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This paper introduces a method for high-resolution lattice image reconstruction and dislocation analysis based on diffraction extinction. The approach primarily involves locating extinction spots in the Fourier transform spectrum (reciprocal space) and constructing corresponding diffraction wave functions. By the coherent combination of diffraction and transmission waves, the lattice image of the extinction planes is reconstructed. This lattice image is then used for dislocation localization, enabling the observation and analysis of crystal planes that exhibit electron diffraction extinction effects and atomic jump arrangements during high-resolution transmission electron microscopy (HRTEM) characterization. Furthermore, due to the method's effectiveness in localizing dislocations, it offers a unique advantage when analyzing high-resolution images with relatively poor quality. The feasibility of this method is theoretically demonstrated in this paper. Additionally, the method was successfully applied to observed edge dislocations, such as 1 / 6 [ 21 1 − ] , 1 / 6 [ 2 − 1 1 − ] , and 1 / 2 [ 0 1 − 1 ] , which are not easily observable in conventional HRTEM characterization processes, in electro-deposited Cu thin films. The Burgers vectors were determined. Moreover, this paper also attempted to observe screw dislocations that are challenging to observe in high-resolution transmission electron microscopy. By shifting a pair of diffraction extinction spots and superimposing the reconstructed images before and after the shift, screw dislocations with a Burgers vector of 1 / 2 [ 01 1 − ] were successfully observed in electro-deposited Cu thin films. [ABSTRACT FROM AUTHOR]

After neutron irradiation, RAFM steel will produce two types of interstitial dislocation loops (1/2〈111〉 loop and 〈100〉 loop), resulting in radiation hardening and embrittlement after long service. And different types of dislocation loops may lead to different hardening phenomena. However, the formation and transformation processes of different types of dislocation loops are still obscure. Therefore, it is of great significance to clarify the formation and transformation processes of different types of dislocation loops for the evolution of materials’ microstructures and prediction of their properties. In this paper, we presented an improved parallel replica method (PRD), which improved the application of the original PRD method in dislocation loop evolution simulation. Through analyzing the mechanism characteristics of dislocation loop transition and extracting Burgers vector, the improved PRD method accurately identified the state of dislocation loops, and then calculated the simulation of accelerated transition process from 〈100〉 loop to 1/2〈111〉 loop. By combing the dislocation extraction algorithm in OVITO, the synchronous analysis of Burgers vector in the simulation process was realized. During the dislocation loop transforms, its habit plane will change and eventually affect the change of Burgers vector. So Burgers vector was used to redefine the adjudication for transition events in the original PRD method. We adjudicated whether the system undergoes a transition event, based on the existence of 1/2 〈111〉 Burgers vector in the simulated system and whether the proportion of 1/2〈111〉 Burgers vector increases. With such improvements, it would help us avoid lengthy cyclic iterations at some metastable state in our simulation and realize the simulation of accelerated transition phenomenon of 〈100〉 loop to 1/2〈111〉 loop. Finally, numerical experiments were performed to evaluate the effect of our work. The results show that the improved PRD algorithm successfully simulate the changing process of small size 〈100〉 loop to 1/2〈111〉 loop at 1 000 K, and the transition time is faster than the traditional molecular dynamics method. We also observe the coexistence phenomenon of 〈100〉 dislocation segments and 1/2〈111〉 dislocation segments in large size 〈100〉 loop simulation. So far as to the case of 〈100〉 loop with Ni solute elements, it is found that the complete transition to 1/2〈111〉 dislocation loop is happened. In addition, the accuracy of program simulation was verified, and the parallel performance were also analyzed and evaluated in this paper. We achieve about 90% parallel efficiency in the parallel calculating test, which is found much higher than the original PRD method. Moreover, our program has well-fined scalability, so it can be well expanded for the large-scale parallel calculation.

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This paper introduces a method for high-resolution lattice image reconstruction and dislocation analysis based on diffraction extinction. The approach primarily involves locating extinction spots in the Fourier transform spectrum (reciprocal space) and constructing corresponding diffraction wave functions. By the coherent combination of diffraction and transmission waves, the lattice image of the extinction planes is reconstructed. This lattice image is then used for dislocation localization, enabling the observation and analysis of crystal planes that exhibit electron diffraction extinction effects and atomic jump arrangements during high-resolution transmission electron microscopy (HRTEM) characterization. Furthermore, due to the method’s effectiveness in localizing dislocations, it offers a unique advantage when analyzing high-resolution images with relatively poor quality. The feasibility of this method is theoretically demonstrated in this paper. Additionally, the method was successfully applied to observed edge dislocations, such as 1/6[211−], 1/6[2−11−], and 1/2[01−1], which are not easily observable in conventional HRTEM characterization processes, in electro-deposited Cu thin films. The Burgers vectors were determined. Moreover, this paper also attempted to observe screw dislocations that are challenging to observe in high-resolution transmission electron microscopy. By shifting a pair of diffraction extinction spots and superimposing the reconstructed images before and after the shift, screw dislocations with a Burgers vector of 1/2[011−] were successfully observed in electro-deposited Cu thin films.

