INTERLAYERS FORMED IN THE CARBIDE COATING OF STEEL BY CHEMICAL VAPOR-DEPOSITION

The sequence of carbide layers actually formed when steels are coated with either chromium carbide or titanium carbide by chemical vapour deposition (CVD) has been studied. When the carbon level is sufficiently high an interlayer of cementite is always formed. The results also show, however, that the CVD coating is not necessarily of the composition expected from the phase diagram. Further, when high chrome steel is coated with TiC the development of a Cr7C3 interlayer, which is possible in terms of the phase diagram, does not occur unless sufficient time is allowed for diffusion. The solubility of the steel substrate and the interlayers in TiC coatings is also considered. © 1979.