In situ transmission electron microscopy of crystal growth-mode transitions during rapid solidification of a hypoeutectic Al–Cu alloy

The rapid solidification dynamics of a pulsed-laser-melted hypoeutectic Al–Cu thin-film alloy were monitored using in situ transmission electron microscopy with high spatial and temporal resolutions. Direct observation of the solid–liquid interface during the transformation allowed measurements of the time-evolving solidification front morphology and velocity. Transitions in the growth mode were detected and related to acceleration and instability at the solidification front. A banded structure that forms during instability at high solidification front velocities, previously only observed ex situ in post-mortem analyses, was imaged during formation, providing insight to the growth mechanisms of this banded morphology.