Nanoporous High Entropy Alloys: Overcoming Brittleness Through Strain Hardening

Abstract

Bicontinuous nanoporous materials possess remarkable mechanical properties, such as higher specific strength and lower specific modulus compared to fully dense materials combined with low densities and high specific surface areas. Unfortunately, their practical application is hindered by inherent macroscopic brittleness, mainly due to cascading ligament failure under tension. To address this limitation, we investigate whether high entropy alloys, recognized for their outstanding strength and strain hardening properties, can mitigate nanoporous material's inherent brittleness. Molecular dynamics simulations of nanoporous Al$_{0.1}$CoCrFeNi and NbMoTaW reveal a dual mechanism involving dislocation starvation and sluggish dislocation motion, resulting in specific strength values 5 to 10 times higher than those of single-element nanoporous materials, and a resilience against thermal degradation. Strain hardening, driven by sluggish dislocations, effectively prevents failure of the weakest ligaments under tensile stress in face-centered cubic architectures by trapping stacking faults in the ligaments and dislocation forest hardening in the nodes of body-centered cubic structures, demonstrating their potential to shape the next generation of high strength, low density materials.