Micro-deformation diffusion bonding of Ti-6Al-4V alloy is a key solid-state joining process for manufacturing components with intricate internal channels, as required in diffusion bonding additive manufacturing (DBAM). A critical challenge lies in achieving sound joint performance while limiting uniaxial deformation to below 1% to preserve geometric accuracy. Here, gradient nanostructured surface layers about 25 & micro;m thick were fabricated on Ti-6Al-4 V via high-pressure waterjet peening. The nanostructured surface, with an average grain size of 80 nm at the outermost region (statistically measured over a 2.25 & micro;m & times; 2.25 & micro;m area immediately beneath activated surface), greatly enhanced interfacial diffusion and void closure during bonding at a uniaxial deformation of approximately 0.8%. The bonding ratio rose from 83.2% for non-activated joints to 99.1% and 100% for unilaterally and bilaterally activated joints, respectively. Complete interfacial recrystallization and full interface migration were achieved, forming a fine-grained equiaxed alpha phase band. Compared with non-activated joints, the activated joints showed a 6% increase in ultimate tensile strength (975 MPa) and a 646% rise in fracture elongation (19.4%), outperforming even the base metal. This synergy stems from void elimination, which suppressed premature cracking, and a recrystallized interfacial microstructure that provided a remarkably high and sustained work-hardening rate (maintained above 1100 MPa up to a true strain of 0.117), demonstrating the joint's enhanced capabilities for dislocation accommodation. The approach successfully decouples the traditional trade-off between precision and performance, offering a viable route to high-integrity DBAM components with complex internal features.

A high-entropy interlayer alloy with a composition of Al2Nb48Ta25Ti20Hf5 was developed to improve the strength and ductility of Ti2AlNb diffusion-welded joints. However, the fundamental strengthening and toughening mechanisms at the heterogeneous interface remain unclear. Therefore, in this paper, finite element simulation was employed to investigate the distribution of strain, stress (back stress), and dislocation density in the heterogeneous interface, and Scanning Electron Microscopy-Digital Image Correlation (SEM-DIC) experiments were conducted to validate the strengthening effect of back stress at the grain boundaries. Based on this, design criteria for the Ti2AlNb joint microstructure were proposed. The simulation results show that during tensile deformation, a strain gradient (SGR) forms at the grain boundaries between coarse and fine grains in the heterogeneous microstructure. The intensity of the strain gradient peaks at the grain boundaries and increases significantly with the increasing tensile strain, resulting from the difference in deformation capability between coarse and fine grains. As the strain increases to 10 %, the back stress accounts for approximately 25 % of the joint's strength. The combined effect of back stress and forward stress coordinates dislocation strengthening and fine grain strengthening, which not only strengthens the recrystallized grains but also induces plastic deformation in the surrounding fine-grained structure. This alleviates stress concentration at the grain boundaries, effectively enhancing the joint's strength and ductility. Furthermore, it is proposed to use the intensity, width, and distribution of the strain gradient at the coarse/fine grain boundaries as microstructural control parameters. When the joint forms a hetero-structure with fine grains enveloping coarse grains, the strain is uniformly distributed throughout the joint, effectively improving the mismatch problem between strength and plasticity of the Ti2AlNb joint.

A rolled refractory high-entropy alloy (HEA) interlayer (Hf15Nb40Ta25Ti15Zr5) was employed to achieve reliable diffusion bonding of Ti3Al-based alloys. The effects of bonding temperature on interfacial microstructure evolution and mechanical properties were investigated, and the deformation behavior of the interface was analyzed through in-situ scanning electron microscope-digital image correlation (SEM-DIC) and transmission electron microscopy (TEM) observations. The results reveal that the diffusion reaction layer (DRL) exhibits a continuous B2 solid-solution layer accompanied by nanoscale O-phase precipitation near the Ti3Al substrate. The joint bonded at 960 degrees C achieves an optimal tensile strength of 886 MPa and an elongation of 16.6%. Nanoindentation results show smooth hardness and modulus transitions across the interface, confirming the absence of brittle phase. As the overall strain of the sample increases, dislocations accumulate and interact through processes such as intersection and dislocation cell formation, which hinder dislocation slip and thereby strengthen the joint properties. This study provides a feasible design route for diffusion bonding of Ti3Al-based intermetallics.

