Brazed Joints Research Articles

Effect of SiC particles on microstructure and mechanical properties of SiCp/AZ91 magnesium matrix composite brazed joint

Effect of SiC particles on microstructure and mechanical properties of SiCp/AZ91 magnesium matrix composite brazed joint

Application of energy, electronic and interface bonding properties in highly reliable brazing joints between dissimilar materials

Application of energy, electronic and interface bonding properties in highly reliable brazing joints between dissimilar materials

Analysis of High and Low Temperature Performance of Titanium Zirconium Molybdenum Alloy and High Temperature Alloy Brazed Joint

Abstract Using niobium as the intermediate layer and gold nickel (Au82-Ni) filler metal, TZM alloy and high-temperature alloy GH3128 were brazed. The brazed specimens were subjected to 400 cycles of high and low temperature cycling tests at temperatures ranging from 650 °C ∼ 680 °C (high temperature) to -196 °C (low temperature) for 10 minutes seperately. Then the microstructure variation before and after the experiment were observed and the shear strength of the specimens were tested at room temperature for 50 cycles of 400 high and low temperature testing.. The results show that the microstructure of the transition zone at the brazing interface after brazing is uniform and dense, with good wettability with the substrate and no defects such as cracks. The solder and substrate undergo diffusion reactions, and the molybdenum alloy, niobium, and niobium, high-temperature alloy had each form diffusion layers, formed intermetallic compounds on the brazing surface. After high and low temperature cycling, cracks exist in the braze seam between molybdenum alloy and niobium alloy. The cracking mode should be thermal fatigue based on the fracture morphology and phase analysis. The reasons of interface cracking are that due to different thermal expansion coefficients, low mutual solid solubility, and the formation of a large number of different types of intermetallic compounds, Mo and Nb materials have poor brazing compatibility and lower interface strength. Under cold and hot cycling conditions, brittle intermetallic compounds are prone to form crack source areas. As the number of cycles increases, the cracks gradually expand, ultimately leading to product leakage. In addition, the shear strength of brazed joints shows a decreasing trend with the increase of high and low temperature cycles in 400 high and low temperature tests.

Dispersion, solid solution, and covalent bond coupled to strengthen K4169/TiAl composite brazed joints: First-principles and experimental perspective

Ni/TiAl composite brazed joints could significantly reduce the aircraft's weight. However, low interfacial adhesion, coarse and brittle-hard intermetallic compounds (IMCs) seriously limited the application of Ni/TiAl composite joints in the next generation of aerospace applications. So enhanced K4169/TiAl composite joints were investigated by vacuum brazed with (Ni53.33Cr20B16.67Si10/Zr25Ti18.75Ta12.5Ni25Cu18.75) composite filler metal (CFM) designed based on cluster-plus-glue-atom model. The shear strength of the joint reached 485 MPa, comparable to the 491 MPa of TiAl substrate. The flat and brittle-hard diffusion reaction layer between Zones I and II was eliminated, simultaneously generating CrB4 dispersion strengthening due to the CFM developed with the interfacial solid-liquid space-time hysteresis effect. In Zones II and III, IMCs all transformed into Niss(Cr,Fe)[0–88], Niss(Ti, Al)[004], and Niss(Zr,Si)[11–2] of circular and oval shapes through isothermal solidification. Meanwhile, the residual stresses and hardness were distributed in reticulated cladding characteristics. Thereby, lattice distortion led to solid solution strengthening and increased plastic toughness through crack termination and bridging mechanisms, which inhibited dislocations from plugging and crack propagation. Various interfaces in Zone Ⅳ were regulated into semi- and coherent interfaces. Ni3(Ti,Al)/(Ni,Ti,Al) and (Ni,Ti,Al)/AlNi2Ti were composed of higher interfacial bonding energy (2.771 J/m2, 2.547 J/m2) and Ni-Ni covalent bonds. Interfacial covalent bonding and large interfacial bonding energy coupling strengthened Zone IV. Consequently, cracks initiated at the (Ni,Ti,Al)[013]/Ti3Al[010] and expanded rapidly into TiAl substrate. Therefore, applying this method to design CFMs and regulate the phase, grain morphology, and interface's fine structure could provide new pathways for dissimilar hard-to-join metals.

