Fracture Along Deformation Twin Boundary in Small-Volume Fe₄₀Mn₄₀Co₁₀Cr₁₀ High Entropy Alloy

High-entropy alloys (HEAs) with extraordinary combination of strength, ductility, and toughness have drawn extensive attention in recent years. One of widely accepted explanations for the marked mechanical performance in bulk HEAs is due to the tendency of deformation twinning. Here, the authors perform in situ tensile test on small-volume non-equiatomic Fe₄₀Mn₄₀Co₁₀Cr₁₀ HEA single crystals, and find that deformation twinning is a typical intrinsic factor for accelerating fracture. Profuse needle-like deformation twins are nucleated under loading, while their thickening is very difficult due to high twin boundary migration energy, thus nanoscale surface crack is easily produced, which triggers catastrophic fracture.