Influence of annealing temperature on microstructural evolution and tensile behavior of Ti−6Al−4V alloy manufactured by multi-directional forging

A range of annealing treatments were implemented to regulate the microstructure and mechanical properties of Ti−6Al−4V forging. The results show that both the as-forged and as-annealed microstructures exhibit a bimodal structure composed of equiaxed primary α phase (α_p) and transformed β phase (β_t). With the increase of annealing temperature, the secondary α (α_s) phase precipitates from the β phase. There is no obvious texture and the crystal orientation is uniformly distributed. Meanwhile, strength initially increases and then decreases, whereas ductility remains largely unaffected. The alloy annealed at 860 °C has an excellent combination of strength and ductility, due to the larger content of the fine α_s phase. All fracture surfaces contain massive dimples, which is a typical ductile fracture feature. The characteristics of microcracks, microvoids, and kinked α_p/α_l (equiaxed α_p and lamellar α phase) phases are found near the fracture.