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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,603 records · Page 89
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DOE OSTI2017

Quantitative assessment of carbon allocation anomalies in low temperature bainite

Low temperature bainite is a mixture of ferrite and austenite with a high dislocation density and nanoscale precipitates produced by isothermal transformation of the austenite in high-carbon high-silicon steels. The mass balance for carbon is systematically unsuitable when considering only ferrite and austenite forming the structure, but no attempt has been made to evaluate the amount of carbon located at linear defects and precipitates. Additionally, bainitic ferrite has been recently shown to have a tetragonal crystal structure, allowing greater amounts of carbon in solid solution than those expected by the paraequilibrium phase boundaries. In order to quantify the contribution of all the carbon sinks, we have followed the evolution of carbon in ferrite and austenite, along with the precipitation of cementite and η–carbide, during the isothermal bainitic transformation at 220 and 250 °C by means of in-situ synchrotron high energy X-ray diffraction and complementary transmission electron microscopy (TEM) and atom probe tomography (APT) analyses. Furthermore, this is the first time that the mass balance for carbon is successfully achieved by considering all the transformation products together with an estimation of the carbon segregated to linear defects.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy

To reveal the operating mechanisms of plastic deformation in an FCC high-entropy alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, σ y , the activation volume varies from ~60 b3 at 77 K to ~360 b 3 at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with σ - σ y (Haasen plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-strengthened alloy. Lastly, these results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Composition and automated crystal orientation mapping of rapid solidification products in hypoeutectic Al-4 at.%Cu alloys

Rapid solidification can produce metastable phases and unusual microstructure modifications in multi-component alloys during additive manufacturing or laser beam welding. Composition and phase mapping by transmission electron microscopy have been used in this paper to characterize the morphologically distinct zones developing in hypoeutectic Al-4 at.% Cu alloy after pulsed laser melting for different crystal growth rate regimes. Deviations of the compositions of the alloy phases from equilibrium predictions and unique orientation relationships between the solidification transformation products have been determined. Specifically, for the columnar growth zone at solidification rates of 0.8 m s - 1 < v < v a = 1.8 m s - 1 , two distinct orientation relationships were established between the concomitantly forming non-equilibrium phases, supersaturated α-Al solid solution and the discontinuously distributed α-Al 2 Cu-based θ'-phase, which can be described as {110} θ ∥ {001} α , [001] θ ∥ [110] α and {001} θ ∥ {001} α , [100] θ ∥ [100] α . These orientation relationships permit formation of coherent interphase interfaces with low interfacial free energy. Finally, this endows a kinetic advantage to the thermodynamically less stable θ'-Al 2 Cu phase relative to the more stable equilibrium θ-Al 2 Cu phase during formation of the morphologically modified eutectic of the columnar growth zone grains, since repeated nucleation is required to establish the discontinuous distribution of θ'-Al 2 Cu phase.

36 MATERIALS SCIENCE↗
DOE OSTI2018

GeV ion irradiation of NiFe and NiCo: Insights from MD simulations and experiments

Concentrated solid solution alloys have attracted rapidly increasing attention due to their potential for designing materials with high tolerance to radiation damage. To tackle the effects of chemical complexity in defect dynamics and radiation response, we present in this paper a computational study on swift heavy ion induced effects in Ni and equiatomic Ni -based alloys (Ni 50 Fe 50 , Ni 50 Co 50 ) using two-temperature molecular dynamics simulations (2T-MD). The electronic heat conductivity in the two-temperature equations is parameterized from the results of first principles electronic structure calculations. A bismuth ion (1.542 GeV) is selected and single impact simulations performed in each target. We study the heat flow in the electronic subsystem and show that alloying Ni with Co or Fe reduces the heat dissipation from the impact by the electronic subsystem. Simulation results suggest no melting or residual damage in pure Ni while a cylindrical region melts along the ion propagation path in the alloys. In Ni 50 Co 50 the damage consists of a dislocation loop structure (d = 2 nm) and isolated point defects, while in Ni 50 Fe 50 , a defect cluster (d = 4 nm) along the ion path is, in addition, formed. The simulation results are supported by atomic-level structural and defect characterizations in bismuth-irradiated Ni and Ni 50 Fe 50 . Finally, the significance of the 2T-MD model is demonstrated by comparing the results to those obtained with an instantaneous energy deposition model without consideration of e-ph interactions in pure Ni and by showing that it leads to a different qualitative behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Segregation induced order-disorder transition in Cu(Au) surface alloys

