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

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.