In this study, four Ti50-ZrVNbCr alloys were designed and prepared with the same valence electron concentration (VEC) value, and effects of atomic radius mismatch and Burgers vector magnitude on tensile properties were experimentally investigated. The results showed that multiple slip systems were activated in the alloys. With the increment of atomic radius mismatch and Burgers vector magnitude, the relative activity of {110}<111> slip mode decreased, and the relative activities of {112}<111> and {123}<111> slip modes increased. Atomic radius mismatch dominated the yield strength of the alloys by solid-solution strengthening. The reduction of lattice constant can lead to the increment of dislocation density that favors for increasing ductility. As lattice constant increased, dislocations gradually condensed in some slip-bands that could form shear bands, resulting in a localization of deformation and a stress concentration, which could easily lead to cracks on grain boundaries. • Four Ti50-ZrVNbCr alloys were prepared with a constant VEC value; • Roles of atomic radius mismatch and Burgers vector were addressed; • The relative activities of slip modes vary with radius mismatch and latticeconstant; • Burgers vector magnitude played a dominant role in strengthening these alloys; • Lattice constant dominated the ductility. [ABSTRACT FROM AUTHOR]

In this article, the microstructure and mechanical behavior of the Ti49.1Ni50.9 alloy with a high content of nickel in a coarse-grained state, obtained by quenching, ultrafine-grained (obtained through the equal-channel angular pressing (ECAP) method) and nanocrystalline (high pressure torsion (HPT) + annealing), were investigated using mechanical tensile tests at different temperatures. Mechanical tests at different strain rates for determining the parameter of strain rate sensitivity m were carried out. Analysis of m showed that with an increase in the test temperature, an increase in this parameter was observed for all studied states. In addition, this parameter was higher in the ultrafine-grained state than in the coarse-grained state. The activation deformation volume in the ultrafine-grained state was 2–3 times greater than in the coarse-grained state at similar tensile temperatures. Fractographic analysis of samples after mechanical tests was carried out. An increase in the test temperature led to a change in the nature of fracture from quasi-brittle–brittle (with small pits) at room temperature to ductile (with clear dimples) at elevated temperatures. Microstructural studies were carried out after the tensile tests at different temperatures, showing that at elevated test temperatures, the matrix was depleted in nickel with the formation of martensite twins. [ABSTRACT FROM AUTHOR]

A pseudodifferential operator is constructed that describes the stress field in an anisotropic medium caused by a dislocation with a variable Burgers vector. Under the assumption , analytical expressions for the energy of circular dislocations with a variable Burgers vector in an elastic medium with general anisotropy are obtained for the first time. It was found that in an isotropic medium the energy of formation of an edge dislocation and a slip dislocation is determined only by the uniform norm of the Burgers vector. [ABSTRACT FROM AUTHOR]

A carrot defect with a shallow pit has been detected in a 4H-SiC epitaxial wafer using mirror projection electron microscopy inspection. The origin of the carrot defect and the microstructure of the conversion point at the interface between the epitaxial layer and the substrate were investigated using transmission electron microscopy and high-resolution scanning transmission electron microscopy. We found that two types of threading edge dislocations (TEDs) in the substrate, with b = 1 / 3 2 ¯ 110 and b = 1 / 3 1 ¯ 1 ¯ 20 , generated the carrot defect with a shallow pit in the epitaxial layer. The two TEDs converted to basal plane dislocations (BPDs) at the conversion point. Furthermore, one of the two BPDs led to the pair generation of a threading dislocation running to the epi surface and four partial dislocations propagating on each basal plane. The other BPD joined one of the four partial dislocations at the conversion point; this merged dislocation was assumed to cause a prismatic stacking fault. [ABSTRACT FROM AUTHOR]

