Self-diffusion in carbon-alloyed CoCrFeMnNi high entropy alloys

Tracer diffusion of the substitutional components in interstitial (CoCrFeNiMn)(1-x)C-x high-entropy alloys with nominally x = 0.0 02, 0.0 05 and 0.008 (in at. fractions) is measured at elevated temperatures from 1173 to 1373 K. Two different characteristic effects of interstitial carbon addition on substitutional dif-fusion in these FCC alloys are distinguished. At the highest temperature of 1373 K, alloying by C with relatively low concentrations ( x = 0.002) retards diffusion of the substitutional elements with respect to those in the C-free alloy. At lower temperatures and/or higher C concentrations ( x >= 0.005), an en-hancement of the diffusion rates of all substitutional elements is seen. A model is suggested that relates the self-diffusivities in the CoCrFeMnNi-C alloys with the lattice distortion imposed by interstitially dis-solved carbon. The experimental results are interpreted in terms of a decrease of the migration barriers for vacancy-mediated diffusion due to the presence of interstitial C atoms. (C) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study measured the tracer diffusion of substitutional components in high-entropy alloys with interstitial carbon addition. Two distinct effects of carbon addition on substitutional diffusion were identified. At low concentrations, carbon alloying retards diffusion, while at higher concentrations, it enhances the diffusion of all substitutional elements. A model was proposed to explain the influence of lattice distortion caused by interstitial carbon on self-diffusion.