Electron Beam Welding Joints Research Articles

Microstructure and mechanical properties of LBW and EBW weld joints of CLF-1 steel: A comparative analysis

This study was focused on welding joints of reduced-activation ferritic/martensitic (RAFM) CLF-1 steel medium-to-thick plates produced via laser beam welding (LBW) and electron beam welding (EBW). Such joints were used in the ITER project, in particular, in the back plate mockup of Helium Cooled Ceramic Breeder Test Blanket System developed in China in 2015. The microstructural evolutions and the mechanical properties of fusion zones (FZs), weld zones (WZs), and heat-affected zones (HAZs) of LBW and EBW joints were analyzed and compared using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Moreover, the microstructural differences between the two types of joints and their effect on the impact properties were discussed. Results showed that the well-formed welds without defects, such as pores, incomplete fusion, and cracks, could be obtained via LBW and EBW. Different heat inputs led to the differences in the grain size gradients, the boundary angles, the content of carbides, and the distribution of dislocations. Despite obvious differences in morphology among FZ, WZ, and HAZ, both types of joints exhibited excellent tensile properties and impact toughness. The tensile strengths of the LBW and EBW joints were 633 and 634 MPa at room temperature, respectively, versus 370 and 366 MPa at 550 °C. The mean impact-absorbing energy values of LBW and EBW joints were 251 and 284 J. The further analysis revealed that the low δ-ferrite content, small effective grain size, large grain size gradient, high grain boundary angle, diminutive size of M23C6 carbides, high-Ta content in MX carbides and low dislocation density led to high impact toughness of the LBW joint, while the microstructure of EBW joint failed to show the improvement of impact toughness, and the extraordinary impact toughness could be attributed to the high scattering band.

Comparison of microstructure and mechanical performance of laser and electron beam welded Ti6Al4V alloy

Laser beam welding and electron beam welding are the most recent joining technologies that interface engineering and physics concepts. The present research work focuses on the comparison of the microstructural and mechanical performances of Ti6Al4V, an alloy that displays sensible weldability owing to high susceptibility to oxidation process at elevated temperature, welded joints by using laser and electron beam welding. The as-welded alloy has been examined to study the effect of similar heat input conditions and focal point positions on butt-joint Ti6Al4V specimens in response of the weld morphology, microstructural feature, micro-hardness distribution and angular deformation. The results indicated that electron beam welding process is more appropriate and favorable to join Ti6Al4V alloy specimens and full penetrated electron beam weld joint is procured without any defects. However, narrow weld seam with refined grain structures is developed in the weld zone of laser beam welded specimens. Also, defocusing the beam position by − 1 mm contributed to grain refinement in the weld zone of laser and electron beam welded specimens. Moreover, the magnitude of micro-hardness distribution in the weld zone of laser beam weldments is higher than electron beam weldments by 0.66 times. However, the micro-hardness magnitude is substantially enhanced by 32% and 16% for laser and electron beam weldments, respectively, due to negative defocusing beam position. From the results, it is determined that the magnitude of angular deflection is higher for laser beam weldments than electron beam weldments due to higher difference in fusion zone areas across the neutral axis. Moreover, angular deflection magnitude in electron and laser beam weldments is lowered by 15.8% and 7.4%, respectively, due to negative defocusing beam position.

Effect of deposited layer thickness on the microstructure and mechanical properties of IC10 single-crystal Ni3Al-based alloy electron beam-welded joint

IC10 single-crystal Ni3Al-based alloy has poor weldability by electron beam welding (EBW). However, a defect-free butt joint can be obtained when the Inconel 718 alloy single-crystal deposited layer is used in the IC10 alloy EBW joint as a sandwich structure with a controlled chemical composition. The experimental results show that the optimized IC10 butt joint's microstructure contains preferably orientated columnar grains with deformation twins in the intragranular region and many small NbC particles in the intergranular region. The grain size, misorientation angle, and local grain orientation in weld seam changed with the deposited layer thickness variation. The residual deposited layer was found to be the most fragile zone possessing the lowest microhardness and tensile performance in the optimized IC10 butt joint. The tensile strength of the optimized IC10 butt joints deteriorated with the increasing deposited layer thickness. The optimal design with a 0.4 mm-thick deposited layer significantly improved the EBW joint mechanical properties. In general, the deposited layer thickness strongly influenced the microstructure and mechanical properties of the optimized IC10 butt joint.

