Variation of first pop-in loads in nanoindentation to detect chemical short-range ordering in the equiatomic Cr-Co-Ni medium-entropy alloy

L Li and JP Du and S Ogata and H Inui, ACTA MATERIALIA, 269, 119775 (2024).

DOI: 10.1016/j.actamat.2024.119775

The variations of the first pop-in load in nanoindentation with annealing temperature and time have been investigated both by experiment and theoretical molecular dynamics (MD) simulations for the equiatomic Cr -CoNi medium-entropy alloy (MEA). Regardless of the loading rates, the first pop-in load tends to increase with the increase in electrical resistivity consistently by experiment and MD simulations. The trend in the variation of pop-in load with annealing temperature/time coincides with what is observed in the variation of electrical resistivity in our previous study, indicating that the first pop-in load in nanoindentation can thus be used to qualitatively detect the evolution of short-range ordering (SRO) in the Cr -Co -Ni MEA, and that the peak temperature for SRO for the equiatomic Cr -Co -Ni MEA is 673 K. MD simulations indicate that the first pop-in corresponds to the nucleation of partial dislocation loops beneath the indenter for both annealing conditions and that the increased first pop-in load in nanoindentation is attributed to the higher energy barrier for the nucleation of dislocation loops due to the higher degree of SRO.

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