Heterogeneous structural design is an effective strategy for achieving breakthroughs in the mechanical properties of dissimilar material joints. In this study, a cold spray-assisted brazing technique was proposed to significantly improve the strength of Cf/C-Nb brazed joints by fabricating a dense and uniform Ti-Co-TiC composite interlayer. Research indicates that TiC particles promoted the reconstruction of the brazing seam through heterogeneous nucleation and Zener pinning effects, effectively disrupting the continuous Ti2Co brittle network and constructing a strong-tough interpenetrating structure composed of a ductile β-Ti(s, s) and hard phases. The semi-coherent interfaces (lattice misfit of 6%–8%) formed between TiC and the β-Ti(s, s)/α-Ti phases were accompanied by significant localized strain gradients, leading to the enrichment of geometrically necessary dislocations (GNDs) nearby. This contributed to the accommodation of interfacial strain distribution. The dispersed TiC particles induced crack path deflection and branching by altering the local stress field, increasing energy dissipation during propagation. Combined with the plastic blunting effect of the ductile β-Ti(s, s) phase, a cross-scale synergistic strengthening was achieved. The peak shear strength of the Cf/C-Nb joints using the cold-sprayed interlayer reached 50.1 MPa, compared to 5.6 MPa for conventional powder-brazed joints. This study demonstrates the significant potential of cold spray-assisted brazing in regulating the performance of joints with extreme thermal expansion mismatches, offering a new microstructural construction strategy for high-performance brazed joints.

2219 aluminum alloy (AA2219) is widely used in aerospace structures due to its high strength and excellent corrosion resistance. However, welded joints often suffer from reduced corrosion resistance and compromised reliability due to issues such as elemental segregation, coarse grain structure, and high residual stresses. To enhance the corrosion resistance of welded joints, this study introduces the application of laser beam oscillation process control. The results indicate that oscillation significantly affects the weld solidification process, reducing copper segregation at grain boundaries, refining the grain structure, and promoting a uniform distribution of precipitates. It also alleviates micro-scale residual stresses and improves electrochemical uniformity. Corrosion tests demonstrate a significant improvement in resistance to pitting, intergranular corrosion, and micro-galvanic corrosion. These findings suggest that the combined effects of microstructural homogenization and residual stress regulation enhance the corrosion resistance of AA2219 welded joints, providing a foundation for their reliable service in aerospace applications.

The partitioning of strain and stress among constituent microstructures fundamentally determines the mechanical performance of dissimilar material brazed joints. However, the pronounced thermal expansion mismatch (triangle alpha approximate to 6.3 & times; 10-6/K) between Cf/C and Nb typically triggers severe interfacial stress concentration. This mismatch, coupled with the formation of brittle interfacial reaction products, severely impairs the strain accommodation within the joint. Here, a cold-sprayed Ti-Co filler is employed to braze Cf/C to Nb, spontaneously forming a gradient structure comprising a continuous beta-Ti(Nb, Co) band adjacent to Nb, a (beta + alpha + Ti2Co) multiphase network in the brazing seam, and a thin TiC reaction layer at the Cf/C interface. Continuous modulus-hardness transitions across the gradient layer eliminate interfacial stress singularities. Ti2Co accommodates strain via geometrically necessary dislocations, while ductile beta-Ti undergoes plastic deformation with efficient load transfer through the interpenetrating network. The coherent Ti2Co/alpha-Ti interface, with only 1.34% lattice mismatch, enables elastic self-accommodation without microcrack initiation. This multi-scale strain partitioning strategy yielded a peak shear strength of 36.0 MPa in Cf/C-Nb joints, providing a robust paradigm for joining dissimilar materials with high CTE mismatches.

