The effect of droplets in arc evaporated TiAlTaN hard coatings on the wear behavior

Hard coatings deposited by cathodic arc evaporation are often characterized by droplets, deteriorating their surface roughness and oxidation resistance. Within this work, the response of these droplets to tribological loading and their contribution to the tribological system was investigated. Ball-on-disk tests against Al2O3 counterparts were done on TiAlTaN coated cemented carbide disks at room temperature and 700 °C. Surfaces as well as cross-sections through the wear tracks were investigated by scanning and transmission electron microscopy. While droplets were found to contribute to coating degradation by providing nucleation sites for shear cracks and by the release of abrasive fragments into the sliding contact, oxidation at elevated temperature leads to a more efficient embedding into the surrounding coating matrix. This suggests an oxidation induced self-healing process, contributing to the enhanced wear resistance of TiAlN-based hard coatings at elevated temperatures.