Microstructure, tensile deformation mode and crevice corrosion resistance in Ti–10Mo–xFe alloys

The microstructure, the tensile deformation mode at ambient temperature and the crevice corrosion resistance at a high temperature of 373 K were investigated in the Ti–10Mo–xFe (x = 0, 1, 3, 5) alloys. The stability of the β phase increased, and the formation of the α″ martensite and the athermal ω phase was suppressed by the increase in the Fe content. EPMA examinations indicated that the existence of the α″ martensite in the Ti–10Mo alloy was caused by the solidification segregation of Mo atoms. EBSD observations showed that the deformation mode changed from a {3 3 2}〈1 1 3〉 twinning to a slip by an increase in the Fe content, which coincided with the prediction by the electron/atom (e/a) ratio. The Ti–10Mo–3Fe alloy showed the highest yield strength of 935 MPa among all the alloys, while the Ti–10Mo–1Fe alloy showed the lowest value of 563 MPa due to the change in the deformation mode. On the other hand, all the alloys exhibited a high crevice corrosion resistance in a high chloride and high acidic solution at the high temperature, although the corrosion resistance decreased with an increase in the Fe content. The decrease in the corrosion resistance can be explained by the bond order (Bo). A good combination of tensile properties and crevice corrosion resistance may be obtainable through a further optimization of the Fe content by the e/a ratio and the Bo.