Crack-Healing Behavior of Liquid-Phase-Sintered Silicon Carbide Ceramics

Crack-healing behavior of liquid-phase-sintered (LPS) SiC ceramics has been studied as functions of heat-treatment temperature and crack size. Results showed that heat treatment in air could significantly increase the indentation strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature depends on the softening temperature of an intergranular phase in each material. After heat treatment at the optimum temperature in air, the crack morphology almost entirely disappeared and the indentation strength recovered to the value of the smooth specimens at room temperature for the investigated crack sizes up to ∼200 μm. In addition, a simple heat treatment of SiC ceramics sintered with Al2O3–Y2O3–CaO at 1100°C for 1 h in air resulted in even further improvement of the strength, to a value of 1054 MPa (∼150% of the value of the unindented strength). Crack closure and rebonding of the crack wake due to oxidation of cracked surfaces were suggested as a dominant healing mechanism operating in LPS-SiC ceramics.

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