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

研究了Y2 O3掺杂和SiC共分散对纳米Ni/Al 2 O3杂化材料高温氧化性能的影响。Y_2O_3掺杂和SiC共分散提高了纳米Ni/Al_2O_3的抗高温氧化性能。氧化速率的温度依赖性Y掺杂和SiC共分散样品变得比未掺杂的。由于Ni/Al_2O_3杂化材料氧化区的Al_2O_3晶粒尺寸无明显差异，在Al_2O_3晶界掺杂Y_2O_3和SiO_2，可降低氧在Al_2O_3基体中的晶界扩散。而Y_2O_3和SiO_2对Ni/Al_2O_3氧化速率的降低作用远小于对Al_2O_3晶界氧扩散的抑制作用。在Ni/Al_2O_3氧化过程中，纳米Ni颗粒弥散氧化掺杂的Ni离子也污染了Al_2O_3基体晶界。Ni离子在Al_2O_3晶界的污染可能减弱了Y_2O_3和SiO_2对氧在Al_2O_3晶界扩散的抑制作用。另一方面，纳米Ni/Al_2O_3复合材料具有热氧化修复裂纹的作用。纳米Ni/Al_2O_3复合材料的裂纹愈合过程是一个热激活过程，其表观激活能与Ni在Al_2O_3中晶界扩散的表观激活能一致。裂纹被热氧化过程中阳离子向外扩散形成的氧化物NiAl_2O_4所填充。SiC弥散的纳米Ni/Al_2O_3复合材料也表现出良好的裂纹愈合效果，其愈合速率与纳米Ni/Al_2O_3相当。实现了SiC在纳米Ni/Al_2O_3中的共分散，在不降低裂纹愈合性能的前提下提高了材料的高温抗氧化性能。

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.