Preparation and Characterization of the Anti-high Temperature Oxidation Borosilicate Glass Coating on TC4 Titanium Alloy

During the thermoplastic forming of TC4 alloy parts, the surface of TC4 alloy billets will be severely oxidized, so it is necessary to prepare anti-oxidation lubrication coating on the surface of billets. By comparing the standard free energy of formation of TiO2 and taking the intermediate value of mass percentage of the corresponding oxide in some literatures, the appropriate oxides such as 44.0% SiO2, 25.0% B2O3, 10.0% Na2O, 7.5% CaO, 6.8% MgO, 1.7% Al2O3 and 5.0% TiO2 were selected to prepare the borosilicate glass powder with high temperature solid-state reaction method. Then, the glass coatings with thickness of 0.15-0.3 mm were prepared on the surface of phi 17.5 mm x 7.5 mm TC4 alloy cylindrical samples, by dip coating method with the glass powder. It is found that the glass coating has excellent high temperature oxidation resistance by oxidation experiments holding for 2 hours at different temperatures from 500 to 1050 degrees C. The observations of surface morphology and phase of the glass coating by SEM and XRD found that the glass coating particles with holes between each other, began to melt into amorphous phase at 650 degrees C. With the increase of temperature, especially above 850 degrees C, the glass coating gradually melted into a compact film composed of CaMgSi2O6 and a small amount of CaMg(SiO3)(2) or Na(AlSi3O8). It can tightly enwrap the substrate and physically isolate oxygen from the furnace gas, so can effectively prevent TC4 billets from oxidation in the range of hot working temperature.