Sintering Mechanism for Polycrystalline Diamond

High-performance sintered diamond tools are applied to fields such as wire drawing and rock drilling. They represent a considerable advancement in hard materials sintering. Diamond particles with cobalt are liquid phase sintered to produce a dense composite using high pressure (5 GPa or more) and high temperature (1400 °C or more). Pressure is applied during heating to avoid decomposition into graphite. That pressure is amplified at grain contacts to stabilize diamond, but graphite forms at lower stress regions away from the grain contacts. Sintering occurs when melt spreads between the grains to dissolve carbon, initiating transport from graphite regions to diamond contacts. Necks nucleate on surface defects in preferred crystallographic directions. The sintered diamond exhibits properties, such as high hardness, that reflect the processing parameters or powder size, defect structure, cobalt content, peak temperature, pressure, and hold time.