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 (PO2 ) 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 degrees C for 1-24 h under PO2 from 1 to 5 x 104 Pa. Surface cracks were completely healed at 1300 degrees C for 1 h under all PO2 tested conditions. Higher PO2 contributed to increased selfhealing 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 O2- anions resulted in the formation of an internally oxidized zone (IOZ), following parabolic growth. Higher PO2 results in a thicker IOZ. A kinetic model for high temperature oxidation was developed from diffusion mechanism and defect chemistry viewpoint.