Narrow Results

We report effects of heat treatments on physical properties and finding optimal heating condition to add value to Thai blue sapphires. The color of sapphire arises from the presence of trace 3d-transition ions in its crystal lattice. For blue sapphire, the color is due to a charge transfer mechanism between Fe²⁺ and Ti⁴⁺ ions. However, iron may adopt both Fe³⁺ and Fe²⁺ due to oxygen vacancies. Fe³⁺ and Fe²⁺ yield sapphire yellow and green colors, respectively. Therefore, we have to convert as many as possible of Fe³⁺ to Fe²⁺ by heating the blue sapphire in N₂ atmosphere for 12 h. Experimental results reveal that the ratio of lattice parameter c/a increases with the heating temperature and reaches maximum at 1700°C, which can be caused by displacement of Fe³⁺ ions or more Fe³⁺ ions being converted to Fe²⁺. ESR signals show that the number of Fe³⁺ ions decreases roughly linearly with the heating temperature. The intense sky blue color was achieved after the 1500°C heat treatment, having the ratio ~0.78. The optimal heat treatment should therefore be at 1500°C in flowing N₂ atmosphere for Thai blue sapphires which yield intense sky blue color and good crystal clarity. The blue sapphires exhibited good clarity but light sky blue due to the increase in lightness after the treatment at 1700°C. A monoclinic distortion of the corundum structure has been found to start at the 1600°C treatment by ESR spectrometer. This is also clearly evident from low angle shifts of XRD peaks after heating at 1700°C. We can therefore conclude that the color change of Thai blue sapphires arises from the conversion of Fe³⁺ to Fe²⁺ and thus the change in crystal field. The monoclinic distortion of the crystal structure may also play an important role in coloring the sapphires after the heat treatment at 1600–1700°C.

This study investigated the effect of carbide precipitation hardening of heat-treated SK5M steel on the sliding wear resistance. The cold rolled carbon steel strip samples (J, G, and S-type) were oil quenched after tempering for optimal durations. The wear resistance was evaluated using a pin-on-disk wear test with an alumina counterface against different samples at various loads and distances with a constant running speed. The size and distribution of the precipitated carbides were observed using an image analyzer at various heat treatments. The heat-treated samples presented more dense carbide distribution in an area fraction and the decreased size of carbides. It is confirmed that the wear rate is minimum at an optimized austenitizing temperature of around 800°C. The specific wear rate indicates that the S-type sample has high wear resistance compared to that of J-Type. This is understood by stable wear behavior of S-type sample containing evenly distributed carbide precipitation.

In the present work, monolithic LPS-SiC was fabricated by hot press method with the addition of Al₂O₃, Y₂O₃ and SiO₂ and annealed at different temperatures to observe microstructure evolution. Process temperature was varied from 1760°C to 1800°C. Process pressure and maturing time are 20MPa and 1h respectively. Hot pressed samples were cut into rectangular bars. Three-point flexural strength was measured at room temperature in air with a cross-head speed of 0.1 mm/min and a lower span of 18 mm. Flexural strength and elastic modulus measurement was performed using a universal test machine (INSTRON 5581, USA). The apparent density of the sintered body was measured by the Archimedes method. The specimen dimension of the heat treatments is 4W×25L×1.5T mm. The specimens used for weight-loss measurement were set into an open carbon crucible to avoid nonuniform temperature distribution within the furnace. Post-fabrication heat treatment was performed in vacuum atmosphere (PO2 ≈ 0.01 Pa). The temperature was increased at a rate of 20 K/min to the heat-treatment temperature and maintained for 10 hours, after which the specimens were furnace cooled. After heat-treatment, weight of heat-treated specimens was carefully measured by an electronic balance. In order to reveal the microstructural change in heat-treated specimen, X-ray diffractometry and microstructure observation were performed and compared with those of the as-fabricated one.

