WEB Exploring runaway reactions in metallic multilayers with combined nanocalorimetry and time-resolved X-ray diffractionWednesday (23.09.2020) 09:00 - 09:30 F: Functional Materials, Surfaces, and Devices 1 Part of:
Self-sustaining runaway reactions in reactive multilayers, a sub-class of morphologically imprinted materials, exhibit heat-up with over 1,000,000 K/s to temperatures above 1000 °C. These reaction conditions define unprecedented kinetic regimes for metallurgical phase transformations allowing for the development of alternative microstructure design concepts such as pulsed metallurgy. Here, we consider physical vapor deposited Aluminum/Nickel multilayers as model materials and present an approach enabling us to explore the phase transformations in these kinetic regimes in situ. In detail, we combine nanocalorimetry with time-resolved synchrotron X-ray diffraction. Whereas nanocalorimetry allows for a full thermal analysis of the runaway including the conditions of ignition, time-resolved X-ray diffraction traces the temporal phase evolution. First, we show that an increase of the overall composition of the multilayers decreases the critical heating rate for ignition. Second, we demonstrate that the morphological signature “bilayer thickness” enables for tuning the ignition temperature. Third, we ignite the reaction with heating rates between 500 K/s and 10,000 K/ and analyze heating rate effects on the type of the phase and its morphology. Eventually, the combination of nanocalorimetry and time resolved X-ray diffraction helps us to propose reaction mechanisms dependent on the heating rate. This mechanistic understanding guides our development of novel microstructure design concepts for thin films using metallic multilayers as starting materials.