Substructure evolution in two phases based constitutive model for hot deformation of TC18 inα+βphase region

Theα+βdual phase titanium alloys are key structural materials in aviation and aero-space industries,and the complicated flow behavior of these titanium alloys during hot deformation requires to establish a constitutive model incorporating physical mechanism for optimizing process-ing parameters and designing forming tools.This work aims to establish a constitutive model incor-porating physical mechanism for hot deformation of TC18 inα+βphase region.Firstly,the flow behavior and microstructure evolution for hot deformation of TC18 inα+βphase region are char-acterized.The TC18 shows significant strain hardening rate and negative strain hardening exponent around and after peak flow stress,respectively.After peak flow stress,Dynamic Recovery(DRV)mechanism dominates the evolution of a and b phases according to the results of substructure evo-lution.Then,the internal state variables method is applied to establish a constitutive model incor-porating physical mechanism for hot deformation of dual phase titanium alloys.The variation of dislocation density during the hot deformation of titanium alloys is modeled by considering the accumulation of dislocation due to the impediment to dislocation movement by substructure obsta-cles and the annihilation of dislocation due to the dynamic restoration effect.The interaction between dislocations,the subgrain boundaries and the grain/phase boundaries obstruct the disloca-tion movement in the a phase,and the first two obstructs the dislocation movement in the b phase during the hot deformation of TC18.The dislocation annihilation process in theαandβphases dur-ing the hot deformation of TC18 is dominated by DRV.Finally,the substructure evolution in the two phases based constitutive model for hot deformation of TC18 inα+βphase region is presented.This model is well applied to predict the flow stress and quantitively analyze the role of DRV effect in the evolution ofαandβphases during the hot deformation of TC18.