The oxidation-induced crack healing of an Al₂O₃ composite loaded with various volume fractions of Ti₂Al_0.5Sn_0.5C repair filler particles was investigated by annealing in air at a relatively low temperature of 700°C. After annealing a composite with 20 vol.% repair fillers (with a particle size of ~5.6 µm) for 48 hours, artificial indentation cracks prepared on the surface, as well as pores near the surface, were completely healed by filling with condensed oxidation products. Additionally, minor fraction of metallic Sn was detected. A complementary study by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy revealed that nano-sized oxidation products (SnO₂, TiO₂, and α-Al₂O₃ phase) were formed as major crack-filling species. After healing, the strength recovery of the Al₂O₃ composites was significantly improved in the composites loaded with more than 10 vol.% repair fillers and achieved 107% at 700 for 48 hours.

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Crack healing in MAX phase-based ceramics is mainly attributed to the reaction of M and A metal with oxygen penetrating into the crack. The intrinsic healing mechanisms of Al-contained MAX phases are due to formation of adhesive Al2O3 phase in the crack gaps, while Sn-contained MAX phases are ascribed to formation of major TiO2 and SnO2 in the bigger crack gaps and metallic Sn formation in the smaller secondary cracks. The oxides as well as metallic phase filling the crack may restore the integrity of MAX phase ceramic components. The mechanical strength and the electrical conductivity of the MAX phase ceramics can be fully restored after the healing process. The remarkable healing abilities of those MAX phases make them promising repair fillers for those ceramics with poor healing ability. Al2O3 mixed with Ti2Al0.5Sn0.5C MAX phase was selected as a model to demonstrate the healing efficiency. The fracture strength of 20 vol.% repair filler composites containing artificial indent cracks recovered fully to the level of the virgin material upon isothermal annealing in air atmosphere after 48 h at 700 °C and 0.5 h at 900 °C. The evolution of the crack-filling microstructure was explored by X-ray powder diffraction and transmission electron microscopy analyses.@en