Breaking through the strength-ductility trade-off dilemma in powder metallurgy Ti–6Al–4V titanium alloy

Abstract

A novel approach was developed to fabricate low-oxygen powder metallurgy Ti–6Al–4 V (wt.%) titanium alloy with a highly desirable combination of ultrahigh tensile strength and good ductility. Using clean and unpassivated TiH2 based powder compact, together with cleaning effect of in-situ dehydrogenation during heating the powder compact resulted in a low oxygen content of 0.26% in final extrusion consolidated alloy. The nature of cleaning effect during sintering was proved to be a reduction reaction of TiO2 + 4[H] = Ti + 2H2O (g). Besides, solution & aging treatment produced a unique composite lamellar microstructure, which mainly consists of fine α platelets and β-transformed structures containing high number density of ultrafine acicular α precipitates. Such composite lamellar microstructure gave rise to extra geometrically necessary dislocations during tensile deformation and brought about significant dislocation hardening together with high global strain. Consequently, this Ti–6Al–4 V alloy exhibited a superior ultimate tensile strength of up to 1320 MPa and meanwhile a high elongation to fracture of not less than 12.5%.