Lath decomposition and dispersion induced by heterostructure deformation and associated interactions in a lamellae metastable-β Ti alloy during subtransus processing

Abstract

The mechanisms of lath decomposition and dispersion were hitherto rarely explained due to limited understanding into the heterostructure deformation between two phases and associated interactions. In this work, the lath decomposition and dispersion were systematically investigated in a wide subtransus processing range of 0.001 s−1–1 s−1 and 745 °C–820 °C with the consideration into the heterostructure deformation and associated interactions. The relationship between flowing behavior and microstructure evolution were discussed. Results indicated that the initial buckling of α laths caused high peak strength. The rotation and twist of α laths are helpful to decrease the flow stress, but it caused serious extra deformation and dislocation storage in the β matrix. The lath decomposition dominated by the ablation was greatly contributed by the adiabatic temperature rise (ATR) near boundaries with high energies. The α laths could rotate under low strain rates, and numerous residual laths (RLs) could be obtained. The increment in strain rates to 0.1 s−1 resulted in earlier lath decomposition and softening, as well as to disperse αp particles and homogenize the β matrix. But an overhigh strain rate of ∼1 s−1 caused adiabatic shear bands. The low temperatures are unfavorable to the lath decomposition, while over-high temperatures diminished the extra deformation and ATR. On this basis, a deformation mechanism map for the subtransus processing of lamellae Ti-55531 alloy was established. This investigation sheds deeper insight into the tailoring of microstructure and prediction of flowing behavior for the subtransus processing of lamellae metastable-β Ti alloys.