Selection of healing agents for autonomous healing of alumina at high temperatures

To date, the research aimed at creating a high-temperature alumina (Al2O3) grade capable of autonomously repairing crack damage focussed on the use of SiC particles which turns to SiO2 as the healing agent. The present work presents an unbiased selection procedure to determine other attractive substances and phases which could serve as an effective healing agent for healing at high temperatures. The selection process is based on an analysis of the requested characteristics of the oxide to fill the crack (melting point, adhesion to the alumina matrix and thermal mismatch) as well as those of the healing agent prior to being activated (melting point, volume expansion upon oxidation and thermal mismatch). Application of all selection criteria resulted in identifying granular Ti, Cr, Zr, Nb, Hf, TiC, TiN, Cr3C2, Cr2N, ZrN, NbC and NbN as promising agents for autonomous healing of alumina when used in air at high temperatures.