Microstructure and high temperature mechanical properties of powder metallurgical Ti-45Al-7Nb-0.3W alloy sheets

• The Ti-45Al-7Nb-0.3W alloy sheets showed excellent mechanical properties.
• The brittle-ductile transition temperature was found at between 800 °C and 850 °C.
• The Ti-45Al-7Nb-0.3W alloy sheets could display superplastic behaviors at 950 °C.
• The sheets displayed various deformation mechanisms under different conditions.

The microstructure, high temperature mechanical properties and deformation mechanism of powder metallurgical (PM) Ti-45Al-7Nb-0.3W (at.%) alloy sheets were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The tensile test results showed excellent high temperature mechanical properties with a yield stress (YS) of 670 MPa and an ultimate tensile stress (UTS) of 874 MPa at 700 °C and displayed an anomalous strengthening effect, which could be explained by the pinning mechanism of dislocation locks. In addition, the brittle-ductile transition temperature (BDTT) was found at between 800 °C and 850 °C. When deformed below BDTT, high density of dislocations and mechanical twins were observed in the microstructures. However, with increasing deformation temperature above BDTT, kinking of α2/γ lamellar colonies and dynamic recrystallization also occurred. It was noteworthy that the as-rolled sheets displayed superplastic behaviors at 950 °C with initial strain rates of 1 × 10− 4 s− 1 and 5 × 10− 5 s− 1. At the same time, severe dynamic recrystallization took place and the grain boundary sliding was improved by β phase, which resulted in an elongation of 243% at the strain rate of 5 × 10− 5 s− 1.

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