Study On Hot Deformation Behavior And Microstructure Evolution Simulation Of TC4-DT Titanium Alloy

TC4-DT alloy is a damage-tolerant two phase titanium alloy with moderate strength and high toughness developed in China were designed, which has widespread application prospect in structural of aerospace. Because mainly forming of structure is thermal deformation processing, and its excellent performance is determined by the microstructure after thermal deformation. So the thermal deformation behavior and microstructure evolution of titanium alloy have great significance to formulates the reasonable hot working process and obtain good performance of the parts. In this paper, isothermal compressive tests of TC4-DT titanium alloy at the deformation temperature from 920 ℃ to 1040 ℃ and strain rate from 0.001 s-1 to 50 s-1 was investigated by the hot-simulation machine of Gleeble-3500, combined with metallographic analysis system, the high temperature deformation behavior and processing map for the deformation process parameters of alloy have been studied, then the simulation on the microstructure evolution during thermal deformation has been carried out by using the DEFORM-3D. The main research work as follows:(1) Based on the data of isothermal compression tests, the variation characteristics of flow stress and the dynamic recrystallization behavior of alloy were researched, and the hot deformation activation energy Q and Arrhenius type constitutive equation were got. At the same time, the constitutive equation was verified which found that the models has good accuracy. Through metallographic technique, the microstructure of alloy after deformation was analyzed, which found that dynamic recrystallization of alloy occurs relatively completely at small strain rate, and with the increase of deformation temperature and deformation degree benefit to the dynamic recrystallization occurs. But the dynamic recovery is the main softening mechanism at high strain rate.(2) According to flow stress of the alloy, processing maps based on Presad criterion and Murty criterion of TC4-DT alloy were researched. Processing maps predicted the region of flow instability are in experimental strain rate range, the deformation parameters of deformation instability regions are got which are 920~950 ℃、0.03~50 s-1, 950~1010 ℃、0.56~50s-1 and 1010~1040 ℃、0.58~50 s-1. There are two peak η area at deformation stability regions, which both sides of the phase transformation point. At the same time, the parameters of the reasonable deformation regions are got, they are 920~950℃、 0.001~0.03 s-1 and 960~1040℃、 0.001~0.56 s-1. The microstructure evolution was observed, which shows that in instability region flow instabilities mainly include flow localization and non-uniform deformation of β grains, and in stability region, the dynamic recrystallization occurs sufficient.(3) According to the thermal simulation compression experiment and metallographic experiment, dynamic recrystallization model of TC4-DT alloy was established at β phase area hot deformation process. The microstructure evolution of TC4-DT titanium alloy was simulated on platform of DEFORM-3D at different deformation conditions using cellular automaton. The simulated results show that dynamic recrystallization behavior is more and more fully and grain become uniformly refined with the strain increases. The degree of dynamic recrystallization occurring at different positions of the sample is different, dynamic recrystallization behavior of large deformation area more fully, and finally the dynamic recrystallization percent up to 100%. Dynamic recrystallization behavior is more fully with the reduce of strain rate at the same temperature, but The grain size increases. The simulation results agree well with the experimental results, and the relative error less than 9.2%.