The effect of increasing V content on structure, mechanical and tribological properties of arc evaporated Ti-Al-V-N coatings

In the last years, titanium aluminium vanadium nitride (Ti-Al-V-N) coatings have been introduced as possible candidates for low-friction coatings, based on the formation of vanadium oxide above 550 degrees C. Here we report on the influence of the V content on the mechanical and tribological properties in the temperature range between room temperature (RT) and 500 degrees C. An industrial-scale cathodic arc evaporation facility was used to deposit coatings from powder metallurgically produced Ti33-xAl67Vx targets, with x ranging from 0 to 25 at%. X-ray diffraction experiments displayed a dual-phase structure with hexagonal and face-centred cubic phases for all compositions. However, a decreasing effect of V on the fraction of hexagonal phase was observed. Hardness and Young's modulus increased with increasing V content from 21 to 27.5 GPa and from 250 to 350 GPa, respectively. On the contrary, residual compressive stress decreased with increasing V content from -690 to -330 MPa. Investigations on the wear behaviour at RT revealed decreasing wear coefficients with increasing V content, which is related to reduced tribo-chemical reactions of Ti and the test environment. At 500 degrees C, wear is generally low but increased with increasing V content due to reduced resistance to oxidation. (C) 2008 Elsevier Ltd. All rights reserved.