“Non-equilibrium” grain boundaries in additively manufactured CoCrFeMnNi high-entropy alloy: Enhanced diffusion and strong segregation

• Published in: Journal of applied physics Vol. 132; no. 24
• Main Authors: Choi, Nuri, Taheriniya, Shabnam, Yang, Sangsun, Esin, Vladimir A., Yu, Ji Hun, Lee, Jai-Sung, Wilde, Gerhard, Divinski, Sergiy V.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 28.12.2022
• Subjects: Additive manufacturing; Annealing; Applied physics; Boundaries; Crystal defects; Diffusion rate; Enhanced diffusion; Equilibrium; Grain boundaries; Grain boundary diffusion; Grain boundary migration; High entropy alloys; Phase decomposition; Physics; Rapid solidification
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/5.0133144

Grain boundary diffusion in an additively manufactured equiatomic CoCrFeMnNi high-entropy alloy is systematically investigated at 500 K under the so-called C-type kinetic conditions when bulk diffusion is completely frozen. In the as-manufactured state, general (random) grain boundaries are found to be characterized by orders-of-magnitude enhanced diffusivities and a non-equilibrium segregation of (dominantly) Mn atoms. These features are explained in terms of a non-equilibrium state of grain boundaries after rapid solidification. The grain boundary diffusion rates are found to be almost independent on the scanning/building strategy used for the specimen’s manufacturing, despite pronounced microstructure differences. Grain boundary migration during diffusion annealing turned out to preserve the non-equilibrium state of the interfaces due to continuous consumption of the processing-induced defects by moving boundaries. Whereas the kinetic “non-equilibrium” state of the interfaces relaxes after annealing at 773 K, the non-equilibrium segregation is retained, being further accompanied by a nano-scale phase decomposition at the grain boundaries. The generality of the findings for additively manufactured materials is discussed.