Exploring bonding temperature variations in diffusion brazing of B4C ceramics with Ni-Cr-Si-Fe-B interlayer: Mechanical and microstructural analysis

This study examines the impact of the bonding temperature parameter on the quality of diffusion brazing joints of B4C ceramics using a Ni-Cr-Si-Fe-B interlayer. Various factors including shear strength, hardness, microstructure, interfacial phenomena, elemental diffusion patterns, formed compounds and phases, and fracture surfaces of the samples were analyzed and compared. The brazed sample at 1110 °C for 1/2 h exhibited the highest shear strength of 62 MPa. Increase of the bonding temperature to the optimum level (1090–1110 °C) enhances the fluidity of the molten interlayer, facilitating its diffusion into the porosities of the ceramic components. This increase also promotes higher interactions within the system, creating favorable conditions for element diffusion. However, surpassing the optimum temperature (1110–1130 °C) may lead to increased destructive reactions and intensify the impact of the coefficient of thermal expansion (CTE) mismatch, resulting in residual stresses and a subsequent decrease in bond strength. The excessive increase in the bonding temperature (1130–1150 °C) can lead to the excessive fluidity of the molten interlayer, potentially causing effusion onto the joint's fixture and damaging the samples. The results indicate the formation of various compounds between the elements of the interlayer and carbon and boron elements, including SiC, Ni4B3, CrB2, Fe2B, Ni6Si2B, and B2Fe3Ni3, at the fracture surface of the sample bonded at 1110 °C. The more substantial peaks of these compounds, compared to other samples, could be a reason for the higher strength of this particular sample.

Effect of foam interlayer thickness and pore size on the microstructure and properties of brazed joints

Ni foam was introduced as an interlayer to improve the performance of the brazed C/C composite-TC4 titanium alloy joint, and high-quality brazed connections of c/c composites and TC4 were realized. Compared to a brazing joint without foam, the introduction of a foam Ni interlayer can achieve a more uniform bonding interface. The effects of the thickness and pore size of the foam Ni interlayer on the microstructure, mechanical properties and residual stresses of the joints were investigated. With increasing thickness and pore diameter, Ag-based solid solutions and Ti–Cu intermetallic compounds first become more dispersed and smaller at the center of the brazed joints, and then aggregate to become larger. The brazed interface microstructure with a 0.4 mm thick foam Ni interlayer with a pore size of 0.5 mm was more uniform, and the shear strength of the joint reached 21.23 MPa, representing an 85.96 % increase compared to the joint without the foam Ni interlayer. The residual stress and its distribution calculated by finite element method (FEM), and the residual stress of the brazed joint decreased from 467 MPa/-289.53 MPa to 457.96 MPa/-234.98 MPa. These results indicated that the Ni foam could act as a buffer layer to reduce the residual thermal stress, and improve the mechanical properties of C/C composite-TC4 titanium alloy joint.

Effect of different joining temperatures on IN600/SiC brazed joints

IN600 superalloy and SiC ceramics has been conducted using an active AgCuTi filler, and the composite joints were characterized using scanning electron microscopy coupled with energy-dispersive x-ray spectrometry (SEM–EDS). The results demonstrate successful joining by carefully selecting brazing temperatures and holding times to produce high-integrity joints. The interfacial microanalysis revealed the formation of TiC and Ti5Si3 near the SiC side due to the reaction between titanium, carbon, and silicon. On the IN600 superalloy side, a Ti-Ni compound (TiNi3) was formed as a result of titanium reacting with nickel. The typical microstructure of the brazing joint interface includes: TiC+TiNi3, TiC, Cu(s,s)+Ag(s,s) and TiC+Ti5Si3. Furthermore, the shear strength evaluation of the joints was also conducted at ambient temperatures using a shear test. The experimental findings showed that the sample exhibited the highest shear strength (38 MPa) when subjected to brazing at 910 °C for 10 min. Fracture occurred at the interface between the base material and AgCuTi filler at higher brazing temperature (930 °C).

Effect of brazing temperature on microstructure and tensile strength of γ-TiAl joint vacuum brazed with micro-nano Ti−Cu−Ni−Nb−Al−Hf filler

A novel micro-nano Ti−10Cu−10Ni−8Al−8Nb−4Zr−1.5Hf filler was used to vacuum braze Ti−47Al− 2Nb−2Cr−0.15B alloy at 1160−1220 °C for 30 min. The interfacial microstructure and formation mechanism of TiAl joints and the relationships among brazing temperature, interfacial microstructure and joint strength were emphatically investigated. Results show that the TiAl joints brazed at 1160 and 1180 °C possess three interfacial layers and mainly consist of α2-Ti3Al, τ3-Al3NiTi2 and Ti2Ni, but the brazing seams are no longer layered and Ti2Ni is completely replaced by the uniformly distributed τ3-Al3NiTi2 at 1200 and 1220 °C due to the destruction of α2-Ti3Al barrier layer. This transformation at 1200 °C obviously improves the tensile strength of the joint and obtains a maximum of 343 MPa. Notably, the outward diffusion of Al atoms from the dissolution of TiAl substrate dominates the microstructure evolution and tensile strength of the TiAl joint at different brazing temperatures.

