Dynamic Softening Mechanisms and Microstructure Evolution of TB18 Titanium Alloy during Uniaxial Hot Deformation

Qiang Fu,Wuhua Yuan,Wei Xiang

doi:10.3390/met11050789

Abstract

In this study, isothermal compression tests of TB18 titanium alloy were conducted using a Gleeble 3800 thermomechanical simulator for temperatures ranging from 650 to 880 °C and strain rates ranging from 0.001 to 10 s−1, with a constant height reduction of 60%, to investigate the dynamic softening mechanisms and hot workability of TB18 alloy. The results showed that the flow stress significantly decreased with an increasing deformation temperature and decreasing strain rate, which was affected by the competition between work hardening and dynamic softening. The hyperbolic sine Arrhenius-type constitutive equation was established, and the deformation activation energy was calculated to be 303.91 kJ·mol−1 in the (α + β) phase zone and 212.813 kJ·mol−1 in the β phase zone. The processing map constructed at a true strain of 0.9 exhibited stability and instability regions under the tested deformation conditions. The microstructure characteristics demonstrated that in the stability region, the dominant restoration and flow-softening mechanisms were the dynamic recovery of β phase and dynamic globularization of α grains below transus temperature, as well as the dynamic recovery and continuous dynamic recrystallization of β grains above transus temperature. In the instability region, the dynamic softening mechanism was flow localization in the form of a shear band and a deformation band caused by adiabatic heating.

Highlights

IntroductionThe addition of α phase stabilizing elements, such as aluminum (Al), and β phase stabilizing elements—for instance, vanadium (V), molybdenum (Mo), and chromium (Cr)—gives the alloy good properties but results in a relatively narrow processing window, which is significantly detrimental to its industrial applications
The deformed samples were sectioned parallel to the compression axis and the center part of each section was subjected to optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), electron backscattered diffraction (EBSD), and transmission electron microscope (TEM)
The results indicate that TB18 alloy had greater deformation activation energy in both the (α + β) phase zone and the β phase zone

Summary

Introduction

The addition of α phase stabilizing elements, such as aluminum (Al), and β phase stabilizing elements—for instance, vanadium (V), molybdenum (Mo), and chromium (Cr)—gives the alloy good properties but results in a relatively narrow processing window, which is significantly detrimental to its industrial applications. In this situation, thermomechanical processing is usually adopted to improve the hot workability of titanium alloys, which has been successfully applied to fabricate complicated aerospace components, such as landing gear [4], fuselages, and wings [5]

Methods

Results

Conclusion