Narrow Results

This study is focused on improving the mechanical properties and slurry erosion resistance of traditional Ni–20Al₂O₃ and Ni–20Cr₂O₃ thermal spray coatings by reducing the 5% of Al₂O₃ and Cr₂O₃, respectively, and addition of 5% TiO₂ feedstock in both coatings. Thermal sprayed powders were thermally sprayed on SS-420 substrates with high-velocity oxy-fuel (HVOF) method. A lab-scale pot tester was used to conduct the wear testing at low rotating speeds of 750, 1000, 1250, and 1500 rpm. To create severe accelerated conditions, a high mass flux (35–50 wt.%) of fly ash particles was used. Multi-sized fly ash slurries ranging from $<53$$\mu$m to 250$\mu$m were used during the experiments to evaluate the impact of particle size fraction on the erosion over a 30–120 min time-period. Coatings’ surface characterization was done to examine more about their composition. According to the findings, the addition of 5% TiO₂ powder to both Ni–15%Al₂O₃ and Ni–15%Cr₂O₃ coatings significantly improved their wear resistance of SS-420. This occurred because of the enhancement of hardness as well as brittleness by 5% TiO₂ in matrix of Ni–15%Cr₂O₃ and Ni–15%Al₂O₃ coatings. Moreover, TiO₂ particles aid in strengthening of Cr₂O₃ and Al₂O₃ reinforcements and the binding with matrix. Also, the results showed that Ni–15Cr₂O₃–5TiO₂ coating showed superior wear resistance compared to Ni–15Al₂O₃–5TiO₂ coating.

Hydro turbines are one of the most vital and essential components for the production of hydroelectric power. Since the hydro turbine is always operating under the influence of water and the silt transported by the water from the hilly region, it poses a lot of threat and damage to the turbine blades working constantly under the action of silt laden water. Erosion wear is the most common type of damage, and drastically affects the life of turbine runners and blades. The introduction of thermal spray coatings, namely high-velocity oxy-fuel (HVOF) technique, has resulted in a major improvement in stainless steel erosion resistance. Ceramic coating powders primarily Al₂O₃, Cr₂O₃, and a composite mixture of composition 55% Cr₂O${}_3+45\%$ Al₂O₃ were deposited on stainless steel substrates of grade 304. The thorough experiments utilizing silt slurry are conducted at different particle size of silt in the range 212–250, 150–212 and 53–106$\mu$m. The silt concentration has been varied in the range 12–42% by weight, and the substrate was rotated at a rotational speed in the range 600–1500rev/min for the test time of 4h. SEM images were used to assess the surface morphology of the required testing samples. The erosion observance and the material removal mechanism were investigated and discussed on the basis of microstructure studies. Cr₂O₃ coating is found to be more resistant to erosion than other coatings under all test conditions.

Hydroxyapatite (HAp) was deposited by plasma spraying technique with TiSiN adhesive interlayer on the medical-grade 316 LVM stainless steel. The surface topographies of HAp and HAp/TiSiN were evaluated using X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The important mechanical properties of the films such as hardness ($H$) and elastic modulus ($E$) were determined by the nanoindentation test. Lastly, the adhesion and anti-scratch behaviors of the films were evaluated by Rockwell-C indentation and nanoscratch test, respectively. The elemental analysis showed the values of Ca/P (at.%/at.%) ratio to be 1.80 and 1.59 in HAp and HAp/TiSiN coatings, respectively. The mechanical properties of HAp film with TiSiN interlayer were greatly improved from 1.23$\pm$0.26GPa to 10.6$\pm$1.12GPa for hardness and from 18$\pm$3GPa and 29.8$\pm$ 5GPa for elastic modulus, respectively. The results of the Rockwell-C indentation test showed a significant reduction in HAp coating delamination with TiSiN interlayer which can be categorized with HF2 or HF3 Daimler–Benz quality ranking. What is more, the nanoscratch profile of HAp coating showed wider scratch with evidence of deformation at the edges which got significantly reduced with the TiSiN interlayer. The results are suggestive of improved mechanical properties, viz. hardness and elastic modulus, and improved adhesion strength of HAp coating with TiSiN interlayer.

