Effect of BaO on viscosity and structure of B2O3–SiO2–Al2O3–Na2O–BaO glass lubricant

Glass lubricant with a suitable viscosity is critical for the efficient production of high-quality titanium alloy in hot extrusion process. In this study, a new glass lubricant, (30.93-0.309x)B₂O₃-(48.45-0.485x)SiO₂-(7.22-0.072x)Al₂O₃-(13.4-0.134x)Na₂O-xBaO (BSANB), was proposed for titanium alloy hot extrusion. The effect of BaO content varying from 0 wt.% to 15 wt.% on its viscosity was investigated, and the mechanism of viscosity change was clarified through melt structure analysis by using molecular dynamics (MD) simulation, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The glass viscosity was measured in the temperature range of 950°C to 1100°C, and the atomic self-diffusion coefficient of the glass melt was calculated. The results demonstrated that the BaO content has a significant influence on the viscosity of the BSANB glass at the hot extrusion temperature range. The viscosity value at 950°C was decreased by 52.87%, from 103.5 Pa·s to 48.8 Pa·s, when BaO content was increased from 0 wt.% to 15 wt.%. MD simulation results of the BSANB glass show that the self-diffusion coefficient of Si atoms was lower than that of Al and B atoms, indicating that Si-O bonds were more stable in the melt. The diffusion coefficient of Si atom was directly related to the rheological behavior of the melt, which can be reflected by the melt viscosity. The results of MD simulation, XPS and Raman spectral fitting at 950°C showed an increase in the amounts of Q¹, Q⁰ and [BO₄], while the amounts of Q², Q³, Q⁴ and [AlO₄] were decreased when BaO content was increased from 0 wt.% to 15 wt.%. This demonstrated that the melt network was depolymerized with an increased BaO content, which determined the melt viscosity change. In addition, the mechanism responsible for glass viscosity reduction due to temperature increase was also discussed.