Selective oxidation and chemical state of Al and Ti in (Ti, Al)n coatings

TLDR

Ti,Al)N hard coatings offer improved oxidation resistance compared to TiN. The study investigates oxidation of Ti,Al)N coatings by annealing them in air and vacuum at 500–800 °C. Al chemical states were distinguished using Al 2p XPS and LVV AES peak shifts. Ti–N bonds remain stable while Al is mobile and weakly bonded to nitrogen, leading to Al depletion at the surface during sputtering.

Abstract

Abstract (Ti, Al)N hard coatings are a promising alternative to TiN owing to an improved resistance to oxidation. In order to study the oxidation process in more detail, (Ti, Al)N coatings reactively sputter‐deposited on high speed steel substrates from a target composed of Ti:Al = 50:50 (at%) were annealed in air and in vacuum at temperatures between 500 and 800 °C. Auger electron spectroscopy (AES) sputter depth profiling as well as X‐ray photoelectron spectroscopy (XPS) studies indicate a high stability of the Ti‐N bond, whereas Al has considerable mobility in the mixed nitride. The chemical shift of the Al 2p XPS and LVV AES peaks allow a distinction between oxide, nitride and metallic states of Al. Preferential sputterin during depth profiling with 3 keV Ar + ions resulted in a relative depletion of Al in the surface layer. It is concluded, that the Al in (Ti, Al)N is only weakly bonded to nitrogen as compared to Ti.