ABRASIVE WEAR OF TITANIUM NITRIDE COATINGS

Titanium nitride thin films, deposited by plasma vapor deposition (PVD ) or chemical vapor deposition (CVD), are commonly used on metal cutti ng tools. The TiN coating increases cutting tool-life and extends the tool operating range. This paper examines the behavior of PVD TiN on h igh-speed steel (HSS) substrates under low stress abrasion. High-speed steel bars were coated with TiN by a cathodic are process and by a ma gnetron sputtering process. The samples were then tested using the AST M G65 dry-sand-rubber-wheel abrasive test. The test procedure was modi fied to make runs of short duration to enable periodic weight loss mea surements and examination of the wear scar in a scanning electron micr oscope. As the coating was harder than the silica abrasive, convention al abrasive behavior did not occur. The silica did not abrade the TiN and did not penetrate the coating through deformation of the substrate and collapse of the coating. Adhesive failure of the coating was not observed. The phenomenon observed, in the scanning electron microscope , was micro-fissuring of the surface, where micro-fissuring is defined as multiple cracks, which are long, narrow and parallel to each other . Macro-particles in the deposited coating, common with cathodic are s ource PVD processes, acted as initiation sites for micro-fissuring. A mechanism based on the tangential forces imparted to the coating surfa ces by the moving silica was formulated through an analysis of the for ces on individual silica particles, based on Avery's analysis of the d ry-sand-rubber-wheel abrasive wear process. The results indicate that as long as coating integrity is maintained under the flow of abrasive material, the wear rate of the TiN is small. (C) 1997 Elsevier Science S.A.