Vacuum Electron Beam Research Articles

A new understanding of phase transformation in vacuum electron beam welding of NS163 Co-based superalloy and AISI 410L stainless steel: Based on in situ observation and variant selection

This study establishes a link between crystallographic variants and mechanical properties at both the edge and center regions of NS163 Co-based superalloy wires and AISI 410L stainless steel plates welded joints. The thermal cycle of vacuum electron beam welding was simulated using in situ laser confocal microscopy to clarify the martensitic transformation process. Results indicate that martensite preferentially nucleates at grain boundaries, maintaining the Kurdjumov-Sachs orientation relationship with the parent austenite. Most variant boundaries in these regions correspond to variants within the same crystal packet, with V1/V3&V5 emerging as dominant pairs. At the edge, the increased cooling rate and temperature gradient amplify the driving force for martensitic transformation, fostering the generation of diverse variants. Conversely, lower cooling rate at the center raises the martensitic transformation temperature and expands variant selection. The study notes significant dislocation slip during micropillar compression, with the edge of weld exhibiting finer martensite laths and dense dislocations, which enhances strength (∼1279 MPa) compared to the center (∼1040 MPa), aligning with the results obtained via nanoindentation. The observed "size effect" results in a twice strength as measured by micropillar compression compared to nanoindentation. Additionally, staggered Bain groups at the edge include a greater number of high angle grain boundaries, indirectly improving toughness. This research aligns with recent literature and aids in the development of compositional design and machining techniques for heterogeneous welds.

Insight into the keyhole behaviour and its role on residual stress formation in vacuum electron beam welding of TC4 titanium alloy

Electron beam welding (EBW) is the preferred technique for joining TC4 titanium alloy. Accurately characterizing the welding keyhole and residual stress distribution, along with analyzing their formation mechanisms, is of paramount importance for ensuring high reliability of the TC4 EBW structures. In this regard, a “thermal-fluid-metallurgical-mechanical” multi-field coupling numerical method was developed, which was then validated by the vital experiments. The evolution of the keyhole, molten pool temperature, phase volume fraction and residual stresses was then revealed. The influencing mechanism of keyhole on residual stress was explored comprehensively. The results show that metal vapor recoil pressure serves as the primary factor in keyhole formation, while the surface tension promotes keyhole closure. The β-phase in the weld zone undergoes a complete transformation into α′ acicular martensite. Moreover, the maximum longitudinal stress occurs at the weld center, while the transverse stress exhibits a substantial stress gradient along the thickness direction. Increasing the welding power raises the temperature of molten pool. The keyhole depth and width are also enlarged, accompanying by the increase of residual stress, which is expected to offer a theoretical foundation for managing the keyhole and residual stress generated during the EBW of TC4 titanium alloy.

The microstructure and mechanical properties of electron beam welded Ti2AlNb-based alloy joint with the addition of TiB2

In this paper, 5 mm thick Ti-22Al-25Nb alloy plate was used for vacuum electron beam welding. The effect of TiB2 on the surface forming, macroscopic morphology, microstructure and mechanical properties of the joint was studied by optical microscope, scanning electron microscope and X-ray diffractometer. The results showed that TiB2 had an obvious effect on the microstructure and mechanical properties. The surface forming of the joint was good with the addition of TiB2, while the lower surface of the joint without the addition of TiB2 was discontinuous and presented a droplet state. The phase of WZ with TiB2 was composed of B2 phase, TiB and a small amount of O phase, while it mainly consisted of B2 phase for the joint without addition of TiB2. The hardness of the WZ with different addition of TiB2 was higher than that of the WZ without addition of TiB2. The breaking strength at high temperature of the joint without addition of TiB2 was 639 MPa, which was only 72.5 % of the BM and lower than that of the joint with different addition of TiB2.

