Multiscale modeling of kinetic sluggishness in equiatomic NiCoCr and NiCoCrFeMn single-phase solid solutions

TL;DR

This study uses kinetic Monte Carlo simulations to reveal that vacancies in equiatomic NiCoCr and NiCoCrFeMn alloys exhibit subdiffusive behavior due to lattice distortions, contrasting with pure Ni's diffusion.

Contribution

It demonstrates that vacancy dynamics in complex alloys are subdiffusive and driven by lattice distortions, modeled through fractional Brownian motion, providing new insights into sluggish diffusion mechanisms.

Findings

Vacancies in alloys show subdiffusive dynamics unlike pure Ni.

Long waiting times follow a power-law distribution due to energy barriers.

Lattice distortions cause dynamical sluggishness in atomic diffusion.

Abstract

Complex, concentrated, multi-component alloys have been shown to display outstanding thermo-mechanical properties, that have been typically attributed to sluggish diffusion, entropic, and lattice distortion effects. Here, we investigate two metal alloys with such exemplary properties, the equiatomic, single-phase, face-centered-cubic (FCC) alloys NiCoCr and NiCoCrFeMn, and we compare their microstructural kinetics to the behaviors in a pure-Ni FCC metal. We perform long-time, kinetic Monte Carlo (kMC) simulations, and we analyze in detail the kinetics of atomic vacancies. We find that vacancies in both concentrated alloys exhibit subdiffusive thermally driven dynamics, in direct contrast to the diffusive dynamics of pure Ni. Subdiffusive dynamics shall be attributed to dynamical sluggishness, that is modeled by a fractional Brownian random walk. Furthermore, we analyze the statistics of waiting times, and we interpret long power-law-distributed rest periods as a direct consequence of barriers' energy-scales and lattice distortions.