Table of contents

EBT 2018 - Preface

EBT 2018 was held in hotels Estreya Palace and Estreya Residence, Resort "St. Constantine and Elena" in Varna, Bulgaria from 18 to 22 June 2018. The conference is organized by the Institute of Electronics at the Bulgarian Academy of Sciences, the Technological Centre of Electron Beam and Plasma Technologies, Sofia and the Union of Electronics, Electrical Engineering and Telecommunications – Bulgaria. This biannual (initially it was triannual) meeting brings together physicists, chemists, material, mechanical and electronics engineers from universities, research institutions and industry, who are involved in various studies and applications of electron beam technologies and techniques. The conference has provided an excellent forum for exchange of expertise and forging human links. The conference gives the opportunity to find research project partners and to make new business contacts.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

A normalized processing diagram for powder bed additive manufacturing by concentrated energy beams was constructed on the base of simple analytical model simulating the heating of the powder layers by a moving linear heat source. The distance of the processing regime points below the line of the dependency of the maximal dimensionless temperature (or of the maximal thermal efficiency) on the dimensionless beam velocity gives insight on the processing parameters range and on the possibility for prognosticated optimization of the utilized parameters of the energy beam at selective powder layer melting. The diagram provides useful reference and methodology to aid the selection of appropriate processing parameters during the early development stages of this perspective technology.

This paper focuses on the influence of EB parameters on temperature-time profiles when using an electron beam hardening field with surface isothermal energy distribution. Along with the energy-transfer density eF, the power density in the EBH field q plays a key role in determining the microstructure and hardening depth. For the combined treatment of magnetron-sputtered Ti_1-xAl_xN coatings with subsequent EBH, it was shown that crack formation was reduced and technically relevant surface-hardening depths were achieved without negatively influencing the wear-resistant PVD hard coatings if an EBH field with lower power density was used.

Nitinol, which consists of 50 at.-% nickel and 50 at.-% titanium, and stainless steels. These materials are widely used in medical engineering. Due to the versatile properties of Nitinol, for example shape memory and superelasticity, it finds application in implants and medical instruments. Because of its high-cost and poor machinability, there is a high demand for dissimilar welding of Nitinol components to stainless steel. During welding of titanium-containing alloys, like Nitinol, to ferrous metals like stainless steel, intermetallic phases between titanium and iron are formed. These phases are very brittle and lead to cracks and reduced mechanical properties of the joint. This publication intends to demonstrate the feasibility of producing weld seams with good quality by the use of Micro Electron Beam Welding. Due to a very accurate beam alignment and fast beam deflection, the composition and the level of dilution in the weld metal can be precisely controlled, resulting in a significantly reduced amount of intermetallic phases. Another aim of this paper is to show that the electron-optical monitoring can be used for quality assurance.

Investigation of the variation of the mechanical properties of 316L steel after electron beam surface modification is performed. The samples were processed at an installation in IE BAS - ELIT – 60. The irradiated plates were with thickness of 0.5 mm. The experiments were carried out with a change in the beam power in the range of 0.6 to 0.9 kW and different irradiation times between 1 to 120 seconds. Regression analysis was performed on the obtained results.

This article presents the investigation results of influence of electron beam oscillation on the formation of welded joints of aluminium alloys. It is shown that for EBW with longitudinal oscillation, at a certain frequency and amplitude of oscillation, a lifting force appears. It acts on the metal of welding pool and displaces it from the root of the weld. The maximum lifting effect of liquid metal corresponds to a frequency of 35 Hz at amplitude of 1 mm (for aluminium alloys 12 mm thick at a welding speed of 90 m/h). The detected effect can be used for EBW materials of large thickness with through penetration.

We investigate analytical description of processes for changes in the breaking X-ray radiation due to the welding channel placement relative to the joint of the welded parts during the Electron Beam welding. We establish that dependency of the X-ray radiation on the welding channel placement relative to the joint is extreme. The determination of the beam placement during the Electron Beam welding of dissimilar materials practically does not require accounting for extremum offset of the characteristics relative to the joint. Mathematical models are used to derive a system for automatic seam tracking during the Electron Beam welding.

