Thermal-solutal-fluid flow of channel segregation during directional solidification of single-crystal nickel-based superalloys

Abstract Channel segregation – known as freckle is one of the most complex defects which severely limit mechanical properties investment cast single-crystal turbine blades. The phenomenon induced by thermal-solutal-fluid flow instability during solidification process; it therefore important to gain better understanding fluid flow, heat transfer and species transport casting process. In this work, a three-dimensional Eulerian two-phase model developed investigate chimney behaviours evolution channel in directional nickel-based single crystal superalloy CMSX-4. results reveal that channels are merely distributed on surface ingot backed up with targeted experiments, morphology predicted also consistent observed chains. By ignoring lateral flux, deviation prediction using Rayleigh number criterion anticipated, because not all chimneys can be into under significant perturbation. mushy zone, perturbation melt convection from horizontal direction leads extinction existing chimneys, thereby exacerbating segregation. Once stable formed, will steadily further solute enrichment caused thermal-solutal convection. segregations difficult develop continuously centre representative rod, while near walls more likely along direction. It suggested weaker flux suppress formation segregation, providing an effective process design for mitigation casting.