Abstract A non-equiatomic Co29Cr29Fe29Ni12.5W0.5 high-entropy alloy (HEA) strengthened by two-step rolling was fabricated, and its microstructure evolution and tensile behavior at cryogenic temperatures were investigated. When the temperature decreases from 293 K to 173 K, the yield strength increases from 640 MPa to 1017 MPa. At 77 K, an outstanding strength-ductility synergy can be observed, with a yield strength of 1.33 GPa and an excellent ductility of 46%. Prior to tensile testing, the annealed alloy largely has a single face-centered cubic (FCC) structure, while a hexagonal-close packed (HCP) phase is formed in the cryogenically tensile-fractured alloy along the {111} planes. Such high yield strength and tensile plasticity values at cryogenic temperatures are extremely rare in HEAs and even in metal alloys. The deformation micro-mechanism was carefully investigated by a transmission electron microscope, and the results indicated that the cryogenic-temperature properties could be attributed to stacking faults (SFs) and the phase having a hexagonal-close-packed (HCP) structure. The densities of the SFs and the HCP laths have a considerable influence on the work-hardening behavior.
#1Cheng-bin Wei(DUT: Dalian University of Technology)H-Index: 1
#2Yiping Lu(DUT: Dalian University of Technology)H-Index: 30
Last. Tongmin Wang(DUT: Dalian University of Technology)H-Index: 34
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Abstract Nonequiatomic Co29Cr29Fe29Ni12.5W0.5 high-entropy alloys (HEAs) were prepared by vacuum induction melting and subsequent mechanical processing. The HEA with face-centered cubic and few hexagonal close-packed structure phases exhibited outstanding mechanical properties. After annealing at 725 °C, the yield strength and fracture elongation were 1.13 GPa and 24.3%, respectively. The outstanding mechanical properties were attributed to the addition of the W element and ultrafine grain struc...
Last. Jian Wang(NU: University of Nebraska–Lincoln)H-Index: 71
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Abstract Single-phase face-centered cubic multi-principal-element alloys (fcc MPEAs) comprising transition metal elements Cr, Mn, Fe, Co or Ni generally show strong temperature dependence of stacking fault energy (SFE) of {111} plane, the lower temperature the lower SFE. Through uniaxial tension of a non-equiatomic Cr26Mn20Fe20Co20Ni14 alloy at low temperature, we observed nanoscale microstructures including stacking faults bands, nano-twins, hexagonal-close packed (hcp) phase bands and amorphou...
#1Dong Geun Kim(POSTECH: Pohang University of Science and Technology)H-Index: 8
#2Yong Hee Jo(POSTECH: Pohang University of Science and Technology)H-Index: 14
Last. Sunghak Lee(POSTECH: Pohang University of Science and Technology)H-Index: 63
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Abstract The existing deformation-induced martensitic transformation mostly focuses on overcoming the trade-off of cryogenic strength-ductility; however, an enhancement of cryogenic strength further is still challenging. We present a concept to yield a cryogenic strength of 2 GPa in a duplex V 10 Cr 10 Co 30 Fe 50 alloy. We adopt a thermodynamic calculation to reduce the stability of metastable face-centered-cubic (FCC) matrix, significantly promoting the martensitic transformation. In conjuncti...
#1Sanjie Liu(USTB: University of Science and Technology Beijing)H-Index: 7
#1Shixiang Liu(USTB: University of Science and Technology Beijing)H-Index: 6
Last. Zhaoping Lu(USTB: University of Science and Technology Beijing)H-Index: 56
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Abstract Face-centered cubic (fcc) HEAs, particularly the typical FeCoNiCrMn HEA, are promising for cryogenic applications but generally exhibit relatively low strength at ambient temperature, which limits their widespread uses. In this work, we present a systematic study of enhancing simultaneously the strength and ductility of FeCoNiCrMn HEAs via tailoring the phase stability and stacking fault energy (SFE). It was found that in Fe20CoxNi40-xCr20Mn20 (x = 20–30 at.%) HEAs, with the increase of...
#1T. Yang(CityU: City University of Hong Kong)H-Index: 18
#2Yilu Zhao(CityU: City University of Hong Kong)H-Index: 13
Last. C.T. Liu(CityU: City University of Hong Kong)H-Index: 16
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Abstract We designed a novel nanoparticles-strengthened high-entropy alloy, Ni30Co30Fe13Cr15Al6Ti6, which exhibits excellent strength-ductility combinations at both ambient and cryogenic temperatures. Especially at 77 K, an exceptional strength-ductility synergy can be observed, showing an ultrahigh tensile strength of 1.7 GPa and a large ductility of 51%, accompanied by a distinctive three-stage strain-hardening response. The precipitation-hardening behaviors and deformation micro-mechanisms we...
#1Min Ji Jang(POSTECH: Pohang University of Science and Technology)H-Index: 14
#2Hyunjeong Kwak(POSTECH: Pohang University of Science and Technology)H-Index: 1
Last. Hyoung Seop Kim(POSTECH: Pohang University of Science and Technology)H-Index: 64
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A single FCC phase 40Fe–25Ni–15Cr–10Co–10V high-entropy alloy was designed, fabricated, and evaluated for potential cryogenic applications. The alloy forms a single FCC phase and exhibits higher yield strength, tensile strength, and elongation at cryogenic temperature (77 K) than at room temperature (298 K). The superior tensile properties at cryogenic temperature are discussed based on the formation of deformation twins during the tensile test at cryogenic temperature. In addition, a constituti...
Last. Tong-Yi Zhang(SHU: Shanghai University)H-Index: 45
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Abstract The improvement in strength is usually accompanied by ductility loss in structural materials, which is a long-standing conflict referred as the strength-ductility trade-off. Here we present a heterogeneous-structures-architecting strategy, in which we design bulk high-entropy alloys with the largely-enhanced strength-ductility trade-off, possessing a yield strength of 711 MPa, a tensile strength of 928 MPa, and a uniform elongation of 30.3%. Such an enhancement of the strength-ductility...
#1Jae Wung Bae(POSTECH: Pohang University of Science and Technology)H-Index: 17
#2Jae-Bok Seol(POSTECH: Pohang University of Science and Technology)H-Index: 20
Last. Hyoung Seop Kim(POSTECH: Pohang University of Science and Technology)H-Index: 64
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Abstract High-entropy alloys (HEAs) are a newly emerging class of materials that show attractive mechanical properties for structural applications. Particularly, face-centered cubic (fcc) structured HEAs and medium-entropy alloys (MEAs) such as FeMnCoNiCr and CoNiCr alloys, respectively, which exhibit superior fracture toughness and tensile properties at liquid nitrogen temperature, are the potential HEA materials available for cryogenic applications. Here, we report a ferrous Fe60Co15Ni15Cr10 (...
#1Muxin Yang(CAS: Chinese Academy of Sciences)H-Index: 13
#2Dingshun Yan(CAS: Chinese Academy of Sciences)H-Index: 4
Last. Xiaolei Wu(CAS: Chinese Academy of Sciences)H-Index: 44
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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 gra...
Last. Irina Kireeva(Tomsk State University)H-Index: 19
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ABSTRACTUnusual strain hardening response and ductility of NiCoCr equiatomic alloy were investigated through microstructural analysis of [111], [110] and [123] single crystals deformed under tension. Nano-twinning prevailed at, as early as, 4% strain along the [110] orientation, providing a steady work hardening, and thereby a significant ductility. While single slip dominated in the [123] orientation at the early stages of deformation, multiple slip and nanotwinning was prominent in the [111] o...