Scanning Electron Beam Research Articles

FORMATION AND MONITORING OF SECONDARY X-RAY RADIATION UNDER PRODUCT PROCESSING WITH ELECTRON BEAM

When conducting an industrial radiation processes at an electron accelerator, a part of the beam energy is trans-formed into bremsstrahlung radiation. In such a way, the mixed e,X-radiation is formed in the area behind an irra-diated object. The intensity of the electron and photon components in the radiation is determined by the energy and power of the primary electron beam, as well as by the parameters of the object and devices located behind it. In paper, the characteristics of the e,X-radiation accompanying the product processing by a scanning electron beam with energy 8…12 MeV at a LU-10 Linac of NSC KIPT are studied. The conditions for obtaining a source of sec-ondary X-rays in the state of electronic equilibrium, as well as its monitoring using an extended free-air ionization chamber are explored. Such an extra-source of radiation can be used for carrying out various non-commercial pro-grams like radiation tests, sanitization of archival materials and cultural heritage objects, etc.

FPGA-Based Real-Time Data Acquisition for Ultrafast X-Ray Computed Tomography

Ultrafast X-ray computed tomography (UFXCT) is a fast tomographic imaging technique based on the principle of electron beam scanning. It is used for the investigation of transient multiphase flows. A UFXCT scanner comprises multiple detector modules generating gigabytes of raw data per second for imaging rates of up to 8000 fps. During the data acquisition, these data are stored in RAM on each detector module and can therefore only be accessed after the acquisition. This limits the applicability of UFXCT systems because real-time control of the scanned process or the scanner itself is not possible. To achieve this, data streaming with low latency and high throughput is necessary. Using the newly developed FPGA-based data acquisition described in this article, the data acquisition is enhanced to real-time operation, i.e., streaming the acquired data to the processing computer within microseconds of their acquisition. The developed FPGA hardware implementation handles control of peripherals [such as analog-digital converters (ADC)], synchronization between detector modules, electron beam deflection, and data transfer via Gigabit Ethernet (GbE).

An innovative TiB whisker architecture of titanium matrix composite devised by scanning electron beam remodeling

A high-performance titanium matrix composite with innovative TiB whiskers reinforcement architecture was fabricated using scanning electron beam remodeling. The microstructure and mechanical properties were investigated, and the microstructure evolution and strengthening mechanism were discussed. Results show that a reformative titanium matrix composite with a three-dimensional equiaxed reinforcement architecture was built. The matrix and reinforcement were refined into needle martensite and clustered TiB whiskers with diffusionless transformation and eutectic reaction. With the contribution of fine-grain strengthening, whisker strengthening, and sub-structural strengthening, the ultimate tensile strength of the remodeled titanium matrix composites was 1456 MPa, increasing 275 MPa (23.3%) to the raw material. Moreover, the wear resistance was reinforced by the electron beam remodeling. This research could provide unique thoughts or references for the preparation of higher performance titanium matrix composites.

Effect of scanning electron beam surface tungsten alloying on microstructure and hardness

Scanning electron beam surface alloying can effectively improve the surface properties of metal samples. After tungsten alloying treatment on the surface of 45 steel by scanning electron beam, a strengthened layer consisting of alloying zone and heat-affected zone was formed on the surface. The microstructure in alloying zone is acicular martensite and columnar crystal, the microstructure in heat affected zone is acicular martensite and ferrite, and the matrix microstructure is ferrite and pearlite. With the increase of electron beam power, the columnar crystal content in alloying zone increases, the acicular martensite content in heat affected zone increases and the ferrite content decreases. The thickness of alloy zone and heat affected zone increases nonlinearly, and the surface hardness increases gradually. The maximum hardness of the sample surface is 1170HV, which is more than 5 times that of the matrix.

The microstructure and properties of Mo alloying layer after surface alloying treatment induced by continuous scanning electron beam process

Surface alloying by scanning electron beams can improve the microstructure and mechanical properties of steel. In this study. Four electron energy densities were selected during the alloying process: E1 = 1.5J/cm2, E2 = 2.9J/cm2, E3 = 4.5J/cm2 and E4 = 5.9J/cm2. The obtained results show that the sample surface is composed of alloying zone and heat-affected zone. The microstructure of the alloy zone is concealed acicular martensite and molybdenum carbide particles. The microhardness of this area is 1250HV. The sample treated with an energy density of 5.9J/cm2 has the least amount of wear. After alloying treatment, the microhardness and wear amount of the scanned samples are significantly improved.

