Metal Oxycarbides as Cutting Tool Materials

The role of chemical stability of cutting tool materials in tool wear was investigated by studying the wear characteristics of titanium oxycarbides. The oxycarbides TiC_0.25O_0.75, TiC_0.5O_0.5, TiC_0.6O_0.4, and TiC_0.75O_0.25 were produced by solid state interdiffusion of TiO and TiC. Their hardnesses and lattice spacings were determined as functions of their chemical composition. The chemical interaction of these oxycarbides with steel was investigated by diffusion couple experiments. Then commercially available cemented carbide tools were coated with TiC_0.5O_0.5 and TiC_0.75O_0.25 by RF diode sputtering. The wear resistance of these coated tools was determined by cutting tests. The wear rate of these oxycarbide coated tools was comparable to that of a TiC coated tool, although the free energies of formation of oxycarbides were lower and their hardnesses comparable. It is, therefore, concluded that while the data on free energy of formation and hardness can be useful in the initial screening steps of tool materials, the kinetics of the wear process needs to be more fully understood to define the chemical stability of tool materials in a cutting environment.