Simulations of high-entropy alloys: thermodynamics, mechanical properties, and radiation damage
High entropy alloys (HEA) are being intensely studied due to their extraordinary mechanical properties, radiation damage, corrosion resistance, etcetera. Most simulation studies have focused on random HEA, without any chemical ordering, and we have studied collision cascades  and mechanical properties of fcc [2,3] and bcc alloys [4,5], including porosity and grain boundaries in some cases. Due to large lattice distortion, Machine Learning can help to avoid significant noise in standard structure detection methods .
There are many experimental studies showing the relevance of Short-Range Order (SRO) in determining different properties, and an increasing number of atomistic simulations modify SRO in initially random samples typically using Monte Carlo (MC) or a combination of MC and molecular dynamics (MD). Generally, Kawasaki-type atomic exchanges are used for the MC evolution, and the Warren-Cowley parameter (WCP) for nearest neighbors is employed to quantify SRO evolution. Currently, there are many different strategies, but there are no widely accepted standard procedures to achieve SRO evolution which can be compared to experiments, partly because SRO results depend strongly on stoichiometry and experimental processing conditions. We will discuss some thermodynamic indicators for SRO in both fcc and bcc HEA, including (CoCrFeNi)Al, HfNbTaZr and HfNbTaTiZr. Surfaces can modify SRO and we show some surface segregation in simulations of nanoporous CoCrCuFeNi, but mechanical properties do not change significantly compared to a random sample . We also emphasize that experimental HEA structures can be complex and include several different crystal structures, with different SRO evolution. For some cases this can lead to significant chemical enrichment in one of the phases, affecting mechanical properties and radiation resistance.
We thank support from SIIP-UNCUYO 06/M008-T1, PIP-2021-2023 11220200102578CO, and PICTO-UM-2019-00048.
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