Heterogeneous alloy designs can significantly enhance the mechanical properties of metallic materials through synergistic effects. In this work, the cold spray additive manufacturing (CSAM)-assisted brazing is proposed to significantly improve the mechanical properties of Cf/C and superalloy joint. The CSAM process promotes the atomic diffusion and metallurgical reaction between the interlayer and superalloy substrate. The findings indicate that the diffusion of Fe, Cr, Ni and Ti within brazing seam promotes the formation of a novel dual-phase heterogeneous structure, comprising a Cr-rich σ phase and a Ni3Ti phase. The σ and Ni3Ti dual-phase heterogeneous structure significantly improves shear strength through a synergistic strengthening mechanism, achieving an effective combination of strength and toughness. The ductile Ni3Ti phase enhances the deformation capacity, while the hard σ phase serves as a continuous barrier to dislocation movement, thereby significantly enhancing the mechanical properties of the brazed joint. The highest shear strength of the Cf/C and superalloy brazed joint reaches 20.9 MPa using a CSAM NiTi75 interlayer, compared to only 6.1 MPa for the joint brazed with conventional NiTi75 powder filler. This work demonstrates the significant potential of CSAM-assisted brazing to enhance the mechanical properties of brazed joints, offering a novel approach to directly prepare brazing interlayers from metal powders.

High-entropy ceramics (HECs) have attracted considerable interest due to their distinctive characteristics and promising applications. Developing reliable joining techniques is essential for facilitating their widespread application. In this study, a method for brazing high-entropy ceramic (Ti0.2Zr0.2Ta0.2Nb0.2Cr0.2)C using nickelbased fillers was proposed, and the microstructural changes and shear strength of the brazed joints were studied in detail. The brazing seam primarily consisted of Cr7Ni3, Cr23C6, and Ni(s,s). The interfacial bonding was mainly influenced by the formation of a Cr23C6 reaction layer and the diffusion of Ni into the HEC matrix. Notably, the diffusion of Ni induced a phase transformation from the original HEC to an HEC(Ni diffused) phase with a similar lattice structure. This study presented a novel approach to addressing the issues of inadequate wettability and subpar joint strength in brazing connections of high-entropy ceramics. This facilitated the formation of a semi-coherent interface with a reduced lattice mismatch at the Cr23C6/HEC interface on the highentropy ceramic side. Additionally, the favorable plastic deformation ability of Cr23C6 enhanced joint performance. Consequently, joints brazed at 1100 degrees C for 10 min achieved a maximum shear strength of 124 MPa.

Laser beam oscillation has demonstrated notable effectiveness in welding by modulating mass and heat transfer within narrow and deep molten pools. However, in laser cladding, which is characterized by a shallower and wider molten pool, the influence of oscillation patterns remains insufficiently understood. In this study, a threedimensional finite element model coupling temperature and fluid fields was developed to investigate the effects of five oscillation modes (non-oscillation, circular, infinity-shaped, longitudinal, and transverse) on the thermalfluid behavior and microstructural evolution of single-track Ni60 coatings. Simulation and experimental results indicate that oscillation-induced stirring expands the molten pool length and promotes a more uniform energy distribution, thereby mitigating local overheating. This effect helps establish a more stable melt flow, improves the geometric consistency of the cladding, and effectively suppresses spatter and hump-shaped formation defects. In addition, oscillation reduces the axial temperature gradient (G), while increasing the solidification rate (R), which favors the formation of equiaxed grains. Among all tested modes, circular oscillation produced the most stable melt flow and the most uniform thermal field. Compared with the non-oscillating mode, circular oscillation lowered the molten-pool peak temperature by approximately 1000 K, reduced the mean grain size by about 60 %, increased microhardness by roughly 45 %, and decreased the average friction coefficient by about 17 %. It should be noted that microstructural evolution in the cladding layer is primarily governed by the thermal history, whereas oscillation-induced shear forces have a pronounced effect on layer formation and defect suppression. These findings highlight laser beam oscillation, particularly the circular mode, as a promising strategy for tailoring melt dynamics, controlling solidification pathways, and enhancing the structure-property relationships in high-performance laser-cladded coatings.

