The effect of increasing V content on the structure, mechanical properties and oxidation resistance of Ti–Si–V–N films deposited by DC reactive magnetron sputtering

Abstract

In the last years, vanadium rich films have been introduced as possible candidates for self-lubrication at high temperatures, based on the formation of V2O5 oxide. The aim of this investigation was to study the effect of V additions on the structure, mechanical properties and oxidation resistance of Ti–Si–V–N coatings deposited by DC reactive magnetron sputtering. The results achieved for TiSiVN films were compared and discussed in relation to TiN and TiSiN films prepared as reference. All coatings presented a fcc NaCl-type structure. A shift of the diffraction peaks to higher angles with increasing Si and V contents suggested the formation of a substitutional solid solution in TiN phase. Hardness and Young's modulus of the coatings were similar regardless on V content. The onset of oxidation of the films decreased significantly to 500 °C when V was added into the films; this behaviour was independent of the Si and V contents. The thermogravimetric isothermal curves of TiSiVN coatings oxidized at temperatures below the melting point of α-V2O5 (∼685 °C) showed two stages: at an early stage, the weight increase over time is linear, whilst, in the second stage, a parabolic evolution can be fitted to the experimental data. At higher temperatures only a parabolic evolution was fitted. α-V2O5 was the main phase detected at the oxidized surface of the coatings. Reduction of α-V2O5 to β-V2O5 phase occurred for temperatures above its melting point.