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Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys (ODS-HEAs) were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties. Systematic microstructural analysis was carried out by X-ray diffraction (XRD), electron backscattered diffraction (EBSD), high-resolution transmission electron microscopy (HRTEM), atom probe tomography (APT), and small-angle neutron scattering (SANS). Cryo-milled powder analysis, grain structure evolution after spark plasma sintering, dispersoid characteristics, and matrix/dispersoid interface structure analysis of the in-situ and ex-situ dispersoids within the high-entropy alloy (HEA) matrix were performed. The in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical composition, leading to an increase in the Zener pinning forces on the grain boundary movement. ODS-HEA with in-situ oxide dispersoids enhanced the formation of ultrafine-grained structures with an average diameter of 330 nm at a sintering temperature of 1173 K. This study shows that the Y pre-alloying method is efficient in achieving fine coherent dispersoids with an ultrafine-grained structure, resulting in an enhancement of the tensile strength of the CoCrFeMnNi HEA.

We examined fatigue-crack-growth behaviors of CoCrFeMnNi high-entropy alloys (HEAs) under as-fatigued and tensile-overloaded conditions using neutron-diffraction measurements coupled with diffraction peak-profile analyses. We applied both high-resolution transmission electron microscopy (HRTEM) and neutron-diffraction strain mapping for the complementary microstructure examinations. Immediately after a single tensile overload, the crack-growth-retardation period was obtained by enhancing the fatigue resistance, as compared to the as-fatigued condition. The combined mechanisms of the overload-induced larger plastic deformation, the enlarged compressive residual stresses and plastic-zone size, the crack-tip blunting ahead of the crack tip, and deformation twinning governed the pronounced macroscopic crack-growth-retardation behavior following the tensile overload. A remarkable fracture surface of highly-periodic serrated features along the crack-propagation direction was found in the crack-growth region immediately after the tensile overload. Moreover, a transition of plastic deformation from planar dislocation slip-dominated to twinning-dominated microstructures in the extended plastic zone was clearly observed at room temperature in the overloaded condition, in accordance with the simulated results by a finite element method (FEM). The above tensile overload-induced simultaneously combined effects in the coarse-grained CoCrFeMnNi shed light on the improvement of fatigue resistance for HEAs applications.

Localized residual stresses were correlated to ductile fracture toughness quantitatively in steel and aluminium alloys using in situ neutron diffraction method coupled with elastic-plastic finite element modelling. Local out-of-plane compression (LOPC) method generated compressive and tensile residual stresses in the vicinity of the fatigue pre-crack front in two compact tension (CT) specimens, respectively, and the evolution of the stress fields was simultaneously measured using in situ neutron diffraction technique under mode-I fracture loading. The results clearly showed that the localized tensile residual stress apparently accelerated stress transfer at the mid-thickness of the CT specimen compared to the specimen having compressive residual stress. The coupled quasi-static ductile fracture simulations and neutron diffraction results revealed a clear correspondence of fracture initiation toughness with localized residual stresses in both steel and aluminium alloys. In the aluminium case, tensile residual stress of 208 MPa was obviously detrimental to the fracture toughness resulting in a 43% reduction while compression of −220 MPa increases by up to 14%. On the other hand, localized residual stress in steel hardly affected fracture initiation toughness due to high plastic dissipation energy. This experiment-simulation coupled study quantitatively elucidates the distinctive role of plastic deformation and stress triaxiality in ductile fracture initiation between steel and aluminium alloy.

In the present work, grain boundary sliding (GBS) has been studied for the grains exhibiting different orientations (for indentation parallel and perpendicular to axis) at different temperatures (RT to 200 °C) using nanoindentation in pure Zn. Electron back scattered diffraction was utilized to determine the orientation of the indented grains and identify the deformation mechanism, whereas atomic force microscopy was utilized to systematically quantify the GBS. Results indicated that indentation perpendicular to axis exhibits slip induced GBS, whereas the indentation parallel to axis results in pure GBS. The amount of GBS was also found to be strongly dependent upon the orientation of the neighboring grain. Further, the contribution from GBS towards total stain was found to increase with an increase in temperature.

