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In this article, grain selection in spiral selectors during investment casting of single-crystal (SX) components is simulated using a cellular automaton grain structure model (CAFE) within a finite element thermal model (PROCAST). The models were validated against experimental observations and then were applied to model the effect of geometry of the spiral selectors on grain selection through a systematic approach. It was found that the efficiency of the spiral selector is significantly dependent on its geometry; the spiral becomes more efficient in selecting single grain with a smaller wax wire diameter; larger spiral rotation diameter, and smaller takeoff angle. Recommendations for optimizing the spiral geometry are provided.

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To provide insight into the factors causing recrystallisation of nickel-based single crystal superalloys, analysis of the thermal–mechanical deformation caused by investment casting of these components is presented. Three-dimensional thermal–mechanical finite element analysis is first used to demonstrate that the reaction of the casting and mould—at least in the aerofoil section—can be approximated as one-dimensional. One-dimensional models are then built based upon static equilibrium for plasticity on the microscale caused by differential thermal contraction of metal, mould and core, using temperature dependent material properties. The models take various forms to study the mechanical response under different situations relevant to practical applications. The results indicate that the plastic strain causing recrystallisation is likely to be induced during cooling at temperatures above 1000°C. The relative importance of thicker and stiffer ceramic shells is studied. Our analysis indicates that it is important to account for creep deformation for such applications.

A macro-scale ProCAST and a meso-scale Cellular Automaton Finite Element model (CAFE) are used to simulate the competitive growth and grain selection during solidification in spiral grain selector, which is widely used in industry to produce single crystal turbine blades. The macro-model ProCAST calculates the macroscopic heat transfer and fluid flow and the calculated thermal profiles are then used as input in the meso-scale CAFE model to predict grain structures and grain orientations. Competitive growth and grain selection in the selector has been analysed with emphasis on the shape of the spiral. It is found that the spiral becomes more effective as a grain selector, when it has a smaller "take-off" angle. However, the grain orientations cannot be optimised during the selection event in the spiral. To validate the modelling results, spirals with different shapes were cast in a fully instrumented industrial directional casting furnace and the grain structure and orientations in the spirals were analyzed.