Atomistic simulations of tensile deformation of a nanoporous high-entropy alloy

Abstract

High-entropy alloys (HEAs) display outstanding mechanical properties which make possible new technological applications. There are many studies of bulk HEAs, but here we focus on FeCrNiCuCo single-crystal face-centered cubic (FCC) samples with 40% and 50% nanoscale porosity, where the pores constrain plasticity. In order to disentangle the role of chemical complexity during deformation, we compare HEA samples to Average Atom (AA) samples with the same average properties as the HEA, but where all atoms are equivalent. Elastic modulus and plastic yielding are much higher than expected from Au nanofoam scaling predictions. We find that HEA and AA materials behave similarly to each other and to other FCC nanoporous samples until the point where failure begins. Deformation produces mostly partial dislocations that move and leave behind stacking faults crossing filaments, with sessile dislocations and some dislocation tangles forming due to the large plastic strain. Differences in sample failure modify the evolution of void and ligament size distributions. The AA sample presents ductile necking and ductile fracture of a few filaments, as in other single element FCC nanoporous samples. Failure in the HEA sample not only includes some ductile filaments fracture, but also brittle fracture of the filaments due to localized shear, which causes plane slippage, as identified by machine learning methods. Therefore, chemical complexity diminishes ductility in nanoporous FCC HEA samples.