Mechanical properties and deformation mechanisms of Ti-15 Nb-5Zr-4Sn-1Fe alloy with varying α phase fraction

Abstract

Annealing at different temperatures was applied to a hot-rolled Ti-15Nb-5Zr-4Sn-1Fe (wt%) alloy to obtain α + β dual-phase structure with varying α phase fraction. The evolutions of α + β dual-phase structure, mechanical properties, and deformation mechanisms were systematically investigated. With increasing α phase from 5.5% to 33.7%, the stability of the retained β matrix was gradually enhanced and the β domain size was decreased. The deformation mechanisms changed from stress-induced β to α′ martensitic transformation to stress-induced β to α″ martensitic transformation, mechanical twinning of the β matrix, and finally dislocation slip accompanied with increasing α phase. Accordingly, Young’s modulus decreased monotonously attributed to gradually suppressed athermal ω phase, while the yield strength first decreased slightly owing to the change of stress-induced martensite from α′ to α″, and then increased rapidly when the long-range stress-induced martensite was suppressed. A good combination of low Young’s modulus, high strength, and high ductility was obtained in a microstructure composed of ultrafine grained α + β dual-phase showing dislocation dominated plastic deformation. This study possibly serves as a templet to guide the development of ultrafine grained α + β dual-phase structured metastable β-Ti alloy for biomedical application.