Electron Beam Welding Joints Research Articles

Electron Beam Welding of Dissimilar Stainless Steel and Maraging Steel Joints

The incorporation of additive manufactured (AM) metal parts to real assemblies is a crucial issue for the increasing of their industrial utilization. The presented research is devoted to the electron beam welding (EBW) of dissimilar steel joints. Dissimilarity is defined by the various types of steel and manufacturing processes used for the creation of specimens. Conventional AISI 316 stainless steel, selective laser melted (SLM) SS 316L stainless steel, and SLM M300 maraging steel were welded at variable parameters in the form of a welding current and a welding velocity. EBW joints were evaluated considering the macroscopic and microscopic characteristics, as well as a reached microhardness. The obtained preliminary results represent important input data for the follow-up experiments focused on the setting of optimal EBW parameters of welding the dissimilar joints including SLM products, with the consideration of their basic macroscopical and microscopical characteristics, mechanical properties, and residual stresses.

Nonuniformity of Fatigue Properties of Two‐Sided Electron Beam Welded Joint of Superthick Titanium Alloy

ABSTRACTThe TC4 titanium (Ti) alloy has been widely utilized in various industries such as aerospace and shipbuilding, owing to its numerous advantages. Its exceptional properties have made it a material of choice for applications requiring high performance and reliability. The total weld thickness was 140 mm, and microstructures and high‐cycle fatigue properties were investigated at three different layers within the 140‐mm section. Experimental results show that the overlap area at two weld roots has the highest microhardness and largest nonuniformity of the overall joints, so the area is found to have the poorest high‐cycle fatigue properties. The microstructures in every layer of the weld metal of the joints were analyzed to determine the causes of the poor fatigue properties in the overlapping area at the weld roots. Significant amounts of α′ acicular microstructure are present in the weld metal of joints, while the overlap area at weld roots contains more α′ acicular microstructure with a finer size. Compared with other layers, the weld metal and base metal in Layer 2 (overlap area) have the largest microhardness gradient, where the stress concentration is more serious in the fatigue experimental process. Heat dissipation conditions was a critical factor for the inhomogeneity of microstructure and mechanical properties along the thickness direction of 140‐mm double‐sided electron beam welding joint. Fatigue damage (micropore) is formed at β phases in priority, and fatigue cracks propagate via series connection of micropores, indicative of transgranular ductile cracks.

Study on strengthening mechanism of Al microalloying on softening behavior of Ti2AlNb/TA15 electron beam welding joint

Study on strengthening mechanism of Al microalloying on softening behavior of Ti2AlNb/TA15 electron beam welding joint

Microstructural evolution and mechanical property of high-strength metastable β titanium alloy joint via electron beam welding

Obtaining a fundamental understand of the relationship between weld microstructure and mechanical properties is critical for ensuring a high weld quality. This work explored the micro-mechanism responsible for the mechanical properties of a 10-mm-thickness metastable β titanium alloy (Ti–3Al–5Mo–4Cr–2Zr–1Fe, wt.%) joint welded by electron beam welding (EBW). Weld microstructure and its evolution behavior were revealed by means of multi-scale microstructure characterization. Obtained results indicate that the absence of α phase and formation of nano-scale ω particles occurred in the coarse columnar β grains of the fusion zone (FZ). Intense dissolution and significant coarsening of secondary α phase occurred in the heat affected zone. Between the FZ and HAZ, a partially melted zone was observed and contains few equiaxed β grains. Compared to the base material, the as-welded EBW joint shows significant softening in weld seam and a slight decrease of 17% in ultimate tensile strength, while a severe reduction of 73% in elongation. It was observed that majority of plastic deformation is confined to the narrow FZ, indicating a significant localization of tensile strain. This leads to premature fracture of the joint within the FZ and consequently to significant deterioration of the overall ductility. This work contributes to advancing the understanding of the role of microstructural evolution on the mechanical properties of high-strength titanium alloy joints via EBW.

Microstructure and mechanical properties in electron beam scanning welded joints of super thick titanium alloy plates

It is generally difficult to obtain good weld formation and excellent properties in super thick titanium alloy joints via conventional electron beam welding (EBW) methods due to the fact that the melt pool flow becomes more unstable as the plate thickness increases. In this study, electron beam scanning welding (EBSW) was utilized to weld 100 mm Ti–6Al–3Nb–3Zr–1Mo titanium alloy plates to improve the weld formation and impact toughness through the scanning effect. The results revealed that there were spatter and cutting defects on the surface and inner pore defect in the normal EBW joint, which could be effectively eliminated via EBSW. The decrease of the amplitude of the fluid flow rate and the change of the velocity direction were mainly responsible for this. A large amount of lamellar α phase with similar orientation was formed in the fusion zone (FZ) due to the fast cooling rate. The joint coefficient for both EBSW and EBW reached 100%, with the joint tensile strength of ∼840 MPa. The impact energy of the FZ in the EBSW joint was 70.5 J, reaching 210.4% of that of the BM (33.5 J). The impact toughness increase ratio in this study was far larger than those for Ti alloy welds ever reported, which was mainly attributed to that the high angle α colony boundaries with high preferred orientation in the FZ deflected the crack propagation direction. This study provides a reference for the strength-toughness design of EBWed joints of super thick Ti6331 titanium alloy.

