Low-energy High-current Electron Beam Research Articles

On the correspondence of bump relief on the surface of materials processed with low-energy high-current electron beam to their grain structure

One of the features that appears on the pre-polished surface of metals and alloys as a result of processing with low-energy high-current electron beam is a bump surface relief with the bump size varying from several tens to several hundred nanometers. Some researchers consider these bumps as the trace of the grain structure of the near-surface modified layer of material. The aim of the present work was to show experimental results proving that the bump relief is not related to the grain size in the near-surface layer. The microstructure was studied using reliable complementary methods of transmission electron microscopy and backscattered electron diffraction using Inconel 718 alloy and stainless steel obtained by additive manufacturing and processed with low-energy high-current electron beam.

Influence of Low-Energy High-Current Electron Beam Exposure on the Phase Composition and Corrosion Resistance of the AM60 Magnesium Alloy

Influence of Low-Energy High-Current Electron Beam Exposure on the Phase Composition and Corrosion Resistance of the AM60 Magnesium Alloy

TEM and X-ray diffraction studies of structure of TiNi SMA treated by low-energy high-current electron beam

Advanced scientific and technological achievements in the surface engineering of TiNi shape memory alloys are closely related with their mechanical performance. Electron-beam treatments could be applied in order to modify surface properties of smart materials and promote stress-induced martensitic transformations. The fundamental issue of electron-beam processing is residual elastic stresses arising from the ultrafast quenching (∼108 K/s) of thin (∼2–4 μm) surface layers. We report the experimental results on phase composition, structure and residual elastic stresses formed in the binary TiNi SMA irradiated by a low-energy (< 25 keV) high-current (∼ 25 kA) electron beam. Microstructure, fracture mechanisms and phase analysis of the as-cast and deformed tensile specimens have been studied by X-ray diffraction and electron microscopy. After electron-beam treatment, both martensitic B19′ and R phases are found in the near surface layer. The X-ray diffraction studies indicate that compressive stresses in the B2 phase of the irradiated TiNi alloy reach –460 MPa. In the fractured specimen (after tensile test) the residual stresses decrease to –160 MPa and release through the B2→B19′→B2 martensitic transformation. In-depth gradient distribution of the defect substructures responsible for the mechanical behavior of TiNi alloys was revealed.

Surface Modification of Diatomite-Based Micro-Arc Coatings for Magnesium Implants Using a Low-Energy High-Current Electron Beam Processing Technique

The present study showcases a novel effective technique for the surface modification of micro-arc diatomite coatings using low-energy, high-current electron beams (LEHCEBs). A variety of methods such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, the X-ray diffraction method, scratch testing, the potentiodynamic polarization method, immersion testing in SBF, and flow cytometry have been used to study the coatings. During processing, the electron beams’ energy density ranged between 2.5–7.5 J/cm2. After the LEHCEB treatment, the surface morphology of the coatings changed completely. The corrosion resistance of the LEHCEB-treated coated samples increased significantly, as evidenced by the decrease in corrosion current to 4.6 × 10−10 A·cm−2 and the increase in polarization resistance to 1.4 × 108 Ω·cm2. The electron beam treatment also increased the adhesion strength of the coatings to the magnesium substrate by 1.8–2.5 times compared to untreated coatings. Additionally, biological studies have shown the high viability of the NIH/3T3 cell line after contact with the samples of the coating extracts.

Characteristic features of relief formation on the surface of Ni3Al and Ni3Al-TiC composites as a result of low-energy high-current electron beam irradiation

Using scanning electron microscopy and roughness measurements we studied the relief appeared on the surface of TiC-free Ni3Al and Ni3Al-TiC composites (TiC content was 10 and 30 vol%) as a result of low-energy high-current electron beam irradiation (the surface energy density was in the interval of 8–18.0 J/cm2, the accelerating voltage was 30 kV, the pulse duration was 3.2 μs, the number of pulses was 10 and 30). Using the same materials differing in the content of non-metallic particles for investigation enabled clarification of the role of non-metallic inclusions in the relief formation. The effect of the particles size, surface energy density and number of pulses was also analyzed. Three types of dimples forming the relief were revealed. Each of the type appeared following to its own formation mechanism. The applicability of the models existing in literature to explain relief formation was discussed.

