Deformable κ phase induced deformation twins in a CoNiV medium entropy alloy

An, Fengchao; Hou, Junhua; Liu, Jikui; Qian, Bingnan; Lu, Wenjun

doi:10.1016/j.ijplas.2022.103509

Cited by 32 publications

(5 citation statements)

References 64 publications

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“…The twin boundary difference is 60° and the twin plane is

, as shown in Figure 5 (b5). We speculate that the appearance of twins is closely related to the decrease in the layer fault energy caused by the addition of W. A twin boundary can not only inhibit dislocation motion and increase strength, but can also be used to coordinate the plastic deformation of the slip surface of dislocation, which is significantly important to improving the alloy’s strength and toughness [ 26 ]. Figure 5 (a2,b2) shows the grain boundaries and phase boundaries.…”

Section: Resultsmentioning

confidence: 99%

The Effect of W Content on the Microstructure, Mechanics and Electrical Performance of an FeCrCo Alloy

Wang

Zhang

Liu³

et al. 2023

Materials

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In this paper, FeCrCoW alloys with different W contents (0.4, 2.1 and 3.4 at%) are designed and studied in order to overcome the existing shortcomings of resistance materials. These resistance materials have high resistivity and a low temperature coefficient of resistivity. It is observed that the addition of W has a remarkable effect on the phase structure of the alloy. In particular, when the W content is 3.4 at%, the single BCC phase of the alloy can be transformed into the BCC and FCC phase. Meanwhile, when analyzed by transmission electron microscopy, there are stacking faults and martensite in FeCrCoW alloy with W content of 3.4 at%. These features are related to excessive W content. In addition, the strength of the alloy can be improved, and the ultimate tensile strength and yield strength are both very high, which are considered as grain-boundary strengthening and solid solution strengthening, caused by the addition of W. The electrical resistivity of the FeCrCoW alloys decreases when the content of W is more than 2.1 at%. The maximum resistivity of the alloy is 170 ± 1.5 μΩ·cm. Moreover, the unique properties of the transition metal allow the alloy to have a low temperature coefficient of resistivity in the temperature range of 298~393 K. The temperature coefficient of resistivity values of the W0.4, W2.1 and W3.4 alloys are −0.0073, −0.0052 and −0.0051 ppm/K. Therefore, this work provides a vision for resistance alloys, which can achieve highly stable resistivity and high strengths in a certain temperature range.

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“…The twin boundary difference is 60° and the twin plane is

Section: Resultsmentioning

confidence: 99%

The Effect of W Content on the Microstructure, Mechanics and Electrical Performance of an FeCrCo Alloy

Wang

Zhang

Liu³

et al. 2023

Materials

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“…For the lath-shaped κ phase, the deformation mechanism has been underexplored due to its intrinsic brittleness. When forming a nearly pure κ phase polycrystalline ordered structure, poor ductility and substantially reduced strength are mainly caused by severe intergranular embrittlement ( 26 , 27 ). However, introducing the κ phase embedded in the fcc matrix can effectively avoid the risk of intergranular failure among the κ grains.…”

Section: Discussionmentioning

confidence: 99%

“…However, introducing the κ phase embedded in the fcc matrix can effectively avoid the risk of intergranular failure among the κ grains. By carefully controlling the annealing temperature, a small fraction of κ phase (from 2.3 vol % to 14.2 vol %) is decomposed from the fcc CoNiV MEA ( 27 ). A dislocation-controlled shearing mechanism inside the brittle κ phase is conducive to coordinating plastic deformation at the high strain level ( 27 ).…”

Section: Discussionmentioning

confidence: 99%

“…By carefully controlling the annealing temperature, a small fraction of κ phase (from 2.3 vol % to 14.2 vol %) is decomposed from the fcc CoNiV MEA ( 27 ). A dislocation-controlled shearing mechanism inside the brittle κ phase is conducive to coordinating plastic deformation at the high strain level ( 27 ). In the Ni 2 CoFeV MEA, the κ phase contains heavy addition of Fe compared to the CoNiV-type κ phase, of which crystal symmetry can be notably changed.…”