NiTi intermetallic with nanocrystalline structure was produced by mechanical alloying of the elemental powders and the effect of subsequent heat treatment was investigated. The products were characterized using X-ray diffraction and microhardness measurements. The results showed that after 60 h of mechanical alloying, disordered B2-NiTi phase can be obtained as a metastable phase at room temperature with grain size of 25 nm, lattice strain and high microhardness of 1.2% and 922 HV, respectively.

After heat treatment, disordered structure transformed to ordered NiTi and a small amount of NiTi2 and Ni3Ti phases. The long range order parameters of nanocrystalline NiTi were obtained to be 0.63 and 0.94 after annealing for 30 and 60 mins respectively. After 30 mins of heat treatment, 81.5% of Ni (or Ti) atoms were on the right sites and after 60 mins it increased to 97%. Grain growth and decrease of microhardness and lattice strain were also observed after heat treatment. After 60 mins of heat treatment the grain size, lattice strain and microhardness of NiTi were 95, 0.09 and 624 HV respectively.

Effects of heat treatments on the on-line service life of a press die manufactured by W-EDM are studied. In this work, four manufacturing processes for a press die are considered: (1) milling and then grinding, (2) wire-cut electric discharge machining (W-EDM), (3) low temperature heat treatment after W-EDM, and (4) high temperature heat treatment after W-EDM. On-line punching experiments for an automobile part of BL646-chain are performed. The amount of wear of the die and punch, roll-over and burnish depth in the punched chain are measured every 1,000 strokes. Overall productivities are carefully compared. Finally, it is concluded that heat treatment after W-EDM for a press die can enhance its on-line service life. Especially, high temperature heat treatment after W-EDM is very attractive as a fast and cheap manufacturing method for a press die.

The aim of this research is to develop the high strength Al alloy sheet for the automotive body. For the fabrication Al-Mg alloy sheet, the composition of alloying elements was designed by the properties database and CALPHAD (Calculation Phase Diagram) approach which can predict the phases during solidification using thermodynamic database. Al-Mg alloys were designed using CALPHAD approach according to the high content of Mg with minor alloying elements. After phase predictions by CALPHAD, designed Al-Mg alloys were manufactured. Addition of Mg in Al melts were protected by dry air/Sulphur hexafluoride (SF₆) mixture gas which can control the severe Mg ignition and oxidation. After rolling procedure of manufactured Al-Mg alloys, mechanical properties were examined with the variation of the heat treatment conditions.

Phase Transition Cooling (PTC), using the absorbed latent heat during the melting of phase transition cooling medium to cool and solidify alloys in the process of casting, is a new casting technology. Specimens of A356 casting aluminum alloy were prepared by this method in the paper. The new heat treatment process (cast and then aging directly without solid solution) of A356 alloy was performed. For comparison, the conventional T6 heat treatment (solution and then aging treatment) was performed too. The mechanical properties of A356 alloy with different heat treatments were measured by tensile strength testing methods and microstructures of the alloy with different heat treatment process were investigated by optical microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-rays diffraction (XRD) and transmission electron microscopy (TEM) too. The results show that ultimate tensile strength (UTS) of A356 alloy with the new heat treatment process is much higher than that with conventional heat treatment while the elongations with the two heat treatment processes are very close. This is due to the grain refinement obtained after PTC processing.

Ti-43Al-9V-Y alloy billets was prepared by the quasi-isothermal canned forging processing, and effect of heat treatment processes on the microstructure of as-forged Ti-43Al-9V-Y alloy was investigated. The results show that, as-forged Ti-43Al-9V-Y alloy has streamline microstructure including a large number of recrystallized grains and broken lamellae, and different heat treatment processes were employed to obtain different microstructures of Ti-43Al-9V-Y alloy. After heat treatment at 1250°C, the microstructure of as-forged Ti-43Al-9V-Y alloy becomes γ+B2 microstructure. Comparing with the microstructure after HT of 1250°C/30 min, the precipitation of B2 lath phase in γ equiaxed grains increased and γ grains refined after HT of 1280°C/30min or 1320°C/30min. However, after the heat treatment of 1300°C/30 min, the duplex microstructures can be gained.

