Crack-healing ability of structural ceramics and a new methodology to guarantee the structural integrity using the ability and proof-test

Recently, the authors developed Si3N4, Al2O3 and mullite ceramics with good self-crack-healing abilities. It was shown that the optimized crack-healing condition to get high temperature strength was: 1573 K, 1 h, in air, and the healed zone exhibited the same strength as the base material up to about 1573 K (Si3N4 and Al2O3) and 1473 K (mullite), respectively. Using this good crack-healing ability, a new methodology to guarantee the reliability of ceramic components [crack-healing + proof test] was proposed. It was shown that reliability could be guaranteed before service by this technique, using about 200 samples. However, if a crack initiated during service, reliability would be severely impaired. Therefore, if a material can heal a crack during service, and if the healed zone has enough strength at the temperature of healing, it would be very desirable for structural integrity. From the above points of view, a new methodology to guarantee the structural integrity of ceramic components using in situ crack-healing ability was proposed and the usefulness is discussed using the test results in terms of crack-healing behavior and proof test theory by the authors.