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Microstructural changes will occur in tungsten when used as plasma-facing material in future fusion reactors due to the high operation temperatures. Potassium doping has proven to delay such undesired changes in drawn tungsten wires. The same strategy is adapted to thin cold-rolled tungsten sheets containing 80 ppm potassium. Their thermal stability is characterized by isochronal annealing for two hours as well as isothermal annealing at selected temperatures for longer times. Mechanical degradation is quantified by micro hardness testing; microstructure and texture evolution are investigated using scanning electron microscopy and electron backscatter diffraction. During annealing for two hours at temperatures between 800 °C and 1400 °C, the potassium-doped tungsten sheets undergo recovery. The strong rotated cube texture present in the as-rolled condition intensifies enormously during annealing for two hours, but does not change significantly during further annealing. Isothermal annealing at temperatures between 1300 °C and 1400 °C causes significant loss in hardness during the first two hours, but only smaller changes further on, indicating that solely extended recovery is occurring. No evidence for primary recrystallization is found as recrystallization is retarded by a combination of high angle boundaries being absent due to the strong texture and their immobilization by potassium bubbles. The recovery kinetics is quantified based on Kuhlmann’s recovery model and compared with observations on differently rolled thin plates of pure tungsten. Despite different amounts of recoverable hardness, the recovery parameters resolved for potassium-doped tungsten fit nicely to the master curve for recovery obtained earlier on pure tungsten plates confirming that recovery is indeed the dominating restauration mechanism and that doping with 80 ppm potassium does not alter the recovery mechanism fundamentally.

The formation mechanism of a recrystallisation internal friction (IF) peak superimposed on a grain boundary (GB) IF peak for deformed copper was studied. The P1 peak, associated with the recrystallisation process, was observed at ∼ 599 K (2 K/min) during the first heating process. Subsequently, the P2 peak, located at ∼ 510 K (0.2 Hz), corresponded to GB relaxation during the cooling process. The P1 peak showed minor relaxation at higher frequencies owing to the influence of GB relaxation. To accurately determine the temperature of the P1 peak in this scenario, two methods were used: fitting the measured IF spectra and performing IF measurements at lower frequencies and/or with faster heating rates to minimise the impact of GB relaxation. This work investigated the formation mechanism of the recrystallisation peak and supplemented the method for determining the recrystallisation temperature through IF measurements when the GB peak occurs at a nearby temperature. [ABSTRACT FROM AUTHOR]

This paper presents a novel methodology that addresses the limited predictive capability of the existing crystal plasticity (CP) method in interfaces modeling. Our approach incorporates interfacial parameters generated from molecular dynamic (MD) simulations into the continuum-level crystal plasticity finite element analysis (CPFEA) model. To address the inherent scale mismatch between atomistic and continuum models, we employ two essential techniques—the nucleation theory and machine learning (ML) method. The nucleation theory is utilized in conjunction with the nudged elastic band (NEB) method to extrapolate the low strain-rate yield stresses from the high strain-rate MD simulation results. To overcome the length scale limitation of MD, we use a method that was recently developed by the authors—a two-step approach that utilizes MD-calculated stress–strain data to train a probabilistic ML model for predicting stress–strain behaviors at larger scale. The resulting flow parameters and extrapolated yield stresses are then integrated into the atomistic-informed interface region of the CPFEA model. This multiscale computational method that combines MD, CPFEA, nucleation theory, NEB and ML enables a grain-level large time scale crystal plasticity modeling with atomic accuracy at the interfaces, as demonstrated by carefully validating it through a bicrystal Cu model with experimental results. This validation highlights the importance of accurately describing interfaces in the modeling of material mechanical behavior. Notably, our proposed methodology is not limited to interfaces but can be applied to other microstructures requiring atomic accuracy. The method opens up new possibilities for comprehensively understanding and designing materials with complex microstructure for various engineering applications. Practical Applications: The methodology presented in this paper offers significant practical applications for materials engineering, particularly in industries where materials are subjected to high stress and strain, such as aerospace, automotive, and structural engineering. By integrating atomistic interfacial parameters into the crystal plasticity finite element analysis (CPFEA) model, this approach allows for more accurate predictions of material behavior at the grain level, leading to better-informed decisions in material design and optimization. The ability to model interfaces with atomic accuracy means that engineers can design materials with enhanced mechanical properties, such as increased strength and ductility, by understanding and manipulating the behavior of grain boundaries. This is crucial for developing advanced materials that can withstand extreme conditions, thereby improving the safety and performance of critical components in various engineering applications. Additionally, the use of machine learning to predict stress–strain behaviors at larger scales from molecular dynamics data provides a powerful tool for scaling up the modeling process, making it more feasible and efficient for practical use. This comprehensive multiscale framework opens new avenues for innovation in material science, allowing for the design of next-generation materials with tailored properties for specific engineering challenges. [ABSTRACT FROM AUTHOR]

