Autonomous crack healing ability of SiC dispersed Yb2Si2O7 by oxidations in air and water vapor

Abstract

Yb 2 Si 2 O 7 is a popular environmental barrier coating; however, it decomposes into Yb 2 SiO 5 in high-temperature steam environments. The thermal mismatch between Yb 2 Si 2 O 7 and Yb 2 SiO 5 leads to the cracking and failure of the disilicate coating via oxidation. Dispersing SiC nanofillers into the Yb 2 Si 2 O 7 matrix is suggested to maintain the Yb 2 Si 2 O 7 matrix and promote crack self-healing. This study is aimed at clarifying the effect of water vapor on the self-healing ability of such composites. X-ray diffraction analysis and scanning electron microscopy were used to monitor the surface composition and the crack formation, respectively, in 10 vol% SiC-dispersed Yb 2 Si 2 O 7 composites. Annealing at temperatures higher than 750 °C in air or in a water vapor rich atmosphere led to strength recovery and the self-healing of indentation-induced surface cracks owing to volume expansion during the oxidation of SiC. The self-healing effect was influenced by the oxidation time and temperature. Rapid diffusion of H 2 O as an oxidizer into the SiO 2 layer promoted self-healing in a water vapor rich atmosphere. However, accelerated oxidation at temperatures higher than 1150 °C formed bubbles on the surface. Fabricating composites with a small amount of Yb 2 SiO 5 will be a solution to these problems.