Atomic-scale characterization and modeling of 60 degrees dislocations in a high-entropy alloy
TM Smith and MS Hooshmand and SD Esser and F Otto and DW McComb and EP George and M Ghazisaeidi and MJ Mills, ACTA MATERIALIA, 110, 352-363 (2016).
High-entropy alloys (HEAs) are an exciting new class of multi-component alloys some of which have unusual and remarkable properties. As of yet, little is understood about dislocation core structure and stacking fault energies in these alloys. For this study, a five-component, equiatomic alloy (CrMnFeCoNi) was deformed to 5% plastic strain at room temperature. Post-test observations using diffraction contrast scanning transmission electron microscopy (DC-STEM) analysis provide evidence for numerous planar slip bands composed of,1/2 < 110 > dislocations. More detailed analyses of dislocation separation distances were performed using high-order diffraction vector DC-STEM and atomic resolution high angle annular dark field (HAADF) STEM on 1/2 < 110 > dislocations in 60 degrees orientation. Large variations in dissociation distances are found, leading to the concept of a local stacking fault energy (SFE). This finding is supported through embedded-atom-method (EAM) calculations of a model, concentrated, three-element solid solution. For the first time, the Nye tensor and center of symmetry analysis were used collectively to accurately determine dissociation distance. Lastly, using high-resolution energy dispersive X-ray spectroscopy, no ordering or segregation was observed, indicating that this alloys is a true solid solution down to the atomic scale in the recrystallized and lightly deformed state. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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