Influence of Oxide Inclusions on the Creep Properties of Electron Beam Welds in Ti-added Reduced Activation Ferritic/Martensitic Steel

In this study, the effects of reducing oxide inclusions on the microstructure, tensile properties at 550 ℃, and creep resistance of electron beam welded (EBW) joints in Ti-added reduced activation ferritic/martensitic (RAFM) steel were investigated. Two RAFM steels, designated as Steel A and Steel B, were prepared by adjusting the Al and Si contents to contain different fractions of oxide inclusions. The microstructures of the base metal and heat-affected zone (HAZ) were analyzed, and the mechanical properties of the welds were evaluated. Reducing the Al and Si content in Steel B resulted in a decrease in both the fraction and size of oxide inclusions compared to Steel A. Both steels exhibited tempered martensitic microstructures with M23C6 and MX precipitates. Hardness tests revealed that the over-tempered HAZ (OTHAZ) was the weakest region. However, both tensile test and creep tests at 550 ℃ showed fractures occurring in the base metal, indicating that the low heat input of EBW effectively minimized the weak HAZ regions. Steel B demonstrated improved tensile properties and creep resistance due to the reduced oxide inclusions. It was found that Steel B had a significantly longer creep life than Steel A at 550 ℃. SEM analysis revealed ductile fracture characterized by dimples, where oxide inclusions containing Al, Si, Ta, and Ti were predominant. The presence of these inclusions reduced the effectiveness of solid solution and precipitation strengthening by consuming Ta and Ti. Additionally, microvoids could easily nucleate at the interface between the hard oxide inclusions and the soft metal matrix during creep. Therefore, the reduction of oxide inclusions improved deformation resistance and high-temperature stability, resulting in better creep resistance in Steel B. In conclusion, the reduction of oxide inclusions in Ti-added RAFM steel enhances the high-temperature mechanical properties and creep resistance of EBW joints, underscoring the importance of oxide control in the development of RAFM steels for fusion reactor applications.

Improvement of the fatigue life of an electron-beam welded Ti2AlNb joint subjected to an electromagnetic coupling treatment

The local stress concentration created by the seam welding process often reduces the fatigue life of the material along and around the seam. Post-welding heat treatment is usually used to improve the weld performance, but the improvement effect on fatigue life may not be obvious. In this study, a new treatment method of electromagnetic coupling was applied to regulate the Ti2AlNb electron beam weld after heat treatment, so as to improve the fatigue properties of the welded joint. The results show that after electromagnetic coupling treatment, the fatigue limit of the welded joint is increased by 10.4 %, the residual compressive stress is increased, and the fatigue crack propagation rate is decreased. The microstructure analysis shows that after electromagnetic coupling treatment, the fatigue crack source starts in the subsurface layer, the substructural crystals in the fusion zone and the heat affected zone decrease, the recrystallization content and the large angle grain boundary increase, and the dislocation density increases and tends to be homogenized. An increase of at least 2.3 % in hardness of the welded joints also indicates the increase in the dislocation density. Local high density dislocation is found in the grain, which causes dislocation entanglement and hinders crack initiation and propagation and this provides an important basis for improving fatigue properties. This study provides a new method for improving the fatigue properties of Ti2AlNb electron beam welds which can also be used to study the properties of other welded joints.

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.

Comparison of fatigue crack growth design curves on GMAW and EBW joints of high strength steels

There is a growing demand in the industrial sector for the use of high-strength structural steels (HSSSs), which can achieve a significant weight reduction in structures. These structural steels are usually produced by quenching and tempering (Q + T) or thermomechanical treatment (TM), and their applications in welded structures pose several challenges for the users. In industrial practice, gas metal arc welding (GMAW) is basically the most commonly used fusion welding process, which has a relatively high heat input. However, at HSSSs, there is a need for low heat input but, at the same time, productive welding processes. High-energy density welding processes, e.g., electron beam welding (EBW), offer a unique opportunity to weld these steels. The widespread use of HSSSs is also hampered by the fact that the benefits of high strength can be exploited primarily under static loading. At the same time, different welded structures made of HSSSs are often subjected to cyclic loading, and possible weld defects and material discontinuities are major risks in this case. During our experiments, GMAW and autogenous EBW processes were applied to make welded joints from S960 Q + T and TM structural steels. The fatigue resistance of the welded joints was characterized by fatigue crack growth (FCG) tests, considering the increased crack sensitivity of HSSSs. A statistical approach was followed both in the design of the experiments and in the evaluation of their results. Based on the test results fatigue crack propagation design curves were determined for the investigated GMAW and EBW welded joints. The design curves were compared with each other, with design curves of lower strength material (S690QL) and with the recommended fatigue crack growth laws of BS 7910.

