Exploiting multiscale dynamic toughening in multicomponent alloy metamaterials for extreme impact mitigation.

Mechanical metamaterials can unlock extreme properties by leveraging lightweight structural design principles and unique deformation mechanisms. However, research has predominantly focused on their quasi-static characteristics, leaving their behavior under extreme dynamic conditions, especially at length scales relevant to practical applications largely unexplored. Here, we present a strategy to achieve extreme impact mitigation at the macroscale by combining shell-based microarchitecture with an additively manufactured medium-entropy alloy (MEA) featuring low stacking fault energy (SFE). Notably, the shell-based architecture amplifies the effective dynamic stress within the metamaterial compared to truss-based morphologies, leading to the earlier activation of multiscale toughening mechanisms in the alloy. The low SFE of the MEA enables the evolution of a diverse array of defect types, thereby prolonging strain hardening behavior across seven orders of magnitude in strain rate. These fundamental insights could establish the groundwork for developing scalable, lightweight, impact-resistant metamaterials for structural and defense applications.