High-entropy alloys (HEA) form solid solutions with large chemical disorder and excellent mechanical properties. We investigate the origin of HEA strengthening in face-centered-cubic (fcc) single-phase HEAs through molecular dynamics simulations of dislocations, in particular, the equiatomic CrCoNi, CrMnCoNi, CrFeCoNi, CrMnFeCoNi, FeNi, and, also, Fe0.4Mn0.27Ni0.26Co0.05Cr0.02, Fe0.7Ni0.11Cr0.19. The dislocation correlation length ξ, roughness amplitude Ra, and stacking fault widths WSF are tracked as a function of stress. All alloys are characterized by a well defined depinning stress (σc) and we find a regime where exceptional strength is observed, and a fortuitous combination takes place, of small stacking fault widths and large dislocation roughness Ra. Thus the depinning of two partials seems analogous to unconventional domain wall depinning in disordered magnetic thin films. This regime is identified in specific compositions commonly associated with exceptional mechanical properties (CrCoNi, CrMnCoNi, CrFeCoNi, and CrMnFeCoNi). Yield stress from analytical solute-strengthening models underestimates largely the results in these cases. A possible strategy for increasing strength in multicomponent single-phase alloys is the combined design of stacking fault width and element-based chemical disorder. A hardening factor represents this strategy where combination of low stacking fault and high misfit parameters (and thus high roughness of dislocation at depinning stress) leads to stronger fcc multicomponent alloys.Received 5 October 2021Accepted 2 May 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L022043Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCompositionHardnessMechanical & acoustical propertiesMechanical deformationMicrostructurePlasticityStressCondensed Matter, Materials & Applied Physics
High entropy alloys (HEAs) represent highly promising multicomponent crystals that form concentrated solid solutions (CSSs) and may violate traditional thermodynamic rules of mixing, ultimately leading to excellent physical properties. For a deeper understanding, we investigate seven CSSs, including Co-Cr-Ni-Fe-Mn elements, at experimentally relevant compositions and conditions, through molecular simulations, and we use 1-1 comparisons to corresponding glass state characteristics, attained through rapid cooling protocols. We determine the behavior of various structural features, including the configurational entropy for a set of CSSs in their crystalline and vitreous states numerically. We employ swap Monte Carlo (MC) simulations, in combination with the reversible scaling method, to efficiently compute the configurational entropy (${S}_{\text{conf}}$), and show that the entropic rule of mixing is not always adequate for predicting alloy formation. We study the stability and formability of crystalline solid solutions, as well as glasses, while following the thermodynamics of ${S}_{\text{conf}}$. An apparent entropic similarity between CSSs and corresponding glasses leads us to use a Kauzmann-like ansatz, relating the CSSs at ${S}_{\text{conf}}\ensuremath{\rightarrow}0$ with the emergence of a CSS order-disorder transition, at temperature ${T}_{OD}$. In the context of glasses, a comparison between kinetic and thermodynamic fragilities allows the association of sluggish diffusion onset to a drop in ${S}_{\text{conf}}$ at ${T}_{K}$. Analogously, we classify CSSs as ``strong'' or ``fragile'' in the sense of their ability to migrate across CSS crystal configurations at high temperatures, distinguishing its formability. We argue that the magnitude of ${T}_{OD}$ may be an excellent predictor of CSS single-phase stability, which appears to scale with well-known HEA predictors, in particular we notice that VEC and ${T}_{OD}$ have in relation to the others a significantly large Pearson correlation coefficient, much larger than most other observables (except $\mathrm{\ensuremath{\Delta}}{H}_{\text{mix}}$).
Under plastic flow, multi-element high/medium-entropy alloys (HEAs/MEAs) commonly exhibit complex intermittent and collective dislocation dynamics owing to inherent lattice distortion and atomic-level chemical complexities. Using atomistic simulations, we report on an avalanche study of slowly-driven model face-centered cubic (fcc) NiCoCrFeMn and NiCoCr chemically complex alloys aiming for microstructural/topological characterization of associated dislocation avalanches. The results of our avalanche simulations reveal a close correspondence between the observed serration features in the stress response of the deforming HEA/MEA and the incurred slip patterns within the bulk crystal. We show that such correlations become quite pronounced within the rate-independent (quasi-static) regime exhibiting scale-free statistics and critical scaling features as universal signatures of dislocation avalanches.
The shear-banding instability in quasi-statically driven bulk metallic glasses emerges from collective dynamics, mediated by shear transformation zones and associated non-local elastic interactions. It is also phenomenologically known that sharp structural features of shear bands are typically correlated to the sharpness of the plastic yielding transition, being predominant in commonly studied alloys composed of multiple different elements, that have very different atomic radii. However, in the opposite limit \remove{of high-entropy multicomponent alloys,} where elements' radii are relatively similar, plastic yielding of bulk metallic glasses is highly dependent on compositional and ordering features. In particular, a known mechanism at play involves the formation of short-range order dominated by icosahedra-based clusters. Here, we report on atomistic simulations of multi-component metallic glasses with different chemical compositions showing that the degree of strain localization is largely controlled by the interplay between composition-driven icosahedra-ordering and collectively-driven shear transformation zones. By altering compositions, strain localization ranges from diffuse homogenized patterns to singular crack-like features. We quantify the dynamical yielding transition by measuring the atoms' susceptibility to plastic rearrangements, strongly correlated to the local atomic structure. We find that the abundance of short-range ordering of icosahedra within rearranging zones increases glassy materials' capacity to delocalize strain. The kind of plastic yielding can be often qualitatively inferred by the commonly used compositional descriptor that characterizes element associations, the misfit parameter $\delta_a$, and also by uncommon ones, such as shear-band width and shear-band dynamics' correlation parameters.
