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Plastic deformation of crystalline materials with isotropic particle attractions proceeds by the creation and migration of dislocations under the influence of external forces. If dislocations are produced and migrated under the action of local forces, then material shape change can occur without the application of surface forces. We investigate how particles with variable diameters can be embedded in colloidal monolayers to produce dislocations on demand. We find in simulation that when embedded clusters of variable diameter particles are taken through multiple cycles of swelling and shrinking, large cumulative plastic slip is produced by the creation and biased motion of dislocation pairs in the solid for embedded clusters of particular geometries. In this way, dislocations emitted by these clusters (biased “dislocation emitters”) can be used to reshape colloidal matter. Our results are also applicable to larger-scale swarms of robotic particles that organize into dense ordered two-dimensional (2D) arrangements. We conclude with a discussion of how dislocations fulfill for colloids the role sought by “metamodules” in lattice robotics research and show how successive applications of shear as a unit operation can produce shape change through slicing and swirling.

Single and dual-beam self-ion irradiations were performed at 500 °C on ultra-high purity Fe14%Cr alloy to ~0.33 displacements-per-atom (dpa), and 0 or 3030 atomic-parts-per-million (appm) helium/dpa, respectively. Using transmission electron microscopy, we reveal that helium can drastically modify the dislocation loop Burgers vector in Fe-Cr alloys. Helium co-implantation caused complete disappearance of a/2 type dislocation loops, and the microstructure consisted of only a loops. Conversely, a/2 type loops were predominant without He co-implantation. The total loop density remained largely unaffected. The results strikingly contrast literature asserting that helium stabilizes a/2 type loops in bcc Fe alloys, based on low temperature irradiations. Collectively analyzing the results with literature suggests that the small positive interaction between helium and self-interstitial atoms (SIA) in Fe, predicted by atomistic simulations, maybe insufficient to holistically explain the dislocation loop microstructure development in presence of helium. Helium-SIA positive binding inadvertently implies elevated a/2 loop fraction and higher loop densities that the present results contradict. Helium induced high cavity density causing a preferential loss of highly glissile clusters, leaving the matrix saturated with type clusters is proposed as a potential mechanism. Further, the in-situ irradiations combined with Burgers vector analysis strengthened the evidence of Cr-induced dislocation loop mobility reduction that appears to stabilize the a/2 type loops and causes higher loop densities in Fe-Cr alloys.

We show here how density functional theory calculations can be used to predict the temperatureand orientation-dependence of the yield stress of body-centered cubic (BCC) metals in the thermallyactivated regime where plasticity is governed by the glide of screw dislocations with a 1/2 Burgers vector. Our numerical model incorporates non-Schmid effects, both the twinning/antitwinning asymmetry and non-glide effects, characterized through ab initio calculations on straight dislocations. The model uses the stress-dependence of the kink-pair nucleation enthalpy predicted by a line tension model also fully parameterized on ab initio calculations. The methodology is illustrated here on BCC tungsten but is applicable to all BCC metals. Comparison with experimental data allows to highlight both the successes and remaining limitations of our modeling approach., Comptes Rendus Physique, Centre Mersenne, In press

We consider non-linear plane gravitational waves as propagating space-time defects, and construct the Burgers vector of the waves. In the context of classical continuum systems, the Burgers vector is a measure of the deformation of the medium, and at a microscopic (atomic) scale, it is a naturally quantized object. One purpose of the present article is ultimately to probe an alternative way on how to quantize plane gravitational waves., Comment: 18 pages, 5 figures, published in the Eur. Phys. J. C

The microscopic mechanism by which amorphous solids yield plastically under an externally applied stress or deformation has remained elusive in spite of enormous research activity in recent years. Most approaches have attempted to identify atomic-scale structural "defects" or spatio-temporal correlations in the undeformed glass that may trigger plastic instability. In contrast, here we show that the topological defects which correlate with plastic instability can be identified, not in the static structure of the glass, but rather in the nonaffine displacement field under deformation. These dislocation-like topological defects (DTDs) can be quantitatively characterized in terms of Burgers circuits (and the resulting Burgers vectors) which are constructed on the microscopic nonaffine displacement field. We demonstrate that (i) DTDs are the manifestation of incompatibility of deformation in glasses as a result of violation of Cauchy-Born rules (nonaffinity); (ii) the resulting average Burgers vector displays peaks in correspondence of major plastic events, including a spectacular non-local peak at the yielding transition, which results from self-organization into shear bands due to the attractive interaction between anti-parallel DTDs; (iii) application of Schmid's law to the DTDs leads to prediction of shear bands at 45 degrees for uniaxial deformations, as widely observed in experiments and simulations., Comment: v2: matching the published version

Nickel is widely used as a fcc model material to obtain insight into fundamental mechanisms of radiation damage. This work presents irradiation of high-purity nickel using self-ions at 450 °C and fine analysis of dislocation loops in specimens prepared by Focus Ion Beam using Transmission Electron Microscopy. For the first time to our knowledge, an inversion of loop nature (vacancy-type in irradiated zones v.s. interstitial-type in unirradiated zones) and a change of loop Burgers vector (1/3 and 1/2 loops v.s. only 1/2 loops) is identified along the implantation direction in irradiated nickel. This change may be attributed to the formation of interstitial 〈110〉 crowdions and their long-range one-dimension migration. A defect-free layer related to the annihilation of vacancy defects by injected atoms is detected. . It allows the identification of the injection peak which is uncommon for self-ion irradiated specimens and validates the damage calculations.

The structure and thermal boundary conductance of the wurtzite GaN/AlN (0001) interface are investigated using molecular dynamics simulation. Simulation results with three different empirical interatomic potentials have produced similar misfit dislocation networks and dislocation core structures. Specifically, the misfit dislocation network at the GaN/AlN interface is found to consist of pure edge dislocations with a Burgers vector of 1/3(1 (2) over bar 10) and the misfit dislocation core has an eight-atom ring structure. Although different interatomic potentials lead to different dislocation properties and thermal conductance values, all have demonstrated a significant effect of misfit dislocations on the thermal boundary conductance of the GaN/AlN (0001) interface. Published under an exclusive license by AIP Publishing.

The effect of neutron irradiation on the microstructure of EUROFER-ODS alloy reinforced with an addition of 0.5% Y2O3 was analyzed by transmission electron microscopy. The irradiation of up to 16.2 dpa damage dose at 300°C and 400°C was performed in Petten High Flux Reactor. This study focuses on the imaging, identification, and quantitative analysis of interstitial loops and voids located on ODS particles. The nano-sized loops and point defects with b½〈111〉 Burgers vectors are preferentially located near structural defects such as the line dislocations or impurities in the material irradiated at 300°C. Homogeneously distributed loops having Burgers vectors of b½〈111〉 and b〈100〉 types were found in the material irradiated at 400°C. The obtained quantitative data on radiation-induced defects such as size, number density and relaxation volume were compared with EUROFER97 irradiated at the same conditions. It was found that the occurrence of radiation induced defects depends on the local number density and the size distribution of the ODS particles and not only on the irradiation damage and temperature.

During service of gas turbine engines, high cycle fatigue of titanium is a leading cause of component failure highlighting the need for better understanding of the crack initiation mechanism to predict initiation sites. In this study, the relationship between plastic slip activity and fatigue crack initiation was investigated in a near-α titanium alloy using cyclic four-point bending at up to 90% of the proof stress. The finding from surface characterization show that plasticity at such low stress levels was dominated by the basal slip and two types of cracking were seen parallel to basal slip traces. Detailed 3D analysis of both crack types highlighted out-of-plane Burgers vector activity for the observed basal slip associated with crack initiation, consistent with the classic surface roughening mechanism. The transgranular crack initiation was accompanied by the formation of crystallographic facet which was identified to be 6° away from the basal plane due to additional prismatic slip activation during multi-step crack formation. The intergranular crack facet along the boundary between primary α grain pairs, which have their c-axes aligned nearly parallel to each other but with mis-aligned prismatic planes, was formed by an easy cleavage in one step along the basal plane. Statistical evaluation demonstrated that grains combining a moderately high Schmid factor for basal slip, high resolved tensile stress along the c-axis and the Burgers vector being oriented strongly out-of-surface plane favoured transgranular crack initiation. Based on those observations a new parameter involving these three geometrical factors was developed to predict transgranular surface crack initiation sites.

The Ni-base superalloy 718 is the most widely used material for turbomachinery in the aerospace industry and land-based turbines. Although the relationship between processing and the resulting properties is well known, an understanding of the specific deformation mechanisms activated across its application temperature range is required to create more mechanistically accurate property models. Direct atomic-scale imaging observations with high angle annular dark-field scanning transmission electron microscopy, complemented by phase-field modeling informed by generalized stacking fault surface calculations using density functional theory, were employed to understand the shear process of ${\gamma}''$ and ${\gamma}'/{\gamma}''$ co-precipitates after 1 \% macroscopic strain at lower temperature (ambient and $427 {\deg}C$). Experimentally, intrinsic stacking faults were observed in the ${\gamma}''$, whereas the ${\gamma}'$ was found to exhibit anti-phase boundaries or superlattice intrinsic stacking faults. Additionally, the atomically flat ${\gamma}'/{\gamma}''$ interfaces in the co-precipitates were found to exhibit offsets after shearing, which can be used as tracers for the deformation events. Phase-field modeling shows that the developing fault-structure is dependent on the direction of the Burgers vector of the $a/2 \langle110\rangle$ matrix dislocation (or dislocation group) due to the lower crystal symmetry of the ${\gamma''}$ phase. The interplay between ${\gamma}'$ and ${\gamma}''$ phases results in unique deformation pathways of the co-precipitate and increases the shear resistance. Consistent with the experimental observations, the simulation results indicate that complex shearing mechanisms are active in the low-temperature deformation regime and that multiple $a/2 \langle110\rangle$ dislocations of non-parallel Burgers vectors may be active on the same slip plane., Comment: 32 pages, 17+6 figures, submitted to Acta Materiallia

The origin of twinning during the Czochralski (CZ) growth of 36°-RY lithium tantalate (LiTaO3) single crystals is examined, and it is shown that lineages composed of dislocation arrays act as an initiation site for twinning. Two types of lineages expand roughly along three different {12¯10} planes and two different {11¯00} planes. The former lineages and some latter lineages are composed of two types of mixed-dislocations with different Burgers vectors, while the other lineages are composed of only one type of edge-dislocation. All the dislocations have the Burgers vector of ⟨12¯10⟩ type with the compression side at the +Z side. Twin lamellae on {101¯2} are generated at a lineage during the CZ growth. We have hypothesized that dislocations in the lineage with b = 1/3⟨12¯10⟩ change their extension direction along a slip plane of {101¯2}, and they dissociate into pairs of partial dislocations with b = 1/6⟨22¯01⟩and 1/6⟨02¯21¯⟩ forming twin lamellae on {101¯2}.

In this paper, the geometric dislocation density tensor and Burgers vector are studied using an elastic–plastic decomposition of Laplace stretch $$\varvec{\mathcal {U}}$$ . The Laplace stretch arises from a $$\mathbf {QR}$$ decomposition of the deformation gradient and is very useful, as one can directly and unambiguously measure its components by performing experiments. The geometric dislocation density tensor $${\tilde{\mathbf {G}}}$$ is obtained using the classical argument of failure of a Burgers circuit in a suitable configuration $$\tilde{\kappa }_p$$ where the deformation of a body is solely due to the movement of dislocations. The geometric features of space $$\tilde{\kappa }_p$$ are explored. It is shown that the derived geometric dislocation tensor is related to the torsion of $$\tilde{\kappa }_p$$ , which serves as a measure of incompatibility in this space. Additionally, $${\tilde{\mathbf {G}}}$$ vanishes only when the space $$\tilde{\kappa }_p$$ is compatible. A balance law for geometric dislocations is derived taking into account the effect of the dislocation flux and source dislocations. The physical meaning of the plastic Laplace stretch, and consequently, of the derived geometric dislocation tensor proves to be particularly useful in the classification of dislocations. Finally, the significance of the dislocation density tensor is discussed. The derived geometric dislocation density tensor could be specifically useful in developing a strain-gradient and size-dependent theory of plasticity.

We modified the conventional etching-optical method to measure dislocation direction in a KDP crystal. As burgers vector of dislocation in the KDP crystal must match the minimum periodic vector of the crystal lattice, we suggest that dislocations with a burgers vector of [101], [102] and [103] exist. Atomic force microscopy was employed to characterize the morphology of growth spirals on the hillock of (101) faces. Multi-spirals consisting of more than two element steps with a height of 0.5 nm which is equal to (101) face interplanar distances were observed. We propose the multi-spiral structure is determined by the burgers vector of the corresponding dislocation, and constructed a geometric model of the crystal with screw dislocation to derive the relationship. Growth spirals on the (101) face present a particular triangular morphology and we proved that the triangle structure is formed by connected steps in the 1/2[111] and [010] direction. Micropipes form when the magnitude of the dislocation's burgers vector exceeds 1 nm, as predicted by BCF theory. Interaction between dislocations was observed also.

