Hot Deformation Behavior and Microstructural Characteristics of Ti–46Al–8Nb Alloy

Abstract

Hot deformation behavior, microstructural evolution and flow softening mechanism were investigated in Ti-46Al-8Nb alloy via isothermal compression approach. The true stress-strain curves exhibited typical work hardening and flow softening, in which the dependence of the peak stress on temperature and strain rate was obtained by hyperbolic sine equation with Zener-Hollomon (Z) parameter, and the activation energy was calculated to be 446.9 kJ/mol. The microstructural analysis shows that the alternate dark and light deformed ribbons of Al-rich and Nb-rich regions appeared and were associated with local flow involving solute segregation. The Al segregation promoted flow softening mainly arising from the recrystallization of c phase with low stacking fault energy. The coarse recrystallized c and several massive c phase were observed at grain boundaries. While in the case of Nb segregation, b/B2 phase harmonized bending of lamellae, combined with the growth of recrystallized c grains and a ? b ? c ? a ? c transition under conditions of temperature and stress, leading to the breakdown of a 2 /c lamellar colony. During the hot compression process, gliding and dissociation of dislocations occurred in c phase that acted as the main softening mechanism, leading to extensive c twins and cross twins in a/c lamellae and at grain boundaries. In general, homogeneous microstructure during the hot deformation process can be obtained in TiAl alloy with high Nb addition and low Al segregation. The deformation substructures intrinsically promote the formability of Ti-46Al-8Nb alloy.

Flow Stress Prediction and Hot Deformation Mechanisms in Ti-44Al-5Nb-(Mo, V, B) Alloy

“…Further, studies of flow stress and hot deformation behavior are meaningful for TiAl alloys to determine the optimized deformation parameters, including deformation force, strain, strain rates and deformation temperatures. It may be noted that the complex non-linear relation among deformation parameters are usually described by an Arrhenius-type constitutive equation (ACE) based on dynamic material model (DMM) for TiAl alloys in many studies [ 9 , 10 , 11 , 12 , 13 ]. However, only a few studies focused on the study of flow stress of TNM alloys during hot deformation [ 14 , 15 , 16 ].…”

The Effects of Hot-Pack Coating Materials on the Pack Rolling Process and Microstructural Characteristics during Ti-46Al-8Nb Sheet Fabrication

“…Chemical analysis results were analyzed by inductively coupled plasma mass spectrometry (ICPMS) for both the alloys. Subsequently the homogenization heat treatment was performed at 1200 • C for 4 h. The microstructure is comprised of the α2/γ lamellar colony, B2 phase, and grain-boundary γ phase [23]. The samples were machined from the ingot by a spark machining and sandwiched with the packaging layer for the hot compression by the plane strain technique.…”

“…The thin diffusion interface is obtained between TC4 layer and TiAl matrix, and also between the TC4 layer and the outer stainless steel, as shown in Figure 5c, which shows the favorable interface protection through the packaging materials and structure design for the sheet fabrication. Finally, the macrostructure of the high-deformed TiAl sheet takes on the alternate structure of the dark grain-boundary Al-enriched ribbons [23] and the elongated lamellar structure, as shown in Figure 5d. The detailed microstructural evolution and flow behavior for the heat-deformed Ti-46Al-8Nb alloy is presented later.…”

Hot deformation of high-Nb-containing γ-TiAl alloy in the temperature range of 1000–1200 °C: microstructural attributes to hot workability

“…However, the very poor hot workability remains one of the major areas of concern for the successful application of high-Nb-containing alloys. In another study, hot deformation behavior of a similar cast alloy has been characterized at various temperature and strain rates, but workability aspect of the alloy is largely ignored [6]. Hence, the reasons for poor hot workability of high-Nb-containing γ-TiAl alloys are not fully understood yet.…”