The paper presents the differential equation which is a mathematical model of a whole class of phenomena of thermal conductivity and has an infinite number of solutions. Modelled thermal processes at electron beam welding and the resulting expression is the base for building thermal models that take into account different types of dynamic positioning electronic beam. At electron beam welding the beam oscillations on trajectories of various type are applied, in most cases, to eliminate the characteristic defects taking place when welding by a static beam. The following types of beam oscillations are most widely used: longitudinal, transverse and x-shaped. They are chosen for the construction of thermal models. The calculations showed that the proposed model of the heat source for electron beam welding with a static beam and the obtained on its basis solution of the heat problem, permit to describe the geometry of the weld. The method of Green functions as one of the universal ways to build thermal models in electron beam welding with various dynamic positioning of the beam is implemented.

This article discusses the experimental results from multi-pool electron beam welding, with dynamic positioning of the electron beam (beam splitting) [1], resulting in the formation of two consecutive welding pools. The 12Cr18Ni10Ti stainless steel samples are welded with a change in the process parameters: the distance between the two electron beams (electron beam positions) and the ratio between the two mean electron beam powers, the frequency of the deflection signal, the beam current and the welding velocity. The focusing current is kept at a constant value. The weld cross-sections, experimentally obtained at different process parameters, are used to train, validate and test neural models. The accuracy of prediction of the shapes of the welds (the form of the molten pool) is discussed and compared with that of an estimated regression model.

This work aims to assess the bremsstrahlung X-Ray signal from the processing zone obtained by the use of a solid wire during electron beam surfacing. Applications of the bremsstrahlung X-Ray signal in the control systems allow positioning of the filler wire. During the experiments, a scintillation detector based on monocrystalline iodine cesium and silicone photomultiplier was used for registration of the X-Ray signal. Circle oscillations of the electron beam create the informative component. Synchronous storage method was applied for mathematical treatment of the recorded signal.

With the Variocathode EB Gun series completed in 2004 and the fully digital control of High Voltage Power Supplies introduced in 2014, the focus of EB product development has now been directed to the BeamGuidance System. This year, the new VON ARDENNE BeamGuidance will be implemented for the first large EB melting furnace and EB production coater.

Based on standard industrial hardware components, a completely new signal processor and HMI software was developed. Sophisticated procedures implemented on the signal processor calculate all dynamic beam scanning sequences for multiple EB guns in real time including automatic figure movements, coordinate transformations and dynamic corrections. Although the beam scanning sequences are defined with discrete coordinates, the new BeamGuidance allows for both quasi-digital (point to point) and analog (continuous) electron beam movement. With further new key features like synchronization of multiple beams, synchronization to external events and extended time and power distribution based figure manipulations, the new BeamGuidance System provides a new quality for control of EB processes.

Possible applications of a wide-aperture (750 × 150 mm) electron source with a grid plasma cathode based on a low-pressure arc discharge and the output of a large cross section beam through an output foil window are given. The mesh (layer) stabilization of the emission plasma boundary in such cathode makes it possible to generate an electron beam in a wide range of its parameters with weak dependence on each other (beam energy up to 200 keV, beam current in the atmosphere up to 30 A, pulse duration up to 100 μs, frequency pulse repetition up to 50 s^-1). In particular, preliminary experiments were conducted on the use of such a beam in the processes of radiation cross-linking of natural latex without any chemical additives accelerating the vulcanization process; the principal possibility of the formation of carbon structures in polyvinyl chloride films is shown; preliminary experiments were conducted on electron-beam disinfection of agricultural products in the atmosphere. The promise of using such an electron source confirms the unconditional need for the further development of such technologies for the possibility of applying them both for scientific and industrial purposes.

This publication presents the advantages of NVEB technology as an universal tool for material processing based on our investigations on welding and cutting of high-strength S960QL, S1100 and S1300 steels. In this work, the effect of welding cooling time t_8/5 on the microstructure of the heat-affected zone (HAZ) and mechanical properties of the joints were investigated. The new process NVEB-cutting with a local suction produces extremely high cutting speeds, up to 17 m/min with high quality edges, render this method a significant development for new NVEB-applications. To demonstrate the capabilities of the non-vacuum electron beam as a universal tool for the technological process chain, the samples of steel S1100QL were made, while cutting and welding was carried out by one machine basement. The experimental results will be shown and discussed.