In this study, the structures of threading dislocations (TDs) in a 4H-SiC epilayer were directly characterised using large-angle convergent beam electron diffraction (LACBED) via transmission electron microscopy (TEM), by examining the splitting of reflections due to the presence of dislocation lines. Previously, X-ray topography (XRT) mapping in combination with ray-tracing simulations has been shown to be an efficient method for imaging and differentiating common TD types and variants in 4H-SiC. In this work, the validity of XRT-based results was verified by LACBED through direct evaluation and differentiation of the Burgers vectors and physical crystallographic features of all a threading edge, c threading screw, and c + a threading mixed dislocations variants. The LACBED results agreed with the XRT-based results with respect to TD type and variant. The screw-sense or half-plane orientation and Burgers vector determined from LACBED analysis for each TD were self-consistent. For the case of ⟨ a ⟩ -TEDs, atomic-resolution analysis of the core structure, through high-angle annular dark field scanning TEM, directly revealed two half-planes, each with a 1 3 1 1 ¯ 00 Burgers vector component, and the sum of these components was confirmed to be 1 3 11 2 ¯ 0 . Finally, an algorithm for efficient LACBED analysis of TDs in 4H-SiC was discussed. [ABSTRACT FROM AUTHOR]

Non-destructive characterization of crystalline defects in SiC wafers is important for manufacturing high-performance SiC power devices with high productivity. The present study shows that the edge component of the Burgers vector can be identified by birefringence imaging under conditions deviating slightly from the crossed-Nicols condition and by calculation of the in-plane shear stress distribution. It is also found that the combination of birefringence observation and X-ray topography allows the discrimination of the family of threading screw dislocations. The present results will further the understanding of the relationship between defect structure and the properties of SiC power devices. [Display omitted] • Birefringence imaging applied to SiC wafer defect analysis. • Edge-component of Burgers vector in SiC identified. • TSD families differentiated using lab-scale apparatus. • Detailed SiC defect analysis enhances power device performance. [ABSTRACT FROM AUTHOR]

In this article, the microstructure and mechanical behavior of the Ti49.1Ni50.9 alloy with a high content of nickel in a coarse-grained state, obtained by quenching, ultrafine-grained (obtained through the equal-channel angular pressing (ECAP) method) and nanocrystalline (high pressure torsion (HPT) + annealing), were investigated using mechanical tensile tests at different temperatures. Mechanical tests at different strain rates for determining the parameter of strain rate sensitivity m were carried out. Analysis of m showed that with an increase in the test temperature, an increase in this parameter was observed for all studied states. In addition, this parameter was higher in the ultrafine-grained state than in the coarse-grained state. The activation deformation volume in the ultrafine-grained state was 2–3 times greater than in the coarse-grained state at similar tensile temperatures. Fractographic analysis of samples after mechanical tests was carried out. An increase in the test temperature led to a change in the nature of fracture from quasi-brittle–brittle (with small pits) at room temperature to ductile (with clear dimples) at elevated temperatures. Microstructural studies were carried out after the tensile tests at different temperatures, showing that at elevated test temperatures, the matrix was depleted in nickel with the formation of martensite twins.

In this paper, we propose a canonical variational framework for rate-independent phenomenological geometrically linear gradient plasticity with plastic spin. The model combines the additive decomposition of the total distortion into non-symmetric elastic and plastic distortions, with a defect energy contribution taking account of the Burgers vector through a dependence only on the dislocation density tensor Curl p giving rise to a non-symmetric nonlocal backstress, and isotropic hardening response only depending on the accumulated equivalent plastic strain. The model is fully isotropic and satisfies linearized gauge invariance conditions, i.e., only true state variables appear. The model satisfies also the principle of maximum dissipation which allows to show existence for the weak formulation. For this result, a recently introduced Korn's inequality for incompatible tensor fields is necessary. Uniqueness is shown in the class of strong solutions. For vanishing energetic length scale, the model reduces to classical elasto-plasticity with symmetric plastic strain ε p and standard isotropic hardening. [ABSTRACT FROM AUTHOR]