In the present work, the tensile properties of 15–5 PH steel fabricated by selective laser melting (SLM) were examined with respect to the transient austenite phase. Compared with the 8%-transient-phase sample, the 18%-transient-phase one shows higher ultimate tensile strength and relatively low yield strength, as well as hardening behavior. We conducted in-situ neutron-diffraction study to examine the microstructure evolution for mechanistic understanding. After applying the external load, most non-equilibrium, retained austenite in the 8%-transient-phase sample transforms before the yield strength, whereas in the 18%-transient-phase sample only 50% of the austenite transforms. Accompanying with the phase transformation, a decrease in the dislocation density and the dislocation strain energy-assisted phase transformation of the ferrite phase are found in the 8%-transient-phase sample even before yielding, which, however, is not the case in the 18%-transient-phase sample. The study demonstrates the SLM enables tuning the amount of transient-phase ratio and coherency between phases to realize a mechanical property control for additive manufactured steel.

Influences of chemical dilution and the number of weld layers on residual stresses in a multi-pass low-transformation-temperature (LTT) weld were investigated by finite element modelling and neutron diffraction. A coupled thermal-metallurgical-mechanical (TMM) model that took into account the chemical dilution effect was developed to simulate the complex LTT welding phenomena. The model was strictly validated by comparing the predictions with experimental measurements and the results found good agreement between them. The results showed that a transformation strain caused by LTT martensitic transformation introduced large compressive residual stresses (−500 MPa) into the weld zone and the quantities were closely related to the chemical dilution between welding layers. Simulation results revealed that the chemical dilution helped mitigate the large localized tensile residual stresses by modulating the phase transformation process and a single LTT layer was sufficient to generate high compression near the weld surface (~2.5 mm), which suggests a great importance for repair welding. Keywords: Finite element analysis, Thermal-metallurgical-mechanical model, Martensitic transformation, Residual stress, Chemical dilution, Multi-pass weld

Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys (ODS-HEAs) were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties. Systematic microstructural analysis was carried out by X-ray diffraction (XRD), electron backscattered diffraction (EBSD), high-resolution transmission electron microscopy (HRTEM), atom probe tomography (APT), and small-angle neutron scattering (SANS). Cryo-milled powder analysis, grain structure evolution after spark plasma sintering, dispersoid characteristics, and matrix/dispersoid interface structure analysis of the in-situ and ex-situ dispersoids within the high-entropy alloy (HEA) matrix were performed. In-situ and ex-situ dispersoid formations were observed in the Y2O3-added ODS-HEA, whereas the in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical compositions. In-situ oxide dispersoids enhance the construction of ultrafine-grained structures up to approximately 300 nm in diameter. This study shows that the pre-alloying method, in which yttrium is alloyed, is efficient in achieving fine coherent dispersoids with an ultrafine-grained structure, resulting in a significant enhancement of the tensile strength of the CoCrFeMnNi HEA.

The influence of hydrogen on the mechanical behavior of Inconel 718 fabricated by laser powder-bed-fusion was investigated through a series of tensile experiments. Samples subjected to two different post-fabrication heat treatments, viz. direct aging (DA) and homogenization plus aging (HA), were tested. Detailed microstructural characterization showed that a solidification substructure including a high density of dislocations and precipitates prevails in the DA sample while the HA sample is free from such a substructure. The DA sample exhibited a comparatively higher strength, but a lower resistance to hydrogen embrittlement. By recourse to a statistical analysis of the hydrogen-assisted cracks, the severe hydrogen embrittlement of the DA sample was proven to be due to the significant portion of hydrogen-assisted intergranular cracks that occurred without the aid of slip localization. These results are discussed in terms of the changes in microstructure upon heat treatments, and their influences on the hydrogen trapping sites.

