Plastic Flow and Microstructure Evolution during Low-Temperature Superplasticity of Ultrafine Ti-6Al-4V Sheet Material

Abstract

The low-temperature superplastic (SP) flow behavior of two lots of Ti-6Al-4V sheet, each with an ultrafine microstructure, was established by performing tension tests at temperatures of 775°C and 815°C and true strain rates of 10 À4 and 10 À3 s À1 . The as-received microstructures of the two materials comprised either equiaxed or slightly elongated alpha particles in a beta matrix. The material with equiaxed alpha particles exhibited flow hardening, which was correlated with concurrent (dynamic) coarsening. The rate of dynamic coarsening was rationalized in terms of static coarsening measurements and the enhancement of kinetics due to pipe diffusion. By contrast, the material with initially elongated alpha particles exhibited comparable flow hardening at the lower strain rate but a complex, near-steady-state behavior at the higher strain rate. These latter observations were explained on the basis of the evolution of the alpha particle shape and size during straining; dynamic coarsening or dynamic spheroidization was concluded to be most important at the lower and higher strain rates, respectively. The plastic flow behavior was interpreted in the context of a long-wavelength flow localization analysis.

Low-temperature superplasticity and coarsening behavior of Ti–6Al–2Sn–4Zr–2Mo–0.1Si

“…As shown in Table 2, the coarsening-rate constants K of Ti6242Si are 2.7-4.7 times lower than those of Ti-6Al-4V at similar temperatures in the range 750-775 • C [30]. In this regard, the diffusion-controlled coarsening and growth of alpha particles in alpha/beta titanium alloys have been shown to be controlled by the properties of the solute with the lowest diffusivity [14][15][16]31], i.e., Mo and V solutes in Ti6242Si and Ti-6Al-4V, respectively.…”

“…3a and b) exhibited near steady-state flow for CP samples and flow hardening for FP specimens. These observations can be rationalized in the context of recent research on the superplastic flow behavior of twophase Ti alloys [30]. In this former work, the instantaneous flow response was related to the evolving microstructure using the Bird-Mukherjee-Dorn generalized constitutive equation [35], viz.,…”

Mechanical behavior of a Ti‐6Al‐4 V titanium alloy with microstructural evolution modeling under hot and superplastic conditions

“…Regarding our test conditions, the grain growth effect of the a-phase was assumed to be the major mechanisms affecting the mechanical properties. This phenomenon was taken into account by using evolution equations from literature [5][6][7].…”

Manufacturing Ultrafine-Grained Ti-6Al-4V Bulk Rod Using Multi-Pass Caliber-Rolling

“…It also exhibits excellent corrosion resistance and mechanical stability at various temperatures. Finally, the alloy has good formability at elevated temperatures after applying a certain thermomechanical process due to the superplasticity [2][3][4].…”