Aluminum matrix composites reinforced with ceramic particles have recently received considerable research interest owing to their light weight, high modulus, and high strength. This study fabricated SiC reinforced Al-10 wt%Si-0.35 wt%Mg (AlSi10Mg) alloy matrix composites with high relative density using a laser-based powder bed fusion (LPBF) process. The reaction phase of Al4SiC4 from the interface of the SiC particles occurred under LPBF and its fraction increased with increasing energy density. A high compressive stress of >600MPa was obtained for the AlSi10Mg/SiC composite produced via LPBF at an optimum energy density (250 J/mm³). This study analyzed the mechanical properties of the LPBF composite hierarchically from micro to macro levels. A higher Young's modulus (evaluated using a compression test) was obtained for the AlSi10Mg/SiC composite fabricated using LPBF than the AlSi10Mg alloy. From the micro level analysis on mechanical properties, the increased Al4SiC4 formation with an increase in energy density improved the hardness and Young's modulus compared to those of the AlSi10Mg alloy. However, SiC in the composite is more effective for being high strength and Young's modulus than Al4SiC4. [ABSTRACT FROM AUTHOR]

The current trend in research on the physical properties of high-entropy alloys has been progressively increasing as there are many unknown possibilities for developing high-entropy alloys for advanced applications. This study investigated the effect of microstructures of rolled high-entropy alloy from the viewpoint of crystal orientation and dislocation density distribution to reproduce mechanical anisotropy using crystal plasticity finite element simulation. The crystal orientation and the geometrically necessary dislocation density of the rolled material were quantitatively estimated from experimental data of electron backscatter diffraction. Microstructural observation showed that particular textures were preferably oriented like in typical FCC metals. Even though the simulation results where only the preferred crystal orientation was considered did not show the expected mechanical anisotropy as in the experiment, the computational model with the dislocation density distribution and the preferred orientation showed the same tendency as the experiment. [ABSTRACT FROM AUTHOR]

Grain boundaries (GBs) are transitional, defective, and anisotropic interfaces between adjacent grains with different orientations. However, most models assume that the GB is an isotropic dielectric determined by itself and lacks formation information; these assumptions hinder the theoretical investigation of the effect GBs have on polycrystalline ferroelectrics at the mesoscopic scale. Here, a novel GB model based on the formation mechanism is established for ferroelectric polycrystals. It has been found that the Curie–Weiss temperature range, elastic coefficient, and permittivity of GBs are related to the orientation of adjacent grains and the polarization state. The shielding effect, polarization enhancement, domain continuity, and spontaneous polarization on the GBs are obtained in mesoscopic simulations based on this model. In addition, the proportion of GBs can significantly affect the electric field distribution in grains. It provides a mechanistic explanation for the relationship between the coercive electric field and the proportion of GBs in the previous experiment. By achieving a better mesoscopic description of GBs, the GB model proposed in this work provides an effective investigation tool for electromechanical, electrocaloric, and energy storage of polycrystalline functional materials. [ABSTRACT FROM AUTHOR]

The Geometrically Necessary Dislocation (GND) density was estimated from Electron Backscatter Diffraction (EBSD) data for an AZ31/Mg-0.6Gd (wt.%) hybrid material fabricated by high-pressure torsion (HPT) at room temperature through an equivalent strain range of ϵeq = 0.3–144 using Kernel Average Misorientation (KAM) and the Nye tensor approaches. The results show that generally the GND densities are significant at the beginning of the deformation (ϵeq = 0.3) and decrease in both alloys when ϵeq increases. The Mg-0.6Gd alloy exhibits a lower GND density due to rapid dynamic recrystallization. These results were compared to the GND densities measured in AZ31 and Mg-0.6Gd mono-materials processed separately by HPT under the same experimental conditions. In these mono-materials the GND densities increase with increasing equivalent strain up to 7 and then decrease with further straining. The Mg-0.6Gd and AZ31 regions of the hybrid material exhibit higher GND densities than the mono-materials particularly at low strain where the disc thickness and the bonding of the AZ31/Mg-0.6Gd interfaces cause more deformation heterogeneity in the hybrid material. It is shown that the GND density evolution as a function of ϵeq has the same tendency for the KAM and the Nye approaches but the average values are significantly higher with the Nye approach. An analysis suggests that the Nye approach overestimates the GND density of the Mg-based alloys. [ABSTRACT FROM AUTHOR]

