The origin of negative stacking fault energies and nano-twin formation in face-centered cubic high entropy alloys

Zhang, Y.H.; Zhuang, Yu; Hu, Alice; Kai, Ji‐Jung; Liu, C.T.

doi:10.1016/j.scriptamat.2016.11.014

Cited by 256 publications

(93 citation statements)

References 21 publications

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“…SFs and twinning became active later. This observation provided important clues regarding the microscopic origin of the increased work hardening at 15 K. It has been predicted by first-principle calculations that, for the HEAs studied here, the stable phase is hcp (19,38,39). An fcc to hcp phase transition has been reported in CrMnFeCoNi under pressure, demonstrating the metastable nature of the fcc phase at room temperature (40).…”

Section: Discussionsupporting

confidence: 65%

Cooperative deformation in high-entropy alloys at ultralow temperatures

et al. 2020

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High-entropy alloys exhibit exceptional mechanical properties at cryogenic temperatures, due to the activation of twinning in addition to dislocation slip. The coexistence of multiple deformation pathways raises an important question regarding how individual deformation mechanisms compete or synergize during plastic deformation. Using in situ neutron diffraction, we demonstrate the interaction of a rich variety of deformation mechanisms in high-entropy alloys at 15 K, which began with dislocation slip, followed by stacking faults and twinning, before transitioning to inhomogeneous deformation by serrations. Quantitative analysis showed that the cooperation of these different deformation mechanisms led to extreme work hardening. The low stacking fault energy plus the stable face-centered cubic structure at ultralow temperatures, enabled by the high-entropy alloying, played a pivotal role bridging dislocation slip and serration. Insights from the in situ experiments point to the role of entropy in the design of structural materials with superior properties.

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Section: Discussionsupporting

confidence: 65%

Cooperative deformation in high-entropy alloys at ultralow temperatures

et al. 2020

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“…2A). For the CrCoNi alloys with random compositional disorder, 108 independent as-assigned supercells were considered in total; the resulting calculated values of isf γ are shown in the inset to (25) that were also calculated using supercell methods. We view these differences with our present value of -42.9 mJ.m -2 as reflecting the need, as illustrated in Fig.…”

Section: Local Chemical Order In Crconi Solid-solution Alloysmentioning

confidence: 99%

“…3E, for a large number of samples to achieve wellconverged averaged results (only limited configurations were considered in refs. [11,17,25]…”

Section: Local Chemical Order In Crconi Solid-solution Alloysmentioning

confidence: 99%

Tunable stacking fault energies by tailoring local chemical order in CrCoNi medium-entropy alloys

Ding

Asta

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

601

243

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High-entropy alloys (HEAs) are an intriguing new class of metallic materials due to their unique mechanical behavior. Achieving a detailed understanding of structure-property relationships in these materials has been challenged by the compositional disorder that underlies their unique mechanical behavior. Accordingly, in this work, we employ first-principles calculations to investigate the nature of local chemical order and establish its relationship to the intrinsic and extrinsic stacking fault energy (SFE) in CrCoNi medium-entropy solid-solution alloys, whose combination of strength, ductility, and toughness properties approaches the best on record. We find that the average intrinsic and extrinsic SFE are both highly tunable, with values ranging from -43 to 30 mJ⋅m and from -28 to 66 mJ⋅m, respectively, as the degree of local chemical order increases. The state of local ordering also strongly correlates with the energy difference between the face-centered cubic () and hexagonal close-packed () phases, which affects the occurrence of transformation-induced plasticity. This theoretical study demonstrates that chemical short-range order is thermodynamically favored in HEAs and can be tuned to affect the mechanical behavior of these alloys. It thus addresses the pressing need to establish robust processing-structure-property relationships to guide the science-based design of new HEAs with targeted mechanical behavior.

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“…Smith et al [66] measured the partial separation of the a/2<110>{111} 60° mixed dislocations in CrMnFeCoNi HEA and found significantly large variations in . Interestingly, one may notice that for the equiatomic CrCoNi MEA, the values obtained at various magnetic states (NM [26,27], PM and FM in the present work) do not differ significantly. It is likely because that the local magnetic moments on all atoms at the PM or FM states are very small or vanished.…”

Section: Stacking Fault Energymentioning

confidence: 38%

“…Here [24], -24 mJ/m 2 [27] and -43 mJ/m 2 [18]. We mention here that one should not directly compare the theoretical SFE with the experimental values, e.g., 18±4 mJ/m 2 [62] and 22±4 mJ/m 2 [63].…”

Section: Stacking Fault Energymentioning

confidence: 94%

Designing Transformation-Induced Plasticity and Twinning-Induced Plasticity Cr-Co-Ni Medium Entropy Alloys: Theory and Experiment

Yang

Tian

et al. 2020

SSRN Journal

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In order to efficiently explore the nearly infinite composition space in multicomponent solid solution alloys, it is important to establish predictive design strategies and use computation-aided methods. In the present work, we demonstrated the density functional theory calculations informed design routes for realizing transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) in Cr-Co-Ni medium entropy alloys (MEAs). We systematically studied the effects of magnetism and chemical composition on the generalized stacking fault energy surface (-surface) and showed that both chemistry and the coupled magnetic state strongly affect the -surface, consequently, the primary deformation modes. Based on the calculated effective energy barriers for the competing deformation modes, we constructed composition and magnetism dependent deformation maps at both room and cryogenic temperatures. Accordingly, we proposed various design routes for achieving desired primary deformation modes in the ternary Cr-Co-Ni alloys. The deformation mechanisms predicted by our theoretical models are in nice agreement with available experimental observations in literature. Furthermore, we fabricated two non-equiatomic Cr-Co-Ni MEAs possessing the designed TWIP and TRIP effects, showing excellent combinations of tensile strength and ductility. Corresponding authors: a Song Lu, songlu@kth.se b Yanzhong Tian,

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The origin of negative stacking fault energies and nano-twin formation in face-centered cubic high entropy alloys

Cited by 256 publications

References 21 publications

Cooperative deformation in high-entropy alloys at ultralow temperatures

Cooperative deformation in high-entropy alloys at ultralow temperatures

Tunable stacking fault energies by tailoring local chemical order in CrCoNi medium-entropy alloys

Designing Transformation-Induced Plasticity and Twinning-Induced Plasticity Cr-Co-Ni Medium Entropy Alloys: Theory and Experiment

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