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• The microstructure evolution of AXM050703 alloy was systematically studied. • The interaction of {10–12} twins, {10–11} - {10–12} twins and kinks were studied. • The multi-pass rolled samples with different microstructures were prepared. • The strength of these rolled alloy (alloying elements only 1.5 wt.%) is higher than AZ31B. The dynamic microstructure and texture of dilute Mg-0.50Al-0.71Ca-0.33Mn (wt.%) during hot rolling at two slab temperatures were investigated by electron backscattered diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM). The results show that the development of the rolling microstructures is to first form {10–12} extension twins in the original grains, thereby forming the extension-twinned regions, and then to further form {10–11} - {10–12} double twins and kinks in the extension-twinned regions, and finally to form continuous dynamic recrystallized (continuous DRXed) grains in the double twins and the cross parts of the shear-deformed coarse extension-twinned regions. These extension twins, double twins and kinks show a decisive effect on the formation of rolling texture. The number of {10–11} - {10–12} double twins and resultant the continuous DRX process are strongly affected by the rolling slab temperature and the reduction thickness per pass. By optimizing the rolling conditions, texture and microstructures of the multi-pass rolled Mg-Al-Ca-Mn alloy sheets are successfully modified. Although the total alloy content is only 1.5 wt.%, these Mg-Al-Ca-Mn alloy sheets show much higher strength than the commercial Mg-3Al-1 Zn (wt.%) (AZ31B) sheet. [Display omitted] [ABSTRACT FROM AUTHOR]

• Stress relaxation (SR) behavior and mechanism of Ti-6Al-4V load from 0.3% to 10% at 700–850 °C are evaluated. • Different SR behavior at all initial strain levels at 700–750°C is dominated by dislocation-phase interactions. • Similar SR behavior at 800–850 °C is due to the concurrent dislocation and diffusion creep. • Apparent strength loss after SR results from the distorted and fragmented β layers. In this study, the stress relaxation (SR) behaviors of a Ti-6Al-4V alloy pre-loaded from elastic to plastic regions and corresponding strength evolution mechanisms at different temperatures were systematically studied. In order to quantitatively analyze the detailed deformation and strength evolution mechanisms during the whole SR tests, which is composed of the loading stage and subsequent SR stage, the evolutions of α/β structures and dislocations have been identified by a series of microstructural observations, i.e., scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS). A great quantity of entangled dislocations in α phase introduced by the plastic loading at temperatures below 800 °C promotes the emergence of SR behavior with a higher creep rate, leading to the much higher SR level with larger pre-load levels. Diffusion is significantly enhanced by dislocations accumulated at interfaces with higher temperatures (> 800 °C), contributing to a similar SR phenomenon under different initial strain levels. Apparent strength loss has been observed after SR with high temperatures or pre-loaded to the plastic region, e.g., 94 MPa loss for 800 °C, pre-loaded with a stain of 10% and SR for 2400 s. The strength loss mainly comes from the loading stage where distorted and fragmented β layers occur. The subsequent SR stage facilitates interfacial diffusion and results in a higher fraction of granular β phases, leading to a further decrease in yield strength (YS). This study enhances the understanding on the deformation and strength evolution mechanisms of titanium alloys with lamellar structures in the whole SR process, providing a physical foundation for optimizing the processing parameters for manufacturing titanium alloy components with high accuracy and performance. [Display omitted] [ABSTRACT FROM AUTHOR]

• A near-α TNW700 titanium alloy exhibtis excellent superplaticity with elongation above 400% at 925°C. • Flow stress curve behave as long period strain hardening and large strain softening. • Continuous dynamic recrystallization induced primary α phase refinement at the later deformation stage. • The strain hardening is attributed to β grain growth, silicide precipitates and α phase solid solution strengthening. • Dynamic dislocation recovery, α grain refinement and β phase volume fraction increase together cause flow softening. The new near-α TNW700 titanium alloy is a potential candidate material for high performance ultrasonic/hypersonic aircrafts, which is designed for short-term service at 700°C. This study systematically investigated the superplastic deformation microstructure evolution and mechanism of TNW700 alloy at different strain rates and true strains at 925°C. Results show that TNW700 alloy exhibits excellent superplastic behavior in a constant strain rate range of 0.0005–0.005 s−1 with elongation above 400%. The peak stress decreases with decreasing strain rate, which is related to the increase of β-phase volume fraction caused by the increase of thermal exposure time. In addition, significant strain hardening is observed in early-middle stage of superplastic deformation, and flow softening is followed in middle-late stage. To rationalize these complex flow behaviors, electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) were used to characterize the microstructure. Strain hardening is correlated to the synergistic effect of β grain growth, dislocation accumulation, silicide precipitate, and solid solution strengthening of α phase. Continuous dynamic recrystallization (CDRX) induced the fragmentation of primary α grains in middle-late stage of superplastic deformation, and the refinement of α grains, the increase of β phase volume fraction and dynamic dislocation recovery are main causes of high strain softening. In addition, EBSD and TEM observations confirmed texture randomization, fine equiaxed primary α grains and intragranular dislocation movement, indicating that grain boundary sliding (GBS) accommodated by dislocation sliding / climb is the dominant superplastic deformation mechanism of TNW700 alloy. [ABSTRACT FROM AUTHOR]

