Crack-healing performance and oxidation behavior of SiC dispersed yttrium silicate composites

Yttrium silicate-based composites dispersed with silicon carbide particles have been proposed as a novel material concept of self-healing environmental barrier coatings applied for Si-based ceramics and their composites. Crack-healing effectiveness as well as high-temperature oxidation behavior of the yttrium silicate composites was investigated as functions of oxidation time and temperatures. Dense samples of the composites dispersed with 5 vol% SiC particles were fabricated by using the pulsed electric current sintering technique. Thermal oxidation for self-healing was conducted at temperatures ranging from 1000 degrees C to 1300 degrees C for from 1 to 24 h in air. High-temperature oxidation experiments were carried out at temperatures ranging from 1200 degrees C to 1400 degrees C for from 1 to 60 h in air. As a result, the surface cracks with approximately 200 mu m in length introduced on the sample surface were disappeared completely after heat treatment at 1300 degrees C for 1 h in air. Crack-healing performance of SiC/Y2SiO5 is better than that of SiC/Y2Si2O7. The crack-healing performance of SiC/Y2SiO5-Y2Si2O7 is in the middle of that of SiC/Y2SiO5 and SiC/Y2Si2O7. The mechanism of crack healing was identified as the consequence of SiC oxidation into SiO2, which accompanies a volume expansion, and outward diffusion of Y3+ cations caused the formation of Y2Si2O7 outer layer. Oxidation of SiC particles within the matrix developed an oxidized zone. Growth of the oxidized zone obeyed the parabolic law, which meant diffusion process in the oxidized zone is the rate-controlling process.