Dendritic branching patterns in platforms of complex Ni-based single crystal castings

Abstract

Dendritic branching patterns at variable cross-sections in Ni-based single crystal (SX) castings of different generations were investigated using optical microscope (OM), electro probe microanalyzer (EPMA), differential scanning calorimeter (DSC), Thermo-Cal software and Pro-CAST software. Results show that the dendritic branching patterns are similar in outward platform in SXs of different generations. That is, the primary dendrites (PDs) are introduced into the platform by developing a series of secondary dendrites (SDs) to occupy the bottom of the platform, and the ternary dendrites (TDs) originating from these SDs grow upward to fill up the platform. With the SX generation increasing, the undercooling of melts in the inward platform increases significantly due to the increasing alloying elements and the segregation in the directional solidification (DS) process, and the growth velocity of the dendrite tip increases according to the dynamic model of dendrite growth, which is beneficial for the high-order dendrite development. The stronger dendritic branching ability is shown in the inward platform of the higher generation Ni-based SX.