This study carried out a series of experiments viz. impact tests (drop weight & Charpy) and hardness tests after various heat treatments. The fractography observation on normal roll shell steel (NRS), abnormal roll shell steel (ARS), and S25C steel were carried out as well to analyze the cause of brittle fractures and damages in the roll shell steel. The optimal tempering temperature has been characterized for ARS and NRS.

First-principles calculations are performed to study the structural, electronic, thermodynamic and thermal properties of the InP and InAs bulk materials and InAs_xP_1-x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). The dependence of the lattice constant, bulk modulus, band gap, Debye temperature, heat capacity and mixing entropy on the composition x was analyzed. The lattice constant for InAs_xP_1-x alloys exhibits a marginal deviation from the Vegard's law. A large deviation of the bulk modulus from linear concentration dependence (LCD) was observed for our alloys. We found that the composition dependence of the energy band gap is almost linear by using the mBJ and EV-GGA approximations. The microscopic origins of the gap bowing were explained and detailed by using the approach of Zunger and co-workers. Furthermore, the calculated phase diagram shows a miscibility gap for these alloys with a high critical temperature. Thermal effects on some macroscopic properties of InAs_xP_1-x alloys are predicted using the quasi-harmonic Debye model, in which the phononic effects are considered. This is the first quantitative theoretical prediction of the thermal properties of the InAs_xP_1-x alloys, and we still expect the confirmation of experimental studies.

In this paper, Ti-6Al-4V alloy rods were manufactured by the powder compact extrusion of a powder mixture of hydride–dehydride (HDH) titanium powder, elemental aluminum powder and master alloy powder. Extrusions were carried out at 1300°C and with a holding time of 5 min in an argon atmosphere. The effects of different heat treatments (HT1: 960°C/1 h, water quenching, HT2: 960°C/1 h, water quenching + 500°C/6 h, air cooling, HT3: 850°C/2 h, furnace cooling to 540°C, then air cooling) on the microstructure and mechanical properties of as-extruded Ti-6Al-4V alloy rods were investigated. The results showed that a homogeneous microstructure, composed of a lamellar structure with a grain size range of 40–60 μm, was produced by powder compact extrusion of a powder mixture. The mechanical properties achieved were an ultimate tensile strength (UTS) of 1254 MPa, a yield strength (YS) of 1216 MPa and 8% ductility. After quenching at 960°C and with a holding time of 1 h, the UTS and YS of the heat treated Ti-6Al-4V alloy rod were increased to 1324 MPa and 1290 MPa, and the ductility was increased to 12%. After HT2, the UTS and YS of the heat treated Ti-6Al-4V alloy rod were significantly increased to 1436 MPa and 1400 MPa, but the ductility decreased to 4%. After HT3, the mechanical properties of the heat treated Ti-6Al-4V alloy rod were slightly decreased to give a UTS of 1213 MPa and a YS of 1180 MPa, with an increase in ductility to 11%. The microstructural changes of as-extruded Ti-6Al-4V alloy rods were also investigated for the different heat treatments.

In this study, halloysite nanotubes (HNTs) were heat-treated at various temperatures in order to minimize particle aggregation, and the mechanical properties in the humid environment was compared and analyzed to prevent the pore formation and achieve an optimal bonding with epoxy resin. As a result, the glass fiber-reinforced plastic (GFRP), with 0.5 wt.% heat-treated HNT at 700${}^{\circ }$C, showed the highest moisture absorption resistance, tensile strength and interlaminar shear strength.

