Preparation and High-Temperature Tribological Properties of Na2O-CaO-P2O5 Phosphate Glass Coating

Glass lubricants are widely used in titanium alloy extrusion forming due to their excellent high-temperature stability. In this paper, twenty phosphate glass compositions with varying Na 2 O: CaO: P 2 O 5 ratios were designed. Through a series of experiments and analyses, the phosphate glass lubricant suitable for low-temperature titanium alloy extrusion was identified. When the Na 2 O: CaO: P 2 O 5 ratio in the glass lubricant was 3:2:5, the material exhibited the melting temperature of 850 °C and the glass transition temperature below 450 °C. Using methylcellulose (a readily vaporizable binder), the glass lubricant coating was prepared via the slurry method and sprayed at 130 °C. High-temperature tribological tests demonstrated outstanding anti-friction and wear-resistant properties at 750 and 800 °C, with average coefficients of friction of 0.2127 and 0.2112, respectively, and wear rates of 7.85 × 10 −5  mm 3 /N·m and 7.55 × 10 −5  mm 3 /N·m. The lubrication mechanism is attributed to the intrusion of Al 3+ and Ti 4+ ions from the oxide scale on the substrate surface into the phosphate glass. These ions react with the molten liquid, forming the reaction layer of NaAlP 2 O 7 and NaTi 2 (PO 4 ) 3 with three-dimensional open framework. The reaction layer interacts with the molten liquid to form the lubricating film with good elasticity, high density, and uniformity. Furthermore, the ion intrusion shortens the glass chain length, thereby enhancing the anti-friction and anti-wear properties of the glass lubrication coating.