Tracer diffusion in single crystalline CoCrFeNi and CoCrFeMnNi high-entropy alloys: Kinetic hints towards a low-temperature phase instability of the solid-solution?

Tracer-diffusion of constituting elements in single-crystalline CoCrFeNi and CoCrFeMnNi is measured from 923 K to 1373 K. In CoCrFeMnNi, low-temperature deviations from otherwise linear Arrhenius-type dependencies are seen for all elements excluding Mn. The kinks are prominent at about 1100 K for Co and Ni and at 900 K for Cr and Fe indicating the existence of a low-temperature modification of the equiatomic solid-solution phase in CoCrFeMnNi. The temperature-dependent correlation factors of all elements are determined within the framework of the random alloy model providing insights into potential mechanisms of the kinetic anomaly.