Critical stress for twinning nucleation in CrCoNi-based medium and high entropy alloys

Huang, He; Li, Xiaoqing; Dong, Zhihua; Li, Wei; Huang, Shuo; Meng, Daqiao; Lai, Xinchun; Liu, Tianwei; Zhu, Shengfa; Vitos, Levente

doi:10.1016/j.actamat.2018.02.037

Cited by 156 publications

(34 citation statements)

References 46 publications

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“…The critical twinning stress (σ tw ) is described as an equivalent stress of importance to form sufficient stacking faults followed by the measureable deformation twins 8,37 . Several theoretical or phenomenological approaches have determined the σ tw using TEM 8,9 , neutron diffraction 12 or first-principle calculation based on energy barriers of stacking/twin faults 10,37 . It has been estimated for the CrCoNi alloy as 790 ± 100 MPa using TEM 9 , 890 MPa by first-principle calculation 10 , and 680-770 MPa by a numerical model by Steinmetz et al 36…”

Section: Resultsmentioning

confidence: 99%

“…dissociating a perfect dislocation into Shockley partial dislocations and considered as a surface tension pulling the partials, which is inversely proportional to the equilibrium distance between two partials 14 . The key issue of the CrCoNi MEA is the low SFE, which creates a wide stacking fault ribbon limiting the cross slip deformation mode and provides the superior mechanical properties by the dominant deformation twinning [6][7][8][9][10][11] . Up to date, Laplanche et al 9 reported the SFE of 22 ± 4 mJ/m 2 in CrCoNi MEA, which is ~25% lower than CrCoNiFeMn HEA (30 ± 4 mJ/m 2 ) and Liu et al reported as 18 ± 4 mJ/m 2 in CrCoNi MEA and 26.5 ± 4.5 mJ/ m 2 in CrCoNiFeMn HEA using TEM 2,11 .…”

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confidence: 99%

“…Up to date, Laplanche et al 9 reported the SFE of 22 ± 4 mJ/m 2 in CrCoNi MEA, which is ~25% lower than CrCoNiFeMn HEA (30 ± 4 mJ/m 2 ) and Liu et al reported as 18 ± 4 mJ/m 2 in CrCoNi MEA and 26.5 ± 4.5 mJ/ m 2 in CrCoNiFeMn HEA using TEM 2,11 . Besides, a number of ab initio calculations provide mostly negative SFEs (e.g., −26 mJ/m 2 for CrCoNi MEA, −7 mJ/m 2 for CrCoNiFeMn HEA by Huang et al 10 ), which have been simulated under ignoring or including the temperature dependency at a given configuration of atoms and/or with the chemical fluctuations in a mesoscale level [22][23][24] . In recent, Wang et al suggested lower SFE of 13 mJ/m 2 at 77 K than 32.5 mJ/m 2 at 293 K in CrCoNiFe HEA by using in situ neutron diffraction coupled with peak profile analysis 12 .…”

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confidence: 99%

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Stacking Fault Energy Analyses of Additively Manufactured Stainless Steel 316L and CrCoNi Medium Entropy Alloy Using In Situ Neutron Diffraction

Woo

Jeong

Kim

et al. 2020

Sci Rep

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Stacking fault energies (SFE) were determined in additively manufactured (AM) stainless steel (SS 316 L) and equiatomic CrCoNi medium-entropy alloys. AM specimens were fabricated via directed energy deposition and tensile loaded at room temperature. In situ neutron diffraction was performed to obtain a number of faulting-embedded diffraction peaks simultaneously from a set of (hkl) grains during deformation. The peak profiles diffracted from imperfect crystal structures were analyzed to correlate stacking fault probabilities and mean-square lattice strains to the SFE. The result shows that averaged SFEs are 32.8 mJ/m 2 for the AM SS 316 L and 15.1 mJ/m 2 for the AM crconi alloys. Meanwhile, during deformation, the SFE varies from 46 to 21 mJ/m 2 (AM SS 316 L) and 24 to 11 mJ/m 2 (AM crconi) from initial to stabilized stages, respectively. The transient SFEs are attributed to the deformation activity changes from dislocation slip to twinning as straining. The twinning deformation substructure and atomic stacking faults were confirmed by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The significant variance of the SFE suggests the critical twinning stress as 830 ± 25 MPa for the AM SS 316 L and 790 ± 40 MPa for AM CrCoNi, respectively.Excellent combination of strength, ductility, and toughness has been found in an equiatomic, face-centered-cubic CrCoNiFeMn high-entropy alloys (HEA) 1 . The reason of the exceptional properties at cryogenic temperature has been mainly attributed to the evolution of the nanoscale twinning under plastic deformation, so-called twinning-induced plasticity 2,3 . Compared to the HEA, superior mechanical properties of CrCoNi medium-entropy alloys (MEA) have been recently reported at both room and cryogenic temperature 4-13 . High attention has been focused on the evolution of the twinning substructure and/or a new phase with hexagonal close packed structure instead of the initial deformation mode of the dislocation slip in MEAs 6-9 . Systematic examinations of the substructure elucidate that the critical twinning stress of 790 ± 100 MPa reaches at the earlier strain of 9.7-12.9% for CrCoNi MEA than 720 ± 30 MPa at ~25% for CrCoNiFeMn HEA because of higher yield strength and work hardening rate with larger shear modulus of the MEA 8-10 . Earlier formation of the nano-twinning and its activation over a more extended strain range is of importance accepted as the reason of the exceptional strength-ductility-toughness combination in MEA.Stacking fault energy (SFE) has been accepted as a responsible parameter to determine the deformation schemes, which is typically by slip (>45 mJ/m 2 ) to twinning (20-45 mJ/m 2 ) and/or phase transformation (<20 mJ/m 2 ) as often reported in austenitic stainless steels [14][15][16][17][18][19][20][21] . The SFE is defined as the energy per fault area by www.nature.com/scientificreports www.nature.com/scientificreports/ SFE ranges 11-24 mJ/m 2 , b p is the magnitude of the Burgers vector of partials (0.146 nm), G is the shear...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Stacking Fault Energy Analyses of Additively Manufactured Stainless Steel 316L and CrCoNi Medium Entropy Alloy Using In Situ Neutron Diffraction

