207 3rd World Congress on Integrated Computational Materials Engineering (ICME 2015) Edited by: Warren Poole, Steve Christensen, Surya R. Kalidindi, Alan Luo, Jonathan D. Madison, Dierk Raabe, and Xin Sun TMS (The Minerals, Metals & Materials Society), 2015 MODELING AND SIMULATION OF DIRECTIONAL SOLIDIFICATION OF Ni-BASED SUPERALLOY TURBINE BLADES CASTING BY LIQUID METAL COOLING Qingyan Xu, Ning Tang, Liu Baicheng School of Materials Science and Engineering, Tsinghua University, Beijing 100084 China Keywords: directional solidification; numerical simulation; Liquid Metal Cooling; turbine blade Abstract Turbine blades are the key parts of aero-engines and industrial gas turbines. Liquid metal cooling (LMC) method has been used in the directional solidification process to get higher temperature gradient and produce the large size turbine blade casting. To reduce the developing cycle and cost, numerical simulation technology is used to optimize the directional solidification process by liquid metal cooling. In this paper, mathematical models of directional solidification assisted by liquid metal cooling were established, including the heat transfer model which considered the heat convection between mold shell and cooling liquid metal, nucleation and grain growth model, etc. The dynamic change of boundary conditions at different parts of the turbine blade casting in LMC process was identified and described mathematically. Experiments have been done to validate the proposed models for LMC directional solidification. The cooling curves and the grains morphology obtained in the experiments agree well with the numerical results. Compared with conventional Bridgman method, LMC led to narrower and more stabilized mushy zone, higher allowable withdrawal rate and better microstructure. LMC process of a real industrial gas turbine blades was optimized. The morphology of mushy zone in the beginning stage was calculated under the initial and improved processes. The grain structure in the blade body was also simulated. By the optimized process, the grains in the DS blade can be significantly improved and become parallel. Introduction Turbine blades are the key parts of aero-engines and industrial gas turbines and work at the worst condition such as higher temperature and larger thermal stress. In order to get better high temperature performance, directionally solidified microstructure is required to form in the turbine blades. The blades should not contain any casting defects, which would decrease the high temperature mechanical properties. Directional solidification processes are used to obtain directional solidified microstructure and prevent defects. In the past decade, Bridgman process is widely used in directional solidification. However, during High Rate Solidification (HRS), the mushy zone is sometimes very wide, and usually concave, which will easily result in stray grains. Also HRS process cannot provide enough temperature gradient, especially for the blades with large size or transverse cross-section. In recent years, liquid metal cooling (LMC) is introduced in the directional solidification of the blade casting, but still needs to be improved further. Different with HRS, tin or other low melting-point metal is used as cooling liquid metal in LMC directional solidification. Instead of heat radiation, heat convection happens between the cooling liquid metal and the ceramic mold shell below the liquid surface. To reduce the developing cycle and cost, numerical simulation