Abstract The full lattice strain tensor and lattice rotations induced by a dislocation in pure tungsten were mapped using high-resolution transmission Kikuchi diffraction (HR-TKD) in a SEM. The HR-TKD measurement agrees very well with a forward calculation using an elastically isotropic model of the dislocation and its Burgers vector. Our results demonstrate that the spatial and angular resolution of HR-TKD in SEM is sufficiently high to resolve the details of lattice distortions near individual dislocations. This capability opens a number of new interesting opportunities, for example determining the Burgers vector of an unknown dislocation in a fast and straightforward way. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Refining grain size and adding alloying elements are two complementary approaches for enhancing the radiation tolerance of existing nuclear materials. Here, we present detailed in-situ irradiation research on defect evolution behavior and irradiation tolerance of ultrafine W-TiC alloys (thin foils) irradiated with 1 MeV Kr+2 at RT and 1073 K, and compare their overall performance to pure coarse grained tungsten. Loop Burgers vector was studied confirming the presence of <100> loops whose population increased at high temperature. Loop density, average loop area, and overall damage are reported as a function of irradiation dose revealing distinct defect evolution behavior from pure materials. The overall damage generally followed the average loop size trend, which decreased with time for both temperatures, but was higher at 1073 K and attributed to biased vacancy sink behavior of the TiC dispersoids evidenced by large vacancy clusters on their interfaces. By comparison, the overall loop and void damage in pure tungsten was larger by a factor of six and two, respectively. The improved irradiation damage resistance in the alloys is thus attributed to the effect of dispersoids in 1) the enhancement in annihilating defects and mutual defect recombination due to both dispersoids and a higher grain boundary density; 2) decreasing the loop mobility, causing shrinkage and annihilation of loop density, which was confirmed via in-situ video. Several mechanisms are illustrated to describe the performance of the complex alloy system. The results motivate further experimental and modeling research that aims to understand the many different phenomena occurring at different time scales. Graphical abstract Damage evolution behavior for pure W and ultrafine W-TiC alloy irradiated with 1 MeV Kr+2 at 1073 K. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: An important parameter of light-emitting heterostructures is their external quantum efficiency. However, another strict requirement for the structures used in fabricating blue and white light-emitting diodes is that the wavelength in the emission spectrum peak and its spread over the entire structure must be 460 ± 5 nm. This is explained primarily by the most frequently used white light-emitting diode design being based on crystals coated with a luminescent layer of a certain composition excited by blue emissions. Deviating from the specified spectral parameters of heterostructures strongly degrades the light and color characteristics of light-emitting diodes. In this work, we solve the problem of optimizing the design and way of growing the active region of an emitting structure consisting of a set of Ga1 - xInxN quantum wells and wider-gap GaN barriers with a certain wavelength in the emission spectrum peak. The variation in the critical thickness of the pseudomorphic layer in the Poisson ratio ranges of 0 to 0.2 for GaAlN and 0 to 0.4 for GaInN is calculated. The emission wavelength is determined by both the bulk Ga1 - xInxN band gap, which depends on the molar fraction of In in quantum wells, and the quantum well thickness in quantum-sized layers. It is found from the obtained dependences that to obtain the required wavelength of 460 nm in the emission spectrum peak, the Ga1 - xInxN layers must be around 10.3% indium and have a quantum well thickness of about 2.5 nm. The effect the In distribution profile in quantum wells has on the external quantum efficiency, the uniformity of the emission wavelength distribution in the spectral peak, and the emission power distribution over the structure is considered. The best results are obtained for a trapezoidal In distribution, since it ensures the narrowest emission wavelength spread in the spectral peak and the most uniform emission power distribution over the structure. Studying the effect the number of quantum wells has on the properties of a heterostructure shows that the maximum external quantum efficiency corresponds to 4 to 5 quantum wells. The highest emission wavelength uniformity in the spectral peak over the structure is obtained at 5 to 7 quantum wells. The optimum number of quantum wells in the active region of the heterostructure is found to be 5. [ABSTRACT FROM AUTHOR]

Abstract Pure iron was irradiated with 6.4 MeV Fe3+ ions at 300 °C to a displacement damage of 30 dpa at a nominal depth of 600 nm. Distinct microstructures were observed at different depth regions by transmission electron microscopy (TEM). In the range of 0–1.2 μm from the irradiation surface, dislocation loops tended to form ordered loop rafts with their habit plane on {100} , while in the range of 1.6–2.3 μm, both line-shaped dislocations and dislocation loops coexisted. Dislocation loops that formed the loop raft had an average size of 3.5 nm with the number density estimated to be 3.6 × 1023 m−3, considering all three variants of the Burgers vectors b = a 0 < 100 >. However, the dislocation loops in the range of 1.6–2.3 μm were with Burgers vectors, b = a 0 /2 < 111 >, and the number density was one order of magnitude lower. Graphical abstract Image 1 Highlights • Three distinct damaged zones in ion-irradiated pure Fe. • A well-developed dislocation loop raft was observed. • Loop raft has a 2–D distribution on habit plane of {100} with b = a 0 < 100 > • 100 > loops had an average size of 3.5 nm with number density of 3.6 × 1023 m−3. [ABSTRACT FROM AUTHOR]

Within the constitutive framework of second order plasticity, following [4,5], under the assumptions that the plastic distortion is not compatible, and the plastic connection is not compatible with the plastic distortion and has metric property, we define the lattice defects in crystalline elasto-plastic materials. The curl of plastic distortion, which defines the Burgers vector, is a measure of the dislocations. The disclination is characterized in terms of the second order tensor, which enters the expression of the plastic connection and generates the Frank vector. The free energy density is postulated to be dependent on the elastic deformation and the measures of the defects. The non-local, diffusion-type evolution equations for plastic distortion and the damage tensor are derived to be compatible with the dissipation inequality, while the micro stress momenta, associated with the plastic and disclination mechanisms, are derived from the free energy function. We restrict the evolution equations for defects to small elastic and plastic distortions, considered to be wedge disclinations and edge dislocations. The finite element method is applied to numerically study the evolution of the defects, when the initial dislocation heterogeneities are considered.

