Effects of local elemental ordering on defect-grain boundary interactions in high-entropy alloys

SJ Zhao, JOURNAL OF ALLOYS AND COMPOUNDS, 887, 161314 (2021).

DOI: 10.1016/j.jallcom.2021.161314

The way in which defects interact with grain boundaries (GBs) has profound influences on materials performance. In this work, we study defect-GBs interactions in a model CuNiCoFe high-entropy alloy (HEA) based on atomistic simulations. Five representative GBs are considered, namely Sigma 3 < 101 > 11-1 coherent twin GB, Sigma 5 < 103 > 010 twist GB, Sigma 11 < 1-10 > 113 symmetric tilt GB (STGB), Sigma 11 < 1-10 > 554 asymmetric tilt GB (ATGB), and Sigma 45 < 1-20 > 001 tilt GB. A particular focus is placed on the role of chemical disorder and local elemental segregation in influencing the defect-GBs interactions. Specifically, we compare the results obtained within an averaged atom model, the random HEA with randomly distributed elements, and the equilibrated HEA with Cu segregation after a combined MonteCarlo/Molecular statics algorithm. For the pristine CuNiCoFe HEA without GBs, we find chemical occupancy fluctuations tend to lower the formation energies of defects, especially for interstitials because of the larger lattice distortion. For defect-GBs interactions, we find GBs strongly interact with interstitials over vacancies. We further reveal that elemental segregation can enhance the sink strength of GBs towards vacancies, but at the same time, reduce the sink strength toward interstitials. Therefore, the bias effects of GBs toward interstitials and vacancies are suppressed in HEAs due to local ordering, promoting efficient defect annihilation within the grain interiors. We highlight that the local ordering tendency and elemental segregation in HEAs play dominant roles in influencing the defect-GB interactions. (c) 2021 Elsevier B.V. All rights reserved.

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