Optimizing the Wide-Temperature Tribological Properties of HfO2/WS2 Coatings by Tuning Deposition Pressure

To enhance the wear resistance and load-bearing capacity of WS2 coatings, this paper employs unbalanced magnetron sputtering technology to fabricate HfO2/WS2 composite coatings by regulating the deposition pressure (0.6–1.4 Pa), leveraging the superior properties of HfO2. The microstructure, mechanical properties, and tribological behavior across a wide temperature range (room temperature to 450 °C) are systematically investigated. The results demonstrate that deposition pressure significantly modulates the coating structure and properties. At a deposition pressure of 0.6 Pa, a pronounced secondary bombardment effect leads to coarse surface particles, a thickness of only 1.525 μm, and a high hardness of 9.332 GPa, but inferior tribological performance with an average friction coefficient of 0.703. When the deposition pressure is increased to 1.4 Pa, the secondary bombardment effect weakens, resulting in an increased coating thickness of 2.125 μm, a decreased hardness of 3.88 GPa, and a significantly improved friction coefficient of 0.072. At an optimal deposition pressure of 1.0 Pa, the sputtered atoms possess moderate energy and optimal surface mobility, promoting the formation of a dense structure. The coating demonstrates a synergistic balance between mechanical load-bearing capability (hardness: 6.38 GPa) and a highly crystalline WS2 structure, yielding superior frictional behavior characterized by a mean coefficient of friction (COF) of merely 0.062. High-temperature tribological evaluations indicate that the COF displays a non-monotonic trend, declining at first before ascending as the temperature elevates. A minimum value of 0.015 is reached at 300 °C, corresponding to a wear rate of 1.127 × 10−8 mm3·N−1·m−1. At 450 °C, partial oxidation of WS2 to WO3 causes the friction coefficient to rise to 0.045, accompanied by fluctuations. Microstructural analysis confirms that HfO2 doping effectively suppresses the oxidation of WS2 at elevated temperatures and promotes the preferred growth orientation of the WS2(002) plane, thereby synergistically optimizing the wide-temperature-range lubrication performance of the coating. This study provides a novel technical approach for the design of lubricating coatings intended for high-temperature and harsh operating conditions, such as those encountered in aero-engine bearings.