The high temperature strength of SiC ceramics based on SiO2 nano-colloidal employed

This study was carried out on the crack-healing behavior of two types of SiC ceramics based on a SiO2 additive, and mainly on the high temperature strength of crack-healed specimens. The mean particle sizes of the SiC, Al2O3 and Y2O3 powders used in this study were 0.27 μm, 0.1 μm and 33 nm, respectively. The SiO2 employed was a nano-colloidal (SiO2 12% solid solution). The SiC ceramics were prepared using a mixture of 85 or 90 wt.%. SiC powder and sintering additives (Al2O3:Y2O3 = 6:4 and SiO2 = 0 or 3 wt.%). The mixtures were subsequently hot-pressed in N2 gas for 1 h via hot-pressing conducted under 35 MPa at 2053 K. In both specimens, the optimized crack-healing condition was 1373 K for 1 h in air. The crack-healing material of the crack part was the glassy phase of SiO2 by oxidation reaction of SiC and O2. The limiting temperatures for bending strength of smooth and crack-healed specimens of two types of specimens of SAY and SAYS were 1373 K and 1273 K, respectively. That is, the crack-healed specimens had good high temperature strength in spite of the fact that the crack-healing material is the glassy phase of SiO2.