Self-lubrication of nitride ceramic coating by the chlorine ion implantation

Various kinds of ceramic nitride coatings are widely utilized as a protective or tribological film for cutting tools or metal forming dies. Although most of them have a potential to reduce the wear rate of steel, aluminum or titanium alloy parts, further improvement of oxidation resistance and wear toughness with less use of lubricants is still needed to meet the severe wearing conditions required by the coming automotive parts. Dry forming and dry machining has become a promising green, environmentally benign manufacturing process. In addition to diamond-like carbon or MoS₂ coatings, the tribological film via the self-lubrication process is also a useful approach to attain low wear and friction state. In the present paper, ideal tribo-film can be accommodated by the chlorine implantation to titanium nitride (TiN) films. No physical change occurred for surface roughness and lattice structure of TiN. In the presence of chlorine, the vicinity of TiN coating surface is oxidized to significantly reduce the surface hardness. Since the elasto-plastically deforming Magneli phase is in situ formed during wearing, both friction coefficient and wear volume are reduced all through the life of original TiN coating. Through this experimental demonstration of practical usefulness, the further research and development toward dry forming and dry machining is discussed.