in a low initial release. We suggest that poly (orthoesters) can be utilized for microencapsulation of active agents such as protein drugs. By using POEs with various compositions, release profiles of protein drug and the polymer degradation rate can be controlled.

In the last two decades, a variety of bioactive particle filled polymer systems were developed for tissue replacement. In this investigation, hydroxyapatite (HA) reinforced polysulphone (PSU) composites were manufactured and evaluated for potential medical applications. HA was produced in-house by reacting calcium hydroxide with phosphoric acid in appropriate proportions. The precipitates were subsequently spray dried to form HA powder. Characterization of the HA included X-ray diffraction (XRD) analysis, scanning electron microscopic (SEM) examination and particle size analysis. HA/PSU composites containing up to 40vol% of HA have been produced. The composite production consisted of drying, compounding in a mixer, compression moulding into thick plates, and machining. Evaluation techniques used included themogravimetric analysis (TGA), differential scanning calorimetry (DSC), HA particle distribution examination and rheological analysis. TGA verified volume percentages of HA in the composites. DSC showed that the glass transition temperature (T_g) of the PSU was not affected by the incorporation of HA. Rheological tests indicated that unfilled PSU and the composites exhibited pseudoplastic flow behaviour.

Aesthetic revolution in restorative dentistry spins around the development of suitable ceramic materials. Though feldspathic porcelain holds promise as one of the best options due to its aesthetic, durability and biocompacibilty, its application is limited since the strength is relatively low. Dispersion strengthening controlled crystallisation and surface heat treatment have been reported in literature to improve the strength. In the present investigation, feldspathisc dental porcelain (Vivodent PE, Ivoclar, licherstein) with potash to soda ratio 2:1 was used as the starting material. Discs prepared by uniaxial pressing and sintered at 960°C in vacuum were strengthened by, i. Exchanging sodium ion with potassium ion at temperature above and below glass transition temperature, ii. Annealing and iii. Dispersion of PSZ. The results showed that the annealed samples showed significant strengthening followed by ion-exchanged samples. The results are analysed with different strengthening mechanisms.

Tissue engineering is based on the concept that cells seeded on three-dimensional (3D) bioresorbable scaffolds can recapitulate native tissues under appropriate in vitro and in vivo conditions. The necessity of a scaffold structure as the basic template of engineering tissues has encouraged the use of advanced manufacturing technologies. For example, rapid prototyping (RP) technologies such as fused deposition modeling (FDM) and three-dimensional printing (3DP) can be used to fabricate complex 3D structures based on 2D cross-sectional data obtained from slicing a computer-aided design (CAD) model. FDM is currently being applied in our laboratory to fabricate 3D scaffolds of various porosity and micro-architecture. This fabrication technology offers the ease and flexibility of varying the scaffold characteristics to meet specific structural and functional requirements of the tissue of interest. The FDM process involves the extrusion of a polymer filament through a heated nozzle and deposition as thin layers to build a CAD software-designed physical structure. Our current research focuses on the investigation of a bioresorbable composite matrix , namely poly(caprolactone) (PCL) in combination with hydroxyapatite (HA) as the materials of choice to produce scaffolds for tissue engineering bone.

Surface modification, ie. improving or changing surface characteristics of biomaterials in a controlled way, has been attracting attention in biomaterials research because of the low cost and the versatility. Some applications of surface modifications, such as immobilization of albumin, heparin and poly(ethylene oxides) (PEO) on polymer surfaces, seeding of endothelial cells on blood vessels, forming of self-assembled monolayer model surfaces, binding of phospholipid polar group on dialysis membrane, etc., are discussed in the present paper. Some surface modification techniques and principles are also introduced. Investigations and synthesis of ceramic films, such as TiN, TaN, DLC, C-N, Ta doped TiO₂, and TiO_2-x films. are presented.

There have been a number of attempts to create a novel surface that reduces the adverse effects of blood interaction with material. Among various techniques, laser-induced surface modification is highly suitable for this purpose. The paper presents surface modification of PET using CO₂ pulsed laser. The changes in surface properties were investigated by scanning electron microscopy (SEM), attenuated total reflectance infrared spectroscopy (ATR-FTIR) and water drop contact angle measurements. The complicated microstructures on the PET surface were observed in SEM micrographs. ATR-IR spectra showed that the crystallinity decreased in the surface region as a result of laser irradiation. The water drop contact angle also decreased with increasing the laser pulses. The haemocompatibility of CO₂ laser irradiated PET was examined in vitro, evaluating its capability of inducing platelet adhesion in comparison with the unmodified PET. The number of adhered platelets was determined by platelet-rich plasma method and lactate dehydrogenase activity measurements. Platelet adhesion on the untreated PET was relatively high. Laser irradiation of PET surface reduced the number of adherent platelets and prevented platelet spreading on the surface. The extent of platelet adhesion was correlated to the number of laser pulses.

Self-assembled-monolayer (SAM) has a special characteristic that it can template the growth of inorganic crystals under the ordinary conditions, which is similar to the action in the living bodies. In the present study, the precipitation of apatite on "OH" terminated SAM surface(silicon) was observed after soaked in SBF (Simulated Body Fluid). On the contrary, little apatite was formed on the SAM surface with "Phenyl" headgroups. PTCS (Phenyltrichlorosilane) was employed to make "Phenyl" terminated hydrophobic SAM . After UV irradiation for 2 hours, "-OH" terminated hydrophilic SAM was obtained. The effects of such factors as pH and Ca/P molar ratio in SBF solution, soaking temperature and time .etc, on the crystallization of apatite were investigated. XRD results revealed the preferentially oriented crystallization of apatite on "OH" terminated SAM.

The taltanlum nitride films had been synthesized by the reactive magnetron sputtering which deals with the orthogonal design technology of the films including N₂ partial pressure rate, substrate temperature, sputtering pressure and sputtering current. The results showed that the adhesion between the film and substrate was influenced mainly by sputtering pressure and substrate temperature. The hardness of taltanlum nitride films was affected greatly by N₂ partial pressure. The hardness of the taltanlum nitride film was as high as about HK4000. The blood compatibility of the taltanlum nitride films were evaluated by clotting time measurement and platelet adhesion test. The blood compatibility of the TiN, Ta films and low temperature isotropic pyrolytic carbon (LTIC) also were evaluated for comparing. The result showed that the blood compatibility of taltanlum nitride was better than that of the TiN, Ta and LTIC.

Coatings of CN_x have been prepared on the substrates of material Ti6Al4V, of which the big human joint replacements are made. The deposition of the CN_x coating was carried out by PACVD method in apparatus with standard arrangement. The methane and nitrogen have been used as precursors for CN_x compound. The infrared absorption spectroscopy and Rutherford backscattering spectroscopy were applied on diagnostics of prepared CN_x layer. Beside carbon and nitrogen the hydrogen and oxygen were found in the coatings. The sliding tests were carried out with the samples. The counter parts were the cylinders made of the polyethylene of the same type as for big joint prostheses is used. The tests were carried out in the medium of physiological solution. The CN_x coatings perform well under the lower load of 25 and 50 N. When the load is increased to 100 N, the friction coefficient slowly increases, but measured values of µ are typical for boundary lubrication.

Hydrogel polymers are the material of choice for optical prostheses, particularly in the form of soft contact lenses. In the development of lens materials, it is essential that their mechanical properties be determined. However, there are currently no standards (or recommended procedures) for the testing of this type of materials. In this investigation, various standards for testing plastic sheets were assessed for testing hydrogel membranes and appropriate testing procedures were established. The membranes for novel contact lenses were supplied by an established lens manufacturer. Mechanical characterisation consisted of tensile and tear tests. Three ASTM standards for testing plastics were evaluated for such tests. Miniature specimens were employed both for the ease of handling and for economical reasons. It was found that the tensile stress-strain relationship was different for different lens materials. The mechanical parameter which produced the most repeatable data for hydrogel membranes was tensile modulus. Values of both ultimate tensile strength and fracture strain demonstrated significant variability, especially for soft membranes. Tear testing of hydrogel membranes required the use of two ASTM standards due to different mechanical behaviour of lens materials. Mechanical characterisation provided useful information about hydrogel polymers that were being developed for novel contact lenses.

In this study, yttria stabilized zirconia has been applied to reinforce hydroxyapatite coatings. HA/YSZ composite powders and YSZ reinforced HA coatings have been prepared by plasma spraying processing. Yittria stabilized zirconia reinforced hydroxyapatite coatings were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray analyzer (EDX). The addition of zirconia proved to be beneficial to reduce the other phases (CaO, TCP, TTCP) formation in the coatings. Meanwhile, a trace of CaZrO₃ formed in the coatings. A significant improvement in mechanical properties was achieved.

Mechanical evaluations of plasma sprayed HA coatings have assumed vast importance in the orthopaedic applications where the demands of operational stresses of the coatings are stringently required. The determination of the mechanical properties such as Knoop hardness, elastic modulus, fracture toughness and bond strength are therefore essential and necessary for the assessment of the service behaviour and performance of the bioceramic coatings. The inherent properties of the coatings have been investigated and were found to have direct and impacting relationship with the feedstock characteristics, processing conditions as well as microstructural deformities. The presence of inter- and intralamellar thermal microcracks, voids and porosities with limited true contact between lamellae were found to degrade the mechanical characteristics of the coatings.

This paper aims to provide an insight to the mechanical properties of the HA coatings by plasma spray process, and the effect of microstructural defects on the resultant mechanical and structural integrity of the coatings. The elastic response behaviour and fracture toughness of both the as-sprayed and heat-treated HA coatings using Knoop and Vickers indentations at different loadings have been investigated. Results have shown that the mechanical properties (hardness, modulus, fracture toughness and bond strength) of the coatings have improved significantly despite increasing crack density after heat treatment. These properties were also found to deteriorate with increasing spray distance and particle size.

Calcium phosphate coatings produced by means of ion beam sputter deposition are amorphous and therefore exhibit high dissolution rate. Heat treatments can provide the energy needed to form crystalline hydroxyapatite-like coatings. In this investigation, to produce crystalline coatings, conventional heat treatment using an electric furnace was conducted. X-ray diffraction (XRD) results showed that heat treatments conducted at temperature higher than 500°C produced crystalline phases in the coatings. The higher the temperature, the more the crystalline phases were produced. However, the heat-treated coatings tended to crack easily. Therefore, it was very important to find a suitable heat treatment that produces crystalline coatings without weakening their adhesion to the metallic substrate. The dissolution properties of coatings in the 0.9% NaCl solution were evaluated. Results indicated that heat treated coatings dissolved slower than those of the amorphous coatings. The cracking mechanisms of the heat treated coatings were also proposed.