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.

Microstructure and residual stress distribution of electron beam-welded joints of a 50 mm-thick TA15 titanium alloy plate

Abstract Vacuum electron beam welding was applied to a 50 mm-thick TA15 titanium alloy plate. Microstructure observation and microhardness testing were performed. Meanwhile, the residual stress on the surface at different distances from the weld centre was measured via the hole drilling method. A finite element model for electron beam welding of the TA15 titanium alloy plate was constructed on commercial finite element software. Experimental results showed that the microstructure of the weld zone consisted of a basket martensitic phase. The highest microhardness in the weld zone was 409 HV, and the microhardness of the base metal was the lowest. The maximum gradient change area was located at the HAZ near the base metal. The peak value of longitudinal residual stress from the simulation was 880 MPa, which was in the weld metal. The sharp change area of longitudinal residual stress gradient was located in the base metal near HAZ.

Metallurgical Microstructure Complexity in the Electron Beam Welding (EBW) Joint of Ti6246

Metallurgical Microstructure Complexity in the Electron Beam Welding (EBW) Joint of Ti6246

Tensile properties and fracture behaviors of electron-beam welded Ti6242 titanium alloy joints

The microstructure, tensile properties and fracture behaviors of electron-beam welded Ti6242 titanium alloy joints were systematically investigated. The as-received alloy exhibited a typical duplex microstructure consisting of equiaxed primary α phase and laminated secondary α phase/β phase. The high cooling rate during welding resulted in substantially microstructure evolution in the fusion zone (FZ) of the joints, leading to the formation of large columnar β grains with embedded acicular α′ martensitic phase platelets. The influences of such microstructure variations on the mechanical properties and fracture behaviors at different temperatures were analyzed and discussed. In principle, the hard-yet-brittle α′ martensitic phase induced significantly strengthening of the FZ. As a result, for the un-notched specimens, the plastic deformation was concentrated to the soft base material with subsequent ductile fracture via micro-void coalescence mechanism. But for the notched specimen, in which the notch located just within the FR, cracks initiated and proceeded along the FR in a brittle manner.

Effect of post-welding heat treatment on microstructure and properties of electron beam welding joint of new high-strength TB18 titanium alloy

Effect of post-welding heat treatment on microstructure and properties of electron beam welding joint of new high-strength TB18 titanium alloy

Numerical investigation of the impact of thermoelectric effect on electron beam welding of dissimilar materials

Electron beam welding of GH4169 and Ni is required in the manufacture of the regenerative cooling system of the liquid rocket motor. The thermoelectric effect is observed during the welding of dissimilar metals; however, there has been a lack of investigation into the influence of this effect on electron beam welding joint formation and its dependence on test plate thickness. The thermoelectric effect of electron beam welding between GH4169 and Ni with varying thicknesses, as well as the influence of induced magnetic fields on electron beam trajectories, are investigated through the establishment of a numerical model incorporating thermal-electric-magnetic coupling.The results show that when the test plate increases from 2.5 mm to 10 mm the peak current density increases from 5.1 × 106 A/m2 to 7.6 × 106 A/m2, and the maximum magnetic flux density increases from 1.49× 10−2 T to 1.77 × 10−2 T. The increase in magnetic flux density results in a greater displacement of the electron beam spot away from the interface between the two materials, thereby causing incomplete fusion defects in the joints. This study elucidates the fundamental physical principles underlying the occurrence of incomplete fusion defects in electron beam welding joints, thereby furnishing essential theoretical underpinnings for enhancing the quality of dissimilar metal electron beam weld joints.

Comparison of low-cycle fatigue properties of two kinds of high energy beam welded joints of TC4 alloy

The low-cycle fatigue properties of 30 mm Ti6Al4V titanium alloy joints welded by vacuum electron beam welding and laser wobble welding with filler wire were compared. The test results show that the low-cycle fatigue performance of the electron beam welding joint is close to that of the base meal, while the low-cycle fatigue performance of the laser wobble welding with a filler wire joint is clearly inferior to that of the electron beam welding joint and base meal. An examination of the microhardness of the base metal, heat-affected zones and weld area of the two joints found that the microhardness of the weld area of the electron beam welding joint is close to that of the base meal, but is lower than that of the heat-affected zones on both sides. The weld area of the laser wobble welding with the filler wire joint is significantly weakened.

