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

Abstract

To elucidate the hot deformation characteristics of TiAl alloys, flow stress prediction, microstructural evolution and deformation mechanisms were investigated in Ti-44Al-5Nb-1Mo-2V-0.2B alloy by isothermal compression tests. A constitutive relationship using the Arrhenius model involving strain compensation and back propagation artificial neural network (BP-ANN) model were developed. A comparison of two models suggested that the BP-ANN model had excellent capabilities and was more accurate in predicting flow stress. Based on the microstructural analysis, bending and elongation of colonies, γ and B2 grains were the main microstructural constituents at low temperature and high strain rate. Dynamic recrystallization (DRX) of γ and dynamic recovery (DRY) of β/B2 were the main deformation mechanisms. With the increase of temperature and decrease of strain rate, phase transformation played an important role. The flake-like γ precipitates in B2 grains, and a coarsening of γ lamellae via α lath dissolution during compression were observed. Additionally, the flow softening process commenced with dislocation pile-up and formation of sub-grain boundaries, followed by grain refinement, twins and nano-lamellar nucleation. Continuous DRX and phase transformation promoted the formability of Ti-44Al-5Nb-1Mo-2V-0.2B alloy.

Integrating Hip and Homogenisation Heat Treatment and its Effect on the Workability of a Conventional Peritectic Tial Alloy

“…The β phase fraction (B2/β 0 ) is accentuated by segregation [20]. At the lower working temperatures used in this study, also examined by Tetsui et al and others, the long range ordered version of the β structure (B2/β 0 ) is present [21][22][23]. This has limited deformability due to the loss of symmetry seen in the unit cell upon ordering and β 0 concentrates dislocation pile-ups, as identified by Molénat et al, its presence contributing little to workability [24].…”

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

“…Additionally, the elongated lamellar colony and dark grain-boundary Al-enriched ribbons are observed during the rolling process, in which the local recrystallization first occurs at the grain boundary with 40% deformation. Then, the recrystallization region gradually increases, accompanied by the breakdown of α2/γ lamellar colony; and finally, the massive recrystallization and elongated retained α2/γ lamellar [26,27] are obtained in the pack-rolled Ti-46Al-8Nb alloy, as shown in Figure 6d. The results above are mainly attributed to the anisotropic plastic flow of lamellar colonies during rolling process.…”

Effect of Radial Forging on the Microstructure and Mechanical Properties of Ti-Based Alloys

“…There is a large number of scientific papers [10][11][12][13][14], in which the processes of evolution of the structure and properties of titanium-based alloys are investigated under deformation by various methods. It is known [15][16][17] that the formation of structure in a material is largely determined by the degree of deformation, and its scheme and conditions. There is a large amount of experimental data on the effect of deformation on the structural state of titanium-based alloys [18,19].…”

“…According to [3,10,[15][16][17], thermomechanical processing of titanium-based alloys such as Ti-Al-Mo-V and containing Mo and V may lead to the changes in X-ray diffraction patterns owing to texture formation caused by dopant redistribution, forward and backward decomposition of the β-phase, and partial transformation of the α-phase in a metastable α"-phase. These phenomena may arise individually or overlap with each other.…”