Pseudo-4D view of the growth and form of locked eutectic colonies

TL;DR

This paper introduces a high-resolution, synchrotron-based X-ray imaging method to study the 3D development of eutectic microstructures in aluminum alloys, revealing the mechanisms behind morphological transitions such as lamella-to-rod changes.

Contribution

The study presents a novel pseudo-4D imaging technique that captures in-situ, high-resolution 3D microstructural evolution during solidification, overcoming traditional space-time limitations.

Findings

Visualized crystallographically locked eutectic microstructures.

Identified impurity-driven forces causing lamella-to-rod transition.

Demonstrated the method's ability to observe in-situ morphological changes.

Abstract

We investigate solidification of an Al-Al2Cu as a model system to understand the emergence of patterns (such as lamellar, rod and maze-like) within eutectic colonies. To uncover the morphological transitions in-situ and in 3D, we introduce here a new synchrotron-based, X-ray imaging procedure. Our method simultaneously maximizes the temporal (200 ms) and spatial resolution ($0.69^2 \mu m^2/pixel$) over that of traditional imaging approaches. The wealth of information obtained from this procedure enables us to visualize the development of a crystallographically `locked' eutectic microstructure in the presence of thermosolutal convection. This data provides direct insight into the mechanism of the lamella-to-rod transition as the eutectic accommodates fluctuations in interfacial composition and growth velocity. We find that this transition is brought about by impurity-driven forces acting on the solid-solid-liquid trijunction that must overcome the stiffness of the solid-solid interfaces. Our pseudo-4D imaging strategy holds broad appeal to the solidification science community, as it can overcome the space-time trade-off in conventional in situ X-ray microtomography.