Backscattered Electron Imaging Mode Research Articles

A strong and ductile biocompatible Ti40Zr25Nb25Ta5Mo5 high entropy alloy

A non-equiatomic high entropy alloy (HEA) Ti40Nb25Zr25Ta5Mo5 (at.%) was designed by replacing 5% Ta with 5% Mo in a precursor Ti40Nb25Zr25Ta10 HEA for improved mechanical properties and reduced density. The Ti40Nb25Zr25Ta5Mo5 HEA fabricated by copper mould casting exhibited a nearly equiaxed grain structure (grain size: 96 ± 16 μm), but within each equiaxed grain, dendritic structures are discernible in the backscattered electron imaging mode. These dendrites are enriched in Ta, Nb and Mo, while the inter-dendritic regions contain higher Zr and Ti. The as-cast HEA achieved tensile yield strength (σ0.2) of 976 ± 8 MPa and strain to fracture (εf) of 16.80 ± 1.86%, well above the minimum requirements of σ0.2 and εf for medical-grade titanium alloy Ti–6Al–4V (759 MPa and 10%). The formation of microscale and nanoscale shear bands and the presence of significant dislocations in the shear band boundary region played a key role in allowing this as-cast HEA to achieve the excellent combination of tensile strength and ductility. Furthermore, the HEA exhibited a lower wear rate, lower coefficient of friction and much higher corrosion resistance in Hank's solution (electrochemical assessments) than Ti–6Al–4V, making it a promising alternative biomedical alloy.

Effect of Ni on the Suppression of Sn Whisker Formation in Sn-0.7Cu Solder Joint.

The evolution of internal compressive stress from the intermetallic compound (IMC) Cu6Sn5 growth is commonly acknowledged as the key inducement initiating the nucleation and growth of tin (Sn) whisker. This study investigates the effect of Sn-0.7Cu-0.05Ni on the nucleation and growth of Sn whisker under continuous mechanical stress induced. The Sn-0.7Cu-0.05Ni solder joint has a noticeable effect of suppression by diminishing the susceptibility of nucleation and growth of Sn whisker. By using a synchrotron micro X-ray fluorescence (µ-XRF) spectroscopy, it was found that a small amount of Ni alters the microstructure of Cu6Sn5 to form a (Cu,Ni)6Sn5 intermetallic layer. The morphology structure of the (Cu,Ni)6Sn5 interfacial intermetallic layer and Sn whisker growth were investigated by scanning electron microscope (SEM) in secondary and backscattered electron imaging mode, which showed that there is a strong correlation between the formation of Sn whisker and the composition of solder alloy. The thickness of the (Cu,Ni)6Sn5 IMC interfacial layer was relatively thinner and more refined, with a continuous fine scallop-shaped IMC interfacial layer, and consequently enhanced a greater incubation period for the nucleation and growth of the Sn whisker. These verification outcomes proposes a scientifically foundation to mitigate Sn whisker growth in lead-free solder joint.

Development and characterization of AISI 316L micro parts produced by metal powder hot embossing

Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce metallic parts with aspects in micron scale. In this study, scanning electron microscopy (SEM) is employed for evaluating the shape retention and the homogeneity of microstructure of replicated geometries into AISI 316L powder feedstock by the secondary electron imaging (SEI) and the backscattered electron imaging modes, the distribution of chemical composition by the electron-dispersive spectroscopy (EDS) mapping, and grain structures by the electron backscatter diffraction technique. Moreover, the SEI and EDS techniques completed the failure analysis of tensile tests. Nanoindentations were also performed to assist phase identification analysis in the densified microstructure. Different geometries in the micron scale (micro wall half-reservoirs, micro channel half-flanges, convex and concave micro gear configurations, and micro tensile specimens) were selected for replication. Shaping limitations were attributed to the geometry, convex or concave, and the stiffness of the die. Micro gear and micro wall configurations were shaped using a stiffer elastomer (T = 230 °C and P = 11.3 to 14 MPa for 45 min) and a metallic die (T = 170 °C and P = 11.3 MPa for 10 min), respectively. The shaping of concave geometries was achieved regardless of the metal powder concentration, 60 and 65 vol.%. Densified parts retained the replicated micro configurations after long periods of thermal debinding and sintering, with densification above 95%. The chemical composition in sintered parts was homogeneous. The microstructure was principally composed of austenitic grains. The 316L stainless steel sintered part produced through MPHE presented an ultimate tensile strength of 458 ± 15 MPa, similar to that of a wrought AISI 316L alloy; the fracture type in the micro tensile specimen was ductile.

