APPLICATION AND VALIDATION OF A DIRECTIONAL SOLIDIFICATION MODEL AND DENDRITE MORPHOLOGY CRITERION FOR COMPLEX, SINGLE-CRYSTAL CASTINGS

摘要

Extensive work is required to determine optimal processing conditions (e.g. withdrawal, rate furnace temperature) for directional solidification of single crystal castings in the complex geometries required for modern flight hardware. Prior work used fundamental solidification theory and modeling to adapt classical defect-formation criteria to realistic non-planar solidification and develop a geometric-independent metric for preferred casting conditions. The continuation of this work consists of applying and validating these learned metrics to representative blade geometries. The overarching objective is to develop an integrated set of modeling tools capable of linking process parameters and alloy properties to modern design methods through the prediction of critical microstructural features: dendritic structure, defect formation, and porosity. Thermocouple measurements from directional solidification experiments and full-cross-section metallographic characterization of resulting castings have been compared to model predictions and show good agreement. New parameters from solidification models have been developed and demonstrated for the onset and extent of dendrite morphology changes in a turbine blade geometry.