Plasma spraying of hydroxyapatite coatings onto titanium alloy implants is a standard procedure that is widely used in medical technology. However, the adhesive strength to substrate of such coatings is generally insufficient. Adhesion of these coatings to the substrate is considered being dominated by mechanical attachment to rough surface rather than by chemical bonding between the substrate and coating. This paper presents investigations into influencing factors of the sand-blasting process on the surface roughness of substrate. The most important factors were found to be sand size, followed by air pressure, sand type, and blasting time. The surface texture parameters and surface profiles were measured using a Talysurf 120L machine interfaced with a PC and equipped with the surface texture analysis software. The relationship between surface roughness and adhesion of the HA coating was investigated. Residual stress in plasma-sprayed coatings has been an inherent problem caused by the large difference in the coefficient of thermal expansion (CTE) between the coating and substrate materials coupled with the high cooling rate. The cooling rate may be decreased by the substrate roughness. The performance of the coating was highly related to the residual stress. An X-ray diffraction (XRD) technique was applied to measure the residual stresses in HA coatings, which had been plasma-sprayed on substrates with different surface roughness. It is shown that substrate surface roughness has effect on not only mechanical attachment of the coating but also the residual stress in the coating.

A bioactive composite material consisting of hydroxyapatite (HA) ceramic particles and high density polyethylene (HDPE) has been developed in recent years for hard tissue replacement. In this investigation, HA/HDPE composites were produced and characterised, with the rheological behaviour of both filled and unfilled polyethylene being studied in detail. The composite powders, with the HA volume percentage of up to 30% were produced by a manufacturing process which consisted of compounding and milling. A weight driven capillary rheometer was used for the rheological tests. Parameters that were studied included viscosity, shear rate, shear stress, temperature, die swell and extrudate distortion. Both filled and unfilled HDPE exhibited discontinuity in the shear rate curves, which is believed to have been caused by the extensive entanglement network in the HDPE matrix. The HDPE and HA/HDPE melts showed pseudoplasticity. Melt viscosity increased as the HA content increased in the composites. Extrudate distortion and die swell were reduced significantly in the presence of HA particles.

This investigation made use of the precipitation reaction between calcium hydroxide and orthophosphoric acid to produce a stoichoimetric hydroxyapatite (HA) slurry, which was then spray-dried to form hydroxyapatite powders. Different reaction temperatures (22, 27, 40, 60 and 75°C) and reactant concentrations (0.5, 1.0 and 1.5M) were used to study their influences on the thermostability of the spray-dried HA powders. All slurries were spray-dried at 200°C and with a feeding rate of 2.5 liters per hour. HA discs were made by cold uniaxial pressing at a pressure of 20 MPa. They were subsequently sintered to compare their thermostability with that of HA powders. X-ray diffraction patterns of HA powders and discs sintered at temperatures between 600-1400°C were analyzed. Lattice parameters of HA powders produced under different reactant concentrations were measured to investigate the controlling factors of HA thermostability. Experimental results showed that, for HA powder, lower reactant concentration and higher reaction temperature resulted in higher thermostability. Powders produced under 0.5M and at 60°C could withstand a temperature of up to 1350°C, at which the apatite structure was still the dominant phase. On the contrary, powders produced at other parameters decomposed at lower temperatures. Powders produced under 1.5M and at 40°C started decomposing at 700°C and fully decomposed at 900°C. The decomposition products of all HA powders were initially β-TCP and finally α-TCP only. This result was further verified by the thermostability of the sintered HA discs, which demonstrated the same thermostability as the spray-dried HA powders. Lattice parameters measurement indicated that low reactant concentrations resulted in smaller lattice parameters. The smaller the lattice parameters, the higher the thermostability.

Hydroxyapatite (HAp) compact and HAp / Ti composite with functionally graded structure were fabricated by underwater-shock compaction technique. The shock pressure obtained by using this technique was 6GPa. The characteristics of the resultant products were investigated by measurements of relative density, hardness, fracture test and SEM-EDX microanalysis. Sound compacts of HAp and HAp / Ti composite without any cracks and tears were fabricated. For HAp compacts, relative density of as-consolidated state was 74% and that of sintering at 1273K for 2h reached to 90%. Sintering temperature of HAp compacts is low compared with the temperature of conventional powder metallurgy process and fracture toughness values of sintered compacts is 1.2MPam^1/2. Continuous compositional change of composites was also confirmed.

Hydroxyapatite (HA) is an attractive material for human hard tissue implantation as it offers both biocompatibility and bioactivity. Thermal spraying techniques are generally used to deposit HA on Ti implants. For economical purposes, the HA powders in our thermal spraying work were produced in-house by spray-drying a HA suspension which is obtainable by the wet reaction. This paper reports our efforts in obtaining HA powder with good purity, crystallinity and flowability.

It has been known that the surface characteristics of scaffold material had significant effect on cell adhesion and its function in tissue engineering. The scaffold material of artificial tendon must have the following characteristics: biocompatibility, high tensile strength, low immunogenicity and absorbability. Human hair is soft and smooth. It has little elasiticity and good flexibility. Keratin is the main component of hair. But human hair is absorbed with difficulty in vivo. If tempting to use it as scaffold materials for artificial tendon, it must be modified through changing the surface structure of human hair. The transformed human tendon cells (THTC) with modified human hair and PGA fibers were cultured in vitro and were transplanted to nude mice. The biocompatibility and biomechanical characteristics were observed.

Titanium oxide films doped with tantalum were synthesized on titanium and silicon wafer by sputtering deposition. The structure was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Blood compatibility of the films was evaluated by clotting time measurement, platelet adhesion investigation and protein adsorption. In vivo experiment was further performed. The result showed that the Ta doped titanium oxide film has attractive blood compatibility which exceed low isotropic pyrolytic carbon. The mechanism of the behavior of blood compatibility of Ta doped film was discussed.

Polymethylmethacrylate (PMMA) is the most widely used material for denture base constructions. However, its resistance to impact, bending and fatigue is somewhat poor. Therefore, fracture of acrylic resin denture bases is still a frequently encountered problem in prosthodontics. The impact strength, transverse strength and fatigue resistance of heat polymerised acrylic resin reinforced with chopped strand mat (CSM), surface tissue (ST) and unidirectional laminate (UL) from E-Glass of various volume (2.5, 3.0, 4.0, 5.0%) were investigated and assessed. The fractured surface photographs were taken by SEM. The results revealed that in comparison with the unreinforced specimens were significantly increased.

The effects of doping small amounts (0.03 – 1wt.%) of manganese oxide (MnO₂) on the densification behaviour of Hydroxyapatite(HA) have been studied. The HA powder used in this study was prepared via a wet chemical precipitation method with starting materials Ca(OH)₂ and H₃PO₄. Prepared doped samples from this powder were easily compacted and sintered without cracking at a temperature range of 900°C-1100°C. X-ray Diffraction analysis revealed the presence of only HA phase in all samples regardless of the amount of MnO₂ added. Bulk density measurements showed high density values (greater than 99% of theoretical value) for the samples doped with 0.03wt.% MnO₂. This value is higher than those obtained for pure HA samples and was achieved at a lower sintering temperature of 1000°C. The presence of small amounts of MnO₂ is believed to act as a sintering aid for HA.

Human teeth have been designed by nature to provide wear and fracture resistance to high stresses. Hitherto, the dental materials and implants are based on metals, ceramics, and polymeric composites. Here, a new design strategy and testing methodology of novel biocompatible dental materials by mimicking the microarchitecture of human teeth are described. This approach involves either an infiltration or a controlled dispersion of hydroxyapatite (HA) in epoxy resin. Such process offers a simple and cost-effective means of tailoring the graded composition and microstructure to mimick the virtues of human teeth.

The Vickers indentation is used to study and compare the hardness depth profile and the effects of load and time on the hardness responses and damage of human teeth and graded hydroxyapatite (HA)-epoxy systems. A "bonded-interface" technique is also used to reveal the nature and degree of deformation-microfracture damage around and beneath Vickers contacts in these materials. Results show that the characteristics of graded hardness, load-dependent hardness, and indent profiles are strikingly similar between human teeth and HA-epoxy systems. Their ability to absorb and distribute damage in large scale Vickers indentations is also similar although the HA-epoxy systems appear to be superior. Depth profiling· of hardness shows gradual changes in microhardness from the enamel to dentine and pulp, thus confirming the graded nature of human teeth. Vickers hardness of the natural and synthetic enamel is load-dependent but load-independent in the dentin. Although the HA-epoxy systems are superior in damage resistance, they are viscoelastic, softer, and coarser in microstructure. The implications for the microstructure design of high-strength and high-toughness materials are discussed in the light of graded natural and synthetic architectures.

In order to know the impact behavior of turbine blade-grade monolithic silicon nitride ceramic, particle impact tests have been carried out at room and elevated temperatures with and without tensile load, which simulates the centrifugal force of blade rotation. In the experiments, a 1 mm diameter samarium-cobalt particle is impacted at velocities up to 900 ms^-1. The main results are : 1) Degradation of impact strength was clearly observed at elevated temperature and under tensile stress. 2) The critical stresses for the ring cracking were evaluated from both dynamic and static loading tests and were compared with each other. For a candidate material the reasonable stress value was supposed to be 14 GPa or less. 3) Moreover, X-ray inspection revealed that the radial cracks were prevailing in impacts at elevated temperatures.

Novel processes for fabricating micro/nano sized oxide devices employing self-assembled monolayers (SAM) were developed. SAM of PTCS (phenyltrichlorosilane) was modified to have a phenyl / hydroxyl-group pattern by UV irradiation using a photomask and was used as a template to arrange inorganic fine particles. Surface modification of micro/nano sized inorganic particles and chemical reactions between those particles and SAM were studied. Two-dimensional arrangement of functional particles on a SAM in a controlled manner through the formation of strong chemical bonds, such as amide or ester bonds, can be applied to the future microelectronics and photonics.

