Study on Strain-Induced α Dynamic Phase Transformation of Ti-55511 Titanium Alloy During Hot Working

The study systematically investigates the strain-dependent β→α phase transformation kinetics in Ti-55511 titanium alloy during thermomechanical processing at 740 °C followed by 840 °C heat treatment. Experimental evidence reveals that strain-induced β→α transformation exhibits significant strain sensitivity, with maximum transformation efficiency achieved below the critical strain threshold of 1.3 where dynamic recrystallization (DRX) remains limited. In this regime, most α precipitates strictly obey the Burgers orientation relationship (BOR). Beyond the critical strain of 1.3, microstructural evolution undergoes a marked transition characterized by the appearance of recrystallized α phases at serrated β grain boundaries and intragranular regions, accompanied by substantial orientation dispersion. Quantitative variant analysis demonstrates systematic evolution of α phase selection, with dominant variants shifting from 50–60 deg/< − 12–10> to 80–90 deg/< − 12–10> configurations with increasing strain. Post-treatment crystallographic analysis identifies two distinct nucleation behaviors: α phases at β high-angle grain boundaries display more than 20 deg BOR deviations, while those at multi-junction β subgrain boundaries exhibit moderate 10 to 20 deg deviations. Notably, thermal annealing enhances BOR fidelity, with the population of near-BOR α phases (0 to 5 deg deviation) increasing by 38 pct compared to the deformed state, demonstrating partial crystallographic restoration through heat treatment.