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This work investigated the influence of friction stir welding (FSW) parameter on forming the dissimilar T-joint of aluminum alloy 6061 (AA6061) to pure copper (C1100). The experimental outcomes indicated that the hook formation trended to move toward the center of welding line at low welding and/or high rotational speeds. In all cases, the kissing bond (KB) defects were significantly observed in advancing (AS) compared to retreating sides (RS). The thickness of diffusion and intermetallic compound (IMC) layers decreased with increasing welding and/or decreasing rotational speeds. A highest joint efficiency was attained with approximately 74% at 500/125 rev/mm of the skin test and 34% at 500/100 rev/mm of the stringer tests. The fracture process under the stringer test initiated from the AS to the RS along the interface while that of the skin test cracked in the heat affected zone. Improving dissimilar T-joint of AA6061/C1100 was impacted not only by controlling the KB defect but also the IMC layer thickness. [ABSTRACT FROM AUTHOR]

The article explores the microstructure, mechanical, and fractographic behavior of diffusion welded joints of AA2219 and Ti-6Al-4V for aerospace applications. The study focuses on the challenges and advancements in welding technologies for joining aluminum and titanium alloys, emphasizing the importance of welding reliability and intermetallic formation. Various welding techniques, such as vacuum diffusion welding, are discussed for joining dissimilar metals with low heat input conditions to ensure bonding joint integrity. The research findings highlight the relationship between holding time, diffusion zone thickness, hardness, shear strength, and fracture morphology of the welded joints, providing insights into optimizing the welding process for aerospace applications. [Extracted from the article]

The use of inserts allows for the selective reinforcement of castings to improve mechanical properties, including surface hardness and wear rate. Metal surfaces that undergo wear on account of friction can be strengthened using metal matrix composite (MMC) inserts. An essential factor in the manufacture and application of compound casting involving MMC inserts has been the bond strength between the insert and alloy. This work studied fluxes (CsAlF4 and LiAlF4), preheating, and nickel (Ni) plating to improve the bond strength between A206 and A201-Al2SiO5 fiber MMC. It was observed that Flux 1 (G-2004), Flux 2 (CS-2020), and Ni plating, when used with preheating the insert up to 200 °C, led to the formation of a diffusion bond. The effect of fluxes and plating has been discussed, along with the impact of the insert oxide layer on the formation of diffusion bonds. The microstructure formed at the interface between casting and insert was analyzed. [ABSTRACT FROM AUTHOR]

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The formation of transition zones during explosive welding of aluminium with copper in vacuum and in air is studied. The distribution of element concentrations is used to determine the coefficient of mutual mass transfer in the undetachable Al--Cu joint. It turns out that the mass transfer of copper into aluminium in the conditions of explosion welding occurs at greater depths compared to the depth of penetration of aluminium into copper. This is explained by the fact that the nature of the penetrating atoms does not have such a strong influence as in conditions of diffusion annealing, and the determining factor is the lattice period, which in aluminium is larger than in copper. Concentration curves are plotted for the Al--Cu interaction zone during explosion welding, in which there are no intermetallic phases corresponding to the equilibrium diagram of state. The coefficient of mutual mass transfer turns out to be several orders of magnitude higher than the heterodiffusion coefficient of the same elements under diffusion-annealing conditions. The explosion welding is performed using a coaxial scheme by throwing a copper tube on an aluminium rod. [ABSTRACT FROM AUTHOR]

Multilayer Al/Cu foils have a high potential to be used as filler materials for diffusion welding or friction stir welding of difficult-to-weld materials. In this work, we study EB-PVD-deposited multilayer Al/Cu foils with the modulation periods (sum thickness of one Al layer and one Cu layer) of 50 nm and 1000 nm. The total composition for both the foils is of about Al--30 wt.% Cu and the total thickness is varied from 20 µm to 30 µm. The phase formations within the foils during heating up to 500°C are investigated by x-ray diffractometry, scanning and transmission electron microscopies, differential scanning calorimetry, and electrical-resistance measurement. The correlation between the modulation period and the formation of the Al2Cu, AlCu3, and Al4Cu9 phases is studied. The sequence, temperatures, and kinetics of phase transformations, as well as the heat of the reactions, are found to correlate significantly with the modulation period. Mechanisms of the phase formations within the foils and their mechanical properties are discussed. [ABSTRACT FROM AUTHOR]

Due to its super plasticity, low weight, and high mechanical resistance properties, generally, Ti6Al4V is used for aeronautical applications. However, it has low resistance to plastic shearing. In addition, it has poor wear resistance. For these reasons, a lot of techniques have been developed to improve its wear resistance. Investigations of microstructure and interfacial reactions of diffusion bonding of Ni and Ti6Al4V materials have been performed experimentally. Ni samples were prepared with 50 ± 5 µm Ni powders in cylindrical shape. For diffusion bonding, Ag foil was used for improving the interlayer and connection quality. Nickel and its alloys can be joined by using some different processes, and the use of an interlayer can further facilitate the joining process and improve the joint quality. The experiments were carried out under the protected atmosphere. Argon gas was used for protection. The experiments were performed under 5 MPa pressure for 60 min duration at 850 °C, 900 °C, and 950 °C thermal conditions. Investigations of metallurgical structure occurring in the interface areas were examined by optic analysis of EDS, SEM, and X-ray. The strength of the joints was tested by lap-shear tests. From observations, the best quality of the coalescence at interfaces was indicated at elevated temperatures. [ABSTRACT FROM AUTHOR]