Metallurgical patterns of the formation of W–Zr surface alloys via pulsed electron-beam processing

In this study, W–Zr surface alloys (SAs) were synthesized by low-energy high-current electron beam (LEHCEB) processing of preliminary deposited tungsten films on zirconium substrates in a single vacuum cycle. Then, their microstructure, as well as both chemical and phase compositions were investigated. Also, computer simulation of the dynamics of temperature fields was carried out. After LEHCEB processing of the Zr substrate with the preliminary deposited W film, the constituent element distributions were non-uniform over the surface of the W–Zr SA at the energy density of 3.5 J/cm2. Rising the energy density up to 5.5 J/cm2 resulted in a smoother and more homogeneous W–Zr SA. At the energy density of 3.5 J/cm2, the average tungsten content over the surface was 53 ± 39 at.%, while it was only 26 ± 2 at.% at 5.5 J/cm2. All W–Zr SAs consisted of the W phase (in different proportions), tungsten-rich solid solutions in the stabilized β-Zr phase, and the W2Zr intermetallic compound. The contents of the β-Zr and W2Zr phases enhanced with rising the energy density due to a greater amount of dissolved tungsten. Based on the obtained results, a scheme was proposed describing the formation of the SAs upon LEHCEB processing.

The effect of low-energy high-current pulsed electron beam irradiation on the structure, phase composition and mechanical properties of Ni3Al and Ni3Al-TiC composites

Using scanning and transmission electron microscopy, X-ray diffraction, indentation and bending tests we studied the evolution of microstructure, phase composition and mechanical properties of TiC-free Ni3Al and Ni3Al-TiC composites (TiC content was 10 and 30 vol%) fabricated by self-propagating high-temperature synthesis (SHS) under pressure induced by low-energy high-current pulsed electron beam (LEHCEB) irradiation with the surface energy density of 8, 12 and 18 J/cm2. It was found that the irradiation results in the improvement of phase composition of the near-surface layer by way of the increase of yield of SHS reaction. LEHCEB irradiation enables formation of nanocomposite structure in the near-surface layer of Ni3Al-TiC composites with decreased grain size of Ni3Al matrix, refined TiC particles and increased volume fraction of TiC. This structure leads to the increase of microhardness but decrease of strength under bending. Two mechanisms of TiC particles refining are suggested. The effect of surface energy density on the manifestation degree of the found phenomena is discussed. The contribution of different hardening mechanisms to the overall hardening is considered.

Formation of Fe–Cr–Al–Zr Surface Alloy on a Zirconium Substrate Using a Low-Energy High-Current Electron Beam

Formation of Fe–Cr–Al–Zr Surface Alloy on a Zirconium Substrate Using a Low-Energy High-Current Electron Beam

Nanobubbles and physical-mechanical properties of the Ti-Ni-Ta-Si-based metallic glass surface alloy fabricated on a TiNi SMA substrate by additive thin-film electron-beam method

An additive thin-film electron-beam method for the synthesis of micron-thick surface alloys is a promising method for modifying the surface layers of metallic materials. This method allows to functionalize the surface properties (corrosion resistance, radiopacity, biocompatibility), as well as to improve the physical-mechanical properties. The amorphous Ti-Ni-Ta-Si-based surface alloy (~1.6 μm thick) was synthesized by 10-fold alternation of operations of the deposition of an alloying film (Ti60Ta30Si10 (at. %), ~100 nm thick) and the liquid-phase mixing of the [film/substrate] system using a pulsed low-energy high-current electron beam. Spherical nanobubbles (diameter varies from ~2.5 up to ~50 nm) were observed within the surface alloy. The additional electron-beam treatments were used to reduce the concentration of the nanobubbles. The paper presents the results of the influence of the electron-beam treatments on the concentration and size of the nanobubbles, and their in-depth distribution. It was found that the single-step electron-beam treatment effectively reduced the concentration of the nanobubbles and affected on their size and distribution. The two-step electron-beam treatment almost restored the characteristics of the nanobubbles. The influence of the characteristics of the nanobubbles on the strength and elastic-plastic parameters of the amorphous Ti-Ni-Ta-Si-based surface alloy was revealed. The characteristics of the nanobubbles had a major effect on the elastic-plastic parameters of the surface alloy while the strength parameters remained practically the same. It was found that a purposeful change of the characteristics of the nanobubbles is an effective tool for controlling physical-mechanical properties of the amorphous Ti-Ni-Ta-Si-based surface alloy fabricated on a TiNi SMA substrate.

