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Title: Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy

Abstract

Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dual function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness.

Authors:
 [1];  [2];  [3]; ORCiD logo [4];  [1];  [5];  [1];  [6]; ORCiD logo [7]
  1. Zhejiang Univ., Hangzhou (China). Dept. of Materials Science and Engineering. Center of Electron Microscopy. State Key Lab. of Silicon Materials
  2. George Mason Univ., Fairfax, VA (United States). Dept. of Physics and Astronomy
  3. Xi'an Jiaotong Univ., Xi'an (China). Dept. of Materials Science and Engineering
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Sciences and Technology Division
  6. Zhejiang Univ., Hangzhou (China). Dept. of Materials Science and Engineering. Center of Electron Microscopy. State Key Lab. of Silicon Materials; Univ. of Pittsburgh, PA (United States). Dept. of Mechanical Engineering and Materials Science
  7. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Engineering
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); State Key Program for Basic Research in China
Contributing Org.:
Univ. of California, Berkeley, CA (United States); Univ. of Pittsburgh, PA (United States); Xi'an Jiaotong Univ., Xi'an (China); George Mason Univ., Fairfax, VA (United States)
OSTI Identifier:
1376451
Alternate Identifier(s):
OSTI ID: 1398464
Grant/Contract Number:
AC05-00OR22725; AC02-05CH11231; DMR-1611064; 2015CB65930
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 8; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Nanoscience and technology; Structural materials

Citation Formats

Zhang, Zijiao, Sheng, Hongwei, Wang, Zhangjie, Gludovatz, Bernd, Zhang, Ze, George, Easo P., Yu, Qian, Mao, Scott X., and Ritchie, Robert O. Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy. United States: N. p., 2017. Web. doi:10.1038/ncomms14390.
Zhang, Zijiao, Sheng, Hongwei, Wang, Zhangjie, Gludovatz, Bernd, Zhang, Ze, George, Easo P., Yu, Qian, Mao, Scott X., & Ritchie, Robert O. Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy. United States. doi:10.1038/ncomms14390.
Zhang, Zijiao, Sheng, Hongwei, Wang, Zhangjie, Gludovatz, Bernd, Zhang, Ze, George, Easo P., Yu, Qian, Mao, Scott X., and Ritchie, Robert O. Mon . "Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy". United States. doi:10.1038/ncomms14390. https://www.osti.gov/servlets/purl/1376451.
@article{osti_1376451,
title = {Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy},
author = {Zhang, Zijiao and Sheng, Hongwei and Wang, Zhangjie and Gludovatz, Bernd and Zhang, Ze and George, Easo P. and Yu, Qian and Mao, Scott X. and Ritchie, Robert O.},
abstractNote = {Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dual function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness.},
doi = {10.1038/ncomms14390},
journal = {Nature Communications},
number = ,
volume = 8,
place = {United States},
year = {Mon Feb 20 00:00:00 EST 2017},
month = {Mon Feb 20 00:00:00 EST 2017}
}

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  • Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dualmore » function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness.« less
  • The high-entropy alloys are an intriguing new class of metallic materials that derive their properties not from a single dominant constituent, such as iron in steels, nor from the presence of a second phase, such as in nickel-base superalloys, but rather comprise multi-element systems that crystallize as a single phase, despite containing high concentrations (~20 at.%) of five or more elements with different crystal structures. Indeed, we have recently reported on one such single-phase high-entropy alloy, NiCoCrFeMn, which displays exceptional strength and toughness at cryogenic temperatures. Here which displays unprecedented strength-toughness properties that exceed those of all high-entropy alloys andmore » most multi-phase alloys. With roomtemperature tensile strengths of almost 1 GPa and KJIc fracture-toughness values above 200 MPa.m 1/2 (with crack-growth toughnesses exceeding 300 MPa.m 1/2), the strength, ductility and toughness of the NiCoCr alloy actually improve at cryogenic temperatures to unprecedented levels of strengths above 1.3 GPa, failure strains up to 90% and K JIc values of 275 MPa.m 1/2 (with crackgrowth toughnesses above 400 MPa.m 1/2). These properties appear to result from continuous steady strain hardening, which acts to suppress plastic instability, resulting from pronounced dislocation activity and deformation-induced nano-twinning.« less
  • High-entropy alloys are an intriguing new class of metallic materials that derive their properties from being multi-element systems that can crystallize as a single phase, despite containing high concentrations of five or more elements with different crystal structures. Here we examine an equiatomic medium-entropy alloy containing only three elements, CrCoNi, as a single-phase face-centred cubic solid solution, which displays strength-toughness properties that exceed those of all high-entropy alloys and most multi-phase alloys. At room temperature, the alloy shows tensile strengths of almost 1 GPa, failure strains of ~70% and K JIc fracture-toughness values above 200 MPa m 1/2 ; atmore » cryogenic temperatures strength, ductility and toughness of the CrCoNi alloy improve to strength levels above 1.3 GPa, failure strains up to 90% and K JIc values of 275 MPa m 1/2 . Such properties appear to result from continuous steady strain hardening, which acts to suppress plastic instability, resulting from pronounced dislocation activity and deformation-induced nano-twinning.« less