Predicting the Location of Low-Angle Boundaries in Single-Crystal Castings
R E. Napolitano, Robert J. Schaefer
A set of nickel-based superalloy single-crystal investment castings was produced and evaluated for crystal perfection. Defect structures near the seed emergence point and other geometric features were examined using x-ray topography. Topographic images were compared with metallographically observed dendritic structures to establish a convergence-fault criterion for the location of low-angle boundaries. A trip-growth model for simulation of the growth of the dentritic network was developed. This model predicts the local primary growth direction and identifies regions of convergent growth. A connectivity parameter is used to map the locations which are most vulnerable to convergence-fault formation. Predictions are compared with experimental observation.