Fine particles of barium hexaferrite were synthesized by chemical co-precipitation method in the nitrate (barium and iron nitrates) and acetate-nitrate (barium acetate + iron nitrate) systems. Thermal properties, phase composition and morphology of hexaferrite powders obtained from two chemical systems were studied. Simultaneous DTA/TG and XRD indicated that the formation of the barium hexaferrite in the acetate-nitrate system occurs at a relatively low temperature. The SEM investigations indicated that the mean particle size of barium hexaferrite increases by increasing the calcination temperature. In the acetate-nitrate system the Fe/Ba molar ratio of 12 (stoichiometric ratio) is favourable. In the nitrate system excess Ba²⁺ is needed.

The effect of adding sintering aids (either Cr and C or Cr₃C₂) during the pressureless sintering process of titanium boride (TiB₂) ceramics was investigated and the effects from microstructural and compositional viewpoints discussed. The addition of either Cr and C or Cr₃C₂ as sintering aids accelerated the densification of TiB₂ significantly. Simultaneous addition of 7.5 wt.% Cr and C or Cr₃C₂ resulted in high density, high bending strength, and high Vickers hardness. According to the X-ray diffraction data of TiB₂ composites fired at 1173 to 2173 K, Cr and C or Cr₃C₂ reacted with TiB₂ to form CrB and TiC at the grain boundaries of TiB₂ during the sintering process. Also, we recognized a solid solution between TiB₂ and the sintering aid. SEM micrograph observation supported the observation that a liquid phase was definitely present during the sintering of TiB₂.

Alumina + zirconia (PRD-166) and Saphikon fibers reinforced glass matrix composites with and without a SnO₂ interphase were prepared by slurry infiltration and their mechanical characteristics were evaluated. Longitudinal bend strength increased with volume fraction of fibers in both PRD-166/glass and PRD-166/SnO₂/glass matrix composites. PRD-166/glass matrix composites failed in a brittle manner whereas PRD-166/SnO₂/glass matrix composites exhibited non-planar failure with crack deflection and fiber bridging as major toughening mechanisms. Saphikon/SnO₂/glass matrix composites failed in a tough manner with extensive fiber pullout. The difference in the failure mode between PRD-166/SnO₂/glass and Saphikon/SnO₂/glass matrix composites was due to fiber roughness.

A novel method has been developed for incorporating aluminium titanate into an alumina preform using a liquid infiltration route. A porous alumina preform is submerged in a titania rich solution for a given time, then heat treated and sintered at temperatures of 1550 °C for 4 hours. The net result is a dense ceramic material that displays a graded character through the cross-section. Analysis using x-ray diffraction has confirmed the existence of a concentration gradient through the material, with the aluminium titanate content decreasing with increasing depth in the material. Microstructural examination of the functionally graded material has shown the presence of aluminium titanate effectively inhibits the growth of the alumina grains. The thermal expansion behavior of the functionally graded material is also modified by the presence of the graded structure of the material.

Results of highly intensive mechanical comminution of α-Al2O3 in planetary ball mill with the use of a substance preventing the formation of hard aggregates and growth of crystallites are presented. Depending on experimental conditions mean size of the ground particles ranged from 18 to 40nm., findings of different methods of particle size determination being consistent with each other. The powders exhibit unexpectedly good formability allowing achievement 60-65% green density by uniaxial dry pressing. The powder compacts show enhanced sintering kinetics resulting in dense material with fine microstructure at low temperatures.

The promising role of structural ceramics in many useful devices and structures has in turn led to realization of the importance of developing ceramic joining techniques, which is perhaps one of the most important areas in the ceramic field for research and development. The increasing demand for joining ceramics arises from: a) fabrication of ceramic components of complicated shape or large size in one piece can be very expensive and in some cases impractical, and b) in many cases, because of the limitation of ceramics resulting from poor impact properties and lack of tensile ductility they have to be attached to metals, which must withstand stresses or temperature gradients too great for ceramics. This paper covers methods and problems of joining of ceramics with emphasis on brazing technique. This also includes examples of joining silicon nitride ceramic to itself and to molybdenum.

The indentation responses and nature of deformation-microfracture damage around Vickers indentations in a functionally-graded aluminium titanate/alumina (AT/A) composite (FGM) are described. Samples with a homogeneous layer of alumina and a graded layer of heterogeneous AT/A are fabricated by an infiltration route. Depth profiling of Vickers hardness shows that the hardness of the FGM is depth-dependent with a relatively soft graded surface layer but a hard homogeneous core. The microhardness of the graded layer is load-dependent with 10.4 GPa as the asymptotic value at high loads.

The evolution and accumulation of damage modes beneath Hertzian contacts are examined using "bonded-interface" sections. The stress-strain response of the FGM is monitored by Hertzian tests. The graded layer exhibits a distinctive "softening" in the stressstrain curve, indicating a microscale quasi-plasticity which can be associated with grain debonding, grain sliding, diffuse microcracking, grain push-out, and grain bridging. No contact-induced cracks are observed in the graded layer and the micro-damage is widely distributed within the shear-compression zone around and below the contacts. The capability of the FGM to absorb energy from the loading system and to distribute damage is somewhat akin to that of ceramics with heterogeneous microstructures.

Zirconia-mullite composites were fabricated by infiltration of porous 3Y-TZP pellets with an ethanol solution of aluminum nitrate and tetraethyl orthosilicate (TEOS). The ratio of aluminium nitrate and TEOS in the ethanol was such that, upon pyrolysis, it would convert into mullite. The pellets were dried and pyrolyzed at 700 °C after each infiltration to decompose the infiltrant and to form amorphous mullite precursor. The infiltrated mullite precursor would increase with each infiltration-pyrolysis cycle and would eventually reach a saturation amount. The number of infiltration-pyrolysis cycle to reach saturation depended primarily on the initial porosity. The repeated infiltration-pyrolysis reduced more effectively the pore size than the total porosity of the green compacts. After sintering at 1500 °C for 2 hours, the infiltrated pellets became dense composites of tetragonal zirconia/mullite or tetragonal zirconia/SiC/mullite. From SEM and EDS analyses, it was found that the zirconia grain size appeared to be unaffected by the infiltration of mullite and the spatial distribution of mullite was not uniform throughout the pellets.

Cluster diamond (CD) synthesized by a detonation method consists of ultra-fine diamond particles (5 nm on average). It has the unique properties of excellent lubrication and wear resistance. In this study, CD dispersed TiO₂ composites are developed as a new bio-material with self-lubricating ability. In order to achieve a homogeneous mixture between CD and TiO₂, a sol-gel method is selected. Thermogravimetry and differential thermal analysis results show that the optimum conditions of heating rate and temperature to dry TiO₂ gels are 1 K/min, 573 K respectively. The gels dried are finely powdered by ball milling and consolidated by spark plasma sintering. X-ray diffraction analysis shows that the TiO₂/CD composite has an anatase phase at the sintering temperature of 1073 K, and that the anatase phase is transformed into a rutile phase at 1173 K. The microstructures are observed by transmission electron microscopy. Friction properties are measured by ball-on-disk method at 1.0 mm/s and 0.2 N. The results show that the addition of 1vol%CD to TiO₂ gives improvement in the coefficient of friction.

A method of fabricating ZrO₂-mullite composites based on plasma spraying of alumina and zircon mixtures has been proposed and developed (3Al₂O₃+2ZrSiO₄ = 2Al₂O₃·2SiO₂ +2ZrO₂). The feedstock is prepared by a combination of mechanical alloying which allows formation of fine grained, homogeneous solid solution mixtures and following plasma spheroidization that yields rapid solidified microstructures and enhanced compositional homogeneity. The homogeneity is further realized when the plasma spray coatings are formed at last, and mullite formation temperature is expected to decrease by the unique preparation technique adopted in this study. Microstructure of the coatings were studied using the transmission electron microscope (TEM), and the mechanical properties such as hardness and fracture toughness of the coatings were measured with the indentation technique. The relationship between the mechanical properties and microstructure were investigated.

Strontium silicate precursor powder was prepared by sol-precipitation. After TGA/DTA measurements, the powder was heated at 973K for 8 hours to obtain the corresponding compound. It is indicated from x-ray diffraction patterns that the major compound is SrSiO₃.

The preparatory conditions of forming strontium silicate powder in an alkaline solution, such as the effects of pH value and alkoxy ligand on the powder, have been studied.

In this study, it is indicated that:

(1) Using various alkoxy groups as the ligand, the less carbon number of alkoxy group has, the much faster of the hydrolysis is. It makes the particle size much bigger.

(2) In various pH values, the higher pH value has, the much faster of the hydrolysis is, and the larger of the particle size becomes.

(3) The sintering behaviours of various particle size powders are also investigated. The more carbon number of alkoxy group has, the bigger the grain size is, the more densification of the bulk density and the less of the linear shrinkage in sintering are. The electrical resistivity of the sintered body is 10⁴~10⁸ ohm-cm, belonging to a semiconductor material.

(4) From the variations of susceptibility with temperature analyzed by SQUID, we found that this compound is diamagnetism substance.

(5) The electrical resistivity and dielectric constant of SrSiO₃ are also determined.

Hollow ceramic microspheres have found many applications as fillers in functional and structural materials. The preparation methods commercially ȧvailable or being developed in laboratories are reviewed, focusing on the introduction and comparison of the process of the physical properties of the microspheres prepared. Finally, we report a novel method developed in our laboratories that can produce hollow microspheres of ceramics, such as Al₂O₃ and AlN. Some basic properties of the microspheres prepared are presented.

Strontium hexaferrite powder synthesised conventionally has been treated in nitrogen atmosphere and subsequently calcined in air (Nitrogen Treatment and Re-calcination : NTR Process). The phase identification studies by means of X-ray diffraction (XRD) showed decomposition of strontium hexaferrite and reduction of the resultant iron oxide (Fe₂O₃) during the reaction with nitrogen. According to high resolution scanning electron microscopy (HRSEM) studies, reduction during nitrogenation, resulted in the division of some big grains into much finer sub-grains, strontium hexaferrite, Fe₃O₄ and Sr₇Fe₁₀O₂₂ were the main phases obtained after reduction. The hexaferrite phase reformed on subsequent calcination. The magnetic measurements indicated a significant decrease in the intrinsic coercivity during nitrogenation due to the formation of Fe₃O₄. However, after a re-calcination process, the remanence and maximum magnetisation (i.e. magnetisation at 1100 kA/m ) exhibited values close to the initial values before treatment but the value of the intrinsic coercivity was higher than that prior to nitrogenation. The microstructure showed that this could be attributed to very fine grains which originated from the fine sub-grains formed during nitrogenation.

