Sliver Defects in Seeded Single Crystal Castings: Insights From in Situ Time Resolved X-Ray Imaging and Orientation Imaging Microscopy

Seeded single crystal turbine blades are often used in situations where orientation must be carefully controlled to minimise engine resonance effects. Such turbine blades are particularly vulnerable to a number of casting defects: stray grains at the melt-back interface, and sliver defects at changes in mould cross section. The sliver defect arises from deformation during solidification, which remains poorly understood owing to the difficulties of obtaining experimental evidence on this topic. We probe this experimentally using time-resolved X-ray imaging using synchrotron radiation and orientation imaging using both electron backscattered diffraction (EBSD) and spatially resolved acoustic spectroscopy (SRAS). X-ray imaging gives us insight into the dynamics of deformation, whilst EBSD and SRAS give insight into the resulting deformation structures at the dendritic and component length scales respectively. Finally, we use PROCAST simulations to explore the predictive capability of continuum models in mitigation of this defect.