Dendrite deformation and fragmentation-induced sliver defects during solidification of nickel-based single-crystal superalloys

Sliver is a casting defect formed during solidification of nickel-based single-crystal superalloys, which degrades the high temperature properties of superalloys. However, the formation mechanism of sliver cannot be fully deduced from the solidified microstructure alone and thus requires clarification. In this work, a multi-scale model of thermo-mechanical deformation was developed to investigate the formation of sliver. Results reveal that casting contraction-driven dendrite deformation induces significant plastic strain localisation, which is inferred as a key step to dendrite fragmentation and formation of sliver defects. Two distinct dendrite deformation mechanisms during sliver formation are identified: The first mechanism is contraction-driven plastic deformation of dendritic trunks along 45°, and the second mechanism arises from constraint from mould protuberances causing large-angle bending of dendrites. This work sheds light on the cross-scale mechanisms of dendrite deformation and fragmentation for sliver defect formation, providing a basis for defect mitigation.