Interfacial oxides play a critical role in the direct diffusion bonding of dissimilar nickel-based superalloys GH4099 and GH3128. However, the mechanisms of their evolution and their regulatory effects on joint mechanical performance remain unclear. To clarify these fundamental issues, two representative bonding were designed as comparative frameworks. By combining multiple microstructural characterization techniques with in-situ tensile testing, the evolution behavior of interfacial Al2O3 oxides and their influence on joint performance were systematically investigated. The results reveal a clear correlation among the evolution state of Al2O3, the interfacial constraint intensity, and the grain boundary migration capability. Insufficiently dissolved residual Al2O3 enhances interfacial constraint and suppresses grain boundary migration, resulting in extremely poor joint ductility, with a room-temperature elongation of only 0.67%. In contrast, after sufficient dissolution and redistribution, nanoscale-dispersed Al2O3 particles significantly weaken interfacial constraints, increase the grain boundary migration ratio to 48.9%, and markedly improve joint ductility, achieving a room-temperature elongation of 18.8%. This study provides a solid theoretical basis for the fabrication of dissimilar nickel-based superalloy joints with high reliability.

To address the strength-ductility trade-off in diffusion-bonded joints of Inconel 617 superalloys, this paper proposes an interface optimization strategy based on insert layer thickness regulation. Using Inconel 617 alloy as the base material, diffusion bonding was performed with pure Ni foils of varying thicknesses (3-100 μm) as insert layer. The effects of insert layer thickness on the mechanical response and microstructural evolution of the joints were systematically investigated. Results show that joint properties do not evolve linearly with thickness. In-situ tensile electron backscatter diffraction (EBSD) characterization revealed that the 30 μm joint exhibits a dispersed network-like distribution of geometrically necessary dislocation (GND) density, effectively alleviating stress gradients at the interface. In contrast, the 100 μm joint undergoes severe strain localization, with GND density one order of magnitude higher than that of 30 μm insert layer joints, leading to early plastic instability. This study confirms that precisely controlling insert layer thickness to optimize geometric constraint effects and strain distribution patterns is key to achieving high-strength and high-toughness connections in dissimilar metals.

Rotary friction welding (RFW) was employed to join dissimilar compressor alloys TC17 and TA19. To quantify how axial pressure governs the interfacial microstructure, Electron Backscatter Diffraction (EBSD) was combined with a parent-β reconstruction algorithm grounded in the Burgers orientation relationship. Tubular joints were produced at 80, 120, and 160 MPa under fixed linear speed and burn-off. Increasing pressure refined dynamically recrystallized prior-β grains on both sides of the interface (TC17: 3.40 → 3.27 → 3.01 µm; TA19: 2.86 → 2.80 → 2.33 µm). In contrast, the TA19 α′-lamella thickness after cooling displayed a non-monotonic trend, peaking at 0.73 µm at 120 MPa (vs 0.54 µm at 80 MPa and 0.49 µm at 160 MPa), due to the interplay between prior-β grain size and high-temperature dwell/cooling history. The intermediate pressure resulted in the best interfacial microstructural matching. Uniform equiaxed β grains were formed across the interface, while the α′ colonies on the TA19 side were moderately coarsened. This improved matching led to better tensile behavior, with a UTS of about 750–765 MPa and an elongation approximately 50