W and W-based high-entropy alloys (HEAs) are promising candidates for plasma-facing materials in fusion reactors. While irradiation studies on W have revealed a tendency for helium (He) bubble formation and radiation-induced defects, investigations of WTaCrV HEA have demonstrated superior radiation resistance, whether under He+ irradiation or heavy ion irradiation. To assess material performance under conditions relevant to fusion reactors - characterized by fast neutrons and gas production from transmutation reactions - complex irradiation environments need to be modeled. Using molecular dynamics simulations, we examined defect evolution in W and equimolar WTaCrV HEA with and without preexisting He atoms under cascade overlap conditions up to 0.2 dpa at 300 K. In W, dislocation loops and large interstitial clusters formed readily, with increasing He content leading to higher dislocation densities and the formation of polygonal interstitial networks. In contrast, the WTaCrV alloy exhibited strong resistance to the formation of dislocation loops and large interstitial clusters but was more susceptible to the formation of bubbles at higher He concentrations. Bubble growth was driven by helium trapping at vacancy sites and the coalescence of smaller bubbles. Larger bubbles remained stable against cascade overlap, limiting further growth by coalescence.
The shear-banding instability in quasistatically driven bulk metallic glasses emerges from collective dynamics, mediated by shear transformation zones and associated nonlocal elastic interactions. It is also phenomenologically known that sharp structural features of shear bands are typically correlated to the sharpness of the plastic yielding transition, being predominant in commonly studied alloys composed of multiple different elements, that have very different atomic radii. However, in the opposite limit where elements' radii are relatively similar, plastic yielding of bulk metallic glasses is highly dependent on compositional and ordering features. In particular, a known mechanism at play involves the formation of short-range order dominated by icosahedra-based clusters. Here, we report on atomistic simulations of multicomponent metallic glasses with different chemical compositions showing that the degree of strain localization is largely controlled by the interplay between composition-driven icosahedra-ordering and collectively-driven shear transformation zones. By altering compositions, strain localization ranges from diffuse homogenized patterns to singular crack-like features. We quantify the dynamical yielding transition by measuring the atoms' susceptibility to plastic rearrangements, strongly correlated to the local atomic structure. We find that the abundance of short-range ordering of icosahedra within rearranging zones increases glassy materials' capacity to delocalize strain. This could be understood on the basis of structural heterogeneities that are enhanced by the presence of local order. The kind of plastic yielding can be often qualitatively inferred by the commonly used compositional descriptor that characterizes element associations, the misfit parameter ${\ensuremath{\delta}}_{a}$, and also by uncommon ones, such as shear-band width and shear-band dynamics' correlation parameters.
High-entropy alloys (HEA) form solid solutions with large chemical disorder and excellent mechanical properties. We investigate the origin of HEA strengthening in face-centered cubic (FCC) single-phase HEAs through molecular dynamics simulations of dislocations, in particular, the equiatomic $\rm CrCoNi$, $\rm CrMnCoNi$, $\rm CrFeCoNi$, $\rm CrMnFeCoNi$, $\rm FeNi$, and also, $\rm Fe_{0.4}Mn_{0.27}Ni_{0.26}Co_{0.05}Cr_{0.02}$, $\rm Fe_{0.7}Ni_{0.11}Cr_{0.19}$. The dislocation correlation length $\xi$, roughness amplitude $R_{a}$, and stacking fault widths $W_{SF}$ are tracked as a function of stress. All alloys are characterized by a well defined depinning stress ($\sigma_c$) and we find a novel regime where exceptional strength is observed, and a fortuitous combination takes place, of small stacking fault widths and large dislocation roughness $R_{a}$. Thus the depinning of two partials seems analogous to unconventional domain wall depinning in disordered magnetic thin films. This novel regime is identified in specific compositions commonly associated with exceptional mechanical properties ($\rm CrCoNi$, $\rm CrMnCoNi$, $\rm CrFeCoNi$, and $\rm CrMnFeCoNi$). Yield stress from analytical solute-strengthening models underestimates largely the results in these cases. A possible strategy for increasing strength in multi-component single-phase alloys is the combined design of stacking fault width and element-based chemical disorder.
The glassDef dataset contains a set of text-based LAMMPS dump files corresponding to shear deformation tests on different bulk metallic glasses. This includes FeNi, CoNiFe, CoNiCrFe, CoCrFeMn, CoNiCrFeMn, and Co5Cr2Fe40Mn27Ni26 amorphous alloys with data files that exist in relevant subdirectories. Each dump file corresponds to multiple realizations and includes the dimensions of the simulation box as well as atom coordinates, the atom ID, and associated type of nearly 50,000 atoms. Load glassDef Dataset in Python The glassDef dataset may be loaded in Python into Pandas DataFrame. To go into the relevant subdirectory, run cd glass{glass_name}/Run[0-3]/ where “glass_name” denotes the chemical composition. Each subdirectory contains at least three glass realizations within subfolders that are labeled as “Run[0-3]”. > cd glassFeNi/Run0; python > import pandas > df = pandas.read_csv("FeNi_glass.dump",skiprows=9) One may display an assigned DataFrame in the form of a table: > df.head() To learn more about further analyses performed on the loaded data, please refer to the paper cited below. glassDef Dataset Structure glassDef Data Fields Dump files: “id”, “type”, “x”, “y”, “z”. glassDef Dataset Description Paper: Karimi, Kamran, Amin Esfandiarpour, René Alvarez-Donado, Mikko J. Alava, and Stefanos Papanikolaou. "Shear banding instability in multicomponent metallic glasses: Interplay of composition and short-range order." Physical Review B 105, no. 9 (2022): 094117. Contact: kamran.karimi@ncbj.gov.pl
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