This work investigated the impact of deformation temperature in metastable austenite zone on microstructure evolution and mechanical and corrosion properties of high Cr ferriticmartensitic steel. The martensitic lath characteristics and the size and distribution of precipitates of the steels were observed using transmission electron microscopy (TEM). The results show that narrowing of the lath width occurs as the deformation temperature reduces from 800 to 600?C. During subsequent high-temperature tempering, the martensitic lath recovery degree of the tempered steel gradually increases, and the size of the precipitates gradually decreases with the decrease of the previous deformation temperature. A tensile test was conducted on the steels subjected to high-temperature tempering. The tensile strength of deformed steel is found to be higher than that of undeformed steel. The tensile properties of the deformed steels decrease with the decrease of the deformation temperature. The electrochemical polarization curve confirms that the corrosion resistance of the deformed steel subjected to tempering is gradually improved with decreasing deformation temperature. This work clarifies the influence mechanism of deformation temperature on the microstructure and properties of high Cr ferritic-martensitic steel and provides a reliable basis for actual industrial production. [ABSTRACT FROM AUTHOR]

Time-domain Brillouin scattering (TDBS) uses ultrashort laser pulses to (i) generate coherent acoustic pulses of picoseconds duration in a solid sample and (ii) follow their propagation in order to image material inhomogeneities with the axial resolution that can be deeply sub-optical, to nm-scale, and the lateral one down to the optical diffraction limit (half the optical wavelength of the probe laser). TDBS permits highly resolved 3D-imaging of grains in polycrystalline transparent samples with unlimited lateral sizes and thicknesses of at least 10 μ m also when samples are orientationally textured and/or located in devices permitting access along one direction and from one side only. This optical technique presents, accordingly, clear advantages compared to any x-ray based computed tomography (neither back-projection algorithm nor multiple viewpoints of the sample are needed) and classical spectroscopic methods. Here, we applied TDBS to the 3D-imaging of a sample of polycrystalline water ice containing two high-pressure phases. The imaging, accomplished via a simultaneous detection of quasi-longitudinal and quasi-shear waves, provided shape, coordinates, phase content, and crystallographic orientation of resolved crystallites in a common coordinate system. Monitoring of acoustic pulses simultaneously propagating in two neighboring grains provided a new tool for the localization of grain boundaries. [ABSTRACT FROM AUTHOR]

The present study conducts a comprehensive study on heat-treatment-induced cracking of Inconel 738 (IN738) alloy fabricated by laser powder bed fusion (LPBF) using scanning electron microscopy (SEM), energy dispersion spectrum (EDS), and electron backscatter diffraction (EBSD). The results indicate that the macroscopic crack is dominantly triggered by the strain-age cracking mechanism and propagates along grain boundaries. The initiation of cracking is facilitated by the superimposition of residual stress induced by the LPBF process and contraction stress induced by precipitation, while the reopening of compress pores at grain boundaries weakens the grain boundaries and provides fast channels for cracking. These results revealed the coupling effects in triggering heat-treatment-induced cracking, offering a fundamental guideline for crack control during heat treatment of additively manufactured IN738 alloy. [ABSTRACT FROM AUTHOR]

Advanced low‐density steels that meet energy shortages and high safety requirements have become a hot research topic in materials science. The addition of light elements with medium‐Al content (5 wt%) to ultrahigh‐strength pearlite cable steel alloy reduces the material density and causes a microstructural change from traditional θ‐pearlite (ferrite + cementite) to θ‐pearlite and κ‐pearlite (ferrite + cementite + κ‐carbide). The results show that the moderate addition of Al and Mn (5 wt%) promotes the formation of κ‐carbide, which inhibits the diffusion of C and significantly delays the eutectoid transformation process of pearlite. Meanwhile, the transformation free energy of pearlite increases and obviously refines the lamellar spacing of the ultrafine pearlite by κ‐carbide. Simultaneously, the interaction between κ‐carbides and dislocations is initiated, which increases the strain hardening rate of ultrafine pearlitic steel. [ABSTRACT FROM AUTHOR]

