Influence of Ni Ion Diffusion of Growth of NiAl<sub>2</sub>O<sub>4</sub> Self-healing Layer on Al<sub>2</sub>O<sub>3</sub> Matrix Dispersed with Ni Particles Composite

It is known as Al2O3 dispersed with Ni particles composite (Ni/Al2O3) has self-healing function which recovers mechanical properties by the high-temperature oxidation of dispersoids. Ni/Al2O3 appear self-healing function not only by the contribution of high-temperature oxidation of Ni particles exposed on sample surface, but also contribution of grain boundary diffusion of Ni ions through Al2O3 matrix. The objective of this study is to investigate the influence of Ni ion diffusion on the growth of NiAl2O4 self-healing layers with different Ni volume fractions. Dence Ni/Al2O3 were prepared and etched nitric acid to remove surface Ni particles. Samples were heat treated at 1100–1355℃ for 6–48 h in air. NiAl2O4 self-healing layer is observed on the sample surfaces with and without etching. The NiAl2O4 self-healing layer grows with parabolic manner with respect to the heat treatment time, indicating that the diffusion of Ni ion through the Al2O3 grain boundary is the rate-controlling. The contribution of surface Ni to the growth of NiAl2O4 layers is independent of heat treatment conditions due to the surface Ni particles are defined by the Ni dispersion ratio. The contribution of Ni ion diffusion increases linearly with increasing Ni volume fraction. It indicates that the amount of Ni ions diffused through the grain boundary is proportional to the Ni volume fraction.