Comparative study on the oxidation resistance between Ti-Al-Si-N and Ti-Al-N coatings

High-temperature oxidation behaviors of Ti-Al-Si-N and Ti-Al-N films were comparatively investigated in this work. Two kinds of Ti0.75Al0.25N and Ti0.69Al0.23Si0.08N films were deposited on WC-Co substrates by a DC magnetron sputtering method using separate Ti3Al(99.9%) and Si(99.99%) targets in a gaseous mixture of Ar and N-2. Si addition of 8 at.% into Ti-Al-N film modified its microstructure to a fine composite comprising, Ti-Al-N crystallites and amorphous Si3N4, and to a smoother surface morphology. While the solid solution Ti0.75Al0.25N film had superior oxidation resistance up to around 700 degrees C, the composite Ti-Al-Si-N film showed further enhanced oxidation resistance. Both Al2O3 and SiO2 layers played roles as a barrier against oxygen diffusion for the quaternary Ti-Al-Si-N film, whereas only the Al2O3 oxide layer formed at surface did a role for the Ti-Al-N film. Oxidation behavior and mechanical stability of the films after oxidation were compared between two films using instrumental analyses such as XRD, GDOES, XPS, and scratch test.