Conventional brazing requires prolonged heating to form joints, which often results in a continuous brittle intermetallic layer that can initiate microcracks. Moreover, heating the entire workpiece induces substantial thermal stress and deformation, leading to detrimental residual stresses that impair joint performance. To address these limitations, this study adopts electric field-assisted brazing (EFAB), which utilizes pulsed electric current to generate Joule heating and electromigration effects, enabling rapid and efficient bonding at shorter processing times. EFAB was developed to join Ti2AlNb and Ti60 alloys at 900 degrees C within < 1 s using a Ti-Zr-Ni-Cu-Co-Nb amorphous filler under 150 V/135 A/mm(2). Compared to conventional brazing (15 min dwell), EFAB eliminates brittle (Ti, Zr)(2)(Cu, Ni) intermetallics through a uniform distribution of brittle elements driven by electromigration and concentration gradients, forming defect-free brazing seams comprising alpha-Ti + alpha '-Ti martensite (Ti60 side), alpha '-Ti martensite (brazing center), and alpha + beta duplex (Ti2AlNb side). Finite element simulations confirm EFAB reduces residual stress by 83 % via rapid Joule heating and alpha '-twinning. Interfacial electronic analysis reveals that the alpha-Ti/beta-Ti interface exhibits remarkable charge accumulation and symmetric decay in differential charge density profiles, along with continuous transitions and robust orbital hybridization in the projected density of states. Additionally, it demonstrates an 8.7 % enhancement in separation work, with values reaching 0.3393 eV/& Aring;(2) compared to 0.3123 eV/& Aring;(2) (Ti2Cu/alpha-Ti). These properties enable a semi-coherent alpha-Ti/beta-Ti interface (22.4 % mismatch) versus incoherent Ti2Cu/alpha-Ti (58.6 %). Consequently, EFAB joints achieve 221.9 MPa shear strength (30 % higher than conventional joints) with ductile fracture, demonstrating high-efficiency dissimilar joining of advanced titanium alloys. (c) 2026 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

High-performance powder metallurgy materials are ideal for fabricating complex aerospace components, owing to their near-net-shape forming and exceptional mechanical properties. This work first systematically investigated the vacuum brazing of powder metallurgy CuCrNb (PM-CCN) alloy and 304 stainless steel (304SS) with AgCuIn filler metal. It focused on the effect of modulating brazing temperatures from 750 to 780 degrees C on the microstructure and mechanical properties of the brazed joints. Joints formed at 750 to 770 degrees C exhibited a multilevel heterostructure, which includes grain size gradient and a soft-hard-soft structure of phase hardness and modulus, consisting of coarse-grained Ag-Cu eutectic zone, (Cr, Fe)2Nb-strengthened reaction layers and finegrained filamentary penetration zone, while excessive base metal dissolution and shrunken brazing seams occurred at 780 degrees C. The shear and tensile strengths first increased and then decreased with temperature, reaching maximum values of 227.04 MPa and 205.44 MPa at 760 degrees C, respectively. The superior performance was attributed to hetero-deformation induced (HDI) strengthening, as well as solid-solution and dispersion strengthening of (Cr, Fe)2Nb. Microstructural finite element method (micro-FEM) revealed high stress gradients around heterogeneous interfaces and hard (Cr, Fe)2Nb particles. This study supports the brazing of powder metallurgy materials and the fabrication of aerospace composite components.

2219 aluminum alloy (AA2219) is widely used in aerospace structures due to its high strength and excellent corrosion resistance. However, welded joints often suffer from reduced corrosion resistance and compromised reliability due to issues such as elemental segregation, coarse-grain structure, and high residual stresses. To enhance the electrochemical corrosion resistance of welded joints, this study introduces the application of laser beam oscillation process control. The electrochemical corrosion behavior of the joints was comprehensively evaluated through a combination of electrochemical measurements (potentiodynamic polarization and EIS) and corrosion morphology observations. The results indicate that the ‘Line’ shaped oscillation significantly governs the microstructural evolution induced by oscillation-facilitated grain refinement during weld solidification, reducing the average grain size from 28.1 μm to 16.7 μm and decreasing the transverse residual stress from 128.6 MPa to 41.5 MPa (a 67% reduction). Electrochemical measurements show that the linear-oscillated joint achieves a polarization resistance (Rf) of 7023 Ω·cm2, more than double that of the non-oscillated joint (3379 Ω·cm2), while the Volta potential difference decreases to only 0.053 V compared to 0.110 V for the non-oscillated joint. Morphological observations reveal that the non-oscillated joint suffers from severe continuous intergranular cracking and catastrophic exfoliation, whereas the linear-oscillated joint maintains a smooth and intact surface. These improvements are attributed to the ‘solute trapping’ effect induced by the high-velocity melt flow, which facilitates uniform Cu distribution and thereby reduces the driving force for micro-galvanic corrosion.

Reliable brazing of Ti2AlNb to Ti60 alloy is critical for advanced hypersonic vehicles but remains challenging due to the formation of brittle intermetallics containing Cu and Ni. A novel Cu/Ni-free Ti-25Co-8Fe-5Sn (at. %) amorphous filler, developed independently, was compared with conventional Ti-Zr-Cu-Ni-based fillers. Multiscale characterization combined with first-principles calculations revealed the microscopic origins of performance differences between the joints. The Ti-Co-Fe-Sn amorphous filler exhibits an exceptionally low surface energy (0.0570 eV/Å2), requiring only 20–30 °C of superheat to achieve excellent wettability and spreading behavior, thereby resulting in defect-free joints. Microstructural analysis reveals a “tough α-Ti matrix + discretely distributed bulk Ti3Sn and strip-like Ti2(Co, Fe) hard phases” architecture. The key α-Ti/Ti3Sn interface was semi-coherent (lattice mismatch 21.1%) and achieved strong bonding through intense Ti-d and Sn-d orbital hybridization, with an interfacial separation work of 0.3248 eV/Å2, 5.8% higher than that of the reference interface. Consequently, the Ti-Co-Fe-Sn brazed joint achieved a room-temperature shear strength of 247.7 MPa, ~46% higher than conventional joints, along with significantly improved fracture toughness. This study provides a design strategy and theoretical foundation for developing novel filler systems for high-performance titanium alloy brazing.

2219 aluminum alloy (AA2219) is widely used in aerospace structures due to its high strength and excellent corrosion resistance. However, welded joints often suffer from reduced corrosion resistance and compromised reliability due to issues such as elemental segregation, coarse-grain structure, and high residual stresses. To enhance the corrosion resistance of welded joints, this study introduces the application of laser beam oscillation process control. The results indicate that oscillation significantly affects the weld solidification process, reducing copper segregation at grain boundaries, refining the grain structure, and promoting a uniform distribution of precipitates. It also alleviates micro-scale residual stresses and improves electrochemical uniformity. Corrosion tests demonstrate a significant improvement in resistance to pitting, intergranular corrosion, and micro-galvanic corrosion. These findings suggest that the combined effects of microstructural homogenization and residual stress regulation enhance the corrosion resistance of AA2219 welded joints, providing a foundation for their reliable service in aerospace applications.

Interface residual stress concentration is one of the key factors limiting the mechanical reliability of ceramic/metal brazed joints. Etching subtractive micro-scale structures on ceramic surface can be used to modulate residual stress in brazed joints; however, micro-scale structures designed via the ”subtractive” approach share the same composition as the ceramic matrix, resulting in a significant thermal expansion mismatch between the joint components. This study investigates brazed joints between ZrO2 and GH536. By introducing additive micro-scale structures with designable material properties, multiple regulatory effects are achieved: these micro-scale structures not only interrupt continuous stress transmission on the ceramic side and promote the redistribution and transfer of residual stress but also alleviate thermal mismatch in the joint through a low coefficient of thermal expansion (CTE) phase, thereby significantly enhancing the mechanical performance of the joint. This work provides a new strategy for interface design in ceramic/metal brazed joints and offers a generalizable approach for residual stress management and performance optimization in dissimilar brazed components.

The rapid development of modern railways imposes higher requirements on the welding quality of seamless rails, and linear friction welding (LFW) is expected to become a preferred welding method. In this study, LFW experiments and finite element simulations were conducted on scaled-down U75V rail specimens to systematically reveal the microstructural and mechanical evolution and the underlying thermo-mechanical coupling mechanisms of the rail-profile joint. Experimental results indicate that the joint exhibits significant heterogeneity: the welding process leads to complete austenitization of the interface, and rapid cooling post-weld causes the weld zone (WZ) to transform into a mixed microstructure of martensite and pearlite. The thermo-mechanically affected zone (TMAZ) undergoes partial dynamic recrystallization, predominantly consisting of fine pearlite. Furthermore, the hardness and tensile strength distributions across the rail head, web, and base differ significantly, and the intricate plastic flow induced by the complex cross-section makes the joint susceptible to local unbonded defects. Finite element simulations confirm that the differences in thermal cycles, caused by the severely uneven distribution of the interfacial temperature field, are the fundamental cause of the microstructural heterogeneity. Meanwhile, the significant stress concentration near the interface at the rail head and base explains the local deterioration of mechanical properties. Based on the aforementioned mechanisms, this study clarifies the regulation direction for process parameters, providing a theoretical and empirical basis for exploring the engineering application of LFW in seamless rails.

