The effects of Fe content on the microstructural evolution and tensile properties in Ti–6Al–4V-(2, 4)Fe alloys fabricated by thermomechanical powder consolidation

Abstract

Two Ti–6Al–4V-(2, 4)Fe (wt.%) alloys were fabricated by thermomechanical powder consolidation. With 2 wt%Fe, the microstructure consists of grain boundary α layers and interpenetrating networks of α plates filled by the α/β lamellar structure. In contrast, with 4 wt%Fe, the microstructure consists of grain boundary α layers and α plates dispersed within a matrix of ultrafine β transformed structure. Fe partition between β and α and the β stabilization effect of Fe restrict the growth of α and depress the β→α phase transformation to a lower temperature. Hence, the volume fraction of β increases with the increasing Fe content. Due to solution hardening of Fe and α/β interface strengthening, a 4 wt%Fe addition increases the yield strength to 1.342 GPa. However, the high flow stress sustained by 78 vol% ultrafine β transformed structure may cause a significant strain localization in the weak grain boundary α layers, leading to intergranular fracture at a fairly small strain of only 1.6%. In contrast, with the addition of an appropriate amount of Fe which is likely around 2 wt%, a good combination of strength and tensile ductility can be achieved.