The hard coating was formed by TIG cladding (TC) of the Stellite31-NB powders on TA18 titanium alloy, enhancing greatly the performance of the TA18 surface. This TC coating was investigated by the characterization means, indicating that a great number of the fine particles gathered near to the rod-shape precipitates, also restraining the growth of, so partial of the formed rods exhibited the acicular-shape morphologies. Due to the complex chemical compositions between the crystals and the amorphous phases (APs), the interface region owned the different lattices parameters, favoring the lattice distortions to be produced after a solidification process. The wear volume loss of the TC coating of the arc-treated specimen was about 1/5 of TA18, the better wear performance of a TC coating can be primarily ascribed to the features of this TC coating, such as the including ceramics also the other hard compounds.

The use of thermal spray coatings provides protection to the surfaces operating in severe environments. The main goal of the current work is to investigate the possibility of using a high velocity air fuel (HVAF) thermally sprayed wear resistant Ti(Al,O)/Al₂O₃ coating on tool steel (H13) which is used for making dies for aluminium high pressure die casting and dummy blocks aluminium extrusion.

A feedstock of Ti(Al,O)/Al₂O₃ composite powder was produced from a mixture of Al and TiO₂ powders by high energy mechanical milling, followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity air-fuel (HVAF) technique onto H13 steel substrates to produce a composite coating.

The present study describes and compares the tribological properties such as friction and sliding wear rate of the coating both at room and high temperature (700°C). The wear resistance of the coating was investigated by a tribometer using a spherical ended alumina pin as a counter body under dry and lubricating conditions. The results showed that composite coating has lower wear rate at high temperature than at room temperature without using lubricant. The composite coating was characterized using scanning electron microscopy (SEM), optical microscopy and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses the wear resistance performance of the coatings at room and high temperatures.

A hard film coat can improve a tool's performance. In this study, the frictional properties of an uncoated tool and a coated tool with TiN were measured against that of SCM440 (42CrMo4) steel. The results showed there was no significant difference between the friction coefficient of the high-speed steel tool and the tool coated with TiN but the friction coefficient of uncoated tool was slightly lower than that of the steel. In the second part of the study, coats of TiN, TiC, CrN, and TiAlN were deposited on high-speed steel and the wear characteristics were determined with a pin-on-disk wear examination. The differences in the friction coefficients were attributed to the difference in the wear of the slipping material. There were large differences in the adhesion characteristics on the surface of the slipping material. The author suggest that these differences influence the characteristics of the cutting tool.

The effect of spraying power and immersion time on the microstructure and electrochemical corrosion behavior of plasma-sprayed Ni-5wt.%Al alloy coatings were studied. The spraying powers have a great influence on the electrochemical corrosion behavior of the coatings by affecting their surface roughness and porosity. The self-corrosion current density of the coatings was much lower when the surface roughness and porosity of the coatings were both lower. In addition, with the increase of immersion time, the self-corrosion current density of the coatings was decreased first, then increased, and finally decreased, which may be related to the formation and disappearance of Al₂O₃ in the coatings.

The nature of the zeolite 4A coatings prepared by using the substrate heating method was investigated. It was determined that the fractal dimensions of the surfaces of the coatings varied between about 1.14 and 1.19 with respect to the coating thickness in a mesh size range of about 1.5 μm - 48.5 μm. The fractal dimension value increased to some extent for the thicker zeolite coatings. It is hypothesized that the significance of nucleation is relatively high in the substrate heating method when compared to conventional synthesis methods and this leads to zeolite coatings with fractal surfaces and intercrystal porosity.

In the present study, the effect of various N₂ gas flow rates on friction coefficient and surface roughness of TiN-coated D2 tool steel was examined by a commercially available cathodic arc physical vapor deposition (CAPVD) technique. A Pin-on-Disc test was carried out to study the Coefficient of friction (COF) versus sliding distance. A surface roughness tester measured the surface roughness parameters. The minimum values for the COF and surface roughness were recorded at a N₂ gas flow rate of 200 sccm. The increase in the COF and surface roughness at a N₂ gas flow rate of 100 sccm was mainly attributed to an increase in both size and number of titanium particles, whereas the increase at 300 sccm was attributed to a larger number of growth defects generated during the coating process. These ideas make it possible to optimize the coating properties as a function of N₂ gas flow rate for specific applications, e.g. cutting tools for automobiles, aircraft, and various mechanical parts.