SX steels, a type of stainless steel enriched with high silicon content, are frequently used in critical applications of the industry due to their resistance to many acids. Areas of use are acid tanks, acid coolers, acid pipe systems and acid radiators. Increasing areas of use have increased the need to combine with different materials. This study aimed to join the different layers by diffusion welding method using Cu, Ni, Al7072 and Al8079. The samples were combined by keeping them under 5 MPa pressure for 60 minutes at 1000°C in an argon gas environment. Phase changes occurring in the junction area due to the effect of different interlayers were tried to be determined by SEM-EDS and XRD analyses. The changing metallographic structure of the intermediate layers was examined using an optical microscope, and the microhardness change of the joining region was determined with the HV hardness measuring device. While alpha-ferrite structure was observed in the Cu interlayered connections in the samples, multiphase structures were observed in the Al7072 and SX-Al8079 interconnected samples, and the presence of intermetallic phases was detected in both the interface and diffusion zones in the Ni interlayered samples. [ABSTRACT FROM AUTHOR]

In this study, we optimized the parameters of diffusion bonding on multi-layered stainless steel 316L and 430 stacks. The preparation process for diffusion bonding is crucial, as the bonding surfaces need to be polished and meticulously cleaned to ensure a smooth bonding process. We fabricated twelve-layer plates consisting of 55 mm × 55 mm × 3 mm and 100 mm × 50 mm × 3 mm dimensions, and the bonding response was investigated by evaluating the tensile strength of the bonding zone under varying bonding conditions, with a bonding temperature ranging from 1000 to 1048 °C, a bond time ranging from 15 to 60 min, pressure ranging from 10 to 25.3 MPa, and under a vacuum environment. SS430 exhibits a significantly higher compression creep rate than SS316L. The compressibility of diffusion welding materials does not impact the diffusion bonding strength. Multi-axial tensile strength tests confirmed strong bonding joint strength in various axes. The tensile strengths of monolithic and Diffusion bonding (DB) specimens tested in parallel are essentially identical. The optimized diffusion bonding parameters (Condition G2C: 1048 °C/25.3 MPa/15 min) are ideal for producing SS316L stainless steel cores in compact heat exchangers, offering a superior bonding quality and reduced costs. These findings have practical implications for the production of stainless steel cores in compact heat exchangers, demonstrating the relevance and applicability of our research. [ABSTRACT FROM AUTHOR]

Hydrogen can cause weld cold cracking even days after fabrication. In this respect, higher strength steels present a challenge to established cold crack testing. In general, the tolerable hydrogen concentration for crack prevention decreases with increasing material strength. In addition, advanced welding processes require changes in weld geometry and heat input. This directly influences the formation of crack-critical microstructures, e.g. in hardened areas of the heat-affected zone. The limits of use and application of modern cold cracking tests are evaluated by (1) the externally loaded Implant-test and (2) the self-restraint Tekken-test. In particular, external mechanical stresses, which cause additional mechanical loads on the components during welding, must be considered due to the component-specific stiffness of high-strength steels. Accompanying test methods for determining hydrogen concentration and diffusion in welds are presented, such as carrier gas hot extraction for determining hydrogen concentration (ISO 3690) or temperature-dependent diffusion coefficients. These values are of great importance for a holistic approach to the evaluation of the cold cracking sensitivity of high strength steels. [ABSTRACT FROM AUTHOR]

Diffusion welding of YG8 and 40Cr was carried out by spark plasma sintering. The influence of Ni interlayer with different thicknesses varying from 0 to 500 μm on the welding morphology and mechanical properties of joints was studied. The fracture position moved from the cemented carbide substrate toward the connection interface with the increase in the thickness of the Ni intermediate layer. The joint with nickel-free interlayer and 100-μm thick fractured during electrical discharge machining due to the large residual stress. The bending strength of the joints enhanced with the increase in the Ni intermediate layer from 200 to 300 μm, and a maximum flexural strength of 982 MPa was obtained with the thickness of the Ni intermediate layer to be 300 μm, which was up to 97% of the strength of the cemented carbide substrate. However, the further increase in Ni intermediate layer from 300 to 500 μm resulted in a decrease in the bending strength, which was due to the coupled effects of residual stress and interlayer plastic constraint. Besides, fracture cracks were also observed at the interface of Ni/40Cr with the thickness of Ni intermediate layer to be 400 and 500 μm. The formation of Kirkendall pores in the interface of Ni/40Cr due to different diffusion coefficients of Fe (1.468 × 10−14 m2/s) and Ni (2.15 × 10−14 m2/s) was responsible for the crack initiation and propagation in the Ni/40Cr interface. [ABSTRACT FROM AUTHOR]

6061 aluminum alloy and 304 stainless steel were joined successfully by thermo-compensated resistance diffusion welding (abbreviated as TC-RDW) technology with Ni interlayer via pre-resistance seam welding (abbreviated as RSW). Experimental results indicated the metallurgical bond between interlayer and steel based on pre-RSW achieved a large-area Al/Ni/steel joint with better interfacial structure by subsequent TC-RBW process. An obvious diffusion layer with the main components of Al solid solution (s.s) was formed between Al alloy and interlayer in the final Al/steel joints. The interfacial structure was changed as follows: Al alloy, diffusion layer, interlayer, and steel. The tensile-shear load of the final Al/Ni/steel welded joint by this method reached 1793.3N, which was more than 3 times higher than that of the Al/steel joint via TC-RBW directly. The specimens mainly fractured at the interface between Al alloy and Ni interlayer after tensile-shear experiments. XRD analysis results confirmed that Al (s.s), Fe (s.s), and Ni (s.s) were generated at the fracture surface. [ABSTRACT FROM AUTHOR]