Strengthening Ti3SiC2/Cu brazed joint assisted with cold spray additive manufacturing: Lower brazing temperature through interdiffusion and graded reinforcement for stress relaxation

Graded composite fillers exhibit unique advantages in alleviating residual stress in ceramic/metal brazed joints. However, traditional methods for preparing graded composite fillers are often complex and may deplete their strengthening phases. In this study, cold spray additive manufacturing was employed to fabricate yttria-stabilized zirconia (YSZ)-Ti25Zr25Ni25Cu25-Ag graded composite coatings on Cu substrates to serve as fillers. The graded composite coatings and the resultant Ti3SiC2/Cu brazed joints were systematically characterized to elucidate the deposition mechanism of the coatings and its residual stress-relaxed mechanism. The bondings between particles in the coatings, based on their plastic deformation ability, were classified into noncrystalline weak bonds and homogeneous strong bonds. Both bondings facilitated the elemental interdiffusion between filler and Cu substrate during the heating process, which contributed to the formation of Ag-Cu eutectic. This significantly reduced the required brazing temperature and its induced residual stress. Furthermore, the solid phase transformation of graded-distributed YSZ within the brazing seam from tetragonal to monoclinic achieved a smooth thermal transition and releasing residual stress at the same time. Consequently, the shear strength of the brazed joint reached to the highest value of 110.23 ± 3.45 MPa, which was Much higher than the previously reported values. This study introduces a novel method for residual stress relaxation assisted with cold spray technology and broadens its application in the brazing field.

Electrophoretic deposition of CNTs on a Cu foam interlayer for enhancing Cf/SiC–Nb brazed joint performance

The high residual stress and low toughness of ceramic matrix composite/metallic brazed joints poses severe challenges for the stable operation of high-speed aircraft under harsh conditions. This article innovatively tackles this issue with electrophoretic deposition (EPD), creating a CNT covered Cu foam composite interlayer for brazing Cf/SiC and Nb with an Ag–Cu–Ti alloy filler. A layer of mass ratio-controllable and percolated CNTs was physically adsorbed on the surface of the Cu foam substrate. EPD time was systematically investigated for its impact on the microstructure and mechanical properties of the joints. Results indicate that during brazing, the CNTs reacted with the active Ti element, transforming into ultrafine TiC grains with particle sizes ranging from 6 to 16 nm. These were dispersed evenly in the Ag solid solution. The elastic recovery rate of the cluster regions showed an increase of 123 % compared to the Ag solid solution, showing improved toughness of the seam. When the EPD time was 80 min, the shear strength of the joint produced with the composite interlayer reached 128.6 MPa, a 69 % increase over the directly brazed joint. Moreover, the fracture location of the joint shifted from the brazed seam towards the interior of the bulk Cf/SiC. Additionally, finite element analysis was utilized to confirm a significant decrease in residual stresses within the joint, and verified the findings.

Modal analysis for the non-destructive testing of brazed components

Abstract In brazing processes, the formation of defects within the brazing joint due to deviations in brazing process and material is a recurring problem. These affect the component quality as well as the component properties. In this study, modal analysis is fundamentally investigated as a potential tool for non-destructive testing of brazing joints as well as for fast quantification of the precision of the brazing process. The aim of the investigation is to detect defects in brazed components. For this purpose, test specimens in defect-free and defect-containing form are brazed by means of a high-vacuum furnace. The subsequent recording and real-time analysis of the oscillation behavior of these test specimens is to be used to evaluate the quality of these brazed joints. A method, developed specifically for this purpose, automatically evaluates the recorded oscillation profile based on several defined frequency positions. For the first time, the results show that a reproducible classification of brazing seam quality into OK and not-OK can be made by comparing several frequency positions with already known oscillation profiles.