Using in-situ transmission electron microscopy and atomistic simulations, we report atomic-scale observations of segregation-induced structure changes in the surface and subsurface region of a Cu(Au) solid solution in both reductive and oxidative environments. In a H 2 atmosphere, Au segregation induces the formation of a two-atomic-layer thick ordered surface alloy with an L1 0 terminated surface layer. By switching to an O 2 atmosphere, the outermost surface develops into an Au-missing row reconstruction and simultaneously the second layer experiences an order-disorder transition via intralayer atomic exchanges. The chemical disordering then propagates to the outermost surface, driven by oxygen adsorption induced Cu surface segregation. This transforms the L1 0 missing-row reconstruction into a non-reconstructed, oxygenated surface. Furthermore, these observations provide a mechanistic detail regarding the evolution of the surface and subsurface of this alloy in response to environmental stimuli, and are relevant to a wide range of technologically relevant processes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Study of slip activity in a Mg-Y alloy by in situ high energy X-ray diffraction microscopy and elastic viscoplastic self-consistent modeling

Slip activity from various slip modes largely determines the yield strength and ductility of Mg alloys. Solid solution elements in Mg can change the slip activity dramatically. In this paper, far-field high energy X-ray diffraction microscopy (FF-HEDM) is employed to study slip activity in a Mg-3wt%Y alloy during an in situ tensile experiment. The specimen was incrementally loaded up to 3% engineering strain along the rolling direction. At each load step, FF-HEDM data were collected to track the crystallographic orientation, center of mass, and stress tensor changes of nearly 1000 grains in the probed volume. By analyzing the change in orientation and stress tensor of individual grains at different load steps, it is possible to identify the activated slip systems and measure their critical resolved shear stress (CRSS) values. Prismatic slip and pyramidal I slip are found to be very active in this alloy. The estimated CRSS values for basal slip, prismatic slip and pyramidal I slip are 12 MPa, 38 MPa, and 36 MPa, respectively. These CRSS values were applied in a dislocation-based elastic viscoplastic self-consistent (EVPSC) model that successfully simulated the tensile stress-strain curve from the FF-HEDM experiment. The model also qualitatively predicted the crystal rotation in most of the selected grains, though it underestimated the internal stress and the magnitude of crystal rotation in these grains. Influence of solute Y on the strength and ductility of Mg alloys is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Lattice distortion in a strong and ductile refractory high-entropy alloy

Here, the maximization of the mixing entropy with the optimal range of enthalpy in high-entropy alloys (HEAs) can promote the formation of a stable single solid-solution phase with the absence of competing intermetallic compounds. The resultant effects, such as lattice distortion, can contribute to excellent mechanical properties, which has motivated numerous efforts to develop and design single-phase HEAs. However, challenges still remain, particularly on quantifying the lattice distortion and relating it to materials properties. In this study, we have developed a NbTaTiV refractory HEA with a single body-centered-cubic (BCC) structure using an integrated experimental and theoretical approach. The theoretical efforts include thermodynamic modeling, i.e., CALculation of PHAse Diagram (CALPHAD). The microstructural evolutions have been investigated by systematic heat-treatment processes. The typical dendrite microstructure was observed, which is caused by the elemental segregation during the solidification in the as-cast condition. The structural inhomogeneity and chemical segregation were completely eliminated by the proper homogenization treatment at 1200 °C for 3 days. The homogeneous elemental distribution was quantitatively verified by the Atom Probe Tomography (APT) technique. Importantly, results indicate that this HEA exhibits the high yield strength and ductility at both room and high temperatures (up to 900 °C). Furthermore, the effects of the high mixing entropy on the mechanical properties are discussed and quantified in terms of lattice distortions and interatomic interactions of the NbTaTiV HEA via first-principles calculations. It is found that the local severe lattice distortions are induced, due to the atomic interactions and atomic-size mismatch in the homogenization-treated NbTaTiV refractory HEA.