A SEM-based method to determine the mineralogical composition and the particle size distribution of suspended sediment

A robust method for characterizing the mineralogy of suspended sediment in continental rivers is introduced. It encompasses 3 steps: the filtration of a few milliliters of water, measurements of X-ray energy dispersive spectra using Scanning Electron Microscopy (SEM), and robust machine learning tools of classification. The method is applied to suspended particles collected from various Amazonian rivers. A total of more than 204,000 particles were analyzed by SEM-EDXS (Energy Dispersive X-ray Spectroscopy), i.e. about 15,700 particles per sampling station, which lead to the identification of 15 distinct groups of mineralogical phases. The size distribution of particles collected on the filters was derived from the SEM micrographs taken in the backscattered electron imaging mode and analyzed with ImageJ freeware. The determination of the main mineralogical groups composing the bulk sediment associated with physical parameters such as particle size distribution or aspect ratio allows a precise characterization of the load of the terrigenous particles in rivers or lakes. In the case of the Amazonian rivers investigated, the results show that the identified mineralogies are consistent with previous studies as well as between the different samples collected. The method enabled the evolution of grain size distribution from fine to coarse material to be described in the water column. Implications about hydrodynamic sorting of mineral particles in the water column are also briefly discussed. The proposed method appears well suited for intensive routine monitoring of suspended sediment in river systems.

Application of Air-cooled Blast Furnace Slag Aggregates as Replacement of Natural Aggregates in Cement-based Materials: A Study on Water Absorption Property

The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.

Experimental Investigation of the Isothermal Section in Fe-Gd-Pd Ternary System at 873 K

Isothermal section of Fe-Gd-Pd ternary system at 873 K has been established by means of x-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscope (SEM) with energy disperse x-ray spectroscopy (EDS) in backscattered electron imaging modes. The isothermal section consists of 14 single-phase regions, 25 two-phase regions, and 12 three-phase regions. At 873 K, no ternary compound was found and the binary inermetallic compounds Gd3Pd and Fe23Gd6 are not stable, whereas the compound Fe23Gd6 decomposes into compounds Fe17Gd2 and Fe3Gd. The XRD and the SEM/EDS analysis show that there is almost no solubility of Gd in the FePd and FePd3 phases, and the solubilities of Pd in Fe17Gd2, Fe3Gd and Fe2Gd and Fe in GdPd2, α-Gd3Pd4 and Gd3Pd2 are all less than 1 at.%. Meanwhile, the solubilities of Fe in GdPd3, α-GdPd and Gd7Pd3 are determined to be as high as 1.37, 5.31, and 4.18 at.% Fe, respectively.

Digital image analysis to quantify carbide networks in ultrahigh carbon steels

A method has been developed and demonstrated to quantify the degree of carbide network connectivity in ultrahigh carbon steels through digital image processing and analysis of experimental micrographs. It was shown that the network connectivity and carbon content can be correlated to toughness for various ultrahigh carbon steel specimens. The image analysis approach first involved segmenting the carbide network and pearlite matrix into binary contrast representations via a grayscale intensity thresholding operation. Next, the carbide network pixels were skeletonized and parceled into braches and nodes, allowing the determination of a connectivity index for the carbide network. Intermediate image processing steps to remove noise and fill voids in the network are also detailed. The connectivity indexes of scanning electron micrographs were consistent in both secondary and backscattered electron imaging modes, as well as across two different (50× and 100×) magnifications. Results from ultrahigh carbon steels reported here along with other results from the literature generally showed lower connectivity indexes correlated with higher Charpy impact energy (toughness). A deviation from this trend was observed at higher connectivity indexes, consistent with a percolation threshold for crack propagation across the carbide network.

Characterization of SEM speckle pattern marking and imaging distortion by digital image correlation

Surface patterning by e-beam lithography and scanning electron microscope (SEM) imaging distortions are studied via digital image correlation. The global distortions from the reference pattern, which has been numerically generated, are first quantified from a digital image correlation procedure between the (virtual) reference pattern and the actual SEM image both in secondary and backscattered electron imaging modes. These distortions result from both patterning and imaging techniques. These two contributions can be separated (without resorting to an external caliper) based on the images of the same patterned surface acquired at different orientations. Patterning distortions are much smaller than those due to imaging on wide field images.