Optical waveguides fabricated in single crystals offer crucial passive/active optical components for photonic integrated circuits. Single crystals possess inherent advantages over their amorphous counterpart, such as lower optical losses in visible-to-mid-infrared band, larger peak emission cross-section, higher doping concentration. However, the writing of Type-I positive refractive index modified waveguides in single crystals using femtosecond laser technology presents significant challenges. Herein, this work introduces a novel femtosecond laser direct writing technique that combines slit-shaping with an immersion oil objective to fabricate low-loss Type-I waveguides in single crystals. This approach allows for precise control of waveguide shape, size, mode-field, and refractive index distribution, with a spatial resolution as high as 700 nm and a high positive refractive index variation on the order of 10 -2 , introducing new degrees of freedom to design and fabricate passive/active optical waveguide devices. As a proof-of-concept, this work successfully produces a 7 mm-long circular-shaped gain waveguide (≈10 µm in diameter) in an Er 3+ -doped YAG single crystal, exhibiting a propagation loss as low as 0.23 dB cm -1 , a net gain of ≈3 dB and a polarization-insensitive character. The newly-developed technique is theoretically applicable to arbitrary single crystals, holding promising potential for various applications in integrated optics, optical communication, and photonic quantum circuits., (© 2024 Wiley‐VCH GmbH.)

Laser shock peening (LSP) is an innovative technique that is used to enhance the fatigue strength of structural materials via the generation of significant residual stress. The present work was undertaken to evaluate the degree of plastic strain introduced during LSP and thus improve the fundamental understanding of the LSP process. To this end, electron backscatter diffraction (EBSD) and nano-hardness measurements were performed to examine the microstructural response of laser-shock-peened Ti-6Al-4V alloy. Only minor changes in both the shape of α grains/particles and hardness were found. Accordingly, it was concluded that the laser-shock-peened material only experienced a small plastic strain. This surprising result was attributed to a relatively high rate of strain hardening of Ti-6Al-4V during LSP. [ABSTRACT FROM AUTHOR]

The photoelectron momentum microscope (PMM) in operation at BL6U, an undulator-based soft x-ray beamline at the UVSOR Synchrotron Facility, offers a new approach for μm-scale momentum-resolved photoelectron spectroscopy (MRPES). A key feature of the PMM is that it can very effectively reduce radiation-induced damage by directly projecting a single photoelectron constant energy contour in reciprocal space with a radius of a few Å−1 or real space with a radius of a few 100 μm onto a two-dimensional detector. This approach was applied to three-dimensional valence band structure E(k) and E(r) measurements ("stereography") as functions of photon energy (hν), its polarization (e), detection position (r), and temperature (T). In this study, we described some examples of possible measurement techniques using a soft x-ray PMM. We successfully applied this stereography technique to μm-scale MRPES to selectively visualize the single-domain band structure of twinned face-centered-cubic Ir thin films grown on Al2O3(0001) substrates. The photon energy dependence of the photoelectron intensity on the Au(111) surface state was measured in detail within the bulk Fermi surface. By changing the temperature of 1T-TaS2, we clarified the variations in the valence band dispersion associated with chiral charge-density-wave phase transitions. Finally, PMMs for valence band stereography with various electron analyzers were compared, and the advantages of each were discussed. [ABSTRACT FROM AUTHOR]

The effect of hydrogen on the fatigue behavior of materials has been studied extensively during the past 100 years, but is just poorly understood due to the complex interplay between hydrogen and deformation processes. In this context, hydrogen damage of metals is becoming one of the major challenges of decarbonization. While most work focuses on f.c.c. materials, the availability of relevant results becomes sparse when considering technologically highly relevant b.c.c. metals such as structural steels. This work uses in situ electrochemical hydrogen charging of α‐iron steels to investigate the formation and evolution of intrusions and extrusions prior to fatigue crack initiation using a new charging setup by which the specimens are charged from the interior. The advantage of this innovative technique is that the surface of the specimens can subsequently be characterized using atomic force microscopy without artefacts from electrochemical charging or corrosion. Hydrogen is shown to enhance slip localization at the early stages of damage. The developed persistent slip lines are less pronounced. By means of transmission Kikuchi diffraction, it is shown that orientation gradients between cells in the dislocation structure are much weaker in the presence of hydrogen. Hence, hydrogen appears to promote slip reversibility in b.c.c. materials. [ABSTRACT FROM AUTHOR]

