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Title: Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength

Abstract

Ductility, i.e., uniform strain achievable in uniaxial tension, diminishes for materials with very high yield strength. Even for the CrCoNi medium-entropy alloy (MEA), which has a simple face-centered cubic (FCC) structure that would bode well for high ductility, the fine grains processed to achieve gigapascal strength exhaust the strain hardening ability such that, after yielding, the uniform tensile strain is as low as ∼2%. Here we purposely deploy, in this MEA, a three-level heterogeneous grain structure (HGS) with grain sizes spanning the nanometer to micrometer range, imparting a high yield strength well in excess of 1 GPa. This heterogeneity results from this alloy’s low stacking fault energy, which facilitates corner twins in recrystallization and stores deformation twins and stacking faults during tensile straining. After yielding, the elastoplastic transition through load transfer and strain partitioning among grains of different sizes leads to an upturn of the strain hardening rate, and, upon further tensile straining at room temperature, corner twins evolve into nanograins. This dynamically reinforced HGS leads to a sustainable strain hardening rate, a record-wide hysteresis loop in load−unload−reload stress−strain curve and hence high back stresses, and, consequently, a uniform tensile strain of 22%. As such, this HGS achieves, in amore » single-phase FCC alloy, a strength−ductility combination that would normally require heterogeneous microstructures such as in dual-phase steels.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Johns Hopkins Univ., Baltimore, MD (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1537275
Grant/Contract Number:  
FG02-03ER46056
Resource Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 115; Journal Issue: 28; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
Science & Technology - Other Topics

Citation Formats

Yang, Muxin, Yan, Dingshun, Yuan, Fuping, Jiang, Ping, Ma, Evan, and Wu, Xiaolei. Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength. United States: N. p., 2018. Web. doi:10.1073/pnas.1807817115.
Yang, Muxin, Yan, Dingshun, Yuan, Fuping, Jiang, Ping, Ma, Evan, & Wu, Xiaolei. Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength. United States. doi:10.1073/pnas.1807817115.
Yang, Muxin, Yan, Dingshun, Yuan, Fuping, Jiang, Ping, Ma, Evan, and Wu, Xiaolei. Tue . "Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength". United States. doi:10.1073/pnas.1807817115. https://www.osti.gov/servlets/purl/1537275.
@article{osti_1537275,
title = {Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength},
author = {Yang, Muxin and Yan, Dingshun and Yuan, Fuping and Jiang, Ping and Ma, Evan and Wu, Xiaolei},
abstractNote = {Ductility, i.e., uniform strain achievable in uniaxial tension, diminishes for materials with very high yield strength. Even for the CrCoNi medium-entropy alloy (MEA), which has a simple face-centered cubic (FCC) structure that would bode well for high ductility, the fine grains processed to achieve gigapascal strength exhaust the strain hardening ability such that, after yielding, the uniform tensile strain is as low as ∼2%. Here we purposely deploy, in this MEA, a three-level heterogeneous grain structure (HGS) with grain sizes spanning the nanometer to micrometer range, imparting a high yield strength well in excess of 1 GPa. This heterogeneity results from this alloy’s low stacking fault energy, which facilitates corner twins in recrystallization and stores deformation twins and stacking faults during tensile straining. After yielding, the elastoplastic transition through load transfer and strain partitioning among grains of different sizes leads to an upturn of the strain hardening rate, and, upon further tensile straining at room temperature, corner twins evolve into nanograins. This dynamically reinforced HGS leads to a sustainable strain hardening rate, a record-wide hysteresis loop in load−unload−reload stress−strain curve and hence high back stresses, and, consequently, a uniform tensile strain of 22%. As such, this HGS achieves, in a single-phase FCC alloy, a strength−ductility combination that would normally require heterogeneous microstructures such as in dual-phase steels.},
doi = {10.1073/pnas.1807817115},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 28,
volume = 115,
place = {United States},
year = {2018},
month = {6}
}

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Works referenced in this record:

Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes
journal, May 2004

  • Yeh, J.-W.; Chen, S.-K.; Lin, S.-J.
  • Advanced Engineering Materials, Vol. 6, Issue 5, p. 299-303
  • DOI: 10.1002/adem.200300567