Effect Of Structure Dimensions On Recrystallization Of Single Crystal Superalloy

Nickel-based single crystal superalloy has been preferred material of the key components of modern aero-engines because of its excellent high-temperature mechanical properties.In the process of investment casting of single crystal turbine blade,it is easy to induce recrystallization during solution heat treatment.The recrystallization seriously damages the fatigue and creep of single crystal blades,thus the appropriate technological parameters or structural dimensions must be selected to avoid recrystallization.In this study,a thin-walled model close to the actual single crystal blade was designed,and the effect of structure dimensions on the recrystallization of single crystal superalloy was studied by numerical simulation and experimental research.The specific studies are as follows:The temperature field and elasto-plastic mechanical model of single crystal superalloy have been established by ProCAST finite element software.The plastic strain during the directional solidification of single crystal superalloy was successfully simulated and used to infer the recrystallization tendency.A thin-walled model close to the actual single crystal blade was designed and calculate.It is predicted that the cross sections of single crystal blade are the areas with larger plastic strain.Several groups of recrystallized test specimen with different structural dimensions were designed to process directional solidification and heat treatment experiments.The experiments results are consistent with the simulated prediction.It is proved that the thermo-elastic-plastic model could effectively predict the plastic strain during the directional solidification of single crystal superalloy,which is a semi-quantitative method to predict the recrystallization of single crystal superalloy.With the increase of the thickness of the blade,the recrystallization degree generally decreases.When the thickness of the blade change from 0.5 mm to 1.2 mm,the recrystallization degree decreases obviously.When the blade thickness larger than 1.2 mm,the recrystallization degree are similar.As the blade corner radius increases,the recrystallization degree decreases.The microstructure of the specimens after heat treatment was observed and it was found that the recrystallization grain was generated from the bottom corner of the blade and then grew along the vertical direction.The growth direction was inclined to a certain degree by the blade corner radius.The distribution of recrystallized grains does not have obvious preferred orientation and belongs to random distribution.