A plastic accommodation mechanism based on the morphological evolution of interfacial oxides is proposed to elucidate the yielding and plastic deformation behavior of GH4099/GH3128 dissimilar nickel-based superalloy diffusion-bonded joints. This mechanism couples the interactions among grain-boundary migration, and residual oxides, and introduces the grain-boundary migration ratio to characterize the degree of interfacial microstructural continuity, thereby avoiding the oversimplified view that oxides merely act as detrimental inclusions. By analyzing the evolution of interfacial oxide states under different thermo-mechanical paths, it is found that, under the low-temperature/high-pressure route, limited diffusion transport causes residual Al2O3 to remain near the original bonding interface, strengthening interfacial constraint. As a result, the joint exhibits a high yield-to-tensile strength ratio of 0.79 but a very limited elongation of only 0.67%. In contrast, under the high-temperature/low-pressure route, atomic diffusion and grain-boundary migration are significantly enhanced. No obvious residual oxides are observed at the interface, and the grain-boundary migration ratio increases from 36% to 77%, leading to an improved elongation of 18.8% and a reduced yield-to-tensile strength ratio of 0.64, while maintaining a comparable tensile strength. These residual oxides can increase interfacial constraint and the yield-to-tensile strength ratio, but at the expense of ductility. Enhanced diffusion transport and grain-boundary migration can promote oxide elimination or displacement away from the original interface, thereby releasing the plastic accommodation capability of the joint.

This study investigates the effect of diffusion bonding temperature on the microstructural evolution and mechanical behavior of Ti-10V-3Al-2Fe alloy joints. Bonding was performed below, within, and above the reported α+β → β phase transformation temperature range to clarify the relationship between phase transformation and joint performance. At sub-transus temperatures (650 – 750 °C), the joints exhibited incomplete interfacial bonding characterized by microvoids and spheroidized α phases. At a near-transus condition (775 °C, corresponding to the lower bound of the reported transformation range), an interlaced α+β structure developed, while the precipitation of acicular secondary α phases was associated with a reduction in ductility. At super-transus conditions (800 – 850 °C), grain boundary migration and coarsening of α phases further suppressed elongation. Mechanical properties exhibited a temperature-dependent evolution up to 725 °C, with simultaneous improvements in strength and ductility. Beyond this range, strength gains were limited, whereas elongation declined sharply due to phase transformation and grain growth. These findings highlight the complex interplay between bonding temperature, microstructural evolution, and mechanical response, providing practical guidelines for optimizing diffusion bonding parameters of near-β titanium alloys.

This study investigates the effect of diffusion bonding temperature on the microstructural evolution and mechanical behavior of Ti-10V-3Al-2Fe alloy joints. Bonding was performed below, within, and above the reported alpha+ (3 -> (3 phase transformation temperature range to clarify the relationship between phase transformation and joint performance. At sub-transus temperatures (650 - 750 degrees C), the joints exhibited incomplete interfacial bonding characterized by microvoids and spheroidized alpha phases. At a near-transus condition (775 degrees C, corresponding to the lower bound of the reported transformation range), an interlaced alpha+ (3 structure developed, while the precipitation of acicular secondary alpha phases was associated with a reduction in ductility. At supertransus conditions (800 - 850 degrees C), grain boundary migration and coarsening of alpha phases further suppressed elongation. Mechanical properties exhibited a temperature-dependent evolution up to 725 degrees C, with simultaneous improvements in strength and ductility. Beyond this range, strength gains were limited, whereas elongation declined sharply due to phase transformation and grain growth. These findings highlight the complex interplay between bonding temperature, microstructural evolution, and mechanical response, providing practical guidelines for optimizing diffusion bonding parameters of near-(3 titanium alloys.

Interfacial void evolution is critical to the service reliability of diffusion-bonded Ti-6Al-4 V components with complex internal cavities or microchannel structures, which are widely used in aerospace, marine, and energy industries. This study establishes a quantitative framework linking process parameters, void characteristics, and mechanical performance of Ti-6Al-4 V diffusion-bonded joints through multi-scale experiments, mechanical modeling, and machine learning. The diffusion-bonded joints with designed void characteristics were prepared by tailoring process parameters and surface topography, from which the interfacial bonding ratio and key void descriptors were extracted. The bonded zone achieved metallurgical bonding through the synergistic action of dynamic recrystallization, grain boundary migration, and elemental interdiffusion. Quantitative "S-curve" relationships were established between the bonding ratio and both the tensile strength and fracture elongation of the joints. Furthermore, the void-tip stress concentration coefficient and the ratio of void spacing to width are proposed as supplementary metrics for a more comprehensive assessment of interfacial quality. Among four machine-learning models evaluated, the meta-learning approach exhibited the highest accuracy and convergence efficiency in predicting void morphology and bonding ratio under multi-parameter coupling. This work provides a theoretical and data-driven framework for precisely controlling interfacial integrity and optimizing the performance of diffusion-bonded components.