Austenitic stainless steels with a bimodal harmonic structure, in which the fine grain structure (Shell) exists around the coarse grain structure (Core), are prepared by powder metallurgy to improve both strength and ductility. Herein, X‐ray diffraction contrast tomography, a 3D grain mapping technique for polycrystalline materials using ultrabright synchrotron radiation X‐rays, is used to reconstruct the grain shape and location and to evaluate the average excess dislocation density of the Core and Shell structures. This technique allows one to evaluate the excess dislocation density not only on the surface, but also inside the sample where damage occurs in tensile tests. The results show that the excess dislocation density of the Shell structure is higher than that of the Core structure. The excess dislocation density of homogeneous austenitic stainless steels with grain sizes similar to the Core structure of the harmonic structured stainless steel is higher than that at comparable stresses, indicating that the deformation of the bimodal harmonic structured alloy is localized in the fine grain structure. This is consistent with the results obtained from electron backscatter diffraction analysis, in which the surface grains are evaluated. [ABSTRACT FROM AUTHOR]

This overview article discusses the Equal Channel Angular Pressing (ECAP) processing of different metallic materials. Particular emphasis is given to the microstructural evolution from the coarse grain (CG) to the ultrafine-grained (UFG) states throughout the electron backscattering diffraction (EBSD) technique. Iron-based alloys, such as duplex and 1020 low-carbon steels reached higher hardening with a lower deformation and lower non-ultrafine average grain sizes than the ultrafine pure iron condition due to fast grain fragmentation, i.e., more geometrically necessary dislocation (GND) grouping. Moreover, due to the magnesium adhesion, copper alloys reached superior mechanical properties compared to pure copper even when the initial grain size for as-cast alloys was over 1000 µm. On the other hand, low melting temperature (TMP) materials processed at 250°C, like the ZK60 magnesium and AA6082 aluminum alloys (i.e., homologous temperatures (TH) of 0.38TMP and 0.37TMP, respectively), showed grain refinement without reaching the ultrafine regime and mechanical softening due to the static and dynamic recrystallization phenomena. CP titanium also displayed heterogeneous grain sizes with average values of above 1 µm after four ECAP passes for temperatures ranging between 150°C and 400°C (TH between 0.09TMP = 0.24TMP). The evolution of the GNDs suggested that the initial deformation stages of severe plastic deformation (SPD) by ECAP produced the most notorious density increments from 1012m-2 to 1014m-2, which level up at high deformations (more than four ECAP passes) around 10141015m-2, explaining the fast and slow grain size reduction rates, respectively. The ECAP processing on different metallic material systems showed a larger grain fragmentation capacity in high melting points and alloyed materials, giving rise to steep yield strength increases and low ductility. The low ductility and grain size saturation correspond to a low capacity to create new grain boundaries manifested by the GNDs saturation in the UFG range. [ABSTRACT FROM AUTHOR]

This report is aimed at giving an overview of the significance of the novel and innovative microstructural and microscopic characterization techniques for bulk nanostructured metals processed by severe plastic deformation, specifically high-pressure torsion (HPT). In practice, the microstructural relaxation behavior upon heating of nanostructured 316L stainless steel and CoCrFeNi high-entropy alloy was characterized by in-situ heating neutron diffraction measurements; the heterogeneous phase distribution of an HPT-bonded hetero-nanostructured AlMg alloy was examined using synchrotron high-energy X-ray diffraction; and the microstructural evolution upon heating of a nanostructured CoCrFeNiMn high-entropy alloy was examined by laser-scanning confocal microscopy. These novel techniques are complementary to each other and any other in- or ex-situ testing methods, especially when nanocrystalline metals are transforming microstructurally and compositionally with temperature and time in a hierarchical manner. The outcomes of the studies emphasize the importance of the methodologies and the development of characterization techniques for further in-depth exploration in the research field of severe plastic deformation. [ABSTRACT FROM AUTHOR]

