Microstructure and mechanical properties of liquid-phase-sintered SiC+Si3N4 composites

The microstructure and some mechanical properties (Young's modulus, hardness, fracture toughness, and flexural strength) of as-received and heat-treated liquid-phase-sintered SiC + Si3N4 composites have been investigated. The hardness and the fracture toughness were determined by Vickers indentation method and the Young's modulus was measured by depth-sensing indentation test. Flexural strength measurement was performed by means of four-point bend test. The characteristic flexural strength and Weibull modulus were computed using two-parameter Weibull distribution. Fractographic analysis of broken flexural specimens was used to characterize the fracture initiation origins. The strength of the investigated materials was degraded by the present processing flaws in the form of pores and clusters of pores. The fracture toughness was enhanced by changing the SiC grains size and aspect ratio after the heat treatment at 1850 degrees C/5 h.