Woo

Jeong

Kim

et al. 2020

Sci Rep

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“…The f 1 (w c1 ) and f 2 (w c1 ) values for large d are entirely fixed by σ, a value roughly scaling with the inverse of the unstable stacking fault energy (USFE), σ ∼ γ USF[52]; accurate estimate of σ would be required. For smaller separation distances, d and σ both induce variations in f 1 (w c ) and f 1 (w c ), meaning that in these cases the knowledge of both SFE and USFE is important for the strength.Discussing now specifically the case of HEAs, both experiments and ab initio calculations estimated low γ SF / large d values[53][54][55] for the Co-Cr-Fe-Ni-Mn class of HEAs, suggesting that the exact knowledge of d would not be necessary for HEA strength at low to intermediate temperature. Concerning σ, a value of 1.5b was proposed[27] as a typical value resulting from atomistic simulations of model EAM HEAs and various elemental alloys, and provided good agreement with experimental strengths[27,39,40].…”

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Solid solution strengthening theories of high-entropy alloys

LaRosa¹,

Shih²,

Varvenne³

et al. 2019

Materials Characterization

131

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We present a review of solid solution strengthening models for random concentrated solid solutions of which high entropy alloys are an interesting subset. High entropy alloys (HEAs) usually refer to a class of multicomponent alloys in equal or near equal concentrations. These complex compositions break the conventional notion of solutes and solvents. Few attempts have been made to extend the conventional solute strengthening models to HEAs. Among these, the model based on an average effective medium , does not include any adjustable parameter, allows all model inputs to be computed by atomistic simulations, and has predicted the strength of fcc HEAs in good agreement with experiments. The basic concepts of this theory is explained and its capabilities are compared with few other existing models for solute strengthening of HEAs. a CRL and MS made equal contributions to this work.

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“…The accuracy of the EMTO method and the CPA for the elastic properties and planar fault energies of random alloys including HEAs was demonstrated previously [48][49][50][51]. Table 2: Material parameters of the five bcc HEAs, arranged in order of increasing VEC, used in the LEFM analysis: the elastic constants (in units of GPa), and the relaxed surface energies and USF energies for selected fault planes (in units of J/m 2 ).…”

Section: Details Of the Density-functional Theory Calculationsmentioning

confidence: 84%

Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys

Irving

et al. 2020

Acta Materialia

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Understanding the strengthening and deformation mechanisms in refractory high-entropy alloys (HEAs), proposed as new high-temperature material, is required for improving their typically insufficient room-temperature ductility. Here, density-functional theory simulations and a continuum mechanics analysis were conducted to systematically investigate the competition between cleavage decohesion and dislocation emission from a crack tip in the body-centered cubic refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This crack-tip competition is evaluated for tensile loading and a totality of 15 crack configurations and slip systems. Our results predict that dislocation plasticity at the crack tip is generally unfavorable -although the competition is close for some crack orientations, suggesting intrinsic brittleness and low crack-tip fracture toughness in these five HEAs at zero temperature. Fluctuations in local alloy composition, investigated for HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip system relative to the configuration average of that slip system, but do not change the dominant cracktip response. In the case of single-crystal MoNbTaW, where an experimental, room-temperature fracture-toughness value is available for a crack on a {100} plane, theoretical and experimental results agree favorably. Factors that may limit the agreement are discussed. We survey the effect of material anisotropy on preferred crack tip orientations, which are found to be alloy specific. Mixedmode loadings are found to shift the competition in favor of cleavage or dislocation nucleation, depending on crack configuration and amplified by the effect of material anisotropy on crack tip stresses.

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Critical stress for twinning nucleation in CrCoNi-based medium and high entropy alloys

Cited by 156 publications

References 46 publications

Stacking Fault Energy Analyses of Additively Manufactured Stainless Steel 316L and CrCoNi Medium Entropy Alloy Using In Situ Neutron Diffraction

Stacking Fault Energy Analyses of Additively Manufactured Stainless Steel 316L and CrCoNi Medium Entropy Alloy Using In Situ Neutron Diffraction

Solid solution strengthening theories of high-entropy alloys

Ductile and brittle crack-tip response in equimolar refractory high-entropy alloys

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