Wear Behaviour of Filtered-Arc Deposited Titanium Nitride Coatings

The project is dedicated to the study of wear behaviour of titanium nitride (TiN) coating on as-ground SUS304 stainless steel (SS) at prescribed different surface roughness. It is considered essential to append more information of the situation. TiN is already well-known of having excellent wear properties. Mechanical properties and tribological parameters of TiN coatings are exhaustively studied and are often regarded as references to many other hard coatings. The surface roughness of the SS samples was varied by applying different grinding procedures. Three types of surface roughness, in the range of 2.66nm to 651nm were studied; smooth, medium-rough and very rough. A profiler machine was utilized to examine the surface roughness parameters i.e. Ra, RMS or Rq, Rt, Rv etc. of the samples prior coating process. Atomic Force Microscopy (AFM) technique was applied to verify the roughness parameters value measured by the stylus profiler. The TiN coatings were deposited onto the SS substrates in two batches by the Filtered Arc Physical Vapour Deposition system (FADS-PVD) technique using the Tool Coater CTC 600 at the CSIRO, Sydney. The coating thickness was measured by AFM to be approximately 1.5μm and 2µm respectively and believed to be relatively optimum sizes for this study. Pin-on-disc CSM Tribometer wear testing is conducted on each samples to characterize the wear behaviour of TiN coating with respect of the various surface roughness parameters of the SS substrate. Additionally, to be able to see the influence of normal load in a wear operation, two loads; 2N and 10N were applied in the wear testing. A comparison was made with polished samples (TiN coating on smooth SS) to identify the effect of surface roughness on the coating’s wear performance. Microstructural characterisation of the PVD thin film coatings was executed by using focused ion beam milling (FIB) techniques. Microscopic examination of the subsurface was utilized to understand the wear behaviour of TiN coating on as-ground SS. Thorough studies of the resultant smooth and polished-like wear tracks on the TiN surfaces demonstrated combination of abrasive, adhesive and brittle wear mechanisms with the first former was the dominant mechanism. This research showed that TiN coatings deposited on rough substrates exhibited outstanding wear behaviour with coating thickness of 2μm displayed better performance than the thinner set. The finding was believed to be attributed to the high adhesion between TiN with the rough surface and the presence of hard asperities with small contact area to resist wear operation.