Oxide nanoparticles are quintessential for ensuring the extraordinary properties of oxide dispersion strengthened (ODS) steels. In this study, the crystallographic structure of oxide nanoparticles, and their interface with the ferritic steel matrix in an Al-alloyed ODS steel, i.e. PM2000, were systematically investigated by high-resolution transmission electron microscopy. The majority of oxide nanoparticles were identified to be orthorhombic YAlO3. During hot consolidation and extrusion, they develop a coherent interface and a near cuboid-on-cube orientation relationship with the ferrite matrix in the material. After annealing at 1200 °C for 1 h, however, the orientation relationship between the oxide nanoparticles and the matrix becomes arbitrary, and their interface mostly incoherent. Annealing at 1300 °C leads to considerable coarsening of oxide nanoparticles, and a new orientation relationship of pseudo-cube-on-cube between oxide nanoparticles and ferrite matrix develops. The reason for the developing interfaces and orientation relationships between oxide nanoparticles and ferrite matrix under different conditions is discussed. [ABSTRACT FROM AUTHOR]

Aluminum matrix composites reinforced with ceramic particles have recently received considerable research interest owing to their light weight, high modulus, and high strength. This study fabricated SiC reinforced Al10 wt%Si0.35 wt% Mg (AlSi10Mg) alloy matrix composites with high relative density using a laser-based powder bed fusion (LPBF) process. The reaction phase of Al4SiC4 from the interface of the SiC particles occurred under LPBF and its fraction increased with increasing energy density. A high compressive stress of >600 MPa was obtained for the AlSi10Mg/SiC composite produced via LPBF at an optimum energy density (250 J/mm3). This study analyzed the mechanical properties of the LPBF composite hierarchically from micro to macro levels. A higher Young's modulus (evaluated using a compression test) was obtained for the AlSi10Mg/SiC composite fabricated using LPBF than the AlSi10Mg alloy. From the micro level analysis on mechanical properties, the increased Al4SiC4 formation with an increase in energy density improved the hardness and Young's modulus compared to those of the AlSi10Mg alloy. However, SiC in the composite is more effective for being high strength and Young's modulus than Al4SiC4. [ABSTRACT FROM AUTHOR]

Here the possibility of utilizing X‐ray reflectivity for visualization with ≈µm spatial resolution of a surface with a heterogeneous electron density due to a partial coverage by another nanometrically thin material is demonstrated. It requires the sample to be convexly bent, thus reflecting the collimated incident beam onto a magnified image recorded by a position‐sensitive detector. By the use of a small, intense, and parallel beam such as provided by the most recent synchrotron sources, one can record such spatially resolved X‐ray reflectivity with 0.1–1 kHz frame rate. The use of the method for in situ, time‐resolved characterization of single‐layer graphene domains during their chemical vapor deposition on a naturally curved surface of a liquid copper drop is demonstrated. This method can follow the growth kinetics, including the coverage ratio, 2D crystal (flake) sizes, and distances between flakes. By taking a single scan, the individual X‐ray reflectivity curves can be reconstructed, of both covered and noncovered parts of the surface, allowing to deduce the corresponding electron density profiles perpendicular to the surface. The technique has a promising perspective for in situ study of 2D materials, ultrathin films, and self‐assemblies on liquid as well as solid surfaces. [ABSTRACT FROM AUTHOR]

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The statistical analysis and recovery behavior of dislocations in cold-rolled and annealed reactor pressure vessel steels with a thickness reduction of 50% were investigated by using x-ray diffraction and electron backscattered diffraction analysis in this study. A new modified Kubin & Mortensen’s method was proposed to evaluate the geometrically necessary dislocation density, and this method could effectively improve the accuracy of geometrically necessary dislocation evaluation by eliminating the effect of step size and measurement noises. Comparison analysis between modified Williamson-Hall and modified Kubin & Mortensen’s methods was also performed in this study, which shows different recovery behavior of dislocations. The electron backscattered diffraction results show that geometrically necessary dislocation density remained unchangeable after annealing treatment below and at 550°C, and it occurred to decrease above 550°C due to the occurrence of recrystallization. However, dislocations started to migrate and annihilate at 340°C according to x-ray diffraction results. A possible explanation is a difference in the effect of pairwise dislocation annihilation on statistically stored dislocations and geometrically necessary dislocations. [ABSTRACT FROM AUTHOR]