Preparation of Cross-sectional Specimen for High Resolution Observation of Coating Structure and Visualization of Styrene/butadiene Latex Binder

To characterize the coating structure, diverse methods such as mercury intrusion, nitrogen adsorption and oil absorption methods have been developed and widely employed. These indirect techniques, however, have some limitation to explain the actual coating structure. Recently microscopic observation methods have been tried for analyzing structural characteristics of coating layers. Preparation of the undamaged cross section of a coating layer is essential for obtaining high quality image for analysis. In this study, distortion-free cross-section of the coating layer was prepared using a grinding and polishing technique. The coated paper was embedded in epoxy resin and cured. After curing the resin block it was ground with abrasive papers and then polished with diamond particle suspension and nylon cloth. Polished coating layer was sufficient enough to obtain undamaged cross sectional images with scanning electron microscope under backscattered electron image mode. In addition, the SEM images allowed distinction of the coating layer components. Also S/B latex film formed between pigment particles was visualized by osmium tetroxide staining. Pore size distribution and pore orientation were evaluated by image analysis from SEM cross-sectional images.

Microstructural characterization of as-cast hf-b alloys

An accurate knowledge of several metal-boron phase diagrams is important to evaluation of higher order systems such as metal-silicon-boron ternaries. The refinement and reassessment of phase diagram data is a continuous work, thus the reevaluation of metal-boron systems provides the possibility to confirm previous data from an investigation using higher purity materials and better analytical techniques. This work presents results of rigorous microstructural characterization of as-cast hafnium-boron alloys which are significant to assess the liquid composition associated to most of the invariant reactions of this system. Alloys were prepared by arc melting high purity hafnium (minimum 99.8%) and boron (minimum 99.5%) slices under argon atmosphere in water-cooled copper crucible with non consumable tungsten electrode and titanium getter. The phases were identified by scanning electron microscopy, using back-scattered electron image mode and X-ray diffraction. In general, a good agreement was found between our data and those from the currently accepted Hafnium-Boron phase diagram. The phases identified are αHfSS and B-RhomSS, the intermediate compounds HfB and HfB2 and the liquide L. The reactions are the eutectic L ⇔ αHfSS + HfB and L ⇔ HfB2 + B-Rhom, the peritectic L + HfB2 ⇔ HfB and the congruent formation of HfB2.

Quantitative Electron Microscopy of Cellulose Nanofibril Structures from Eucalyptus and Pinus radiata Kraft Pulp Fibers

This work comprises the structural characterization of Eucalyptus and Pinus radiata pulp fibers and their corresponding fibrillated materials, based on quantitative electron microscopy techniques. Compared to hardwood fibers, the softwood fibers have a relatively open structure of the fiber wall outer layers. The fibrillation of the fibers was performed mechanically and chemi-mechanically. In the chemi-mechanical process, the pulp fibers were subjected to a TEMPO-mediated oxidation to facilitate the homogenization. Films were made of the fibrillated materials to evaluate some structural properties. The thicknesses and roughnesses of the films were evaluated with standardized methods and with scanning electron microscopy (SEM), in backscattered electron imaging mode. Field-emission SEM (FE-SEM) and transmission electron microscopy (TEM) were performed to quantify the nanofibril morphology. In this study, we give additional and significant evidences about the suitability of electron microscopy techniques for quantification of nanofibril structures. In addition, we conclude that standard methods are not suitable for estimating the thickness of films having relatively rough surfaces. The results revealed significant differences with respect to the morphology of the fibrillated material. The differences are due to the starting raw material and to the procedure applied for the fibrillation.

Isothermal section of the Al–Dy–Ge ternary system at 673 K

The isothermal section of the phase diagram of the Al–Dy–Ge ternary system at 673 K has been investigated by X-ray powder diffraction and scanning electron microscope equipped with energy dispersive X-ray spectroscopy in backscattered electron imaging modes. The existence of thirteen binary compounds including Dy 3Ge 4 in the system Dy–Ge has been confirmed. Four ternary compounds, namely AlDyGe, Al 3Dy 2Ge 4, AlDy 2Ge 3, and AlDy 2Ge 2 were observed, and five new ternary compounds, i.e., Al 0.33DyGe 2, AlDy 2Ge 6, Al 2DyGe 2, AlDy 3Ge 3, and Al 3− x Dy 11Ge 7+ x ( x ≤ 0.7), and one pseudo-binary compound Al 3− x DyGe x were found in this system at 673 K. The maximum solid solubility of Ge in the pseudo-binary compounds Al 3− x DyGe x is about 7.5 at.% with x = 0.3 at 673 K.