The residual stresses, microstructural heterogeneities, and mechanical properties were extensively examined in a 25 mm thick weld consisting of two regions which respectively undergo phase transformation at relatively low (100 °C) temperature (LTT) and high (670 °C) temperature (HTT) during cooling. Due to the LTT martensitic transformation, which features a transformation strain of ~4000 μe, large compressive residual stress (−510 MPa) was generated as confirmed by neutron diffraction and contour method. Meanwhile, significant heterogeneities were observed in terms of the chemical composition, yield strength, and microhardness across the interface between the LTT and HTT regions. The dependency of martensitic transformation starting temperature (Ms) on chemical composition is empirically formulated, and it reveals that the dependency of Ms on the Ni and Cr compositions becomes stronger when the temperature is lower than 200 °C. The maximum change of residual stresses (σxmax) exponentially decreases as Ms decreases in the manner of σxmax = 97.5 exp(Ms/227)-649. The fracture behavior was found highly dependent upon the volume fraction of retained austenite influenced by Ms. While a ductile fracture mode was found in the cellular LTT region containing relatively higher amount of retained austenite (~10%), the interface shows transgranular brittle fracture features and sub-cracking due to the relatively small amount of retained austenite and the predominant martensite constituent.

Surface-enhanced Raman spectroscopy (SERS) based on metallic nanoparticles has suffered from poor reproducibility and line broadening of SERS signals. To overcome these problems, we newly propose the SERS substrate incorporating periodic hybrid nanopillar arrays combined with gold nanorods on a flat gold surface. Low reproducibility caused by inhomogeneously distributed and aggregated gold nanoparticles could be improved by employing periodic nanopillar arrays. In addition, we experimentally found that the hybrid nanopillar, in which a dielectric layer is sandwiched between a flat gold film and a gold nanopillar, can reduce line broadening of SERS signals significantly. In this study, the proposed SERS substrate has the potential to provide SERS signals with higher reproducibility and smaller line broadening for high-sensitivity detection of target molecules.

An equal-molar CoCrFeMnNi, face-centered-cubic high-entropy alloy system is investigated using in-situ angular-dispersive X-ray diffraction under hydrostatic compression up to 20 GPa via diamond anvil cell. The evolutions of multiple diffraction peaks are collected simultaneously to elucidate the phase stability field. The results indicated that an irreversible phase transformation had occurred in the high entropy alloy upon decompression to ambient pressure. A reference material (n-type silicon-doped gallium arsenide) was investigated following the same protocol to demonstrate the different deformation mechanisms. It is suggested that the atomic bonding characteristics on the phase stability may play an important role in the high entropy alloys.

CoCrNi medium entropy alloy (MEA) and stainless steel 316L (SS316L) were manufactured by direct energy deposition of additive manufacturing (DED-AM). Exceptional mechanical properties of DED CoCrNi at 210K were achieved by the activities of a multiple deformation scheme that changed from dislocation slip to twinning-induced plasticity followed by transformation-induced plasticity. While SS316L at room temperature has micro-twins, CoCrNi at 210K exhibited nano-twins, resulting from lower stacking fault energy. Moreover, transformed hexagonal close-packed (HCP) phases were found near the face-centered cubic (FCC) {111} grain boundaries, where remarkable stacking faults and severe lattice distortion were measured. The formation of HCP substructure was understood from stacking fault probability, mean square strain, and lower temperature, which increased the strain hardening rate of several orientations in the FCC matrix, finally improving the strength of CoCrNi at 210K. A combination of CoCrNi MEA and DED-AM achieves a synergistic effect of strength, ductility and toughness for low temperature applications.

We examined the repetitive stress relaxation behavior of extruded AA7075 subjected to different heat-treatments (solid-solutionized (SS), under-aged (UA), peak-aged (PA)). Compared to SS and UA, the PA showed the highest stress drop (Δσs), plastic strain change (Δep) and re-yielding (Δσr), in conjunction with the largest reduction in mobile dislocation density right after stress relaxation. As stress relaxation cycles repeated, the stress drop decreased due to lower activities of mobile dislocations. During stress relaxation, the harder the grain orientation was, the more was the reduction in lattice strain. However, this tendency was not consistent with the order in the magnitude of the shear stresses imposed on the respective grains based on Schmid's law. The current results confirm the grain-orientation dependency on the relative activities of dislocation slip and diffusion-controlled creep during the stress relaxation at room temperature.

After tensile overloading during fatigue crack growth, retardation of the crack growth rate was significant. Neutron diffraction was employed to examine the evolution of crack-tip residual stress fields during constant-amplitude cyclic loading and during fatigue crack growth following the overload. It was found that the tensile overload induces larger compressive residual stress and zone size near the crack tip in the crack-growth and crack-opening direction. For the maximum crack growth retardation, the largest compressive residual stresses were measured in the region between an overloading point and the current propagating crack tip, for all three of the orthogonal directions. Such large compressive residual stresses in the crack-wake region are thought to reduce the crack tip driving force, thereby retarding the crack propagation rate significantly. Residual stress mapping was performed to examine the effect of the fatigue stress state on the residual stresses in the three different regions from the centerline to the surface, along the through-thickness direction in the compact-tension specimen. Much larger compressive residual stresses were measured at the surface than at mid-thickness. It is thought that larger compressive residual stresses at the surface result from the plane stress condition, resulting in a slower fatigue crack growth rate at the surface of the specimen.

Half-scan image reconstruction with Parker weighting can correct motion artifacts in dental CT images taken with a slow scan-based dental CT. Since the residual half-scan artifacts in the dental CT images appear much stronger than those in medical CT images, the artifacts often persist to the extent that they compromise the surface-rendered bone and tooth images computed from the dental CT images. We used a variation of generative adversarial network (GAN), so-called U-WGAN, to correct half-scan artifacts in dental CT images. For the generative network of GAN, we used a U-net structure of five stages to take advantage of its high computational efficiency. We trained the network using the Wasserstein loss function on the dental CT images of 40 patients. We tested the network with comparing its output images to the half-scan images corrected with other methods; Parker weighting and the other two popular GANs, that is, SRGAN and m-WGAN. For the quantitative comparison, we used the image quality metrics measuring the similarity of the corrected images to the full-scan images (reference images) and the noise level on the corrected images. We also compared the visual quality of the surface-rendered bone and tooth images. We observed that the proposed network outperformed Parker weighting and other GANs in all the image quality metrics. The computation time for the proposed network to process 336 × 336 × 336 3D images on a GPU-equipped personal computer was about 3 s, which was much shorter than those of SRGAN and m-WGAN, 50 s and 54 s, respectively.

Graphical abstract Image 1, Highlights F0FC • In-situ thermal cycling neutron diffraction experiments. F0FC • The effect of thermal history during additive manufacturing was revealed. F0FC • During cycling, phase transformation changed from fully-reversible to irreversible. F0FC • Inhomogeneous residual stresses were developed. F0FC • Martensite showed higher compressive residual stress and lower dislocation density.

The effect of a small lanthanum (La) addition on Mg–10 wt% Dy alloy has been studied using isothermal aging at 120 °C. A combination of scanning transmission electron microscope (STEM) imaging and high-angle annular dark field (HAADF) based electron tomography has been used to characterize the precipitates. β F ′ and β′ precipitates were determined, where β F ′ precipitates form a bridge connecting two β′ precipitates, thus forming a continuous network of precipitates. This network results in a significant increase in hardness.

Manipulation of dispersion curve for enhancing surface plasmon resonance (SPR) detection is proposed. Based on strong correlation between slope of dispersion curve and SPR angle shift, it is confirmed that dispersion curve characteristics can be employed as an analysis tool to evaluate SPR sensor performance and to predict anomalous plasmonic behaviors. Complicated resonance shift in SPR angle, especially in the presence of metallic nanograting, such as negative shift, can be controlled reliably by engineering the dispersion curve. As it has a dependence on geometrical parameters of metallic films and gratings, dispersion relation engineering is also useful in optimizing the sensor sensitivity. For a wavelength of λ =630 nm, introduction of a gold nanograting shows a significant improvement in sensitivity by more than 5 times, compared to a traditional thin-film-based SPR structure. In addition, we find that use of a longer wavelength in near-infrared region can be advantageous for avoiding a negative SPR shift and obtaining a narrow and deep SPR curve. Our approach is expected to extend the applicability of dispersion-based sensitivity engineering technique to a variety of SPR platforms for highly enhanced SPR detection.

Lead-free BNT-ST and La 0.5 Ni 0.5 O 3 (LNO) bottom electrode films were epitaxially grown onto CeO 2 /YSZ (yttria stabilized zirconia) buffered Si (001) substrates via pulsed laser deposition. The lattice alignment of CeO 2 /YSZ and BNT-ST/LNO showed 45° twisted cube-on-cube epitaxial relationship, indicating high crystallinity for the BNT-ST and LNO films. The constituent elements in the BNT-ST/LNO/CeO 2 /YSZ structure showed no distinct diffusion between the layers. The BNT-ST epitaxial films demonstrated ferroelectric properties, but exhibited a high degree of leakage current density.

The cyclic deformation behavior of extruded Mg-8.5wt.%Al alloy with a conventional extrusion texture and a modified texture is systematically investigated by in-situ neutron diffraction and elastic viscoplastic self-consistent (EVPSC) modeling incorporating a twinning/de-twinning (TDT) scheme. The role of twinning and de-twinning on the deformation behavior of Mg-8.5wt.% Al alloy is investigated in terms of the macroscopic stress-strain response, the evolution of the activities of various deformation mechanisms, the texture evolution, the evolution of the internal elastic strains, and the evolution of the diffraction peak intensities. The alloy with the conventional extrusion texture undergoes twinning during initial compression and de-twinning during reverse tension. The same alloy does not favor twinning during initial tension, but rather during reverse compression. The alloy with a modified texture undergoes twinning during initial tension followed by detwinning during reverse compression. The results provide insights into the effect of initial texture, loading path, slip, twinning, de-twinning on the cyclic behavior of magnesium., Comment: 19 pages, 8 figures, intended to submit to Acta Materialia

All available phase diagram data for the (Ce + Mg + Zn) system were critically assessed. In-situ neutron diffraction (ND) experiments were performed on selected samples to identify phases and transition temperatures. A critical thermodynamic evaluation and optimization of the (Ce + Mg + Zn) system were carried out and model parameters for the thermodynamic properties of all phases were obtained. The phase transformation behaviour of selected samples was well resolved from the ND experiments and experimental data were used to refine the thermodynamic model parameters.

This study developed multi-functional acrylic urethane coating materials with anti-graffiti, anti-contamination, and anti-adhesion properties. The newly-developed coating was synthesized by high glass transition temperature ( T g ) acrylic polyol and low-viscosity single-end-type silicone oil. The coating materials were chemically bonded and reacted with isocyanate to form acrylic urethane. The hardness, surface energy, color difference value, and anti-adhesion properties were examined using nanoindentation, a contact angle analyzer, a color difference meter, and a universal tensile test machine, respectively. In addition, the degradation of the coating was evaluated using an accelerated weathering test, taking into account various degradation factors (UV, humidity, high temperature, and water). In general, the properties of the coating degraded due to the loss of silicone oil after the accelerated weathering test. However, the degradation was retarded when high T g acrylic polyol and low-viscosity single-end-type silicone oil were chemically bonded. The newly-developed multi-functional acrylic urethane coating exhibited long-term stability against an accelerated weathering test of 120 h. The developed coating will be useful in broad applications, including harsh environments such as underground walls, heritage, facilities, and subways.

The complex thermal cycle in additive manufacturing (AM) strongly depends on process parameters such as the building direction, scanning strategy, layer thickness and particle size. It is difficult to predict the mechanical properties determined by the process parameters because different parameters lead to various thermal gradients, which influences the microstructural evolution and mechanical properties of the materials. In this study, we investigated the microstructural evolution and local mechanical properties of direct melting laser sintered (DMLS) 15-5 PH stainless steel as a function of the building direction (i.e., vertical and horizontal) and the heat-treatment conditions (i.e., solid solution, aging). AM samples are composed of much smaller grains and exhibit a finer microstructure, together with a higher hardness, compared to conventional 15-5 PH samples. The AM process transforms martensite to austenite, but the solution heat treatment impedes this transformation. The austenite obtained using the AM process reverted to martensite with decrease in hardness after solid solution treatment. In case of aging, although the hardness increased, values are independent of the grain size and microstructural morphologies. 15-5 PH fabricated in the horizontal direction have higher hardness than those in the vertical direction, except for aged samples. The grain size and morphology, which were similar in both building directions, does not have any significant effect on the hardness anisotropy. The AM process, which has building directionality in heat dissipation, exhibits hardness anisotropy from differences in the inherent structure on a much smaller scale.

