Microstructure, Mechanical Properties, and Springback of Ti-Nb Alloys Modified by Mo Addition

A series of Ti-(38-2x)Nb-xMo (wt.%) alloys are designed using 1% Mo to replace 2% Nb in order to gradually increase the beta stability and obtain a low springback. The alpha '' phase is exhibited in Ti-38Nb and suppressed with an increasing Mo content. The Ti-38Nb and Ti-34Nb-2Mo alloys show stress-induced alpha '' martensite transformations during cold rolling and double yielding behavior in tensile tests. The Ti-30Nb-4Mo and Ti-26Nb-6Mo alloys exhibit nonlinear deformation owing to the metastable beta phase. With an increase in the Mo content, Young's modulus increases slightly from 68 GPa in Ti-38Nb to 73 GPa in Ti-26Nb-6Mo, owing to the increase in beta stability. Mo shows a solution strengthening effect that gradually increases the tensile strength. Although a higher Young's modulus was not observed to be induced through deformation in Ti-(38-2x)Nb-xMo alloys, low springback was obtained according to the three-point bending loading-unloading test. In particular, the Ti-38Nb and Ti-34Nb-2Mo alloys with stress-induced alpha '' martensite transformations exhibit low yielding stress and are thus easily deformed. The deformed alpha '' phase hardly reverts to the beta matrix after unloading, and therefore, the plastic deformation is maintained.