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, 11 wt.%) 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 11 wt.% 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 (84 GPa) 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.

Additive Manufacturing of Titanium Alloys by Electron Beam Melting: A Review

“…However, it has been reported that the use of Ti–6Al–4V alloy as an implant would harm people's health by releasing Al and V elements. Furthermore, high Young's modulus and brittle deformation behavior, caused by the α ′ phase formed inside the struts of the porous sample, may have an adverse effect in longer‐term medical applications . To remove the above disadvantages, low‐modulus β ‐type titanium alloys containing non‐toxic elements may be used as alternative implant materials.…”

A Review on Biomedical Titanium Alloys: Recent Progress and Prospect

“…Basically, pure Ti has a hexagonal close‐packed (hcp) structure at room temperature, called α phase . A phase transformation from hcp structure to body‐centered cubic (bcc) structure would take place for pure Ti at 883 °C (allotropic temperature), namely β phase . Many previous investigations show that the phase transformation temperature of pure Ti can be strongly influenced by alloying elements .…”

Microstructure, Texture Evolution and Mechanical Properties of VT3-1 Titanium Alloy Processed by Multi-Pass Drawing and Subsequent Isothermal Annealing

“…[4,14,33]. In order to test these effects, tensile properties (i.e., UTS: ultimate tensile strength, YS: yield strength, RA: reduction in area, and EL: elongation) for VT3-1 alloy in various states were evaluated.…”

“…Meanwhile, the strength of IA samples increases with increasing drawing deformation. Because the retained β phase is dispersed at triple points of α phase and α phase bears a large fraction of total deformation [2,4], the similar volume fraction of equiaxed α grains (~80%) for IA samples is chosen to assess the mechanical properties. The Hall-Petch equation has been described for several classes of two-phase alloys [34,35]:…”

“…In particular, two-phase titanium alloys are widely used as structural materials owing to their high strength and adequate ductility [1][2][3][4]. Among them, the Ti-6Al-1.5Cr-2.5Mo-0.5Fe-0.3Si alloy (known as VT3-1) is a typical two-phase titanium alloy, mainly used for gas turbine blades and fasteners owing to the balance of strength and ductility, toughness, and temperature capability up to 400-450 • C [5,6].…”