Influence of phase composition and stress on the corrosion behavior of metastable β titanium alloy Ti-5Mo-5V-6Cr-3Al in 15 wt% HCl solution

Immersion experiments, electrochemical tests under different tensile stresses, and microstructure observation using SEM, EBSD, and TEM were carried out on three Ti-5Mo-5V-6Cr-3Al alloys with different phase compositions in 15 wt% HCl solution to clarify the effects of the phase compositions and stresses on the corrosion behavior of metastable β-titanium alloys in acidic media. The microstructure with only primary α-phase on the β-matrix (No. M1) presents the smallest corrosion current density and the highest corrosion potential, indicating relatively the best corrosion resistance; the microstructure with both primary and secondary α-phase on the β matrix (No. M2) has moderate corrosion resistance; and the microstructure with secondary α-phase precipitated on the β matrix (No. M3) has the relatively poorest corrosion resistance. The results of the immersion experiments show the same regularity as the electrochemical tests. The corrosion resistance of all three microstructures decreases as the degree of stress loading increases. The apparently small amount of α-phase content in M1 is the reason for the difference in corrosion resistance between M2 and M3, M3 alloys with larger average grain sizes exhibit better corrosion resistance than M2 alloys. Under tensile loading, disruption of the surface passivation film and pitting promoted by dislocation slip are the main reasons for the reduction in the corrosion resistance of the alloy.