Papers by Author: Ya Zhe Xing

Abstract: The effects of CuO, TiO₂ and B₂O₃ oxides and nanocrystalline Al₂O₃+ TiO₂ particles on the sintering of Al₂O₃ glass-ceramics were investigated by X-ray diffraction and scanning electron microscopy. The CuO and TiO₂ oxides can effectively facilitate the formation of CuO–Al₂O₃–TiO₂ glass ceramic. The CuO, TiO₂ and Al₂O₃ oxides can form the new phase Cu₂Ti₄O and CuAl₂O₄. They wrapped the Al₂O₃ grains tightly, so the density ceramic was fabricated successfully sintered at 1300°C. Analyzing the fracture surface morphology, the ceramic added CuO, TiO₂ oxides shows the mixed mode of intergranular and transgranular fracture. However, after added B₂O₃ oxides the B₂O₃-CuO–Al₂O₃–TiO₂ glass ceramic shows the mode of intergranular fracture. The ceramic added nanocrystalline Al₂O₃ + TiO₂ was more density and fine organization. The fracture mode is as same as the ceramic added CuO, TiO₂ oxides.

Abstract: In this work, three cast iron coatings were produced by atmospheric plasma spraying. During spraying, the surface temperature of three coatings (substrate temperature) was controlled to be averagely 50oC, 180oC and 240oC by changing the processing parameters. X-ray diffraction (XRD) was employed to analyze the phase structure of the starting powder and the coatings. The results showed that the powder was mainly composed of (Fe,Cr)7C3 and martensite and both the spraying processing and the substrate temperature exerted no influence on coating phase structure. An optical microscope (OM) was used to characterize the microstructure of the cross-section and surface of the coatings. It was found that the cross sectional hardness increased with the increase of the substrate temperature due to the improvement in interlamellar bonding.

Abstract: A composite layer was prepared on the Ti-6Al-4V alloy surface by ion nitriding, magnetron sputtering Mo and ion sulfurizing composite treatment technique. The phase structure, morphology, and cross-sectional element distribution of composite layer were analyzed. Friction and wear properties of composite layer were tested by MM-200 laboratory tester. XRD analysis showed that the composite layer was mainly comprised of Ti, Mo, MoS2, TiN, and transition layer. This composite layer is perfect wear-resistant surface due to existence of self-lubricating MoS2 on hard Mo and TiN layers with good anti-friction ability. Thereby, the results of friction and wear test showed that anti-wear performance of Ti-6Al-4V alloy after composite treatment was remarkably improved under dry and sliding conditions. Both the friction coefficient and the wear loss of the nitriding-Mo plating-sulfurizing layers were lower than that of the nitriding layer due to the formation of the MoS2 layer on Mo and TiN layers.

Abstract: Three composite coatings were prepared by nitriding-sulfurizing processing of Ti-6Al-4V alloy at different sulfurizing temperatures. The microstructure and phase structure of the coatings were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Furthermore, the hardness of the coatings was measured. The effect of the sulfurizing temperature on microstructure of coatings was investigated. The results indicated that the composite coating was mainly comprised of titanium nitrides, titanium sulfides, and titanium. It was found that the phase composition of composite coating changed with the variation of the sulfurizing temperature.

Abstract: In this work, an experiment was performed to demonstrate the possibility of the metallurgical bonding in plasma-sprayed cast iron coatings at high substrate temperature. A quantitative analysis of splat cooling and rapid solidification of cast iron splat is then presented. The effect of the substrate temperature on the development of melt undercooling within the splat is investigated in detail. The results indicated that the initial substrate temperature has a profound effect on the development of melt undercooling in a splat, the splat bottom melt temperature, and the substrate surface temperature. A high initial temperature of the substrate restrains the cooling of the splat and leads to a high melt temperature that may promote the grain growth directly on cast iron substrate surface to form the metallurgical bonding.

Abstract: YSZ molten droplets created by plasma spraying were deposited on the YSZ substrate preheated to different temperature from 75oC to 1000oC. The results showed that there is little change in crack spacing when substrate temperature is less than about 740oC, and a significant increase in crack spacing from 3.54 μm at 740oC to 10.91 μm at 1000oC was observed. A simple qualitative model was proposed on the basis of the origin of thermal stresses to explain the influence of substrate initial temperature on crack density characterized by crack spacing. The analysis indicates that the results can be ascribed to the changes in tensile stress and splat/substrate adhesion resulting from changes of substrate initial temperature.