Multi-scale Numerical Simulation And Solidified Defects Prediction Of Industrial Gas Turbine Blade Casting During Directional Solidification

Industrial gas turbine(IGT)engines are widely used in energy,national defense and other fields,and the development level of IGT engines is related to the national economic and national defense security.IGT blades,as the key hot end components of IGT engines,are usually produced by directional solidification(DS)process.However,many defects are occurred during DS process,such as stray grains,freckles,and so on,due to the fact that IGT blades are large-size and complicated,and even present cambered and hollow structure.Numerical simulation technology as a powful tool which can predict the macro temperature field,meso grain structure and micro dendrites of the IGT blades during DS process.Moreover,the solidification process parameters can be optimized by numerical simulation technology,thus providing the actual industrial production with theoretical and technical support.According to the characteristics of physical information transmission among macro,meso and micro units,interpolation algorithm was used to establish a coupled multi-scale mathematical model of DS process.Energy uniform distribution method and an algorithm of intersection point between large step of ray line and furnace were adopted to calculate the radiation heat transfer during DS process.Grain structures of large IGT blades which are over 300 mm in length were successfully simulated by using stratification and parallel computation methods.Considered the effects of solute diffustion,interface curvature and anisotropy,a 3D dendrite gowth model was built.The evolution behavior of dendritic structures in Ni-based superalloys was systemically studied based on the simulation and experiment methods.The nucleation and growth of dendritic structures were observed in-situ by using high temperature confocal laser scanning microscopy(HT-CLSM).The 2D and 3D single dendrite and multi dendrites were simulated based on the experimental conditions,and the simulation results agree well with the experimental results.The competitive growth behavior of DS dendrites was further analyzed by the proposed model.The proposed model was verified by both HRS and LMC process.The experimental results of cooling curves,grain structures and dendritic structures present a reasonable agreement with the simulation results.Two castings with different geometrical shapes were designed to study the grain selection behavior between HRS process and LMC process.The results showed that the grain orientation under HRS process with an appropriate withdrawal rate was better than that in LMC process.Moreover,the grain selection was disabled during LMC process while without considering the effects of ceramic beads.The complex DS and single crytal(SC)IGT blades was simulated by the multi-scale model.The influence of different process parameters to the microstructure of DS blades was studied.The parameters of withdrawal rate,pouring temperature,preheating temperature and the local shell thickness were discussed in detail to optimize the process.As a result,the parallel degree of the blade grains has been significantly improved.Subsequently,temperature field and grain structures of a complex SC blade was simulated and analyzed.A method for inserting a conductive graphite block to the mold shell in order to eliminate the stray grains in listrium was suggested.