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Abstract: In this work, the oxidation‐induced crack healing of Al2O3 containing 20 vol.% of Ti2AlC MAX phase inclusions as healing particles was studied. The oxidation kinetics of the Ti2AlC particles having an average diameter of about 10 μm was studied via thermogravimetry and/or differential thermal analysis. Surface cracks of about 80 μm long and 0.5 μm wide were introduced into the composite by Vickers indentation. After annealing in air at high temperatures, the cracks were filled with stable oxides of Ti and Al as a result of the decomposition of the Ti2AlC particles. Crack healing was studied at 800, 900, and 1000°C for 0.25, 1, 4, and 16 hours, and the strength recovery was measured by 4‐point bending. Upon indentation, the bending strength of the samples dropped by about 50% from 402 ± 35 to 229 ± 14 MPa. This bending strength increased to about 90% of the undamaged material after annealing at 1000°C for just 15 minutes, while full strength was recovered after annealing for 1 hour. As the healing temperature was reduced to 900 and 800°C, the time required for full‐strength recovery increased to 4 and 16 hours, respectively. The initial bending strength and the fracture toughness of the composite material were found to be about 19% lower and 20% higher than monolithic alumina, respectively, making this material an attractive substitute for monolithic alumina used in high‐temperature applications. [ABSTRACT FROM AUTHOR]

We report on the use of TiC particles as high temperature healing agent in alumina based composites. The selection of TiC was based on a theoretical analysis of its high temperature stability in contact with Al 2 O 3 , its volumetric expansion upon oxidation and the adhesion between the reaction product TiO 2 with Al 2 O 3 . Fully dense 15 and 30 vol.% TiC-Alumina composites were made by Spark Plasma Sintering. Initial damage was produced by Vickers indentations. The strength recovery was determined for temperatures between 400 and 800 °C. The mechanical measurements were complemented by microstructural characterization of the base material and the healed cracks. [ABSTRACT FROM AUTHOR]

To date, the research aimed at creating a high-temperature alumina (Al 2 O 3 ) grade capable of autonomously repairing crack damage focussed on the use of SiC particles which turns to SiO 2 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, Cr 3 C 2 , Cr 2 N, ZrN, NbC and NbN as promising agents for autonomous healing of alumina when used in air at high temperatures. [ABSTRACT FROM AUTHOR]