Mechanical modification and damage mechanism evolution of TiN films subjected to cyclic nano-impact by adjusting N/Ti ratios

For the purpose of optimizing the anti-impact performance of TiN film, a series of TiN films with different N/Ti ratios were investigated. The phase evolution and mechanical properties of TiN films were explored. In particular, the cyclic nano-impact tests with impact energy ranging from 0.1 μJ to 0.9 μJ were conducted to evaluate the anti-impact performance of TiN films. It was found that the non-stoichiometric phases of TiN_0.30, Ti₂N and TiN_0.61 reduced with increasing N/Ti ratio in TiN films. The hardness of film increased with increasing stoichiometric TiN phase in films, while as an indicator of toughness, the H³/E² ratio decreased. The anti-impact performance of TiN films displayed a close relationship with both hardness and H³/E² ratio, in which a high enough hardness was the prerequisite of outstanding impact resistance, and H³/E² ratio was an important factor affecting the damage mechanism. As the H³/E² ratio decreased, the damage mechanism of TiN film transformed gradually from plastic fatigue damage to brittle fracture failure. Especially, the TiN film featuring N/Ti ratio of 0.780 (TiN-16) was not only hard enough to resist penetration, but also tough enough to prevent the film from fracturing, thus it exhibited the best comprehensive anti-impact performance.