Bright-field Transmission Electron Microscopy Research Articles

Influence of frictional heat spread pattern on the formation of intermetallic layers at the dissimilar FSW joint interface between AA 5083 and HSLA steel

The dissimilar weld interface for the AA5083 and HSLA steel alloy pair made by FSW technique was investigated to explore the impact of the friction heat flow across the thickness on the types and nature of IMC layer. The detail transmission electron microscopy (TEM) and atom probe tomography (APT) were performed to characterize the IMCs at different layer thicknesses and compositional mixing patterns of the interface. Also, a 3D moving heat source thermomechanical model was developed to simulate the FSW joining of Fe/Al alloy pair and explored the existence of heat flow pattern along the sheet thickness. The detail analysis of SAED pattern obtained from TEM bright field images was conducted to characterize the presence of types and nature of IMCs at different layer thicknesses. In this study the proximity histogram data from APT were investigated for further confirmation of existence of observed Fe/Al IMCs and atomic mixing pattern at the interface. The study identified the presence of Fe2Al9, Fe4Al13 and FeAl6 which are distinctly distributed over the thickness. The relative richness of Fe and Al in these IMCs are found significantly influenced by the thermal gradient in turn typically control their distribution over thickness. The Al rich IMCs such as FeAl6, possessing large ΔGf and low activation energy, found away from the frictional surface of heat source. While Fe rich IMCs form with relatively lesser ΔGf and higher activation energies are seen near the frictional surface of heat source.

Large (anti)ferrodistortive NaNbO3-based lead-free relaxors: Polar nanoregions embedded in ordered oxygen octahedral tilt matrix

Relaxor ferroelectric perovskites have experienced a revival of interest in recent years accompanying the deeply exploration of the fine local structure of polar nanoregions, which are thought to be the structure root for unique electrical properties. Interestingly, a new type of low-tolerance relaxor ferroelectric, which exhibits both cation displacement and large oxygen octahedral tilt, exhibiting anomalous microdomains were found in NaNbO3-based lead-free perovskites, breaking through the limits of the relaxor ferroelectric models proposed from classical relaxors. Atomic-scale annular bright-field scanning transmission electron microscopy images indicate that the microdomains are formed by long-range ordered oxygen octahedral tilt. At the same time, substructure of randomly embedded nanoregions with inhomogeneous polarization vectors can be mapped, being the main reason for relaxor behavior. Based on this special ferroelectric-improper ferroelastic state, delayed polarization saturation can be obtained under strong electric field, providing an opportunity for generating excellent energy storage properties. The results found in this work not only open up a new kind of relaxor ferroelectrics but also will lead to the reconstruction of relaxor models and theories built for more than half a century.

Origin of spurious intensity in vacuum near sample edge in bright field TEM images

Bright-field transmission electron microscope (BFTEM) images exhibit spurious image intensity in the vacuum near the sample edge. The spurious intensity gradually decreases with increasing distance from the sample edge. By taking into account angular and energy loss distribution of the scattered electrons and lens aberrations, the origin of the spurious intensity of BFTEM images can be explained. The spurious intensity extent and magnitude can be significantly reduced by using either electron energy filtering or a small collection semiangle.

Local structure elucidation of tungsten-substituted vanadium dioxide (V_{1-x}W_xO_2)

Initially, vanadium dioxide seems to be an ideal first-order phase transition case study due to its deceptively simple structure and composition, but upon closer inspection there are nuances to the driving mechanism of the metal-insulator transition (MIT) that are still unexplained. In this study, a local structure analysis across a bulk powder tungsten-substitution series is utilized to tease out the nuances of this first-order phase transition. A comparison of the average structure to the local structure using synchrotron x-ray diffraction and total scattering pair-distribution function methods, respectively, is discussed as well as comparison to bright field transmission electron microscopy imaging through a similar temperature-series as the local structure characterization. Extended x-ray absorption fine structure fitting of thin film data across the substitution-series is also presented and compared to bulk. Machine learning technique, non-negative matrix factorization, is applied to analyze the total scattering data. The bulk MIT is probed through magnetic susceptibility as well as differential scanning calorimetry. The findings indicate the local transition temperature (T_c) is less than the average T_c supporting the Peierls-Mott MIT mechanism, and demonstrate that in bulk powder and thin-films, increasing tungsten-substitution instigates local V-oxidation through the phase pathway VO_2, rightarrow V_6O_{13} , rightarrow V_2O_5.