36 MATERIALS SCIENCE↗
DOE OSTI2018

High temperature thermal and mechanical stability of high-strength nanotwinned Al alloys

Al alloys have widespread applications, but often suffer from low yield strength. Recently, nanotwinned Al-Fe solid solution alloys have shown high flow stress (>1.5 GPa), ascribed to nanograins with abundant incoherent twin boundaries and solute-stabilized 9R phase. However, the high temperature mechanical behaviors of high-strength twinned Al-Fe alloys remain unknown. In this study, we show that nanotwinned microstructures are stable up to 280 °C, followed by recrystallization at 300 °C. In-situ uniaxial compression tests in a scanning electron microscope show that the nanotwinned Al alloys retain their high flow stress of ~1.3 GPa when tested up to 200 °C, and substantial softening occurs at a test temperature of 300 °C. This work reveals the superb thermal stability and high temperature mechanical behaviors of the nanotwinned Al-Fe alloys, and offers a new perspective to design future strong and thermally stable nanostructured Al alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A phase-field model for hydride formation in polycrystalline metals: Application to δ-hydride in zirconium alloys

We report a phase-field model for simulating metal hydride formation involving large volume expansion in single- and polycrystals. As an example, we consider δ-hydride formation in α-zirconium (Zr), which involves both displacive crystallographic structural change and hydrogen diffusion process. Thermodynamic Gibbs energy functions are extracted from the available thermodynamic database based on the sublattice model for the interstitial solid solutions. Solute-grain boundary interactions and inhomogeneous elasticity of polycrystals are taken into consideration within the context of diffuse-interface description. The stress-free transformation strains of multiple variants for hcp -Zr (α) to fcc -hydride (δ) transformation are derived based on the well-established orientation relationship between the α and δ phases as well as the corresponding temperature-dependent lattice parameters. In particular, to account for the large volume expansion, we introduced the mixed interfacial coherency concept between those phases—basal planes are coherent and prismatic planes are semi-coherent in computing the strain energy contribution to the thermodynamics. We analyzed the morphological characteristics of hydrides involving multiple structural variants and their interactions with grain boundaries. Moreover, our simulation study allows for the exploration of the possible hydride re-orientation mechanisms when precipitating under applied tensile load, taking into account the variation in the interfacial coherency between hydrides and matrix, their elastic interactions with the applied stress, as well as their morphology-dependent interactions with grain boundaries. Here, the phase-field model presented here is generally applicable to hydride formation in any binary metal–hydrogen systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interactions between zirconia–yttria–tantala thermal barrier oxides and silicate melts

The effects of TaO 2.5 additions to Y 4 Zr 3 O 12 (YZO) on its interactions with calcium-magnesium alumino-silicate (CMAS) melts are investigated herein. YZO is a candidate material for the protection of novel ZrO 2 -YO 1.5 -TaO 2.5 based thermal barrier coatings (TBCs) against CMAS attack, but thermochemical considerations dictate that YZO contain TaO 2.5 for interfacial compatibility. Oxides based on Y 4 Zr 3-x Ta x O 12+0.5x ( x = =0, 0.7, 1.4) were mixed with various ternary and quinary silicate compositions ranging in Ca:Si ratio from 0.35 to 1.13 and equilibrated at 1300 °C. The results show that all combinations form the desired apatite phase except for the mixture of the higher Ta 5+ content with the lowest Ca:Si melt. It is found that the addition of Ta 5+ increases the capture of Y 3+ by the reprecipitated fluorite, decreasing the amount available to form apatite and eventually suppressing it at low Ca:Si. The effect is ascribed to the attractive interactions between Y 3+ and Ta 5+ in solid solution, similar to that found in tetragonal zirconia, but with concurrent incorporation of anion vacancies associated with excess Y 3+ that stabilize the cubic form. As the Ca 2+ content of the melt increases, so does the amount of Ca 2+ incorporated in fluorite. The latter also interacts attractively with Ta 5+ and leads to a reduction of captured Y 3+ in fluorite as the Ca content in the reacting deposit increases. This serves to increase the amount of Y 3+ available in the melt to form apatite in TBC-CMAS interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

