Influence of Oxide Formation Following Ultrashort Pulsed Laser Micromachining on Self‐Propagating Reactions in Free‐Standing Ni/Al Reactive Multilayer Foils

Abstract

Reactive metallic multilayers, renowned for their exothermic self-propagating reactions, show a distinct ability to achieve minimal thermal influence in processes such as welding and soldering, where minimizing the thermal impact on the material being joined is crucial. Ultrashort pulsed lasers offer precision micromachining with negligible thermal damage, making them ideal for processing such sensitive materials. However, the formation and redeposition of oxide phases is a commonly observed side effect, especially when structuring in ambient air. This study investigates the effects of oxide formed after femtosecond laser treatment on self-propagating properties, including propagation velocity and microstructure of Ni/Al reactive multilayer foils. Samples with varied line spacings between laser-cut trenches are created. Scanning electron microscopy, high-speed camera videography, and image analysis are employed to analyze the microstructure and quantify velocities. Thermal simulations enhance the understanding of the oxide’s role in self-propagating dynamics. The findings suggest that even a small oxide layer significantly decelerates the self-propagating reaction. The oxide functions as a thermal ballast by absorbing the thermal energy generated during the reaction, without actively participating in the reaction mechanism.