Evaluation of wear resistance of thin hard coatings by a new solid particle impact test

For the evaluation of tribological properties of thin hard coatings, several experimental techniques are normally used, such as scratch testing and testing against abrasive, erosive, and sliding wear, and fretting. In this paper, we propose slurry jet, a new type of solid particle impact test, in order to quickly evaluate wear properties of thin, single layered or multilayered physical vapor deposited (PVD) coatings. By slurry jet 1 μm alumina particles were impacted at high velocity perpendicular to thin PVD coatings of TiN, TiN/NbN, TiN/TaN, TiN/CrN, TiN/TiAlN deposited on a high speed steel (HSS) substrate material. The coatings proved to have much higher erosion resistance than the substrate material and, consequently, the wear rate increased significantly to the higher level of the HSS material when the coatings were penetrated. The maximum peak-to-valley roughness (Ry) of the eroded coatings was of the order of 0.1–0.5 μm, suggesting that the size of the detached particles was of the same order. The ranking of erosion resistance and correlation to the mechanical properties, such as hardness and critical normal load obtained by scratch testing are discussed. We conclude that the proposed evaluation test is fast and easy to accomplish. It generates reproducible results and is very sensitive to the quality of the coating. Thus, it can preferentially be used as a screening test when evaluating coatings and coated materials. In particular, the interface strength of multilayered coatings with very thin lamella can be assessed. For the coatings included in this study, the TiN/TiAlN proved to have the highest erosion resistance, whereas the TiN/CrN was the worst.