Achieving high precipitation phase proportion and mechanical properties of vacuum electron beam oscillation welded joints of near β titanium alloy thick plates by the interlayer addition

The strengths of near β titanium alloy thick plate joints are usually reduced after fusion welding since only a small amount of α phase precipitates during cooling. In this study, vacuum electron beam welding (VEBW) with a 1-mm-thick Ti-6Al-4V (Ti-64) interlayer using novel sawtooth scanning (SS) pattern was designed to regulate the morphology and proportion of α phase in 30-mm-thick near β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe, which largely enhanced the joint properties. The SS-joint with Ti-64 interlayer enhanced the joint strength most, with the increase in the tensile strength from 849 MPa for the joint without interlayer addition to 991 MPa for the SS-joint, which could usually reach similar strengths to the annealing treatment joints as reported. The improved strength was mainly attributed to largely increased proportion of acicular α phase for the SS-FZ with Ti-64 interlayer. The fracture location of the SS-joint with Ti-64 interlayer was in the heat affected zone (HAZ). Furthermore, the impact energy of HAZ in SS-joint was slightly higher than that of HAZ without interlayer addition, even superior to that of base material. This study provides a new economy and high efficiency welding method to improve the mechanical properties of near β titanium alloy thick plates.

Factorized form of the dispersion relations of a traveling wave tube

The traveling tube (TWT) design in a nutshell comprises of a pencil-like electron beam (e-beam) in vacuum interacting with guiding it slow-wave structure (SWS). In our prior studies the e-beam was represented by one-dimensional electron flow and SWS was represented by a transmission line (TL). We extend in this paper our previously constructed field theory for TWTs as well the celebrated Pierce theory by replacing there the standard TL with its generalization allowing for the low frequency cutoff. Both the standard TL and generalized transmission line (GTL) feature uniformly distributed shunt capacitance and serial inductance, but the GTL in addition to that has uniformly distributed serial capacitance. We remind the reader that the standard TL represents a waveguide operating at the so-called TEM mode with no low frequency cutoff. In contrast, the GTL represents a waveguide operating at the so-called TM mode featuring the low frequency cutoff. We develop all the details of the extended TWT field theory and using a particular choice of the TWT parameters we derive a physically appealing factorized form of the TWT dispersion relations. This form has two factors that represent exactly the dispersion functions of non-interacting GTL and the e-beam. We also find that the factorized dispersion relations comes with a number of interesting features including: (i) focus points that belong to each dispersion curve as TWT principle parameter varies; (ii) formation of “hybrid” branches of the TWT dispersion curves parts of which can be traced to non-interacting GTL and the e-beam.

Effect of Ta/Ni dual-interlayer on the microstructure and properties of high strength titanium alloy and steel composite plate

The combination of ultra-high-strength Ti-6Al-4V (TC4) titanium alloy and 30CrNiMoNb (6211) steel was achieved by adding Ta/Ni dual-interlayer and rolling at 950 °C through welding a symmetrical blank sleeve with a vacuum electron beam. In order to unveil the metallurgical bonding mechanism and the interfacial structure, SEM, XRD, and compression-shear performance tests were used. The results revealed the presence of thin-film brittle TiC, TiFe, and TiFe2 compounds at the TC4/6211 interface, resulting in an increased risk of interface mismatch and brittle fracture along the matrix phase interface, and the average interfacial bonding strength was tested at 323 MPa.In contrast, the TC4-Ta interface and the 6211-Ni interface in the TC4/Ta/Ni/6211 composite plate displayed good solid solution formation. The strengthening mechanism of the Ta/Ni dual-interlayer interfacial bonding was analyzed using selected area electron diffraction (SAED), revealing that the Ta-Ni diffusion region consisted of Ni3Ta and Ni2Ta. The addition of the Ta/Ni dual-interlayer prevented the aggregation of Ti and Fe atoms to form Ti-Fe compounds. The malleable intermetallic compounds of Ni3Ta and Ni2Ta effectively coordinated deformation, leading to an average interfacial bonding strength of 469 MPa, which was 45.2 % higher than the composite plate without Ta/Ni dual-interlayer.

Compressive behavior and deformation mechanisms of gradient microstructures in a dissimilar welded joint

In this study TC4/TC17 titanium alloy dissimilar joints were obtained via vacuum electron beam welding. The compressive behavior of base metals and joint at different strain levels was studied, along with microstructural and fracture surface observations. The true stress–strain curves of base metals and joint at different strains demonstrated smooth and continuous plastic deformation characteristics. The compressive yield strength of the joint (1065 MPa) was basically equivalent to that of TC17 alloy (1196 MPa), which was significantly higher than that of TC4 alloy (920 MPa) for the failed samples. However, the compressive fracture strain of the joint was lower than that of base metals. Comparison of the microstructures of base metals and joint deformed at different strains, it revealed that the equiaxed α phase in TC4 alloy mainly underwent the deformation, while the TC17 alloy mainly relied on the rotation of lamellar grains to resist the deformation. In the dissimilar joint with a large microstructural gradient, the compressive deformation of several zones, including the weld zone, far heat-affected zone and the base metal, was also related to the rotation of finer grains.

