PAS烧结SiC/h-BN复相陶瓷的韧性表征

In order to investigate the failure characteristics of SiC/h-BN ceramic composites prepared by the plasma activated sintering (PAS) process, three kinds of toughness characterization methods (fracture toughness K_IC, toughness ratio and R curve) were used as the basis to toughness for failure judgment of these composites. The microstructure of crack extension was also analyzed and discussed, and the failure model of the composites was established. The results show that both K_IC was decreased with the h-BN content increase for the composites. The toughness ratio (TI) increased with the increasing h-BN content indicating the better toughness. Combined with the result of R curves, the composite with more h-BN content exhibited steeper rise R curve tendency, which had a lower crack extension threshold. So, there is a contradiction between the three kinds of toughness results. Based on the microstructure analysis, the h-BN plates existing in the composites could consume more fracture surface energy, and the cracks deflection, branching and bridging were occurred during cracks extension. Hence, K_IC as the toughness index reflected the resistance of crack initiation, and TI indicating the crack extension resistance. To guide the application and failure evaluation of these ceramic composites, proper parameter should be used to characterize toughness under the different stress state of materials in engineering application.