Brazing carbon fiber reinforced carbon matrix composites (Cf/C) to metals remains a core technological challenge in manufacturing high-temperature composite components for aerospace applications. Although traditional active brazing filler metals can achieve good wetting of the composites, uncontrolled interfacial reactions on the Cf/C side lead to the formation of continuous brittle phases, and large residual stress undermine the reliability of the joint. In this study, a self-prepared face-centered cubic (FCC) FeCoNiAlCuTi high-entropy alloy was used as the brazing filler metal. The aim was to exploit its high mixing entropy to suppress the formation of a continuous brittle phase at the Cf/C interface. Experimental results showed that the brazed seam forms a multi-layered structure, mainly composed of the Cf/C side reaction zone, the Nb solid solution banded zone, and the eutectic zone. No continuous brittle layer formed at the Cf/C side interface, and a gully-shaped interlocking interface was formed with the FeCoNiAl ductile phase. This strategy transfers part of the joint stress to the internal FCC phase. Finite element simulations indicated that the peak Mises stress was reduced from 371 MPa to 274 MPa. Under the optimal brazing parameters of 1340 ℃ for 20 min, the shear strength of the joint reaches 40.7 MPa. Briefly stated, this study alleviated the initiation and growth of brittle reactive layers at the interface of Cf/C composites, providing important support for the development of high-performance bonding processes for Cf/C composites and facilitating their practical application in high-temperature aerospace components.

Continuous brittle carbide layers formed at Cf/C and braze interfaces have long constituted a critical microstructural bottleneck to achieving mechanically reliable brazed joints. Their low intrinsic deformability and severe thermomechanical mismatch at heterogeneous interfaces induce local stress concentration and crack initiation, degrading joint integrity under harsh service conditions. This work presents a novel brazing approach for Cf/C composites, employing rapid solidification after Joule heating to trap carbides and suppress the formation of brittle interfacial reaction layers. Microstructural characterization demonstrates a contrast with conventional furnace brazing. Cr-C exhibits a fine needle morphology and TiC displays a band morphology. These carbides disperse homogeneously within the brazed seam of the joint developed in this work. The continuous and intact face-centered cubic (FCC) solid solution replaces the brittle interfacial reaction layer at the composite and brazing seam interface, effectively eliminating microstructural defects in the brazed joint. Mechanical test results show that the average shear strength of joints fabricated with optimal processing parameters reaches 42.21 MPa, an increase of 56.97% compared with conventional furnace-brazed joints. The finite element analysis (FEA) results show that the rapid solidification strategy reduces the peak stress of the joint by 39% by changing the spatial distribution of the carbides in the brazed joint. These results further confirm that the optimized interfacial microstructure contributes significantly to the improved mechanical performance of brazed joints. This work presents a feasible strategy for controlling the growth and spatial distribution of carbides and offers a new reference for optimizing composite material joining technologies.

Reliable brazing of Ti2AlNb to Ti60 alloy is critical for advanced hypersonic vehicles but remains challenging due to the formation of brittle intermetallics containing Cu and Ni. A novel Cu/Ni-free Ti-25Co-8Fe-5Sn (at. %) amorphous filler, developed independently, was compared with conventional Ti-Zr-Cu-Ni-based fillers. Multiscale characterization combined with first-principles calculations revealed the microscopic origins of performance differences between the joints. The Ti-Co-Fe-Sn amorphous filler exhibits an exceptionally low surface energy (0.0570 eV/& Aring;(2)), which reduces the thermodynamic barrier for wetting and spreading, enabling defect-free joints with only 20-30 degrees C of superheat. Microstructural analysis reveals a "tough alpha-Ti matrix + discretely distributed bulk Ti3Sn and strip-like Ti-2(Co, Fe) hard phases" architecture. The key alpha-Ti/Ti3Sn interface was semi-coherent (lattice mismatch 21.1%) and achieved strong bonding through intense Ti-d and Sn-d orbital hybridization, with an interfacial separation work of 0.3248 eV/& Aring;(2), 5.8% higher than that of the reference interface. Consequently, the Ti-Co-Fe-Sn brazed joint achieved a room-temperature shear strength of 247.7 MPa, similar to 46% higher than conventional joints, along with significantly improved energy absorption capability. This study provides a design strategy and theoretical foundation for developing novel filler systems for high-performance titanium alloy brazing.