Investigation on the room temperature compressive creep behavior of TC4 titanium alloy joints with vacuum electron beam welding

The room temperature compressive creep behavior is a key issue for the titanium alloys welded structural components served in deep-sea environment. In the present work, the compressive creep behavior of different areas for TC4 titanium alloy joints with vacuum electron beam welding was systematically studied, and it is found that the fusion zone (FZ) of TC4 titanium alloy joints has the minimum creep strain rate. This is mainly because the creep deformation of TC4 titanium alloy is mainly controlled by the movement of dislocations in the α or α′ phases, the size of α′ phase in FZ is small, and thus the dislocation slip is limited. MD simulation results have further revealed that the room temperature compressive creep nature of α-Ti can be regarded as a dynamic hysteresis phenomenon in plastic strain and is dominated by the dislocation movement.

Numerical simulation and properties analysis of Ta10W alloy joints prepared by electron beam welding

Vacuum electron beam welding has the characteristics of concentrated energy, controllable heat input, almost no pollution, and a small heat-affected zone. In this study, the Ta10W alloy was successfully connected by electron beam welding (EBW), and numerical simulations were employed to examine the distribution of temperature and stress fields throughout the welding process. Additionally, the influence of EBW on the microstructure and corrosion resistance of the welded joints was scrutinized. Findings indicate that the welding heat process led to a reduction in grain boundary energy, thereby facilitating thermal activation processes that contributed to grain growth. Grain boundary migration and possible dynamic crystallization led to the appearance of the coarse columnar crystal structure in the welded joint. A three-dimensional, nonlinear, transient, thermo-mechanically coupled finite element model was developed for the electron beam welding of Ta10W alloy. The shape characteristics and size of the weld and transient thermal cycles calculated by numerical simulations were in reasonable agreement with experimental results. Electron beam welding reduced the corrosion resistance of the Ta10W alloy, and the corrosion product was mainly composed of Ta, O and Na.

High temperature oxidation behavior of a Ni–Co-based superalloy

Oxidation behavior of a Ni–Co-based superalloy prepared by vacuum induction melting (VIM) plus electron beam smelting layered solidification technology (EBSL) and VIM plus electro slag remelting (ESR) at 1180 °C was investigated. The predominant oxides from the outer layer to the inner layer are TiO2, Cr2O3, (Al, Ti)-rich oxide and Al2O3, respectively. The (Al, Ti)-rich oxide is considered to be Al2Ti4O9, which is formed by TiO2 and Al2O3. At high temperature, the external oxides experienced significant spalling, particularly in ESR-alloy, which indicated that the EBSL-alloy is more preferable in terms of oxidation resistance. This can be attributed to the presence of finer grains in EBSL-alloy, which facilitates the diffusion of elements and promotes the rapid formation of oxidation scales on the surface of the alloy. Additionally, the presence of a TiO2 layer cover on Cr2O3 reduces the degree of spalling of oxides in EBSL-alloy.

Fabrication and manipulation for key elements of magnetic-driven speed-reduction micro-motor

The motion of magnetic-driven micro motor is controlled by external magnetic field, does not need any fuel which has good biocompatibility. However, its driving torque needs to be further improved. For it, a magnetic-driven micro-motor with speed-reduction function is proposed. The main elements for the micro-motor includes wave generator, central ring, and movable tooth frame which had to be fabricated with Electron beam lithography and vacuum evaporation coating technology. So, related processing parameters should be optimized to obtain high quality elements of the micro-motor. Here, a magnetic-driven micro-motor with speed-reduction function is proposed. Fabrication and manipulation techniques of the main elements for the micro-motor, such as wave generator, central ring, and movable tooth frame, are studied. Electron beam lithography, electron microscope, and atomic force microscopy (AFM) are applied to optimize the parameters of electron beam lithography. The optimized photolithography parameters are obtained, by which the micro movable tooth frame is successfully developed, and the photoresist molds of the wave generator and central ring is produced. Using vacuum evaporation coating technology, effect of evaporation rate on the quality of micro-parts is studied. The optimized evaporation rate is obtained, by which the nickel-based wave generator and copper-based center ring are successfully developed. The nickel-based wave generator and copper-based central ring are effectively peeled off from the substrate by ultrasonic oscillation technique. The effective manipulation of the wave generator and central ring is accomplished by AFM and piezoelectric-driven micro-probe.

