On the real-time atomistic deformation of nano twinned CrCoFeNi high entropy alloy.

Author(s) Yan, S.; Qin, Q.H.; Zhong, Z.
Journal Nanotechnology
Date Published 2020 Jun 05

High entropy alloys (HEAs) holding several principal elements in high concentration represent unprecedented combination properties. Designing strong and well ductile HEAs has been attracting extensive attentions from researchers in the last decade, such as mechanisms in inducing different types of phases and nano-sized precipitates. Since some HEAs have low stacking fault energy, nano-twins prefer to form in plastic deformation process or magnetron sputtering, resulting in enhanced mechanical properties by the existence of twin boundaries, which implies that the addition of twin boundary in HEAs is a promising method in engineering HEAs. Understanding how twin boundaries affect the mechanical properties of nano twinned HEAs is a key for designing strong and ductile nano twinned HEAs. In this study, we have performed large-scale molecular dynamic simulation to investigate the mechanical properties of HEAs with different twin boundary spacings at various temperatures. Results show that the strength of HEAs at all tested temperatures increases with decreasing twin boundary spacing until below a critical value, which is 1.83 nm close to the experimental value (2 nm). The strength of HEAs at all tested temperatures decreases while further decreasing twin boundary spacing. There is a transition of dislocation motion at critical twin boundary spacing. In sample with twin boundary spacing bigger than 1.83 nm, Shockley dislocations tend to intersect twin boundaries and glide in hardening modes; while Shockley dislocations travel along the direction parallel to twin boundaries in samples with a twin boundary spacing smaller than 1.83 nm, leading to detwinning and softening in HEAs. The dislocation motion and entanglement at 1 K are respectively slower and stronger than those at 300 K; the grain boundary activity is more obvious at higher temperature. A mechanistic theoretical model together with Hall-Petch relationship is then proposed to consider the coupled twin-boundary and temperature effect on the deformation of nano twinned HEAs.

DOI 10.1088/1361-6528/ab99ef
ISSN 1361-6528
Citation Nanotechnology. 2020.

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