Preparation and surface alloying of Al@Dy and Al@Y core-shell particles by magnetron sputtering and pulsed electron beam treatment

The paper is devoted to preparation Al@Dy and Al@Y core-shell structures by magnetron sputtering of Dy and Y on an Al powder. A unique powder holder system is used to obtain continuous powder movement and conglomerates destruction during the treatment. It has been established that powder particles treated using the powder holder system have a uniform coating over the entire surface. The powder coating process regularities were studied depending on the deposition time and the powder charge weight. Simple evaluation criteria for powder coating system efficiency and deposited material content based on the deposition rate were proposed. The complex modification consists of the initial core-shell structure formation and subsequent pulsed low-energy high-current electron beam treatment in the surface layer melting mode was demonstrated. The main goal of the electron beam treatment is to provide better adhesion of the “shell” material to the “core” material. Such treatment led to the deposited shell element alloying into the depth of core particles. Moreover, such electron beam treatment led to the synthesis of intermetallic compounds. In further studies, the prepared structures will be used for the uniform distribution of Dy and Y over the frame elements of self-propagating high-temperature synthesized porous materials.

Increasing the Pulse Energy of a Radially Converging Low-Energy High-Current Electron Beam

Increasing the Pulse Energy of a Radially Converging Low-Energy High-Current Electron Beam

Ti-based surface alloy formed on AISI 316 L austenite steel surface using low-energy high-current electron beam

Titanium and Ti-based alloys possess good biocompatibility and excellent corrosion resistance. This paper is devoted to an effort to create Ti-based surface alloy on specimens made of the AISI 316 L austenite steel. The Ti-based surface alloy is created by the Ti film deposition using the magnetron sputtering method followed by the low-energy high-current electron beam irradiation of the Ti film–316 L steel substrate system surface. Transmission electron microscopy shows that the surface alloy consists of several sublayers having different structures and phase compositions. In particular, these are α-Ti; TiSi2; FeTi and Fe2Ti; Fe2SiTi; Fe2Ti3O9 phases and more complex Cr13Fe35Ni3Ti7, Cr12Fe32Mo7Ni7, Cr12Fe36Mo10, Mo5Cr6Fe18 phases nearby the substrate. Phase compositions of the surface alloy layers are determined by the change in the chemical composition of the titanium–steel system and the heat depth distribution. It is shown that the formation of the Ti-based surface alloy on the AISI 316 L austenite steel surface, provides the increase in the polar component of the free surface energy from 3.2% to 34.5%.

COMBINED HYDRODYNAMIC INSTABILITIES AND THEIR ROLE IN THE FORMATION OF MICRO- AND NANOSTRUCTURES OF MATERIALS UNDER PLASMA INFLUENCES

The formation of micro- and nanostructures in titanium alloys subjected to combined treatment, including exposure to heterogeneous plasma flows and subsequent modification of the surface layer by a low-energy high-current electron beam, was studied. It is established that the main mechanism for the formation of structural-phase states of the micro and nanoscale range under the influence of plasma flows created by an electric explosion of conductors is the joint manifestation of Kelvin-Helmholtz and Rayleigh-Taylor instabilities at the interface of the media. It is shown that the maximum growth rate of disturbances with acceleration of the second layer g = 5 ×109 m/s2 and a transverse velocity of 0 m/s falls on the wavelength λm = 6.76 µm. If the velocity value of the second layer is u0 = 10 m/s, then λm = 6.23 µm, and at u0 = 50 m/s ‒ λm = 1.24 μm. The mechanism of formation of micro- and nanostructures during subsequent electron beam processing is a combined thermo-evaporative, concentration- capillary and thermoelectric instability. It is shown that if the influence of the concentration gradient, thermoelectric and evaporative effects is not taken into account, the maximum value of the growth rate will be observed at a wavelength of 113 µm. Taking into account thermoelectric phenomenon leads to a decrease in the value of λm to 48 μm. It is established that at the value of the thermoelectric coefficient γ = 0.1 V/K, the maximum growth rate is observed at λm = 300 nm.

Melting Thresholds of the Film-Substrate System Irradiated with a Low-Energy High-Current Electron Beam

Melting Thresholds of the Film-Substrate System Irradiated with a Low-Energy High-Current Electron Beam

Changes in the Surface Structure and Properties of Zirconium Upon Exposure to a Low-Energy High-Current Electron Beam

Changes in the Surface Structure and Properties of Zirconium Upon Exposure to a Low-Energy High-Current Electron Beam

Evolution of morphology, microstructure and phase composition of zirconia thin coating on copper as a result of low energy high current pulsed electron beam irradiation