First-principles prediction of incipient order in arbitrary high-entropy alloys: exemplified in Ti 0.25 CrFeNiAl

High-temperature disordered multi-component alloys, including high-entropy alloys, experience either segregation or partially-ordered phases to reach low-temperature phases. For Ti 0.25 CrFeNiAl x (0 ≤ x ≤ 1), experiments suggest a partially-ordered B2 phase, whereas CALculation of PHAse Diagrams (CALPHAD) predicts a region of L21+B2 coexistence. We employ first-principles KKR-CPA to assess stability of phases with arbitrary order and a KKR-CPA linear-response theory to predict atomic short-range order (SRO) in the disorder phase that reveals the competing long-range ordered (LRO) phases in a given Bravais lattice. The favorable SRO provides a specific concentration-waves (site occupation probabilities and partially-ordered unit cells) and estimated energy gains that can then be assess directly by KKR-CPA formation enthalpies. Our results are in good agreement with experiments and CALPHAD in Al-poor regions (x ≤ 0.75) and with CALPHAD in Al-rich region (1≥ x >0.75). Our first-principles KKR-CPA and SRO-based concentration-wave analysis is shown to be a powerful and fast method to assess competing LRO phases in complex solid-solution alloys, and our results suggests more careful experiments in Al-rich region are needed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Revisit the VEC rule in high entropy alloys (HEAs) with high-throughput CALPHAD approach and its applications for material design-A case study with Al–Co–Cr–Fe–Ni system

Valence electron concentration (VEC) was treated as a useful parameter to predict solid solution phases, and the VEC rule was proposed for high entropy alloys (HEAs). However, this empirical rule has its limitations, which restricts its applications for phase predictions in HEAs. In this paper, we revisited the empirical VEC rule with the HT-CALPHAD approach in the Al–Co–Cr–Fe–Ni system. Our investigation showed that more than 90% compositions are observed to have BCC structures when 5.7≤VEC≤7.2 and we got 100% FCC structures when VEC≥8.4. Meanwhile, we proposed a data screening procedure to classify and discover the new HEAs. The concepts of average density (ρHEA), highest BCC/FCC temperatures ($T$ $^{max}_{BCC/FCC}$), and temperature ranges (ΔT BCC/FCC ) were introduced as useful data screening criteria to down-screen the candidate alloy compositions for specific engineering applications. In the current work, we have identified three HEA categories (refractory BCC HEAs, light-weight BCC HEA and refractory FCC HEAs) in the Al–Co–Cr–Fe–Ni system and proposed the best candidate in each group. Here, our investigation showed the HEA non-equiatomic composition space provides ample opportunities for the discovery of the next-generation HEAs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Plastic deformation of single crystals of the equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy in tension and compression from 10 K to 1273 K

In this report the plastic deformation behavior of single crystals of the quinary, equiatomic Cr-Mn-Fe-Co-Ni high-entropy alloy (HEA) with the face-centered cubic structure has been investigated in tension and compression as a function of crystal orientation and temperature from 10 K to 1373 K. The critical resolved shear stress (CRSS) for {111}<110> slip at room temperature is 42-45 MPa. It does not depend much on crystal orientation (i.e., the Schmid law holds true) and the sense (tension vs. compression) of the applied load. The CRSS for {111}<110> slip increases with the decrease in temperature, without showing any significant inertia effects at cryogenic temperatures below 77 K. Extrapolation from the measured yield stresses down to 10 K yields a CRSS value at 0 K of 168 MPa. At cryogenic temperatures, the measured strain-rate sensitivity of flow stress is consistent with a very small activation volume. The concept of stress equivalence holds true both for the temperature dependence of CRSS and the stress dependence of activation volume, indicating that solid-solution hardening is the major strengthening mechanism. Deformation twinning occurs at 77 K but not at room temperature, resulting in higher tensile elongation to failure at 77 K than at room temperature. Deformation twinning at 77 K occurs at a shear stress of 378 MPa on conjugate ($\bar1\bar11$) planes in the form of Lüders deformation after large plastic strain (about 85%) achieved by the stage I (easy glide) and stage II (linear work-hardening) deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of Solidification Cooling Rates on Microstructures and Physical Properties of Fe-6.5%Si Alloys

