Orientation-Dependent Mechanical Responses and Plastic Deformation Mechanisms of FeMnCoCrNi High-entropy Alloy: A Molecular Dynamics Study

HF Zhang and HL Yan and F Fang and N Jia, ACTA METALLURGICA SINICA- ENGLISH LETTERS, 34, 1511-1526 (2021).

DOI: 10.1007/s40195-021-01260-y

Mechanical properties of high-entropy alloys (HEAs) with the face- centered cubic (fcc) structure strongly depend on their initial grain orientations. However, the orientation-dependent mechanical responses and the underlying plastic flow mechanisms of such alloys are not yet well understood. Here, deformation of the equiatomic FeMnCoCrNi HEA with various initial orientations under uniaxial tensile testing has been studied by using atomistic simulations, showing the results consistent with the recent experiments on fcc HEAs. The quantitative analysis of the activated deformation modes shows that the initiation of stacking faults is the main plastic deformation mechanism for the crystals initially oriented with 001, 111, and 112, and the total dislocation densities in these crystals are higher than that with the 110 and 123 orientations. Stacking faults, twinning, and hcp- martensitic transformation jointly promote the plastic deformation of the 110 orientation, and twinning in this crystal is more significant than that with other orientations. Deformation in the crystal oriented with 123 is dominated by the hcp-martensite transformation. Comparison of the mechanical behaviors in the FeMnCoCrNi alloy and the conventional materials, i.e. Cu and Fe50Ni50, has shown that dislocation slip tends to be activated more readily in the HEA. This is attributed to the larger lattice distortion in the HEA than the low-entropy materials, leading to the lower critical stress for dislocation nucleation and elastic-plastic transition in the former. In addition, the FeMnCoCrNi HEA with the larger lattice distortion leads to an enhanced capacity of storing dislocations. However, for the 001-oriented HEA in which dislocation slip and stacking fault are the dominant deformation mechanisms, the limited deformation modes activated are insufficient to improve the work hardening ability of the material.

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