Numerical Simulation and Microstructure and Properties of 45 Steel by Scanning Electron Beam Bevel Polishing

In order to obtain metal products with good surface quality, it is necessary to develop an efficient bevel polishing method. Therefore, this article Uses continuous scanning electron beam polishing. The surface of the material undergoes rapid melting and solidification and generates a dynamic temperature field. The polishing treatment improves the microstructure of the surface layer of the quenched and tempered 45 steel, and significantly increases the microhardness of the surface layer. The hardness after treatment can reach up to 747.6Hv, which is about 2.4 times higher than the matrix; the structure after hardening is transformed from the mixed phase of coarse acicular martensite and lath martensite to hidden acicular martensite and retained austenite a mixed phase thereof. In addition, after bevels with different inclination angles are subjected to electron beam surface polishing modification treatments with different scanning speeds, under the same parameters, as the inclination angle increases, the hardness value at the same position decreases.

Current Status of Electron Beam Selective Melting Additive Manufacturing Technology

Electron beam selective melting is a metal additive manufacturing technology, through electron beam scanning, melting powder materials, layer-by-layer deposition to manufacture three-dimensional metal parts, suitable for the forming and manufacturing of refractory, high-performance metal materials such as titanium alloys and titanium-aluminum-based alloys. Because it can form high-performance metal parts with complex shapes, it has broad application prospects in aerospace, biomedical, automobile manufacturing and other fields. This article summarizes the principles, compares the advantages of selective melting with laser, shows the modern application of the technology, and points out the current technical difficulties and future development direction.

Modeling and numerical study of the molten pool dynamics during scanning electron beam welding of aluminum alloys: Physical mechanism, prediction and parameter selection

Physical understanding of the scanning electron beam welding (EBW) process and prediction of weld forming quality are always a focus and a challenge in the field of material processing. In this paper, a three-dimensional molten pool model is developed to study the molten pool dynamics during EBW with beam oscillation. The model involves an innovative heat source model that considers the broadening effect of metal vapor on the electron beam radius and direct coupling between the electron beam and keyhole wall. The model is validated by comparing the areas of the weld longitudinal section and weld dimensions from experiments and simulations. In addition, the number of porosity defects in the experimental weld seam is examined to prove the rationality of the theoretical analysis. Based on the molten pool model and the theoretical analysis, a Gaussian process regression (GPR) method for rapidly predicting the weld dimensions and a new method for quantifying the molten pool stability are proposed. Eventually, we propose an innovative and rapid method for selecting welding process parameters. This study is expected to provide a deeper understanding of the scanning EBW process and to improve confidence in optimizing and controlling the actual welding process.

3D electron backscatter diffraction characterization of fine α titanium microstructures: collection, reconstruction, and analysis methods

3D electron backscatter diffraction (3D-EBSD) is a method of obtaining 3-dimensional crystallographic data through serial sectioning. The recent advancement of using a Xe+ plasma focused ion beam for sectioning along with a complementary metal-oxide semiconductor based EBSD detector allows for an improvement in the trade-off between volume analyzed and spatial resolution over most other 3D characterization techniques. Recent publications from our team have focused on applying 3D-EBSD to understand microstructural phenomena in Ti-6Al-4V microstructures as a function of electron beam scanning strategies in electron beam powder bed fusion additive manufacturing. The microstructures resulting from this process have fine features, with α laths as small as 1 μm interwoven in a highly complex fashion, presenting a significant challenge to characterize. Over the course of these fundamental works, we have developed best-practice 3D-EBSD collection protocols and advanced methods for 3D data reconstruction and analysis of such microstructures which remain unpublished. These methods may be of interest to the 3D materials characterization community, especially considering the lack of standard commercial software tools. Thus, the current paper elaborates on the methods and analysis used to characterize fine titanium microstructures using 3D-EBSD and presents a detailed description of the new algorithms developed for probing the unique features therein. The new analyses include algorithms for identifying intervariant boundary types, classifying three-variant clusters, assigning grains to variants, and quantifying interconnectivity of branched α platelets.

