High temperature behavior of nanolayered CrAlTiN coating: Thermal stability, oxidation, and tribological properties

Abstract

Hard protective nitride coatings are often applied to cutting tools operating at high temperature. To further develop and optimize their performance, in-situ investigation of structure, oxidation, mechanical and tribological properties at elevated temperature is required. In this study we focus on the high temperature behavior of a nanolayered CrAlTiN coating deposited on WC substrates by cathodic arc evaporation. The coating's chemical composition and the bonding state were evaluated by electron probe microanalysis and by X-ray photoelectron spectroscopy (XPS). The structure of as-deposited and annealed samples was analyzed using X-ray diffraction. The adhesion was investigated by scratch test and the mechanical properties were studied by depth sensing nanoindentation. The main objective of this work was to have a detailed analysis of friction and wear properties tested by high temperature tribometer (pin-on-disc) with alumina balls as counterparts in the temperature range of 20–800°C. Selected wear track cross-sections were prepared by focused ion beam and analyzed by transmission electron microscopy; the wear track was investigated as well by XPS (chemical depth profile) and by Raman spectroscopy. The coating showed an excellent thermal stability and wear resistance. The friction reached a maximum at 500°C and then decreased, whereas the wear rate was negligible up to 600°C and then increased significantly for higher temperatures. Oxidation of the worn surfaces was surprisingly low even at the highest temperature corroborating results of oxidation tests. The main identified wear mechanism was polishing combined with a nanoscale delamination of thin coating layers; nanoscale multilayer proved to be a vital factor blocking vertical crack propagation.