Bonding properties evaluation for an EBW joint of RAFM steel by using notched small tensile specimens

Besides fusion structural materials themselves, research and development of small specimen test technologies (SSTTs) are also important for their joints for mechanical properties evaluation on resistance to neutron irradiation. Because the specimens usually fracture at the base metals (BM), not at the weld metal (WM), and the bonding properties of the joints cannot be obtained directly during tensile tests, small tensile specimens with different sizes of notches at the WM were utilized to try to extrapolate the bonding properties in the present study. A joint of reduced-activation ferritic/martensitic (RAFM) steel CLF-1 made by electron beam welding (EBW) after post-weld heat treatment (PWHT) were utilized to demonstrate the feasibility of this method. By combining tensile experiments, optical digital image correlation technology, and finite element method (FEM) simulation, effects of notch sizes on bonding properties such as strain, stress, and stress triaxiality were investigated. Finally, bonding properties for the joint were tentatively extrapolated from the results of the specimens with notches.

Zoning study on the fatigue crack propagation behaviors of a double-sided electron beam welded joint of TC4 titanium alloy with the thickness of 140 mm

This study investigated fatigue crack propagation rates in the base metal (BM), heat affected zone (HAZ) and weld metal (WM) of a double-sided electron beam welded (EBW) joint of Ti alloy with a thickness of 140 mm in different layers. Firstly, this research measured fatigue crack propagation rates at different zones in each layer of the joint and drew curves thereof. The results demonstrate that the WM in the second layer of the double-sided EBW joint shows poor resistance to fatigue crack propagation. Secondly, the metallographic microstructures of different zones in different layers of the joint were observed. It is found that there are a lot of needle-shaped martensites growing in a specific direction at the HAZs in different layers of the joint. Finally, precipitates in different zones in each layer of the joint were studied by using a high-resolution scanning electron microscope (SEM). The results show that needle-shaped martensites in the WM of the joint are interlaced and present basketweave microstructures, while there are needle-shaped, lamellar martensites at the HAZs in each layer of the joint.

Electron beam welding of a novel near α high temperature titanium alloy powder compact: effect of post-welding heat treatment on tensile properties

A novel near α high temperature titanium alloy (Ti55) was produced from powder compact through hot isostatic pressing. Electron beam welding (EBW) was used to join the Ti55 alloy powder compact and effects of annealing treatment on the microstructure and mechanical properties of EBW joints were investigated. The residual stress distribution of as-welded joint was calculated using finite element method (FEM). The results show that the microstructure and microhardness profiles are non-uniform across the EBW joints. The tensile residual stresses are confirmed across the as-welded joints based on FEM analysis. All of tensile specimens failed at the base metal, indicating that the mechanical properties of EBW joints are equal to those of base metal, or better. The tensile strength of as-welded and as-annealed joints increases slightly compared with base metal. An obvious reduction on the reduction of area of EBW joints was obtained after annealing at 500 °C. Related mechanisms were discussed based on the residual stress, tensile deformation and the strain rate sensitivity.

Evaluation of bonding properties by flat indentation method for an EBW joint of RAFM steel for fusion application

Abstract Welding is essential to construction and safe operation of fusion reactors. Besides fusion materials themselves, small specimen test technologies (SSTT) are also essential to evaluate bonding properties of the joints for fusion application. In the present study, flat indentation method based on energy–density equivalent principle was utilized for bonding properties evaluation for an electron beam welded (EBW) joint of a reduced-activation ferritic/martensitic (RAFM) steel, CLF-1. The energy–density equivalent principle describes relationships among the material parameters of Hollomon’s power law, indenter diameter, energy, and indentation displacement. The flat indentation method can determine the Hollomon’s power law parameters of materials directly. For the base metal (BM), the true strain–stress data from flat indentation tests are almost consistent with the results obtained via uniaxial tensile tests and are proved to be reliable. When the indentation tests executed on the weld metal (WM), the bonding properties can be reliably obtained by this method. The WM shows larger yield strength, ultimate tensile strength, and uniform elongation, but a little smaller strain hardening index than the BM.

