Title: Phase transformations of Al-bearing high-entropy alloys Al_xCoCrFeNi (x = 0, 0.1, 0.3, 0.75, 1.5) at high pressure

Abstract

Pressure-induced structural modifications in high-entropy alloys with varying Al contents, Al_xCoCrFeNi (x = 0, 0.1, 0.3, 0.75, 1.5), have been investigated at pressures up to ~50 GPa by synchrotron X-ray diffraction and, following depressurization, by transmission electron microscopy (TEM). In Al_xCoCrFeNi compounds with x ≤ 0.3, all of which exhibit an initial single-phase face-centered cubic (fcc) structure, proportionality between the Al content and the critical pressure for transformation to hexagonal close-packed (hcp) phases, distinguished by a distinct planar stacking sequence, is observed. This is attributed to the structural distortion arising from the large size of Al atoms relative to those of the other constituent elements, which results in an increase in the formation energy of stacking faults and a decrease in compressibility. High-resolution TEM results demonstrate variation of the stacking sequence from ABCABC, typical of fcc materials, to ABABAB, typical of hcp materials, in CoCrFeNi following high pressure. In Al_0.75CoCrFeNi, which exhibits an initial dual-phase structure [fcc and body-centered cubic (bcc)], the result again shows the formation of a (hcp) phase despite its higher Al content, suggesting that the bcc phase may be more amenable to pressure-induced phase modification than is the fcc phase, which is absent for lower Almore » contents. However, the trend of transformation inhibition by increasing the Al content is again observed, with Al_1.5CoCrFeNi retaining its initial structure up to the highest pressure achieved. Furthermore the determination of these compositional trends in the high-pressure phase response of these materials may enable the production of new phase mixtures with precisely tuned phase proportions and potentially desirable properties.« less

Authors:

Wang, Chenxu ^[1]; Tracy, Cameron L.  ^[2];

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• Search DOE PAGES for ORCID "0000-0002-0679-8522"

Park, Sulgiye ^[1]; Liu, Jin ^[1]; Ke, Feng ^[1]; Zhang, Fuxiang ^[3]; Yang, Tengfei ^[4]; Xia, Songqin ^[5]; Li, Congyi ^[4]; Wang, Yugang ^[5]; Zhang, Yong  ^[6];

• Search DOE PAGES for author "Zhang, Yong"
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Mao, Wendy L. ^[7]; Ewing, Rodney C. ^[1]

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+ Show Author Affiliations

1. Stanford Univ., Stanford, CA (United States)
2. Stanford Univ., Stanford, CA (United States); Harvard Univ., Cambridge, MA (United States)
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. Univ. of Tennessee, Knoxville, TN (United States)
5. Peking Univ., Beijing (China)
6. Univ. of Science and Technology Beijing, Beijing (China)
7. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)

Publication Date:

Tue Mar 05 00:00:00 EST 2019

Research Org.:

SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1504572

Grant/Contract Number:  

AC02-76SF00515; 11675005; 51471025; 51671020

Resource Type:

Accepted Manuscript

Journal Name:

Applied Physics Letters

Additional Journal Information:

Journal Volume: 114; Journal Issue: 9; Journal ID: ISSN 0003-6951

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE