Influence of Heat Treatment on the Mechanical Characteristics of Diamond Powders

Improvement in the efficiency of diamond tools is inextricably linked with the use of high-strength heat-resistant diamond grains for tooling. Hence, study of the effect exerted by heat treatment on changes in the mechanical characteristics of diamonds produced in various growth systems is a relevant task. The effect of heat treatment (in an inert atmosphere) of diamond powders produced in growth systems using ferroalloys to dissolve carbon and promote the conversion of graphite into diamond on the mechanical characteristics of diamonds and elemental composition of inclusions formed on the crystal surfaces during heat treatment is examined. Following heat treatment in the range 700–1100°C, inclusions are observed on the crystal surfaces in diamonds produced in the Fe–Co–C and Fe–Ni–C growth systems. In our opinion, the effect results from ejection of the liquid metal phase to the surface by capillary forces. In crystals with a higher content of inclusions, the phenomenon of capillary ejection is manifested at lower temperatures than the melting of carbon solvent alloys in the diamond growth process. This is confirmed by a sharp change in the specific magnetic susceptibility shown by the samples with a high content of intracrystalline inclusions in the temperature range 400–800°C. For diamonds with a high content of intracrystalline inclusions, with increase in the heat treatment temperature in the range 700–1100°C, the precipitation of the solvent alloy on the surface of diamond crystals leads to crack generation and decreases the strength of diamond crystals. For diamond samples with a low content of inclusions, when the heat treatment temperature increases to 800°C, the specific magnetic susceptibility and strength hardly change (taking into account the relative error of the data obtained).