In situ high temperature transmission electron microscopy on melting mechanism of secondary copper smelting slag

A new technique for investigations in nano-scale is applied to secondary copper smelting slag with the aim to understand melting mechanism and phase development within the material: in situ transmission electron microscopy at high temperatures. Heating the material step by step with accompanying EDX analysis allows detailed tracking of phase transformations, including changes in chemical composition. The behavior of Cu nano-spheres as well as Fe and Zn in different phases is described in detail. Evaporation of Cu, Fe and Zn is compared to available thermodynamic data, showing relatively good agreement for Cu and Fe, but different results for Zn. The observation of liquid Fe formation is a new phenomenon, which needs further investigation. High temperature transmission electron microscopy is found to be a suitable method for certain research questions, when taking limiting factors like vacuum conditions and electron beam effects into account.

Initiation and propagation mechanism of fatigue crack in ultra-thick titanium alloy vacuum electron beam welding joint

The investigation delved into the fatigue properties across various layers of joints in a 130-mm-thick Ti6Al4V- damage tolerance titanium alloy, which had been fabricated through vacuum electron beam welding. Microstructures in welds are inhomogeneous along the thickness direction of joints. The fatigue properties of various layers of joints exhibit minimal differences, with the fatigue limit consistently exceeding 90 % of the base metal. The cracks always initiate on the sample surface, with numerous fatigue striations present on all fractures. Additionally, many dimples are observed in all fracture zones. The fatigue crack propagation mechanism is depicted as a series connection of micro-pores. Micro-pores are formed by inward pitting of material surfaces and nucleate in local plastic deformation zones of the material. Stress concentration of microstructures is an important cause for formation of local plastic deformation zones. After high cycle fatigue experiments, martensite lath-shaped α′ phase in microstructures in the weld is broken and the broken α′ phase pins the dislocations, resulting in microscopic stress concentration.

Research on electronic optical monitoring technology and system design for vacuum electron beam welding process

Electron beam welding technology is increasingly used in industrial manufacturing due to its high power density and the purity of welded joints. In vacuum environments, traditional optical and machine vision monitoring methods are susceptible to contamination by metal vapors, which hinders the monitoring effect. Due to the limitations of optical monitoring methods, electronic optical imaging technology is a new alternative monitoring method that has been introduced into the electron beam processing in recent years, but the complexity of the industrial electron beam welding environment makes it relatively less studied in the field of electron beam welding. In this study, a YAG scintillator detector is proposed to collect the backscattered electron information generated by the interaction of electrons with the sample, and an FPGA real-time processing system is used to realize the weld quality monitoring in the industrial electron beam welding processes. The distribution law of backscattered electrons in space is simulated by Monte Carlo method, and the results show that the number of distribution in the 40°∼60° angle region is more, the backscattering coefficient increases with the increase of the incident angle of the electron beam, and the backscattering coefficient of the samples with large atomic numbers is relatively high. The field monitoring experiments show that the designed system exhibits good sensitivity to the characteristic morphology, and the imaging resolution reaches more than 200 μm, and the weld hole defects are clearly visible. A good linear correlation between the current change curve during scanning and the actual shape profile is shown, while the image resolution is better when the spot current is 1 mA.

Comparative study on microstructure and properties of HR-2 anti-hydrogen steel weld joints with different section shapes by vacuum electron beam welding

The forming, microstructure, mechanical properties and corrosion resistance of three kinds of vacuum electron beam welded joints with different shapes were studied. The results of X-ray inspection of the joints showed that the three shapes of welded joints could meet the requirements of the quality inspection. The results of microstructure characterization show that the worm or bone-like δ-ferrite appears in the upper and lower regions of the funnel-shaped and bell-shaped joints, while only a small amount of δ-ferrite appears in the local regions of the nail-shaped joints. The test results of mechanical properties show that the micro-hardness of the weld center in the three kinds of shaped joints is the lowest. All the specimens fracture in the weld, and the bell-shaped weld presents the highest impact energy and bending load. Funnel-shaped weld shows the worst corrosion resistance due to the element segregation of the weld. Thus, the bell-shaped joint exhibits the best comprehensive performance.

