Effects of Fe addition on tensile deformation mode and crevice corrosion resistance in Ti–15Mo alloy

The tensile deformation mode at ambient temperature and the crevice corrosion resistance at a high temperature of 373 K were investigated in Ti–15Mo and Ti–15Mo–1Fe (mass%) alloys. The β phase stability increased, and the formation of an athermal ω phase was suppressed by the Fe addition. EBSD and TEM observations showed that the deformation mode in the Ti–15Mo alloy changed from a {3 3 2}〈1 1 3〉 twinning to a slip by the Fe addition, which coincided with the predictions from the electron/atom (e/a) ratio and the Mo equivalency. EPMA examinations indicated that the existence of twins in a few regions in the Ti–15Mo–1Fe alloy was caused by the solidification segregation of Mo and Fe atoms. The yield strength of the Ti–15Mo–1Fe alloy of 837 MPa was much higher than that of the Ti–15Mo alloy of 439 MPa due to the change in the deformation mode. The Ti–15Mo–1Fe alloy maintained an extremely high crevice corrosion resistance in a 10% NaCl water solution with a pH value of 0.5 at 373 K since there was no significant decrease in the average value of the bond order (Bo). A good combination of tensile properties, crevice corrosion resistance and cost is thought to be obtainable through further optimization of the chemical compositions by the e/a ratio, the Mo equivalency and the Bo.