WEAR OF PHYSICAL VAPOR-DEPOSITION TIN COATINGS SLIDING AGAINST CR-STEEL AND WC COUNTERBODIES

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. Amon g the parameters affecting the wear resistance of PVD TiN coatings, th e most crucial ones are the deposition temperature and the coating thi ckness. This paper presents an experimental investigation of the wear characteristics of PVD TiN coatings produced at two deposition tempera tures (around 220 degrees C and 371 degrees C) and for a range of coat ing thicknesses (0.48 mu m to 3.25 mu m). A ball-on-flat configuration was used in the study. The flat specimen, made of M2 tool steel coate d with TiN, was slid against a 52100 chromium steel (Cr-steel) or a tu ngsten carbide (WC) ball, dry.These two counterbody materials were cho sen because of their different properties. The wear volume was measure d and wear scar examined with a 3-D optical profilometer. The worn sur faces and debris were analyzed with scanning Auger microscopy (SAM) an d an electron probe microanalyzer (EPMA). Quantitative data were obtai ned for the wear volume and coefficient of friction (COF) as functions of the sliding cycles. In the case of TiN versus Cr-steel, the presen ce of transferred wear debris.on the flattened ball surface and iron o xide in the wear tracks of the coating surface was a major factor cont rolling 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 tempera ture, wear was significantly reduced by thinner coatings. However, for the higher deposition temperature, wear reduction was only obtained w ith the Cr-steel counterface.