Secondary phases in AlxCoCrFeNi high-entropy alloys: An in-situ TEM heating study and thermodynamic appraisal

J. C. Rao, H. Y. Diao, V. Ocelík, D. Vainchtein, C. Zhang, C. C. Kuo, Z. Tang, W. Guo, J. D. Poplawsky, Y. Zhou, P. K. Liaw*, J. Th M. De Hosson

*Corresponding author for this work

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    Abstract

    Secondary phases, either introduced by alloying or heat treatment, are commonly present in most high-entropy alloys (HEAs). Understanding the formation of secondary phases at high temperatures, and their effect on mechanical properties, is a critical issue that is undertaken in the present study, using the AlxCoCrFeNi (x = 0.3, 0.5, and 0.7) as a model alloy. The in-situ transmission-electron-microscopy (TEM) heating observation, an atom-probe-tomography (APT) study for the reference starting materials (Al0.3 and Al0.5 alloys), and thermodynamic calculations for all three alloys, are performed to investigate (1) the aluminum effect on the secondary-phase fractions, (2) the annealing-twinning formation in the face-centered-cubic (FCC) matrix, (3) the strengthening effect of the secondary ordered body-centered-cubic (B2) phase, and (4) the nucleation path of the σ secondary phase thoroughly. The present work will substantially optimize the alloy design of HEAs and facilitate applications of HEAs to a wide temperature range.

    Original languageEnglish
    Pages (from-to)206-220
    Number of pages15
    JournalActa Materialia
    Volume131
    DOIs
    Publication statusPublished - 1-Jun-2017

    Keywords

    • Atom-probe-tomography
    • High-entropy alloy
    • In-situ heating TEM
    • Secondary phases
    • Thermodynamic calculations

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