アルミ拡散コーティングを施した単結晶 Ni 基超合金のクリープ強度に及ぼす有害拡散層および熱処理の影響

The detrimental effect of the diffusion zones between coating and the substrate had been investigated by performing creep tests on aluminized Ni-based single crystal superalloys. In present study, creep test-pieces that had two kinds of sub-surface crystallographic orientations, <100> and <110>, were aluminized by the pack-cementation process at 1000°C for 5 h. To exclude the influence of the coating heat treatment on the creep strength of the bulk material, a set of specimens without coating was heat treated in vacuum at 1000°C for 5 h, which was equivalent to the condition during aluminizing process, for comparisons the creep rupture test was carried out at 900°C and 392 MPa. The cross-sectional microstructures of the as-aluminized and creep rupture specimens were observed by SEM using the backscattered electron image mode (BSE) and TEM. Analysis indicated that creep strength of the aluminized samples was decreased by the formation of the inter-diffusion zone (IDZ) and the substrate diffusion zone (SDZ); both of them reduced the load bearing thickness, thus resulting an increase in the effective stress. Furthermore, it was found that the disappearance of the secondary precipitate during coating treatment also decreased the creep strength. The IDZ, which formed at the coating/substrate interface grew more rapidly on the {110} plane than that on the {100} plane because of the preferential growth of the Topological-Close Paced (TCP) phase. Ru addition on the substrate could enhance the creep strength and the SDZ formation between the IDZ/substrate interface.

Detection of elemental mercury in abdominal wall soft tissue

A 19-year-old male with an unremarkable medical history presented with his father, who requested an evaluation of a pathology specimen from a reported "lump" under the skin in the middle of the son's lower abdomen. The lump had been excised by a surgeon approximately 3 months prior, per parental request. Upon gross inspection, the specimen appeared to contain small metallic droplets. The patient denied self-injection of any metals, including mercury, despite the results of a 24-hour urine heavy-metal screen (without chelation) that revealed an elevated concentration of mercury (87.6 microg/g creatinine; reference range for nonexposed adults: <4 microg/g creatinine). Confirmatory analysis of the tissue sample included gross and microscopic examination, electron microscopy using secondary and backscattered electron imaging modes, and energy dispersive x-ray spectrum analysis of isolated tissue particles. Grossly, the tissue had small silver spherules suggestive of elemental mercury; these droplets were identified histologically with associated foreign body reaction. Numerous smooth, round-to-oval particles scattered randomly throughout the tissue were identified ultrastructurally, which produced an x-ray energy spectrum corresponding to mercury. Elemental mercury is liquid at room temperature and may be injected into the body for recreational, psychiatric, and other purposes. Isolated cases of mercury injection following accidents with broken thermometers have been reported, as well as cases of elevated metallothionein concentration following human gingival amalgam tattoos. In cases of surreptitious injection, histology and ultrastructural evidence may be used to confirm the presence of mercury.

Visualising impregnated chitosan in Pinus radiata early wood cells using light and scanning electron microscopy

Chitosan, a deacetylated product of an abundant naturally occurring biopolymer chitin, has been used in a range of applications, particularly in food and health areas, as an antimicrobial agent. In the work reported here Pinus radiata wood was impregnated with chitosan as an environmentally compatible organic biocide ( Eikenes et al., 2005a,b) to protect wood against wood deteriorating microorganisms and to thus prolong the service life of wooden products. We developed sample preparation techniques targeted to visualise impregnated chitosan within wood tissues using light microscope and field-emission scanning electron microscope (FE-SEM). Sections were viewed with the light microscope without staining with a dye as well as after staining with the dye toluidine blue. Light microscopy was also undertaken on sections that had been stained with 1% aqueous osmium tetroxide (OsO 4). For SEM observations, the sections were treated with OsO 4 and then examined with the FE-SEM, first in the secondary electron imaging mode (SEI) and then in the backscattered electron imaging (BEI) mode, imaging the same areas of a section in both SEI and BEI modes. The preparation techniques employed and the combined use of light and scanning electron microscopy provided valuable complementary information, revealing that chitosan had penetrated into the cavities (cell lumens, intercellular spaces) of all sizes present within wood tissues and had also impregnated early wood cell walls. The information obtained is discussed in relation to its importance in further development of chitosan formulations and refinement of impregnation technologies to optimise chitosan impregnation into and distribution within wood tissues as well as in assessing chitosan efficacy.

Computer-assisted quantification of the multi-scale structure of films made of nanofibrillated cellulose

Films made of nanofibrillated cellulose (NFC) are most interesting for use in packaging applications. However, in order to understand the film-forming capabilities of NFC and their properties, new advanced methods for characterizing the different scales of the structures are necessary. In this study, we perform a comprehensive characterisation of NFC-films, based on desktop scanner analysis, scanning electron microscopy in backscatter electron imaging mode (SEM-BEI), laser profilometry (LP) and field-emission scanning electron microscopy in secondary electron imaging mode (FE-SEM-SEI). Objective quantification is performed for assessing the (i) film thicknesses, (ii) fibril diameters and (iii) fibril orientations, based on computer-assisted electron microscopy. The most frequent fibril diameter is 20–30 nm in diameter. A method for acquiring FE-SEM images of NFC surfaces without a conductive metallic layer is introduced. Having appropriate characterisation tools, the structural and mechanical properties of the films upon moisture were quantified.