The selected temperature was 950°C for nitrogenation and 1000°C for re-calcination. The time and initial pressure were selected to be 5 hours and 1 bar respectively. The highest coercivity obtained after re-calcination was 340 kA/m.

Using a nano-indentation and a nano-scratch technique, chemo-mechanical effect on surface properties of fused-silica glass were evaluated in water and alcohols. In order to measure nano-mechanical properties precisely under liquid conditions, a depth sensing indentation technique was improved with a liquid cell. Experimental results, however, showed that the nano-hardness values and the nano-scratch depth profiles were hardly affected by a series of liquids. The difference in mechanical behaviors among a series of liquids was shown in the friction coefficients during the scratch. In theses experiments, the maximum penetration depth was approximately 75nm. It means that the indentations were processed under an elastic/plastic-contained condition. It suggests that water and alcohols have little effect on the elastic and plastic deformation properties of a fused-silica glass. The chemo-mechanical effect is considered to have influence on fracture behavior, because the friction is strongly related to the fracture phenomena in sliding interfaces. Such chemo-mechanical effect would be applied to improve non-defective precision machining for glasses and ceramics by recognizing the fundamental mechanism.

Directional short fibre reinforced Li-Al-Si (LAS) glass-ceramic matrix composites (GCMC) were fabricated by hot pressing at 1450°C. Effect of different fibre volume on the properties of composites was studied. R-curves for composites were investigated using a simple compliance method. A remarkable change in the mechanical properties of GCMC was observed by adding short carbon fibre. Fracture toughness, the crack resistance to crack propagation (R-curve behaviour) and the fracture strength showed considerable improvement. Study shows that improvement in crack resistance was attributed to the extensive interaction of cracks with the short fibres. Composites with 30% volume of fibre showed the best crack-growth resistance. Based on microstructural observations, multiple matrix cracks were found to be arrested in matrix around fibre. Fractures observed include multiple matrix cracking (similar to microcracking) crack branching and crack deflection in crack frontal zone.

Electrophoretic deposition (EPD) has attracted huge attention in the recent years due to its ease and cost effectiveness in the forming of ceramic components. In the present work, forming of Zirconia and PZT (PbZr_0.5 Ti_0.5O₃) films using EPD technique are studied. Al₂O₃ substrates are used as the cathode, on which ceramic films were deposited. Fine ceramics powders were dispersed in ethanol to form suspension. HNO₃ acid was found to be an effective additive for the good deposition. The applied voltage, current and time of deposition were found to be important factors for the formation of the films. The deposition process was characterized by the deposition thickness as a function of voltage and the sintered microstructure. The experimental deposit thickness obtained is also compared to theoretical prediction.

Hollow carbon microspheres have found applications used to produce carbon foam or as functional fillers in the lightwerght composites and so on. The hollow carbon spheres were prepared by pyrolyzed the hollow phenolic resin spheres in inert gas. The compressive strengths of the hollow spheres were measured by an isotatic compression test in the different media of water, ethanol and acetone. The particle size and the crystalline of the spheres were presented. Some properties of the hollow phenolic spheres are also presented for comparison with that of hollow carbon spheres.

One of the authors has pioneered a novel grinding technology that incorporates in-process dressing of metal bonded superabrasive wheels known as electrolytic in-process dressing (ELID). This technology provides dressing to metal bonded wheels, during the grinding process, for continuous protrudent abrasive from superabrasive wheels. ELID grinding was performed on two types of silicon nitride materials with various grit sized diamond grinding wheels. A mirror surface finish with a R_a(center line average) value of 3.2 run was achieved when ELID grinding was performed with a # 8000 grit sized (average grain size = 1.76 µm) wheel.

ELID-Lap Grinding is an extension of the ELID grinding technology. It is a method of constant pressure grinding which employs the electrically conductive bonded wheel and electrolytic in-process dressing (ELID). ELID-Lap Grinding was performed on brittle materials such as silicon and glass BK 7 with wheels of different grit sizes. The results of experiments showed that stable grinding can be achieved with the # 8000 to # 3000000 (average grain size = 5 nm) metal resin bonded diamond wheels (MRB-D). With the # 3000000 MRB-D wheel, a very smooth surface finish was obtained for silicon (2.8 nm) and for glass (2.5 nm) (peak to valley). The results of this investigation will be reported in this paper.

In this paper, Hot pressing technology was used to fabricate the high performance TiB₂-BN composites materials, microstructure and electric conduct mechanism were studied, the relationship between microstructure and physical property was discussed. The results showed that microstructure of composites have a great influence on the physical property of composites. The TiB₂-BN composites with excellent mechanical strength and stable resistivity can be obtained by optimizing the processing parameter and controlling microstructure of composites.

The effects of doping small amounts of CuO up to 1 wt% on the densification behaviour of alumina (Al₂O₃) ceramics were investigated. The pellets were sintered in air at temperatures ranging from 1400°C to 1600°C, at a furnace ramp rate of 10°C/min. and soaking time of 2 hours. Sintered samples were characterised to determine phases present, bulk density, hardness and grain size. It has been found that all the doped samples exhibited higher bulk density (> 3.85 Mgm^-3) compared to the undoped samples. X-ray diffraction analysis revealed that only α-Al₂O₃ were present in the structure regardless of sintering temperature or CuO doping. The hardness of the undoped Al₂O₃ samples were lower than the CuO-doped material when sintered below 1550°C. However, maximum hardness of 21 GPa was measured for the undoped ceramics when sintered at 1600°C. Copper oxide doping is one economical way of improving the densification of Al₂O₃ without significantly affecting hardness.

Porous ceramics have been used extensively in liquid or gas filtration and as thermal insulation. In this study, a porous ceramic was fabricated using diatomite by roller pressing technique. The diatomite was intensively mixed with methylcellulose in water that was premixed with some plasticizers. Glaze was used in the mixture as high temperature bonding agent for the diatomite powder. The pressed specimens were dried at 110°C and subsequently subjected to heat treatment from 900°C to 1100°C, with one hour soaking time. The sintered specimens were evaluated for shrinkage, bulk density, modulus of rapture and porosity. The microstructural changes during sintering were determined by using scanning electron microscopy. High porosity of > 65% were obtained for most specimens, which is suitable for filtration of water under gravitational force. By controlling the sintering temperature, the pore and the strength of the ceramics can be manipulated to the required filtering applications. The primary advantage of using this method is the potential for economical mass producing of filters.

Immediately after Self-propagating High-Temperature Synthesis (SHS), when the synthesized sample is still in red hot soft state, a pseudo-isostatic force is acted on the sample quickly. In this way, synthesis and densification are combined in one step. The method was named SHS/QP. In this paper, fabrications of cermets and multiphase ceramics by SHS/QP were reported. The effect of different parameters on the SHS/QP process were analyzed. By optimizing the SHS/QP process, dense composites with good mechanical properties were obtained.

Vapor phase hydrogen transfer reaction between acrolein and isopropanol has been investigated using a Ag₂O-B₂O₃-MgO catalyst in a conventional fixed bed flow system at atmospheric pressure. A high selectivity (95.4%) of allyl alcohol was obtained with 100% of conversion at 270°C, isopropanol/Acrolein volume ratio = 15, contact time = 57.6 g-cat hr/mol. Under this condition, both activity and selectivity of Ag₂O-B₂O₃-MgO catalyst were sperior to that of the B₂O₃-MgO catalyst. The former catalyst had a long-lived activity more than the latter catalyst.

The effects of sonication during electrolysis include the cavitation phenomena. The collapse of a bubble near the surface of substrate causes the formation of high-speed liquid jet towards the surface of substrate, which travels along its surface. The liquid jet speed is 120 m/s, the water hammer pressures is 200 MPa and shock wave pressure is 1000 MPa. In this work the crystal orientation and hardness of zinc electrodeposited films were determined by frequency of ultrasonic irradiation, flow rate and hydrostatic pressure. The texture coefficient of {002} plane increased, and {100} and {102} planes decreased with sonication and increasing of acoustic intensity. These effects maximized at 45 kHz and 0.35 W/cm². The texture coefficient of {002} plane increased, and {100} plane decreased with increasing of hydrostatic pressure. The crystal orientations were not affected with liquid flow. The hardness of deposited films increased with increasing of acoustic intensity and maximized at 45 kHz and 0.35 W/cm². The hardness decreased with increasing of hydrostatic pressure. It was concluded that the effects of sonication on the hardness were shock wave pressures.

Synthesis of aluminum nitride (AlN) whiskers by reduction-nitridation of alumina-calcia compounds and their chemical properties were investigated. Five kinds of the oxide compounds (CaA₁₂O₁₉, CaAl₄O₇, CaAl₂O₄, Ca₁₂Al₁₄O₃₃, Ca₃Al₂O₆) which were prepared by firing at 1300°C for 240 min in air, were fired at 1800 to 1900°C for 60 to 240 min in a nitrogen (N₂) atmosphere. Transparent AlN whiskers were deposited on the inner surface of carbon crucible in the specimens of CaA₁₂O₁₉, CaAl₄O₇ and CaAl₂O₄. However, no whisker was produced in the specimens of Ca₁₂Al₁₄O₃₃ and Ca₃Al₂O₆. Both diameter and length of the whiskers produced in this study increased with increasing CaO content in the oxide compounds. Since the system in this study includes no iron and/or other metals at the tip of the whiskers, the growth mechanism is thought to be vapor-solid (VS). Transparency of AlN whiskers was maintained after exposing in air for 6 months, and no weight gain was observed through oxidation in air. The whiskers had such a stability in air that extreme low oxidation rates were observed, obeying the parabolic law. The activation energies were 109 kJ/mol at 900-1000°C and 237 kJ/mol at 1000-1200°C, respectively.

