The new parameter to assess cavitation erosion resistance of hard PVD coatings

Most machinery elements are coated with hard coatings to prolong their lifetime and to improve working efficiency. Cavitation test was used as a tool for studies of dynamic impact degradation. Ti- and Cr-based coatings were chosen for investigations. The TiN and Cr–N coatings with various thicknesses were deposited on stainless steel by means of the cathodic arc evaporation method at various deposition parameters. Tests were performed in the cavitation chamber with a system of barricades. Nearly all the TiN and Cr–N coatings have undergone micro-undulation. The first cohesive fractures have occurred on top of the micro-folding and at delamination spots. The analysis of degradation mechanism of thin hard coatings under repeated impact loading has resulted in deriving a new empirical parameter suitable for description of the hard coating cavitation resistance. The derived parameter is proportional to the plasticity index, H/E (defined as ratio of hardness, H, and Young’s modulus, E), adhesion force, LC2, ratio of thermal conductivity of the coating to that of the substrate, and inversely proportional to the number of phases in the coating phase composition, the ratio of the thermal expansion of the coatings to that of the substrate and the square root of the coating thickness. The new endurance parameter shows good correlation with the mass loss of all the tested hard coatings indicating a continuous improvement in the erosion resistance with the increase of the new parameter.