A method for high-scale 225Ac-production for medical application from a massive metallic 232Th-target irradiated with 160 MeV-protons is described. The target was made of a metallic Th disk of few mm thickness encapsulated in Nb shell using diffusion welding that provided effective target cooling under an intensive proton beam. Chemical processing started with selectively dissolving Nb and Th in mixtures of HF and HNO3 of different concentrations. The further chemical treatment included two sequential extractions of Th(IV) with di(2-ethylhexyl)orthophoshoric acid (HDEHP) and purification of Ac by extraction chromatography with DGA-, LN- and TRU-resins. The "end-to-start" technique, where the eluate of the column filled with one sorbent serves as the eluent for the column with next sorbent, was realized. The achieved total chemical yield of 225Ac was 87% and radionuclidic purity was better than 99.8% (excepting 0.1–0.2% 227Ac generated at the end of irradiation). The presented method can provide a hundred GBq of 225Ac in one irradiation run. [ABSTRACT FROM AUTHOR]

In this paper, the effect of ER2209 multi-stranded wire compared to single wire on the microstructure and pitting resistance of 2205 duplex stainless steel submerged arc welded joints was studied using electron backscatter diffraction, scanning electron microscopy, energy spectrum analysis, electrochemistry and other detection techniques. Compared with single-wire welding of duplex stainless steel, the multi-stranded wire deposited more metal and doubled the welding efficiency with the same heat input, while increasing the elemental concentration of Ni in the weld metal and the proportion of austenite in the heat-affected zone. Compared with single-wire welding, multi-stranded wire welding promotes the diffusion of the main alloying elements (Cr, Mo, Ni, N) in the welded joint and improves the mechanical properties and pitting resistance of the welded joint. [ABSTRACT FROM AUTHOR]

Vacuum diffusion welding of magnesium alloy MA2-1 is considered in the paper. It was found that welding of the magnesium alloy without using intermediate layers does not ensure formation of high-quality joints. Separate flat pores, elongated along the joint line, are observed in the joint, causing low mechanical properties of the joints. Using intermediate layers made of low-alloy nickel or titanium alloys and forming matrices during welding, which increase plastic deformation on the contact surfaces of the samples during the thermal-deformation welding cycle, allows producing joints without defects. Metallographic studies show significant plastic deformation of the intermediate layer (Ni or Ti), which is a harder material compared to the magnesium alloy. The mechanical properties and microhardness of the welded joints were determined. [ABSTRACT FROM AUTHOR]

The work is concerned with the study of the process of joint formation during pressure welding by pulse current through a layer of hydrocarbon substance. During the development of this welding method, there was no necessary amount of scientific knowledge about concomitant physicochemical processes. Interdisciplinary experimental studies performed by different authors have allowed establishing scientific facts necessary for the formation of a hypothesis about the mechanism of formation of a welded joint. Carbon nanoformations are found and their properties are studied. The phenomena accompanying the passage of pulse electric current through them are studied. The phenomena of anomalous mass transfer under the action of shock loading during diffusion welding of dissimilar materials are studied. It is experimentally proved that electroexplosive and electromagnetic phenomena as well as shock waves activate diffusion processes, when applied to the surface layers of metal. The hypothesis assumes that, when a pulsed electric current of constant polarity is passed, an electrical explosion of contacting metallic microblasts occurs. The formation and subsequent microexplosions of conductive carbon particles occur. Microexplosions and shock waves activate diffusion processes on the surfaces to be joined. The process is completed after the ‘Coulomb explosion’ and the release of pyrolysis products from the central part of the joint of the welded surfaces. It is experimentally proved that the formation of the joint occurs at temperatures below the melting point of the materials to be welded. The time of joint formation at the same temperature is much shorter than during diffusion welding in vacuum. The structure of the welded joint is similar to the structure obtained by diffusion welding in vacuum. The methodology is developed, and experimental studies are carried out. The obtained results confirm the put forward hypothesis and correspond to the previously performed interdisciplinary studies of specialists. [ABSTRACT FROM AUTHOR]

Compact heat exchangers, commonly used in oil and gas offshore platforms, are thermal devices that promote high heat transfer rates due to a large ratio of the heat transfer surface area per volume. It is manufactured commonly through diffusion welding, a thermo-mechanical process that joins flat surfaces in contact by applying pressure and temperature, during a defined time. In this context, surface quality is a highly relevant topic since the machining process affects the surface and consequently the contact area for diffusion welding, having an impact on the quality of welding. Photochemical machining is the main process used to machine the channels in compact heat exchangers. As an alternative process to fabricate channeled plates, abrasive waterjet machining can be used, being a process where abrasive particles are accelerated through a waterjet at high speed, used to cut out parts and generate complex 2D profiles geometries with a potential to high productivity in comparison to the other process. These two-machining processes affect the surface quality of the piece, increasing the roughness, reducing the surface homogeneity with the formation of craters and other voids, which can be a source of defects and stresses and can also increase the accumulation of fouling and the tendency to corrosion in these places. To avoid these effects, it is necessary to employ postprocessing techniques to homogenize and improve the surface quality, like electropolishing that is a surface finishing process used to remove roughness through anodic dissolution and to promote a homogeneous oxide passive layer. The present work aims to compare quantitatively the surface topography of machined sheets using surface characterization techniques of electron microscopy and optical interferometry. The surface quality of the initial commercial stainless sheet was compared, as a reference, after abrasive waterjet and photochemical machining, as well as after the electropolishing of abrasive waterjet machining and photochemical machining. It was observed that abrasive waterjet machining presented burr at the channel's edge and had an approximately 35% increase in Sa parameter when compared with the initial condition. Photochemical machining, however, did not have burr at the machined region but presented a decrease in quality of more than 90% regarding the Sa parameter compared with the base material. The use of electropolishing removed the burrs from the abrasive waterjet machining and reduced surface roughness after the two machining methods, with more than 50% for Sa, Sq, and Pt, being a potential technique to be used to improve the surface integrity in both machining processes and guarantee an effective diffusion welding. [ABSTRACT FROM AUTHOR]