Study on surface alloying of 38CrMoAl steel by electron beam

TiN/Ni alloying of 38CrMoAl steel surface was carried out by continuous scanning electron beam. The effect of electron beam process parameters on the surface microstructures and mechanical properties of 38CrMoAl steel was studied. The results shows that the sample surface was divided into three regions: alloying layer, heat affected zone and substrate. Alloying layer made up with equiaxed crystals and short columnar crystals, microstructure of the heat affected zone was acicular and lath martensite, microstructure of substrate was tempered sorbate. The microhardness of the sample section first increased and then decreased, at a depth of 400 μm, the microhardness reached a maximum of 817.9 HV. When the beam current reached 12 mA and the moving speed reached 5.5 mm/s, the surface microhardness of the sample reached the highest 1209HV and the abrasion loss reached the lowest 4.6 mg.

Dosimetry of a novel converging X-ray source for kilovoltage radiotherapy.

The objective of this work was to evaluate phantom dosimetry of a novel kilovoltage (kV) X-ray source, which employs a stationary tungsten anode and a linearly swept scanning electron beam. The source utilizes converging X-ray collimation along with orthogonal mechanical rotation to distribute surface flux over large area. In this study, this was investigated as a potential solution to fast-falloff limitations expected with kV radiotherapy. This was done with the aim of future clinical development of a lower cost radiotherapy alternative to megavoltage (MV) linac systems. Radiochromic film was employed for dosimetry on the kV X-ray source of the linear-converging radiotherapy system (LCRS). The source utilizes charge particle optics to magnetically deflect and focus an electron beam along a stationary, reflection tungsten target in an ultra-high-vacuum stainless-steel chamber. Resulting X-rays were collimated into converging beamlets that span a large planar angle and converge at the system isocenter. In this study, radiochromic film dosimetry was done at 140 and 145 kVp for a designated planning treatment volume (PTV) of 4 cm diameter. An acrylic phantom was employed for dose distribution measurements of stationary and rotational delivery. Film dosimetry was evaluated in planes parallel to the source X-ray window at various depths, as well as in the plane of gantry rotation. At 140 and 145 kVp and using a collimated 4 cm square field at depth, lesion-to-skin dose ratio was shown to improve with additional beams from different relative source positions, where the different beams are focused at the same isocenter and do not overlap at the phantom surface. It was only possible to achieve a 1:1 Dmax -to-surface ratio with four delivery beams, but the ratio improved to 4:1 with 12 beams, focused at the same isocenter depth of 7.8cm in an acrylic phantom. For the tests conducted, the following Dmax -to-surface ratios were obtained: 0.4:1 lesion-to-skin ratio for stationary delivery from one entry beam, 0.71:1 lesion-to-skin ratio was obtained for two beams, 1.07:1 ratio for four beams, and 4:1 for 12 beams. Dose-depth profiles were evaluated for stationary and rotational dosimetry. Additionally, rotational dosimetry was measured for a case more analogous to a clinical scenario, where the isocenter was located at an off-center simulated lesion. The results demonstrate potential dose-depth improvements with kV arc therapy by distributing the surface flux with a wide converging beam along with perpendicular mechanical source rotation of the LCRS. The system delivered tolerable dose to a large surface area when a threshold of multiple, separated beams was reached. The radiochromic film data support the feasibility of the construct of the LCRS kV radiotherapy system design.

Study on micro – Melt polishing and strengthening mechanism of scanning electron beam surface

Scanning electron beam micro-polishing is a new technique to reduce surface roughness using molten metal to fill pits under gravity's action spontaneously. In this study, through the establishment of the electron beam heat source model and heat conduction model, it is easy to obtain the mathematical and physical model of heat balance for continuous scanning electron beam process under micro-melting polishing and to discuss the influence of regularity of electron beam process parameters on the surface morphology and microstructure. The results showed that the surface roughness of 45 steel was reduced after scanning electron beam processing. The lowest value was 0.34 μm with a reduction of 83%. It was found that the melt zone was mostly martensite with fine grains by further measuring and analyzing the microstructure and hardness of the polished sample. The maximum hardness was 870 HV in the subsurface layer.