Periodic hexagonal gold crystal spherical nanoparticle arrays with controllable size and periodicity are fabricated by physical vapor deposition and further heat treatment based on monolayer colloidal crystal template. The size and center-to-center spacing of nanoparticles (NPs) were manipulated conveniently by tuning the deposition thickness of Au film and the size of colloidal spheres of the template, respectively. The thickness range of deposited Au film dependent on the size of colloidal spheres was investigated comprehensively. Dewetting model was established and employed to analyze the whole process of the evolution from gold film to spherical nanoparticle with uniform size. Additionally, localized surface plasmon resonance (LSPR) responses of these Au nanoparticle arrays were systematically measured. It is found that the extinction properties are significantly influenced by the particle size and periodicity of arrays. With the increase of particle size, the LSPR peak shows a red shift due to the quantum size effect of the nanoscaled Au particle. Meanwhile, the diffraction peaks also show small red shift due to a slight increase of average refractive index of arrays. This is highly helpful to improve its practical applications for detecting biochemical molecules based on LSPR and diffraction peak sensing.

The high manganese steel surfacing layer was deposited on Q235 steel by flux-cored wire gas shielded welding. The as-welded surfacing layer was heated at 1050${}^{\circ }$C and quenched in the water, then was tempered at 300${}^{\circ }$C. The microstructure, hardness and wear resistance of as-welded surfacing layer and that after heat treatment were comparatively analyzed. The results showed that compared with the as-welded surfacing layer, a large number of fine carbides dispersed in the austenite matrix for the surfacing layer after heat treatment. Meanwhile, the hardness and wear resistance of surfacing layer were slightly improved. The furrow in the abrasive wear for surfacing layer was shallower. Under the action of work hardening, the hardness of high manganese steel surfacing layer gradually increased while the loss weight decreased with the wear time less than 30 min. The hardness of surfacing layer reached the maximum and the loss weight of wear remained unchanged when the wear time was 30–60 min.

Amorphous Ni–W–P coatings were prepared by electroless plating and annealed at 250${}^{\circ }$C for different times to obtain different microstructures. The local atomic structure of these amorphous coatings was analyzed by calculating the atomic pair distribution function from the XRD patterns. The type of crystals in coatings was obtained from the TEM image and corresponding selected area diffraction (SAED) pattern. The proportion of microscopic particles in the matrix was roughly estimated from the first DSC exothermic peak area. Corrosion resistance in 0.5-M sulfuric acid solution was investigated via electrochemical techniques. Experimental results showed that all annealed coatings still held amorphous structure, albeit the microstructure had been changed. The correlation radius and the atomic number of clusters had increased, especially when the annealed time extended to 12 h and 20 h. The number of microscopic particles in the amorphous matrix also increased with rise in heat treatment time. The type of crystals in these amorphous matrices increased from Ni/Ni (W) to Ni/Ni (W), Ni₁₂P₅ and Ni₅P₄. The decreasing corrosion resistance was in agreement with the increasing number of microscopic particles and higher-order clusters in annealed Ni–W–P coatings. These microscopic particles could form micro-galvanic cells in corrosion solution. The higher-order clusters increased the composition difference in the amorphous matrix, and this also promoted to form micro-galvanic cells in solution.

A suitable heating condition designed for a particular type of ruby is used to enhance the quality to increase its value. Heating Vietnamese rubies in an oxygen atmosphere may improve color and clarity, and thus increase their prices. The color of rubies is due to the presence of trace amounts of Cr³⁺. Fe³⁺ yields a pale yellow color and the charge transfer mechanism between Fe²⁺ and Ti⁴⁺ gives ruby an undesirable bluish color. Reducing this mechanism is possible by heating the ruby in oxygen so that most of the Fe²⁺ is converted into Fe³⁺ ions and thus they appear a more intense red. By using XRD we found that the c/a ratio of the hexagonal structure was smallest after heat treatment at 1300°C. The number of Fe²⁺ ions converted to Fe³⁺ was detected by an electron spin resonance spectrometer and found to increase with temperature. The ruby appeared a most intense red after heating at 1500°C for 12 hours. The color change is due to both the decrease in c/a ratio and the increase in the number of Fe³⁺ ions. ESR experiments on ruby crystals by rotation about their c-axis show that Fe³⁺ ions are a little off axis before heat treatment. After heat treatment at 1300°C they move to new asymmetric equilibrium positions towards larger O^2- triangles. It is not clear, however, if this Fe³⁺ movement is related to the change in color. The asymmetry may arise due to some O^2- vacancies.