In the electronic industry, the composite of copper (Cu) and aluminum nitride (AlN) is widely used, but obtaining Cu/AlN/Cu functionally gradient materials (Cu/AlN/Cu FGMs) in a single step using traditional laminated sintering processes has proven challenging due to significant differences in their physical properties. To address this issue, molybdenum (Mo), with a high melting point and low expansion, was involved in creating a continuous gradient structure with AlN and a quasi-continuous interfacial structure with Cu. The continuous interfacial structure of Mo/AlN gradient materials was obtained by hot pressing at 1650°C. Subsequently, the quasi-continuous interfacial structure of Cu/Mo heterogeneous metal joints with high shear strength was achieved by utilizing the diffusion welding method at 700-950°C. The results indicated that the optimum shear strength of Cu/AlN/Cu FGMs is around 90 MPa. However, Cu/AlN/Cu FGMs with different diffusion interlayers failed in different ways when shear occurred, which greatly depends on the phase compositions at the joint. The challenges are overcome by utilizing Mo to construct the continuous and quasi-continuous interfaces, resulting in Cu/AlN/Cu FGMs with improved shear properties. [ABSTRACT FROM AUTHOR]

The possibility of evaluating the quality of thermal diffusion welding of two yttrium aluminum garnet crystals in a composite optical disk has been studied using the optoacoustic method. To obtain acoustic images of thermal diffusion welding, an optoacoustic transducer connected through an optical fiber with a pulsed laser (wavelength of 532 nm, pulse duration of 10 ns) were used for scanning over the disk surface. The ultrasonic pulses in the frequency range up to 80 MHz are recorded simultaneously with movement of the transducer over an area of 16×16 mm with a step of 0.1 mm. Two ultrasonic scanning modes were used: forward and backward. The 15-mm-diameter composite disks with different quality of thermal diffusion welding were tested. The possibility of quantifying the quality of the diffusion layer using an optoacoustic method for objective comparison of the disks is discussed. The obtained data are confirmed by the results of measurements using an optical projection method. [ABSTRACT FROM AUTHOR]

In order to improve the stability of Bi2Te3-based thermoelectric devices, we attempted to prepare a barrier layer via diffusion welding using Co powder as the barrier materials. The diffusion welding process was conducted at 674 K for a duration of 5 min. The optimal connection was achieved at the interfaces of Co/Bi0.4Sb1.6Te3 and Co/Bi2Te2.7Se0.3. The results showed that the Co/Bi0.4Sb1.6Te3 joint had diffusion thickness of 1.6 µm, contact resistivity of 0.83 µΩ cm2, and bonding strength of 4.86 MPa for the barrier layer. Similarly, the Co/Bi2Te2.7Se0.3 joint had diffusion thickness of 1.6 µm, contact resistivity of 0.75 µΩ cm2, and bonding strength of 3.99 MPa for the barrier layer. The thermoelectric device fabricated through this process exhibited a hot–cold cycle number of 35,000, which was significantly higher than the device with a Ni-based barrier layer under similar experimental conditions. Thus, it indicates that Co is a promising material for the preparation of barrier layers in Bi2Te3-based thermoelectric devices. [ABSTRACT FROM AUTHOR]

Using BNi as the interlayer material, transient liquid phase diffusion welding experiments were conducted on Q355 steel at a welding temperature of 1050 °C under different holding times (10, 15, 20, 25 min). The welded joint microstructure, element diffusion migration, and phase composition were analyzed by using modern analytical testing instruments such as optical microscope (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The mechanical properties of the joint were tested and analyzed by using a microhardness tester, universal testing machine, and impact testing machine. The electrochemical corrosion property of the welded joint was analyzed and studied by using an electrochemical workstation. The results showed that under the conditions of 1050 °C and 6 MPa pressure, the Q355 steel TLP welded joint with better property could be obtained with a 20-min holding time. With the increase of holding time, the width of the bonding interface layer increased first and then decreased, and the microstructure tended to be more uniform. The shear strength gradually increased, reaching a maximum of 496.7 MPa (25 min), but the impact toughness increased first and then decreased, with a maximum of 250.61 J/cm2 (20 min). The corrosion resistance of the joint also improved first and then weakened. [ABSTRACT FROM AUTHOR]

Water electrolysis will be an essential element of the future energy system, with hydrogen serving as a climate-friendly energy storage medium. To make electrolyzers suitable for market penetration at scale, the cost of manufacturing megawatt electrolyzers must be minimized, with no detrimental effects to their performance and lifetime. Here we show a facile and cost-effective manufacturing method to produce one-piece Ti-based bipolar plates. Low-cost and commercially and readily available feedstock materials (blank sheets, expanded metals and nonwovens) are positively joined using an innovative welding process, diffusion bonding. This approach reduces the contact resistances that can occur with multi-part bipolar plates by around 75%, reducing the number of components and therefore significantly simplifying stack assembly. Ex-situ tests on the contact pressure distribution on the active cell surface reveal a homogeneous pattern with values of about 3.75 MPa (± 1.25 MPa). In a first proof-of-concept, a five-cell short stack with a 100 cm2 active cell area, average cell voltages of 1.71 V at 2 A cm−2 could be achieved using our new stack concept. • Detailed insight into the plate design, construction, production and verification. • Main feature of the novel bipolar plate is the one-piece-approach. • Development of a welding-based production process; elimination of contact resistances. • Approach increases the reliability and decreases the duration of the stack assembly. [ABSTRACT FROM AUTHOR]

