Enhancement of high-temperature performance in graphite-based coatings via magnesium silicate hydroxide modification

The paper introduces a composite coating achieves significant tribological performances under open-air conditions and a temperature range of 20∼700 °C during sliding. The coating was developed by uniformly brushing a mixture of aluminum phosphate acid compounds, magnesium silicate hydroxide (MSH), and graphite onto a titanium alloy substrate. Tribological experiments conducted across various temperatures revealed that as the testing temperature increased from 20 °C or 100 °C up to 200 °C or higher (up to 300 °C and 400 °C), the coefficient of friction for the MSH/Graphite composite coating rapidly decreases from 0.16∼0.19 to 0.02–0.05, due to the superlubricity of MSH without interlayer absorbent water. At temperatures of 500 °C, 600 °C, and 700 °C, although the friction coefficient remained relatively high at 0.13–0.3, the coating did not suffer significant damage but became denser under the combine effects of high pressure and severe frictional shear forces. This impressive tribological performance is attributed to the hydrogen bonding effect of MSH, which enhances the glass-forming ability of the H₂O-H₃PO₄-Al(OH)₃-graphite system, significantly improving the high-temperature oxidation resistance of the graphite within the coating. These findings offer a promising approach for designing solid lubricant solutions for high-temperature tribological applications.