The effects of adding aluminum on crystal structure, mechanical, oxidation resistance, friction and wear properties of nanocomposite vanadium nitride hard films by reactive magnetron sputtering

Vanadium nitride films exhibited excellent tribological properties due to the formation of Magnéli phases during the wear test, while the poor thermal stability, low hardness and high wear rate restricted it applied in cutting tool field. In this paper, aluminum was added into the vanadium nitride matrix in order to improve the thermal stability, mechanical and tribological properties. V-Al-N films with various Al content were deposited by reactive magnetron system and the effects of Al content on the micro-structure, oxidation resistance, mechanical and tribological properties of V-Al-N films were investigated. The results showed that V-Al-N films regardless of Al content exhibited a single face-centered cubic (fcc) structure. There was an increase in hardness when the content of Al was below 4.7 at.% with a corresponding decrease in room temperature friction coefficient (μ) and wear rate (WR). Rising Al content improved the oxidation resistance, while degraded the fracture toughness. The film at 4.7 at.% Al with highest hardness and lowest μ and WR was chosen to investigate its high temperature tribological properties. The rising temperature induced both the wear mechanism change and tribo-film vanadium oxides phase transition, and increased μ to 0.7 at 300 °C firstly and then dropped to 0.28 at 700 °C, while WR increased gradually. The film at 4.7 at.% Al was found to be optimized for cutting tool application.