Development of a hybrid coating process as an advanced surface modification for cutting tools and moulds

We have developed new ion plating equipment that has made it possible to perform coating after performing plasma nitriding in the same chamber. First, the nitriding behavior of various steels was investigated using this equipment. A nitrogen diffusion layer thickness of 40 μm and a maximum hardness of 1400 HV50 were obtained without a compound layer on top of the nitrided SKH57 by treating for 60 min at 450 °C in Ar–N2 plasma. Secondly, plasma nitriding and TiN coating were carried out successively, using what is referred to as hybrid coating, in the same chamber, and the change in film characteristics with or without nitriding was clarified. Using nitriding as a pretreatment, the apparent film hardness was increased and adhesion between the film and nitrided substrate was improved compared with an untreated substrate. There was no change in the surface roughness after film deposition due to the nitriding. Finally, it was confirmed by results of a drill test that the performance of TiN coating with plasma nitriding was superior to that of a TiAlN film.