The thick ceramic coatings were prepared on 6061 aluminum alloys by microarc oxidation in a silicate electrolyte. The morphology and phase constituent of the coatings with different thickness were studied by scanning electron microscope, and X-ray diffraction. Scratch and thermal shock tests were employed to evaluate the adhesion between the coating and alloy substrate. The maximum microhardness and its position away from alloy/coating interface increases with increasing the coating thickness. The critical scratch force for the coating break was about 55 N in the 50 μm thick coating. Thermal shock resistance of the coatings depend on their thickness and thinner coating has better thermal shock resistance. The coated alloy with 50 μm thick coating can be subjected to 50 times thermal cycles of heating up to 500°C followed by quenching into water.

Substrates of Ti-based coatings were investigated regarding wear resistance and refractoriness. Substrates with and without the TiAl₃ coating formed by the ion plating method with evaporation of Al are considered. Additionally, the paper briefly presents principles of kinetics of the formation of the TiAl₃ coating.

In situ synthesized TiC reinforced composite coating was fabricated by laser cladding of Al-Ni-Cr-C powders on titanium alloys, which can greatly improve the surface performance of the substrate. In this study, the Al-Ni-Cr-C laser-cladded composite coatings have been researched by means of X-ray diffraction, scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA). There was a metallurgical combination between the Al-Ni-Cr-C laser-cladded coating and the Ti-6Al-4V substrate, and the micro-hardness of the Al-Ni-Cr-C laser-cladded coating was in the range of ~1200–1450 HV_0.2, which was ~3–4 times higher than that of Ti-6Al-4V substrate. Furthermore, the reinforcement of theAl-Ni-Cr-C laser-cladded coating were mainly contributed to the action of the TiC, Ti₃Al, Cr₇C₃, Al₈Cr₅ phases and the solution strengthening.

This paper is based on the dry sliding wear of Stellite SF12-B₄C-TiN-Mo composite coating deposited on a pure Ti using a laser cladding technique, the parameters of which provide almost crack-free composites with low porosity. To the best of our knowledge, it is the first time that Stellite SF12-B₄C-TiN-Mo mixed powders are deposited as the hard composites by a laser cladding technique. Scanning electron microscope images indicate that the nanoscale particles are produced in such coating. The fact that due to the sufficiently rapid heating and cooling rates of the laser cladding technique, the ceramics, such as TiC or TiB₂ did not have enough time to grow up, resulting in the formation of the nanoscale particles. Compared with a pure Ti substrate, the increments of the micro-hardness and wear resistance are obtained for such composite coating.

This work is based on the dry sliding wear of the MgAl₂C₂-TiB₂-FeSi composite coating deposited on a pure Ti using a laser cladding technique. Scanning electron microscope images indicate that the nanocrystals and amorphous phases are produced in such coating. X-ray diffraction result indicated that such coating mainly consists of MgAl₂C₂, Ti-B, Ti-Si, Fe-Al, Ti₃SiC₂, TiC and amorphous phases. The high resolution transmission electron microscope image indicated that the TiB nanorods were produced in the coating, which were surrounded by other fine precipitates, favoring the formation of a fine microstructure. With increase of the laser power from 0.85 kW to 1.00 kW, the micro-hardness decreased from 1350 ~ 1450 HV_0.2 to 1200 ~ 1300 HV_0.2. The wear volume loss of the laser clad coating was 1/7 of pure Ti.

In this paper, the wettability properties of coatings with hierarchical surface structures and low surface energy were studied. Hierarchically structured coatings were produced by using hydrophobic fumed silica nanoparticles and polytetrafluoroethylene (PTFE) microparticles as additives in polyester (PES) and polyvinyldifluoride (PVDF). These particles created hierarchical micro–nano structures on the paint surfaces and lowered or supported the already low surface energy of the paint. Two standard application techniques for paint application were employed and the presented coatings are suitable for mass production and use in large surface areas. By regulating the particle concentrations, it was possible to modify wettability properties gradually. Highly hydrophobic surfaces were achieved with the highest contact angle of 165${}^{\circ }$. Dynamic contact angle measurements were carried out for a set of selected samples and low hysteresis was obtained. Produced coatings possessed long lasting durability in the air and in underwater conditions.