AlON ceramics having translucence were prepared by using the powder mixture of AlN and Al₂O₃ powder. AlN powder synthesized by fluidizedbed nitridation and commercial Al₂O₃ powder, were used as a raw materials. The AlN composition in the powder mixture was varied from 10 to 30 mol%, and weight of the powder compact sintered in this experiment was 4 g. Hot-pressing was carried out under 30 MPa. Sintering temperature and time were changed from 1700 to 1900°C and from 30 to 120 minutes, respectively. AlON ceramics sintered at 1900°C for 120 minutes in N₂ atmosphere under 30 MPa using the powder mixture of 20 and 25 mol%AlN had translucence. The translucent AlON ceramics had the thermal conductivity of 12.4 W/m.K, thermal expansion of 7.9 × 10^-6/, and the Vickers hardness of 1750 kg/mm².

Ceramic components for engineering applications are generally produced by the powder route. Residual stress and inhomogeneities in the process can result in defects and hence affect the component properties. As a result, a full understanding of the material constitutive modeling governing the sintering process is necessary.

In the present work, we examined the constitutive laws of the sintering mechanisms and identified the most appropriate constitutive relationship and mechanism for stage 1 of sintering of Al₂O₃ ceramics. With this identified constitutive relationship, sintering potential involved during sintering can be found and the process can be improved.

To identify the dominant constitutive law and corresponding sintering mechanism, pure alumina powder was used as raw material and two sintering methods (free sintering and hot pressing) were employed. Experiments were designed in such a way that the results can be used to determine the sintering potential and verify the appropriate sintering mechanism. It was concluded that interface reaction controlled sintering dominates the stage 1 of sintering in our selected experiment parameters.

Improved of chemical corrosion resistance of silicon nitride (Si₃N₄) ceramics is strongly desired. However, there is not enough information on chemical corrosion at present. In this paper, corrosion resistance of two kinds of Si₃N₄ based ceramics with different additives developed for bearing material was investigated. One of the specimens is composed of Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂, the other of Si₃N₄-SiC-MgAl₂O₄-SiO₂-TiO₂. A corrosion test was conducted under conditions of 240h-soaking at 30°C and 100h-soaking at 80°C in acid and base solutions. The weights of both specimens after soaking were confirmed to decrease with decreasing concentration of sulfuric acid. The bending strength also decreased in proportional to the weight change. Contrary to the results in acid solutions, the weights of the specimens decreased with increasing concentration of sodium hydroxide solutions. The weight changes at 80°C were much larger than those at 30°C. The extent of corrosion was found to depend on the composition of the ceramics. Specimens with additives of Y₂O₃, Al₂O₃, AlN, and TiO₂ tended to corrode more easily than those with SiC, MgAlO₄, SiO₂ and TiO₂. A correlation between the weight loss and the bending strength was established.

A new process through which pores with relatively large sizes in activated carbon are converted to pores with higher adsorption potential was investigated. The principle of this method is based on carbon deposition according to the Boudouard reaction of 2CO→C+CO₂. The deposition was tried at 400 to 500°C, introducing a CO rich atmosphere which was evolved in carbon bed adjusted at 800°C. An activated carbon with surface area of 900 m²/g made from Yallourn brown coal was selected for this study. It was confirmed that the weight increases with increasing deposition time. No deposition based on the weight gain was observed on a demineralized activated carbon prior to run. Deposition on an activated carbon added Fe after demineralization was confirmed. Therefore, the deposition was proved to strongly affected by the impurities such metals as Fe. It was recognized that the surface areas increase with increasing deposition amount. For example, the specimen deposited for 12h had a BET surface area of 1400 m²/g.

Preparation of spinel-type oxides, Mn_(1.5-0.5X)Co_(1+0.5X)Ni_0.5O₄ (0≦X≦1), and their electrical properties were investigated. Starting oxides, containing metals with desired molar ratios, were heated to 1400°C and held for 3 h in argon. The sintered specimens were cooled to 800°C then oxidized for 48 h in air to convert them into spinel-type oxides. The electrical conductivity (σ) of the sintered bodies was confirmed to increase exponentially with increasing temperature. The σ values decreased with increasing X. The Seebeck coefficients (Qs) were independent of the temperature. In all ranges of X, the Qs values decreased with decreasing X. In the region of 0≦X≦0.25, the Qs values were positive, indicating that the carrier of the oxides is holes. In the region of 0.5≦X≦1, the Qs values were negative, indicating that the carrier of the oxides is electrons. It seemed likely that the composition dependence of the electrical properties was based on the existence ratio of Mn³⁺ to Mn⁴⁺ in octahedral sites of spinel. The hole concentration of all specimens is estimated to be ~10²⁸ m^-3. The mobility (µ) of the oxides increased exponentially with increasing temperature. Since the activation energies calculated from µ were 0.28 to 0.32 eV, the electrical conduction of the oxides was considered to be controlled by a small polaron hopping mechanism.

The cubic (Ll₂) titanium trialuminide intermetallics obtained by alloying a tetragonal (DO₂₂) Al₃Ti compound with Cu, Ni, Fe, Cr, and Mn have low densities, excellent oxidation resistance up to 1000°C, good mechanical strength up to fairly high temperatures and a substantial apparent ductility in compression. All these attributes make them potential candidates for engineering applications as high temperature materials. Unfortunately, despite their cubic crystallographic structure they are brittle in tension and exhibit rather limited fracture toughness at ambient temperature (~4 MPam^1/2). This paper is an overview of our efforts to improve mechanical properties of Ll₂-stabilized titanium trialuminides by producing a nanostructured material employing a controlled ball milling of powders and subsequent consolidation into bulk form by various methods with the major goal of retaining their nanocrystalline microstructure. The nanostructured, disordered (most probably FCC solid solution) ball milled powders of Mn – stabilized titanium trialuminide (Al₃Ti (Mn)) were successfully consolidated into low – porosity, ordered (Ll₂) ordered bulk compacts by hot pressing at ~900°C for ~15 min under continuous pressure (210 – 430 MPa). In order to retain the nanostructure the heating time to the hot consolidation temperature must be minimized (< 4 – 5 min). The as – milled disordered powders can also be consolidated into low – porosity compacts by a triple shock – wave loading. Shock consolidated compact made from the as – milled disordered Al₃Ti(Mn) exhibits a web of fine microcracks indicating its brittleness and the powder particles in the compact do not exhibit plastic deformation during shock - wave consolidation. The indentation fracture toughness of the hot consolidated, fully ordered powder compact of cubic (Ll₂) titanium trialuminide with possibly nanocrystalline structure, is only ~2 MPa m^0.5 compared to 4 – 5 MPa m^0.5 for a coarse-grained, homogenized Ll₂ Al₃Ti (Mn). It seems that the nanostructure does not automatically guarantee high toughness of nominally brittle intermetallics.

This article represents a survey on the microstructure evolution of isothermally hot pressed silicon alloyed gamma titanium aluminide alloys. Due to inhomogeneous nature of the microstructures prior to deformation process, dynamic recrystallisation was observed to occur inhomogeneously throughout the matrix. Dynamic recrystallisation took place within single-phase gamma regions, the matrix of eutectic silicides, the lamellar α₂+γ grains and their grain boundaries. Thin foil electron microscopy revealed transmission of deformation induced defects such as twins and slip bands through various interfaces in the as deformed samples.

Surface modification of IMI 318 titanium alloy substrate was carried out using tungsten inert gas (TIG)arc heat source by melting a pre-placed commercial purity aluminium sheet of thickness lmm. Melting was carried out beneath the torch with five operating currents (60, 80, 100, 120 and 140 A) and three traverse speeds (3, 4 and 5 mms^-1). Glazing was repeated twice on the track with about 25% over lapping. The alloyed layers were characterized using Scanning electron microscope, x-ray, hardness tester, and sliding wear apparatus.

In this preliminary study, it is shown that TIG is capable forming titanium aluminides up to a depth of 3 mm. A good wetting of Al on pure Ti substrate has been found under all experimental conditions. When glazed at a traverse speed of 3 mms^-1 under a torch produced with 140 A, a homogenous coating of γ-TiAl without much variation in the composition and structure was formed on the substrate. At lower currents, and at 4 & 5 mms^-1 traverse speeds, the microstructure of the alloyed region was mostly α-Al and TiAl₃. Attempts were made to identify the phases formed during alloying at different processing conditions. The study reveals that solidification sequence occured in the following stages, depending on the operating current.

1) L→α(Al) → L + α(Al) + α₂(TiAl₃) → α(Al) + α₂(TiAl₃)

2) L→α(Al) → L + α(Al) + α₂(TiAl₃) → α₂(TiAl₃) + γ-TiAl

3) L→γ-TiAl

The surface glazed under 3mms^-1 speed with the torch produced at 140A, where the γ-TiAl is the prime phase, showed superior wear resistance.

In this paper is presented and discussed the damage tolerance and fracture characteristics of three rapidly solidification processed magnesium alloys. Test specimens of the magnesium alloy were deformed under both quasi-static and fully reversed total strain amplitude controlled cyclic loading. The quasi-static and cyclic stress response characteristics are discussed in light of the competing and synergistic influences of nature of loading, response stress, intrinsic microstructural effects, dislocation-microstructural feature interactions and macroscopic fracture.

Magnesium alloys, owing to their low densities and high specific strength, have been attractive to designers where weight saving has been an important consideration. However, low fatigue strength under service conditions has been an important factor in limiting the use of magnesium alloys in highly stressed designs. As there have been few publications on the fatigue behaviors of magnesium alloys and magnesium composite materials, it is the aim of this study to establish the relationship between microstructure and fatigue property for AZ91D alloy through ingot metallurgy route. An AZ91D alloy was subjected to different thermal treatments to produce various microstructures. Fatigue life of each of the microstructures was then characterized using cylindrical tension-compression type specimens at a fixed frequency of 25 Hz and load ratio (R) of 0.1. Crack growth study was conducted by using half-compact tension specimens with the same load ratio of R=0.1. Crack path was recorded using optical and scanning electron microscope to understand the influence of microstructure on crack path morphology and fatigue threshold.

With advantages like reducing pollution, conserving resources and energy, recycling is an important solution for waste management. The goal of recycling is to use materials again. However, for recycling to be commercially viable, the effects it has on the properties of materials have to be understood and reviewed. In the present study, the effect of recycling on the microstructure and mechanical properties of a metal matrix composite is being investigated. A magnesium-silicon carbide composite was successfully synthesized and recycled using an innovative disintegrated melt deposition technique. Microstructural characterization studies conducted on the original and recycled composites in the extruded condition using optical and scanning electron microscopy revealed marginal decrease in porosity and no significant change in grain morphology, distribution of reinforcement and interfacial integrity between matrix and reinforcement. Mechanical properties characterization conducted using a servohydraulic Instron machine revealed no change in elastic modulus, and a marginal increase in 0.2% yield strength, ultimate tensile strength and ductility. The results of the mechanical properties were then rationalized in terms of the microstructural characteristics associated with the composite samples. An attempt was also made in rationalizing the variations in microstructural characteristics and mechanical properties with the recycling of the composite.

