Influence of Nb on the β → α″ martensitic phase transformation and properties of the newly designed Ti–Fe–Nb alloys

Abstract

A series of Ti–7Fe–xNb (x=0, 1, 4, 6, 9, 11wt.%) alloys was designed and cast to investigate the β→α″ martensitic phase transformation, β phase stability, the resulting microstructure and mechanical properties. Phase analysis revealed that only Ti–7Fe–11Nb alloy shows a single body-centred cubic β phase microstructure while the others are comprised of β and orthorhombic α″ phases. Moreover, Nb addition up to 11wt.% enhances the stability and volume fraction of β phase in the microstructure, hence reducing the propensity of the alloy system to form α″ phase during quenching. Compressive yield strength and hardness of the alloys are (985–1847) MPa and (325–520) Hv respectively. Additionally, Ti–7Fe–11Nb possesses the lowest Young's modulus (84GPa) and the highest deformability (42% strain) among the designed alloys due to the single β phase microstructure. This high deformability is also corroborated by the large plastic deformation zone underneath the Vickers indenter. In contrast, the fractured surfaces of Ti–7Fe and Ti–7Fe–1Nb alloys after compressive tests mostly contain shallow dimples, verifying their low ductility. The good combination of mechanical properties obtained for Ti–7Fe–11Nb renders it more desirable than commonly used CP-Ti and Ti–6Al–4V materials and makes it a promising candidate for biomedical application.