Time-resolved x-ray microdiffraction studies of phase transformations during rapidly propagating reactions in Al/Ni and Zr/Ni multilayer foils

We showed how intermetallic formation reactions can be studied under rapid heating (106–107 K s−1) using x-ray microdiffraction with temporal resolution on microsecond time scales. Rapid heating was achieved by initiating an exothermic reaction in multilayer foils comprising alternating nanoscale layers of elemental metals. The reaction occurred in a front ∼100 μm wide which propagated across the foil at ∼1–10 m s−1. By using synchrotron x-rays focused to a small spot (60 μm diameter) and a fast pixel-array detector, we were able to track the evolution of phases in the reaction front during the initial heating transient, which occurred in approximately 1 ms, through cooling over a period of hundreds of milliseconds. In Al/Ni multilayer foils, the first phases to form were an Al-rich liquid and the cubic intermetallic AlNi (which likely formed by nucleation from the liquid). In foils of overall composition AlNi, this is the stable intermetallic and the only phase to form. In foils of composition Al3Ni2, du...