The outwards diffusion of Al and Si elements in Al-containing and Si-containing MAX phases endows them one natural advantage to form anti-oxidation layer and strong interfacial bonding strength with different materials, including metals and ceramics. This magic phenomenon allows MAX phases to be used in different areas, such as diffusion and fusion welding, coating and laser cladding layer. In order to give one comprehensive and systematical summarization, this review covers important research work on the atomic-level interfacial evolution of Al-containing and Si-containing MAX phases in air or with metals. This will provide an effective guidance for researchers to select the type and adjust the proportion of A-site elements in MAX phases in reference to the applied circumstances. The interfacial structure between Al-containing and Si-containing MAX phase coatings and metals matrix will be reasonably realized. [ABSTRACT FROM AUTHOR]

The diffusion welded joint of oxide dispersion strengthened tungsten (ODS-W) and Mo-Ti-Zr-C alloy (TZC) was successfully fabricated with the use of spark plasma sintering (SPS) at a vacuum level of 10 Pa. This study systematically investigates the microstructure, mechanical performance, and thermal shock resistance of the ODS-W/TZC connector at four different temperatures, ranging from 1300 to 1600 °C. The diffusion distance between the W and Mo atoms at the interface of ODS-W/TZC joint raises as the sintering temperature increases, with a maximum diffusion distance of up to 2 μm at 1500 °C, but then slightly decreases at 1600 °C. The ODS-W/TZC connector bonded at 1500 °C exhibits the best tensile performance, with tensile strengths of 459 MPa and 786 MPa at room temperature and 500 °C, respectively. A maximum hardness of 446 HV is obtained at the interface when the sample is sintered at 1600 °C. Thermal shock tests are conducted on the surface and interface of the ODS-W/TZC connector sintered at various temperatures. ODS-W/TZC samples prepared below 1500 °C were severely damaged, leading to exfoliation after laser thermal shock, while samples prepared above 1500 °C produced fewer damage cracks. Confocal laser scanning microscope (CLSM) analysis demonstrated that the ODS-W/TZC joint fabricated at 1500 °C exhibited substantially reduced height perturbation of both its surface and interface compared to that of ODS-W, providing evidence for its superior thermal shock resistance. [ABSTRACT FROM AUTHOR]

Continuous laser lap welding for a dissimilar combination of aluminum (Al) and copper (Cu) was achieved successfully. The successful welding was achieved by varying laser power between 500 and 900 W with an interval of 100 W, whereas the variation in welding speed was maintained between 10 and 45 mm/min with an increment of 5 mm/min. A combination of various laser power and weld speed generated a broad range of volume energy inputs, among which acceptable welding with no macroscopic defect could only be generated between 1.81 and 7.64 kJ/mm3. The volume energy required to achieve successful welding increased with the increase in bottom Cu sheet thickness. The joint's mechanical properties were significantly enhanced for thicker bottom Cu sheets as the welding was carried out at a higher volume of energy achieving higher depth of penetration of 0.65 mm in case of 1.5-mm bottom Cu sheet thickness. Lap shear tensile tests and Vickers's microhardness testing confirmed the abovementioned results as the highest breaking load of 373.79 N, and Vicker's hardness of 350 Hv inside Al and 750 Hv inside Cu was obtained. Furthermore, SEM results on the weld cross sections showed that welds with thicker bottom Cu sheets exhibit a higher penetration depth and lower top weld bead. Detailed electron microscopy and spectroscopy revealed the formation of hard intermetallic compounds (IMCs) inside the weld zone due to the Cu diffusion inside the weld. They correlated well with the measured mechanical and electrical properties. Electron back-scattered diffraction (EBSD) revealed a sudden concentration of high-angle boundaries (HAB) inside the weld, confirming the presence of hard IMCs. Inside the weld, most of the grain boundaries transformed into HAB, which explains the joints' enhanced mechanical properties. [ABSTRACT FROM AUTHOR]

Diffusion welding of heat-resistant alloys has attracted interest in the manufacturing of components with complex configurations. Controlling secondary precipitates along the interface is necessary to enhance the quality of the diffusion welding. Surface treatment to increase the solubility product (Ksp) of Ti-rich carbide is proposed to accomplish such an enhancement. The reduction of secondary precipitates along the interface induced grain boundary migration across the interface. The chemical compositions at/near the interface satisfied the material specifications. The mechanical properties of the diffusion weldment were similar to those of Alloy 800H that underwent the same thermo-mechanical processes in the range of 25–700 °C. At 25 °C, the tensile strength was 553 MPa, which satisfied the minimum specified tensile strength described in ASTM B: 409-22. The location of failure was random in the gauge section, and dimples, the evidence of the macroscopic plastic deformation, were observed on the fracture surface. [ABSTRACT FROM AUTHOR]

Superplastic forming (SPF) is a material forming technique that uses superplastic exceptional elongations and deformation characteristics to form superplastic materials into certain shapes. The combination of superplastic forming with diffusion bonding (SPF/DB) gives rise to an almost unlimited extension of superplastic forming since more integral lightweight cellular structural components can be manufactured. This paper discusses numerical modelling of the mechanism of superplasticity in metallic materials. The SPF computational method based on the finite element technique augmented with the controlling rate of deformations is developed to examine a range of design or operating conditions leading to more economical forming processes. The non-Newtonian 'viscous flow' material is used to model the constitutive of superplastic material during the forming period. The contact mechanics between the sheet material and the mold surface and the intersheet material contact mechanics are imposed using the penalty control method, in which the sticking contact boundary conditions are employed. The space discretization is carried out using the membrane element under plane strain and axisymmetric flow stress conditions, while the implicit time integration technique is utilized to follow the shape changes of the formed sheet material. The validation of the SPF finite element formulation was performed by comparing it with the available analytical solution of Hydraulic Free Bulging of Thin strips. The SPF of a hemispherical dome made of 7475 aluminum sheet alloy was performed to demonstrate the forming process as well as to validate the results obtained between the SPF finite element numerical simulation and the experimental results. The SPF/DB of the multicell component section is considered in the final part. [ABSTRACT FROM AUTHOR]

