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

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. Published under an exclusive license by AIP Publishing.

Automated summary

This study systematically investigates the grain boundary diffusion in an additively manufactured equiatomic CoCrFeMnNi high-entropy alloy. It is found that the grain boundaries in the as-manufactured state exhibit significantly enhanced diffusivities and non-equilibrium segregation, which can be attributed to the non-equilibrium state of grain boundaries after rapid solidification. The study also reveals that the grain boundary diffusion rates are almost independent of the scanning/building strategy used for specimen's manufacturing.