Insight of the dendrite's deformation and fracture in large-sized single-crystal superalloy blades for the formation of slivers

Abstract

The manufacturing of single-crystal superalloy blades consistently aims to avoid grain boundary defects that compromise crystal integrity. Although slivers represent a significant type of grain boundary defect, their formation mechanisms remain inadequately defined. This study investigates sliver formation mechanisms, revealing that slivers in single-crystal blades extracted at a variable rate originate from dendritic fractures. Conversely, slivers in blades extracted at a constant rate stem from dendritic deformation. Temperature field simulations indicate that the cooling rate for blades withdrawn at variable rates varies significantly, generating higher thermal contraction stresses compared to those withdrawn at a constant rate. This increased stress precipitates dendrite fractures, leading to sliver formation. Following dendrite fractures or deformation, shrinkage cavities emerge, resulting from the obstruction of liquid flow by dendrite arms. Moreover, the impact of alumina protrusions in the mold on sliver formation is explored. This research advances our comprehension of dendritic evolution in sliver formation and offers theoretical insights for mitigating sliver defects in single-crystal blade production.