Crack Disappearance Effect of Fe-Dispersed Alumina Composite Ceramics using High-Temperature Oxidation of Metallic Iron Particles

Abstract

Self-healing function in the ceramic-based composites is one of unique characteristics to improve the strength reliability by oxidation of dispersoids. Metallic iron particles are one of base metal and easy to oxidize at air atmosphere. The objective of this study is to investigate the crack disappearance behavior of Fe-dispersed alumina composite ceramics by high-temperature oxidation.

Surface cracks were introduced on Fe/Al₂O₃ samples. The samples were heat treated at 700–900°C for 1–24 h in air. Crack lengths were measured before/after heat treatment and the crack disappearance rates were calculated. The introduced cracks disappear by the formation of Fe₂O₃. The formed oxides appear to have a spider-web shape. The mesh diameter of spider-web is approximately 1–2 µm, which corresponds to the Al₂O₃ grain size of sintered body. The crack disappearance rate increases with increasing heat treatment temperature and time. From the temperature dependence of the crack disappearance rate, the apparent activation energy for the crack disappearance is found to be Q = 160 kJ/mol. The value of activation energy in this study is lower than the values of volume diffusion of Fe ions through Al₂O₃. It implies that grain boundary diffusion of Fe ions contributes to the crack disappearance.