Silver sulfide as a staining agent for scanning electron microscopy of nylon 6/MXD6 blends

AbstractBACKGROUND: In transmission and scanning electron microscopy imaging, the ability to obtain sufficient contrast between the components of a blend when they are both of a similar chemical structure still remains problematic. This paper investigates the domain morphology of a polymer blend containing two polyamides, nylon 6 and the semi‐aromatic polyamide poly(m‐xylene adipamide) (MXD6), using scanning electron microscopy in backscattered electron imaging mode. The efficiency of three staining agents, ruthenium tetroxide, phosphotungstic acid and silver sulfide, in obtaining optimum phase contrast between the two polymers is discussed.RESULTS: The use of silver sulfide as a staining agent was found to be a fast and reliable approach which required basic sample preparation and provided excellent compositional contrast between the phases present in the nylon 6/MXD6 blends compared to the other staining agents.CONCLUSIONS: The technique described in this paper is believed to be a novel and versatile method that has the potential to further improve the ability to study complex polymer blends where one polymer contains an aromatic ring. Copyright © 2009 Society of Chemical Industry

Transmission and scanning electron microscope study on the secondary cyclic hardening behavior of interstitial-free steel

Strain controlled fatigue experiment was employed to evaluate automotive grade interstitial-free ferrite steel. Hundreds of grains were examined by scanning electron microscope under electron channeling contrast image technique of backscattered electron image mode for comprehensive comparison of micrographs with those taken under transmission electron microscope. The cyclic stress responses clearly revealed that rapid hardening occurs at the early stage of cycling as a result of multiplication of dislocations to develop loop patches, dipolar walls and dislocation cells at various total strain amplitudes. After primary rapid hardening, stress responses varied from being saturated to further hardening according to dislocation structure evolution at various strain amplitudes. The fatigue failure was always accompanied with further hardening including secondary hardening. The corresponding dislocation structures with the three types of hardening behaviors are discussed. Once the secondary hardening starts, dislocation cells began to develop along grain boundaries in the low strain region and then extended into grain interiors as strain amplitudes increased and cycling went on. The secondary hardening rates were found to be directly proportional to their strain amplitudes.

Brief communication: Paleohistopathological analysis of pathology museum specimens: Can periosteal reaction microstructure explain lesion etiology?

The assertion that the microstructure of periosteal new bone formation can be used to differentiate between disease etiologies (Schultz: Yrbk Phys Anthropol 44 2001 106-147; Schultz: Identification of pathological conditions in human skeletal remains, 2nd ed. London: Academic Press 2003 73-109) was tested in a pilot-study, using diagnosed bone specimens from St George's Hospital Pathology Museum, London, UK. Embedded bone specimens exhibiting pathological periosteal new bone formation were examined using scanning electron microscopy in back-scattered electron imaging mode (SEM-BSE). The results suggest that several histological features (i.e. Grenzstreifen, Polsters, and sinuous lacunae) deemed to be diagnostic of specific pathological conditions are of no specific diagnostic value, as they are encountered in pathological conditions of differing disease etiology. These results tie in with a previous investigation demonstrating a lack of diagnostic qualitative or quantitative characteristics seen in the macroscopic and radiographic appearance of periosteal reactions (Weston: Am J Phys Anthropol 137 2008 48-59).

Cyclic hardening behavior for interstitial-free steel

Strain-controlled fatigue experiments were employed to evaluate automotive-grade interstitial-free ferrite steels under R = 0. Hundreds of grains were examined by scanning electron microscope (SEM) under electron channeling contrast image technique of backscattered electron image mode (BEI/ECCI) for comprehensive comparison of micrographs with those taken under transmission electron microscope (TEM). It is clearly revealed that cyclic hardening was virtually unobvious and dislocation cell structures were very rare when Δe/2 was controlled to within 0.1%. When Δe/2 was increased to 0.2%, the general dislocation structure exhibited a predominately dislocation wall structure prior to the secondary cyclic hardening, after which the formation of dislocation cells were observed. At Δe/2 = 1.0%, following an initial rapid-hardening stage, the dislocation cell structure of low-angle misorientation formed in the early stage was gradually converted into high-angle misorientation as the cyclic strain continued to be imposed.