Fatigue Strength of an Al2O3/SiC Composite and a Monolithic Al2O3 Subjected to Crack-Healing Treatment
Kotoji ANDO, Byung-Soo KIM, Shin KODAMA, Sung-Po LIU, Koji TAKAHASHI and Shinji SAITO
Abstract:Three point bending (rectangular bar) specimen was made from sintered Al2O3/SiC composite and commercial Al2O3. A semi-elliptical surface crack of 100ƒÊm in diameter (aspect ratioà0.9) was introduced on the sample by indentation method. The sample was subjected to the following crack-healing treatment; Al2O3/SiC composite (temperature: 1573K, crack-healing time: 1 h), and monolithic Al2O3 (temperature: 1373K or 1723K, crack-healing time: 1 h). Monolithic Al2O3 was able to recover strength of cracked sample by heat treatment at 1723K. The recovery was caused by the secondary sintering process. However, the cracked sample recovered strength slightly by the heat treatment at 1373K. The incomplete strength recovery of cracked sample was caused by the removal of tensile residual stress ahead of crack. The Al2O3/SiC composite exhibited large crack-healing ability. The bending strength of the cracked Al2O3/SiC sample was about 180MPa. By the crack-healing treatment, the strength recovered up to about 850MPa. And also, crack-healed Al2O3/SiC sample exhibited very high static and cyclic fatigue limit of 600MPa and 700MPa, respectively. From these test results, it can be concluded that Al2O3/SiC has excellent crack-healing ability and the crack-healing is a desirable technology for the structural integrity of Al