Microstructure, Composition and Performance of PVD Coatings Designed for Successful Dry High Speed Milling

摘要

Dry high speed machining (HSM), particularly dry high speed milling, demands hard coatings, which exhibit high toughness, high oxidation resistance, a limited amount of residual stress and excellent adhesion to the cemented carbide (CC) substrate. These requirements are met by TiAlCrYN coatings grown by the combined cathodic arc/ unbalanced magnetron deposition method. Fully sufficient adhesion is achieved by ion implantation of Cr into the CC prior deposition. Residual stress is controlled by an Y ― free base layer; high oxidation resistance is provided by an Y― containing 3μm thick hard coating with 29 GPa hardness and a residual stress well below -7 GPa. Under the influence of temperatures above 800℃, Y segregates along the columns of TiAlN and plugs the in/ outdiffusion of elements. A top layer of Y― containing oxynitride reduces the friction against the work piece material (0.9 to 0.65). Cutting tools coated as such may be used for dry milling up to 25k rpm in steels HRC > 60.