| Titanium alloy had excellent comprehensive mechanical properties and was often used in engineering fields such as aviation,aerospace,and shipping.TA7 titanium alloy had large deformation resistance and poor process plasticity during the cold forming process of?single-phase region.During high temperature hot deformation,due to its own large deformation resistance,the deformation process was difficult,and it was particularly sensitive to change in thermal deformation parameters.The resulting structural defects were inevitable and affected the physical and mechanical properties of titanium alloy materials.In this paper,the isothermal hot compression experiment of TA7 titanium alloy material was carried out by Gleeble-3500 thermal simulator to study the high temperature hot deformation behavior of the alloy in the?+?two-phase region and?single-phase region.The experimental condition was set to a maximum true strain of 1.2,the deformation temperature range was850-1090?,and the strain rate range was 0.001-1 s-1.Through hot compression experiment data and microstructure characterization,the high temperature hot behavior of TA7 titanium alloy and the hot workability of the material under different deformation conditions were studied.Hot deformation parameter had a great influence on the flow stress and the evolution of microstructure.The results of the true stress-strain curve showed that TA7 titanium alloy was a deformation temperature-sensitive and strain rate-sensitive titanium alloy,and the deformation resistance increased with decreasing temperature and increasing strain rate.Arrhenius-based constitutive model was used to describe the power exponential function relationship between the flow stress of TA7 titanium alloy and the strain,deformation temperature and strain rate.The calculated thermal activation energy Q values of the TA7 titanium alloy in the?+?two-phase region and?single-phase region were 689.7788 k J/mol and 505.2747 k J/mol,respectively,and it was inferred that the deformation mechanism of the alloy was dynamic recrystallization.When the?+?two-phase region was deformed,the size of?grains increased with the increase of the deformation temperature,the phase content of the?phase decreased with the increase of the deformation temperature,and the phase content of the?phase increased with the increase of the deformation temperature.As the strain rate decreases,because the material had sufficient time to dynamically recrystallize,the dynamic recrystallization content and size would increase accordingly.In addition,the influence of the deformation temperature on the alloy was reflected in the change of the morphology and quantity of the?phase,while the influence of the strain rate on the deformation was reflected in time.Based on the DMM dynamic material modeling,the thermal processing maps of TA7 titanium alloy materials under various strain conditions of 0.1,0.2,0.4,0.8,1.0,and 1.2 were established.The results showed that with the increase of the amount of strain,when the?+?two-phase region was deformed,the area of the instability region became larger and larger.There were two instability regions under the strain 1.2,and the deformation temperature was 850-907?,the strain rate was 0.001-0.005 s-1;the strain rate was 907-970?,the strain rate was 0.004-0.037 s-1,the optimal processing parameter was that the deformation temperature was 930?,the strain rate was 0.001s-1and the maximum energy dissipation efficiency was 65%.When the?single-phase region was deformed,the area of the instability region increased first and then decreased.The instability region under strain 1.2 was that the deformation temperature was 1033-1068? and the strain rate was 0.001-0.007 s-1.The optimal processing parameter was a deformation temperature of 1090?,a strain rate of 0.001s-1,and a maximum energy dissipation efficiency of 72%. |
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