Wear Mechanisms of (Cr,Al,Y)N PVD Coatings at Elevated Temperatures

Over the past years there have been developments in machining operations to replace the use of liquid cooling by dry cutting operations. This results in higher loads for the tools and therefore demands the continuous development of surface coatings. (Cr,Al,Y)N-coatings designed at the Institute of Materials Technology in Darmstadt, Germany, show beneficial tribological properties especially at high loads and high temperatures. Samples of different yttrium content have been distinguished and compared to an industrial TiAlN coating. Even though the configuration of the (Cr,Al,Y)N coatings is not yet as optimised as that of the TiAlN, which leaves plenty of room for improvement, the (Cr,Al,Y)N shows comparable and partly superior properties to the TiAlN coating. An increasing yttrium content of the (Cr,Al,Y)N leads to a more amorphous microstructure and to finer and denser morphology with a smoother surface. The TiAlN, in contrast, exhibits a porous, columnar structure. This results in advantages in the wear behaviour as well as in the oxidation resistance. Furthermore, a distinct improvement of the adhesion of the layer to the carrier is determinable, which results in higher sustainable loads at the scratch test.