The Constitutive Equation-Based Recrystallization Mechanism of Ti-6Al-4V Alloy during Superplastic Forming

Abstract

The present paper is concerned with the dynamic recrystallization of the Ti-6Al-4V alloy. Electron Backscatter Diffraction (EBSD) observations are performed after high-temperatures tensile tests, with the temperature ranging from 700 to ~950 °C, and the strain rates varying between 10−4 and 10−2/s. Based on the analysis of flow behavior, the dominant mechanism is identified, and a mechanism map is proposed. In particular, the conditions of 890 °C and strain rates ranging from 10−3 to ~10−2/s serve as the delineating boundary of dynamic recovery (DRV) and dynamic recrystallization (DRX). For superplastic deformation, the dominant softening mechanism is DRV. Consequently, the occurrence of continuous dynamic recrystallization (CDRX) can naturally be ascribed to the process of grain refinement. Then, a multi-scales physical-based constitutive model of CDRX is developed, demonstrating a good agreement is obtained between the experimental and calculated grain sizes, so the above model could be used to describe the grain growth for superplastic deformation. In conclusion, DRV and DRX in the superplastic forming of Ti-6Al-4V are studied in this study, the condition boundaries of their occurrence are distinguished, and a constitutive equation-based CDRX recrystallization mechanism is given, which might be employed in the fracture mechanism research.

Brazing Temperature Effects on the Microstructure and Mechanical Properties of Ti-45Al-8Nb Joints Using TiZrCuNi Amorphous Interlayer

“…To overcome these disadvantages, TiAl alloy, with its lower density, higher melting point, exceptional strength, and resistance to hot oxidation and creep, has been gradually replacing traditional high-temperature alloys [5][6][7]. Ti-45Al-8Nb alloy, a type of TiAl alloy, exhibits improved room-temperature plasticity, high-temperature strength, and fracture toughness due to its high Nb content, surpassing that of ordinary TiAl alloys [8][9][10]. However, achieving practical applications of high Nb-TiAl alloy better, such as fabricating components with complex shapes or large-sized parts, and achieving the application of TiAl alloys in aerospace engine turbine blades, requires solving the problem of connecting high Nb-TiAl alloy with itself and dissimilar materials [11][12][13][14].…”