Investigation of Solidification Defect Formation by Three-Dimensional Reconstruction of Dendritic Structures.

Abstract

Convective flow within the mushy zone of directionally solidified superalloys can result in the formation of freckles and misoriented grains. These defects signal not only a disruption in the columnar or single crystal nature of the component but also a tendency toward reduction in life and performance. Approximations of the onset of convective flow in the mush have primarily used the Rayleigh criteria as a predictor for the occurrence of freckles. However, a detailed understanding of fluid flow at the scale of the dendritic structure is still lacking. This research utilizes three-dimensional dendritic structures obtained from the solid-liquid interface of directionally solidified nickel-base superalloys as direct inputs to fluid flow models. These models have been utilized to assess the permeability of the dendritic array. Implications of simulations will be discussed with reference to the Rayleigh criteria and freckle prediction.Ph.D.Materials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/76001/1/jonnymad_1.pd