Study On Fine Crystal Heat Treatment Diagram And Dynamic Recrystallization Behavior Of TC4 Titanium Alloy

TC4 titanium alloy has excellent mechanical properties and can be applied in a wide range,which has attracted the attention of many scholars at home and abroad.In recent years,with the development of science and technology,higher requirements have been put forward for the production,design and performance of alloy products.During hot working,some internal defects will occur due to the increase of deformation resistance and the sensitivity of deformation parameters,which will affect the structure and properties of the material.By means of thermal simulation compression test,hot working diagram and numerical simulation,the processing,structure and properties can be analyzed together to achieve the purpose of controlling parameters and improving performance.The experimental material used in this paper is fine grained structure after continuous variable cross-section cyclic extrusion(CVCE).The average grain size is 2-3 ?m by this method.The strain rate of fine grained materials is 0.001~1 s-1 and 750~950 ?.The true stress-strain curves under different deformation conditions are obtained.The curves show obvious dynamic recrystallization characteristics.The rheological stress increases with the increase of strain rate and the decrease of deformation temperature.The true stress-strain curves obtained from experiments were modified by friction and temperature rise.Based on the revised data,a constitutive model was constructed.The model can accurately describe the stress variation of the alloy.The average error of the model is 5.712%.Within the range of processing parameters and based on the theory of dynamic material model,different parameters are fitted and calculated,and corresponding hot working maps are drawn.The results show that the high dissipation rate ? is concentrated in the range of 820~920 ? and the low strain rate is concentrated in the range of deformation rate 0.03~1 s-1.The final optimal processing range is 820~920 ? and 0.001~0.003 s-1.The deformation mechanism was analyzed with the alloy structure diagram of the corresponding processing zone.The results show that there are many defects in the unstable zone and the structure is not uniform.The dynamic recrystallization is Inadequate.The structure of the safe zone is uniform and machinability is high,and dynamic recrystallization is the main deformation mechanism.The dynamic recrystallization kinetics and kinematics equations of the alloy during hot compression were constructed.The critical strain value ?c of recrystallization increases with the increase of strain rate ?(5)and the decrease of temperature T.The change of recrystallization percentage XDRX is proportional to the strain and temperature,and inversely proportional to the change of strain rate.The two mathematical models were introduced into Deform-3D,and the thermal deformation process was simulated.The influence of processing parameters on the recrystallization distribution was analyzed.The results show that the large deformation zone inside the workpiece begins to recrystallize first.As the degree of deformation increases,recrystallization occurs on the outside and upper and lower sides of the workpiece,but the degree of dynamic recrystallization occurs at the core.The law of equivalent strain change is almost the same as the distribution law of recrystallization percentage.The influence of processing parameters on the law of recrystallization change is consistent with the experimental data and model analysis results.The fitting value and the experimental value reach a high matching degree,and the correlation coefficient R=0.937.