Effects of heat treatment on mechanical and thermophysical properties of KD-SA SiCf/SiC composites

The mechanical and thermophysical properties of KD-SA SiCf/SiC composites manufactured by the hybrid chemical vapor infiltration (CVI)-precursor impregnation and pyrolysis (PIP) technique were systematically studied at 1400, 1600, and 1800 degrees C, respectively, under argon atmosphere for 1 h. The results show that Si element in SiC fiber escapes and diffuses to pyrolytic carbon (PyC) interphase after 1400 degrees C heat treatment, forming a Si-rich line in PyC interphase. With a further increase of heat treatment temperature, the Si sublimation in the Si-rich line leads to the cracking of the PyC interphase as well as the increase of the order degree of the PyC interphase, resulting in a significant decrease in the interfacial shear strength of the composite. Due to the decomposition of PIP SiC matrix and Si sublimation of SiC fiber, the flexural strength of the composite decreases after heat treatment at 1400 degrees C. When the heat treatment temperature increases to 1600 and 1800 degrees C, the flexural strength of the composite is slightly increased compared with 1400 degrees C. Moreover, the thermal conductivity of the composites has been improved significantly by raising temperatures due to an increase of the crystallinity of the PIP SiC matrix.