Self-assembly dynamics and effect on synthetic nanobio-optical properties by hybrid monocolored silica nanoparticle labeling of Escherichia coli

The deposition of silica nanoparticles on Escherichia coli bacteria was investigated. The noncovalent interaction between the silanized surfaces and polar components of the biomembrane resulted in a nanobiostructure. This hybrid architecture showed stable conformation characteristics evaluated with different microscopy techniques, such as bright field confocal microscopy and transmission electron microscopy (TEM). Nanobioarchitectures were detected within colloidal dispersions and in the absence of aqueous media. Nanobiointeractions were related to strong polar and hydrogen bridges’ noncovalent interactions. Thus, well-constituted and defined nanobiostructures were observed by bright field confocal microscopy and TEM after their preparation in optimal conditions. However, to evaluate their stability and internanobiostructure interactions, size distributions within variable periods were determined. Variable nanobioaggregate sizes were recorded according to nanoparticles and bacteria concentrations. From single nanolabeled E. coli with well dispersible properties, low bacteria concentrations were observed. In intermediate and high concentrations, different distributions of nanobiostructures were observed in different periods. It was observed that the incorporation of silica nanoparticles into E. coli increased their dispersibility; however, their modified E. Coli membranes with silanized nanosurfaces augmented their internanobiostructure interactions through time. Here, we discuss the dynamics and nanobio-optics properties of E. coli. Their nanobiostructures could not be considered to be static systems; their interactions are regarded as important factors for dispersibility, stability, and effects against additional chemical agents such as antibiotics.

Cholecalciferol induces apoptosis via autocrine metabolism in epidermoid cervical cancer cells.

The anti-cancer effects of vitamin D are of fundamental interest. Cholecalciferol is sequentially hydroxylated endogenously to calcidiol and calcitriol. Here, SiHa epidermoid cervical cancer cells were treated with cholecalciferol (10-2600nmol/L). Cell count and viability were assayed using Crystal Violet and Trypan Blue, respectively. Apoptosis was assessed using flow cytometry for early and late biomarkers along with brightfield microscopy and transmission electron microscopy. Autocrine vitamin D metabolism was analysed by reverse transcription-quantitative PCR and immunoblotting for activating enzymes: 25-hydroxylases (CYP2R1 and CYP27A1) and 1α-hydroxylase (CYP27B1), the catabolic 24-hydroxylase (CYP24A1), and the vitamin D receptor (VDR). Data were analysed using one-way ANOVA and Bonferroni post-hoc test, and p<0.05 was considered significant. After cholecalciferol, cell count (p=0.011) and viability (p<0.0001) decreased, apoptotic biomarkers were positive, mitochondrial membrane potential decreased (p=0.0145), and phosphatidylserine externalisation (p=0.0439), terminal caspase activity (p=0.0025), and nuclear damage (p=0.004) increased. Microscopy showed classical features of apoptosis. Gene and protein expression were concordant. Immunoblots revealed increased CYP2R1 (p=0.021), VDR (p=0.04), and CYP24A1 (p=0.0274) and decreased CYP27B1 (p=0.031). The authors conclude that autocrine activation of cholecalciferol to calcidiol may mediate VDR signalling of growth inhibition and apoptosis in SiHa cells.

Elevated barrier height originated from electric dipole effect and improved breakdown characteristics in PtOx/β-Ga2O3 Schottky barrier diodes

The higher Schottky barrier height of PtOx/β-Ga2O3 Schottky barrier diode (SBD) was derived from the electric dipole effect of PtOx Schottky electrode. And the higher Schottky barrier height effectively improved the reverse breakdown characteristics of β-Ga2O3 SBD. In this work, PtOx/β-Ga2O3 and Pt/β-Ga2O3 SBDs were fabricated, and the Schottky barrier height of PtOx SBD increased with the increment of oxygen element component in PtOx electrode, which were all higher than the Schottky barrier height of Pt SBD. Kelvin probe force microscope measurement indicated that Fermi level pinning effect and the variation in work functions of Schottky electrodes were irrelevant to the higher barrier height. Moreover, with the increment of inserting PtOx layer thickness in Pt/PtOx/β-Ga2O3 SBDs, the Schottky barrier height increased from 1.32 eV to 1.82 eV. Bright-field scanning transmission electron microscopy image demonstrated that PtOx was mainly polycrystal with layer structure near the Schottky interface. The layer structure composed of Pt ions and O ions induced electric dipole effect, and the electric dipole effect led to the increase of Schottky barrier height for PtOx SBD. Lower leakage current density, higher breakdown voltages and more concentrated breakdown voltage distribution were obtained for PtOx SBDs. Furthermore, the barrier heights of PtOx SBDs gradually increased as the temperature raised, resulting in their reverse leakage current increased much more slowly with temperature than that of Pt SBD. The above results demonstrated that PtOx/β-Ga2O3 SBD had great potential in enhancing reverse blocking characteristics and high-temperature environment applications.

Nanostructural Analysis of Co‐Re/γ‐Al2O3 Fischer‐Tropsch Catalyst by TEM and XRD

AbstractA rhenium promoted Fischer‐Tropsch (FT) cobalt catalyst supported on γ‐Al2O3 has been investigated by Transmission Electron Microscopy (TEM) and X‐ray Diffraction (XRD), before and after reduction. Electron diffraction, High Resolution TEM and Electron Energy Loss Spectroscopy were used to confirm the oxidation state. Cobalt aggregate, particle and crystallite sizes have been studied in detail and measured by TEM and XRD. A cobalt particle size of 10.0±2.4 nm obtained from bright field TEM images for the reduced material is consistent with the XRD analysis of the calcined catalyst. After reduction dark field TEM imaging gave a volume‐weighted crystallite size of 7.5±2.5 nm, which is close to the value obtained by XRD. The particles had lost the parallel orientation and physical continuity within the alumina pore structure that were present before reduction. The latter was confirmed by electron tomography. Lamellae identified with the presence of Hexagonal Close Packed cobalt were observed in the predominantly Face Centred Cubic particles.

In vivo appraisal of oxidative stress response, cell ultrastructural aberration and accumulation in Juvenile Scylla serrata exposed to uranium

In vivo studies were performed to evaluate the organ specific tissue accumulation and cellular toxicity of uranium to mud crab Scylla serrata. The specimens were acclimated in natural seawater and the exposure to 50–250 μg/L uranium was investigated up to 60 days. The present study examined the effects of concentration and duration of uranium exposure in the tissue of S. serrata at cellular and subcellular level using scanning electron microscopy and bright field transmission electron microscopy in addition to histological analysis. The results indicated that accumulation of U in S. serrata was organ specific and followed the order gills > hepatopancreas > muscle. The response of key antioxidant enzyme activities such as SOD, GPx and CAT in different organs of crabs indicated oxidative stress due to U in the ambient medium and tissue. At 50 and 100 μg/L of U exposure, individuals were able to acclimate the oxidative stress and withstand the uranium exposure. This acclimation could not be sustained at higher concentrations (250 μg/L), affecting the production of CAT in the tissues. Cellular and subcellular changes were observed in the hemocytes with reduction in their number in consonance with the antioxidant enzymes. Histological aberrations like lamellar disruption of gill, necrosis of hepatopancreas, disruption and rupture of muscle bundles were observed at different concentrations and were severe at higher concentration (250 μg/L). Necrosis was observed in the electron micrographs of tissues shortly after 15 days of exposure. SEM micrograph clearly shows disrupted lamellae, folding of marginal canal and reduction of inter lamellar spaces in the gills of crab exposed to high concentration of uranium. Mitochondrial anomalies are reported for the first time in the present study in addition to the subcellular changes and vacuoles on exposure uranium in the cells of gill and hepatopancreas.

Synergies between H, He and radiation damage in dual and triple ion irradiation of candidate fusion blanket materials

Three ferritic/martensitic alloys were studied to understand the synergistic effect between single ion beam (Fe2+), dual ion beam (Fe2++He2+ and Fe2++H+), and triple ion beam (Fe2++He2++H+) irradiations on cavity evolution. A commercial alloy, F82H, a castable nanostructured alloy, CNA3, and a high purity model alloy, Fe8Cr2W, were irradiated at 400°C to 600°C to a damage level of 50 dpa at a damage rate of 1 × 10−3 dpa/s with He and H injection rates of 10 and 40 appm/dpa, respectively. Post-irradiation characterization via bright field transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy was performed on all irradiated conditions to characterize the cavity size distribution and determine the effects of H/He injection on cavity microstructure. In all three alloys, hydrogen co-injection with helium resulted in an increased cavity number density and maximum cavity size, producing an increase in swelling over that from helium injection alone. Swelling in F82H appears to peak between 450°C and 500°C. At 600°C, swelling was minimal and cavities of high density and small size were confined to grain boundaries and dislocations while at 400°C, swelling is also low with a nearly homogeneous, high density, distribution of very small cavities throughout. Swelling was least in the commercial alloy F82H due to the high sink strength. The CNA3 alloy underwent dissolution of precipitates that lowered the sink strength and resulted in higher swelling than F82H, but less than the model alloy. Electron energy loss spectroscopy (EELS) elemental mapping revealed hydrogen forming a halo-like structure about the periphery of the cavities and helium residing within the cavities themselves. This observation suggests that hydrogen reduces the surface energy of helium-filled cavities which results in both increased cavity number density and cavity size in triple beam irradiation over dual beam irradiation.

Insight into Structural Changes and Electrochemical Properties of Spark Plasma Sintered Nanostructured Ferritic and Austenitic Stainless Steels.

Nanostructured ferritic (Fe(82−x)-Cr18-Six, x = 0–3 wt %) and austenitic (Fe(73−x)-Cr18-Ni9-Six, x = 0–3 wt %) stainless steel (SS) alloys were developed by mechanical alloying (MA) and spark plasma sintering (SPS). The unit cell parameter estimated from X-ray diffraction spectra exhibited a decreasing trend with an increase in wt % of Si content in both alloy systems. The particle size of powders estimated using bright field transmission electron microscopy images for ferritic (3 wt % Si) and austenitic (3 wt % Si) SS powders was found to be 65 ± 5 nm and 18 ± 3 nm, respectively. In case of the ferritic system, 3 wt % Si exhibited the highest densification (~98%) and micro-hardness of about 350.6 ± 11.2 HV, respectively. Similarly, for the austenitic system (3 wt % Si), maximum densification and micro-hardness values were about 99% and 476.6 ± 15.2 HV, respectively. Comparative analysis of potentiodynamic polarization, linear polarization, and electrochemical impedance spectroscopy results indicates an increase in electrochemical performance of both alloy systems as the wt % Si was increased. The increase in electrochemical performance is directly related to the increase in densification owing to Si addition in these alloys.

High-Energy Electron Scattering in Thick Samples Evaluated by Bright-Field Transmission Electron Microscopy, Energy-Filtering Transmission Electron Microscopy, and Electron Tomography.

Energy-filtering transmission electron microscopy (TEM) and bright-field TEM can be used to extract local sample thickness $t$ and to generate two-dimensional sample thickness maps. Electron tomography can be used to accurately verify the local $t$. The relations of log-ratio of zero-loss filtered energy-filtering TEM beam intensity ($I_{{\rm ZLP}}$) and unfiltered beam intensity ($I_{\rm u}$) versus sample thickness $t$ were measured for five values of collection angle in a microscope equipped with an energy filter. Furthermore, log-ratio of the incident (primary) beam intensity ($I_{\rm p}$) and the transmitted beam $I_{{\rm tr}}$ versus $t$ in bright-field TEM was measured utilizing a camera before the energy filter. The measurements were performed on a multilayer sample containing eight materials and thickness $t$ up to 800 nm. Local thickness $t$ was verified by electron tomography. The following results are reported:•The maximum thickness $t_{{\rm max}}$ yielding a linear relation of log-ratio, $\ln ( {I_{\rm u}}/{I_{{\rm ZLP}}})$ and $\ln ( {I_{\rm p}}/{I_{{\rm tr}}} )$, versus $t$.•Inelastic mean free path ($\lambda _{{\rm in}}$) for five values of collection angle.•Total mean free path ($\lambda _{{\rm total}}$) of electrons excluded by an angle-limiting aperture.•$\lambda _{{\rm in}}$ and $\lambda _{{\rm total}}$ are evaluated for the eight materials with atomic number from $\approx$10 to 79.The results can be utilized as a guide for upper limit of $t$ evaluation in energy-filtering TEM and bright-field TEM and for optimizing electron tomography experiments.

Two-Dimensional Metal–Organic Frameworks with Unique Oriented Layers for Oxygen Reduction Reaction: Tailoring the Activity through Exposed Crystal Facets

Two-Dimensional Metal–Organic Frameworks with Unique Oriented Layers for Oxygen Reduction Reaction: Tailoring the Activity through Exposed Crystal Facets

Fracture behavior and deformation-induced structure changes of a Ti-based metallic glass using micro-sized cantilevers

Micro-cantilever bending tests are performed to quantify the fracture toughness and reveal the deformation mechanism of a Ti-based metallic glass. Plastic deformation is localized in shear bands initiating from the roots of the notches of the cantilevers. Although the load-displacement curves show considerable ductile failure characteristics, the notch fracture toughness values that obtained from the bending tests are extremely low (∼4.7 MPa m). Size dependent fracture is thought to be observed, where the fracture toughness increases with decreasing the uncracked ligament size of the cantilevers. TEM bright field images show that the shear bands with the width of 4–7 nm present brighter contrast. The regions in vicinity of the shear bands show dark zones (ranging from 3 to 5 nm in size) surrounded by continues bright zones. Cu nanocrystals are found not only inside the shear bands, but also around them. The free volume theory together with the simulation results is applied to explain the formation of shear bands in this Ti-based metallic glass during the bending deformation. The observed Cu nanocrystals are thought to be formed as a consequence of plastic-deformation-assisted crystallization. It is suggested that local atomic rearrangements lead to shifting of Cu nanocrystals towards more stable positions and cause the formation of Cu nanocrystals in regions subjected to high shear stress field.

Comparison of ion irradiation effects in PM-HIP and forged alloy 625

The nuclear industry has growing interest in replacing forgings with structural components fabricated by powder metallurgy with hot isostatic pressing (PM-HIP), owing to their chemical homogeneity, uniform grain structure, and near-net shape production. This study compares the ion irradiation response of PM-HIP and forged Alloy 625, over 50 and 100 dpa, 400 °C and 500 °C. Microstructure is characterized using down-zone bright-field scanning transmission electron microscopy (DZBFSTEM), and hardening is characterized using nanoindentation. PM-HIP Alloy 625 has a lower initial dislocation line density, resulting in a more rapid onset of dislocation loop growth and unfaulting than the forged material. But the total defect population (i.e. loop line length plus dislocation density) is insensitive to fabrication method. This finding shows promise for the eventual qualification of PM-HIP alloys for nuclear applications.

Combining Experimental and DFT Investigation of the Mechanism Involved in Thermal Etching of Titanium Nitride Using Alternate Exposures of NbF5 and CCl4, or CCl4 Only

AbstractThermally activated chemical vapor‐phase etching of titanium nitride (TiN) is studied by utilizing either alternate exposures of niobium pentafluoride (NbF5) and carbon tetrachloride (CCl4) or by using CCl4 alone. Nitrogen (N2) gas purge steps are carried out in between every reactant exposure. Titanium nitride is etched in a non‐self‐limiting way by NbF5–CCl4 based binary chemistry or by CCl4 at temperatures between 370 and 460 °C. Spectroscopic ellipsometry and a weight balance are used to calculate the etch per cycle. For the binary chemistry, an etch per cycle of ≈0.8 Å is obtained for 0.5 and 3 s long exposures of NbF5 and CCl4, respectively at 460 °C. On the contrary, under the same conditions, the etch process with CCl4 alone gives an etch per cycle of about 0.5 Å. In the CCl4‐only etch process, the thickness of TiN films removed at 460 °C varies linearly with the number of etch cycles. Furthermore, CCl4 alone is able to etch TiN selectively over other materials such as Al2O3, SiO2, and Si3N4. X‐ray photoelectron spectroscopy and bright field transmission electron microscopy are used for studying the post‐etch surfaces. To understand possible reaction products and energetics, first‐principles calculations are carried out with density functional theory. From thermochemical analysis of possible reaction models, it is found that NbF5 alone cannot etch TiN while CCl4 alone can etch it at high temperatures. The predicted byproducts of the reaction between the CCl4 gas molecules and TiN surface are TiCl3 and ClCN. Similarly, TiF4, NbFCl3, and ClCN are predicted to be the likely products when TiN is exposed to both NbF5 and CCl4. A more favorable etch reaction is predicted when TiN is exposed to both NbF5 and CCl4 (ΔG = −2.7 eV at 640 K) as compared to exposure to CCl4 only (ΔG = −2 eV at 640 K) process. This indicates that an enhanced etch rate is possible when TiN is exposed alternately to both NbF5 and CCl4, which is in close agreement with the experimental results.

Assessment of Novel MgCe4P6O24 Ceramic Electrolyte in Fabricating Mg-Sensors: Focus on Structure and Electrochemical Impedance Spectroscopy

In this study, a high-temperature ceria-based phosphate ceramic electrolyte, MgCe4P6O24 prepared using a modified sol-gel chemical method produced pure dried xerogel powders is presented [1-3]. The dried xerogel powders were then calcined at 900 oC to produce MgCe4P6O24 single phase nanopowders using data extracted from thermal analysis (TGA-DSC) on the dried xerogel powders. The nanopowders were further pelletised and sintered at 1300 oC to produce a single phase dense pellets preparatory for electrochemical impedance spectroscopy analysis. X-ray diffraction (XRD) reveals that the calcined nanopowders possess an excellent crystalline structure with an average crystallite size of 52 ± 1 nm, and having a monoclinic phase, which invariably was confirmed using the High Resolution TEM (HRTEM), as presented in Figure 1. In using electrochemical impedance spectroscopy [1-3], ionic conductivity of MgCe4P6O24 ceramic electrolyte = 2.14 x 10-3 Scm-1 at an impedance bulk temperature of 744 oC was achieved. In adapting the electrochemical method [2,3], thermodynamic and kinetic data computed in this study shows the transport number of Mg2+-cation = 0.85 ± 0.03 at 700 ± 5 oC. The structural orientation, transport number and ionic conductivity data of MgCe4P6O24 ceramic electrolyte suggests the ionic conductor as a suitable solid-state ceramic electrolyte for fabricating high-temperature Mg-sensors. Figure 1(a):Bright-field TEM image showing SAED with crystalline particles (insert), and (b) HRTEM micrograph showing corresponding SAED patterns for MgCe4P6O24 nanoparticles detailing d-spacing from lattice fringes of the HRTEM patterns in b(iii).

Major Factors Influencing the Size Distribution Analysis of Cellulose Nanocrystals Imaged in Transmission Electron Microscopy.

