Hierarchical toughening mechanisms in face centered cubic CoCrFeMnNi high-entropy alloy at room temperature and cryogenic temperatures

As a class of promising structural material, recently synthesized face centered cubic phased high-entropy alloys (HEAs) exhibit excellent room-temperature (RT) fracture toughness as well as an abnormally increasing one at cryogenic temperatures (CTs). The intrinsic toughening mechanisms are not yet well understood. Attention here is focused on the atomistic crack initiation and propagation in a model HEA CoCrFeMnNi under RT and CTs, by means of atomistic simulations integrated with theoretical analysis. Hierarchical deformation mechanisms of the incipient plasticity; the local amorphization; and the formation, growth, and coalescence of voids are found, based on which the strain energy stored in the material is continually dissipated, resulting in the outstanding fracture toughness of the HEA at both RT and CTs. The origin for low-temperature toughening may be attributed to fewer immobile dislocations at CTs, delaying the occurrence of amorphization and microvoids. The differences in mechanisms for low-temperature toughening of the HEA and low-temperature embrittlement of traditional metals are further comparatively revealed. This study provides mechanistic insights into the fundamental understanding of intrinsic toughening mechanisms in the HEA.