Influence of Al content on microstructure, mechanical and tribological properties of Ti-W-Al-N composite films

Ti-W-Al-N films with various Al content (0 at.% ∼ 12.4 at.%) were deposited by reactive magnetron sputtering. The composition, microstructure, mechanical and tribological properties of Ti-W-Al-N films were investigated by EDS, XRD, HRTEM, SEM, Nano-indentation, Ball-on-disk tribometer. It is found that Ti-W-Al-N films consist of Ti-W-Al-N phase, Ti2N phase and W2N phase below 2.9 at.% Al. Ti2N phase disappears at 5.6 at.% Al and h-AlN phase forms at 12.4 at.% Al respectively. The hardness firstly increases and then decreases with increasing Al content and the highest hardness is 35.7 GPa at 8.7 at.% Al. At room temperature, the friction coefficient continuously increases, whereas the wear rate firstly decreases and then increases with increasing Al content. The lowest wear rate of 1.79 × 10−8 mm3N−1mm−1 is obtained at 8.7 at.% Al. As the temperature increases from room temperature to 700 °C, the friction coefficient firstly increases and then decreases, while the wear rate gradually increases. The tribological properties of the film depended on the testing temperatures significantly because the testing temperatures influenced the hardness, the tribo-films and wear mechanism of the film.