Microstructural Variation and a Physical Mechanism Model for a Ti-55511 Alloy during Double-Stage Hot Deformation with Stepped Strain Rates in the β Region

Abstract

The microstructural variation and high-temperature flow features of a Ti-55511 alloy in the β region are studied by utilizing double-stage compression with a stepped strain rate. The results demonstrate that the stresses in the latter stage of hot compression markedly reduce as the strain at the previous stage or the strain rate at the previous/latter stage drops. Moreover, the annihilation/interaction of substructures is promoted, and the distinct refinement of the dynamic recrystallization (DRX) in the β grain can be found. However, the coarsening of the β grain and the consumption of dislocation substructures are accelerated at high temperatures. Furthermore, the principal DRX nucleation mechanism of the Ti-55511 alloy during double-stage compression with a stepped strain rate in the β region is discontinuous DRX. Additionally, by using the microstructural variation characteristics related to the forming parameters, a physical mechanism equation is modeled to forecast the forming features, the DRX fraction, and the size of the β grain in the investigated alloy. The forecasted results are in accordance with the tested results, indicating that the established model can accurately forecast the microstructure variation and flow features of the studied alloy.

Dislocation Substructures Evolution and an Informer Constitutive Model for a Ti-55511 Alloy in Two-Stages High-Temperature Forming with Variant Strain Rates in β Region

“…As revealed in Figure 3a, the true stresses at the first and second stages of hot compression exhibit a diminishing tendency with rising compression temperature. One principal reason for this experimental result is that the DRX behavior dramatically proceeds as the compressed temperature (T) ascends [6]. Moreover, the visible evolution of substructures occurs with the elevated compression temperature, as depicted in Figure 4a,b.…”

“…For the compressed temperature of 920 • C and strain rate of 0.01 s −1 , the formation of high-density dislocation clusters can be detected (Figure 4a). Then, the prominent work-hardening (WH) effect is inspired owing to the acute interaction of adjacent substructures, and the rise in true stress occurs quickly [6,16]. When the compressed temperature is elevated from 920 • C to 950 • C, the intensive migration/interaction of dislocations and grain boundary occurs, and the substructures are apparently consumed (Figure 4b).…”

“…Usually, hot deformation is necessarily utilized to improve the microstructures and further optimize the practical performance of titanium alloys [3][4][5]. The coupling effects of multiple forming parameters induce intricate evolving characteristics of microstructures and high-temperature flow behavior of titanium alloys [6][7][8][9][10]. Hence, investigations on the microstructural evolution and accurately modeling the true stress-strain characteristics of titanium alloys are significant.…”

Hot Deformation Behavior of Hastelloy C276 Alloy: Microstructural Variation and Constitutive Models

“…Furthermore, the is usually determined as [ 52 ] where is the work hardening coefficient, and can be identified as where , and represent the material constants.…”

“…During hot deformation, the is normally defined as [ 52 ] where is the material coefficient, and can be expressed as [ 39 ] where , and are the material constants.…”