Abstract Scope |
We investigate the interaction between three-phase eutectic and a primary phase during solidification of an off-eutectic Al-Ag-Cu alloy through correlative imaging. In situ synchrotron X-radiography reveals the locations and orientation of the primary Al2Cu phase, with respect to the eutectic, which strongly influence the eutectic growth velocity. By combining these results with three-dimensional (3D) focused ion beam tomography, scanning electron microscopy, and electron backscatter diffraction, we provide evidence of two-dimensional (2D) dendrites, or fingers, of Al and Ag2Al that spread along the primary Al2Cu surfaces; meanwhile, protrusions of Al2Cu grow in between pockets of the fingers and into the surrounding eutectic, preserving their crystallographic orientations in the process. We propose a competitive growth relationship between the three phases to explain these features as well as the diversity of two- and three-phase microstructures obtained at the onset of eutectic solidification. |