Optimization of strength, ductility and corrosion resistance in Ti-Mo base alloys by controlling Mo equivalency and bond order

The crevice corrosion resistance in high chloride and high acidic solution at high temperature in Ti-15Mo-5Zr and Ti-15Mo-5Zr-1Fe alloys and the tensile properties at ambient temperature in Ti-15Mo-5Zr-1Fe alloy were investigated in this study. The crevice corrosion resistance in Ti-15Mo-5Zr alloy with a Mo equivalency of 18.2 mass%, which was previously reported to show a combination of the high yield strength and the significant uniform elongation, was almost twice as high as that in Ti-15Mo alloy when the bond order (Bo) increased from 2.8126 to 2.8232. A linear correlation between the crevice corrosion resistance and the Bo was confirmed in the Ti-Mo base alloys with the Bo between 2.7900 and 2.8232. Although the high crevice corrosion resistance, Ti-15Mo-5Zr-1Fe alloy with a Mo equivalency of 21.2 mass% showed high yield strength but negligible uniform elongation due to the deformation by dislocation slip. This study suggested that the two parameters of the Mo equivalency and the Bo are useful for an optimization of strength, ductility and corrosion resistance in Ti-Mo base alloys.