Ceramic coating chemically vapour deposited on high speed steel substrates: Scratch adhesion test phenomena

Abstract

AbstractThe scratch test is widely used to assess the adhesion of ceramic coatings deposited on cermet and alloy substrates by both physical vapour deposition and chemical vapour deposition (CVD). It has been observed during such tests that, depending on the coating type, complete coating removal from the scratch channels can be preceded by flaking of the coating at the edges of the channels. An attempt has been made to ascertain, for CVD coated powder metallurgy (PM) high speed steel (HSS) cutting tool inserts, whether a relationship exists between the presence/absence and type of pre‐critical load coating flaking observed during scratch testing and interfacial compositional variations determined by Auger electron spectroscopy (AES). Scratch test and AES results are presented for the following CVD coated PM HSS inserts: titanium nitride (TiN) coated, where no flaking has been observed; titanium carbide (TiC) coated, where mixed adhesive/cohesive flaking of the TiC coating has been observed and multilayer aluminium oxide (Al2O3) coated, where adhesive flaking of the Al2O3coating has been observed. In the case of the TiN and TiC coated inserts it is not considered that differences in coating/substrate interdiffusion zone thickness alone are responsible for the observed divergence in scratch test behaviour. Differences in coating microhardness are also suggested to be a significant factor. The behaviour of the multilayer Al2O3 coated insert during scratch testing is thought more likely to be singularly associated with interfacial chemistry.