Voigt and Reuss models do not make any assumption regarding composite microstructure, but they are only able to estimate bounds rather than values of composite properties. To enable the models to predict elastic properties of particulate composites, we isotropized Voigt and Reuss models based on the equivalence of normal and shear strain energy respectively in a representative volume element, and derived a set of simple and uncoupled equations for the prediction of composite Young's modulus and shear modulus. Composite bulk modulus and Poisson's ratio can then be determined either by the elasticity relationships or by generalization of the isotropized Voigt-Reuss equations. Validation with reported experimental data show that, for composites with phase properties of either small or large contrast, isotropized Voigt-Reuss model has similar accuracy as the widely used micromechanical models, for the prediction of Young's modulus and shear modulus. [ABSTRACT FROM AUTHOR]

This review summarizes the current knowledge on the α″ martensite transformation in metastable β Ti alloys under different stress state conditions gained using various in situ techniques that range from the meso‐ to the nanoscale. Compared to ex situ observations, in situ observation can be conducted on a single region while changing external stimuli, and are therefore capable of elucidating the interim microstructural evolution. The strengths and shortcomings of different techniques to give insight into the martensitic transformation are identified. Both the formation of α″ martensite and its reversion on load removal are addressed. The phenomena of α″ martensite formation including preferential nucleation sites, its growth, interactions, and variant selection are described. The review also discusses the details of the macro‐ and micro‐level mechanical behavior caused by the phase transformation and highlights the research questions for further investigation. [ABSTRACT FROM AUTHOR]

Among various types of stainless steel, 304L and 316L have the most engineering applications. Herein, 304L and 316L powders with similar size distributions and morphologies are used as raw materials for selective laser melting (SLM) using the same parameters. It is found that SLM 304L has two phases, γ‐austenite (≈95%) and δ‐ferrite (≈5%) phases, while SLM 316L contains only γ‐austenite phase. The average grain size is found to be 4.9 μm (average grain size of γ‐austenite phase: 5.0 μm; δ‐ferrite: 3.4 μm) for SLM 304L and 16.7 μm for SLM 316L. The small grain size of 304L is attributed to the peritectic reaction during solidification. δ‐ferrite acts as a heterogeneous nucleation site for γ‐austenite. SLM 316L has higher hardness and yield strength than 304L. Results obtained from the comparative study indicate that adding ferrite stabilizer elements (e.g., Cr, Mo, Si, Nb, or Ti) into 316L can lead to peritectic reaction or austenite to ferrite solid phase transformation, which is a possible approach for grain refinement. [ABSTRACT FROM AUTHOR]

This paper studies the influence of the regression re‐aging (RRA) process on the mechanical properties and corrosion resistance of 7075. In the RRA heat treatment, the material properties are markedly affected by the variation of parameters in the regression stage. When the regression temperature and the regression duration increase, the mechanical properties of the material decrease. There was no intergranular corrosion in the samples treated by RRA, while obvious intergranular corrosion occurred in the T6 sample. Compared with the T6 sample, the RRA‐190‐0.5 sample with optimized parameters has a higher density of the precipitated phase and narrower precipitate‐free zone, and the precipitated phase along the grain boundary is discontinuous, isolated, and short. Compared with the single‐stage peak aging treatment, the RRA treatment can considerably improve the corrosion resistance and stress corrosion resistance but slightly reduce the strength. The best heat treatment process condition is 120°C/24 h + 190°C/0.5 h + 120°C/24 h. [ABSTRACT FROM AUTHOR]

The dislocation pattern of cold deformed FCC metals follows an orientation-dependent rule. However, only final orientation after deformation has been considered in related studies, i.e. without considering lattice rotation effect, although metals have undergone heavy lattice rotation during plastic deformation. In this work, the lattice rotation effect on the dislocation structures of Cu is investigated by combining electron backscatter diffraction, focused ion beam lift-out and scanning transmission electron microscopy techniques. The dislocation patterns of [110]-[110], [111]-[111] and [110]-[111] type grains deformed in tension under room temperature are compared. The notation [h1k1l1]-[h2k2l2] represents the lattice rotation history of a grain, meaning that the grain rotates from [h1k1l1] corner to [h2k2l2] corner during tension. It is found that for a given strain range, the dislocation cell structure is observed in [111]-[111] grain, while the dislocation cell block structure is dominant in [110]-[111] grain. This demonstrates that for Cu grains with a final orientation near [111] corner, dislocation pattern type is influenced by the lattice rotation feature. Same with [110]-[111] type grain, cell block structure is the main feature found in [110]-[110] grain, indicating that for grain with initial orientation near [110] corner, lattice rotation has a marginal effect on the dislocation structure. The relation between the dislocation structure, lattice rotation, slip system and strain level of Cu is discussed. [ABSTRACT FROM AUTHOR]

The usability of the magnetic Barkhausen noise (MBN) technique for monitoring the critical state of plastic straining in the case of interstitial free (IF) steel is demonstrated. IF steels are frequently employed in the automotive industry (e.g., automotive body parts—doors, trunks, wheel arches, etc.), and rupture of components made of these steels occurs during cold forming. Alteration of microstructure expressed in many terms and the corresponding MBN features after the variable degree of plastic strains developed by the uniaxial tensile loading are investigated. It is reported that the effective value of MBN, as well as the shift of MBN envelopes toward higher magnetic fields, can be proposed as the suitable MBN features alerting the incoming matrix breakage. Moreover, the higher MBN in the direction of exerted load at the expense of the perpendicular direction can be found as a result of domain walls realignment. [ABSTRACT FROM AUTHOR]

The evolution of deformation structures in individual grains embedded in polycrystalline copper specimens during strain path changes is observed in situ by high-resolution reciprocal space mapping with high-energy synchrotron radiation. A large number of individual subgrains is resolved; their behavior during the strain path change is revealed and complemented by the analysis of radial x-ray peak profiles for the entire grain. This allows distinction between two different regimes during the mechanically transient behavior following the strain path change: Below 0.3% strain, the number and orientation of the resolved subgrains change only slightly, while their elastic stresses are significantly altered. This indicates the existence of a microplastic regime during which only the subgrains deform plastically and no yielding of the dislocation walls occurs. After reloading above 0.3% strain, the elastic stresses of individual subgrains are about the same as in unidirectionally deformed reference specimens. They increase only slightly during further straining-accompanied by occasional emergence of new subgrains, abundant orientation changes, and disappearance of existing subgrains. [ABSTRACT FROM AUTHOR]

The correct description of the mechanical behaviour of metallic materials after deformation to large strains requires the quantitative determination of substructure characteristics on different length scales. Important tools for this purpose are transmission electron microscopy (TEM), electron backscattering diffraction (EBSD) and X-ray diffraction (XRD), which lead to quantities such as the mean total dislocation density, the density of excess dislocations stored in dislocation walls, the distributions and the averages of local lattice rotations and the size (chord length) of the lattice regions (cell blocks, fragments) of the mesoscale substructure. This present paper illustrates the application of EBSD and XRD for the analysis of the deformation substructure occurring in polycrystalline Al during uniaxial compression up to strains ε ≈ 2. [ABSTRACT FROM AUTHOR]

Microstructural internal lengths play an important role on the local and macroscopic mechanical behaviors of steels. In this study, the dislocation density gradients near grain boundaries in a ferritic steel are investigated using SEM/EBSD together with instrumented nanoindentation for undeformed and pre-deformed aluminum-killed steels (Al-k) at 3% and 18% tensile plastic strains. The effect of the distance to grain boundaries on Geometrically Necessary Dislocations (GND) densities is first determined by analyzing orientation gradients from 2D-EBSD maps. Then, nanohardness measurements are performed in the vicinity of grain boundaries. Data analyses show a clear correlation between the spatial gradients of GND density and the ones of nanohardness. Using a mechanistic model, the total dislocation densities are estimated from the measured nanohardness values. From both GND and total dislocation density profiles, the value of an internal length, denoted λ, is estimated from the analysis of dislocation density gradients near grain boundaries. At the end, the capabilities of 2D-EBSD and nanoindentation methods to assess this value are discussed. [ABSTRACT FROM AUTHOR]

The reliability of semiconductor materials with electrical and optical properties are connected to their structures. The elastic strain field and tilt analysis of the crystal lattice, detectable by the variation in position and shape of the diffraction peaks, is used to quantify defects and investigate their mobility. The exploitation of high‐resolution X‐ray diffraction‐based methods for the evaluation of structural defects in semiconductor materials and devices is reviewed. An efficient and non‐destructive characterization is possible for structural parameters such as, lattice strain and tilt, layer composition and thickness, lattice mismatch, and dislocation density. The description of specific experimental diffraction geometries and scanning methods is provided. Today's X‐ray diffraction based methods are evaluated and compared, also with respect to their applicability limits. The goal is to understand the close relationship between lattice strain and structural defects. For different material systems, the appropriate analytical methods are highlighted. [ABSTRACT FROM AUTHOR]