1989 Volume 38 Issue 435 Pages 1415-1421
Evaluations of thermal shock resistance, including the onset of crack propagation and progressive crack growth, and examinations to the deterioration property for tetragonal zirconia polycrystalline (TZP), silicon nitride and silicon carbide were conducted under various repeated thermal shock conditions. Vickers indented specimens with various surface flaws sizes were employed for these experiments.
The results obtained were summarized as follows:
(1) The minimum thermal shock condition required for the onset of crack propagation was proportional to the inverse square root of surface crack length under repeated thermal shock conditions.
(2) The actual stress intensity factor KI of crack near the specimen surface was obtained by using a fracture mechanics formula for semielliptical flaws and making some corrections to the thermal stress value by taking the Biot modulus difference into considerations. As a result, KI values of TZP, silicon nitride and silicon carbide were found to be about 17-33%, 17% and 6.9% compared with those calculated without corrections from the surface half crack length by employing usual fracture mechanics formula.
(3) TZP, which has the largest KIc value and bending strength, showed superior character, when the resistance of material under repeated thermal shock conditions was evaluated by the amount of crack growth per each cycle. Silicon carbide had the smallest resistance under the repeated thermal shock condition.