Research On Simulation Of Directional Solidification Process And Control Of Microstructure Of Ni-based Single Crystal Blade

As a key component of aero engine which have to endure high temperature and complex stress,single crystal blades are mainly made through directional solidification by high rate solidification(HRS).The growth of single crystal microstructure is very difficult for directional solidification process.The process parameters are the main factors affecting the temperature field distribution in the directional solidification process.The change of the temperature field will further lead to the change of the shape of the mushy zone and the temperature gradient of the solid and liquid phase,thus affecting the growth of the single crystal structure.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 single crystal blade.The study of the temperature field includes the study of the basic law of heat dissipation and the influence of the process parameters on the temperature field;The microstructure simulation and experimental study includes the study on the grain selection behavior and the formation rule of the platform;Finally,based on the simulation results,the optimal control scheme of single crystal hollow blade is proposed.The main contents and conclusions are as follows:The temperature measurement experiment is carried out to validate the accuracy of the simulation results.The basic law of the temperature field distribution of the directional solidification is simulated.The isotherms showed a skewed distribution.The results show that in the heating zone above the heat shield,the heat dissipation near the furnace wall is slower than that of the center of the furnace while the cooling area below the baffle is reversed.The influence of the process parameters(the withdraw rate and the blade phase)on the temperature field of the single crystal solid blade were studied.The results show that when the convex surface of the blade faces the furnace wall,the isotherms show a downward trend,when the concave surface of the blade faces the furnace wall,the isotherm is convex,when the edge of the blade faces the furnace wall,the isotherms near the furnace wall is lower than that of the furnace center.In addition,at the top of mushy zone,the isotherms showed a convex tendency.With the increase of the withdraw rate,the convex extent decreases and the temperature gradient decreases.The temperature field of single crystal hollow blade was simulated.The results show that the core of the single crystal hollow blade has a thermal insulation effect on the blade.The thermal insulation effect not only makes the temperature field distribution of the single crystal hollow blade different form the single crystal solid blade,moreover,the temperature field distribution of the different structure of the single crystal hollow blade is also different.Selection behavior of a grain selector is studied,The main role of the starter block is to optimize grain orientation.In order to optimize the grain orientation,the height of the starter block must reach the stable region of grain number;The spiral part can not optimize the final orientation of the grains,which can provide a platform for the competitive growth of multiple grains and eventually form a single crystal.The spiral structure of the spiral part can effectively make a plurality of grains eventually grow into a single crystal,and the grains near the edge of the spiral structure will eventually grow into single crystals.Simulation and experimental study on directional solidification process of platform were carried out.The main reason for the formation of stray grain in the platform is that the platform is in undercooling condition.But simply in the undercooling condition Can not form stray grain in the platform.Before the secondary dendrite develop into platform,when the bottom of platform reach critical nucleation undercooling,stray grains will form;With the increase of the horizontal height,the cooling efficiency decreases,and the undercooling of the platform is graduallyreduced,so the size of the stray grain decreases with the increase of the horizontal plane until stray grains disappear.Based on the analysis of computer simulation results,the simulation results show that the withdraw rate of single crystal hollow blade is different for different crystal structures.The parts below the blade exhaust side,the blade with the exhaust side and the edge plate and the above,adopt three different withdraw rate in the directional solidification.The experimental results show that the technology of variable withdraw rate can effectively avoid the formation of stray grains and improve the quality of the single crystal hollow blade.