PROPERTIES OF ULTRA-FINE GRAIN BINDERLESS CEMENTED CARBIDE RCCFN

Conventional binderless cemented carbide is known as WC-3% TiC-2% TaC cemented carbide with a mean WC grain diameter of about 2 mu m, which does not include a binder phase. This alloy, however, has no binder phase and therefore low strength. The authors investigated the effects of mean diameter of raw WC powder on mechanical characteristics, and found that the smaller the mean diameter of raw WC powder, the lower the temperature at which sintering is possible and the higher the hardness and strength becomes. An investigation was also made on the effects of grain growth suppression additives on the alloy using 0.6 mu m diameter WC powder, which offers the highest mechanical characteristics, with the objective of enhancing characteristics through finer grains. Hardness increased with additional amounts of Cr3C2 and VC. Strength peaked at a certain additive amount, with superior values of H(R)A = 95.5 and transverse-rupture strength = 1.8 GPa. The microstructure was found to be composed of only very fine and uniform carbides; a mirror surface of 7 nm Rtm was obtained by mirror polishing. These characteristics make it possible for this alloy to be used in various optical applications.