High thermal stability of diamond–cBN–B4C–Si composites*

Improving the thermal stability of diamond and other superhard materials has great significance in various applications. Here, we report the synthesis and characterization of bulk diamond–cBN–B4C–Si composites sintered at high pressure and high temperature (HPHT, 5.2 GPa, 1620–1680 K for 3–5 min). The results show that the diamond, cBN, B4C, Bx SiC, SiO2 and amorphous carbon or a little surplus Si are present in the sintered samples. The onset oxidation temperature of 1673 K in the as-synthesized sample is much higher than that of diamond, cBN, and B4C. The high thermal stability is ascribed to the covalent bonds of B–C, C–N, and the solid-solution of Bx SiC formed during the sintering process. The results obtained in this work may be useful in preparing superhard materials with high thermal stability.