Microstructure evolution analysis of aeroengine turbine disk Zhang Haoqiang

Dissertation

College of Industrial Education (CIE) Doctor of Technology Technological University of the Philippines-Manila 2023

" Aeroengine turbine disk has been working in an extremely harsh environment for a long time. The working environment of high temperature, high pressure and high speed requires the turbine disk to have very high comprehensive mechanical properties. The composition of GH4065 material for manufacturing turbine disk is known. The comprehensive mechanical properties of turbine disk will largely depend on the microstructure of the material obtained by reasonable hot forging process. Therefore, the research on the microstructure evolution behavior of turbine disk material is of great practical significance for the forming quality and final mechanical properties of •:urbine disk.ln this paper, a series of isothermal compression experiments and grain growth experiments of GI-14065 nickel base superalloy with different process parameters were carried out. The thermal deformation behavior, dynamic recrystallization law and grain growth law of GH4065 nickel base superalloy were comprehensively analyzed and studied according to the obtained series of experimental results. According to the research results, the constitutive model, dynamic recrystallrzation model and grain growth model of GH4065 nickel base superalloy based on artificial neural network are established. Combining the three models with DE:FORM-3D finite element software, the finite element model of GH4065 superalloy turbine disk hot forging process is established. According to the finite element model, the microstructure evolution law of GF-I4065 superalloy turbine disk hot forging process is systematically studied. By designing the pal drawing of turbine disk with corresponding dimensions, the forging drawing is designed with reference to the part drawing of turbine disk, and the hot forging process of turbine disk forging is designed. The forming test of the turbine disk is carried out according to the forming process. Through the analysis of the grain size of the tracking point, it is verified that the DEFORM-3D finite element numerical simulation results can fully reflect the actual process results. The main work and conclusions of this paper are as follows: (1) In order to study the high temperature plastic deformation behavior, dynamic recrystallization behavior and grain growth behavior of GH4065 superalloy, Gleeble 3500 thermal simulation testing machine and GMF3212 numerical control digital display gold melting furnace were used. The thermal simulation testing machine is used in the isothermal compression experiment of GH4065 superalloy, and the numerical control digital display gold melting furnace is used in the grain growth experiment of GH4065 superalloy. (2) When other thermodynamic parameters are kept at fixed values, the flow stress of GH,I.065 superalloy has extremely complex nonlinear characteristics, which is manifested in that the flow stress decreases with the increase of temperature and increases with the increase of strain rate.ln orcer to build a back- propagation neural network model that can accurately characterize and predict the high-temperature flow behavior of GH4065 superalloy, the input variables are deformation temperature, strain rate and strain, and the output variables are flow stress. The back-propagation neural network model has two hidden layers, and each hidden layer has 11 neurons. (3) The softening of GH4065 superalloy is realized through dynamic recrystallization mechanism. When the temperature increases, the volume fraction of dynamic recrystallization increases and the grail size of dynamic recrystallization increases; When the strain rate increases, the volume fraction of dynamic recrystallization decreases and the grain size of dynamic recrystallization decreases. Through the calculation and analysis of experimental data by using Origin data analysis software, the dynamic recrystallization critical strain model, volume fraction model and grain size model of GH4065 superalloy are finally established. (4) In the study of the grain size cata obtained from the grain growth experiment of GH4065 superalloy, it is found that the growth law of GH4065 superalloy is different at high temperature. When the high temperature is set as a fixed value, the grain size of GH4065 superalloy will grow with the increase of holding tine, but the growth speed will gradually decrease; When the holding time is set as a fixed value, I:he grain size of GH4065 superalloy will grow with the increase of temperature, and the grain growth rate increases with the increase of tempevature.Finally, by using Origin data analysis software to calculate and analyze the experimental data of grain growth, the grain growth model of GH4065 superalloy is established. (5) The forging design of the turbine disk is completed according to the part drawing of the turbine disk, and the forming process route of heating and heat preservation - transfer - free forging and upsetting - transfer - secondary heating and heat preservation - transfer - die final forging and pressure holding - cooling is fo,mulated. (6) The microstricture evolution of GH4065 high temperature turbine disk forging process is simulated by multi-scale vortex force finite element method. According to the numerical simulation results, the evolution law of grain size of turbine disk in the stages of heating, heat preservation, transportation, upsetting, final forging and air cooling is deeply and carefully analyzed. Finally, the detailed evolution law and distribution of grain size in each part of turbine disk forging are obtained. (7) According to he forming process test of turbine disk, the forming of turbine disk is completed. Through the sampling and microstructure comparison of the actually formed turbine disk, it is found that the average grain size of the numerical simulation of each part is close to the average grain size of the actual forging, and the error is no more than 13.5%. It is verified that the numerical simulation of microstructure has high reliability.- Author's abstract
Keywords: Turbine disk, GH4065 nickel base superalloy, Artificial neural networks, Dynamic recrystallization, Grain growth, Molding process, Numerical simulation "