Phase Transformations under Rapid Heating in Metallic Micro- and Nanolaminates

Heating rate effects on phase transformations in metallic materials are of importance for many applications. Here, we consider reactive materials in metallic systems. Metallic reactive materials are layered or particulate mixtures of metals producing large amounts of energy when their formation reaction is initiated. They can be utilized as local heat sources for soldering and brazing. During initiation and the subsequent self-propagating reaction, the mixture transforms to intermetallic compounds under heating rates up to 107 K/s. Hence, aside to the mentioned applications, we also use reactive materials as model materials for basic studies concerning heating rate effects on phase transformations. In greater detail, we choose nanoscaled, sputter deposited Al/Ni multilayers and use techniques such as nanocalorimetry, dynamic transmission electron microscopy or synchrotron radiation to reveal the nucleation and growth processes of the intermetallics under heating rates up to 105 K/s. In addition to heating rate effects, nanoscaled multilayers also enables us to investigate the role of steep concentration gradients on nucleation. The results are discussed within the classical nucleation theory. Finally, we outline how the fundamental results of heating rate effects on phase transformations help us to develop “pulsed metallurgy” as a novel microstructure design tool. We discuss the fabrication of nano-composites with tailored mechanical properties as one potential application.