Diffusion-bonded dissimilar nickel-based superalloy joints may exhibit markedly different yielding and plastic responses despite having comparable ultimate tensile strengths, owing to differences in their interfacial microstructural states. In this study, GH4099/GH3128 joints were fabricated using two thermo-mechanical routes, 1000 °C-70 MPa-60 min and 1160 °C-10 MPa-60 min, and systematically characterized by SEM, TEM, EDS, EBSD/TKD, in-situ tensile testing, and tensile tests at room temperature and 650 °C. At 1000 °C-70 MPa-60 min, the original bonding interface remained clearly distinguishable, with a grain-boundary migration fraction of only 36%. Residual voids, high local misorientation and orientation gradients, together with discretely distributed Al2O3 particles, were observed near the interface. Pronounced retained deformation and dislocation accumulation were associated with the higher initial yield strength, whereas interfacial discontinuities and second-phase particles may have promoted premature damage initiation and restricted post-yield uniform plastic deformation and strain hardening. Consequently, the joint exhibited a room-temperature yield-to-tensile strength ratio of 0.79 and an elongation of only 0.67%. For the joint bonded at 1160 °C-10 MPa-60 min, the grain-boundary migration fraction increased to 77%, accompanied by more extensive microstructural recovery and improved interfacial continuity, while the localized Al-O-enriched regions on the fracture cross-sections exhibited a more diffuse distribution. Accordingly, the elongation increased to 18.8% and the yield-to-tensile strength ratio decreased to 0.64, while a comparable ultimate tensile strength was maintained. A similar trend was also observed at 650 °C. These results indicate that the yielding and plastic responses of the joints are closely associated with retained deformation, grain-boundary migration, interfacial continuity, and the spatial distribution of local defects.

The diffusion bonding of 6063 aluminum alloy with surface pretreatment was carried out in this paper. The 6063 aluminum alloy (AA6063) is often used in the manufacture of micro-channel heat exchangers (PCHE). However, due to the existence of a stable surface oxide film (Al2O3) with a high melting point, which prevents the close contact of the surface to be bonded and the diffusion of atoms. This paper designed the acid and alkali washing cleaning before the bonding process. Three protection schemes were designed for the cleaned surface protection, namely, ethanol protection, α-terpineol surface protection, and magnesium powder terpineol mixed protection. The bonding temperature of diffusion bonding was 540 580 °C, the pressure was 4 MPa, and the bonding time was 120 min. The microstructure of the joint was studied by scanning electron microscopy. The mechanical properties of the joint were evaluated by a tensile test. The results show that with the optimal process of 570 °C–4 MPa–120 min, the α-terpineol-protected joint achieved a tensile strength of 113.3 MPa and an elongation of 28.1

Reliable joining of nickel‐based superalloys, composites, or other dissimilar materials combinations remains a persistent challenge in aerospace and nuclear energy applications, where brittle intermetallic compound (IMC) formation, residual interfacial defects, and insufficient service performance restrict the practical deployment. This review systematically examines high‐entropy alloy (HEA) interlayers as a promising solution to these challenges. From a compositional perspective, this review discusses the evolution from single‐phase solid‐solution HEAs to dual‐phase, eutectic, and refractory systems. It highlights how their sluggish diffusion kinetics and high phase stability suppress undesired IMC formation and promote sound metallurgical bonding. In terms of structural design, the transition from single‐layer to double‐layer and sandwich/composite configurations is discussed, demonstrating how these architectures accommodate thermomechanical mismatch and reduce interfacial defects. However, achieving superior joint performance under extreme service conditions requires a synergistic compositional and structural design strategy. Building on these design principles, the novel multiinterlayer composite bonding (MICB) strategy employing a BNi‐2/HEA/BNi‐2 sandwich interlayer is innovatively developed. Incorporating a core of L1 2 ‐strengthened HEAs or chemically complex intermetallic alloys (CCIMAs), this approach effectively addresses the long‐standing strength–ductility trade‐off in superalloy joints. Finally, future challenges are also outlined, including the artificial intelligence (AI)‐assisted compositional design, high‐precision manufacturing methods, and comprehensive performance evaluations.

