Strength and ductility improvement of the axial gradient microstructure TC21 titanium alloys manufactured by electropulsing plus step-quenching treatment

In order to reduce the weak area caused by traditional connection method and improve the structural efficiency of aircraft, the design concept of an integral component with dual microstructure is proposed. The electropulsing treatment (EPT) was used to produce an axial gradient microstructure (AGM) in TC21 titanium alloy, followed by the step-quenching treatment (SQT) to tailor the precipitation behavior of the α phase. Results demonstrate that the AGM produced by the combination of EPT and SQT achieves a simultaneous enhancement in both strength and plasticity of the alloy. Compared to EPT alone, the SQT results in the dissolution of the bimodal microstructure region with small-sized α phase, and an increased density of secondary α phase precipitation in both the transition and lamellar microstructure regions. During room temperature tensile deformation, coordinated distribution of deformation occurs sequentially in various regions, the 10 1 ̅ 0 11 2 ̅ 0 type of prismatic slip and deformation nanotwins exist in the equiaxed and lamellar α phase, respectively. Moreover, the deformation gradually declines from the bimodal region to the lamellar region, leading to the fracture of AGM in the bimodal region and an overall augmentation of the strength and plasticity of TC21 alloy. Hence, the results of this paper can provide research basis for the strength and plasticity improvement and deformation damage mechanism of high strength and toughness titanium alloy.