High thermal stability of diamond-cBN-B_4C-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, B_xSiC, 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 B_xSiC formed during the sintering process. The results obtained in this work may be useful in preparing superhard materials with high thermal stability.