Magnesium-based metal matrix composites (MMCs) have been receiving attention in recent years as potential materials for aerospace and automobile applications because of their low density and superior specific properties. In the present study, magnesium based metal matrix composites containing up to 21.3 weight percentage of SiC particulates were successfully synthesized using disintegrated melt deposition technique. Microstructural characterization studies conducted on the composite samples revealed a uniform distribution of SiC particulates, finite amount of porosity and good particulate/matrix interfacial integrity. Results of thermal analysis and mechanical properties showed an increase in elastic modulus, no significant change in the yield strength, and decrease in coefficient of thermal expansion, ultimate tensile strength and ductility with an increase in the weight percent of the SiC particulates. An attempt is made to correlate the physical and mechanical properties obtained with the microstructural characteristics of the composites.

Magnesium AZ91D alloys reinforced with fine SiC particles (AZ91/SiCp) were fabricated by mechanical milling, hot pressing and extrusion. The properties of AZ91D alloy composites were generally improved by SiC addition. The Young's modulus and hardness increased correspondingly with SiC addition up to 20-volume percent. However, the UTS and proof stress showed a maximum value at 15-volume percent and decrease at 20-volume percent. Nevertheless, the UTS values of the 20-volume percent SiC composites increased when the milling duration was increased. The influence of the volume fraction of SiC particle and milling term on mechanical properties, microstructure and density will be discussed.

The dry sliding wear behaviour of cast aluminium reinforced with hematite was investigated by means of pin-on-disc wear testing machine. The composite specimens were prepared using liquid metallurgy technique. Wear rates of the composites varying from 0 to 5 % by weight hematite were measured over a load range of 9.81 to 49.05 N at sliding velocities of 1.35,1.8 and 2.25 m / sec. Detailed scanning electron micrography (SEM) was done to verify the effect of addition of hematite on wear mechanism with and without heat treatment. Observations indicate that wear rate of the composites was less than that of the matrix alloy, but increased with the increase in load and the sliding velocity. Heat treatment at 220-degree centigrade upto 5 hours in steps of 2 hours duration improves the wear resistance of the composites.

Magnesium alloy metal matrix composite have been produced by squeeze casting using AZ91 magnesium alloy reinforced with 10% silicon carbide particles. The composite was subjected to solution heat treatment or solution and artificial aging to produce different microstructures. Tensile test was carried out at room temperature and fractographs were taken using the scanning electron microscope to correlate and understand the effect of microstructure on tensile fracture behaviour of the composite at room temperature. The experimental results show that appropriate heat treatment can improve tensile properties. Fatigue crack growth rate was studied using compact tension specimens with load ratio R=0.1. Crack path was recorded using optical and scanning electron microscope to understand the influence of magnesium matrix.

The solidification microstructure of cast SiC particles reinforced magnesium composite has been studied using optical and transmission electron microscope (TEM). Metallographical examination showed that the grain size of magnesium composite was much smaller than that of unreinforced magnesium alloy. In the mean time most SiC particles were pushed and segregated at the grain boundaries while few SiC particles were entrapped in the magnesium grain. The primary magnesium phase which heterogeneously nucleated on the SiC particle surface has been identified with a small lattice disregistry (2.3%) while their crystallographic orientation relationship was . Finally, the grain refining mechanisms in SiC particles reinforced magnesium composite have been proposed.

Effects of bismuth and antimony additions on the microstructure and mechanical properties of Mg-9Al-0.8Zn-0.2Mn (AZ91) alloy have investigated. The results indicated that small amount of bismuth or antimony additions to the alloy of AZ91 results in significant increases in yield strength and creep resistance but slight decreases of ductility at elevated temperatures up to 200 °C. The highest creep resistance has been obtained from the alloy with combined additions of bismuth and antimony. Microstructural observations reveal that the additions of bismuth or antimony have the effect on refining the β (Mg₁₇Al₁₂) precipitates in the as-cast alloys and suppressing discontinuous precipitation of the β phase effectively during aging process. Some needle-shaped Mg₃Bi₂ or Mg₃Sb₂ particles distributed mainly at grain boundaries have been observed in the alloys with bismuth or antimony additions. Both of Mg₃Bi₂ and Mg₃Sb₂ have high thermal stability at elevated temperatures and play important roles of improving creep resistance of the alloys at elevated temperatures.

The effect of microconstituents on the corrosion and electrochemical behaviour of AZ91D alloy prepared by die-casting and ingot casting route has been investigated. The studies were carried out in 3.5% NaCl solution at pH 7.25 using constant immersion technique, potentiodynamic polarisation experiments and surface topographic analysis. Microstructural areas with aluminium concentration less than about 8% (primary α phase and surroundings) were found to be more prone to corrosion attack compared with either those with higher amount of aluminium (eutectic α phase and its surroundings) or β phase. Die-cast material with smaller grain size and fine β phase offered marginally higher corrosion resistance and better passivation compared with the ingot.

The design and optimisation of the runner and gating systems is a key factor involved in the die casting of high quality products. Poor gating designs can lead to various defects such as gas porosity, shrinkage porosity, flow lines, cold shuts and poor surface finish. CAE techniques are considered as the most cost-effective way in optimisation of the runner and gating design. A thin-walled magnesium telecommunication part was selected to be hot chamber die cast. Both computer aided design and numerical simulation techniques were applied for the optimisation of the runner and gating. The runner and gating system for the thin-walled part was designed with the aid of CASTFLOW. "Cast shots" were then simulated on a computer using a commercial software "MAGMAsoft" to numerically analyse the mould filling pattern. Die inserts were fabricated based on the simulation results. A series of casting experiments were conducted. The short shot filling tests proved that the simulation results matched the actual casting results very well. The castings were sectioned for microstructural examinations. Good quality thin-walled telecommunication parts with sound microstructure were produced.

PAM-CAST™/SIMULOR^® provides the foundry industry with a reliable simulation package including filling, solidification and defects prediction for casting process optimisation. Through the active collaboration of Aluminium Pechiney and foundry industries, PAM-CAST™/SIMULOR^® has been validated on a wide range of applications from gravity to low and high pressure die casting. Recently, a specific thixocasting module based on a non-newtonian fluid behavior and Bingham power law has been developped and successfully applied to simulate semi-solid casting processes of aluminum and magnesium alloys. Results show that ,with an accurate representation of the metal flow inside the mold cavity, defects such as misruns and air entrapments can be identified allowing process engineers to optimize their gating geometry and mold designs. Future functionalities, including a fully coupled Finite Element thermo-mechanical solver are currently being validated.

Numerical simulation software has been recognized as a useful tool in product design and optimization of die casting design. The paper presents three examples where numerical simulation has been used to optimize parts for production in magnesium high pressure die casting.

Magnesium die casting has grown rapidly because of its excellent mechanical, electromagnetic and thermal properties, but it is still a trail and error process to design the gating system. In this paper, a commercial software package was used to simulate the filling process of die casting of a test bar. Two different gating systems were examined. It is shown from the simulation results that the melt fills the far end first and fills the rest of the part. The last filled sections are near the gates. No major difference was found between the filling processes of the two different gating systems. Compared with the experiment data of porosity level, it is shown that the porosity distribution in the final casting has a good agreement with that guessed by filling process.

The influence of chloride ion concentration and pH on the corrosion and electrochemical behaviour of die-cast and ingot cast AZ91D alloy has been investigated. The experimental techniques used include constant immersion test, potentiodynamic polarisation and scanning electron microscopy. Die-cast and ingot showed a linear increase in corrosion rate and I_corr with increase in chloride ion concentration with a change in slope for ingot above 5% NaCl. Open circuit corrosion potential shifted to more negative (more active) values as chloride ion concentration increases. The corrosion rate and I_corr are very high in highly acidic conditions (1-2.0 pH) and tend to decrease as pH increases. A synergism has been observed between the effect of chloride ion concentration, pH and microstructure of the material. Observation of the corrosion morphologies revealed preferential attack on β (Mg₁₇Al₁₂) and adjacent α regions (α regions with higher Al content) in highly acidic and higher chloride ion concentrations.

The corrosion behaviour, as investigated using hydrogen evolution testing in 3% NaCl (0.51M) solution and using electrochemical techniques in 0.01M NaCl solution has been determined for melt-spun amorphous Mg alloy ribbons containing 21 at% Cu and 18 at% Ni addition with and without ternary addition of Y and Nd. The results show that both the addition of Cu and Ni to pure Mg caused the corrosion rate to increase. Ternary addition of Y and Nd to Mg-Cu and Mg-Ni respectively reduce the corrosion rate of both the alloys. XPS depth profiling shows that Nd was present from the surface to the bulk of the ternary alloy and it reduced the Cl^- content significantly compared to the binary alloy. The results are discussed in the context of other reported observations on the corrosion behaviour of rapidly solidified Mg-based alloys.

The corrosion behaviour of melt-spun amorphous Mg₈₂Ni₁₈ and Mg₇₉Cu₂₁ ribbons has been investigated using hydrogen evolution testing in 3% NaCl (0.51M) solution and electrochemical techniques in 0.01M NaCl. Open circuit potential measurements showed that the as-spun alloys were more electrochemically noble than that of pure Mg. Dissolution rate measurements showed that the corrosion rates of the partially crystallised samples were lower than that of the fully amorphous samples. Potentiodynamic polarisation results showed that although there was ennoblement in the corrosion potential E_corr, the corrosion current density i_corr was higher for the melt-spun alloy than for pure Mg. Comparison of the polarisation responses for the partially crystallised samples in 0.01M NaCl showed that the passivation current density i_p was lower than for the as-spun amorphous sample. With prolonged heat treatment duration, fully crystallised samples exhibit a marked deterioration of corrosion resistance. The corrosion results have been discussed and correlated with the progress of crystallisation processes by means of XRD and TEM.