Compared to the widely used Fe-3.2wt%Si steel, Fe-6.5wt%Si has superior electric and magnetic properties, including higher electrical resistivity, lower iron loss, higher permeability, and near zero magnetostriction. However, Fe-6.5wt%Si sheet is difficult to produce using traditional manufacturing processes as the high silicon content favors the formation of ordered phases that embrittle the material. Fortunately, these ordered phases can be suppressed if the alloy is cooled fast enough from a high temperature kinetically trapping the disordered solid solution or amorphous state. Planar flow casting is known for its rapid solidification rate. In order to consider it as a viable method to manufacture ductile Fe-6.5wt%Si sheets, the effect of cooling rate on physical properties of Fe-6.5wt%Si alloy are systematically investigated. In this work, various cooling rates are achieved by changing melt-spin wheel speeds, which significantly affect the solidification temperature profile and have profound effects on ordering, microstructures, textures, hardness, and magnetic properties. High cooling rates result in refined grains, reduced ordering, enhanced <100> out of the plane texture, decreased hardness, and increased coercivity. This study demonstrates a critical cooling rate at ~1.7 × 10 5 K/s, corresponding to a tangential wheel speed of 5-7 m/s, below which the hardness significantly increases in agreement with the sudden increase of the ordered phases that causes the material embrittlement.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Elemental segregation to lattice defects in the CrMnFeCoNi high-entropy alloy during high temperature exposures

The influence of small plastic pre-strains on the elevated-temperature stability and microstructure of the equiatomic CrMnFeCoNi FCC solid solution is investigated. Particular attention is given to whether any of the alloy elements segregate to individual dislocations. To that end, CrMnFeCoNi samples were first deformed in tension at room temperature to plastic strains of 0.2 and 2.3%, and subsequently annealed at 973 K for 800 hours. The pre-strains activated planar slip of 1/2<110>-type dislocations on {111}-type glide planes. Interactions of this planar slip with special Σ3 grain boundaries formed a large number of dislocation segments with a <110>-type crystallographic orientation suitable for a credible end-on analysis of dislocation cores in HR-STEM. The cores of the 1/2<110> dislocations pushed up against the investigated grain boundaries were found to be close to the compact configuration. Within the sensitivity of the Super-X EDS mapping, no concentration gradient was detected near dislocations that would indicate enrichment at dislocation cores of any of the elemental constituents of the alloy after the pre-deformation and annealing. However, a Cr-rich tetragonal sigma phase nucleated and grew at grain boundary triple junctions during this anneal, processes that were not accelerated by the enhanced dislocation density present after pre-strain. A clear chromium gradient was observed in the Cr-depleted zones near grain boundaries suggesting that Cr transport occurred by relatively slow diffusion from the bulk to the grain boundaries and then by relatively fast diffusion along the grain boundaries to the precipitates. Accompanying the Cr depletion near grain boundaries is a simultaneous Ni and Mn enrichment, which promotes formation of the L1 0 NiMn phase that is observed on the grain boundaries after prolonged annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High Density of Strong yet Deformable Intermetallic Nanorods Leads to an Excellent Room Temperature Strength-Ductility Combination in a High Entropy Alloy

