THE INFLUENCE OF TITANIUM INTERLAYERS ON THE ADHESION OF TITANIUM NITRIDE COATINGS OBTAINED BY PLASMA-ASSISTED CHEMICAL VAPOR-DEPOSITION

The use of a thin titanium interlayer has been found to considerably improve the adhesion of titanium nitride coatings produced by physical vapour deposition (PVD). This is believed to arise from two factors: the dissolution of weak native oxide layers by the titanium (a chemical gettering effect) and the compliance of the relatively soft interlayer which reduces the shear stresses across the coating-substrate interface. In this study the effects of a titanium interlayer on the adhesion of titanium nitride deposited by plasma-assisted chemical vapour deposition (PACVD) have been investigated. As observed for the PVD coatings the critical load for coating detachment increases with increasing interlayer thickness but in contrast with PVD coatings no maximum was observed over the range of interlayer thickness investigated. In PVD coatings the titanium interlayer has a significant gettering effect as shown by secondary-ion mass spectrometry depth profiles; however, in the PACVD coatings, owing to the more effective pre-cleaning stage, the improved adhesion with increasing interlayer thickness is attributed more to its compliance.