Scanning electron beam alloying of composite gradient coatings

The surface WC/Ni-Co based alloying treatment of 30CrMnSi steel was carried out using scanning electron beam technology, and the tissue distribution after alloying were tested and investigated. The results show that the cross-section of the alloyed specimen consists of three parts: the alloy layer, the heat affected zone and the substrate. The thickness of the alloy layer was increased by 18.3 μm compared to the thickness of the pre-coated layer. The alloy layer is organised in a composite gradient, consisting of martensite and ledeburite with carbides.

Influence of Beam Power on Young’s Modulus and Friction Coefficient of Ti–Ta Alloys Formed by Electron-Beam Surface Alloying

In this study, we present the results of Young’s modulus and coefficient of friction (COF) of Ti–Ta surface alloys formed by electron-beam surface alloying by a scanning electron beam. Ta films were deposited on the top of Ti substrates, and the specimens were then electron-beam surface alloyed, where the beam power was varied from 750 to 1750 W. The structure of the samples was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Young’s modulus was studied by a nanoindentation test. The coefficient of friction was studied by a micromechanical wear experiment. It was found that at 750 W, the Ta film remained undissolved on the top of the Ti, and no alloyed zone was observed. By an increase in the beam power to 1250 and 1750 W, a distinguished alloyed zone is formed, where it is much thicker in the case of 1750 W. The structure of the obtained surface alloys is in the form of double-phase α’and β. In both surface alloys formed by a beam power of 1250 and 1750 W, respectively, Young’s modulus decreases about two times due to different reasons: in the case of alloying by 1250 W, the observed drop is attributed to the larger amount of the β phase, while at 1750 W is it due to the weaker binding forces between the atoms. The results obtained for the COF show that the formation of the Ti–Ta surface alloy on the top of Ti substrate leads to a decrease in the coefficient of friction, where the effect is more pronounced in the case of the formation of Ti–Ta surface alloys by a beam power of 1250 W.

Polymeric Microfiltration Membranes Modification by Supercritical Solvent Impregnation-Potential Application in Open Surgical Wound Ventilation.

This study investigated supercritical solvent impregnation of polyamide microfiltration membranes with carvacrol and the potential application of the modified membranes in ventilation of open surgical wounds. The impregnation process was conducted in batch mode at a temperature of 40 °C under pressures of 10, 15, and 20 MPa for contact times from 1 to 6 h. FTIR was applied to confirm the presence of carvacrol on the membrane surface. In the next step, the impact of the modification on the membrane structure was studied using scanning electron and ion beam microscopy and cross-filtration tests. Further, the release of carvacrol in carbon dioxide was determined, and finally, an open thoracic cavity model was applied to evaluate the efficiency of carvacrol-loaded membranes in contamination prevention. Carvacrol loadings of up to 43 wt.% were obtained under the selected operating conditions. The swelling effect was detectable. However, its impact on membrane functionality was minor. An average of 18.3 µg of carvacrol was released from membranes per liter of carbon dioxide for the flow of interest. Membranes with 30–34 wt.% carvacrol were efficient in the open thoracic cavity model applied, reducing the contamination levels by 27% compared to insufflation with standard membranes.

Inverse Columnar-Equiaxed Transition (CET) in 304 and 316L Stainless Steels Melt by Electron Beam for Additive Manufacturing (AM)

According to Hunt’s columnar-to-equiaxed transition (CET) criterion, which is generally accepted, a high-temperature gradient (G) in the solidification front is preferable to a low G for forming columnar grains. Here, we report the opposite tendency found in the solidification microstructure of stainless steels partially melted by scanning electron beam for powder bed fusion (PBF)-type additive manufacturing. Equiaxed grains were observed more frequently in the region of high G rather than in the region of low G, contrary to the trend of the CET criterion. Computational thermal-fluid dynamics (CtFD) simulation has revealed that the fluid velocity is significantly higher in the case of smaller melt regions. The G on the solidification front of a small melt pool tends to be high, but at the same, the temperature gradient along the melt pool surface also tends to be high. The high melt surface temperature gradient can enhance Marangoni flow, which can apparently reverse the trend of equiaxed grain formation.

