Development of low-Young’s modulus Ti–Nb-based alloys with Cr addition

Different amounts of Cr were added to a metastable β-type Ti–22Nb (at.%) alloy to obtain desirable mechanical properties, including a low Young’s modulus, high strength, and good plasticity. The mechanical properties and microstructural changes were investigated. Cr has a high ability to stabilize the β phase, as well as suppress both α″ martensite and ω phase transformations during quenching and the stress-induced α″ martensite transformation during tension. Solid solution strengthening is scarcely achieved by Cr addition. The changes in mechanical properties can be attributed to the different β stabilities. The Ti–22Nb–(0,1)Cr alloys have metastable β phases and exhibit double yielding phenomena, indicating a stress-induced α″ martensite transformation. The Ti–22Nb–(2,3)Cr alloys with stable β phases exhibit distinct work hardening caused by a {332}β β twinning, which also occurs in the Ti–22Nb–(0,1)Cr alloys, but not in the Ti–22Nb–4Cr alloy. Low Young’s moduli of approximately 60 GPa are obtained for the Ti–22Nb–(1,2)Cr alloys. The Ti–22Nb–2Cr alloy exhibits desirable properties for biomedical applications, including an ultimate tensile strength of approximately 600 MPa and elongation of approximately 20%.