Cathodic arc-deposited AlTiN hard coating tribology at elevated temperatures

Abstract

Cathodic arc evaporation (CAE) is the most commonly used physical vapor deposition (PVD) method to deposit protective coatings on cutting and forming tools. However, this deposition method results in a relatively rough surface due to micro-droplet emission. The first contact between the coating and the workpiece surface is at the sites of these growth defects, influencing the state of the contact, such as particle formation and oxidation spots. Growth defects significantly impact the coating's wear and friction properties. Their impact is not limited to the beginning of the contact formation but also expands in the long run, and they can deteriorate the coatings much sooner than expected. This research aims to monitor the wear and friction properties of the cathodic arc deposited AlTiN hard coating during the running-in and steady-state periods under different temperature conditions. Tribological tests against the Al₂O₃ counterbody were carried out at different temperatures, from room temperature up to 700 °C. The sliding distance at specific temperatures, ranging from 50 to 140,000 cycles, enabled us to monitor the wear progression from first contact formation at the growth defects to the complete coating wear from the WC-Co substrate.

After tribological tests, the samples were analyzed using detailed 3D profilometry, SEM, and FIB analysis to determine the wear mechanisms in different stages of high-temperature wear. Attention was focused on the growth defects, their impact on the running-in behavior, and the oxygen diffusion pathways along growth defects that ultimately lead to the delamination of the coating from the substrate.