Thermal and grain-structure simulation in a land-based turbine blade directionally solidified with the liquid metal cooling process

ddThe thermal field and the grain structure of a cored superalloy turbine b lade, which has been directionally solidified with the liquid metal cooling (LMC) process, has been simulated in three dimensions using a cellular aut omaton (CA) coupled with finite-element (CAFE) model. The cooling induced b y the liquid aluminum bath has been replaced by a heat-transfer coefficient , whose temperature- and time-dependence has been adjusted on the basis of natural convection simulations and dimensionless analyses. The simulated gr ain structure and crystallographic texture have been compared with the micr ostructure, and the electron back-scattered diffraction (EBSD) results were obtained for a real blade. In both the experiment and the simulation, it h as been found that the grains do not exhibit a well-defined (001) texture, even near the top of the blade, mainly as a result of a concave liquidus su rface. In order to improve the texture and decrease the number of stray cry stals, the LMC process was then optimized by changing several parameters. T he baffle geometry, the liquid bath level, and the thermal conductivity of the ceramic mold were found to be the dominant parameters. Using the optimi zed design, the effect of the withdrawal rate on the resulting grain struct ure was investigated.