Composition dependence of Young's modulus in beta titanium binary alloys

Composition dependence of Young's modulus in β Ti-Nb and Ti-V binary alloys was investigated at room temperature to obtain fundamental information for development of low Young's modulus Ti alloys. With increasing Nb or V content, Young's modulus of quenched alloys decreases, exhibits a minimum value and then increases in good agreement with that in references. In a region where the modulus decreases, athermal ω particles are observed by transmission electron microscopy (TEM) more distinctly at lower alloying contents. Very weak athermal ω reflections are seen in TEM diffraction patterns at the composition corresponding to the minimum. When an alloy with the composition at the minimum is aged at 300°C, it is hardened by isothermal ω precipitation, thereby increasing Young's modulus. Compression tests of β Ti-Nb and Ti-V binary alloy single crystals revealed that {332}〈113〉 twinning occurs as a plastic deformation mode in the composition region where the modulus decreases, and crystallographic slip occurs with further increasing Nb or V content. It is concluded that ω particles strongly influence Young's modulus, hardness and plastic deformation mode in β Ti-Nb and Ti-V binary alloys, and the minimum in Young's modulus is associated with athermal ω formation. Ternary Sn addition further decreases Young's modulus, which is attributable to suppression of ω formation.