In a recent experimental study of indentation creep, the strain rate sensitivity (SRS) and activation volume v* have been noticed to be dependent on the indentation depth or loading force for face-centered cubic materials. Although several possible interpretations have been proposed, the fundamental mechanism is still not well addressed. In this work, a scaling law is proposed for the indentation depth or loading force-dependent SRS. Moreover, v* is indicated to scale with hardness H by the relation &part, ln(v*/b3)/&part, lnH=&minus, 2 with the Burgers vector b. We show that this size effect of SRS and activation volume can mainly be ascribed to the evolution of geometrically necessary dislocations during the creep process. By comparing the theoretical results with different sets of reported experimental data, the proposed law is verified and a good agreement is achieved.

The interactions between edge dislocations and -axis symmetric tilt grain boundaries (GBs) in copper have been investigated by atomistic simulations. Molecular dynamics simulations and the nudged elastic band method were implemented to investigate the atomistic reaction between the two defects and the activation energy required to trigger such an event in various stress or strain states. The results showed that although different GBs were introduced, the most common scenarios were dislocation absorption into the GB and transmission through the GB. In most cases, the leading partial dislocation was absorbed into the GB once these two crystallographic defects impacted. In contrast, the trailing partial dislocation played a crucial role in determination of the threshold reaction stress. From transition state theory, the reaction energy barriers showed a linear relationship with the resolved shear stress or strain state. The constant activation volume was in the range 22-53b3, where b is the Burgers vector. Furthermore, the corresponding strain rate sensitivities obtained through the activation volumes showed good agreement with the experiment data.

Discrete dislocation plasticity is a modeling technique that treats plasticity as the collective motion of dislocations. The dislocations are described through their elastic Volterra fields, outside of a cylindrical core region, with a few Burgers vectors of diameter. The contribution of the core fields to the dislocation dynamics is neglected, because it is assumed that their range is too short to be of influence. The aim of this work is to assess the validity of this assumption. In recent ab-initio studies it has been demonstrated that the dislocation core fields are significant up to a distance of ten Burgers vector from the dislocation line. This is a longer range influence than expected and can give rise to changes in the evolving dislocation structure and in the overall response of a plastically deforming body. It is indeed experimentally observed that dislocations pile up against strong interfaces, and that the spacing between dislocations at the front of these pile-ups can be less than ten Burgers vectors. In this work, 2-D discrete dislocation plasticity simulations are performed to investigate the effect of core fields on edge dislocation interactions. The results of the simulations, which include core fields for the first time, show indeed that dislocations that are very closely spaced experience additional glide or climb due to core fields. The effect is however negligible when compared to glide and climb due to Volterra fields or due to the external load.

Slip activity in body-centered cubic chromium is modeled by means of ab initio calculation of screw dislocations core properties and Peierls potential. As dislocations having 1 / 2 〈 111 〉 Burgers vector and also 〈 100 〉 , both gliding in { 110 } crystallographic planes have been reported experimentally, both screw dislocations are modeled. A generalized yield criterion incorporating physical ingredients necessary to account for deviations from the Schmid law is obtained for 〈 111 〉 { 110 } and 〈 100 〉 { 110 } slip systems. We report a broad range of crystal orientations for which 〈 100 〉 screw dislocations are easier to activate than the conventional 1 / 2 〈 111 〉 in tension and compression. These results hold for both the non-magnetic and antiferromagnetic phases of body-centered cubic chromium, with only a marginal effect of magnetism.