Section: Discussionmentioning

confidence: 99%

“…In the equimolar CoFeNiV MEA, a single-phase L1 2 ordered structure emerges after a complete disorder-to-order transition, showcasing a high UTS of 1.1 GPa and good ductility of 20%, yet displaying a low yield strength of 380 MPa ( 25 ). Upon removal of Fe, the equimolar CoNiV MEA annealed below 800°C attains a nearly pure κ phase structure, resulting in substantially reduced strength (below 250 MPa) and extremely poor ductility less than 1% ( 16 , 26 , 27 ). In conclusion, the completely ordered MEAs are susceptible to intergranular embrittlement and exhibit low yield strengths at room temperature.…”

Section: Introductionmentioning

confidence: 99%

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Ultrastrong and ductile medium-entropy alloys via hierarchical ordering

Gu,

Zhao,

et al. 2024

Sci. Adv.

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Long-range ordered phases in most high-entropy and medium-entropy alloys (HEAs/MEAs) exhibit poor ductility, stemming from their brittle nature of complex crystal structure with specific bonding state. Here, we propose a design strategy to severalfold strengthen a single-phase face-centered cubic (fcc) Ni 2 CoFeV MEA by introducing trigonal κ and cubic L1 2 intermetallic phases via hierarchical ordering. The tri-phase MEA has an ultrahigh tensile strength exceeding 1.6 GPa and an outstanding ductility of 30% at room temperature, which surpasses the strength-ductility synergy of most reported HEAs/MEAs. The simultaneous activation of unusual dislocation multiple slip and stacking faults (SFs) in the κ phase, along with nano-SF networks, Lomer-Cottrell locks, and high-density dislocations in the coupled L1 2 and fcc phases, contributes to enhanced strain hardening and excellent ductility. This work offers a promising prototype to design super-strong and ductile structural materials by harnessing the hierarchical ordered phases.

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The effects of grain size and temperature on mechanical properties of CoCrNi medium-entropy alloy

2023

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In this paper, the molecular dynamics method was used to analyze mechanical properties and microscopic deformation mechanisms of CoCrNi medium-entropy alloy with different average grain sizes at various temperatures. Its elastic modulus and Poisson's ratio were first calculated by the constant pressure molecular dynamics method. It is found that the elastic modulus increases with the average grain size increasing and is reduced at elevated temperatures. However, its Poisson's ratio decreases with the average grain size increasing and is not sensitive to temperatures.Simulations of simple tension were carried out and the results show that: (1) when the average grain size exceeds 15.2 nm, its yield stress and maximum flow stress decreased with the average grain size raising (Hall-Petch relationship), in this situation it is speculated that the dislocation slips and deformation twins within the grains dominate the plastic deformation; (2) when the grain size is smaller than 15.2 nm, the two stress parameters instead increase with the average grain size increasing (Inverse Hall-Petch relationship), such a plastic deformation mechanism is understood mainly due to grain boundaries migrations and grain rotations. In the end, as temperature effects on microscopic deformation mechanisms are concerned, it is found that more dislocations tend to be plugged near grain boundaries which have lower mobility at lower temperatures. Accordingly, the two stress parameters increase as the temperature decreases.

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Deformable κ phase induced deformation twins in a CoNiV medium entropy alloy

Cited by 32 publications

References 64 publications

The Effect of W Content on the Microstructure, Mechanics and Electrical Performance of an FeCrCo Alloy

The Effect of W Content on the Microstructure, Mechanics and Electrical Performance of an FeCrCo Alloy

Ultrastrong and ductile medium-entropy alloys via hierarchical ordering

The effects of grain size and temperature on mechanical properties of CoCrNi medium-entropy alloy

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