In the present study, the influence of yttrium (Y) addition on the recrystallization, texture and mechanical properties of Mg–Y alloys has been examined. In particular, the properties of two binary Mg–Y alloys viz. Mg–5Y and Mg–10Y have been compared. The addition Y appears to enhance the propensity of contraction twinning and double twinning. This also results in variable stored energy prior to recrystallization in the Mg–5Y and Mg–10Y alloys. The results suggested that increasing the Y content substantially retards the recrystallization kinetics, which was attributed to the increase in the extent of pinning of the grain boundaries due to an increase in the solutes. Moreover, increasing the amount of Y was also found to significantly weaken the texture in both the as-rolled and annealed conditions. Overall, Mg–10Y alloy exhibited much better mechanical properties as compared to Mg–5Y alloy.

This study used in-situ neutron diffraction measurements and Elastic ViscoPlastic Self-Consistent polycrystal plasticity model, which incorporates a Twinning and DeTwinning scheme (denoted by EVPSC-TDT), to examine the macro-and micro-mechanical behaviors of a rolled AZ31B plate subjected to uniaxial tension. Three specimens were specifically designed for minimum, maximum and intermediate twinning: (1) loading along the rolling direction, (2) loading along the plate normal, and (3) loading along the direction 45° with respect to the plate normal. Apart from the macroscopic stress strain response, the measured diffraction intensities and internal elastic strains were obtained to examine the activities of the deformation modes at the grain level. The diffraction intensity evolution signaled the volume fraction change of twinning, while the internal elastic strain evolution designated the stress partitioning among the grain orientations. The effect of the surrounding grains on the development of the internal elastic strain was investigated by identifying the corresponding deformation mechanisms. Notably, the corresponding modeling work revealed that the EVPSC-TDT model permitted the prediction of the strain hardening and anisotropic behavior along the directions with minimum, maximum and intermediate twinning at the macroscale, and the evolution of the diffraction intensities and internal strains at the microscale. The results provide a physical understanding of the effects of the load direction, texture and surrounding grains on the role of the deformation modes in hexagonal close-packed polycrystalline materials.

Thin-film multi-layer ceramic capacitors (MLCCs) were prepared using high-dielectric constant Bi 2 Mg 2/3 Nb 4/3 O 7 thin-films deposited at room temperature via radio-frequency magnetron sputtering. The multi-layer capacitors, in sizes 0402, 0603 and 1005, were well equipped with both inner and outer Cu electrodes. The capacitances of the bi-layer capacitors were twice that of the single-layer version in sizes 0402, 0603, and 1005. The 200 nm-thick Bi 2 Mg 2/3 Nb 4/3 O 7 thin-films would be suitable for thin-film multi-layer capacitor applications.

The effect of the shear deformation and the superimposed hydrostatic pressure on the formability of magnesium alloy sheet is simulated in terms of the forming limit diagram (FLD). The model employed is the elastic viscoplastic self-consistent (EVPSC) crystal plasticity model, which accounts for both slip and twinning systems as the deformation mechanisms. The conventional sheets have low formability at room temperature due to the strong basal texture developed by the rolling process. However differential speed rolling process develops relatively weak basal texture by introducing shear deformation. Therefore the formability of the sheets produced by differential speed rolling is enhanced. In terms of the superimposed hydrostatic pressure, it delays the onset of necking and therefore improves the formability of sheets. In addition, the effect of crystal elasticity on the formability of sheets is numerically studied.

A strategy is proposed to enhance the microstructure and mechanical properties of Mg–Zn alloys by combining microalloying additions of the rare earth element Ce and the non-rare earth element Ca. The double additions of Ce–Ca are found to significantly increase tensile elongation compared to binary Mg–Zn, or single additions of either Ce or Ca. Microstructure analysis reveals that the Ce–Ca additions increase ductility by modifying texture and refining grain size. Texture modification is attributed to solute effects from the microalloying elements, particularly Ca, while grain refinement is additionally influenced by a fine dispersion of Mg6Ca2Zn3 precipitates that form during rolling and pin grain boundaries. The microalloying element additions also lead to large secondary phase particles in the alloys, which can limit ductility enhancement by promoting early fracture. By scaling Zn content in the Mg–Zn–Ce–Ca alloys, the Mg6Ca2Zn3 phase fraction and Zn solute content can be controlled for optimum ductility or strengthening potential.

In situ neutron diffraction and elastic–viscoplastic self-consistent (EVPSC) modeling have been employed to understand the deformation mechanisms of the loading–unloading process under uniaxial tension in a solid-solution-strengthened extruded Mg–9 wt.% Al alloy. The initial texture measured by neutron diffraction shows that the {00.2} basal planes in most grains are tilted around 20–30° from the extrusion axis, indicating that basal slip should be easily activated in a majority of grains under tension. Non-linear stress–strain responses are observed during unloading and reloading after the material is fully plastically deformed under tension. In situ neutron diffraction measurements have also demonstrated the non-linear behavior of lattice strains during unloading and reloading, revealing that load redistribution continuously occurs between soft and hard grain orientations. The predicted macroscopic stress–strain curve and the lattice strain evolution by the EVPSC model are in good agreement with the experimental data. The EVPSC model provides the relative activities of the available slip and twinning modes, as well as the elastic and plastic strains of the various grain families. It is suggested that the non-linear phenomena in the macroscopic stress–strain responses and microscopic lattice strains during unloading and reloading are due to plastic deformation by the operation of basal 〈a〉 slip in the soft grain orientations (e.g. {10.1}, {11.2} and {10.2} grain families).

Plastic anisotropy and deformation-induced phase transformation of additively manufactured (AM) stainless steels were investigated via in-situ neutron diffraction, electron backscatter diffraction, metallography, and fractography. Two types of tensile specimens were manufactured: (1) One sample was vertically fabricated with its tensile axis parallel to the z-direction (AM-V), (2) The other sample was horizontally fabricated with its tensile axis perpendicular to the z-direction (AM-H). A commercial 15-5PH stainless steel (CA) was used for comparison. AM steel revealed enhanced yield strength, tensile strength, and uniform elongation over CA, which was mainly due to grain refinement and transformation induced plasticity (TRIP). Different onsets of strain nonlinearity between AM-V and AM-H were closely related to martensitic phase transformation. Stresses estimated from lattice strains measured by neutron diffraction matched well with the applied stress-strain curves. After plastic deformation, voids were formed and congregated near the solidified line where fine grains were populated. Higher dislocation density was observed in the fine grain zone, and lower density was shown in the relatively coarse grain zone. AM steels exhibited significant anisotropic fracture behavior in terms of loading direction. In contrast to isotropic failure for CA and AM-V, AM-H revealed anisotropic failure with elliptical formation of the fracture feature. The fracture surface of AM-H possessed many secondary cracks propagating perpendicular to the building direction. The occurrence of secondary cracks in AM-H resulted in rapid load drop during tensile loading after necking.

The deformation dynamics and the effect of deformation history on plastic deformation in a wrought magnesium alloy at room temperature have been studied by real-time in situ neutron diffraction measurements under a continuous loading condition. The experimental results reveal that no detwinning occurred during unloading after compression and even in an elastic region during reverse tension. It is found that the serration behavior is closely related to the twinning- and detwinning-dominated deformation.

In-situ neutron diffraction was employed to directly measure the crystallographic-orientation-dependent (i.e. hkl) internal strains as a function of distance from the crack tip on the pre-cracked Hastelloy C-2000 compact-tension specimen. Both in-plane (IP) and through-thickness (TT) strain evolutions for various grain orientations were examined during tensile overloading and compressive underloading cycles. After overloading, underloading and their combination loadings were applied and unloaded, the significantly different {hkl} residual strain profiles were obtained in the vicinity of the crack tip. The load responses of the {200} grain orientation in both the IP and TT directions were more significant than those of any other orientations. It is suggested that the different orientation-dependent strain distributions around the crack tip are caused by the combined effects of elastic and plastic anisotropy of each {hkl} reflection upon loading and the subsequent development of residual stresses generated near the crack tip during unloading as a result of the plastic deformation.

In-situ neutron diffraction was used to investigate the twinning and detwinning behavior during fatigue-crack propagation on a wrought magnesium alloy, AZ31B, compact-tension specimen, where fatigue loading was applied parallel to the plate normal. Reversible twinning and detwinning characteristics were observed as a function of the distance from the crack tip. While twinning was activated above a certain critical stress value, detwinning occurred immediately upon unloading. It is thought that the development of compressive residual stresses generated around the crack tip during unloading is responsible for the detwinning behavior. Neutron bulk texture measurements were performed at several locations away from the crack tip (i.e. locations behind, right in front of, and far away from the crack tip) to quantitatively examine the volume fraction of {10.2}〈10.1〉 extension twins in the vicinity of the crack tip. The texture analyses demonstrated that the texture in the fatigue-wake region did not change significantly, compared to that in the undeformed region far away from the crack tip, and approximately 11% of the residual twins were left behind the crack tip. The current results reveal that the reversible twinning and detwinning are the dominant deformation mechanisms for the studied material subjected to cyclic loading, and only a small amount of residual twins remain after the crack propagation. The spatial distribution of twinning/detwinning transitions correlates well with our previous predictions of the stress fields in the vicinity of a fatigue crack tip.

Background Many reports have described tracheal replacement using aortic allografts, with varying results and minimal understanding of the mechanism of tracheal regeneration. The present study attempted tracheal regeneration in adult dogs using fresh aortic allografts (FAA) and cryopreserved aortic allografts (CAA). Materials and Methods Twelve adult beagles underwent tracheal resection and were transplanted with FAA ( n = 5) or CAA ( n = 7). Animals were followed-up with serial radiography and magnetic resonance imaging, and were euthanized at predetermined times up to 16 mo post-surgery. Results There were no procedural deaths, but two animals died due to stent migration. Stent migration occurred in seven of the 12 animals. Evidence of regeneration of tracheal epithelium was observed in the surviving animals, with the transformation of squamous metaplasia to mucociliary epithelium being time-dependent. Islet of cartilage were observed in animals after 6 mo, but ring-like cartilage structures were absent, even after 16 mo. During autopsy, axial graft contractions up to 68% were observed. Serial radiographs show that most of the contraction occurred within 1 mo. The results of the MRI showed that the graft area was strongly enhanced for up to 2 mo, but was clearly reduced after 3 mo. Conclusions Tracheal replacement in adult dogs using FAA or CAA is feasible. However, immaturity of the neotracheal cartilage did not allow the tissue to function as native tracheal tissue. Prolonged stenting should be considered in adult if the procedure is to be clinically contemplated.

Strain distribution in compressed tissues gives information about elasticity of the tissues. We have measured strain from two sets of 3D micro-CT images of a breast-mimicking phantom; one obtained without compressing the phantom and the other with compressing it. To measure strain, we first calculated compression-induced displacements of high-intensity feature patterns in the image. In measuring displacement of a pixel of interest, we searched the pixel in the compressed-phantom image, whose surrounding resembles the uncompressed-phantom image most closely, using the image correlation technique. From the displacement data, we calculated average strain at a region of interest. With the calculated average strains, we could distinguish the hard inclusion in the phantom which was not distinguishable from the background body of the phantom in the ordinary micro-CT images. The calculated strains account for stiffness of the tissue of interest, one of the important parameters for diagnosing malignant tissues. We present experimental results of the displacement and strain measurement along with FEM analysis results.

This study aimed to investigate the hypothesis that administration of the air with 30% oxygen compared with normal air (21% oxygen) enhances cognitive functioning through increased activation in the brain. A visuospatial task was presented while brain images were scanned by a 3 T fMRI system. The results showed that there was an improvement in performance and also increased activation in several brain areas in the higher oxygen condition. These results suggest that a higher concentration of breathed oxygen increases saturation of blood oxygen in the brain and facilitates performance.

The average cerebellar volume of Korean men (135.19 cm3) is larger than that of Korean women (123.06 cm3), and that of subjects in their twenties (134.28 cm3) is larger than that of subjects in their forties (121.83 cm3). Atrophy of the cerebellum is more markedly observed in men than in women. There is a relation between body weight and cerebellar volume for men, but not for women.