Evolution of Microstructural and Mechanical Properties during Cold-Rolling Deformation of a Biocompatible Ti-Nb-Zr-Ta Alloy

Abstract

In this study, a Ti-32.9Nb-4.2Zr-7.5Ta (wt%) titanium alloy was produced by melting in a cold crucible induction in a levitation furnace, and then deforming by cold rolling, with progressive deformation degrees (thickness reduction), from 15% to 60%, in 15% increments. The microstructural characteristics of the specimens in as-received and cold-rolled conditions were determined by XRD and SEM microscopy, while the mechanical characteristics were obtained by tensile and microhardness testing. It was concluded that, in all cases, the Ti-32.9Nb-4.2Zr-7.5Ta (wt%) showed a bimodal microstructure consisting of Ti-β and Ti-α″ phases. Cold deformation induced significant changes in the microstructural and the mechanical properties, leading to grain-refinement, crystalline cell distortions and variations in the weight-fraction ratio of both Ti-β and Ti-α″ phases, as the applied degree of deformation increased from 15% to 60%. Changes in the mechanical properties were also observed: the strength properties (ultimate tensile strength, yield strength and microhardness) increased, while the ductility properties (fracture strain and elastic modulus) decreased, as a result of variations in the weight-fraction ratio, the crystallite size and the strain hardening induced by the progressive cold deformation in the Ti-β and Ti-α″ phases.

The Effect of Solution Treatment Duration on the Microstructural and Mechanical Properties of a Cold-Deformed-by-Rolling Ti-Nb-Zr-Ta-Sn-Fe Alloy

“…The existence of a single β-Ti phase in the microstructure of our studied alloy can be justified by its chemical composition, knowing the fact that by adding β-isomorphous elements, like Niobium (29.72 wt.%) and Tantalum (4.97 wt.%), to produce Ti-based alloys, one will most likely obtain an alloy consisting of a single phase, thanks to their full solubility in β-Ti [36]. Although Zirconium (11.87wt.%) is known to be a neutral element, its presence in Ti-based alloys, together with Nb and Ta, can slightly increase the β-Ti phase stability and enhance its strength [37][38][39]. According to the XRD pattern presented in Figure 4a, the TNZTSF alloy in its asreceived (AR) state exhibits a microstructure made up of a single β-Ti phase, which has the (110), ( 200), (211), and (220) corresponding planes.…”

“…What causes the alloy behavior during the deformation mechanism was studied on various types of Ti-based alloys, and it seems to be related mainly to the grain size and the β-phase fraction, which can cause stress-induced β → α″ martensitic transformation along with The existence of a single β-Ti phase in the microstructure of our studied alloy can be justified by its chemical composition, knowing the fact that by adding β-isomorphous elements, like Niobium (29.72 wt.%) and Tantalum (4.97 wt.%), to produce Ti-based alloys, one will most likely obtain an alloy consisting of a single phase, thanks to their full solubility in β-Ti [36]. Although Zirconium (11.87 wt.%) is known to be a neutral element, its presence in Ti-based alloys, together with Nb and Ta, can slightly increase the β-Ti phase stability and enhance its strength [37][38][39].…”

Effects of Cold Rolling or Precipitation Hardening Treatment on the Microstructure, Mechanical Properties, and Corrosion Resistance of Ti-Rich Metastable Medium-Entropy Alloys

“…Furthermore, the elastic anisotropy caused by cold rolling could have led to the increase in the elastic modulus of CR50 and CR75 [41]. The lower elastic modulus of CR75 compared to CR50 is attributed to an increase in the amount of cold rolling, which induced a greater α phase and increased dislocation density [42][43][44][45]. Overall, the bending strength and yield strength of the Ti 80 -Nb 10 -Mo 5 -Sn 5 were improved significantly at the cost of a slightly increased elastic modulus after 75% cold rolling.…”