Zr-4 alloys exhibit limited oxidation resistance at elevated temperatures, severely restricting their use in extreme environments. High-entropy ceramics (HECs), owing to their exceptional thermal stability and oxidation resistance, have emerged as promising candidates for protective cladding applications. However, reliable joining techniques and a comprehensive understanding of the interfacial phenomena between HECs and Zr-4 alloys are still lacking. In this study, reliable HEC/Zr-4 joints were successfully fabricated via reactive brazing using a pure Ni interlayer. Optimal joining of HEC and Zr-4 was achieved at 1100 degrees C for 10 min, forming a microstructure of HEC/TaC + ZrC/Zr2Ni + Zr(s, s)/Zr-4. A continuous ZrC layer effectively alleviated thermal expansion mismatch, achieving high shear strengths of 118 MPa at room temperature (RT) and 109 MPa at 800 degrees C. Oxidation tests demonstrated that residual Ni at the interface facilitated the formation of a compact oxide layer, which significantly suppressed oxygen ingress. After oxidation at 900 degrees C for 4 h, the joints retained 90 % of their initial shear strength, indicating excellent high-temperature stability and oxidation resistance.

Precise control of interfacial metallurgy is a critical challenge in brazing powder metallurgy CuCrNb (PM-CCN) for aerospace applications. An interfacial engineering strategy using AgCu filler with an amorphous BNi2 barrier layer was proposed. The effects of holding time (10-25 min) at 940 degrees C on microstructural evolution and mechanical properties of PM-CCN/304 stainless steel (304SS) joints were systematically investigated. Results indicated that direct brazing led to full penetration of the AgCu filler into the PM-CCN matrix, forming an uncontrolled mixed zone with a maximum depth of 313.4 mu m at 25 min. Conversely, the BNi2 barrier induced an in-situ composite layer consisting of gamma-Ni and CrB intermetallic compounds (IMCs), accompanied by a Ni-Cu solid-solution layer. This reaction-derived architecture effectively suppressed excessive filler diffusion and stabilized the seam width within 160.7-163.8 mu m. Consequently, the BNi2-added joint achieved a peak shear strength of 233.14 MPa at 10 min, representing a 28.8% increase over the direct-brazed counterpart. Prolonging the holding time to 25 min, however, triggered barrier disintegration due to excessive Ni diffusion, shifting the fracture path from the ductile Ag-Cu seam back to the disordered penetration zone. This fracture mode transition, driven by the loss of barrier integrity, significantly degraded the mechanical properties. Overall, this study clarifies the underlying regulation mechanism and provides a theoretical foundation for high-reliability aerospace brazing.

A novel strategy combining cold spray additive manufacturing (CSAM) with brazing was developed to overcome particle agglomeration and enhance the mechanical properties of SiCf/SiC composite joints. Cu-Ti-TiC composite interlayers with different TiC volume fractions were fabricated via CSAM, and their effects on microstructure evolution and shear strength of the brazed joints were systematically investigated. A comparative analysis between CSAM-assisted brazing and conventional powder brazing was conducted, and the formation mechanism of the brazed joint was elucidated. Experimental results demonstrated that CSAM facilitated the uniform distribution of TiC particles within the brazing seam, effectively preventing the agglomeration defects commonly observed in conventional brazing. Notably, when the TiC volume fraction in the spray powder reached 40%, the brazed joints exhibited a shear strength of 81.3 MPa, significantly surpassing the 28.3 MPa of conventional powder-brazed joints. During brazing, controlled interfacial metallurgical reactions generated dispersed TiSi2 second-phase particles. These particles synergistically interacted with TiC, suppressing grain coarsening in the brazing seam and substantially enhancing the overall mechanical performance of the joints. This work provides a new technical route for optimizing the brazing process of ceramic matrix composites, offering both experimental and theoretical insights for designing high-performance composite brazing interlayers.