Control of the electron beam active zone position in electron beam welding processes

It is known that charged particles emitted from the region of electron beam (EB) interaction with the material being processed, are an important source of information for the understanding of EB welding processes. Measurements for the three largest groups of charged particles, namely, backscattered electrons, true secondary electrons and ions are presented here. It was estimated that only the signals of the direct component amplitude of these particles’ currents, processed by neural networks, could be used to effectively control the EB welding process. Computer simulations of various models of neural networks are described. The best result was obtained for a network that determines an optimal value of focusing current for the weld being made, based on the amplitude of signals measured with a moderately defocused EB.     

Stability of Ag nanoparticles fabricated by electron beam lithography

The stability of silver nanoparticles on indium tin oxide coated glass substrates under atmospheric condition was investigated. These nanoparticles were fabricated using electron beam lithography. Energy dispersive spectroscopy analysis revealed a high concentration of sulfur in the silver nanoparticles exposed to laboratory air for 12 weeks at room temperature. Morphological changes in the silver nanoparticles were also observed for nanoparticles stored under the same conditions. In contrast, silver nanoparticles kept in vacuum did not show chemical or morphological changes after 12 weeks. The present work clearly shows the need to consider ambient exposure when using Ag nanoparticles for sensors.     

Design optimization of a hairpin electron source for electron beam welding

We report the optimization of the design and performance of recently reported hairpin tungsten electron source as a cathode in diode type geometry of the gun. The temperature maximum has been shifted close to the crown of the source. Focusing of the beam has been achieved up to 1 mm in diameter with Gaussian profile of the beam at the target. The perveance and power density measured are 10⁻⁵ A V^−3/2 and 10⁶ W cm⁻², respectively.     

砷化镓扩散长度的变加速电压束感生电流法测量

计算了变加速电压的速感生电流法测定扩散长度理论公式，并用电子探针和扫描电镜测量了各种ＧａＡｓ材料的扩散长度。     

Morphology and phase modification of HVOF-sprayed MCrAlY-coatings remelted by electron beam irradiation

The electron beam remelting process is one of the most convenient processes to reduce the disadvantages of thermal-spray coatings. The effect of high-energy electron beam irradiation on surface remelting and microstructural modification in MCrAlY coatings are investigated in this study. This surface treatment is made to modify the morphology and the phases of the coated layer in order to improve the corrosion resistance. The specimens were remelted by using a high-energy electron beam accelerator. The microstructure, corrosion resistance and phase modification were examined. Scanning Electron Microscopy, light microscopy and X-Ray Diffraction were performed to characterize the phase modification and morphology before and after the treatment.     

Microstructure modifications and corrosion behaviors of Cr4Mo4V steel treated by high current pulsed electron beam

In this work, Cr4Mo4V steel was irradiated by high energy current pulsed electron beam (HCPEB) with energy density of 6 J/cm². Morphology and phase composition of the surface layer were analyzed using scanning electron microscopy (SEM) and glancing angle X-ray diffraction (GXRD). The crater-like morphology was observed on surface after HCPEB treatment, and the thickness of melted layer was ∼7 μm. Results from GXRD revealed that HCPEB treatment could suppress martensite transition and the content of retained austenite in the melted layer increased with irradiation number. The corrosion resistance was evaluated by electrochemical polarization tests in neutral 3.5% NaCl solution. Compared with the untreated Cr4Mo4V steel, corrosion potential of the samples treated by HCPEB improved and the corrosion current density decreased. The improved corrosion resistance is attributed to the absence of the carbide, formation of retained austenite and dissolution of alloy elements, particularly of Cr and Mo, into the matrix.     

Signal formation analysis of the electron beam current distribution measurements

The Fourier spectra of signals and the modulation transfer functions are chosen as main characteristics of the electron beam (EB) analyzers. This approach can be used for EB analyzer design and optimization. It is concluded that the space-frequency characteristics of the scanning (modulation) system are the limiting factors for the signal distortion. A matrix of more than 32×32 sufficiently short impulses and at a transfer rate twice higher than the maximum spectrum frequency can create an adequate image of the beam current radial or angular distribution. At the data processing of the rotating probe or of the moving slit measurements an inverse transformation is needed and a false minimum can appear in the calculated current distributions.     

Reversible formation of CdSe nanoparticles in aqueous solutions by high-energy electron beam irradiation

An unusual reversible effect was observed in the synthesis of CdSe nanoparticles in the aqueous tertiary butanol solutions containing equimolar Cd[NH₃]₄SO₄ and Na₂SeSO₃ by the high-energy electron beam irradiation. These nanoparticles were found to be unstable in the aqueous solutions and decomposed upon exposure to air/oxygen. However, they were stable in the de-aerated aqueous solutions and both aerated and de-aerated organic solvents. The decomposed aqueous solutions again produced these nanoparticles upon irradiation with the electron beam. On the contrary, the cadmium selenide nanoparticles synthesized with the cobalt-60 γ-irradiation, were stable under ambient conditions and did not exhibit any reversible behavior. This was attributed to the vast differences in the dose rates involved in the two types of synthetic processes, leading to a remarkable variation in the crystal structure and size of the nanoparticles.     

