Highly Reactive Prestressed Aluminum under High Velocity Impact Loading: Processing for Improved Energy Conversion

Abstract

Harnessing greater power from metal particle combustion requires engineering the core‐shell particle structure to more rapidly release stored chemical energy upon ignition. This study examines the metallurgical process of prestressing to increase the strain inside aluminum (Al) particles, then links increased strain to altered reaction mechanisms under high velocity impact. Results show that the quenching rate during prestressing changes the Al reaction mechanism. At faster quenching rates (900 K min−1), roughly 50% of the interfacial surface between the Al core and Al2O3 shell delaminates based on a model developed to understand the measured strain. Without core reinforcement, the shell fractures readily upon impact causing dramatically increased ignition sensitivity (measured in terms of pressurization rate) and reactivity (measured in terms of flame spreading). For slower quenching rates (200 K min−1), the core‐shell interface remains intact but strain in the particle increases by an order of magnitude. In addition, elastic stiffness in the shell may increase during prestressing. Increased elastic stiffness can effectively reduce ignition sensitivity and higher strain may contribute energy toward the nearly 40% increase in reactivity for the slower quenched aluminum powder. These results establish a link between altering mechanical properties of particles and their ignition and reactivity under dynamic loads.