Evolution laws of microstructures and mechanical properties during heat treatments for near-α high-temperature titanium alloys

Evolution laws of microstructures, mechanical properties, and fractographs after different solution temperatures were investigated through various analysis methods. With the increasing solution temperatures, contents of the primary α phase decreased, and contents of transformed β structures increased. Lamellar α grains dominated the characteristics of transformed β structures, and widths of secondary α lamellas increased monotonously. For as-forged alloy, large silicides with equiaxed and rod-like morphologies, and nano-scale silicides were found. Silicides with large sizes might be (Ti, Zr, Nb)₅Si₃ and (Ti, Zr, Nb)₆Si₃. Rod-like silicides with small sizes precipitated in retained β phase, exhibiting near 45° angles with α/β boundaries. Retained β phases in as-heat treated alloys were incontinuous. 980STA exhibited an excellent combination of room temperature (RT) and 650°C mechanical properties. Characteristics of fracture surfaces largely depended on the evolutions of microstructures. Meanwhile, silicides promoted the formation of mico-voids.