Nanoscale directional etching features and mechanism of HF/HNO3 etchant

Large-scale and periodic silicon nanostructure arrays are an essential component for various functional devices. However, the conventional selective etching mechanism of specific crystal faces for monocrystalline silicon generally achieves slope or vertical morphology, which greatly limits the preparation of other morphology of silicon nanostructures. In this work, the conventional isotropic etchant HF/HNO3 has successfully achieved nanoscale directional etching and cambered morphology on monocrystalline silicon surface for the first time by changing the synchronous process of oxidation and dissolution into an asynchronous process. Based on the self-assembled monolayer colloidal crystal templates, large-area and high-quality nanopore arrays are prepared on the monocrystalline silicon surface. Particularly, the directional etching ability of HF/HNO3 etchant is further confirmed by combining with electron beam lithography and scanning probe lithography technologies. Hence, this nanoscale directional etching mechanism and etchants provide a promising strategy to achieve cambered morphology nanopores on the monocrystalline silicon surface.

Electron impact excitation of glutamine molecules irradiated with an M-30 microtron with an energy of 11.5 MeV

The process of excitations of the glutamine molecules in the gas phase during collisions with low-energy electrons (0–70 eV) for samples before and after irradiation (11.5 MeV) at the M-30 microtron with doses of 10 kGy have been investigated by the optical spectroscopy method. Optical spectra were studied in the wavelength range 200–520 nm; the effects caused by both external radiation and the scanning electron beam with the 30, 50, and 70 eV energy were investigated. For the most intense emission of the molecular fragments, their thresholds and excitations’ energy dependences were determined in the range of electron energies up to 30 eV. The new effect has been established: for λ > 310 nm, the irradiated samples’ emission increased both by increasing the scanning beam’s electron energy and the emitted light wavelength. However, for values of λ < 310 nm, there is an opposite dependence. The simulation of the glutamine transformations under irradiation was carried out within the method of structural combinations, which allows determining all sets of molecular structures of glutamine without and in the presence of ‘broken’ chemical bonds. The role of radiation in the formation of metastable molecular structures, which determine the features of the optical and mass spectra of irradiated glutamine samples, is investigated.

A Study on the Large-Area Image Acquisition Using Stage Transfer Synchronization Method in a Low-Energy Microcolumn System

We studied the stage transfer synchronization method to improve the low throughput which is the biggest drawback of the raster scan method when applied to image acquisition in a low energy microcolumn system. Through preliminary experiments, we were able to acquire some sample images and some images of the measured samples by applying the synchronization method to a conventional single-microcolumn system. The image acquired in this preliminary experiment was three times larger than that acquired by the raster scan method in the vertical direction. In this study, we tested two types of the synchronization method: the first method acquires an image by horizontal electron beam scanning followed by a vertical stage transfer, and the second one acquires an image by vertical electron beam scanning followed by a horizontal stage transfer. By applying the vertical stage transfer synchronization method, we could acquire a larger image than that acquired by the conventional raster scan method. The vertical stage transfer synchronization method image was 1.8 times larger in the horizontal direction and 6 times larger in the vertical direction. In addition, a larger image approximately nine times in the horizontal direction and five times in the vertical direction was acquired by applying the horizontal stage transfer synchronization method.

Fabrication and characterization of a miniaturized octupole deflection system for the MEMS electron microscope

This article describes a miniature electron beam scanning system based on an octupole electrode as the key stage of the implementation of the MEMS electron microscope. The scanning system consists of a silicon electrode with a central hole, containing 8 properly powered elements and a special electronic system controlling voltage. Octupole electrode was made using MEMS technology. First, it was examined using computer simulations, and then the operation of the octupole system was tested using a reference electron beam in the SEM JEOL microscope. The scanning system parameters depend on the electron beam energy, distance between the octupole and the sample, and the applied voltage. It is possible either to obtain an octupole scanning system resolution of 27 nm (for electron beam energy E = 4 keV and octupole observation plane distance H = 1 mm) or a large scanning area up to 2.7 mm (E = 4 keV, H = 20 mm), without any significant distortion of the sample image. Subsequently, the first model of the MEMS electron microscope microcolumn was assembled, containing the field-emission cathode, an extraction electrode, a focusing electrode, an octupole electrode, and an anode. The first images of the observed hexagonal metal grid placed on the silicon anode were recorded inside a reference high vacuum chamber.