Oxidation, graphitization and thermal resistance of PCD materials with the various bonding phases of up to 800 °C

• Thermal resistance of diamond composite depends mainly on oxidation process.
• Bonding phase has strong influence on the oxidation of graphite and diamond.
• Diamond–TiB2 composite retains high hardness at temperatures of up to 700 °C.
• Carbides as bonding phase are not resistant to oxidation at high temperatures.

Three types of polycrystalline diamond composites (PCDs) were studied. The first material was sintered using the mixture containing 80 wt.% diamond, 15 wt.% of Ti–Si–C powder (mixture of 47.1 wt.% Ti3SiC2 and TiSi2, TiC and SiC, from self-propagating high-temperature synthesis) and 5 wt.% nanometric Ti(CN) powders. The second material was prepared using diamond powder and 10 wt.% of titanium diboride. Materials were sintered using a Bridgman-type high-pressure apparatus at 8 GPa and at the temperature of 2000 °C. The third material was a commercial PCD containing 88 wt.% of diamond, 10 wt.% of Co and 2 wt.% of WC. The coefficients of friction for diamond composites in a sliding contact with an Al2O3 ceramic ball were determined from room temperature of up to 800 °C, in air. X-ray diffraction patterns of diamond composites after HP–HT sintering and wear tests are presented. In the studies, due to the use of Raman spectroscopy the strong influence of the bonding phase on the oxidation of diamond composites was confirmed. The most thermally stable material is the diamond composite with TiB2. High temperature bonding phase for diamond composites guarantees higher hardness and low coefficient of friction at elevated temperatures.