BPANN modified constitutive descriptions for flow behavior and softening mechanism in the plus phase region of Ti-55511 alloy with equiaxed microstructure

The deformation behavior of Ti-55511 alloy was investigated by hot compression tests conducted at deformation temperatures of 993 similar to 1113 K and strain rates of 0.001-1 s(-1) . To eliminate the effects of friction and adiabatic temperature rise on the flow stresses, the flow curves were corrected. Subsequently, a strain compensated Arrhenius (SCA) model was developed and further modified using the back propagation artificial neural network (BPANN) method. The modified model exhibits significant improvements compared to the SCA model. The average absolute relative error (AARE) decreases from 4.895 % to 0.756 %, while the relative error (delta) range decreases from - 14.75 %-17.99 % to - 4.78 %-8.01 %. Moreover, cross-validation also confirms the modified model has higher generalization ability and prediction accuracy than the SCA model. Microstructural characterization reveals dynamic recrystallization (DRX) of the alpha phase and dynamic recovery (DRV) of the beta phase are the main mechanisms responsible for softening, and their volume fractions increase with decreasing strain rate and increasing deformation temperature. The equiaxed alpha phase undergoes elongation first, followed by gradual migration and transformation of grain boundaries. Finally, the beta phase wedges into the alpha phase until the alpha phase separates. The continuous dynamic recrystallization (CDRX) of beta phase accompanies its DRV, which is mainly characterised by progressive sub-grain rotation. The alpha grains aggregated by dislocations promote CDRX of the beta phase.