Tribological Characterization and Wear Mechanisms of Novel Oxynitride PVD Coatings Designed for Applications at High Temperatures

Abstract

In recent years, newly developed protective coatings for cutting tools have become more and more wear and abrasion resistant to the extreme environments associated with modern machining processes. On these new coatings the common pin on disk tribological tests have failed, resulting in practically no wear or strongly heterogeneous wear. For efficient tribological testing and determination of wear resistance of the new hard coatings it is therefore crucial to establish a valid set of room temperature and high-temperature wear test conditions. After a large number of preliminary tests performed on a state-of-the-art high-temperature pin on disc tester we identified optimized conditions for characterization of these new types of hard coatings. The investigated coatings comprised AlTiN-based reference, nanostructured Al-Cr-based nitride, oxynitride and oxide coatings deposited using an industrial rotating cathodes arc PVD process on cemented carbide. The nitrogen in the coating was progressively substituted by oxygen up to 100 at.% to create oxide structure in order to avoid oxidation of the coatings at high temperatures. These new oxide coatings are known to withstand extremely high temperatures in dry milling and turning of high-strength materials while exhibiting high wear resistance. However, characterization of their wear resistance by the common tribological tests had proven to be very difficult and new testing procedures had to be established.