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Abstract
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Double-stage hot deformation tests were implemented to systematically reveal the flow characteristics and microstructure evolution of Ti55511 alloy with fully β phase. The double-stage hot deformation parameters cover wide ranges of strain rates (0.001 s–1–0.1 s–1), temperatures (1163–1223 K), first-stage strains (0.3–0.9) and inter-stage holding times (0–120 s). Experimental results show that the reloading yield stress significantly is lower than the yield stress in first-stage (stage-I) deformation. The main softening mechanisms, static recrystallization (SRX) and metadynamic recrystallization (mDRX), contribute to a decrease in the reloading yield stress in the second-stage (stage-II) deformation. When the inter-stage holding time exceeds 60 s, the abnormal grain growth occurs, leading to an increased average grain size. A visco-plastic self-consistent (VPSC) model incorporating double-stage deformation parameters is presented. The model accurately reproduces the microstructure evolution during the double-stage hot deformation. However, its computational efficiency is limited. Therefore, by integrating experimental data with VPSC output, a novel model combining a particle swarm optimization (PSO) algorithm with a long short-term memory (LSTM) network (PSO-LSTM) is introduced to predict flow stress and microstructure evolution. The mean absolute error (MAE), correlation coefficient (R2) and root-mean-square error (RMSE) values between experimental and predicted stresses of the PSO-LSTM model are 0.6252 MPa, 0.9987 and 1.8637 MPa, respectively. Additionally, the proposed PSO-LSTM model can accurately predict the average grain size evolution during the double-stage hot deformation.
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