Strength can be controlled by edge dislocations in refractory high-entropy alloys

Lee, Chanho; Maresca, Francesco; Feng, Rui; Ungár, T.; Widom, Michael; An, Ke; Poplawsky, Jonathan D.; Chou, Yueh-Ching; Liaw, Peter K.; Curtin, W.A.

doi:10.1038/s41467-021-25807-w

Cited by 108 publications

(48 citation statements)

References 35 publications

(44 reference statements)

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“…First, the space of alloy compositions is immense (e.g., more than 10,000,000 alloys in the Ti-Zr-Hf-V-Nb-Ta-Cr-Mo-W family of bcc alloys at 5% composition intervals). 1 Second, to satisfy performance requirements, alloys must have a balance of properties such as high strength at low/high homologous temperatures, sufficient ductility at room temperature for processing and application resilience, good fracture toughness, phase stability over the temperature range of applications, and environmental resistance. The combinatorial problem of composition plus properties has a silver lining: from among the millions of possible alloys, we only need to discover a handful that can satisfy multiple requirements.…”

Section: Overviewmentioning

confidence: 99%

“…Taking the elastic solute/dislocation interaction as -p(x) ΔV n for each solute n in the pressure field p(x) of the dislocation further enables analytic models for τ y (T , ε) ; many predictions agree well with experiments. [26][27][28][45][46][47] Such analytic models can then be used with approximate or computed inputs to guide alloy design/selection, 1 the SSFE, which dramatically affects the partial dissociation distance of the dislocation. In some local regions along a screw dislocation, 5,16,17,[48][49][50] the partial dislocations can constrict and enable cross-slip spontaneously or with very low barrier.…”

Section: Dislocations: a Case Studymentioning

confidence: 99%

“…52 Theories have been developed to handle spontaneously kinked screw dislocations. 34,35 The strength is controlled by (1) the lateral motion of the kinks through the fluctuating solute environment plus (2) cross-kinks that are formed by the intersection of kinks that form on different screw glide planes (Figure 1i). Cross-kinks can only fail by the formation of high-energy vacancies and self-interstitials, conferring high-temperature strength to the alloy.…”

Section: Dislocations: a Case Studymentioning

confidence: 99%

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Progress and challenges in the theory and modeling of complex concentrated alloys

Rao

Woodward

2022

MRS Bulletin

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The high atomic-scale complexity inherent in the aptly named complex concentrated alloys, or high entropy alloys, presents unique challenges in understanding (1) the structure and motion of defects that control mechanical properties and (2) the thermodynamic phase space encompassing stable, metastable, single, and multiphase alloys, possibly with chemical short range ordering. These factors plus the huge range of possible compositions makes computationally guided design of new high-performance alloys difficult but essential. Here, emerging concepts and theoretical frameworks for understanding defect structures, energies, and motion, and thermodynamics are discussed with a focus on yield strength and phase behavior. Pressing directions for future research are suggested to advance toward the predictive capabilities needed for alloy design. Graphical abstract

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Section: Overviewmentioning

confidence: 99%

Section: Dislocations: a Case Studymentioning

confidence: 99%

Section: Dislocations: a Case Studymentioning

confidence: 99%

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Progress and challenges in the theory and modeling of complex concentrated alloys

Rao

Woodward

2022

MRS Bulletin

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“…RMPEAs are chemically disordered at the atomic scale leading to unusual dislocation behavior. Several molec-ular dynamics (MD) simulations and transmission electron microscopy studies alike have pointed to stochastic glide, slip on higher-order glide planes, screw dislocation cross-kinking, and relatively low edge dislocation mobility at higher frequencies in RMPEAs than expected in pure refractories [7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Multi-scale Investigation of Chemical Short-Range Order and Dislocation Glide in the MoNbTi and TaNbTi Refractory Multi-Principal Element Alloys

