Plasma-assisted chemical vapour deposition of TiN and TiC on steel: Properties of coatings

Abstract

TiN and TiC coatings were deposited onto M2 steel and pure iron at temperatures lower than 550 °C by a d.c. glow discharge method using an apparatus similar to the conventional apparatus for ion nitriding of steel. The micro Vickers' hardnesses of the coatings with a chlorine content of less than 5 wt.% were about 2000 and 3000 for TiN and TiC respectively. The hardness decreased with increasing chlorine content. Furthermore, the hardness of the TiC coatings was reduced by the excess carbon. X-ray diffraction lines corresponding to NH 4Cl appeared for the TiN coatings in which the chlorine content exceeded about 10 wt.%. A rolling test with slip showed that the adhesion strength of these hard coatings was superior to that of the TiN coatings formed by ion plating. Comparison of the two kinds of coatings obtained by this process showed that the TiC coatings were more adherent than the TiN coatings. The coatings had an outstanding resistance to wear and galling, as good as that of other hard coatings made by other methods such as ion plating, chemical vapour deposition and salt bath immersion.