Preferred defect cluster configurations and diffusion behavior are calculated with the recently published BMD19 interatomic potential for α -zirconium and compared with results calculated from the M07 potentials. Both potentials predict that small SIA clusters form configurations contained entirely within a single basal plane, while large SIA clusters form perfect dislocation loops on first-order prismatic planes with Burgers vector b ⇀ = 1 3 11 2 ¯ 0 . The M07 potentials predict stable void formation for vacancy clusters while the BMD19 potential accurately indicates a preference for planar configurations on either first-order or second-order prismatic planes. Small basal vacancy clusters are found to form faulted pyramidal structures and only transform to faulted c-loops at larger sizes. In evaluating the defect diffusivity, single vacancies and interstitials are both found to exhibit anisotropic diffusion within the basal-plane. Small SIA clusters are found to migrate exclusively in 2-D within a single basal plane with the BMD19 potential but migrate in 3-D with the M07 #3 potential. Small vacancy clusters are either unstable or immobile with the M07 #3 and #2 potentials, while these clusters exhibit appreciable mobility either along the c-axis or in a quasi-isotropic manner with the BMD19 potential. The apparent difference in the diffusional anisotropies of defect clusters, rather than point defects, could be a critical component for improving predictive capabilities for mesoscale modeling of microstructural evolution in α-zirconium.

Shear stress relaxation through the motion of multiple edge dislocations in a periodic cell is studied by molecular dynamics and discrete dislocation methods. In both methods, we consider systems with an initial edge dislocation on the parallel slip planes. The initial shear strain is applied to the system along the Burgers vector of the dislocations. The velocity profile for a single edge dislocation fitted from a molecular dynamics (Bryukhanov, 2020) is used as the input to discrete dislocation dynamics. The dependence of shear stress, plastic strain, and plastic strain rate on time are analyzed. We show that when dislocations are sufficiently far from each other, relaxation occurs due to dislocation motion, and dislocation velocity can exceed the anisotropic speed of sound. If the dislocations are closer together, relaxation is due to the growth of stacking faults. We find that the stress at which the stress relaxation mechanism changes decreases with increasing dislocation density. Stress relaxation in a Cu–Ni solid solution occurs faster than in pure Cu due to a higher dislocation velocity in the high-velocity regime. However, the shear stress at which nickel atoms increase the plastic strain rate increases with an increase in dislocation density. The dependence of the relaxation time on the dislocation density obtained in discrete dislocation simulations is approximated using the power law. The elastic interaction between dislocations reduces the exponent of the power law from 1 / ρ to approximately 1 / ρ 0 . 8 for both pure Cu and Cu–Ni solid solutions.

Vacuum diffusion bonding (VDB)-prepared 304 austenite stainless steel (SS)/Q235 carbon steel (CS) clad plates were the focus of this study. Specifically, the metallurgically bonded interfaces, which are known to have good mechanical properties, were investigated. The microstructures of the interfaces were extensively investigated using transmission electron microscopy (TEM). The characterization results revealed the existence of annealing twins and lath martensite precipitates at the interface; the high strength and plasticity at the interface were determined to be attributed to these features. In addition, the distribution and Burgers vector of dislocations at the ferrite–austenite interfaces were investigated by using two-beam method of TEM electron diffraction contrast image (EDCI) technology and high-resolution TEM imaging. As a result, the coordination mechanisms at the ferrite–austenite interfaces during the deformation of the SS/CS clad plates were clarified; the observations include: (1) the perfect dislocation with the Burgers vector a 2 ⟨ 111 ⟩ in the ferrite moved across the interface and formed a perfect dislocation with the Burgers vector a 2 ⟨ 110 ⟩ in the austenite; (2) the ferrite lattice was joined to the perfect dislocation with the Burgers vector a 2 ⟨ 110 ⟩ in the austenite; and (3) the ferrite lattice continuously extended across the interface, and was connected to the austenite lattice. According to the results on the Burgers vector of dislocations, two types of dislocation reactions occurred at the ferrite–austenite interfaces during the deformation. Lastly, the transfer matrix of the orientation relationship (OR) between austenite and ferrite was calculated. The results revealed that the OR differed from that of the conventional OR between body-centered cubic and face-centered cubic structures; thus, it can be concluded that the preparation of SS/CS clad plates via VDB technology may lead to the formation of a unique OR between ferrite and austenite.

Transmission electron microscopy (TEM) imaging relies on high energy electrons for atomic scale resolution, however, the electrons themselves interact with and may alter the material being imaged. Using an in situ TEM MEMS-based nanomechanical testing technique, the effect of the electron beam (e-beam) on the deformation behavior of nanocrystalline Al and ultrafine-grained Au is investigated and quantified. We show that the e-beam enhances plastic deformation, leading to an increase in plastic strain rate and a decrease in true activation volume V* in Al (28 to 21b3, with b being the Burgers vector length). The e-beam has a much weaker effect on Au. The e-beam effect is not caused by knock-on damage, but rather an effective temperature increase due to additional atomic fluctuations provided by the e-beam. The effective temperature increase is larger for Al than Au. This e-beam effect does not change the deformation mechanisms, but instead accelerates the stress-driven, thermally activated plastic deformation. These experiments provide insight into the effects of the e-beam on plastic deformation in different metals and underscore the importance of understanding and quantifying these effects for proper interpretation of measured mechanical properties during in situ TEM experiments.

