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

Abstract

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°C–1200 °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.

Keywords

• Diamond
• Mo–B–C coating
• Antioxidant
• B2O3
• Compressive strength