Size distributions of cellulose nanocrystals (CNCs), extracted from softwood pulp via strong sulfuric acid hydrolysis, exhibit large variability when analyzed from transmission electron microscopy (TEM) images. In this article, the causes of this variability are studied and discussed. In order to obtain results comparable with those reported, a reference material of CNCs (CNCD-1) was used to evaluate size distribution. CNC TEM specimens were prepared as-stained and dried with a rapid-flushing staining method or hydrated and embedded in vitreous ice with the plunge-freezing method. Several sets of bright-field TEM (BF-TEM), annular dark-field scanning TEM (ADF-STEM) and cryogenic-TEM (cryo-TEM) images were acquired for size distribution analysis to study the contributing factors. The rapid-flushing staining method was found to be the most effective for contrast enhancement of CNCs, not only revealing the helical structure of single CNCs but also resolving the laterally jointed CNCs. During TEM specimen preparation, CNCs were fractionated on TEM grids driven by the coffee-ring effect, as observed from contrast variation of CNCs with a stain-depth gradient. From the edge to the center of the TEM grids, the width of CNCs increases, while the aspect ratio (length to width) decreases. This fractionated dispersion of CNCs suggests that images taken near the center of a droplet would give a larger mean width. In addition to particle fractionation driven by the coffee-ring effect, the arrangement and orientation of CNC particles on the substrate significantly affect the size measurement when CNC aggregation cannot be resolved in images. The coexistence of asymmetric cross-section CNC particles introduces a large variation in size measurement, as TEM images of CNCs are mixed projections of the width and height of particles. As a demonstration of how this contributes to inflated size measurement, twisted CNC particles, rectangular cross-section particles and end-to-end jointed CNCs were revealed in reconstructed three-dimensional (3D) micrographs by electron tomography (ET).

The possible role of nano sized precipitates on the mechanical properties of additively manufactured IN 718 superalloy

In the present study, three dimensional parts of Inconel 718® (IN 718) superalloy were fabricated using laser powder bed fusion (L-PBF) additive manufacturing (AM). The soundness of the as-built parts was checked by measuring the relative density using Archimedes method. Tensile tests were carried out at the strain rate of 4.6 × 10-3 s-1 at ambient temperature on cylindrical samples extracted from the large size 3D blocks of AM IN 718. Tensile tests were also carried out employing the same test parameters on the wrought counterpart of IN 718 (W IN 718) so as to compare their mechanical properties. The AM IN 718 exhibited about 15% increase in 0.2% yield strength (0.2%YS) as compared to W IN 718. Microstructures of AM IN 718 and W IN 718 were characterized using electron back scattered diffraction. The dislocation substructure of pre-deformed samples was examined using transmission electron microscope (TEM). Bright field TEM images revealed nano-sized precipitates in AM IN 718 and carbides in W IN 718. The marginal increase in 0.2%YS in AM IN 718 is attributed to the impediment to dislocation movements by nano-sized precipitates and high initial dislocation density.

Structure and Bottom-up Formation Mechanism of Multisheet Silica-Based Nanoparticles Formed in an Epoxy Matrix through an In Situ Process.

Organic/inorganic hybrid composite materials with the dispersed phases in sizes down to a few tens of nanometers raised very great interest. In this paper, it is shown that silica/epoxy nanocomposites with a silica content of 6 wt % may be obtained with an “in situ” sol–gel procedure starting from two precursors: tetraethyl orthosilicate (TEOS) and 3-aminopropyl-triethoxysilane (APTES). APTES also played the role of a coupling agent. The use of advanced techniques (bright-field high-resolution transmission electron microscopy, HRTEM, and combined small- and wide-angle X-ray scattering (SAXS/WAXS) performed by means of a multirange device Ganesha 300 XL+) allowed us to evidence a multisheet structure of the nanoparticles instead of the gel one typically obtained through a sol–gel route. A mechanism combining in a new manner well-assessed knowledge regarding sol–gel chemistry, emulsion formation, and Ostwald ripening allowed us to give an explanation for the formation of the observed lamellar nanoparticles.