Subtransus triplex heat treatment of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe near β titanium alloy

Abstract

Laser melting deposition (LMD), which fabricates near-net-shape components directly by melting powder layer by layer, is used to manufacture Ti–5Al–5Mo–5V–1Cr–1Fe near β titanium alloy samples. In as-deposited alloy, ultrafine basket-weave microstructure and continuous grain boundary α (αGB) are observed. And the as-deposited alloy exhibits high strength but low ductility. Then the annealing treatment is applied to improve the ductility, but the strength of the annealed alloy is too low. To obtain good comprehensive tensile properties, the traditional standard triplex heat treatment usually applied for wrought Ti–5Al–5Mo–5V–1Cr–1Fe alloy is employed. The results show that the alloy has high strength. The ductility is also improved, but still not satisfactory, because the continuous αGB remains and is accompanied with soft α phase precipitate-free zones (PFZ) which results in the intergranular fracture. Accordingly, a subtransus triplex heat treatment is designed, which can significantly reduce the continuous αGB. And as expected, the ductility is significantly improved, and the predominant fracture model changes to be transgranular.