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

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America
 [1];  [1];  [2];  [1];  [3];  [2]
  1. Chinese Academy of Sciences (CAS), Beijing (China)
  2. Chinese Academy of Sciences (CAS), Beijing (China); Univ. of Chinese Academy of Sciences, Beijing (China)
  3. Johns Hopkins Univ., Baltimore, MD (United States)

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.

Research Organization:
Johns Hopkins Univ., Baltimore, MD (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
FG02-03ER46056
OSTI ID:
1537275
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Vol. 115, Issue 28; ISSN 0027-8424
Publisher:
National Academy of SciencesCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 313 works
Citation information provided by
Web of Science

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Cited By (13)

Ultrastrong Medium-Entropy Single-Phase Alloys Designed via Severe Lattice Distortion journal December 2018
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Enhanced strength–ductility synergy in ultrafine-grained eutectic high-entropy alloys by inheriting microstructural lamellae journal January 2019
Nanostructuring with Structural-Compositional Dual Heterogeneities Enhances Strength-Ductility Synergy in Eutectic High Entropy Alloy journal August 2019
Microstructure and mechanical properties of large-volume gradient-structure aluminium sheets fabricated by cyclic skin-pass rolling journal May 2019
A simplified model connecting lattice distortion with friction stress of Nb-based equiatomic high-entropy alloys journal April 2019
A Review on Heterogeneous Nanostructures: A Strategy for Superior Mechanical Properties in Metals journal May 2019
Hierarchical features infused heterogeneous grain structure for extraordinary strength-ductility synergy text January 2018
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Hierarchical features infused heterogeneous grain structure for extraordinary strength-ductility synergy text January 2018
Ductility by shear band delocalization in the nano-layer of gradient structure text January 2018
Hierarchical features infused heterogeneous grain structure for extraordinary strength-ductility synergy journal October 2018
High-entropy alloys journal June 2019

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