• The interface of martensite twins in Ti-Ni-Hf shape memory alloy composite was studied. • The formation mechanisms of {111} type I twins in Ti-Ni-Hf alloy was revealed. • The lattice dislocations and misfit dislocations of the interface of martensite variant are identified. In the present study, the interface of martensite twins in Ti-Ni-Hf shape memory alloy composite was studied by high resolution transmission electron microscopy in terms of atomic structure. The results reveal that two varieties of interface structure for {111} type I twins are observed, which is determined by the interior substructure (001) compounds twin. The formation of {111} type I twins can be attributed to the interaction between the misfit dislocations on (001) plane and (1 ¯ 11) twin boundary. In addition, the corresponding characteristic parameters of misfit dislocation were calculated in theory. The theoretical value of disregistry factor and average spacing for the misfit dislocations are well in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Due to the sodium abundance and availability, sodium-ion batteries (SIBs) have the potential to meet the worldwide growing demand of electrical energy storage. P2-type sodium transition-metal layer oxides with a high energy density are considered as the most promising cathode materials for SIBs. We present here a detailed study of the enhanced rate capability and cyclic stability of the Ti-doped Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode material. The combined analysis of ex-situ X-ray absorption fine structure (XAFS) spectroscopy, aberration-corrected high resolution transmission electron microscopy (AB-HRTEM) and X-ray diffraction (XRD) show that the strong Ti–O bond in the transition metal layers stabilizes the local structure, destroy the Na+-vacancy ordering and arrest the irreversible multiphase transformation that occurs during the intercalation/deintercalation process. Actually, Na 0.67 Ni 0.33 Mn 0.52 Ti 0.15 O 2 exhibits a reversible capacity of 89.6 mA h g−1 even at 5 C, an excellent cyclability with 88.78 % capacity retention after 200 cycles at 0.5 C. This study provides a better understanding in optimization of the design of high-energy cathode materials based on titanium doped layered oxides for SIBs. [ABSTRACT FROM AUTHOR]

This work characterizes microstructural evolutions of electron beam melted (EBM) Ti-6Al-4V alloy modified via laser shock peening (LSP). The depth stress distribution and tensile properties of EBM Ti-6Al-4V alloy were measured before and after LSP. The results indicate that microstructure consists of β phase with 7.2% ± 0.4% vol.% and balance α lamellar in EBM sample, and the α lamella was refined into nano-equiaxed grains and submicro-equiaxed grains after LSP. The dominant refinement mechanism is revealed during LSP. Stacking faults were found in the LSP-treated sample, and their corresponding planes were determined as (0001) basal plane, (10 1 ¯ 0) prismatic plane, and (10 1 ¯ 1 ¯) pyramidal plane obtained by high resolution transmission electron microscopy. The subgrains and high-angle grains formed during dynamic recrystallization were identified by selected area electron diffraction pattern. The LSP treatment produces a significantly residual compressive stress approximately -380 MPa with the depth of compressive stress layer reaching 450 μm. Strength and elongation of the EBM sample were significantly increased after LSP. The strength and ductility enhancements are attributed to compressive stress, grain refinement and grain gradient distribution of α phase. [ABSTRACT FROM AUTHOR]

Manufacturing temperatures of severely cold-drawn hyper-eutectoid steel wires are sufficiently high to influence the mobility of dislocations and alloy elements, thereby affecting the materials' mechanical properties. Herein, we describe the evolution of microstructure and tensile strength of the as-drawn 3.45 GPa steel wire during post-deformation annealing for 30 min at 150−450 °C. Annealing at 150 °C raised the strength to 3.77 GPa by age-hardening through activation of dislocations pinning by carbon, while further temperature rising up to 450 °C caused a severe loss of strength. It was proved that annealing at 300 and 450 °C destabilizes the lamellar microstructure, promoting the formation of carbon-deficient (Fe,Mn,Cr) 3 C-type cementite particles with preferentially rounded and partially faceted hetero-interfaces. Annealing at 450 °C yielded the accumulation of Mn and Cr at the ferrite/particle interfaces, and their concentrations at the interfaces were dependent on the interface structure; i.e., lower concentrations at rounded interfaces (formed through capillarity–driven coarsening of the spheroidized cementite), and higher concentrations at faceted interfaces (that are initially existing in the as-drawn state). Our proof-of-principle observations, supported by thermodynamic calculations and kinetic assessments, provide a pathway for understanding the changes in microstructural and tensile properties during manufacturing of the hyper-eutectoid steel wires. [ABSTRACT FROM AUTHOR]

One dimensional Amosic-3 silicon carbide fiber reinforced silicon carbide matrix composites (SiC f /SiC minicomposites) prepared by chemical vapor infiltration were irradiated with 2.8 MeV proton ions. The ion fluences were 1.0 × 1017 and 1.5 × 1017 cm−2 at room temperature and 300 °C, respectively. The microstructure and mechanical properties were investigated before and after proton irradiation. Raman spectra showed no evident change in Amosic-3 fibers regardless of irradiation temperature, which is confirmed by high resolution transmission electron microscopy observation. Pyrolytic carbon interphase showed slightly expansion after 300 °C irradiation, however, no microstructure changes were observed in SiC matrix. Moreover, it can be deduced that no irradiation induced changes in mechanical properties were observed after present proton irradiation. [ABSTRACT FROM AUTHOR]

Self-lubrication is one of the smart material properties required for producing components with enhanced wear resistance and low coefficient of friction. Bidirectional (BD) satin weave polyacrylonitrile (PAN) based carbon fiber (C f) fabric preform was successfully infiltrated with Al 6061 alloy by squeeze infiltration process. The infiltrated composite shows uniform distribution of carbon fibers in the matrix with the elimination of porosities, fiber damage and close control on the formation of deleterious aluminum carbide (Al 4 C 3) phase. C f /Al composite exhibits remarkable wear resistance compared to unreinforced alloy due to the formation of self-lubricating tribolayer on the pin surface, which intercepts the contact of matrix metal to counter surface. The BD carbon fiber enhanced the hardness and compressive strength of the composite by restraining the plastic flow behavior of matrix. High resolution transmission electron microscopy shows the presence of Al 2 O 3 and MgAl 2 O 4 spinel, confirmed by EDS and SAD pattern, at the composite interface. The composite shows a lower density of 2.16 g/cm3 which is a major advantage for weight reduction compared to the monolithic alloy (2.7 g/cm3). [ABSTRACT FROM AUTHOR]

10 1 ¯ 1 compression twins with high density stacking faults were studied at atomic scale using Cs-correction transmission electron microscopy. On one side of the 10 1 ¯ 1 twin boundary, there were many steps arranged alternately with the coherent twin boundaries. Most of the steps were linked with stacking faults inside twins. Burgers vector of twinning dislocations and the mismatch strain at steps were characterized. Due to the compressive mismatch strain at steps, the high density stacking faults inside twins were formed at twin tips during twinning process. The localized strain at the steps would be related to the crack nucleation in magnesium alloys. [ABSTRACT FROM AUTHOR]

Abstract Cold spray additive manufacturing (CSAM) provides a potential solid state manufacturing route to fabricate variety of aluminum matrix composites (AMCs) with reduced possibility of undesired chemical reactions and residual thermal stresses. This study presents a hybrid (i.e. hot compression + hot rolling) post-deposition treatment to reinvigorate the mechanical properties of cold spray additively manufactured Al/B 4 C composites. The as-deposited samples were initially subjected to 30% thickness reduction via hot compression treatment at ∼500 °C followed by a hot rolling treatment with 40% thickness reduction in 2 passes. Electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) results revealed that after hybrid post-deposition treatment (involving 70% accumulative thickness reduction), the aluminum grains in the matrix were extensively refined due to simultaneous operation of continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX). Furthermore, interfacial defects were remarkably reduced while the nature of Al/Al and Al/B 4 C interfacial bonding was changed from sheer mechanical interlocking to metallurgical bonding which facilitated efficient transference of applied load to uniformly dispersed bimodal B 4 C particles. As a result, ultimate tensile strength (UTS) and elongation (EL) of the as-deposited sample were simultaneously improved from ∼37 to 185 MPa and ∼0.3% to 6.2%, respectively. [ABSTRACT FROM AUTHOR]

In the present work, we performed experiments, atomistic simulations, and high-resolution electron microscopy (HREM) to study the creep behaviors of the nanotwinned (nt) and nanograined (ng) copper at temperatures of 22 °C (RT), 40 °C, 50 °C, 60 °C, and 70 °C. The experimental data at various temperatures and different sustained stress levels provide sufficient information, which allows one to extract the deformation parameters reliably. The determined activation parameters and microscopic observations indicate transition of creep mechanisms with variation in stress level in the nt-Cu, i.e., from the Coble creep to the twin boundary (TB) migration and eventually to the perfect dislocation nucleation and activities. The experimental and simulation results imply that nanotwinning could be an effective approach to enhance the creep resistance of twin-free ng-Cu. The experimental creep results further verify the newly developed formula (Yang et al., 2016) that describes the time-, stress-, and temperature-dependent plastic deformation in polycrystalline copper. [ABSTRACT FROM AUTHOR]

In a recent publication, we investigated the prospect of measuring the outer three-dimensional (3D) shapes of nano-scale atom probe specimens from tilt-series of images collected in the transmission electron microscope. For this purpose alone, an algorithm and simplified reconstruction theory were developed to circumvent issues that arise in commercial “back-projection” computations in this context. In our approach, we give up the difficult task of computing the complete 3D continuum structure and instead seek only the 3D morphology of internal and external scattering interfaces. These interfaces can be described as embedded 2D surfaces projected onto each image in a tilt series. Curves and other features in the images are interpreted as inscribed sets of tangent lines, which intersect the scattering interfaces at unknown locations along the direction of the incident electron beam. Smooth angular variations of the tangent line abscissa are used to compute the surface tangent intersections and hence the 3D morphology as a “point cloud”. We have published the explicit details of our alternative algorithm along with the source code entitled “stomo_version_1”. For this work, we have further modified the code to efficiently handle rectangular image sets, perform much faster tangent-line “edge detection” and smoother tilt-axis image alignment using simple bi-linear interpolation. We have also adapted the algorithm to detect tangent lines as “ridges”, based upon 2nd order partial derivatives of the image intensity; the magnitude and orientation of which is described by a Hessian matrix. Ridges are more appropriate descriptors for tangent-line curves in phase contrast images outlined by Fresnel fringes or absorption contrast data from fine-scale objects. Improved accuracy, efficiency and speed for “stomo_version_2” is demonstrated in this paper using both high resolution electron tomography data of a nano-sized atom probe tip and simulated absorption-contrast images. Program summary: Program title: STOMO version 2 Catalogue identifier: AEFS_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFS_v2_0.html Program obtainable from: CPC Program Library, Queenʼs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 2854 No. of bytes in distributed program, including test data, etc.: 23 559 Distribution format: tar.gz Programming language: C/C++ Computer: PC Operating system: Windows XP RAM: Scales as the product of experimental image dimensions multiplied by the number of points chosen by the user in polynomial fitting. Typical runs require between 50 Mb and 100 Mb of RAM. Supplementary material: Sample output files, for the test run provided, are available. Classification: 7.4, 14 Catalogue identifier of previous version: AEFS_v1_0 Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 676 Does the new version supersede the previous version?: Yes Nature of problem: A local electron tomography algorithm of specimens for which conventional back projection may fail and or data for which there is a limited angular range (which would otherwise cause significant ‘missing-wedge’ artefacts). The algorithm does not solve the tomography back projection problem but rather locally reconstructs the 3D morphology of surfaces defined by varied scattering densities. Solution method: Local reconstruction is effected using image-analysis edge and ridge detection computations on experimental tilt series to measure smooth angular variations of surface tangent-line intersections, which generate point clouds decorating the embedded and or external scattering surfaces of a specimen. Reasons for new version: The new version was coded to cater for rectangular images in experimental tilt-series, ensure smoother image rotations, provide ridge detection (suitable for sensing phase-contrast Fresnel fringes and other fine-scale structures), faster/larger kernel edge detection and also greatly reduce RAM usage. Specimen surface normals are also explicitly computed from tangent-line and edge intersections, providing new information for potential use in point cloud rendering. Hysteresis thresholding implemented in the version 1 edge-detection algorithm provided only sparse edge-linking. Version 2 now implements edge tracking using recursion to fully link the edges during hysteresis thresholding. Furthermore in version 1 the minimum number of fitted polynomial points (specified in the input file) was not correctly imposed, which has been fixed for version 2. Most of these changes increase the accuracy of 3d morphology surface-tomography reconstructions by facilitating the use of more/finer tilt angles and experimental images of increased spatial-resolution. The ridge detection was incorporated to specifically improve the reconstruction of internal specimen morphology. Summary of revisions: [•] Included Hessian() function to compute 2nd order spatial derivatives of image intensities (operates in the same fashion as the previous and existing Sobel() function). [•] Changed convolve_Gaussian() function to alternatively use successive 1D convolutions (rather than cumbersome 2D summations implemented in version 1), resulting in a large increase in computational speed without any loss in accuracy. The convolution kernel size was hence widened to three times the full width half maximum of the Gaussian filter to improve scale-space selection accuracy. [•] A ridge detection option was included to compute edge maps sensitive to ridges, rather than edges, using elements from a Hessian matrix; the eigenvalues of which were used to define ridge direction for Canny-type hysteresis thresholding. Function edge_detect_Canny() was also altered to pass the gradient-direction maps (from either Hessian or Sobel based operators) in and out of scope for computation of surface normals; thereby enabling the output of both point-cloud and corresponding unstructured vector-field surface descriptors. [•] Function rotate_imgs() was changed to incorporate basic bi-linear interpolation for improved tilt-axis alignment of the entire tilt series in exp_data.dat. Smoother and more accurate edge maps are thereby produced. [•] Algorithm convert_point_cloud_to_tomogram() was created to output the tomogram 3d_imgs.dat in a more memory efficient manner. The function shell_sort(), adapted from numerical recipes in C, was also coded for this purpose. [•] The new function compute_xyz() was coded to calculate point-clouds and tomogram surface normals using information from single tilt images, as opposed to the entire stack. This function is hence used iteratively throughout the reconstruction as each tilt image is analysed in succession. [•] The new function reconstruct_local() is the heart of stomo_version_2.cpp. the main() source code in stomo_version_1.cpp has been rewritten here to process experimental images and edge maps one at a time, using a buffered 3d array of dimensions dictated solely by the number of tilt images required for the local SVD fit of the angular variations. These changes (along with similar iterative file writing) have been made to vastly reduce memory usage and hence allow higher spatial and angular resolution data sets to be analysed without recourse to high performance computing resources. [•] The input file has been simplified by removing the ‘slices’ and ‘channels’ settings (used in version 1 for crude image binning), which are now equal to the respective numbers of image rows and columns. [•] Every summation over image rows and columns has been checked to enable the analysis of rectangular images without error. For images of specimens with high aspect-ratios, such as narrow tips, these fixes allow significant reductions in computation time and memory usage. [•] Some arrays in the source code were not appropriately zeroed in version 1, causing reconstruction artefacts in some cases. These problems have now been fixed. [•] Fixed an if-statement to correctly impose the minimum number of fitted polynomial points, thereby reducing noise in the reconstructed data. [•] Implemented proper edge linking in the hysteresis thresholding code for Canny edge detection. Restrictions: The input experimental tilt-series of images must be registered with respect to a common single tilt axis with known orientation and position. Running time: For high quality reconstruction, 2–5 min. [ABSTRACT FROM AUTHOR]

Nanocrystalline CdS thin films have been deposited using precursors with different thiourea concentration onto glass substrates by sol-gel spin coating method. The crystalline nature of the films has been observed to be strongly dependent on thiourea concentration and annealing temperature. The CdS films are found to be nanocrystalline in nature with hexagonal structure. The grain size is found to be in the range of 7.6 to 11.5 nm depending on the thiourea concentration and annealing temperature. The high resolution transmission electron microscopy (HRTEM) results of the CdS films prepared using cadmium to thiourea molar ratio of 0.3:0.3 indicate the formation of nanocrystalline CdS with grain size of 5 nm. Fourier transform infrared (FTIR) analysis shows the absorption bands corresponding to Cd and S. The optical study carried out to determine the band gap of the nanostructured CdS thin films shows a strong blue shift. The band gap energy has been observed to lie in the range of 3.97 to 3.62 eV following closely the quantum confinement dependence of energy on crystallite radius. The dependence of band gap of the CdS films on the annealing temperature and thiourea concentration has also been studied. The photoluminescence (PL) spectra display two main emission peaks corresponding to the blue and green emissions of CdS. [Copyright &y& Elsevier]