Thermo-chemical polishing of diamond cutting tool based on carbon diffusion

Nickel may erode diamond efficiently because carbon diffuses into nickel. We conducted erosion tests by bringing a pure nickel wire into contact with a diamond in a vacuum. The results revealed that as the erosion mark on the diamond surface became larger, the carbon content in the surface layer of the nickel wire increased. This implies that a diamond can be thermochemically polished by nickel. On the basis of this result, a diamond cutting tool was polished by bringing its rake face into contact with a nickel plate heated at 523 K for 6 h in a vacuum of 4.2 × 10-3 Pa. Approximately 4 nmthick layer was removed from the rake face. However, this technique had an unexpected adverse effect on the tool durability. The tool had low resistance to chipping of the cutting edge. Therefore, its tool life was extremely short compared with that of a mechanically polished diamond cutting tool. Thus, this implies that diamond cutting tools should be polished by a heated copper plate, that is, by the oxidation-deoxidization reaction discussed in our previous study.