Al-based binary reactive multilayer films: Large area freestanding film synthesis and self-propagating reaction analysis

Abstract

This research mainly focuses on the development of Al-based binary Ti/Al and Zr/Al reactive multilayer films (RMFs). Magnetron sputtered deposited RMFs were investigated by considering two important aspects of large freestanding film synthesis and the analysis of the self-propagating reaction. Here, Ti/nAl (n = 1–3) RMFs with different Al molar ratios and 1Zr/1Al RMFs with various bilayer thicknesses of 20–55 nm were deposited on the copper substrate. To fabricate thick films, two types of processes of the continuous coating (process-1) and the coating with interval etching (process-2) were introduced in the Magnetron Sputter Ion Plating (MSIP) method. Microstructural characterization of as-deposited RMFs by scanning electron microscopy and transmission electron microscopy reveals the columnar microstructural morphology with coherent reactant layers. The coating process-2 exhibits the consistent and uniform film growth through the cross-section compared to the process-1. The use of a cost-effective copper substrate and the modification of the coating process in this work assure the fabrication of about 10 cm long and 45 µm thick freestanding Zr/Al RMFs with homogeneous film growth. Then, self-propagating reaction properties were analyzed after an electrical arc ignition in air. A high-speed microscope and a two-color pyrometer were used to record the reaction propagation and temperature profile simultaneously. Ti/Al and Zr/Al RMFs exhibit the maximum reaction velocity of 2.6 ± 0.6 m/s and 1.22 ± 0.4 m/s, respectively. The maximum reaction temperatures of 1581–1707 °C were found in Zr/Al RMFs, whereas Ti/nAl RMFs show the reaction temperature in the range of 1215–1298 °C. The reaction front velocity and temperature of the self-propagating reaction show the dependency on the reactants combinations, compositions, and bilayer thickness. Furthermore, this work describes the component and morphology dependent reaction properties of Zr/Al and Ti/Al RMFs and a simple approach to fabricate large sized freestanding reactive films.