Effect of heat treatment on the mechanical properties of SiC_f/BN/SiC fabricated by CVI

Three types of SiC fiber reinforced SiC matrix composites (SiC_f/SiC) with BN interphase were fabricated by a chemical vapor infiltration (CVI) method to investigate the effect of heat treatment (HT) on the mechanical properties of the prepared materials. The different mechanical behaviors of the three composites were analyzed based on the He and Hutchinson׳s model. The mechanical properties of SiC_f/SiC composites were improved (366–377 MPa in flexural strength, 13.9–16.2 MPa m^1/2 in fracture toughness) by the HT after the infiltration of SiC matrix through increasing the crystallization degree of BN interphase. As a comparison, the mechanical properties of SiC_f/SiC composites were decreased (366–134 MPa in flexural strength, 13.9–5.2 MPa m^1/2 in fracture toughness) by the HT before the infiltration of SiC matrix mainly due to the degradation of SiC fibers during HT process without the protection of SiC matrix.