Nanocomposite Ti-Si-B-C hard coatings deposited by magnetron sputtering: Oxidation and mechanical behaviour with temperature and duration of oxidation

The oxidation behaviour of nanocomposite Ti-Si-B-C hard coatings on steel substrate deposited by magnetron sputtering process has been studied in the air at different temperatures 700 degrees C to 1100 degrees C and for different durations up to 100 h at 800 degrees C. SEM, TGA, Raman spectroscopy, TEM, XRD, and nanoindentation were carried out on surface and cross section to understand the effect of oxidation on microstructure, phase, mechanical behaviour and the oxidation mechanism. The mass gain followed a parabolic path with time, revealing a diffusion-controlled mechanism. From cross-sectional SEM, Raman spectroscopy, TEM, and XRD, the formation of TiO2 and SiO2 at the surface was confirmed, which was forming passivation layer on the top of the film, retarding further oxidation of the film. The hardness decreased only at surface layers due to the formation of passive oxide layers. The inside layer was still hard revealing it a potential material for high temperature wear applications. (C) 2016 Elsevier B.V. All rights reserved.