Development of Metal/Ceramic Hybrids with High Temperature Oxidation Resistance improved by Grainboundary Controlling

点击翻译按钮获取中文摘要

High-temperature oxidation of nano Ni dispersed Al_2O_3 hybrid materials (nano Ni/Al_2O_3) with effects of Y_2O_3 doping and SiC co-dispersion was investigated. Y_2O_3 doping and SiC co-dispersion improve high temperature oxidation resistance of nano Ni/Al_2O_3. Temperature dependence of oxidation rate of Y-doping and SiC co dispersion samples became larger than that of undoped ones. Because them were no significant difference in Al_2O_3 grain size of the oxidized zone between their Ni/Al_2O_3 hybrids, grain boundary diffusion of oxygen of Al_2O_3 matrix was decreased by doping Y_2O_3 and SiO_2 at Al_2O_3 grain boundary. However the effects of Y_2O_3 and SiO_2 to decrease oxidation rate of Ni/Al_2O_3 is much smaller than that to decrease oxygen diffusion at grain boundary of Al_2O_3. In the case of oxidation of Ni/Al_2O_3, the Al_2O_3 matrix grain boundary is also contaminated with Ni ions doped by oxidation of nano Ni particle dispersion. This contamination of Ni ions at Al_2O_3 grain boundary may decrease the effects of Y_2O_3 and SiO_2 to decrease the grain boundary diffusion of oxygen in Al_2O_3.On the other hand, it is revealed that nano Ni/Al_2O_3 has crack-healing effects by thermal oxidation process. The crack-healing process of nano Ni/Al_2O_3 is a thermal activation process and the apparent activation energy is in good agreement with that of grain boundary diffusion of Ni in Al_2O_3. Cracks are filled up by oxide product, NiAl_2O_4, which was developed by outward diffusion of cations during thermal oxidation process. Nano Ni/Al_2O_3 with fine SiC dispersion also shows the crack-healing effect with comparable heeling rate with nano Ni/Al_2O_3. SiC co-dispersion into nano Ni/Al_2O_3 is realized to improve high-temperature oxidation resistance without decreasing of crack-healing performance.