Microstructure and mechanical behaviour of the isothermally forged Ti–6Al–7Nb alloy

Abstract

The mechanical properties of the Ti-6Al-7Nb alloy, used to manufacture high-strength prostheses, are highly dependent on its microstructure. This work presents the microstructural changes of this alloy under isothermal hot working. It is shown that microstructure is strongly affected by strain rate, temperature and strain. The possible precipitation of intermetallic phases is also evaluated. To define the best processing conditions, compression tests were performed at temperatures varying from 750 to 1030 ºC and deformation speeds of 0.01, 0.1 and 1 mm/s. Tests were carried out in the α+β and β phase regions. Experimental results showed that the best microstructure (recrystallized with equiaxial refined white α grains and acicular dark grains within a β-transformed matrix) was obtained in tests at 950 ºC and 0.01 mm/s. NOTATION e engineering strain [mm/mm] v deformation speed [mm/s] σ e engineering stress [MPa] σ r true stress [MPa]

Quenching temperature influence on elastic and hardness behavior in a biocompatible Ti-based alloy

“…The main β-stabilizing element in Ti-6Al-7Nb is niobium because it is more biologically inert and exhibits better nontoxicity compared to vanadium [2]. Nowadays the Ti-6Al-7Nb alloy for medical implants is manufactured by means of traditional metallurgy methods, e.g., severe plastic deformation [3,4], powder metallurgy processes [5,6], and selective laser melting [7,8], with processing parameters greatly influencing the structure and mechanical properties of semifinished material. It should be noted that the Ti-6Al-7Nb alloy in its equilibrium state possesses rather high elasticity modulus of 105 -110 GPa [9,10] compared to most other Ti-based medical alloys [11,12] because of considerable aluminum content, and this somewhat reduces the alloy biocompatibility for implant application.…”