Microstructure evolution and mechanical properties of the electron-beam welded joints of cast Al–Cu–Mg–Ag alloy

In this work, the microstructures of the electron-beam welded joints of cast Al–Cu–Mg–Ag alloy plate were investigated in terms of the element segregation, grain structure and precipitation behavior by scanning electron microscopy, transmission electron microscopy and atom probe tomography observation as well as differential scanning calorimetry and electron probe micro analysis. The hardness distribution of the weld cross-section was also described using microhardness mapping. A model of strengthening mechanisms was proposed to analysis the microstructure-strength relationship of the welded joint. It is found that the occurrence of softening behavior in fusion zone after welding is closely related to the dissolution of Ω and θ′ strengthening phases. The precipitation of a large number of fine Ω, θ′ plates and some small dispersed precipitates (Ag-rich particles, GP zones and Mg–Ag phases) may be the main reason for the increase in the strength of the welded joint after post-welding heat treatment. It is because the supersaturated solid solution produced after welding due to the rapid cooling rate as well as the strong binding energy between Ag atoms and vacancies/Mg atoms promotes the precipitation of small dispersoids.

Effect of heat input on microstructure and mechanical properties of IC10 Ni3Al-based superalloy electron beam welding joint

IC10 single crystal Ni3Al-based superalloy is an important material for manufacturing turbine blades owing to its excellent high-temperature performance. However, the heat input of electron beam welding would extremely influence on microstructure and mechanical properties of IC10 superalloy in engineering applications. The microstructure of the weld can be transformed from single crystal to poly crystal after welding, where its morphology was observed with equiaxed grains in both sides near fusion line and dendrites in the center area. With the heat input decreased in the weld, the refinement of grain size and the number of LAGB lead to the microhardness increased, but the number and proportion of HAGB reduced which to cased the tensile strength deteriorated. The average value of the microhardness in weldment is up to 430 HV, while the tensile strength is 720 MPa. Moreover, the liquid film of low melting point eutectic phases was prone to crack under the high intergranular stress. Due to the refinement of grain size, the decreasing number of HAGB and the enhancement of local grain orientation, the crack sensitivity reduced with the decreasing heat input.

The role of microstructure on corrosion fatigue behavior of thick-plate Ti–6Al–4V joint via vacuum electron beam welding

The microstructure and corrosion fatigue behavior under artificial seawater environment of 100-mm-thick Ti–6Al–4V alloy joint via vacuum electron beam welding (EBW) was systematically characterized. Obvious microstructural heterogeneity along the transverse direction of as-welded joint was observed. Bimodal-phases microstructure of granular α colonies and β strips compose the microstructure of the base metal (BM). While the microstructure of fusion zone (FZ) comprises single-phase acicular α/α′ martensite. Under corrosive environment of artificial seawater, FZ shows a lower growth rate of corrosion fatigue cracking (CFC) than that in the BM. Increasing content of residual gas contamination worsens the resistance against corrosion fatigue of the FZ of Ti–6Al–4V alloy joint. Results of local electrochemical characterization indicates that the FZ shows a better resistance against electrochemical corrosion than that of the BM. It is deduced that the slower growth rate of CFC observed in the FZ originates from the combined effects of the excellent corrosion resistance of martensite microstructure and the obstructions of interfaces of fine α/α′ laths against growth of CFC. Moreover, the growth mechanisms of CFC in the BM and FZ were discussed involving the microstructural heterogeneity of the EBW joint.

Direct ageing response on the microstructure and mechanical properties of electron beam welds of Ni-Cr-Fe alloy used in vacuum insulated tubing

Incoloy 925 joints of 5 mm thick were accomplished by adopting high energy density, electron beam welding (EBW) process. Although the weld seam microstructure was completely austenitic and free from solidification cracking, the heat-affected zone (HAZ) of EBW joints experienced liquation cracking. The mechanical behaviour of the EB weld seams in the as-welded and direct aged (DA) at 732 °C for 4 h and air-cooled conditions were compared. Electron backscattered X-ray diffraction (EBSD) analysis revealed the formation of strengthening precipitate γ′ in the matrix and the precipitation of sigma (σ) phase, M7C3, M23C6 and Ti-rich carbides formed along the crystallite boundaries in the DA condition. The tensile property outcomes opined that the joint efficiency of the weld seams in the DA condition (99.32 %) was found to be better than the ones in the as-welded condition (71.32 %). Also, the yield strength has been considerably improved in the EB weld seams subjected to DA conditions. The carbide precipitation along the grain boundaries is discontinuous and also not effective in pinning the dislocations under impact loads.

