Superplasticity of Ti-6Al-4V Titanium Alloy: Microstructure Evolution and Constitutive Modelling

Abstract

Determining a desirable strain rate-temperature range for superplasticity and elongation-to-failure are critical concerns during the prediction of superplastic forming processes in α + β titanium-based alloys. This paper studies the superplastic deformation behaviour and related microstructural evolution of conventionally processed sheets of Ti-6Al-4V alloy in a strain rate range of 10–5–10–2 s–1 and a temperature range of 750–900 °C. Thermo-Calc calculation and microstructural analysis of the as-annealed samples were done in order to determine the α/β ratio and the grain size of the phases prior to the superplastic deformation. The strain rate ranges, which corresponds to the superplastic behaviour with strain rate sensitivity index m ˃ 0.3, are identified by step-by-step decreasing strain rate tests for various temperatures. Results of the uniaxial isothermal tensile tests at a constant strain rate range of 3 × 10−4–3 × 10−3 s−1 and a temperature range of 800–900 °C are presented and discussed. The experimental stress-strain data are utilized to construct constitutive models, with the purpose of predicting the flow stress behaviour of this alloy. The cross-validation approach is used to examine the predictability of the constructed models. The models exhibit excellent approximation and predictability of the flow behaviour of the studied alloy. Strain-induced changes in the grain structure are investigated by scanning electron microscopy and electron backscattered diffraction. Particular attention is paid to the comparison between the deformation behaviour and the microstructural evolution at 825 °C and 875 °C. Maximum elongation-to-failure of 635% and low residual cavitation were observed after a strain of 1.8 at 1 × 10−3 s−1 and 825 °C. This temperature provides 23 ± 4% β phase and a highly stable grain structure of both phases. The optimum deformation temperature obtained for the studied alloy is 825 °C, which is considered a comparatively low deformation temperature for the studied Ti-6Al-4V alloy.

Superplastic deformation behavior of ultra-fine-grained Ti-1V-4Al-3Mo alloy: constitutive modeling and processing map

“…Many studies have focused on the superplastic properties and modeling of superplastic deformation behavior of Ti-6Al-4V alloy [6][7][8][9][10][11][12][13][14][15] and only few papers describe these phenomena in Ti-1V-4Al-3Mo alloy [16,17]. The differences in the deformation behavior of Ti-6Al-4V and Ti-1V-4Al-3Mo alloys are shown in [16].…”

Rheological Law and Mechanism for Superplastic Deformation of Ti–6Al–4V

“…The conditions were as follows: heating rate at 10 °C/s, residence time of 3 min, and strain rate at 5 × 10 −4 –0.05 s −1 . Three samples per condition and each specimen were deformed to a real strain of 0.6 and then immediately water-cooled to ambient temperature [25,26].…”

Hot Deformation Behavior Considering Strain Effects and Recrystallization Mechanism of an Al-Zn-Mg-Cu Alloy

“…In previous reports, it has been shown that different order polynomials can be given to well express the effect of strain on these material constants [40][41][42]. So, a seventh-order polynomial is selected for present work, as seen in Equation (8).…”