Dynamic Recrystallization During Elevated Temperature And Grain Growth Behavior Of Ti-47Al-2Nb-2Cr Alloy

As a kind of new structrual material, which possesses excellent mechanical property and is used at high service temperature, Ti Al based alloy has been paid increasing attentions by large amount of materials researchers throughout the world. At present, the main forming method for Ti Al based alloys is hot working. Different forming parameters, by controlling materials‘ dynamic recrystallization behavior, may impose influence on microstructure of materials and thus changing the materials‘ integrated performance. Reasonable selection of hot processing parameters to obtain ideal microstructure is the key to expand industrial application of the material. In the present work, the PM Ti-47Al-2Nb-2Cr alloy is studied and the experiment of hot compression simulations were conducted under different parameters. On the basic of microstructure observation, the dynamic recrystallization behavior of the material was revealed. Based on the finite element simulation platform, the dynamic recrystallization process is studied by using the secondary development technology, which is beneficial to investigate the influence of the hot deformation parameters on the dynamic recrystallization behavior of the material. In addition, the microstructure stability of the Ti Al based alloy after hot deformation was researched by isothermal annealing during constant time or constant temperature. Additions, by establishing the grain growth kinetics equation, the influence of isothermal annealing parameters on the grain growth behavior is predicted. The results may enrich the basic data and theory of hot deformation and isothermal annealing of the Ti-47Al-2Nb-2Cr alloy and promote the design and optimization of hot processing and isothermal annealing parameters.This work studied the hot deformation behavior of the Ti-47Al-2Nb-2Cr alloy during constant deformation rate or constant temperature, and established the dynamic recrystallization kinetics model of the material, and then systematically analyzed the influence of hot deformation parameters on the dynamic recrystallization behavior. The microstructure evolution of the Ti-47Al-2Nb-2Cr alloy is analyzed by EBSD technique, and the accuracy of the dynamic recrystallization kinetics model was evaluated. Secondary development technology, based on the finite element simulation platform, was applied to realize the integration of finite element simulation analysis and the dynamic recrystallization kinetics model of Ti-47Al-2Nb-2Cr alloy, and then predicting the relationship between hot deformation parameters and dynamic recrystallization behavior of the material. The effection of the equivalent strain on the dynamic recrystallization behavior was analyzed by using the equivalent strain distribution maps of different deformation regions. It was demonstrated that the hot deformation temperature, strain rate and strain affect the dynamic recrystallization behavior of the material.Isothermal annealing of the samples after hot deformation was studied. Then, the effect of isothermal annealing parameters on the grain growth behavior is analyzed. After that, the kinetic model for the grain growth of the Ti-47Al-2Nb-2Cr alloy was established. Afterwards, the grain growth activation energy(gE = 151.56 k J/mol) of Ti-47Al-2Nb-2Cr alloy was calculated. The observation of the material‘s microstructure proved that the temperature and time of isothermal annealing had significant influence on the grain size.