Prevention of Alpha-Casing in Ti-6Al-4V during Superplastic Forming Using Thermal Spraying

摘要

Titanium alloys such as Ti-6Al-4V are commonly used in diverse aerospace, industrial and emerging applications due to their unique combination of strength, lightweight, corrosion resistance and other attractive metallurgical properties. However, at elevated temperatures, inverse diffusion of oxygen results in the formation of an alpha surface layer on titanium alloys. As temperature and time increases, this layer, known as alpha case, increases in thickness. This generation of alpha case can modify the mechanical properties of titanium alloy and leaves it brittle and abrasive. In this work, two types of oxygen barrier coating were applied onto the surface of Ti-6Al-4V prior to superplastic forming and the effects of these two coatings on the mechanical properties were also studied. Good surface finish was obtained, and any residual layer was easily removed. Post-forming mechanical properties are also improved with the coating.