Effect of scandium on microstructure and corrosion resistance of Ti64 alloy in NaCl solution

The role of scandium, a rare-earth element, on the corrosion resistance of Ti64 alloy in 0.6 M of a sodium chloride (NaCl) solution is investigated through microstructure characterization, and electrochemical and slow strain rate tensile (SSRT) tests. The results indicate that the addition of scandium (Ti64–0.3Sc) increases the polarization resistance, reduces the corrosion rate and inhibits the formation of corrosion products. Besides, the tensile strength of Ti64–0.3Sc is enhanced with less susceptibility to stress corrosion. The microstructures show that scandium refines the grain size and increases the volume ratio of the β/α phase, the rate of production and stability of the passivation film are enhanced. Moreover, scandium readily reacts with interstitial oxygen in the matrix to form scandium (III) oxide (Sc2O3), hence reducing the aluminum equivalent and phase production in titanium aluminide (Ti3Al), which have a positive effect on increasing the resistance of the alloy to stress corrosion. The findings of this study provide theoretical guidance for the design of high strength and corrosion resistant titanium alloys.