1300°C–1900 °C heat treatment and mechanical properties optimization of RB-SiC ceramics

For reaction-bonded silicon carbide (RB-SiC) ceramics, the use temperature cannot exceed 1300 °C due to the existence of free silicon. In order to improve its high temperature performance, RB-SiC ceramics were treated by vacuum heat treatment above 1300 °C to remove free silicon, and then modified by post-impregnation pyrolysis (PIP) process with polycarbosilane (PCS). The porosity, bulk density, and flexural strength of the ceramics were measured system atacially. The results show that the RB-SiC can completely remove the free Si, when the temperature exceeds 1700 °C. But its mechanical strength is significantly reduced. The strength of RB-SiC heat-treated after 1900 °C is generally higher than that of materials heat-treated below 1800 °C. In the PIP process, the pyrolysis products of PCS are evenly distributed in the pores of vacuum-heat-treated ceramics (VHT-SiC) to replace the initial free silicon. After 5 PIP cycles, the bulk density of the VHT-SiC increased from 2.56 g cm−3 to 2.70 g cm−3, the porosity reduced from 17.22 % to 12.04 %, and the flexural strength increased by 35.56 %. Therefore, this work provides a simple and efficient method for the preparation of complex SiC components with high temperature resistance (>1400 °C).