Plasma electrolytic oxidation （PEO） coatings, formed under various anodic voltages （320-440 V） on biomedical NiTi alloy, are mainly composed of γ-AI203 crystal phase. The evolution of discharging sparks during th...Plasma electrolytic oxidation （PEO） coatings, formed under various anodic voltages （320-440 V） on biomedical NiTi alloy, are mainly composed of γ-AI203 crystal phase. The evolution of discharging sparks during the PEO process under different anodic voltages was observed. The surface and cross-sectional morphologies, composition, bonding strength, wear resistance and corrosion resistance of the coatings were investigated by scanning electron microscopy （SEM）, thin-film X-ray diffraction （TF-XRD）, energy dispersive X-ray spectrometry （EDS）, surface roughness, direct pull-off test, ball-on-disk friction and wear test and potentiodynamic polarization test, respectively. The results showed that the evolution of discharging sparks during the PEO process directly influenced the microstructure of the PEO coatings and further influences the properties. When the anodic voltage increased from 320 V to 400 V, the corrosion resistance and wear resistance of the coatings slowly increased, and all the bonding strength was higher than 60 MPa; further increasing the anodic voltages, especially up to 440 V, although the thickness and γ-AI203 crystallinity of the coatings further increased, the microstructure and properties of the coatings were obviously deteriorated.展开更多
In this research, development of AI356-AI203 nanocomposite coatings has been investigated. AI356-AI203 composite powders were prepared by mechanical milling of AI356 powder and 5 vol.% micro and nanoscaled alumina par...In this research, development of AI356-AI203 nanocomposite coatings has been investigated. AI356-AI203 composite powders were prepared by mechanical milling of AI356 powder and 5 vol.% micro and nanoscaled alumina particles. The milled powders were used as feedstock to deposit composite coatings on A356-T6 aluminum alloy substrate using high velocity oxy-fuel （HVOF） process. X-ray diffractometry, optical and scanning electron microscopy, microhardness and wear tests were used to characterize the composite powders and coatings. The hardness of composite coatings containing micro and nanosized AI203 were 114.1 ± 5.9 HV and 138.4 ± 6.9 HV, respectively which were higher than those for substrate （79.2 ± 1.1 HV）. Nano and microcomposite coatings revealed low friction coefficients and wear rates, which were significantly lower than those obtained for AI356-T6 substrate. Addition of 5 vol.% micro and nanoscaled alumina particles improved the wear resistance by an average of 85% and 91%, respectively. This is mainly caused by the presence of AI203 in matrix and nanocrystalline structure of matrix. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.展开更多
An A1203p/A1 composite was successfully synthesized using a displacement reaction between 80 wt% A1 and 20 wt% CuO powders at a heating rate of 5 ℃/min. Two different sizes CuO particles were used, and all the experi...An A1203p/A1 composite was successfully synthesized using a displacement reaction between 80 wt% A1 and 20 wt% CuO powders at a heating rate of 5 ℃/min. Two different sizes CuO particles were used, and all the experiments were conducted under an argon atmosphere. To analyze the microstructural evolution during synthesis, the A1-20 wt% CuO samples were heated to the temperatures selected according to the differential scanning calorimetry curve and then immediately quenched with water. The phase composites and microstructure of the water-quenching samples were in- vestigated using X-ray diffraction, optical microscopy, scanning electron microscopy and energy-dispersive spectrometry. The results indicate that the CuO particle size has a significant effect on the microstructural evolution of the samples during the heating stage and on the microstructure of synthesized composites. Smaller CuO particles can decrease the reaction temperature, narrow the reaction temperature range at the different reaction stages during the heating stage and make the size and distribution of in situ A1203 particles more uniform. The reaction between A1 and CuO can be complete as the temperature rises to 900 ℃. The size of the in situ A1203 particles is approximately 5 μm when the size of the CuO particles is less than 6 μm. This sample has a relatively high Rockwell hardness of 60 HRB.展开更多
