Effect of O₂ flow rate on the structure, wettability and tribo-mechanical behaviour of Zr-O-N thin films

Structural and tribo-mechanical properties of Zr-O-N films deposited by reactive magnetron sputtering in a mixture of Ar (flow rate = 80 sccm), N₂ (flow rate = 20 sccm) and O₂ with a varying flow rate of 0 to 12 sccm were investigated. The films were characterized using scanning electron microscopy, energy dispersive x-ray analysis, atomic force microscopy, nanoindentation and wear tests. Oxygen content have a significant effect on the microstructure, wettability, tribo-mechanical properties of Zr-O-N films. The Zr-O-N films showed a dense structure with a mixture of zirconium oxides and nitrides and the preferred orientation changed from (111) ZrN to (200) ZrN with increasing O₂ flow rate. The ZrON film, deposited at an oxygen flow rate of 10 sccm exhibited the highest contact angle (147°), the highest hardness (27.1 GPa), the lowest friction coefficient (0.36) and the lowest wear rate (5.8 × 10⁻⁷ mm³·Nm⁻¹). The improvement in the tribological performance of the ZrON film deposited at 10 sccm is attributed to the improved hardness and increased H/E and H³/E² ratios, due to the formation of a hard solid solution by the diffusion of oxygen.