This study conducted process design for rotary friction welding of dissimilar materials with "soft/hard" mismatch, resolving poor forming and welding quality issues in typical difficult-to-weld TC4/GH4169 (25 mm) friction welded joints. Analysis identified the primary causes as mismatched plastic deformation on both sides of the interface and excessive formation of brittle intermetallic compounds. The process design approach prioritized achieving physical and mechanical compatibility between dissimilar materials. The proposed solution involved: preheating the GH4169 hot-worked side to 980 degrees C prior to welding, and selecting welding parameters of low rotational speed (e.g., 400 rpm) and high pressure (e.g., 300 MPa). This process design significantly reduced the intermetallic compound (IMC) layer thickness (similar to 4 mu m) at the interface, effectively suppressing IMC formation and mitigating localized strain caused by mismatched plastic deformation. It achieved an increase in tensile strength (similar to 440 MPa) for the dissimilar joint, representing a strength improvement of approximately 300%, and revealed the bonding mechanism at the TC4/GH4169 rotary friction welded interface. This work provides design insights for enhancing the weldability of dissimilar "soft/hard" mismatched material assemblies in friction welding.

This study focuses on accelerating element diffusion during Transient Liquid Phase (TLP) bonding of AlCoCrFeNi2.1 by incorporating a Ni-Cr-based alloy interlayer. The microstructure, mechanical properties, and their evolution of TLP joints were comprehensively investigated. The addition of the interlayer significantly enhances the element diffusion coefficient during the TLP process. Interdiffusion between the interlayer and the BM results in the formation of an Isothermal Solidification Zone (ISZ) and a Diffusion-Affected Zone (DAZ). The ISZ predominantly consists of (1, (1) over bar, 1) L12 and ((2) over bar, 3, (1) over bar) B2 phases in a semi-coherent relationship, with the presence of nanoscale BCC phases. The DAZ is defined by the diffusion of unique elements from the interlayer into the BM. The mechanical properties of the joint are largely influenced by its microstructure. With an increase in bonding time from 10 min to 120 min, the athermal solidification zone gradually transforms into the ISZ. During this process, the increase in alloying degree, recrystallization, and B2 phase content within the ISZ leads to a greater contribution from solid solution strengthening, grain refinement, enhanced dislocation hardening, and improved lamellar structure. Consequently, the mechanical properties improve. When bonding at 1160 degrees C 4 MPa 90 min, the joint shows the maximum elongation (16.5%) and tensile strength (1062 MPa), matching the values of the base material, with fracture occurring in the BM. However, at 120 min, the grain size up to 40 lm in ISZ promotes crack initiation and propagation along the interface easily under tensile load. The fracture surface exhibits a mixed fracture mode. (c) 2026 The Author(s). Published by Elsevier Ltd on behalf of Chinese Society of Aeronautics and Astronautics. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

The dissimilar 2B06 and 7B04 Al alloy joints were prepared by refill friction stir spot welding (RFSSW), and the microstructural evolution and corrosion behavior of the joints were investigated. Based on microstructural analysis, the welded joints exhibit distinct microstructural zones, including the stir zone (SZ), thermomechanically affected zone (TMAZ), and heat-affected zone (HAZ). The grain size of each zone is in the order of HAZ > TMAZ > SZ. Notably, the TMAZ and HAZ contain significantly larger secondary-phase particles compared to the SZ, with particle size in the HAZ increasing at higher rotational speeds. Electrochemical tests indicate that corrosion susceptibility follows the sequence of HAZ > TMAZ > SZ > BM, with greater sensitivity observed at increased rotational speeds. Post-corrosion mechanical performance degradation primarily arises from crevice corrosion at joint overlaps, but not from the changes in the microstructure.

