Wear of Physical Vapor Deposition TiN Coatings Sliding Against Cr-Steel and WC Counterbodies

Abstract

Cutting tools are often coated with titanium nitride (TiN) for its good wear resistance. The method of coating by physical vapor deposition (PVD) has many superior features over other methods of deposition. Among the parameters affecting the wear resistance of PVD TiN coatings, the most crucial ones are the deposition temperature and the coating thickness. This paper presents an experimental investigation of the wear characteristics of PVD TiN coatings produced at two deposition temperatures (around 220°C and 371°C) and for a range of coating thicknesses (0.48 μm to 3.25 μm). A ball-on-flat configuration was used in the study. The flat specimen, made of M2 tool steel coated with TiN, was slid against a 52100 chromium steel (Cr-steel) or a tungsten carbide (WC) ball, dry. These two counterbody materials were chosen because of their different properties. The wear volume was measured and wear scar examined with a 3-D optical profilometer. The worn surfaces and debris were analyzed with scanning Auger microscopy (SAM) and an electron probe microanalyzer (EPMA). Quantitative data were obtained for the wear volume and coefficient of friction (COF) as functions of the sliding cycles. In the case of TiN versus Cr-steel, the presence of transferred wear debris on the flattened ball surface and iron oxide in the wear tracks of the coating surface was a major factor controlling the wear behavior. In the case of TiN versus WC, no transferred layers were observed; instead, the presence of flake type debris from the coating in the wear tracks appeared to be the controlling factor. It was concluded that deposition temperature, coating thickness, and counterface influenced wear behavior. For the lower deposition temperature, wear was significantly reduced by thinner coatings. However, for the higher deposition temperature, wear reduction was only obtained with the Cr-steel counterface.