Fey¹,

Li²,

Hu³

et al. 2022

Preprint

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Refractory multi-principal element alloys (RMPEAs) are promising materials for high-temperature structural applications. Here, we investigate the role of chemical short-range ordering (CSRO) on dislocation glide in two model RMPEAs -TaNbTi and MoNbTi -using a multi-scale modeling approach. A highly accurate machine learning interatomic potential was developed for the Mo-Ta-Nb-Ti system and used to demonstrate that MoNbTi exhibits a much greater degree of SRO than TaNbTi and the local composition has a direct effect on the unstable stacking fault energies (USFE). From mesoscale phase-field dislocation dynamics simulations, we find that increasing SRO leads to higher mean USFEs, thereby increasing the stress required for dislocation glide. The gliding dislocations experience significant hardening due to pinning and depinning caused by random compositional fluctuations, with higher SRO decreasing the degree of USFE dispersion and hence, amount of hardening. Finally, we show how the morphology of an expanding dislocation loop is affected by the applied stress, with higher SRO requiring higher applied stresses to achieve smooth screw dislocation glide.

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“…Perhaps one of the most crucial aspects separating standard bcc behavior with that of RMEA is the role played by screw and edge dislocations during plastic deformation. Although the experimental evidence is still inconclusive [34][35][36], recent research points to the increased importance of edge dislocation slip relative their role in pure metal bcc systems and dilute alloys [37][38][39][40]. Because chemical fluctuations in HEA take place at the atomistic scale, molecular dynamics (MD) has become the preferred tool to simulate dislocation processes in these systems.…”

Section: Introductionmentioning

confidence: 99%

Thermal super-jogs control high-temperature strength in Nb-Mo-Ta-W alloys

He¹,

Zhou²,

Mordehai³

et al. 2022

Preprint

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Refractory multi-element alloys (RMEA) with body-centered cubic (bcc) structure have been the object of much research over the last decade due to their high potential as candidate materials for high-temperature applications. Most of these alloys display a remarkable strength at temperatures above 1000 ˝C, which cannot be explained by the standard model of bcc plasticity dominated by thermally-activated screw dislocation motion. Recent research on Nb-Mo-Ta-W alloys points to a heightened role of edge dislocations during mechanical deformation, which is generally attributed to atomic-level chemical fluctuations in the material and their interactions with dislocation cores during slip. However, while this effect accounts for levels of strength that are much larger than what might be found in a pure metal, it is not sufficient to explain the high yield stress found at high temperature in Nb-Mo-Ta-W. In this work, we propose a new strengthening mechanism based on the existence of thermal super-jogs in edge dislocation lines that act as strong obstacles to dislocation motion, conferring an extra strength to the alloy that turns out to be in very good agreement with experimental measurements. The basis for the formation of these super-jogs is found in the unique properties of RMEA, which display vacancy formation energy distributions with tails that extend into negative values. This leads to spontaneous, i.e., athermal, vacancy formation at edge dislocation cores, which subsequently relax into atomic-sized super-jogs on the dislocation line. At the same time, these super-jogs can displace diffusively along the glide direction, relieving with their motion some of the extra stress, thus countering the hardening effect due to jog-pinning We implement these mechanisms into a specially-designed hybrid kinetic Monte Carlo/Discrete Dislocation Dynamics approach (kMC/DD) parameterized with vacancy formation and migration energy distributions obtained with machine-learning potentials designed specifically for the Nb-Mo-Ta-W system. The kMC module sets the timescale dictated by thermally-activated events, while the DD module relaxes the dislocation line configuration in between events in accordance with the applied stress. We find that the balance between super-jog pinning and superjog diffusion confers an extra strength to edge dislocations at intermediate-to-high temperatures that is in remarkable agreement with experimental measurements in equiatomic Nb-Mo-Ta-W and several other RMEA. We derive an analytical model based on the computational results that captures this improved understanding of plastic processes in these alloys and and explains the experimental data.

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Strength can be controlled by edge dislocations in refractory high-entropy alloys

Cited by 108 publications

References 35 publications

Progress and challenges in the theory and modeling of complex concentrated alloys

Progress and challenges in the theory and modeling of complex concentrated alloys

Multi-scale Investigation of Chemical Short-Range Order and Dislocation Glide in the MoNbTi and TaNbTi Refractory Multi-Principal Element Alloys

Thermal super-jogs control high-temperature strength in Nb-Mo-Ta-W alloys

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