Welding processes of titanium alloys with steels are analyzed. The following research directions are distinguished: the use of prefabricated bimetallic transition elements (welded by traditional methods); minimization of energy and heat expenditure in the weld area of metals; the use of methods of welding metallurgical engineering. The advances in welding technology have led to innovative solutions such as friction welding with stirring, as well as the use of liquid-phase layers and 3D printing of nanostructured layers at the edges to accelerate diffusion processes in diffusion welding. The new methods in welding metallurgical engineering increase the efficiency of Ti–Fe compounds due to the use of multilayer compositions of tantalum or niobium from the side of titanium and bronze – from the side of steel, and also vanadium inserts and its alloys, for example, alloyed with tungsten or chromium. The urgency of further development of standards for support and dissemination of industrial technologies for welding of Ti–Fe joints, training and preparation of technical personnel for the implementation of these technologies is noted. [ABSTRACT FROM AUTHOR]

The paper gives the results of investigations on vacuum diffusion welding of МА2-1 magnesium alloy. Different technological measures were used in welding: unsupported welding, welding with application of forming matrices, welding without interlayers and with a zinc interlayer. It is found that it is not possible to produce the joint in unsupported welding without an interlayer at 400 °С temperature and process duration less than 60 min. Increase of welding temperature or time leads to considerable grain growth. Application of 250 ~m zinc interlayer and of the following welding mode: Т = 320 ºС, Р = 10 MPa, t = 30 min allows producing the joint. Analysis of chemical composition in different areas of the joint zone shows that development of diffusion processes in the butt during welding results in pore formation with magnesium content on the level of 17.8 – 20.12 wt. % in the zinc interlayer at 2 – 3 ~m distance from magnesium/zinc contact line. In the central part of the joint zone the metal chemical composition is close to pure zinc composition. Application of forming matrices and an interlayer of zinc in the solid-liquid state in welding in the following mode: Т = 340 ºС, Р = 10 MPa, t = 30 min. allows producing sound joints due to localisation of plastic deformation in the butt joint. Results of metallographic investigations showed formation in the butt joint of common grains and remains of the interlayer in the form of dispersed particles of 15…50 ~m size, with chemical composition of Mg–4.53Al–0.20Mn–63.49Zn, wt. %, having an irregular elongated shape. [ABSTRACT FROM AUTHOR]

The paper gives the results of investigations on vacuum diffusion welding of MA2-1 magnesium alloy. Different technological measures were used in welding: unsupported welding, welding with application of forming matrices, welding without interlayers and with a zinc interlayer. It is found that it is not possible to produce the joint in unsupported welding without an interlayer at 400 ℃ temperature and process duration less than 60 min. Increase of welding temperature or time leads to considerable grain growth. Application of 250 μm zinc interlayer and of the following welding mode: T = 320 ℃, P = 10 mpa, t = 30 min allows producing the joint. analysis of chemical composition in different areas of the joint zone shows that development of diffusion processes in the butt during welding results in pore formation with magnesium content on the level of 17.8-20.12 wt.% in the zinc interlayer at 2-3 μm distance from magnesium/zinc contact line. In the central part of the joint zone the metal chemical composition is close to pure zinc composition. application of forming matrices and an interlayer of zinc in the solid-liquid state in welding in the following mode: T = 340 ℃, P = 10 mpa, t = 30 min. allows producing sound joints due to localisation of plastic deformation in the butt joint. Results of metallographic investigations showed formation in the butt joint of common grains and remains of the interlayer in the form of dispersed particles of 15-50 μm size, with chemical composition of mg-4.53al-0.20mn-63.49Zn, wt.%, having an irregular elongated shape. [ABSTRACT FROM AUTHOR]

The possibility of using nanosecond laser pulses for perforation of elements of a diffusion-welded joint of the ceramic–metal–ceramic type has been studied. An improvement in the mechanical properties of compounds with elements pretreated by a repetitively pulsed Nd:YAG laser compared to untreated elements has been experimentally demonstrated. In particular, an increase in the tensile strength of the connection with treated elements from 40 to 50% are shown. Comparative studies of the distribution of strains in diffusion-welded joints with and without preliminary laser treatment were also carried out. The results make it possible to reduce energy consumption for the diffusion welding process and improve the quality of joints of dissimilar materials in general. [ABSTRACT FROM AUTHOR]

A reliable bonding interface between steel and Ti alloy is required for producing a steel/Ti bimetal composite. In this study, molecular dynamic simulations and diffusion welding experiments using the hot isostatic pressing process were conducted to study the atomic diffusion at the Fe-Ti interface. The simulation results indicate that the diffusion layer thickness is thinner in single crystals compared to polycrystals at the same temperature. This difference may be explained by polycrystals having grain boundaries, which increase atomic disorder and facilitate diffusion. The radial distribution function (RDF) curves for Fe-Fe and Ti-Ti exhibit a similar pattern over time, with a main peak indicating the highest atom density within a specific radius range and relatively strong binding between the central atoms and their nearest neighbors. The observed changes in the diffusion coefficient with temperature in the simulations align well with the experimental results. This study enhances the understanding of Fe-Ti interface diffusion mechanism and provides valuable insights for broader applications of steel/Ti bimetal composites. [ABSTRACT FROM AUTHOR]

