Radiotracer diffusion in CoCrFeNi and CoCrFeMnNi FCC high entropy alloys

by Daniel Gaertner (Institute of Materials Physics, WWU Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany)

Tuesday 19 Jun 2018, 14:30 → 15:30 Europe/Zurich

High entropy alloys are multicomponent alloys, which consist of five or more elements in equiatomic or nearly equiatomic concentrations. These materials are hypothesized to show significantly decreased self-diffusivities. For the first time, diffusion of all constituent elements in equiatomic CoCrFeNi and CoCrFeMnNi single crystals and additionally solute diffusion of Mn in the quaternary alloy is investigated using the radiotracer technique, thereby the tracer diffusion coefficients of ⁵⁷Co, ⁵¹Cr, ⁵⁹Fe, ⁵⁴Mn and ⁶³Ni are determined at a temperature of 1373 K. The components are characterized by significantly different diffusion rates, with Mn being the fastest element and Ni and Co being the slowest ones. Furthermore, solute diffusion of Cu in the CoCrFeNi single crystal is investigated in the temperature range of 973 − 1173 K using the ⁶⁴Cu isotope. In the quaternary alloy, Cu is found to be a fast diffuser at the moderate temperatures below 1000 K and its diffusion rate follows the Arrhenius law with an activation enthalpy of about 149 kJ/mol. Moreover, the diffusion kinetics in a CoCrFeMnNi alloy pseudo-binary approach with a Co-15 Ni-25/Co-25 Ni-15 concentration gradient is investigated by a combination of radiotracer and interdiffusion techniques in a way that the composition dependencies of the tracer diffusion coefficients of Co, Cr, Fe and Mn are determined. All elements in equiatomic proportion are found to follow up-hill interdiffusion character. According to the concentration dependent atomic mobilities, all the investigated elements follow an s-shape behaviour with Mn being the fastest element and Ni and Co being the slowest ones.