Effect of spiral shape on grain selection during casting of single crystal turbine blades

Abstract

In the development of turbine blades, solidification structures have progressed from equiaxed to directionally solidified (DS) and then to single crystal (SX). The transition from DS to SX was achieved by introducing a grain selector which consists of two parts: a starter block referring to the grain orientation optimisation and a spiral part to ensure that only one grain can eventually survive and grow into the blade. With emphasis on the spiral selector, the microstructure evolution and grain competitive growth is visualised using a coupled macroscale ProCAST and mesoscale cellular automaton finite element (CAFE) model in this study. To improve the efficiency of the spiral grain selector and to save cost in casting, the effects of spiral geometries on the grain selection are investigated. Simulation results reveal that the spiral becomes more efficient in grain number selection with a smaller spiral thickness (d T) and a larger spiral diameter (d S).