Kinetics of self-healing and thermal oxidation of SiC-dispersed yttrium silicate composites under different oxygen partial pressure in steam-containing atmosphere

Influence of oxygen partial pressure ($P_{O_2}$) on the self-healing and high-temperature oxidation was investigated on Y₂Si₂O₇-Y₂SiO₅-based composites dispersed with SiC particles. Almost fully densified samples were fabricated by using the pulsed electric current sintering technique. Self-healing performance and oxidation resistance was assessed after annealing samples at 1100–1400°C for 1–24 h under $P_{O_2}$ from 1 to 5 × 10⁴ Pa. Surface cracks were completely healed at 1300°C for 1 h under all $P_{O_2}$ tested conditions. Higher $P_{O_2}$ contributed to increased self-healing ability. In this series, the primary mechanism for surface crack recovery is SiC volume expansion, with the outward diffusion of Y³⁺ ions playing a supportive, secondary role. The inward diffusion of O^2- anions resulted in the formation of an internally oxidized zone (IOZ), following parabolic growth. Higher $P_{O_2}$ results in a thicker IOZ. A kinetic model for high temperature oxidation was developed from diffusion mechanism and defect chemistry viewpoint.