Mechanism of pore evolution in electron beam welding joints of Mo-14Re alloy

The mechanism of pore evolution in vacuum electron beam joints of Mo-14Re alloy has been thoroughly investigated. Microscopic characterization methods, including Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), were employed to explore the evolution mechanism of pore defects at different locations. Weld defects were further characterized using Energy Dispersive Spectroscopy (EDS) and Transmission Electron Microscopy (TEM), providing insights into their formation mechanisms. The findings reveal that pores along grain boundaries are the result of MoO and CO bubble aggregation. Non-equilibrium solidification of the melt triggers chemical reactions, transforming MoO and CO bubbles into MoO3 and C, with lower melting points. MoO3 and C persist in the pores, leading to the formation of grain boundary gas hole defects. On the other hand, intragranular pore defects stem from an abundance of pores within the matrix material. Upon entry of gas from these pores into the molten pool, its escape is impeded due to the intense influence of the molten pool. After the molten pool completes the cooling and solidification process, the gas remains within the crystal, resulting in intragranular pore defects.

Synthesis of Corrosion-Resistant Coatings by Non–Vacuum Electron Beam Surfacing: Production, Structure, and Properties

Synthesis of Corrosion-Resistant Coatings by Non–Vacuum Electron Beam Surfacing: Production, Structure, and Properties

Study on field emission performance of SrTiO3 film enhanced by LiF film

A series of monolayer SrTiO3 films and LiF/SrTiO3 bilayer films were prepared on n-Si substrates by using vacuum electron beam vapor deposition (EBVD) technology. The morphologies and thicknesses of the SrTiO3 film and LiF film were controlled through adjustments and optimization of the growth conditions as well as deposition time. The experimental results show that the field emission performance of SrTiO3 film is significantly improved after LiF film is added. Under the research conditions in our laboratory, a large number of LiF/SrTiO3 bilayer film field emission devices have been tested and analyzed in the wide range of LiF film thickness (10–300 nm), and the effective field emission LiF film thickness (50–90 nm) was initially determined. Further study shows that the LiF/SrTiO3 bilayer film has the best field emission performance when the optimal LiF film thickness is 70 nm, and its maximum field emission current density can reach 305.48 μA/cm2. The field emission current density of the LiF/SrTiO3 bilayer thin film device is nearly 4 times compared to that of the monolayer SrTiO3 film when the applied electric field intensity reaches 9.05 V/μm. All the field emission devices exhibit excellent functioning stability and experimental reproducibility.

Electron beam melting efficiency at multiple hafnium e-beam processing

The method of electron beam melting and vacuum refining has clear advantages over other metallurgical methods since it enables manufacturing of refractory and chemically active metals. This study focuses on the efficiency of removing impurities from technogenic hafnium under multiple electron beam melting. Assessments are performed on the efficiency of double and triple e-beam melting processing of refractory metal hafnium. The influence of different e-beam melting technological modes on the refining effectiveness is investigated. A highest hafnium purity of 99.2% was achieved after double and triple e-beam refinements of the investigated materials, with the highest process efficiency reaching 61.58% and 51.07%, respectively.

The microstructure and impact toughness of vacuum electron beam welded joints of a highly alloyed dual phase titanium alloy

Vacuum electron beam welding of 50 mm thick TC18 titanium alloy plates were carried out at different processing parameters, and full penetration welded joints were obtained. The welded joint presents three typical zones, namely, fusion zone, heat affected zone and base metal zone. It is found that processing parameters have no obvious influence on the width of heat affected zone. By using EBSD technology, the changes of phase composition, grain size and grain boundary density from the fusion zone to heat affected zone and then to base metal zone were clearly observed and quantitatively analyzed. The fusion zone shows coarse equiaxed/columnar β grains with an average diameter/width of more than 100 μm. The volume fraction of α phase in the heat affected zone decreases with the decrease of the distance to the fusion zone until it is completely dissolved into β phase. The formation mechanism of microstructure in different zones and its influence on impact toughness were discussed. The β grain size and undissolved/precipitated fine α grain on β grain boundary are two main factors affecting impact toughness.