Microstructural evolution in Ti–10Al–1Zr–1Mo–1Nb alloy under thermomechanical treatment in β-region

Abstract

The influence of temperature and strain rate on microstructural evolution in near α-type Ti–10Al–1Zr–1Mo–1Nb alloy was studied under uniaxial compression in the β single-phase-region. Hot compression tests were conducted for up to 75% reduction at temperatures between 1273 K and 1333 K and strain rates between 0.01 s−1 and 5 s−1. The steady-state of the flow behavior revealed that dynamic recovery in the β single-phase was dominant in the microstructural evolution process, and few dynamically recrystallized grains were detected, except in the vicinity of the pre-existing β grain boundaries. Two types of configurations such as lamellar αL and acicular αAC microstructures were developed, which were consistent with the compressive deformation mechanism in the β-region. The αL microstructure consisted of α platelets that were developed via growth of a specific variant, whereas the αAC microstructure consisted of individual α platelets with a different variant in the prior-β matrix. The stress exponent and activation energy were evaluated to determine the deformation mechanism. The heterogeneous nucleation of individual α platelets in the cellular structure (sub-grains) without a specific orientation in the β matrix resulted in the αAC microstructure. In contrast, the substructure as uniformly distributed dislocations in prior-β grains under the viscous motion of dislocations promoted a single variant selection to form αL platelets in the transformation. When the viscous drag dislocation motion in the β-region is dominant, a large crystal rotation is detected in the acicular (side plate) αSP platelets in the vicinity of the prior-β grain boundary.