Comparative Study on Microstructure and Aluminum Distribution Between Laser Beam Welding and Electron Beam Welding of Ti–6Al–4V Alloy Plates

Ti–6Al–4V alloy plates with a thickness of 4 mm were joined by electron beam welding (EBW) and laser beam welding (LBW). The comparison of LBW and EBW was performed according to grain morphology, microstructure, aluminum distribution, and microhardness of the joints. Results indicate that compared with LBW joint, more equiaxed grains are observed around the central zone of the EBW joint. The microstructure in fusion zone (FZ) of EBW joint presents more uneven with obviously coarser acicular martensite α′. Moreover, the aluminum element content of EBW joint is substantially lower, which demonstrates a more significant burning loss behavior in EBW process. The lower aluminum content in the upper center areas of the joints is attributed to the more significant element burning loss caused by higher temperature, whereas more uniform aluminum distribution in the upper part of the joints is ascribed to stronger convection form within the upper part of the joint. In addition, the characteristics of convection and thermal field within the molten pool are recognized as vital factors influencing the aluminum distribution. The lower microhardness profile in FZ of the EBW joint is principally attributed to coarser acicular martensite α′ and lower aluminum element in EBW joint.

Microstructure and mechanical properties of thick CLF-1 reduced activation steel weld joint made by electron beam welding joint

The effect of post-welded heat treatment (PWHT) on microstructure and mechanical properties of electron beam welded joint of 35 mm thick China low-activation ferrite steel CLF-1 was studied. The results showed that the hardness and microstructure of the joint for both the as-welded and the PWHT were uniform along the thickness direction, and the hardness behaved a W-shaped distribution. The joint microstructure was composed of tempered martensite and precipitated phases which were mainly chromium and tungsten carbides. A small amount of δ-ferrite existed near the fusion line in the fusion zone. With the increase of tempering temperature, the microstructure of joint and base metal didn’t change significantly. With the extension of tempering time, the precipitated phases of base metal grew and the joint microstructure didn’t change significantly. The suitable PWHT was suggested as tempering at 1013 K for 2∼4 h, which not only ensured the strength of base metal, but also greatly improved low-temperature impact energy of the joint at 253 K.

Investigation on the Electron Beam Welding of Al/Cu Composite Plates

The Al/Cu composite plates composed of 2.5 mm thick Al base plate and 0.5 mm thick Cu cladding plate were joined by electron beam welding (EBW). The butt joints of Al/Cu composite plates were obtained successfully in Modes I (Cu cladding plate was placed upon the Al base plate, welding speed of 1400 mm/min) and II (Al base plate was placed upon the Cu cladding plate, welding speed of 1300 mm/min), respectively. The results showed that microstructures under two modes were similar, but there existed some obvious differences in fracture behavior of the joints and damage behavior of Cu cladding plate. For two butt joints, the (Al2Cu + α-Al) eutectic structure was distributed in continuous networks around the α-Al grains in the weld zone. In addition, the interface between Cu cladding plate and weld zone was composed of Al2Cu intermetallic compound and (Al2Cu + α-Al) eutectic structure. The destruction width of Cu cladding plate was greater in Mode I than that in Mode II. Furthermore, the average loads of the EBW joints were 4.8 kN and 4.5 kN in Modes I and II, respectively.

Prevention of Crack Formation in Electron-Beam Welded Joints of Dissimilar Metal Compounds (TiNi/Ti6Al4V)

The microstructure, mechanical properties and element distribution in an electron-beam welded joint of dissimilar metal compounds (TiNi/Ti6Al4V) have been studied. To prevent crack formation, niobium was introduced to the compound as a filler material. The welding line preheating and electron-beam deviation toward the Ti6Al4V alloy were used. It was shown that fracturing of the welded joint occurs within the fusion zone and is characterized by a mixed ductile-brittle behavior.