In this report, Fe³⁺ impurity ions present in green sapphire (Al₂O₃) were studied experimentally, by heating a light green sapphire in flowing oxygen atmosphere for 12 h from 1200, 1300, 1400, 1500 and 1600°C, respectively. Electron spin resonance (ESR) spectra in X-band (~9.45 GHz) were recorded by mounting the crystal with the c-axis perpendicular (θ = 90°) to the magnetic field direction. The spectra were recorded and simulated by a numerical diagonalization of spin Hamiltonian matrix in the range from 0 to 180 degrees for every 15 degrees of rotation angle (φ). In our case, only the last two sets of peaks strongly depend on the rotation angle (φ), and each exhibits C₃ symmetry due to two magnetically inequivalent Fe³⁺ sites in the corundum structure. For polycrystalline ESR spectra, seven main Fe³⁺ ESR absorption peaks occur at the resonance magnetic fields of 100.20, 310.24, 486.80, 525.00, 550.60, 761.00 and 777.00 mT respectively. Specifically, ESR signals show that the number of paramagnetic Fe³⁺ ions increase roughly linearly with the heat treating temperature, having the ratio ~1.41 at 1600°C.

Calcium fluoride additive was used to produce high thermal conductivity AlN ceramics which has no grain boundary phase. Thermal conductivity of AlN is determined by the point defect, represented as oxygen related defect, within the AlN grain. The defect density characterization of high thermal conductivity CaF₂ doped AlN ceramics after heat treatment was conducted by Raman spectroscopy. As measure Raman linewidth broadening, the point defect density variation after heat treatment and corresponding thermal conductivity change was investigated.

High dielectric hafnium oxide films were grown by magnetron sputtering and post heat treatment in nitrogen atmosphere at 500°C for 30 min using vacuum annealing furnace. The film keeps amorphous at 500°C and has better interface quality as revealed by X-ray diffraction and transmission electron microscopy. The influence of TiN and Pt electrodes on the electrical property of the film was compared. For the annealed films, TiN electrode was presented as the optimal one. For the conduction mechanism of Pt/HfO₂/p-Si MOS capacitors under gate electron injection, the dominant conduction mechanism at low electric field is Schottky emission. At high electric field, the conversion of current transport mechanism from Schottky emission to trap-assisted tunneling for the annealed HfO₂ film occurs at 0.64 MV/cm.

(Fe₅₀Co₅₀)_73.5Cu₁Nb₃Si_13.5B₉ amorphous ribbons, a type of Co doped Finemet alloy, were prepared by melt-spinning and annealed at 440–560°C for 30 min. Influences of heat treatment and Co content on the crystallization were analyzed through differential scanning calorimetric (DSC) and X-ray diffractometry (XRD). The microstructure was analyzed by atomic force microscopy (AFM). The magnetic properties of (Fe₅₀Co₅₀)_73.5Cu₁Nb₃Si_13.5B₉ and Finemet ribbons were tested by an alternating current soft magnetic properties measurement system. A comparative study of frequency dispersion properties between (Fe₅₀Co₅₀)_73.5Cu₁Nb₃Si_13.5B₉ and Finemet was conducted. Results indicate that the optimal magnetic property has been achieved when (Fe₅₀Co₅₀)_73.5Cu₁Nb₃Si_13.5B₉ ribbons were annealed at the temperature range of 480°C–520°C, after which the grain size became between 10 nm and 20 nm. Although the permeability of (Fe₅₀Co₅₀)_73.5Cu₁Nb₃Si_13.5B₉ is not as high as that of Finemet, this Co-doped Finemet amorphous alloy presents better high frequency properties, and therefore is a promising candidate for the high frequency field applications.