基金the financial support from the National Natural Science Foundation of China (Grant No. 51101085)the National Natural Science Foundation of Jiangxi Province (Grant No. 20114BAB216014)+1 种基金the Science and Technology Plan Projects of Jiangxi Province (Grant No.20111BBG70007-2)the Science and Technology Plan Projects of Department of Education of Jiangxi Province (Grant No.GJJ12450)
文摘Plasma electrolytic oxidation （PEO） coatings, formed under various anodic voltages （320-440 V） on biomedical NiTi alloy, are mainly composed of γ-AI203 crystal phase. The evolution of discharging sparks during the PEO process under different anodic voltages was observed. The surface and cross-sectional morphologies, composition, bonding strength, wear resistance and corrosion resistance of the coatings were investigated by scanning electron microscopy （SEM）, thin-film X-ray diffraction （TF-XRD）, energy dispersive X-ray spectrometry （EDS）, surface roughness, direct pull-off test, ball-on-disk friction and wear test and potentiodynamic polarization test, respectively. The results showed that the evolution of discharging sparks during the PEO process directly influenced the microstructure of the PEO coatings and further influences the properties. When the anodic voltage increased from 320 V to 400 V, the corrosion resistance and wear resistance of the coatings slowly increased, and all the bonding strength was higher than 60 MPa; further increasing the anodic voltages, especially up to 440 V, although the thickness and γ-AI203 crystallinity of the coatings further increased, the microstructure and properties of the coatings were obviously deteriorated.
文摘In this research, development of AI356-AI203 nanocomposite coatings has been investigated. AI356-AI203 composite powders were prepared by mechanical milling of AI356 powder and 5 vol.% micro and nanoscaled alumina particles. The milled powders were used as feedstock to deposit composite coatings on A356-T6 aluminum alloy substrate using high velocity oxy-fuel （HVOF） process. X-ray diffractometry, optical and scanning electron microscopy, microhardness and wear tests were used to characterize the composite powders and coatings. The hardness of composite coatings containing micro and nanosized AI203 were 114.1 ± 5.9 HV and 138.4 ± 6.9 HV, respectively which were higher than those for substrate （79.2 ± 1.1 HV）. Nano and microcomposite coatings revealed low friction coefficients and wear rates, which were significantly lower than those obtained for AI356-T6 substrate. Addition of 5 vol.% micro and nanoscaled alumina particles improved the wear resistance by an average of 85% and 91%, respectively. This is mainly caused by the presence of AI203 in matrix and nanocrystalline structure of matrix. Scanning electron microscopy tests revealed different wear mechanisms on the surface of the wear test specimens.
基金financially supported by the Inner Mongolia Natural Science Foundation of China (Nos. 2012MS0801 and 2013MS0804)
文摘An A1203p/A1 composite was successfully synthesized using a displacement reaction between 80 wt% A1 and 20 wt% CuO powders at a heating rate of 5 ℃/min. Two different sizes CuO particles were used, and all the experiments were conducted under an argon atmosphere. To analyze the microstructural evolution during synthesis, the A1-20 wt% CuO samples were heated to the temperatures selected according to the differential scanning calorimetry curve and then immediately quenched with water. The phase composites and microstructure of the water-quenching samples were in- vestigated using X-ray diffraction, optical microscopy, scanning electron microscopy and energy-dispersive spectrometry. The results indicate that the CuO particle size has a significant effect on the microstructural evolution of the samples during the heating stage and on the microstructure of synthesized composites. Smaller CuO particles can decrease the reaction temperature, narrow the reaction temperature range at the different reaction stages during the heating stage and make the size and distribution of in situ A1203 particles more uniform. The reaction between A1 and CuO can be complete as the temperature rises to 900 ℃. The size of the in situ A1203 particles is approximately 5 μm when the size of the CuO particles is less than 6 μm. This sample has a relatively high Rockwell hardness of 60 HRB.