Interfacial morphology and reliability of GaN nanocomposite Sn-Ag-Cu lead-free braze joints

Interfacial morphology and reliability of GaN nanocomposite Sn-Ag-Cu lead-free braze joints

Effect of Ti content on microstructure and properties of Cu/AgCuTi/Al2O3 brazed joints

In this study, four groups of Ag-Cu-Ti brazing powder with different Ti contents of 2 wt%, 3 wt%, 3.75 wt% and 4 wt% were prepared by vacuum atomization, and then modulated into brazing pastes. Brazing between oxygen-free copper and alumina ceramics with the brazing pastes and the wettability experiments of the brazing pastes on alumina were done by vacuum brazing process at 880℃ for 30 min. Microstructures and wettability of both the braze alloy and joints were analyzed by scanning electron microscope, energy dispersive X-ray spectrometer and transmission electron microscope, and shear strength of the joints was tested by self-designed fixture. Based on thermodynamic calculation and kinetic analysis, the relationship between the products of the reactive layer and the change of Ti content was plotted to explore the reaction and wetting mechanism of AgCuTi braze alloy on alumina ceramics. The results show that the content of Ti in AgCuTi braze alloy is the main factor affecting the brazing performance and wettability of the braze alloy by affecting the products of AgCuTi/Al2O3 reaction layer. The reaction layer consists of TiO when the Ti content is 2 wt%, the reaction layer comprises of TiO and Ti3Cu3O when the Ti content is 3 wt%, the reaction layer is made up of Ti3O2 and Ti3Cu3O when the Ti content is 3.75 wt%, and the reaction layer consists entirely of Ti3Cu3O when the Ti content is 4.6 wt%. With the increase of the Ti content within the range of 2–4.6 wt%, the wettability of the braze alloy on the alumina ceramics improved, and the shear strength of the Cu/AgCuTi/Al2O3 joints increased.

Optimizing Interfaces in Laser-Brazed Ceramic-Stainless Steel Joints for Hydrothermal Sensors through Finite-Element Modeling

The development of reliable joining techniques for ceramics and metals is crucial for energy applications, such as fuel cells, nuclear reactors, and high-temperature sensors, most especially for the sealing of hydrothermal sensors to study multiphase flows. However, during one-step active laser brazing it is a serious problem that a high thermal stress concentration can occur at the joint interfaces or on the ceramic side of the joint due to mismatches between the CTEs (coefficients of thermal expansion) and/or elastic constants. The uncontrolled thermal residual stress can lead to cracks and defects in the brazement. In the present work, an elastoplastic finite element method/numerical model was formulated to study the thermal residual stresses developed in the brazement between ceramics and austenitic stainless steel during cooling in active laser brazing. Calculations and comparison experiments were conducted to validate the simulated stress distribution in un-patterned ceramics. Stress analyses were conducted for planar and cylindrical specimen geometries (lab joints) relevant for miniaturized energy sensors. Laser interface patterning was employed to create micro-scale features on ceramic interfaces that reduce thermal stress concentrations. The optimization of the interface designing parameters including hatch size, structure width, pattern depth and metal/ceramic thickness ratio was performed using the Taguchi method with orthogonal arrays. The study suggests that laser interface structuring can modify thermal residual stresses in ceramic-to-metal brazements, thereby increasing the reliability of active brazing joints.

Dual optimization of energy-absorbing intermediate layer for diversified enhancement of heterogeneous brazed joints

Dual optimization of energy-absorbing intermediate layer for diversified enhancement of heterogeneous brazed joints

Microstructure and Mechanical Properties of Electrically Assisted Brazing Joints of Dissimilar Aluminum and Steel Alloys

The microstructure and mechanical properties of electrically assisted brazing (EA-brazing) joints of aluminum alloy 6061-t6 (AA6061-t6) and S45C steel are experimentally investigated. During the EA-brazing process, an electric current is directly applied to the cylindrical specimen assembly (S45C and AA6061-t6) and fillers of 88% Al and 12% Si (in the middle of the specimen assembly). The temperature of the specimen assembly rises rapidly to the melting point of the filler and remains nearly constant for a period of time using a pulsed electric current. Two types of EA-brazing joints are fabricated, namely Joint-0s (no temperature holding time) and Joint-12s (12 s temperature holding time). The characteristics of the intermetallic compounds (IMCs) formed at the EA-brazing joint interface are analyzed using scanning electron microscopy and energy dispersive spectrometer. Compared to Joint-0s, the Fe-rich IMCs (FeAl) are observed at the interface of Joint-12s due to the 12 s temperature holding time. In addition, the microstructural analysis shows that the thickness of the diffusion layer increases with increasing temperature holding time. The mechanical properties of the EA-brazing joints are evaluated using bending tests. The results of the mechanical test show that the strength of Joint-12s is higher than that of Joint-0s.

