Oxidation mechanism and high-temperature strength of Mo-B-C-coated diamonds in the 700°C-1200 °C temperature range

To effectively inhibit the thermal oxidation and thermal failure of diamonds when working in a high-temperature aerobic environment, a Mo-B-C coating was designed and prepared to protect diamonds from oxidation. A two-step synthesis method was used to form coatings with different B contents on diamonds by adjusting the reaction temperature, and the oxidation kinetics and oxidation mechanism of the coated diamonds were investigated in the temperature range of 700 degrees C-1200 degrees C. The mechanism of diamond protection in this study was the preferential oxidative sacrifice of Mo-B-C coatings to form a stable oxide layer on the diamond surface. For low-B coatings, the four stages of coating oxidation, low-temperature volatilization of MoO3, stable protection by B2O3, and rapid evaporation of B2O3 were experienced sequentially with an increase in temperature. For high-B coatings, the preferential self-healing flow of B2O3 not only inhibited the volatilization of MoO3 but also provided a reducing environment for MoO3 to generate high melting-point MoO2 and Mo2C, which resulted in the formation of a double synergistic protective oxide layer and greatly enhanced the oxidation resistance of diamonds. Meanwhile, the protection of the oxide layer also maintained the compressive strength of diamonds under a high-temperature oxidizing atmosphere, indicating its excellent high temperature applicability. This study provides an effective method for enhancing the high-temperature oxidation resistance and strength of diamonds, which can be effectively applied to the extreme environmental use of diamond tools.