In this paper, effects of electron beam melting process parameters (e-beam power, refining time, etc.) and the number of melting operations for fulfilling the requirements concerning the composition and the structure of metals obtained after e-beam processing are studied. Results obtained at electron beam melting of molybdenum and tungsten technogenic materials are presented and discussed. The refining efficiency is evaluated and effective technological regimes (process parameters) for production of metals which meet specific requirements for high-purity and good-quality structure after electron beam melting of Mo and W technogenic materials are proposed.

Electron beam smelting has been applied in refining nickel-based superalloys, which has been proved to be an effective method for removing inclusions. The inclusions are aggregated at the circular region (last solidified region) of the ingot surface periphery where the electron beam finally stayed by induced directional solidification after electron beam smelting. The relationship between the cleanness of nickel-based superalloys and the refining times was investigated. Based on the different refining times, the removal efficiency of inclusions was also discussed and the corresponding experiment was carried out to be compared. The results show that the area of the last solidified region on ingot surface decreases with the increasing of the refining times. The optimal refining time of nickel-based superalloys is considered in order to obtain a relatively high removal efficiency of inclusion and a low mass loss rate.

Theoretical and experimental study on developed profiles in the positive tone PMMA (polymethyl-methacrylate) resist and e-beam lithography process parameters was performed. E-beam lithography control system Elphy Quantum (Raith) installed on Scanning Electron Microscope Quanta FEG (FEI) with a field emission cathode and Gaussian intensity distribution has been used for the conducted experiments. Simulation results obtained by different models concerning the geometry of the developed resist profiles in PMMA were compared and verified with experimental data for improvement characterization of PMMA resist. The estimated models presented are useful for prediction and optimization of the developed resist profiles at electron beam lithography.

In this paper, a study based on the mathematical modelling, applying different process simulation tools (CASINO, TREM, SELID) for characterization of PMMA resist and for the improvement of the resolution concerning the critical dimensions of nano-patterning by electron beam lithography (EBL) is presented. Data for important EBL characteristics (energy deposition function, proximity effect parameters, solubility rate, etc.) are obtained by applying different approaches (Monte Carlo methods, regression models, etc.).

The challenge of this paper consisted in optimization application in the case of starch grafting with a vinyl monomer under accelerated electron field. Thus, the robust engineering approach and multi-criteria optimization were considered. Methods based on graphical optimization as well as on overall optimization were implemented. Moreover, a graphical user interface previously developed was uplifted and its usage mode is detailed in the present work. To uplift the graphical interface both previously reported experimental data and new one were used. This graphical user interface is useful for investigation, optimization and education in the field of material processing by using ionizing radiation. Furthermore, other new functions can be implemented in the future.

An experimental investigation of the electron beam irradiation induced grafting of acrylamide onto corn starch was performed. In this way the synthesis of water-soluble copolymers having flocculation abilities is realized. The acrylamide monomer provides a polar graft side chain which turns it into a hydrophilic copolymer. The robust engineering approach was implemented for the estimation of models for the means and the variances of the investigated quality parameters in production conditions, aiming the assurance of low toxicity of the synthesised copolymer, process economic efficiency, copolymer efficiency in the flocculation process and its good solubility in water. In order to improve the accuracy of the estimated models, performing new experiments was planned, based on the sequentially generated D-optimal designs. An approach for the generation of such designs for several quality parameters is presented.

The paper presents the results of a study of the formation of the structure and properties of metals in the technologies of additive processes, namely plasma, arc and laser surfacing of high-alloy Chromium-Nickel alloys. The main problem of Chromium-Nickel alloys in the processing of highly concentrated energy sources (welding, surfacing, soldering, plasma and laser processing) is insufficient strength and heat resistance after high heating and rapid cooling, characteristic of these methods. The paper presents the results of a study of the structure, phase formation and properties of Chromium-Nickel alloys in plasma surfacing of high-alloy steel wire. To study the possibilities of modifying the structure during argon-arc surfacing, additional ultrasonic action on the deposited material was applied with the help of a waveguide connected to the lower surface of the sample. A comparison of the structures of the surfacing alloy obtained by laser cladding found that arc welding of alloy in combination with ultrasonic action created the additional effect of increasing the dispersion of the phases, which led to increased high-temperature strength of the alloy.