Three-dimensional characterization and real-time interface dynamics of aluminum-copper dendritic microstructures.

摘要

The morphological evolution of initially equiaxed dendritic and directionally solidified Al-Cu microstructures are studied in three dimensions. Initially equiaxed dendritic Al-20wt%Cu and Al-14wt%Cu microstructures are analyzed ex-situ, and data is collected using serial sections and X-ray tomography. Samples of the same composition, along with initially directionally solidified Al-26wt%Cu and Al-15wt%Cu samples, are coarsened in-situ, and data is collected at temperature using X-ray tomography.;The ex-situ studies show that the microstructures evolve into highly interconnected structures, where the inverse of specific surface area S-1v scales linearly with t1/3. As the size scale of the microstructure increases, the interface shape distributions (ISDs) change only slightly. The distributions of interface normals indicate that the microstructures are approximately isotropic. The scaled genii are also independent of coarsening time within the error of the experiments. Thus, the microstructures evolve self-similarly, both morphologically and topologically. The differences in scaled morphologies and topologies can be attributed to the difference in solid volume fraction, with the higher volume fraction sample exhibiting a more compact ISD and a smaller scaled genus.;The in-situ coarsened samples are analyzed using a new 4D characterization technique. Expanding on the idea of an ISD, the probability of finding any three characteristics of the interface in relation to one another is determined. This results in a plot of semi-transparent isosurfaces of constant probability. In order to connect the velocity of an interface to its morphology, the principal curvatures, kappa1 and kappa2, and velocity, V, are examined.;Comparing Al-26wt%Cu (42% solid) and Al-15wt %Cu (74% solid), as solid volume fraction increases, the diffusional distance, or distance in which shapes interact, decreases. In the 74% solid samples, specific interface shapes (e.g.-parabolic or hyperbolic) have equal and opposite velocities in close proximity to one another. There is no evidence of this in the 42% solid sample. Thus, there is more interaction between all shapes, which also indicates the diffusional distance is longer. Further, as the diffusional distance increases, the dispersion of velocities with respect to a specific pair of principal curvatures decreases. Thus, predicting how interface shapes evolve in these microstructures will be much more straightforward.