The effects of various process parameters on microstructure, tensile strength, temperature distribution, and weld quality were investigated during friction stir welding (FSW) of Al-Si alloys. The weld process factors altered the microstructure, with non-uniform grains seen at lower tool rotation rates and enhanced mixing at higher speeds. During force balancing, hyper eutectic alloys generated a substantial amount of heat, resulting in increased temperatures. The tool had difficulties while progressing through hyper eutectic alloys, resulting in greater temperatures and a reduction in weld quality. The study emphasised the need of selecting the right process parameters, such as plunging force, mixing, and plastic flow, to achieve the necessary weld quality and joint strength. Overall, this study emphasises the importance of accurate process parameter control to obtain optimal microstructures, tensile strength, and weld quality in Al-Si alloy FSW. Further optimisation can result in improved weld joint characteristics, which will improve the performance of these alloys in actual applications. [ABSTRACT FROM AUTHOR]

Filament‐based material extrusion (MatEx) additive manufacturing has garnered great interest due to its simplicity, customizability, and cost‐effectiveness. However, MatEx of semicrystalline polymers is still largely relegated to prototyping applications. Major issues involving volumetric shrinkage and warpage of the printed parts must be addressed in order to employ them for printing functional parts. Moreover, the crystallization behavior and rheology of the polymer are dependent on the MatEx processing conditions. In the current work, the printability of blends of isotactic polypropylene with a soft, low crystallinity propylene based homopolymer is evaluated. Addition of the homopolymer resulted in an increase in the crystallization window of the blends by ~6°C that had a profound impact on the interlayer adhesion and residual stress state. The shear‐dependent melt flow behavior inside the printing nozzle as well as the interlayer chain diffusion and interlayer welding on the print bed were investigated. Rheological characterizations also indicate sufficient dispersion and miscibility of the homopolymer in the neat polypropylene matrix. The incorporation of the homopolymer as an additive significantly improved the dimensional accuracy of the printed parts through better dissipation of the entrapped residual stresses during MatEx. Moreover, the degree of mechanical anisotropy of the parts was significantly lower than that obtained using many 3D printable grade polymers. The findings from this study can be leveraged in toolpath planning, process parameter optimization, and new feedstock development, highlighting current limitations as well as providing valuable insights into necessary processing modifications in order to enable MatEx of next generation semicrystalline polymers. [ABSTRACT FROM AUTHOR]

5A06 aluminum alloy bar was brazed by temperature gradient transient liquid phase diffusion welding (TG-TLP). The effects of brazing temperature on the microstructure and the tensile strength of the brazing joints were investigated. Three typical brazing filler alloys (1# Al-20Cu-6Si-2Ni, 2# Al-10Cu-10Si-3Mg-1Ga, and 3# Al-6Cu-10Si-2Mg-10Zn) were prepared by smelting, and TG-TLP diffusion bonding was carried out at different brazing temperatures (550 °C~590 °C). The results show that with the increase in brazing temperature, the oxide films at the brazing junction are easier to be broken and dispersed, but the oxidation extent will also increase. The oxidation products enriched were mainly Al2O3 and SiO2 at the brazing junction. There are different optimal brazing temperatures corresponding to the different filler alloys. For 1#, the optimal temperature is 570 °C; for 2# is 580 °C; for 3# is 580 °C. For 1# brazing joints, the maximum tensile strength was 113 MPa, and for 2# was 122.4 MPa. Under the experimental conditions of this study, the maximum tensile strength of the TG-TLP joint is 147.4 MPa of 3# brazing sample (at 580 °C), which has increased by 30% and 20% compared to 1# and 2# respectively. The nickel-rich phase at the interface (of 1# brazing filler) could form a brittle fracture, which was unfavorable for interface bonding. For TG-TLP brazing of 5A06, the filler alloy with high Al:Cu ratio (12:1 wt.%) needs a sufficient temperature gradient to exert the film-breaking effect, while the filler alloy with low Al:Cu ratio (3.6:1 wt.%) needs to accurately control its brazing temperature to avoid excessive oxidation. There are many research gaps in the influence of brazing material composition and brazing temperature on the microstructure and mechanical properties of 5A06 aluminum alloy TG-TLP joints. The research results can provide a theoretical basis for formulating the TG-TLP brazing specification of 5A06 aluminum alloy. [ABSTRACT FROM AUTHOR]

Diffusion welding, also known as solid state welding or pressure welding, is a type of welding process that involves bonding two metal surfaces together by applying heat and pressure, without or using any interlayer material. In this study, the effect of GR and SX materials of welding temperature on the connection is examined with the diffusion welding method using a copper intermediary layer. The material pairs are combined with a pressure of 5 MPa and a fixed welding time of 60 minutes in an argon gas environment in a silicon bar oven at the temperature of 980, 1000, and 1020°C. The SEM-EDS-AFM analysis of the combined samples is performed, the metallographic structure of the intermediary layer in the diffusion-affected region is examined by the optical microscope, and the possible phases are tried to be determined by the XRD analysis. The micro stiffness values of the connection area are analyzed. Diffusion welding, also known as solid state welding or pressure welding, is a type of welding process that involves bonding two metal surfaces together by applying heat and pressure, without or using any interlayer material. In this study, the effect of GR and SX materials of welding temperature on the connection is examined with the diffusion welding method using a copper intermediary layer. The material pairs are combined with a pressure of 5 MPa and a fixed welding time of 60 minutes in an argon gas environment in a silicon bar oven at the temperature of 980, 1000, and 1020°C. The SEM-EDS-AFM analysis of the combined samples is performed, the metallographic structure of the intermediary layer in the diffusion-affected region is examined by the optical microscope, and the possible phases are tried to be determined by the XRD analysis. The micro stiffness values of the connection area are analyzed. [ABSTRACT FROM AUTHOR]

