  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.