Synchrotron monochromatic-beam x-ray topography observation has been performed on high-quality ammonothermal gallium nitride single crystal to evaluate threading dislocations (TD) in a nondestructive manner. Asymmetric diffractions with six equivalent g-vectors of 11-26, in addition to a symmetric diffraction with g = 0008, were applied to determine the Burgers vectors (b) of dislocations. It was found that pure edge-type TDs with b=11-20/3 did not exist in the sample. A dominant proportion of TDs were of mixed type with b=11-20/3+0001, i.e., so-called c + a dislocations. Pure 1c screw dislocations with b=0001 and TDs with c-component larger than 1c were also observed. [ABSTRACT FROM AUTHOR]

Displacement damage, through heavy ion irradiation was studied on two tungsten grades (coarse grained tungsten (CGW) and nanocrystalline and ultrafine grained tungsten (NCW)) using different displacement per atom rates and different irradiation temperatures (RT and 1050 K). Percentage of <111> and <100> type loops at the irradiation conditions was determined. Irradiation damage in the microstructure was quantified using average loop areas and densities (method A) and loop areal fraction in the grain matrices under 2-beam diffraction conditions (method B). Average values of <111> and <100> loops were calculated from method A. Loop coalescence was shown to occur for CGW at 0.25 dpa. Using both methods of quantifying microstructural damage, no effect of dpa rate was observed and damage in CGW was shown to be the same at RT and 1050 K. Swelling from voids observed at 1050 K was quantified. The loop damage in NCW was compared to CGW at the same diffraction and imaging conditions. NCW was shown to possess enhanced irradiation resistance at RT regarding loop damage and higher swelling resistance at 1050 K compared to CGW. For irradiation at 1050 K, the NCW was shown to have similar defect densities to the CGW which is attributed to higher surface effects in the CGW, vacancy loop growth to voids and a better sink efficiency in the CGW deduced from the vacancy distribution profiles from Kinetic Monte Carlo simulations. Loop density and swelling was shown to have similar values in grains sizes that range from 80 to 600 nm. No loop or void denuded zones occurred at any of the irradiation conditions. This work has a collection of experiments and conclusions that are of vital importance to materials and nuclear energy communities. [ABSTRACT FROM AUTHOR]

Dislocation loop rafting and dislocation decoration have been previously observed in neutron and heavy ion irradiated materials. Understanding the fundamental aspects of these phenomena assist in evaluating irradiation damage of nuclear materials. Multiple different mechanisms have been suggested to explain loop rafting. Here, we performed a detailed transmission electron microscopy study on dislocation loop rafts in heavy ion irradiated tungsten. Different imaging conditions showed that the rafts are of <111> Burgers vector type and specifically the same <111> Burgers vector variant (<1 1 ¯ 1>) in the particular grain analyzed. Some rafts were associated with dislocation lines while some form as a result of alignment of dislocation loops. They were shown to form at both room temperature (RT) and high temperature with stronger rafts forming at RT. These observations confirm the mechanism previously suggested by Wen et al. which explains raft formation due to loop glide, cluster-cluster and grown-in dislocation-cluster interaction with subsequent Burgers vector rotation. Similar irradiation studies on nanocrystalline tungsten showed that these materials are more resistant to raft formation at RT irradiations. [ABSTRACT FROM AUTHOR]

YB 4 /YB 6 two-phase alloys were prepared by arc-melting of high purity elemental materials. The Young's moduli of YB 4 and YB 6 were evaluated by nanoindentation technique. During loading of nanoindentation, pop-in events were clearly observed for YB 4 and YB 6 , suggesting that both have some capability of dislocation emission at room temperature. TEM observation depicts that dislocations have formed in YB 4 and YB 6 due to the thermal stress that developed during cooling following arc-melting. The Burgers vectors of these dislocations were identified to be [001] for YB 4 , and 〈100〉 for YB 6 . Potential slip systems that are indicated to operate were (100)[001] for YB 4 and {100}〈001〉 for YB 6 . [ABSTRACT FROM AUTHOR]