Phase transformations during rapid heating of Al/Ni multilayer foils

We have used self-propagating exothermic reactions in Al/Ni multilayers as a means to explore the effect of rapid heating on phase transformations. Using time-resolved synchrotron x-ray microdiffraction with an extremely fast detector, we were able to examine the reaction sequence in detail at heating rates of ∼106 K s−1. We observed that the intermediate phases formed during the self-propagating reactions are different from those formed at lower heating rates, even though the final phases are the same. In situ characterization is essential, as other means of studying self-propagating reactions (such as quenching the reaction followed by ex situ analysis) provide different—and potentially misleading—results.