Title: Interdiffusion in Cr–Fe–Co–Ni medium-entropy alloys

Abstract

Diffusion in multi-component alloys is attracting renewed attention because of the worldwide interest in high- and medium-entropy alloys (HEAs/MEAs). In the present work, we used diffusion multiples made from MEAs of the quaternary Cr–Fe–Co–Ni system arranged as six distinct pseudo-binary diffusion couples (Cr₂₉Fe₁₃Co₂₉Ni₂₉–Cr₂₉Fe₂₉Co₂₉Ni₁₃, Cr₂₉Fe₂₉Co₁₃Ni₂₉–Cr₂₉Fe₂₉Co₂₉Ni₁₃, and so on, where the interdiffusing elements are italicized for clarity). In the two halves of each couple, the starting concentrations of the interdiffusing elements (Fe,Ni and Co,Ni in the above examples) were different while those of the background elements (Cr,Co and Cr,Fe in the above examples) were the same. The diffusion multiples were annealed at temperatures between 1153 and 1355 K at times from 100 to 900 h, after which the concentrations of the different elements were measured as a function of distance across each couple. Interdiffusion coefficients were derived from such concentration profiles using the standard Sauer-Freise method and compared with literature data as well as with published tracer diffusion coefficients. Although the background elements were homogeneously distributed initially, some of them developed distinct sine-wave shaped concentration gradients near the interfaces after annealing, implying that uphill diffusion of these elements had occurred. We show using a kinetic model for substitutional diffusion via vacancy hopping that such uphill diffusion can occur even in the absence of thermodynamic interactions, i.e. in ideal solid solutions in which the thermodynamic factor $\Phi$ of each element is equal to one ( ${\Phi }_i=1+\partial \ln f_i/\partial \ln c_i$ where $f_i$ and $c_i$ are the activity coefficient and mole fraction of element $i$, respectively). The model accounts for all elemental fluxes and also rationalizes the diffusion profiles of the major interdiffusing elements.

Authors:

Durand, A.; Peng, L.; Laplanche, G.; Morris, J. R.; George, E. P.; Eggeler, G.

Publication Date:

Wed Jul 01 00:00:00 EDT 2020

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE; International Max Planck Research School SurMat; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division; German Research Foundation (DFG); Center for Interface-Dominated High Performance Materials (ZGH)

OSTI Identifier:

1769531

Alternate Identifier(s):

OSTI ID: 1616827

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Published Article

Journal Name:

Intermetallics

Additional Journal Information:

Journal Name: Intermetallics Journal Volume: 122 Journal Issue: C; Journal ID: ISSN 0966-9795

Publisher:

Elsevier

Country of Publication:

United Kingdom

Language:

English

Subject:

36 MATERIALS SCIENCE; Multicomponent diffusion; High-entropy alloys (HEAs); Uphill diffusion; Vacancies; Kinetics; Interdiffusion