CHARACTE TERIZATI TION OF THREE-DIMENSI SIONAL DENDRITI TIC STRUCTURES ES IN NICKE KEL-BASE SESI SINGLE LE CRYSTALS LS FOR INVESTI STIGATI TION OF DEFECT FORMATI TION

摘要

During solidification, solute-induced convective instabilities at thesolid - liquid interface can result in the formation of defects suchas freckles and misoriented grains in superalloy single crystals.These defects can be particularly detrimental to the properties ofsingle crystal nickel-base superalloys. Unfortunately, detailedunderstanding of fluid flow at the scale of the dendritic structurehas yet to be fully understood, particularly under conditions inwhich heat extraction is non-axial. The objective of this researchis to develop a technique for quantifying the dendritic structureand morphology at the solid – liquid interface for the purpose ofproviding direct input into computational fluid flow modeling.Using the RoboMET.3D serial sectioning system, three-dimensional datasets of dendritic structure at the solidificationfront have been obtained for René N4 abruptly decanted duringsolidification. Distribution and arrangement of solid and liquid inthe vicinity of dendrite tips is analyzed and the implications fordefect formation are discussed.