Process Simulation for the Directional Solidification of a Tri-Crystal Ring Segment via the Bridgman and Liquid-Metal-Cooling Processes

Abstract

The feasibility of a monocrystalline ring comprised of a multiply-seeded, SX ring separated by low-angle boundaries was investigated for two thicknesses and two processing techniques. In particular, solidification experiments using 1.9- and 5.1-cm-thick tri-crystal castings were conducted in a furnace capable of either the Bridgman or liquid metal cooling (LMC) mode. LMC is a high-gradient directional solidification process that provides refinement of dendritic structure by submerging the casting in a liquid-metal-coolant bath upon withdrawal from the mold heater. The degree of structure refinement was investigated in these castings with varying cross-sectional areas. Solidification modeling was used to optimize process conditions and investigate the thermal characteristics of each process for both casting configurations. Predicted relationships between dendritic structure, cooling rate, and thermal gradients in the axial and transverse directions are presented. A model for the prediction of thermal behavior for Bridgman and LMC techniques using complex casting configurations with section-thickness variations, encompassing a broad range of thermal conditions, was validated. A viable processing route for a monocrystalline ring was identified using the LMC technique, which mitigates the detrimental effects of radiation view factors present in the Bridgman process. Solidification modeling identified the process conditions required to produce a new casting configuration with minimal casting trials.