This paper introduces a new microstructural template for high entropy alloys (HEAs), where the face centered cubic (FCC) complex concentrated solid solution is reinforced with a high density of strong, yet deformable, nanorods of an ordered multi-component intermetallic L12 compound. Thermodynamic modeling has been employed to design this HEA with a large L12 volume fraction. Thermo-mechanical processing by isothermal annealing of the conventionally processed bulk cold-rolled alloy directly at precipitation temperatures, has been applied to produce a high density of uniformly distributed L12 nanorods within refined FCC grains, resulting from concomitant recrystallization and discontinuous precipitation processes. The nanorod morphology of the discontinuous L12 product has been established from three-dimensional atom probe tomography. The refined grains result in a complete coverage of the microstructure with discontinuously precipitated intermetallic nanorods. This nanorod strengthened HEA exhibits an exceptionally high room temperature yield strength of ~1630 MPa, good tensile ductility of ~15%, and an ultimate tensile strength of ~1720 MPa. Furthermore, a single L12 phase alloy, melted based on the precipitate composition in the two-phase FCC + L12 HEA, exhibits very high compressive deformability and strain hardenability, unusual for ordered intermetallic compounds. These results open a new strategy for design of fine-grained microstructures strengthened via ordered intermetallic phases, exploiting the beneficial effects of discontinuous precipitation, for achieving very high room temperature tensile strengths while maintaining good ductility.

Gwalani, Bharat↗
DOE OSTI2021

Enhanced work hardening from oxygen-stabilized ω precipitates in an aged metastable β Ti-Nb alloy

High levels of oxygen in solid solution in Ti alloys are considered detrimental to mechanical properties because of embrittlement concerns. In metastable β titanium alloys, the formation of isothermal ω precipitates is also known to cause severe embrittlement and ductility reduction. However, oxygen has been shown to partition to the ω phase during ageing, and this partitioning behavior may potentially impact ω’s mechanical contribution. Using micropillar compression, we compared the deformation behavior of Ti-20Nb (at. %) with oxygen-stabilized ω precipitates to the behavior of oxygen-free specimens. The oxygen-stabilized microstructures showed increased compressive yield strength and enhanced work hardening behavior compared to oxygen-free specimens. In the absence of oxygen, the compressed pillars showed slip band formation and catastrophic failure, and transmission electron microscopy imaging revealed that ω precipitates were sheared within the continuous deformation channels resulting in slip localization. In contrast, oxygen-stabilized ω precipitates were harder to shear and the formation of continuous deformation channels was suppressed during compression, leading to improved work hardening behavior up to 15% strain. Furthermore, this counter-intuitive role of oxygen may offer design strategies to address the significant embrittlement and loss of ductility observed for ω-strengthened β Ti alloys without oxygen and avenues to expand the use of β Ti alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2021

On the origin of internal obstacles to dislocation glide in single-phase NiFe random alloys

Over the past decade, a new class of unconventional alloys, where several constitutive elements are presented in close to equal concentrations, is considered as promising structural materials in many applications. Properties and behavior of many concentrated solid solution alloys (CSSAs) under different conditions, including mechanical loading, differs from that of conventional alloys and has been the subject of intensive studies by different techniques. A key feature of these materials is that there is no clear distinction between solute and solvent species of atoms, which is the conventional approach to considering dislocation motion in alloys. To understand this regime, we have recently reported on the glide of a screw dislocation glide in a simple equiatomic NiFe alloy and reported the two-mode character. At low applied stress, the dislocation motion is similar to a glide through a field of obstacles. In this work, we report the results of a detailed study on the nature of these internal obstacles. We demonstrate that these are not conventional localized “obstacles” but is the result of significantly different energies of instantaneous dislocation configurations over the alloy bulk. The strong pinning positions are associated with composition changes in the partial dislocation cores, while observing no significant composition changes along the stacking faults. Local energies can vary significantly, as demonstrated using simulations of short-periodicity dislocation lines. Therefore, the critical stress to move a dislocation under such conditions is not a constant Peierls stress but represents a wide spectrum of barriers between different non-straight valleys that the dislocation line accommodates in the bulk at particular stress/strain conditions.

36 MATERIALS SCIENCE↗