Microstructure and Mechanical Properties of Ti-Based Amorphous Solder Vacuum Brazing Joint for Stainless Steel

Microstructure and Mechanical Properties of Ti-Based Amorphous Solder Vacuum Brazing Joint for Stainless Steel

Microstructural and mechanical characterizations of SiC–304SS joints brazed with Cu–10TiH2 filler

A high-quality brazed joint of SiC ceramic and 304 stainless steel (SiC–304SS) was achieved by Cu–10TiH2 brazing alloy. The effects of brazing temperature on the interfacial microstructure and mechanical properties of SiC–304SS were analyzed. The typical interfacial microstructure of joints brazed at 1030 °C for 10 min was 304SS/σ-phase/(Fe, Cr) Ti/Fe2Ti/Cu(s,s) + Fe2Ti + TiC/SiC ceramic. With the brazing temperature increasing, the element Fe continued diffusing into the brazing seam and reacted with the element Ti. Then the width of σ-phase and the amount of Fe2Ti phase became increasing, and Fe2Ti phase became continuous. While, due to the reaction between Fe and Si, a buffer layer formed in SiC–304SS joints brazed at 1040 °C and 1050 °C. The main component of the buffer layer was FeSi2, TiC phases and carbon particles. In addition, the buffer layer contributed to forming a good gradient transition of coefficient of thermal expansion (CTE), releasing residual stress and improving shear strength of the joints. When brazing at 1050 °C for 10 min, the maximum shear strength of the joint was 100 MPa at room temperature and 53 MPa at 600 °C.

Brazing of sintered iron to mild steel for wind turbine brake pad applications

The demand for renewable energy has prompted an increasing interest in wind turbine technology, where efficient and reliable brake systems play a critical role in ensuring safety and performance. This study investigates the brazing process to join sintered iron to mild steel for wind turbine brake pad applications. The sintered iron components were synthesized using iron powder with an average particle size of 30 µm and sintered at different temperatures under vacuum and hydrogen environments. Eutectic CuSil with added copper powder was employed as the brazing alloy to join the sintered iron and mild steel. The brazed joints were characterized using various techniques, including optical microscope, scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffractometer, and microhardness tester. The microhardness of the sintered iron was ∼580 HV for SICV and ∼620 HV for SICH due to oxide formation during processing. The microhardness of the braze joint was 72 HV, and mild steel exhibited 110 HV. Tribological testing was performed to analyze the wear behavior of the sintered iron specimens (before and after the brazing). SICH specimens showed a wear rate of 1.3 × 10−4 g/Nm, and SICV specimens exhibited a wear rate of 5.3 × 10−4 g/Nm. Brazing the sintered iron component (SICV) with mild steel using eutectic CuSil and a modified assembly method in a vacuum successfully achieved a satisfactory joint with improved wear resistance. The study emphasizes the potential of this approach for efficient and reliable brake pad fabrication for wind turbines.

A new strategy of Al0.1CoCrFeNi high entropy alloys and Inconel 625 alloys joining technology

A new strategy that utilizes the nano-multilayer foils with a high-entropy design as the filler metal to join the Al0.1CoCrFeNi and Inconel 625 alloy dissimilar materials was proposed, which provides theoretical and technical guidance for the development of aerospace technology and nuclear power. The coexistence of the nano-multilayer foils with a high-entropy design was envisaged to improve the role of mixing entropy and retard the atomic diffusion between the filler metal and base metals, inhibiting the formation of intermetallic compounds. To give a theoretical analysis of the phase evolution of the joint and verify the feasibility of this strategy, joining of the Al0.1CoCrFeNi and Inconel 625 alloy with Ni/Al nano-multilayer reaction foils, CrNi/CoFe nano-multilayer films, and Al foils as the filler was performed. The result showed that a defect-free brazing joint was formed and solid solution phase then occurred from solid solution reaction accompanied by solid solution strengthening effect to the joint as the temperature increased. The shear tests showed the highest shear strength (203.5 MPa) can be obtained. Additionally, prolonging the holding time and increasing brazing temperature made the shear strength of joint increase gradually and the fracture mechanism of the joint transformed from the inter-granular fracture to the trans-granular fracture. This effort offers a novel process for brazing Inconel 625 alloys and Al0.1CoCrFeNi, opening up a neo-field in the production of HEAs-related joints.