A solid-phase diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and electrochemical corrosion was shown to have a preferentially intercrystalline character. In the case of the presence of macrodefects, crevice corrosion of the welded joints was observed. The resistance of the alloys against the intercrystalline corrosion was found to be determined by the concentration of vanadium at the titanium grain boundaries, by the size and volume fraction of the β-phase particles, and by the presence of micro- and macropores in the welded joints. The specimens of the welded joints of the UFG alloy are harder and have a higher resistance to hot salt corrosion and electrochemical corrosion. [ABSTRACT FROM AUTHOR]

Interdiffusion of the elements in a diffusion pair consisting of Ti and an equiatomic high-entropy alloy (HEA) TiZrHfNbTaMo in the temperature range of 1473–1673 K has been studied. A calculated results phase diagram of the alloy by Thermo-Calc 2021-B software as used to determine the temperature stability range of the β-phase in the alloy. Ti–HEA diffusion pairs were obtained by low = temperature welding and then diffusion annealing was carried out at temperatures of 1473, 1573, and 1673 K during 12, 9, and 6 h, respectively. The interdiffusion zone was profiled using electron probe microanalysis (EPMA). The diffusion parameters of the HEA's elements were obtained using Hall's method. An experimental results discussion is given. [ABSTRACT FROM AUTHOR]

During the explosive welding, the bonding interface of welded materials was fast heated due to high strain rate and drastic plastic deformation. The periodical wave interface, with an amplitude of ~300 μm and a period wavelength of ~800 μm, was identifiable as a uniform wave interface formed in the bonding interface. The details of the formation of melting zone and mixing zone of welding materials at the interface were observed. Combined with the Ti-Fe binary phase diagram and the principle of diffusion welding, the phase composition and evolution process of the melting and mixing zone of the bonding interface were investigated by transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). Significance of the intermetallic compound was found in the mixing zone and melting zone, which was mainly TiFe, TiFe2, TiO2, Fe2O3 and some other intermetallic oxides. Meanwhile, the phenomenon of the titanium agglomeration and oxygen precipitation was observed in the melting zone. The bonding interface could be determined as a mixing welding of mechanical mixing, melting, diffusion and solidification that occurred in the mixing zone, and melting welding and diffusion welding mainly occurred in the melting region. [ABSTRACT FROM AUTHOR]

Diffusion welding is a solid-state welding process and is characterised by the process parameters temperature, compression force and process time. Usually, the process force is applied as static load, and high demands with respect to specimen surfaces (low roughness, cleanliness) are common. The aim of this work was to improve the necessary technology for diffusion welding and, above all, to increase the quality of the joints by using cyclically pulsative joining forces to minimise the time or surface-specific conditions, which are typical for this process. For this purpose, a corresponding system technology had to be designed and manufactured. The basis of the system was a modified machine concept for materials testing. As a result, the modified system and the modified process were able to reduce the process time by a factor of 5 to 6 compared to the conventional joining time. [ABSTRACT FROM AUTHOR]

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• The fatigue performance of Bronze/Steel diffusion welded joints is investigated through tests. • The CDM is applied to calculate the fatigue life of Bronze/Steel diffusion welded material. • Database expansion of ANN models is realized by CDM-FEM and dispersivity of fatigue life. • The transfer learning is employed for the fatigue life prediction of Bronze/Steel diffusion welded material. The bronze/steel diffusion welded (BSDW) bimetallic material is often applied in the rotors of piston pumps to withstand complex alternating loads under high-speed operating conditions. Although diffusion welding is a type of solid-phase welding method to achieve high-quality material connections, the fatigue problems still deserve our attention, especially the very high cycle fatigue (VHCF) and high cycle fatigue (HCF) problems. However, due to the high cost of obtaining data, it is necessary to find an efficient and high-precision fatigue life prediction method for diffusion welded materials with a small sample size. In this study, a novel method continuum damage mechanics − transfer learning method (CDM-TLM) for fatigue life prediction of BSDW material is proposed based on the transfer learning (TL) and continuum damage mechanics − finite element method (CDM-FEM). In comparison with the test results, the predicted values of BSDW material fatigue life all fall within the twice error band of the median values of the test life. The influence of frozen layers during TL and training samples in source and target models on the prediction performance is further discussed. CDM-TLM is an effective life prediction method for high-precision life prediction of BSDW material with a small sample size. [ABSTRACT FROM AUTHOR]

During the service of X80 high-strength pipeline steel, the combined effects of welding residual stress, cyclic loading, and hydrogen complicate the prediction of pipeline fatigue life. This article combines ABAQUS and FRANC3D finite element software to analyze the fatigue crack growth laws of the X80 pipeline with thickness of 22 mm under the combined condition. After heat treatment, the fatigue life of pipelines with annular and axial cracks increased by 19 % and 83 %, indicating that post-weld heat treatment significantly improves the fatigue life of the pipeline. When the crack grows to the outer surface of the pipeline, the fatigue life of a pipeline with a 10 % hydrogen doping ratio is reduced by 77 % compared to one with a 1.5 % hydrogen doping ratio. These findings indicate that toughness of the crack front region is significantly reduced by hydrogen concentration, the crack propagation rate is accelerated, and the fatigue life of the pipeline is significantly reduced. • Combined with ABAQUS and FRANC3D, crack propagation is simulated by using mesh fine division and mesh adaptive updating. • The coupling analysis of welding residual stress, hydrogen diffusion and fatigue crack growth is carried out. • The synergistic effect of residual stress and hydrogen concentration on crack growth is analyzed. [ABSTRACT FROM AUTHOR]