Impact performance and microstructures of thick TA1 titanium alloy sheets welded by vacuum electron beam

Thick TA1 titanium alloy sheets were thoroughly bonded by vacuum electron beam welding (EBW). The results indicated that microstructures in the weld zone (WZ) consisted of coarse α columnar grains, serrated α as well as needle-shaped α′; the microstructure in the heat-affected zone near the WZ side was composed of α′ and α, while the microstructure near the base metal side consisted of α″ and α. The positional relation between the notches and rolling direction had an important role in the impact performance. The EBW joint exhibited higher absorbed impact energy at the weld seam after local heat treatment. Furthermore, lots of dimples were produced on the impact fracture surfaces, exhibiting ductile fractures.

A metallurgical and thermal analysis of Inconel 625 electron-beam welded joints

Inconel 625 is a nickel-based superalloy that finds application in many industrial sectors thanks to its high strength, excellent fabricability, and outstanding corrosion resistance. It is characterized by a good weldability and often used in the as-welded conditions. In the following, a metallurgical and thermal analysis of Inconel 625 Electron-Beam welded joints is described. The thermal analysis was supported by a numerical model that uses a superimposition of a spherical and a conical shape heat source with Gaussian power density distribution in order to reproduce the nail-shape of the fusion zone. The heat source parameters were calibrated by using experimental data coming from metallurgical observations and temperature measurements. Numerical and experimental results were found in good agreement.

Numerical Simulation of the Grains Growth on Titanium Alloy Electron Beam Welding Process

In the paper, the grain growth of TC4-DT (Damage Tolerance) alloy joint during electron beam welding (EBW) process was simulated by using Cellular Automaton method. In order to consider the effects of the growth of neighborhood cellular on the center cells in the model, the solid fraction and solute distribution algorithms of classical CA model were improved. The growth of equiaxed grains and columnar crystals under uniform and nonuniform temperature fields was simulated successfully by applying the modified model, respectively. The temperature distribution near the fusion line of TC4-DT EBW joint was also calculated by using double ellipsoid heat source model. Then, coupling the CA model with the temperature field, the grain growth process of the cross-section of the welded zone was simulated. The simulation result fits well with experimental ones on the morphology and the size of the columnar crystals.

Fracture characteristics of dissimilar electron-beam welded joints between Cr-Mo steel and austenitic steel AISI 304

The mechanical and fracture behaviors of electron-beam welded (EBW) joints between Cr-Mo steel (CS) and austenitic stainless steel type AISI 304 (SS) were investigated. A double notch was created at the middle of the weld area with three different notch depth (D) to weld metal width (2W) ratios, D/W = 0.33, 0.42, and 0.5, to study the strength of weld metal compared to that of CS. The weld metal and heat-affected zones (HAZs) were found to be free of defects. The interface region show that Cr23C6 was formed on the stainless steel side, while a martensitic structure was formed on the Cr-Mo steel side. The hardness of the weld metal was higher than that of the rest of the weld metal and the HAZs. Furthermore, the stress concentration (D/W = 0.33) was insufficient to initiate the crack at the notch root, i.e., the strength of CS was lower than that of weld metal with this defect.

Beam scanning effect on properties optimization of thick-plate 2A12 aluminum alloy electron-beam welding joints

Electron-beam welding (EBW) of a 25-mm-thick 2A12 aluminum alloy was performed. Obvious concave defect was detected at the upper surface of welded joint. The grains in weld were coarse, which reduced the strength of the joint via conventional EBW (CEBW). The tensile strength of the joint was 292 MPa, which reached 64% of the tensile strength of the base metal. Therefore, beam scanning was conducted during the EBW. With the addition of beam scanning, the dendrites near the fusion line were broken, the grains were refined, and the strength was enhanced. Additionally, the welding process tended to be stable, and the formation of the weld joint was improved. The eutectic at the grain boundaries reduced the strength of the joint. There was no obvious preferential growth orientation in the fusion zone (FZ) during crystallization, and the distribution of the grain was more uniform. The number of small-angle grain boundaries increased, which was conducive to the precipitation of the secondary phase. Compared with the case of CEBW, the width of the FZ increased from 2 to 4 mm, and the microhardness was basically unchanged. The average tensile strength of the joint increased by 31.2%, to 383 MPa. Moreover, the fatigue strength of the joints satisfied the engineering requirements.