Long tool life and high material removal rate (MRR) are the two essential requirements in rough cutting of materials. The rapid rate of the flank wear propagation in machining of nickel-based superalloys has induced the utilization of low cutting parameters when the goal was set to maximize the tool life based on the machining time or cutting length. However, this method may not provide an effective rate for the material being cut. This work presents two mathematical models to find the optimum cutting parameters results for the minimum flank wear and maximum MRR. Experimental tests were carried out based on the central composite design (CCD) in rough cutting of Inconel 625 by using TiAlN-coated insert. Maximum flank wear was measured to determine the tool wear propagation. The wear mechanisms which contribute in the tool wear were analyzed by using scanning electron microscope (SEM) to evaluate the effects of cutting parameters on the flank wear propagation. The results showed that cutting speed and depth of cut had the most significant effect on the tool wear. However, optimum cutting condition was achieved by reducing the cutting speed when feed rate and depth of cut maintained at the highest level. This was associated to the interaction of cutting speed and depth of cut, and predominant of abrasion and notching at their highest levels, respectively.

In this paper, we summarize research progress on the design and preparation of organic–inorganic hybrid coating molecular networks, which are based on the basic theory of organic–inorganic hybrid network construction. Among them, we focus on expounding the essential problems of hydrolysis during sol preparation particularly. In addition, the status of research related to titanium-containing organic–inorganic hybrid protective coatings for the surfaces of lightweight alloys such as steel, aluminum and magnesium is introduced here.

Three different types of current-collecting plates for air-hydrogen PEM fuel cell were manufactured and tested: unmodified titanium plates; gold-plated titanium plates and titanium plates treated by carbon ions implantation. It was shown that the applied surface modifications reduce contact resistance between titanium plate and carbon gas diffusion layer. Total ohmic resistance of fuel cell is reduced by 1.8 and 1.4 times in case of gold-plated titanium and carbon-implanted titanium, respectively, in comparison with uncoated titanium. Although gold plating turned out to be more profitable than carbon ion implantation in terms of electrical characteristics, in the last case, the performance enhancement was reached without using precious metals, which at mass production must play more important role. This technology promises to reduce the cost of bipolar plates manufacturing, while maintaining high electrical performance of PEM fuel cells.

In this paper, TiC reinforced composite coatings were fabricated on TC4 alloy by laser cladding Ti,Al,Si, TiC and Y₂O₃ mixed powders. Microstructures and properties of the clad coatings with and without Y₂O₃ were discussed by comparative experiments. SEM, XRD and EDS were employed to discover the microstructures and the composition of phases. The hardness and wear resistance of the coatings were tested by the MM200 wear test machine and a HV-1000 digital hardness tester, respectively. The results showed that the coating was majorly composed of Ti₅Si₃, Ti₇Al₅${\text{Si}}_{12}$, Ti₃AlC₂, Ti₃Al, Al₃Ti, TiAl and Y₂O₃. The dilution zone exhibited a metallurgical bonding without pores and cracks. Compared with the TC4 substrate, the hardness and wear resistance of the coatings were heightened by 5–6 and 4.5–5.8 times, respectively. With 2.0wt.% Y₂O₃ addition, the microstructure of the coating was refined significantly, and the microhardness and dry sliding wear resistance were enhanced further. The effects of Y₂O₃ were attributed to heterogeneous nucleation of the residual Y₂O₃.

A hard coating free of obvious defects is produced on a Ti–6Al–4V (TC4) alloy substrate by means of tungsten inert gas clad (TIGC) of the Deloro22–WC–La₂O₃ mixed powders, which greatly increased the surface performance of the substrate. Test results indicated that large quantities of needle-shape precipitates were formed in the Deloro22–WC TIGC coating, increasing the microhardness significantly, and also lots of pores are produced in this coating, weakening the wear resistance. It was noted that a fine/compact microstructure is obtained in the Deloro22–WC–La₂O₃ TIGC coating, also the defects cannot be observed obviously. La₂O₃ addition can effectively improve the fluidity of melt and hinder the growth of grains in TIGC pool, favoring a fine/compact microstructure to be produced, and also improving the wear property of the TIGC coating.