Magnesium die castings have been increasing by used in automotive structures. Some of the components such as engine box castings are subjected to elevated temperatures, which can be as high as 110°C or so. At these high temperatures, the magnesium die castings will be aged. The present work aimed to assess effect of the long-time aging on the die castings microstructures and mechanical properties. Aging treatment was carried out at 110°C for 1000 hours. Microstructures were examined and mechanical properties were obtained before and after aging for comparison. It is concluded that 1000 hours aging at the temperature of 110°C does not have significant effect on the ultimate tensile strength and yield tensile strength, but reduce the fracture elongation of magnesium die castings.

Hot end is a key part of hot chamber die casting machine. In order to improve shot control and predict the life span of hot end parts, it is important to understand the melt flow and thermal conditions of the hot end in the furnace. A simulation program "VStar_HotEnd" using Finite Difference Method (FDM) is developed. The system consists of three modules: pre-processor, main-solver and post-processor. The pre-processor provides an interface with other CAD software such as Pro-E and AUTOCAD to convert three-dimensional geometric files in STL format into FDM mesh format. Thermal data for some typical materials and boundary conditions are collected in a library. The process of simulation is carried out by the main-solver after parameters are defined by the user. During the simulation the software allows the user to stop and watch the real-time position of melt front and the temperature distribution in the furnace. The post-processor makes it possible to display the simulation results with various points of view and sections and export the screen image to a printer. An example of using VStar_HotEnd to simulate the hot end of a die casting machine is provided.

Magnesium's light weight makes it attractive for structural applications in engine and aerospace applications. Reinforcements in a magnesium matrix reduce the creep rate, enhance fatigue strength and life, increase strength and modulus, and retains strength to well over 50% Tm. Reinforcement types and architectures including particulates with particle sizes down to nanoparticles and fibers including ceramic and graphite as well as hybrid particles and particles and fibers have been processed by squeeze casting, stir casting, and Thixotropic molding to produce a variety of magnesium matrix composites including discontinuously reinforced magnesium (DRM). Composite processing, composite properties and commercial applications will be presented.

The solidification microstructure of AM60 magnesium die casting has been studied using optical and transmission electron microscope (TEM). The results showed that the microstructure of magnesium die casting displayed a divorced eutectic [Mg(α) + Mg₁₇Al₁₂(β)] structure. There was a thin layer adjacent to the surface with a considerably finer microstructure than the interior of the magnesium die castings, which caused the hardness of the skin layer was about 15~20Hv higher than the interior area. Porosity measurement showed that the highest porosity content was at about 60~80mm away from the gate and at the central area of test bar which sites are of the strongest turbulence.

Dense aluminum-lithium alloy reinforced with up to 20 vol.% SiC_p was prepared from powder mixture using spark plasma sintering process (SPS process). The process, originally developed by Sumitomo Coal Mining Co., has been found to be highly effective for the sintering of ceramic, metallic, and composite materials. Aluminum A 8090 was mixed with silicon carbide particles (SiC_p) by mechanical milling before sintered at 723 K under a pressure of 125 MPa for up to 10 minutes. Relative density of the sintered composite reinforced with 10 vol.% SiC_p was found to exceed 99% of the theoretical value. The Young modulus, yield stress, and ultimate tensile stress of the composite were 91 GPa, 256 MPa, and 332 MPa, respectively, which are, approximately, of the same values as those conventionally hot-isostatic press processed. The elongation of the composite was also found to be higher than that of the conventional one. The microstructure of the sintered composite was observed using both optical and scanning electron microscope. In the region away from the contact surface with the mould wall, the matrix powder was compressed along the vertical direction and elongated in the horizontal direction normal to the applied pressure. At the surface where the specimen was in contact with the mould and punch, the friction force controlled the deformation and thus the shape of the sintered powder. In this paper, the influences of reinforcement volume fractions, sintering temperatures, holding time, and applied pressure are also discussed.

Given the limited natural resources and the ever increasing demand for energy and materials, along with accumulating waste has forced us to think about recycling as a solution. However, a constraint is the change in physical, chemical and mechanical properties associated with recycling. Understanding the factors that influence the properties of materials after recycling presents quite a challenge. The present study is undertaken to investigate the effect of recycling on the microstructure and mechanical properties of a metal matrix composite. An aluminum-based metallic matrix was successfully reinforced with silicon carbide using an innovative disintegrated melt deposition technique. With the same technique, the composite was recycled twice. Microstructure characterization studies conducted using optical and scanning electron microscopy revealed a marginal decrease in porosity levels and SiC particulates size, and no change in distribution pattern of SiC particulates, Al-SiC interfacial integrity and matrix grain morphology. Mechanical properties characterization conducted using a servohydraulic Instron machine revealed an increase in elastic modulus, 0.2% yield strength, ultimate tensile strength and ductility of the recycled materials when compared to that of the material in the as-extruded condition. The obtained mechanical properties were then rationalised in terms of the microstructural characteristics associated with the disintegrated melt deposited composite samples. Particular emphasis is placed to study the effect of recycling on the microstructural characteristics and mechanical properties of the composites synthesized.

This paper reports research results on ductile-mode machining of an aluminum-based MMC reinforced with Al₂O₃ particles. Both polycrystalline diamond and single crystalline diamond cutting tools were used to ultra-precision machine the MMC at the depths of cut ranging from 0.4 µm to 1.6 µm. The critical depth of cut for performing ductile-mode turning of the MMC reinforced with Al₂O₃ particles was found to be 1 µm. At such depth of cut, there was almost no sub-surface damage except rare cracked particles. Besides the depth of cut, ductile-mode machining of the reinforcing particles was also affected by the orientation of the particles.

Most reinforcement ceramics such as SiC used in the fabrication of metal matrix composites manifest the advantages of increase in strength and stiffness. In reviewing the chemical interactions between common reinforcement ceramics and magnesium alloys, however, the significance of reinforcement degradation in mechanical properties becomes apparent.

Since there is very little mutual solubility of Mg and Ti in any phase and no intermetallic compounds occur in the system, there is a great interest in synthesising lightweight Mg-based metal-metal composites (MMCs) with ductile Ti as the reinforcement particles and Al as a hardening element in this study.

Elemental powders of Mg, Al and Ti were mechanically alloyed in a planetary ball mill under argon atmosphere for different durations to obtain metal-metal composites of Mg-10.3%Ti and Mg-5%Al-10.3%Ti. Consolidation was then carried out by sintering and hot extrusion of the cold compacted powders.

The microstructure and mechanical properties of the prepared composites were analysed by using optical microscope, scanning electron microscope (SEM), X-ray diffraction (XRD) and tensile test. Microstructure observation revealed that longer milling time resulted in more refined and well distributed Ti particles in the Mg matrix. Tensile measurement showed that there were different effects of milling time on tensile properties of the metal-metal composites with or without Al.

In the present work an attempt has been made to study the drilling characteristics of Aluminium Silicon carbide particulate composites. The composites manufactured through stir casting technique for different volume fraction of SiC was machined with solid carbide drills. The various drilling characteristics studied were drill wear, specific power, surface roughness and hole accuracy. The parameters considered for the study were volume fraction of SiC in composites, speed, feed rate and diameter of the drill. The experimental results were used to develop mathematical models for the different characteristics containing linear, quadratic and interactive effects of the parameters considered. The adequacy of the models developed models were checked using F- test and the insignificant effects were eliminated using t- test. The models developed were then subjected to optimization using non-linear programming for minimizing the drill wear. The models can be used for predicting the drilling characteristics and the optimized drilling conditions can be used for achieving better quality in drilling Al/SiCp composites.

This paper reports a study of the tensile properties of a TiB₂-containing metal matrix composite in comparison with matrix alloy (A356). A new direct pouring system was employed to produce several test strips in dry sand moulds. The test specimens were examined by tensile testing in as-cast condition. A large number of anomalous features is observed on all fracture surfaces. This observation shows that oxide films play an important role in the fracture mechanism. The skewed distribution of UTS results was described by Weibull distribution analysis. The filtered cast strips exhibited higher Weibull modulus both in TiB₂-MMC and matrix alloy.

Metal-matrix composites, including the specific class of discontinuously reinforced aluminum (DRA) have received substantial development in the past decades with minimal penetration into commercial applications. This is primarily due to less than adequate properties including: brittleness and low fracture toughness, difficulty in machining and secondary fabrication, and high cost. It has been demonstrated that select nanoparticle, and combinations of nanoparticle and other reinforcement types can produce DRAs with strain to failure of up to 8% and strength up to and over 700 MPa, which can be secondarily formed and machined with standard tooling to produce a variety of products. These DRAs can be produced for a fraction of the cost above the materials cost in specialized geometries of thin wall tubular forms and net shape cast components which have now reached high volume production. Fabrication processing, properties and example applications will be presented.

This paper compares the research results obtained from ultra-precision turning and grinding of aluminum-based MMCs reinforced with either SiC or Al₂O₃ particles. Both polycrystalline diamond (PCD) and single crystalline diamond (SCD) tuning tools were used to ultra-precision turning the MMCs at the depths of cut ranging from 0 to 1.6 µm. PCD grinding wheels were used to ultra-precision grinding the MMCs at the depths of cut from 0.1 µm to 1 µm. At the same depth of cut, the surfaces ground with PCD grinding wheels revealed much more ductile streaks on the reinforced ceramic particles than those obtained from SCD turning. Grinding using a 3000-grit diamond wheel at depths of cut of 1 µm and 0.5 µm produced ductile streaks on the Al₂O₃ particles and the SiC particles, respectively.

The demand for materials of superior properties is increasing day by day. Due to this materials scientist are developing new materials to meet the demand of growing need of materials. The material scientist for the development of metal matrix composite has been given much attention, which are continuously replacing traditional materials. There are several fabrication techniques for the production of MMC. Among the fabrication processes of MMCs of recent development, powder metallurgy is one of the most widely used fabrication techniques. Powder Metallurgy (P/M) offers designers and users a versatile and efficient method of producing components. The process is versatile because it can be used for simple and complex shapes, and a full range of chemical, physical and mechanical properties is possible to obtain. P/M is efficient because it produces moderate to high-volume net or near-net shapes, with very little raw material loss. In general, the process has very good potential to improve performance through uniform properties, fine grain structures, and chemical homogeneity. During the process, the matrix material powders and the reinforcement particles are blended to produce a homogeneous distribution and fed into a mould of desired shape, hot press to a desired level of compaction and final consolidation by extrusion, forging, rolling or some other hot working method. The powder metallurgy attracted attention of the parts manufacturer during the last decades based on progress in materials, process and equipment. The conventional powder metallurgy process consists of three main-steps: powder mixing, compacting (sintering) and extrusion. To carry out the processing of MMC through powder metallurgy, development of powder metallurgy set up is essential. Powder metallurgy set up consists of several main parts such as die, mould, in which the powder is contained, punches, which are used to apply compacting pressure and heater for hot compaction as well as hot extrusion of MMCs. The main aim of the article is to discuss model design, process planning and fabrication of powder metallurgy set up as well as heating system for hot compacting /extrusion (direct and indirect).

