Grain Selection in Spiral Selectors During Investment Casting of Single-Crystal Turbine Blades: Part I. Experimental Investigation

Abstract

Spiral grain selectors are used to grow single-crystal (SX) turbine blades during investment casting. Competitive growth in the spiral selectors leads to the selection of a single grain that subsequently grows to form the blade. In this study, the effect of spiral design on grain selection during investment casting was investigated through a series of experiments. It is found that the spiral design can effectively reduce the grain number but is not able to optimize axial grain orientations during solidification, the effectiveness of grain selection is strongly dependent on the spiral “take-off” angle, and spirals with smaller take-off angles are most potent. It is proposed that grain selection in the spiral is controlled by the geometry of the spiral via a “geometrical blocking” mechanism.