Effect of welding processes on ferrite content, microstructure and mechanical properties of super duplex stainless steel 2507 welds

Abstract Super duplex stainless steel (SDSS) plates of 6 mm thickness have been welded using tungsten inert gas, activated tungsten inert gas, electron beam welding and friction stir welding processes. Among these, in the first two, melting and solidification of material occurs slowly whereas, it is faster in electron beam welding process and no melting occurs in friction stir welding. Macro and microstructural studies, hardness surveys, tensile tests and percentage of ferrite content were compared for all the welds. The ferrite–austenite phase balance is 50 % each, with electron beam weld metal at about 65 % ferrite. This showed the hardness of the weld metal and heat affected zones to be higher than base metal. The weldment joint efficiencies are more than 90 %. The fracture location is found to be in the weld metal for tungsten inert gas and activated tungsten inert gas weld, in the nugget for friction stir welds and in the base metal for electron beam welds. The ductility of electron beam weld joints is 32 % while it is around 20 % for the others. The preferred order while choosing the welding process should be activated tungsten inert gas welding, tungsten inert gas welding, electron beam welding, and friction stir welding.

Novel fatigue life prediction method of a Ni-based superalloy welded joint considering defect and temperature

Defects are the primary cause of fatigue failure of welded structures, resulting in high dispersion in fatigue test results. In this study, a rapid fatigue life evaluation model is established, which considered both the effects of initial welding defects and service temperature. Firstly, the mathematical relationship between temperature and Vickers hardness is obtained by fitting a series results of high temperature Vickers hardness tests. Then, based on the SEM fracture morphology analysis of fatigue failure samples, the concept and formula of modified stress considering the information of defect size and position are proposed. Finally, a new life prediction model is established by combining the temperature-hardness relationship model with Murakami's model. The fatigue life of GH4169 electron beam welding joints can be evaluated by this model at any temperature, and most of the predicted results are within a scatter band of ±2.

Investigation of microstructure and mechanical properties in dissimilar-metal welding between ferritic stainless steel and Co-based superalloy using electron beam welding

This research investigates the relationship between the microstructure and mechanical properties of electron beam welding joints, with a particular emphasis on the influence of varying electron beam currents on AISI 410L stainless steel plates and NS163 Co-based superalloy wires, which is a rare and novel form of welding. An increase in beam current led to a gradual transformation of the weld microstructure from columnar to equiaxed grains, creating finer and more homogeneous grains. Macrosegregation was also observed, a consequence of the liquidus temperature difference between the weld metal (WM) and base metal (BM). The segregation structure exhibited irregularly shaped beaches near the fusion line and islands of unmixed and partially mixed NS163 within the WM. This phenomenon was more pronounced in samples with a lower beam current. Given the limitations in BM shape and WM size, nanoindentation was employed to characterize the strength of welded joints. In conjunction with microhardness measurements, it was confirmed that the weld is strengthened under different electron beam currents, with higher current resulting in a more significant strengthening effect. This study also underscores the value of nanoindentation in evaluating the weld strength of brush seals without destruction.

Research of Friction Stir Welding (FSW) and Electron Beam Welding (EBW) Process for 6082-T6 Aluminum Alloy.

The paper presents the results of the joining tests of the EN AW-6082 T6 alloy. The materials were joined using the EBW high-energy (electron beam welding) and friction stir welding (FSW) methods. In the case of FSW welding, the following parameters were used: the linear speed was 355 mm/min, and the rotational speed of the welding tool was 710. In the case of EBW welding, the following parameters were used: accelerating voltage U = 120 kV, beam intensity I = 18.7 mA, welding speed v = 1600 mm/min and, in the case of a smoothing weld, U = 80 kV, beam intensity I = 17 mA, and welding speed v = 700 mm/min. Comprehensive microstructural tests of all welded joints (MO, SEM and TEM) and mechanical property tests (tensile and hardness tests) were carried out. The topographies of the fractures after the tensile test were also examined. Based on the results, it was found that the strength properties of the EBW joint were reduced by 23% and the FSW joint by 38% compared to the base material. A decrease in elongation was also noted, with an FSW elongation of 7.2% and an elongation of 2.7% for EBW. In the case of the EBW joint, magnesium evaporation was found in the weld during welding, while in the FSW joint, the dissolution of the Mg2Si particles responsible for strengthening the material during heat treatment to the T6 state was observed.