Research On Simulation Of Directional Solidification Process And Control Of Microstructure Of Nickel-based Single Crystal Hollow Blades

With the continuous increase of the working temperature of turbine blades,the degree of alloying of nickel-base single crystal superalloys for preparing blades has become higher and higher,and the internal structure of the blades has become more and more complex.This has led to a decrease in the casting performance of single-crystal blades and the difficulty in controlling the single crystal ratio.Oxidation behavior at high temperatures is also more complicated.The improvement of computer software and hardware technology makes the numerical simulation technology develop rapidly,and the directional solidification process of turbine blades of aircraft engine can be simulated by numerical methods.The computer simulation technology provides a “ visualization process ” for directional solidification,temperature field and the mushy zone distribution under different process parameters can be directly reflected by simulation results,which provides a convenient and accurate method for Research onsingle crystal directional solidification.In this paper,the computer simulation and directional solidification experiments are carried out to study the directional solidification process and microstructure control of nickel-based single crystal hollow blades.The main contents and conclusions are as follows:(1)The crystal selection process of the spiral crystal selector was simulated and experimentally studied.It is found that as the solid-liquid interface advances in the [001] direction,the number of grains decreases relative to the bottom of the starter block,the crystal deflection angle gradually decreases,and the orientation is optimized;the withdraw speed will affect the temperature field and further influencing the degree of tilt of the tissue growth;the height of the starter block has a significant optimization effect on the crystal grain orientation;so in actual directional solidification process,a suitable drawing speed and height should be established;the spiral part itself cannot optimize the orientation of the crystal grain.(2)The temperature field of single crystal hollow blade was simulated.Studies have shown that the temperature field distribution of the core and blade body have the same overall trend,but the temperature profile of the core is smoother than the blade body.The core has a thermal insulation effect on the blade and the thicker the core,the better the insulation effect.The thermal insulation of the core,the structure of the blade,and the distance between the blade and the insulation heater all determine the differences in the temperature field distribution at different positions of the single crystal hollow blade.The temperature field of the directional solidification of a single crystal hollow blade under different withdraw speeds will also change.(3)The law of microstructure solidification and temperature distribution at the variable cross section of single crystal blade was discussed,and the formation mechanism of the miscellaneous crystal at the variable cross section was analyzed.The results show that the crystal growth starts from the lowest edge of temperature to the blade,and finally merges with the single crystal structures of the blade.The difference in wall thickness has a great influence on primary dendrite.With the increase of wall thickness,the dendrite spacing gradually increases.At the same time,the technology of variable withdraw rate was also used to optimize the directional solidification process parameters.