Research On Mesoscopic Research And Simulation On Hot Deformation Microstructure In TB8 Alloy

Numerical simulation of microstructure evolution during hot deformation process, which provides a new way for predicting and controlling the microstructure and mechanical properties of work piece, will be beneficial for the transition from skill to science. It has been rapidly developed as a remarkable research area in the metal plastic forming industry in the world. In this dissertation, microstructure evolution of a new metastable-type TB8 alloy after hot deformation and solution treatment at mesoscale have been studied by employing plastic forming, metallurgy, finite element method, crystal plasticity theory, and Cellular Automaton method, etc.. Some useful conclusions are obtained. It has important theoretic merits and practical significance for establishing reasonable hot deformation process and promoting development and utility of TB8 alloy.Based on the hot compression test performed on Gleeble-1500 Thermal Simulator and solution treatment experiment, the hot deformation behavior of TB8 alloy has been investigated. The flow stress can be described by the hyperbolic-sine-type equation. On the basis of the metallurgical analysis of the microstructure after hot deformation and solution treatment, qualitative and quantitative research on the influence of deformation temperature, strain rate and deformation degree on the microstructure was carried out. A predicting model for the recrystallization volume and average grain size of the microstructure after solution treatment has been established by a three-layer feed-forward artificial neural network with a back-propagation learning rule. 1 he close agreement of the predicted results with measured ones shows that the neural network is able to successfully predict the variation of the microstructure with the hot deformation parameters. It can provide more scientific foundation for establishing reasonable hot deformation process and the simulation of microstructure evolution.In order to well understand the hot deformation behavior of TB8 alloy, electron backscattered diffraction(EBSD) technique was employed to characterize the initial microstructure and the microstructure after hot deformation and solution treatment. The results indicate that the microstructure after hot deformation show great inhomogeneous plastic deformation, which is the ultimate reason why the effect of inhomogeneous deformation must be considered in the microstructure simulation. The partially dynamic recrystallized microstructures have strong texture, and the relationship between the nucleation and growth of dynamic recrystallized grains and the evolution of deformation substructure.is very intimate. The static recrystallization during solution treatment remarkably promotes the decrease of the deformation structure and texture, and the static recrystallized grains are characterized without preferred orientation.The initial microstructure of TB8 alloy was obtained by the Cellular Automaton method of normal 2D grain growth. On the basis of the coupled thermal-mechanical macroscale simulation of hot compression process and the grain orientation of initial microstructure obtained by EBSD, the crystal plasticity finite element model was established to simulate the hot deformation on mesoscale. The distributions of stress, strain and stored energy was analyzed, and the activated slip systems during the deformation were d(?) scussed. The simulation results reveal that the characteristic of inhomogeneous deformation can be characterized by the stored energy which can be computed by the crystal plasticity finite element method. It can be provided as the physical foundation for the microstructure simulation of subsequent recrystallizaion.On the consideration of the effect of inhomogeneous deformation on the recrystallization behavior, a mesoscopic model for recrystallization of TB8 alloy was developed by coupling Cellular Automaton method with crystal plasticity finite element model. Due to the simulation results such as stored energy corresponding to the integration points of deformed finite element mesh, so an interpolation method of mapping these data of distortion finite element mesh onto regular square lattice of Cellular Automaton method should be put forward at first. Then the local stored energy of deformation is incorporated in the Cellular Automaton as an additional driving force for the nucleation and growth model for recrystallization. In this model, the inhomogeneous plastic deformation was rightly considered, so that it provides more physical foundation for the simulation. Finally, the microstructures of simulation and experiment were compared. The results demonstrate that the simulation using the model put forward in this dissertation can obtain the statistically equivalent microstructure. The process accords with the physical mechanism of the microstructure evolution in practice. It also reflects that this model is reliable. These studies have important significances for optimizing the forming process, controlling the quality of products and directing the manufacture.