Beam quality test technology and devices of electron beam welding

The electron beam four-dimensional quality test system was developed targeted at the 5-100 mA electron beam current of a high-voltage electron beam welding machine. The system includes the control module, sensor module, driver module, and analysis software, which is based on the complex programmable logic device (CPLD). The quality test system obtains the data of quasi-instantaneous power density distribution (QIPDD) of the electron beam by controlling the beam periodically, scanning the surface of a Faraday cup. Fixing the Faraday cup at an X- and Y-axis coordinate position under constant conditions, the three-dimensional graphic of QIPDD of the beam about the data of a single cross-section was showed by using computer reconstruction technology. Several QIPDD of the electron beam cross-section at different working distance in axial direction reconstructed the four-dimensional graphics of the beam.     

Growth and characterization of germanium nanowires by electron beam evaporation

Germanium nanowires were grown on Au coated Si substrates at 380 °C in a high vacuum (5 × 10^− 5 Torr) by e-beam evaporation of Germanium (Ge). The morphology observation by a field emission scanning electron microscope (FESEM) shows that the grown nanowires are randomly oriented with an average length and diameter of 600 nm and 120 nm respectively for a deposition time of 60 min. The nanowire growth rate was measured to be ∼ 10 nm/min. Transmission electron microscope (TEM) studies revealed that the Ge nanowires were single crystalline in nature and further energy dispersive X-ray analysis (EDAX) has shown that the tip of the grown nanowires was capped with Au nanoparticles, this shows that the growth of the Ge nanowires occurs by the vapour liquid solid (VLS) mechanism. HRTEM studies on the grown Ge nanowire show that they are single crystalline in nature and the growth direction was identified to be along [110].     

Effect of electron beam irradiation on the electrical and optical properties of ITO/Ag/ITO and IZO/Ag/IZO films

We have investigated the effect of electron beam irradiation as well as insertion of a Ag layer on the electrical and optical properties of the ITO or IZO films. The results show that electron beam irradiation as well as inserting a very thin Ag layer can significantly reduce sheet resistance of the ITO/Ag/ITO and IZO/Ag/IZO films. The electron beam irradiation also increases light transmittance and optical band gap of the ITO/Ag/ITO multilayer films; meanwhile, it has not influence on the transmittance of the IZO/Ag/IZO films. These results can be explained by that In and Zn cation in IZO film have strong tendency to preserve their coordination with oxygen.     

Thermal and optical properties of electron beam irradiated cellulose triacetate

Cellulose triacetate (CTA) is a polymer which is widely used in a variety of applications in the field of radiation dosimetry. In the present work, CTA samples were irradiated by electron beam in the dose range 10–200 kGy. The modifications in the electron irradiated CTA samples as a function of dose have been studied through different characterization techniques such as thermogravimetric analysis, differential thermal analysis and color-difference studies. The electron irradiation in the dose range 80–200 kGy led to a more compact structure of CTA polymer, which resulted in an improvement in its thermal stability with an increase in activation energy of thermal decomposition.

Also, the variation of melting temperatures with the electron dose has been determined using differential thermal analysis (DTA). The CTA polymer is characterized by the appearance of one endothermic peak due to melting. The results showed that the irradiation in the dose range 10–80 kGy causes defects generation that splits the crystals depressing the melting temperature, while at higher doses (80–200 kGy), the thickness of crystalline structures (lamellae) is increased, thus the melting temperature increased.

In addition, the transmission of these samples in the wavelength range 200–2500 nm, as well as any color changes, was studied. The color intensity ΔE^* was greatly increased with increasing the electron beam dose, and accompanied with a significant increase in the blue color component.     

Argon ion beam and electron beam-induced damage in Cu(In,Ga)Se2 thin films

Ar ion beam and electron beam-induced damages in Cu(In,Ga)Se₂ thin films are investigated by transmission electron microscopy and X-ray energy-dispersive spectroscopy. We find that a high-energy Ar ion beam can cause severe damage in Cu(In,Ga)Se₂ surface regions by preferentially depleting Se and In. The depletion can occur with an Ar ion beam at energy as low as 0.5 keV. High-energy electron beams also cause damage in Cu(In,Ga)Se₂ thin films by preferentially depleting In and Ga. Our results imply that special care must be taken for measurements involving surface treatments using high-energy Ar ion beams or electron beams.     

Effects of electron beam irradiation on tin dioxide gas sensors

In this paper, the effects of electron beam irradiation on the gas sensing performance of tin dioxide thin films toward H₂ are studied. The tin dioxide thin films were prepared by ultrasonic spray pyrolysis. The results show that the sensitivity increased after electron beam irradiation. The electron beam irradiation effects on tin dioxide thin films were simulated and the mechanism was discussed.     