Using X-ray diffraction, scanning and transmission electron microscopy we studied the evolution of the morphology, microstructure and phase composition in the near-surface layer of copper covered with thin (2.8 μm) ZrO2 coating induced by low-energy high-current pulsed electron beam irradiation (the surface energy density was in the interval of 5.0–18.0 J/cm2, the accelerating voltage was 30 kV, the pulse duration was 3.2 μs, the number of pulses was 10). The variation of adhesion of the coating to substrate was evaluated using scratch testing. The evaporation of the upper part of the coating during irradiation was found and the thickness of the coating nonlinearly decreased with the increase of the energy density. We discussed the reasons for the surface cracking taking into account microstructural changes in the near-surface layer of the material. The irradiation was found to transfer most of monoclinic ZrO2 phase in the as-deposited coating to tetragonal and, possibly, cubic one. The factors influencing the adhesive strength of the coating were revealed and a potential for the increase of adhesion was demonstrated. We showed that irradiation with enhanced surface energy density was required to obtain copper-based composite hardened with zirconia nanoparticles in the near-surface layer. The thickness of the composite layer may be as much as 6 μm.

Влияние электронно-пучковой обработки на характер распространения усталостных трещин и формирование пластических зон на поверхностях разрушения в никелиде титана

Influence of surface electron-beam processing on character of fatigue cracks propagation and crack growth rates under cyclic tension in a mode of low-cycle loading of TiNi samples before and after irradiation by low-energy high-current electron beam (LEHCEB) is studied in the work. Correlation between stages of fatigue cracks propagation and formation of plastic zones on surfaces of failure in TiNi samples before and after LEHCEB treatments is established. The LEHCEB treatment of specimen surfaces was carried out at the electron-beam installation “RITM-SP” with the electron beam parameters: energy density ES = 3.7 J/cm2, pulse duration τ = 2.5 μs, number of pulses n = 5. Differences in the stages of propagation of main fatigue cracks during cyclic stretching of TiNi samples before and after LEHCEB have been revealed. Preferential mechanisms of quasistatic and fatigue fracture at different stages of crack propagation are determined. It is shown that LEHCEB treatment leads to a shift of fatigue fracture initiation and the beginning of all stages by ∆N ≥ 3000, increasing the cyclic durability of the specimens by ~ 1.5 times. The greatest influence of surface modification is shown on Stage I of fatigue crack propagation. The lower rate of fatigue crack propagation at this stage in irradiated specimens leads to an increase in its duration as compared to unirradiated specimens. It is concluded that to effectively increase the fatigue life of TiNi specimens by means of LEHCEB treatments it is necessary to create conditions for increasing the number of cycles before the Stage I initiation and maximizing the duration of this stage.

Поверхностный Ti-Ni-Ta-сплав, синтезированный на TiNi-подложке электронно-пучковым способом: структура и физико-механические свойства

The structure and physical-mechanical properties of Ti-Ni-Ta-based surface alloy synthesized on the NiTi-substrate through additive thin-film electron-beam method have been studied. The synthesis of the surface alloy was carried out by 30-fold alternation of operations of deposition of a dopant film (Ti60Ta40 (at.%), ~50 nm thick) and liquid-phase mixing of the film/substrate using a pulsed low-energy high-current electron beam. It was found that Ti-Ni-Ta-based surface alloy, whose thickness is ~1.8 μm, has an amorphous structure. It has been established that the surface alloy has ~2 and ~1.5 times higher values of microhardness HOP and elastic modulus EOP compared to the initial NiTi-substrate, but parameter of plasticity δh and shape recovery ratio η close to the substrate. It is shown that the nature of the change in physical-mechanical properties in Ti-Ni-Ta-based surface alloy and the transition zone depends on the number and thickness of the sublayers, as well as on the structural states of the phases in the sublayers. The evaluation of the mechanical compatibility of the surface alloy with the NiTi-substrate is given.

A Source of Radially Converging Low-Energy High-Current Electron Beams

A Source of Radially Converging Low-Energy High-Current Electron Beams

Prediction of the composition of surface alloys formed via pulsed melting of preliminary deposited coatings

To date, many results of studies of surface alloys have been published, but no approaches have been developed to predict their quantitative composition that can assist to design new types of coatings. This paper proposes a methodology for prediction the atomic and mass contents of elements in the surface alloys formed by pulsed liquid-state mixing of pre-deposited films and an upper layer of a substrate. The methodology validity has been verified experimentally on the example of a Cr–Zr surface alloy that is of particular interest due to its possible use in the nuclear industry. The surface alloy has been synthesized by irradiation of a Cr/Zr film-substrate system with a low-energy high-current electron-beam (LEHCEB) of microsecond duration. The results have showed good agreement between the predicted and experimental data with an accuracy satisfactory for practical applications. Some observed discrepancies are explained by the pulse-to-pulse dispersion of the energy densities during LEHCEB irradiation.