Cavitation erosion resistance parameter of hard CAVD coatings

Abstract

Nowadays the most machining tools are coated with hard coatings to prolong their lifetime and to improve their working efficiency. They are very often used for high wear applications, where they are subjected to cyclic impact loading. Main benefits of hard coatings are based on the combination of high hardness and toughness, properties that are especially important in the conditions of dynamic impact wear when high cyclic local loading is the main cause of coating degradation. A cavitation test can be a useful tool for studies of plastic deformation, crack initiation and propagation in thin hard coatings. Cavitation damage is caused by repeating action of imploding cavitation bubbles in the vicinity of solid surface. Because TiN and Cr–N coatings are the most popular coatings for commercial applications, their cavitation erosion resistance were tested. TiN and Cr–N coatings with various thicknesses were deposited on stainless steel, by means of the cathodic arc evaporation (CAVD) method at various temperatures and bias voltages. All tests were performed in the same cavitation conditions in the cavitation chamber with a system of barricades. Obtained results have showed very good correlation between the mass loss and the new parameter. Analysis of degradation mechanism of thin nanocrystalline coatings under the impact degradation results in the obtainment of a new parameter to assess the resistance of hard coating against cavitation. The cavitation tests showed that plastic properties and adhesion play the main role in the coatings resistance, as well as the structure of a given material and its thermal properties.