Tensile deformation behaviour of cast Ti5553 alloy with different α phase characteristics

In this work, the room temperature tensile deformation behaviour of cast Ti5553 alloy and its relationship with α precipitated phase characteristics by different heat treatment process are investigated. The results show that α twinning during hot isostatic pressing fractures the initial coarse lamellar α of as cast Ti5553 alloy into rod-like or globular α. The solution treatment and ageing (β STA)-Ti5553 with nanoscale fine acicular α phase distributed in a triangular shape has the highest strength but is almost brittle. Compared to hot isostatic pressing (HIP)–Ti5553 and solution treatment and β STA-Ti5553, double annealing (DAN)-Ti5553 with a novel multiscale α phase has the best strength-ductility match, which is markedly superior to that of near beta titanium alloys prepared by selective laser melting and commonly used cast alloys. Nanoscale acicular α phases distributed perpendicularly or parallel can improve the strength without sacrificing ductility. The presence of rod-like α phases capable of inducing α twins and 'fibrous root morphology' α phases with good deformation capability can ensure the ductility of the alloy. The deformation mechanism of cast Ti5553 alloy is dominated by dislocation slip with the auxiliary deformation of α twins exerting a significant influence. α twins induced by hot isostatic pressing revert during tensile deformation due to a change in stress state.