Fracture of Void-Embedded High-Entropy-Alloy Films: A Comprehensive Atomistic Study

Comprehensive molecular dynamics (MD) simulations are performed to study the stress response and deformation mechanism in void-embedded, single-crystal and nanocrystalline, high-entropy-alloy (HEA) films under uniaxial tensile loading. Our results reveal that certain void-embedded HEA films can be, by far, superior to pure Ni in terms of tensile ductility and the resistance to crack propagation. The fracture strains of 10%Co CoCrFeMnNi and the equiatomic CoFeMnNi, respectively, double or triple that of the equiatomic CoCrFeMnNi, which still doubles that of pure Ni. Regarding the deformation mechanism, high tensile ductility of HEAs can be attributed to the formation of partial dislocations, nanotwinning and the impediment of the otherwise glissile dislocations due to the weak pinning effect. The ultimate tensile strength of HEA film shows better resistance against stress deterioration due to elliptical voids. The stress response of the void-embedded, nanocrystalline Ni films obeys the reverse Hall-Petch effect, while the void-embedded, equiatomic HEA film does not. The maximum stresses of nanocrystalline HEA films of different grain size are virtually the same. The void-embedded, finer-grain HEA film exhibits a better tensile ductility than the void-embedded, coarser-grain HEA film.