Study On Microstructure Of Nickel-based Superalloy DZ4125 And Simulation Of Directional Solidification Process

In recent years,with the development of aerospace industry and the gradual improvement of engine performance requirements,ordinary cast superalloys have been unable to meet the performance requirements.The appearance of directional solidification technology has greatly improved the high temperature creep performance and endurance life of engine hot-end structural parts.However,the change of process parameters is still the key factor to determine the product performance,so the temperature field and microstructure of nickel-based superalloy were studied.The main research contents and results are as follows:(1)In the directional solidification process of nickel-based superalloy DZ4125,the temperature field of sample under different process parameters was studied.To master the influence law of sample,furnace wall and water-cooling ring on radiation heat transfer under different technological parameters,and summarize the variation law of temperature field inclination degree and direction.When the number of modules is 8,the temperature field with the pulling speed of lmm/min is the most stable,and when the size of the sample increases from 16mm to 26mm,the temperature field appears concave,which is caused by the difficulty of heat exchange in the center.(2)The temperature field of directional solidification was studied with columnar,variable cross-section and blade samples.And the distribution of temperature field at abrupt crosssection and complex structure edge plate was obtained.It is found that the isotherm inclination is intensified due to the different heat transfer angles.The placement of asymmetric blade samples in furnace was studied.Compared with the vertically placed blade sample,the temperature field and mushy zone of the parallel blade sample are more stable,and good columnar or single crystal can be easily obtained.(3)Based on the study of the temperature field of the column sample,the mushy area of the column sample under different process parameters was studied.With the increase of drawing speed,the inclination degree of mushy area increases and moves down;with the increase of heat preservation temperature,the position of mushy area moves down and the width narrows to 17.5mm;with the increase of the number of modules,the inclination direction of mushy area changes;with the change of sample size,the inclination degree and size of mushy area also increases,and the width of mushy area decreases by 19.2%.It provides a reference for adjusting the drawing process of directional solidification and optimizing the microstructure of superalloy.(4)The grain growth model was established to study the grain growth of variable crosssection samples.Based on the time criterion,the grain growth law of solid-liquid interface passing through the platform of variable cross-section in directional solidification is studied,and then the position of new grain which is different from the original grain orientation is predicted.The grain growth simulation of the blade samples was carried out to grasp the growth law and the formation position of the heterocrysts,and the control was carried out by means of heating temperature and mold formation.(5)The microstructure of directional solidification DZ4125 alloy was studied.The primary dendrites in the longitudinal section of the sample were parallel to each other.The distribution of the ? phase and ?' phase of alloy DZ4125 was analyzed.The directionally solidified structures at different drawing heights were studied.The primary and secondary dendrite spacing remained at 357.63?m and 65.34?m in the stable growth zone.The size of the ?' phase increased with the increase of drawing height,from 0.19?m at H=30mm to 0.59?m at H=120mm.The increase in size reduced the high-temperature performance of the alloy.