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

研究了Y_2O_3掺杂和SiC共分散对纳米Ni/Al_2O_3杂化材料（纳米Ni/Al_2O_3）高温氧化的影响。Y_2O_3掺杂和SiC共分散提高了纳米Ni/Al_2O_3的高温抗氧化性。y掺杂和SiC co分散样品的氧化速率对温度的依赖性大于未掺杂样品。由于Ni/Al_2O_3杂化体氧化区Al_2O_3晶粒尺寸没有显著差异，在Al_2O_3晶界处掺杂Y_2O_3和SiO_2可以降低Al_2O_3基体中氧的晶界扩散。但Y_2O_3和SiO_2对Ni/Al_2O_3氧化速率的影响远小于对Al_2O_3晶界氧扩散的影响。在Ni/Al_2O_3氧化的情况下，Al_2O_3基体晶界也被纳米Ni颗粒分散氧化掺杂的Ni离子污染。Ni离子在Al_2O_3晶界处的污染可能会减弱Y_2O_3和SiO_2对Al_2O_3中氧的晶界扩散的影响。另一方面，通过热氧化工艺发现纳米Ni/Al_2O_3具有裂纹愈合作用。纳米Ni/Al_2O_3的裂纹愈合过程为热活化过程，其表观活化能与Ni在Al_2O_3中的晶界扩散的表观活化能吻合较好。裂纹由氧化产物NiAl_2O_4填充，这是热氧化过程中阳离子向外扩散形成的。具有良好SiC分散体的纳米Ni/Al_2O_3也表现出与纳米Ni/Al_2O_3相当的裂纹愈合效果。实现了SiC共分散到纳米Ni/Al_2O_3中，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.