Crack-Healing Behavior of Monolithic Alumina and Strength of Crack-Healed Member
Byung-Soo KIM, Kotoji ANDO, Min-Cheol CHU and Shinji SAITO
Abstract:Three point bending specimen was made from commercial alumina and Al2O3/SiC composite ceramics. A semi-elliptical surface crack up to 500Κm in diameter (aspect ratioΰ0.9) was introduced on the test specimens. Basic crack-healing behavior was systematically studied as a function of crack-healing temperature, environment and crack size. Three point bending strength was measured at room temperature and elevated temperatures up to 1500. The crack-healing behavior of monolithic alumina was compared with that of Al2O3/SiC. Main conclusions obtained are as follows; (1) Bending strength of pre-cracked specimens of alumina recovered due to crack-healing. A surface crack of 100Κm could be healed by the crack-healing above 1400 for 1h. Difference of annealing environment had no significant effect on the crack-healing behavior of monolithic alumina above 1400. (2) The recovery of strength in monolithic alumina was caused by the sintering process or the removal of tensile residual stress near the pre-crack. Above 1400, the sintering mechanism is assumed to be dominant, however, below 1300, annealing mechanism is dominant. (3)The crack-healing of Al2O3/SiC occurs due to oxidation mainly, which is quite different from that of monolithic alumina. (4) The specimens which was crack-healed above 1400 had similar bending strength to base material up to 1200. Key Words:Monolithic alumina, Crack-healing, Strength recovery by heat treatment, Tensile residual stress, Bending strength at high temperature