Preparation of Tungsten Disulfide Phosphate Coating on Textured Titanium Alloy Surface and Its Tribological Properties at Elevated Temperatures

Titanium alloy has a wide application prospect in many fields due to its excellent comprehensive properties. However, its poor wear resistance greatly limits the application of titanium alloy in the field of tribology. Therefore, it is of great research value to promote the tribological properties of titanium alloy, especially using surface engineering technology to enhance the surface performance of titanium alloy. In this paper, micro-structures were prepared on the surface of titanium alloy by ultraviolet laser micro-machining technology, and then an environmental-friendly phosphate bonding solid lubricant coating was prepared on the surface of textured titanium alloy by spraying process with water as dispersion medium, tungsten disulfide as solid lubricant, zirconium dioxide as reinforcement phase, and aluminum dihydrogen phosphate as binder. A preparation method for a composite lubricating structure was proposed. The friction and wear properties of the coating were investigated at room temperature up to 400 ℃, following by exploring the synergistic friction-reducing and anti-wear mechanism and the influence of surface micro-texture on the wear life of the coating. The results showed that the smooth surface of titanium alloy had a high and fluctuating friction coefficient at different temperatures, showing severe adhesive wear. The tungsten disulfide phosphate bonding solid lubricant coating on the surface of titanium alloy presented superior friction-reducing and wear-resisting performance at elevated temperatures. More importantly, XPS analysis showed that the contents of tungsten trioxide and zirconium dioxide in the coating increased with the increase of temperature, which exhibited a cooperative lubrication effect, and then improved the self-lubrication performance, reduced the wear rate of the coating. At 400 ℃, the wear rate of the coating on titanium alloy surface could be reduced to 1.3×10⁻⁴ mm³/(N·m), which was 45% lower than that of titanium alloy substrate. The wear resistance of the coating could be further improved by constructing micro- structures on the surface of titanium alloy, and the wear life was prolonged at elevated temperatures. When paired with TC4 ball, the friction coefficient of 0.30 or less was obtained, and the wear rate of 1.2×10⁻⁵ mm³/(N·m) below could be achieved on coated textured titanium alloy surface at room temperature up to 400 ℃. At 400 ℃, the much lower and stable friction coefficient (appropriately 0.07) of the textured surface coating was acquired, and the wear rate decreased to 4.6×10⁻⁶ mm³/(N·m). This was mainly ascribed to the reason that the micro-texture existed in the interface between titanium alloy and coating could effectively improve the adhesion of the coating on the titanium alloy surface by adding the contact area and using “mechanical interlocking” effect, which prevented the coating from falling off in the friction process. Meanwhile, surface micro-structures had a reservoir effect, after the surface coating was worn out, the solid lubricant in the micro-texture could play the role of “self-compensating lubrication”, which combined with the surface enhancement effect of high temperature oxidation of titanium alloy. That significantly raised the friction reduction and wear resistance of titanium alloy. It was expected to provide a new approach for the design of highly reliable and long life lubricating coating, and provide theoretical guidance and data support for the further application of titanium alloy in the field of friction.