Analytical solution for three-dimensional model predicting temperature in the welding cavity of electron beam

This paper provides an analytical solution for three-dimensional model predicting temperature in the welding cavity of electron beam. It is not easy to measure the temperature on the keyhole of electron-beam welding. Therefore it is essential to develop an analytical model that can accurately predict the temperature in the keyhole. In this study, the keyhole produced by an electron beam is assumed to be a paraboloid of revolution and the intensity of electron beam is supposed to be Gaussian profile. In order to obtain an analytical solution, the parabolic coordinate system is utilized to analyze the temperature in the keyhole and the parameter approximating convection is proposed to account for the effect of convection of molten metal. Considering the momentum balance at the bottom of the keyhole but neglecting the absorption in the plume, an analytical solution is developed for semi-infinite workpieces. As compared with other analytical solutions, the analytical solution obtained by this model provides the temperature distribution more consistent with the experimental data. The effects of various parameters on the temperature distribution in the keyhole are also discussed in this study.     

Effects of oxygen flow rate on microstructure and optical properties of aluminum oxide films deposited by electron beam evaporation technique

Reactive evaporation technique has been used to deposit thin films of alumina (Al₂O₃) on crystalline Si substrates at ambient temperatures in an electron beam (e-beam) evaporation system using alumina granules as evaporant material. The loss of oxygen due to dissociation of alumina has been compensated by bleeding high purity oxygen gas into the system during evaporation. A set of samples were prepared at different flow rates of oxygen and the films have been characterized by Spectroscopic Ellipsometry (SE), Atomic Force Microscopy (AFM), Grazing Incidence X-ray Reflectivity (GIXR) and X-ray Photoelectron Spectroscopy (XPS) measurements. The density and optical properties of the films showed interesting variation with oxygen flow rates.     

Effect of filament heating current on electron beam of directly heated strip-type electron gun

The method of Electron Beam-Physical Vapour Deposition (EB-PVD) for handling large substrates is well established in the metallurgical industry, where sweeping axisymmetric electron guns or multiple pencil guns are routinely used to cover a large target area. The non-uniformity in current density in those methods can be overcome, to a large extent, by using the strip-type electron gun. In this paper, we propose to use an AC-heated strip-type electron gun to cover large target areas. The magnetic field generated by the alternating filament current oscillates the beam in a direction parallel to the filament length, thereby eliminating the need for applying an external electric or magnetic field for sweeping the beam. The non-uniformity in the current density within the strip electron beam, arising due to finite length of the filament, is reduced by the use of dummy filaments on both ends of the active filament. These results are supported by electron trajectory simulations.     

Characterization of electron beam welded AA2024

For aerospace manufacturing, the perseverance for improving performance (high strength to density ratio) and reducing weight and costs has motivated consideration of welding techniques applicable to aluminum alloys. During fusion welding of aluminum alloy (AA) 2024, the avoidance of defects (e.g., porosity, oxides, solidification cracking, undercutting) and the optimization of the microstructure-property characteristics are of critical concern. In this work, AA2024 was electron beam (EB) welded as part of a study to determine the influence of parametric conditions on the characteristics of the weldment to optimize the joining process. Specifically, the evolution in the weld geometry, microstructure and mechanical properties was examined as a function of the process conditions, including beam current, beam focus, beam oscillation, and welding speed. For optimized parametric conditions, microstructural examination of the joints revealed narrow fusion and heat-affected zones comprising of dendritic structures without the occurrence of defects that enabled a maximized joint efficiency.     

The electron beam gun with thermionic hairpin-like cathode for welding and surface modifications

An axial thermionic electron beam emitter assembly with a special geometry of the cathode along with particular spacing of the electrodes has been used to produce a stable, sharp and high power density image at an acceleration voltage of 10 kV only. A hairpin-like tungsten wire, with diameter of 0.7 mm having semi-spherical emitting area at the crown with an angle of 45 degree at the vertex was used as a cathode. A direct heating method was used to heat the cathode. The emission current of the gun is in accordance with the Langmuir relation. An electromagnetic coil was used for focusing the beam at the target. A two dimensional programmable movement was applied to control the work site in the x-y direction. Focusing of the beam has been achieved up to 1 mm in diameter at an acceleration voltage of 10 kV.Thermionic efficiency of the gun is 4 mA W⁻¹ and the power density measured is ∼10⁵ W cm⁻².The gun was used for welding and surface modification of different materials including refractory metals.     

Application of accelerated electron beam and microwave irradiation to biological waste treatment

The comparative results obtained by applying separate electron beam (EB) irradiation, separate microwave (MW) heating and combined (successive and simultaneous) electron beam irradiation and microwave heating to reduction of viable cells of Escherichia coli, Salmonella typhi, Staphylococcus intermedius, Pseudomonas aeruginosa, and Trichinella spiralis are presented. The results of studies concerning the disinfection by separate and combined EB and MW irradiation of sewage sludge performed from a food industry wastewater treatment station (vegetable oil plant) are also presented. The research results demonstrated that the simultaneous EB and MW irradiation produces the biggest reduction of microorganisms.