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

Abstract

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.

Keywords

solution temperatures / microstructures / mechanical properties / fractographs / silicides

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