Rotary friction welding of dissimilar materials involves strong coupling between plastic flow, heat generation, and interfacial bonding. However, existing analytical models typically require predefined response variables or empirical friction coefficients. In this study, a thermomechanically coupled analytical model was developed for the steady-state, severe plastic deformation stage of rotary friction welding of dissimilar titanium alloys. This model is capable of directly predicting the axial shortening velocity (vx), the width of the plastic deformation zone (B), and the average interface temperature (Ta), thereby fundamentally capturing the intrinsic coupling between process parameters and thermomechanical responses during the friction welding of dissimilar materials, as well as the asymmetric temperature and deformation responses characteristic of dissimilar welding. Experimental validation was conducted using a typical dissimilar titanium alloy system (TC4/TC17). A comparison of the predicted temperature distribution, axial shortening velocity, and deformation zone width with experimental results showed an error range of 10

The transient liquid-phase (TLP) diffusion bonding of GH5188 with a BNi-5 interlayer was focused on. Parameters were chosen and optimized for GH5188 alloy according to the TLP joining mechanism. The microstructure evolution and mechanical properties of the joints were studied. Results show that the relatively complete isothermal solidification zone (ISZ) ensures a reliable connection of the base metal (BM). Within the temperature range of 1110-1190 degrees C, higher bonding temperatures can widen ISZ and promote joint composition homogenization, thus improving mechanical properties. However, the increase in precipitated phase has an adverse effect on the mechanical properties of the joint. The maximum shear strength, reaching 482 MPa, is achieved at 1130 degrees C, representing 84.6% of BM strength. Within the pressure range of 5-15 MPa, both precipitated phases in adiabatic solidification zone (ASZ) and voids generated by partial melting increase. On the contrary, their sizes decrease significantly under higher bonding pressure, resulting in an upward trend in alloy mechanical properties. The maximum shear strength of 490 MPa is attained at bonding pressure of 15 MPa. The joint exhibits a typical mixed fracture pattern, with the small brittle M23C6 phase and voids significantly impacting mechanical properties. Nano-indentation tests indicate that ASZ is a potential source of cracks.

The process of direct diffusion bonding using GH5188 superalloy was investigated. The paper revealed that the bonding interface exhibited varying degrees of grain boundary migration as temperature increased, time extended, and pressure intensified. Furthermore, appropriate bonding pressure effectively promoted recrystallization in the joint, thereby enhancing its mechanical properties. The optimal joint was achieved at 1180 degrees C/60 min/15 MPa parameter, with yield tensile strength (YTS) reaching 467.7 MPa, ultimate tensile strength (UTS) reaching 998.2 MPa, elongation (EL) reaching 73.6 %, axial deformation at this parameter was measured at 2.2 %, with fracture surfaces located at base metal (BM) area, where numerous ductile dimple structures were observed.

TiAl and Ti2AlNb intermetallic alloys are promising alternatives to conventional superalloys due to their high-temperature resistance, which offers potential for energy savings and weight reduction. However, the connection of dissimilar TiAl/Ti2AlNb is still a challenge. This study investigates the linear friction welding (LFW) of TiAl/Ti2AlNb alloys under specific parameters: a frequency of 45 Hz, friction pressure of 120 MPa, amplitude of 2 mm, and a welding time of 5 s. The results showed a well-formed joint with a tensile strength of 332 MPa. Microstructural analysis revealed that the joint consists of three distinct zones: the base material (BM), the thermo-mechanically affected zone (TMAZ), and the weld zone (WZ). In the WZ, the grain morphology exhibits an equiaxed crystalline structure, indicating the occurrence of dynamic recrystallization. The zone widths were wider on the Ti2AlNb side due to differences in thermo-mechanical properties. An 8 mu m thick diffusion layer formed at the weld interface due to elemental diffusion. The interfacial microstructure was TiAl(gamma)-Ti3Al(alpha(2))-[O+alpha(2)]-Ti2AlNb(O), resulting from diffusion and thermal effects. The highest microhardness was found at the weld interface, where a non-uniform alpha(2) layer of 10 similar to 30 mu m thick was present. This alpha(2) layer is prone to cracking and represents the weak link in the joint.