In-situ TEM Investigation of Rapid Solidification of Aluminum and Aluminum Copper Alloys

Measuring and observing rapidly evolving interfaces of irreversible transient states such as rapid solidification have been a long time standing problem in materials science as characterization techniques that deliver the necessary requirements, i.e. nanosecond temporal and nano-meter spatial resolution, have not been present. Dynamical TEM utilizes a process initiation photon laser pulse coupled with a timed electron pulse train to observe transient states of rapidly evolving phase transformations. Nanoscale spatio-temporal resolution in-situ TEM revealed growth mode changes and enabled quantitative measurements of locally resolved instantaneous and averaged interface velocities for pure Aluminum and hypo-eutectic Aluminum-Copper alloys. Post-mortem TEM was employed to gain insights on micro-structural evolution morphology regarding texture, morphology changes, grain size and grain size development, phase formation and orientations relationships during the laser processing. Post-mortem TEM studies revealed that resultant microstructures found in thin film solidification are equivalent with microstructures found in bulk sample experimentation utilizing CW-lasers. DTEM allows systematical studies of far-from equilibrium phase transformation and were employed to investigate PL initiated directional rapid solidification in Al and Al-Cu alloys