Tribochemical evolution and synergistic lubrication mechanisms of sodium silicate coatings on Ti-6Al-4V at elevated temperatures

Effective lubrication is critical for the hot extrusion of titanium alloys to enhance the surface quality of the workpieces and reduce die wear. This study investigates the high-temperature tribological behavior of sodium silicate coatings with varying SiO 2 /Na 2 O molar ratios on Ti-6Al-4V alloy surfaces. High-temperature friction tests reveal that the combination of elevated temperature and high shear stress promotes the depolymerization of the SiO 4 tetrahedral network. This process leads to an increased concentration of non-bridging oxygens (NBOs) and Q 1 units within the melt, which improves the melt fluidity and facilitates the reflow of the melt into the wear track. Concurrently, the high temperature and shear stress accelerate the diffusion-reaction of sodium ions (Na + ), leading to the in situ formation of layered Na 2 Ti 3 O 7 at the interface between the sodium silicate and the TiO 2 . The synergistic lubrication mechanism of Na 2 Ti 3 O 7 , sodium silicate melt, and TiO 2 is the key to the excellent tribological performance of the sodium silicate coatings. This study provides the theoretical basis for designing silicate-based glass lubricating coatings for titanium alloy hot extrusion.