Depending on the stress state, magnesium alloys can display tensile and/or compression twinning. The present letter exploits bimodal textures in alloy Mg-6.5Zn to examine how age hardening impacts on the two different twin types. We found that tensile twinning is stimulated by precipitates (i.e. higher twin volume fractions are seen at an equivalent plastic strain) whereas compression twinning is suppressed by precipitates (i.e. lower twin volume fractions are seen at an equivalent plastic strain). The difference is rationalized in terms of a lower twin surface energy and a larger twinning dislocation Burgers vector in compression twins. The larger Burgers vector renders compression twinning dislocations more resistant to bowing. The surface energy effect is more subtle. All else constant, twins with lower surface energies can propagate with a lower total content of twinning dislocations. Thus, a higher applied stress is required to attain the Peach-Koehler force needed to bypass precipitates.

Superior mechanical response of twinnable materials fundamentally arises from an elevation of Critical Resolved Shear Stresses (CRSS) due to Dislocation-Twin Boundary (D-TB) reactions. These reactions exhibit rich variety with several possible outcomes and exhibit complex dependence on microstructural properties, causing state-of-the-art models to adopt a case-by-case simulation of each reaction relying on empirical potentials or twin-interaction parameters. We develop an analytical “Evolving Dislocation Core” (EDC) model devoid of empiricism, capable of predicting the CRSS-elevation for any reaction, given the microstructural properties (elastic constants, twin crystallography, etc.). The approach is fundamentally rooted in energy-minimization within a fully-anisotropic framework revealing the evolution of dislocation cores with progression of the reaction. The core-structure of complex dislocations (e.g. stair-rod) in the reaction is proposed, for the first time in literature, as a non-planar composite of disregistries distributed on slip and twin planes. The model is applied to multiple slip-incorporation reactions in several Face-Centered-Cubic (FCC) materials (Pb, Ag, Cu, Ni-Co alloys and Ni-Ti alloys and high-entropy alloy FeNiCoCrMn). The predicted CRSS-elevations show agreement with atomistic simulations (Ni) and experiment (FeNiCoCrMn). The model further establishes a strong correlation of the elevation with unstable stacking/twinning fault energy and the magnitude of the sessile dislocation's Burgers vector, while revealing poor correlation with the stable intrinsic stacking fault energy which is a common benchmark. Thus the analytical EDC model developed in this study advances understanding of slip-twin interactions on multiple fronts while serving as an effective predictive model for CRSS-elevation instrumental in materials design.

Multiphasic intermetallic materials are attractive candidates for functional applications where the constituent phases alone do not meet the property targets. The interfaces at the phase boundaries in these materials are central to their macroscopic properties, with the details of the atomic structure underpinning local thermomechanical, electrical, and magnetic behavior. Here, we characterize the interface structure in the biphasic Nb-Co-Sn system consisting of $\mathrm{Nb}{\mathrm{Co}}_{2}\mathrm{Sn}$ full Heusler (FH) precipitates embedded in a NbCoSn half Heusler (HH) matrix, which exhibits semicoherent interfaces with a 3.3% lattice parameter misfit that determines the constitution of the FH/HH interface on the nanometer scale. We use detailed transmission electron microscopy (TEM) and atomistic calculations to precisely determine the dislocation content and structure at the semicoherent interface, which modulates the strain fields in a semiregular pattern. We find that the interface forms regularly spaced paired partial dislocations with a joint Burgers vector of $a/2\ensuremath{\langle}110\ensuremath{\rangle}$, favored by misfit energy relief and chemical ordering. The interface exhibits numerous interface steps (disconnections) which in turn determine the precipitate morphology. Overall, the two phases show full coherency except in the vicinity of the misfit dislocation cores located every 11 nm, leading to a modulated strain field parallel to the interface, and no long-range strain fields as the interfacial dislocations accommodate the misfit strain.