Phase transformation and deformation behavior under isothermal compression in β-quenched metastable Ti-10V-2Fe-3Al alloy

Comprehensive knowledge on the hot deformation behavior and microstructure evolution of metastable titanium alloys is critical for process optimization and microstructure regulation. The isothermal compression of beta-quenched metastable titanium alloys (Ti-10 V-2Fe-3Al) was experimented at different temperatures (600 degrees C800 degrees C) with the strain rate of 10-3 s-1 in present work. The stress-strain curves show that the flow stress reduces with increasing temperature, and the characteristics of the stress-strain curve at low temperature (600 degrees C) are clearly distinct from those at other high temperatures. During the isothermal compression process at 600 degrees C, the deformation went through four stages: initial linear hardening (stage I), Discontinuous yielding phenomenon (DYP, stage II) followed by work hardening (stage III) and final flow softening (stage IV). Further observations of the microstructure throughout each deformation stage revealed that the precipitation of alpha GB and the proliferation of dislocation lead to initial linear hardening behavior. The softening of deformation behavior during the discontinuous yield stage is originated from the fragmentation of alpha GB and the generation of a large amount of moving dislocations. Almost all beta phase transformed into lamellar alpha phase as the deformation degree increased, which is the main cause of work hardening after discontinuous yield. The major causes of final flow softening are the formation of deformation bands and spheroidization of alpha phase. The present work analyses the correlation between the deformation behavior and microstructure features on the deformation mechanisms of metastable beta titanium alloys and reveals the potential mechanism of metastable beta alloy under thermal deformation and provides more comprehensive information for the optimization of the process parameters of hot deformation.