Good adhesion between the reinforcement particle and the metal matrix is a prerequisite for the wider acceptance and use of metal matrix composites. In this study, composites containing up to 12.6 volume percentage of SiC particulate reinforcement, in an LM 10 matrix, were cast using the vortex method. After solidification of the composite and during its cooling to room temperature, tensile and compressive stresses would be setup in the matrix and reinforcement particle respectively, due to differences in their coefficient of thermal expansion. In a well bonded composite, this causes plastic deformation to occur in the matrix near the interface in order to accommodate the stresses. This plastic deformation would result in an increase in the hardness near the particle-matrix interface. In a poorly bonded cast composite, such stress fields would be absent. In this study, the stress field around a reinforcement particle was used to calculate the plastic zone radius around the particle. The hardness gradient near the particle-matrix interface was measured with a microhardness tester under 10 gf load. Preliminary results indicate that the presence of a significant hardness gradient within the plastic zone radius indicates good bonding between the particle and the matrix.

Aluminum alloy - silicon carbide particulate composites are replacing the existing aluminium alloys in automotive and aerospace industries due to their excellent mechanical properties. However the difficulties in secondary processing of these materials restricts the range of their applications. The presence of hard abrasive particles pose severe problems in machining. In the present work the chip formation of Aluminium silicon carbide composites has been studied. An explosive quick stop device was used to freeze the turning process and photographs were taken using a Versamet optical microscope. The cross section of the chips was also analysed for studying the effect of various parameters like volume fraction of SiC, cutting speed, feed and depth of cut. The chip thickness ratio, chip packing ratio which is a measure of chip disposability and shear angle were determined for various cutting conditions. The mathematical models were developed for the above characteristics which can be used for prediction.

The oxidiation of polypropylene homopolymer in air was performed using dodecanol-1 as an accelator. The experiments were conducted under atmospheric at 180-220 °C. Spectroscopic data indicated the formation of polar groups such as ketones, esters, alcohols, anydrides etc. as determined by FTIR and ESCA. The scanning electron microscopy (SEM) showed the variations of mophology of the oxidation products. The variations of solubility of oxidized polypropylene as compared with the original polypropylene were investigated in solvents such as MEK, THF and toluene. The oxidized PP (OPP) may be used as a compatibilizer in polymer blends. The influence of compatibilization on the dynamic-mechanical polypropylene (PP) binary blends with polyamide-6, Talc and OPP have been investigated. Pressed films of blend PP/OPP, PP/OPP/Talc, PP/OPP/PA6 was examined by dynamic-mechanical analyzer (DMA), TGA and SEM. Mechanical Properties such as tenstile strength, modulus of elasticity, MFI, etc. were measured.

Polymer blends of a copolyester liquid crystalline polymer (LCP) and ABS were prepared by melt blending with a twin-screw extruder and the extrudate were obtained at different draw ratio. The morphology and mechanical properties of the extrudate were studied as functions of LCP content and draw ratio.

The mechanical properties (ultimate tensile strength and Young's modulus) of the LCP blends increased with both LCP content and the draw ratio, whereas those of the ABS extrudate was not influenced by draw ratio. It indicated that the mechanical property enhancement in the blends was due to the change of LCP structure. The morphology study revealed that at a given LCP concentration, the L/D ratio of the LCP fibrils increased with draw ratio. At higher LCP concentrations, the LCP fibril diameter increased at a given draw ratio, due to coalescence of LCP fibrils.

This study showed that hot drawing was an effective way to promote the LCP fibrillation in LCP-based polymer blends and extensional stress was responsible for the fibril formation.

This paper describes the use of a of low-energy electron beam radiation cure process to cure epoxy coatings by cationic polymerization. EB curing of coatings has several advantages over conventional thermal curing methods, including reduced cure times, improved quality/performance, curing at low temperature and reduced thermal stresses in the coatings. Cationic photoinitiators at a concentration of 1-3 parts per hundred of the epoxy resin was used for this process. Results indicate that di-functional epoxy resins can be electron beam radiation cured at low energy levels to produce coatings with glass transition temperature equivalent to thermal cured systems. The effect of dark curing as a post curing polymerization phenomenon was also observed to occur. Diaryliodonium salts were also found to be a more effective initiator than the sulfonium salts for the cationic polymerization of the epoxy resins when a low energy electron beam accelerator was used as the source of ionizing radiation. For this research, the difunctional cycloaliphatic epoxide monomer, 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate containing 3 parts per hundred (Union Carbide 6974 triarysulfonium hexafluoroantimonate from Union Carbide was irradiated with different dosages. The relationship between glass transition temperature and irradiated dosage was studied. Glass transition temperature of the cured material was found to more accurately determined by techniques involving the use of the Modulated Differential Scanning Calorimetry (MDSC).

Polyimides in general have found increasing application for microelectronics as a passivation coating layer due to their high service temperatures. In particular Bismaleimide (BMI) have been selected for their relatively lower cost. This project thus reports on the use of e beam for curing of a BMI coating prepared by dissolving in NMP and cured using electron beam in various atmosphere condition.

Study of melts rheological properties of unvulcanized and dynamically vulcanized polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) blends, at blending ratios 10-40 wt%, EPDM, are reported. Blends were prepared by melt mixing in an internal mixer at 190°C and rheological parameters have been evaluated at 220°C by single screw capillary rheometer. Vulcanization was performed with dimethylol phenolic resin. The effects of (i) blend composition; (ii) shear rate or shear stress on melt viscosity; (iii) shear sensitivity and flow characteristics at processing shear; (iv) melt elasticity of the extrudate and (v) dynamic crosslinking effect on the processing characteristics of the blends were studied. The melt viscosity increases with increasing EPDM concentration and decreased with increasing intensity of the shear mixing for all compositions. In comparison to the unvulcanized blends, dynamically vulcanized blends display highly pseudoplastic behavior provides unique processing characteristics that enable to perform well in both injection molding and extrusion. The high viscosity at low shear rate provides the integrity of the extrudate during extrusion, and the low viscosity at high shear rate enables low injection pressure and less injection time. The low die-swell characteristics of vulcanizate blends also give high precision for dimensional control during extrusion. The property differences for vulcanizate blends have also been explained in the light of differences in the morphology developed.

In this paper, the roles of field analysis in the modelling of prepreg moulding, pultrusion and, isothermal and non-isothermal resin transfer moulding processes are examined. Some of the physical phenomena that cannot be modelled by the field equation are highlighted. Numerical concepts used to simulate these phenomena are reviewed. Implementation of the simulation procedure and related issues are discussed. Numerical results on pultrusion process are used as illustrations.

Dynamic mechanical properties and morphology of a thermotropic liquid crystalline polymer poly(HBA/PET 80/20) and polyamide 66 (PA66) blends were studied. Rectangular samples were obtained by injection molding at 280 (C, which is above the nematic transition temperature of the LCP. Two parameters were investigated: LCP content varying from 0 to 100 wt% and the mould cavity thickness ranging from 1 to 4 mm. At a given mould thickness, the storage modulus (E') increased with increasing LCP content, which is due to an enhancement in the concentration of LCP fibers. The tan(peak was broad for the blends and the peak value decreased with increasing LCP content, resulting from the inclusion of rod-like rigid molecules. For pure LCP, E' increased with decreasing mould thickness in the temperature range studied (0-200(C). It was ascertained by XRD and SEM methods that better LCP fibrillation in the skin region could be achieved by increasing the shear rate through the reduction of the mould cavity thickness.

Bismaleimides(BMI) have found increasing interest as a lower cost high temperature resin for applications in the aerospace industries, and more recently in the electronics / microelectronics industries. Its main advantage is its ability to be used continuously at temperatures in excess of what most epoxies can bear, and its relative low cost compared to polyimide type resins. However, their potential low thermal conductivity and the incompatible coefficient of thermal expansion (CTE) with Si present the hindrance for application as electronic packaging materials. This paper investigates into the use of a AlN filler for the resin to increase the thermal conductivity and reduce its CTE value. AlN has the strong advantage of having a high thermal conductivity, compatible CTE with Si and non-toxicity. Whilst the high processing costs limits the application of AlN ceramics as a bulk material, its use as a filler is more prospective. This paper thus reports on some relevant properties of a AlN filler Bismaleimide resin system, indicating its potential use as a microelectronics packaging material.

Ceramic injection moulding is a well established processing technique, but is still limited to thin section components. This paper gives an overview of a variety of defects which appear preferentially in thick moulding sections. The generation of porosity and voidage during packing and solidification are discussed and related to the conditions prevailing during solidification. The use of an insulated sprue extended gate solidification and eliminated voids in thick sections and the use of a polyoxymethylene binder system enabled the progressive removal of binder from large 35 mm sections. Low hold pressure, applied by using a modified injection moulding machine reduced residual stress-induced cracking. Pronounced differential sintering was traced to particle alignment during mould filling and could be eliminated by using equiaxed powders.

Powder injection molding is an important processing method for producing precision metallic or ceramic parts. Experience, intuition and trial-and-error have been the practice for the design and process optimization of such molding operations. However, this practice is becoming increasingly inefficient and impractical for the molding of larger, more complicated and more costly parts. In this investigation, a numerical method for simulating the mold-filling phase of powder injection molding was developed. The flow was modeled using the Hele-Shaw approach coupled with particle diffusion transport equation for the calculation of the powder concentration distribution. The transient behaviour, or the moving boundary, is handled such that the melt front advances automatically in the calculation. The viscosity of the feedstock is evaluated using a power-law type rheological model to account for the viscosity dependency on shear rate and powder concentration. An example is presented and discussed to demonstrate the capabilities and limitations of the simulation algorithm, which has the potential as an analytical tool for the mold designer.

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