Brazing Seam Research Articles

Design a self-reinforcement buffer layer to assist braze SiC and Nb with Cu-xTiH2 filler alloy

A buffer layer was designed to assist to braze SiC and Nb. The effect of brazing temperature and holding time on the microstructure and the shear strength of the joint was analyzed. The strengthening mechanism of the joint was evaluated. The results found that the SiC-Nb joint was brazed with Cu-5TiH2, because of its good wettability on the surface of SiC. The typical microstructure of SiC-Nb joint brazed at 1060 °C for 5 min was SiC/C particles+TiC+Cu(s,s)/α-Ti+Nb(s,s)/Cu(s,s)+(Ti,Nb)5Si3+Ti5Si3/α-Ti/(Ti,Nb)Si/Nb. In addition, a buffer layer formed, which was consisted of two parts: reaction layer (α-Ti+Nb(s,s)) and infiltration layer (much C particles, little TiC and Cu(s,s)). With brazing temperature and holding time increasing, element Nb continuously diffused into brazing seam and solidified into α-Ti. With Nb content increasing, the α-Ti existed in the form of discontinuous to continuous layer, and then to particles. When Nb solidified into α-Ti continuous layer, the strength of the layer was improved and effective joining between SiC and Nb formed. In addition, the buffer layer was contributed to forming a good gradient transition of coefficient of thermal expansion (CTE), and released residual stress. So, the shear strength of the joint was increased to 52.6 MPa.

Interfacial microstructure evolution and mechanical characterization of brazed Al2O3 joints with Ni‒Ti interlayer: An experimental and theoretical approach

Reliable brazing joints of Al2O3 ceramics were obtained using an active Ni‒Ti interlayer under vacuum conditions. The interfacial microstructure and mechanical properties of the joints were studied. The structural, electronic, and elastic properties of the primary interfacial reaction phases were determined using first–principles calculations. After brazing at 1320 °C for 30 min, Ni2Ti4O layer and columnar AlNi2Ti formed at the interface adjacent to the Al2O3 substrate. With increasing brazing temperature between 1300 °C and 1380 °C, Ni2Ti4O layer thickened gradually, and the AlNi2Ti became increasingly longer. As brazing temperature reached 1400 °C, TiO was formed at the interface, and the Ni2Ti4O content decreased significantly; moreover, bulk AlNi2Ti and TiNi3 were distributed in the brazing seam. The highest shear strength of 129 MPa was achieved when brazed at 1350 °C for 30 min. According to the first–principles calculations, Ni2Ti4O is more readily formed than AlNi2Ti, whereas AlNi2Ti exhibits greater stability than Ni2Ti4O. Both AlNi2Ti and Ni2Ti4O possess metallic bonds, contributing to the adhesion of the filler metal to the Al2O3 substrates. The calculated modulus and Poisson’s ratio indicate that both AlNi2Ti and Ni2Ti4O exhibit ductile characteristics, which assist in relieving residual stress within the joint.

Development of a new Mg–25Al–5Zn filler metal containing trace Y for brazing AZ91D magnesium alloy

In this work, the investigation focused on the effects of trace Y on the microstructure and characteristics of the Mg–25Al–5Zn filler metal, and then the optimal Mg–25Al–5Zn-0.5Y was used to braze the AZ91D magnesium alloy. Five kinds of filler metals showed good wettability on AZ91D magnesium alloy. Compared with Mg–25Al–5Zn filler metal, the wetting area of Mg–25Al–5Zn-0.5Y filler metal was increased by 134 % and the wetting angle was decreased by 58 %. This was mainly due to the spontaneous segregation of the active element Y at the interface. Thus, the surface tension was reduced and the wettability of the solder was improved. Different from the precipitation of α-Mg near the interface at different brazing temperatures, the distribution of α-Mg in brazing seam was more homogenous as the holding time increased. The microhardness of the brazing seam gradually increased from AZ91D side to the center of the brazing seam due to a lot of β-Mg17Al12 with high microhardness in joint. However, with the increase of brazing temperature and holding time, a large number of α-Mg solid solutions with low microhardness were precipitated in the brazing seam. As a result, the microhardness of the brazed joint gradually decreased. The shear strength of the brazed joint reached the maximum value (42 MPa) at 520 °C for 60 s. After calculation, the contribution of grain boundary strengthening and solid solution strengthening to shear strength was 67.98 % and 28.96 %, respectively.

Unveiling the strengthening effect of Nb in Ti3SiC2/Ti25Zr25Ni25Cu25 + Nb/GH3536 brazed joint

In order to achieve the ceramic/metal brazed joint with excellent mechanical properties, many kinds of high-entropy alloy (HEA) filler have been developed to acquire the joint. However, in some HEAs with high content of active element, such as Ti25Zr25Ni25Cu25 amorphous HEA, the metallurgical reaction between active element and base materials resulted in the formation of continuous intermetallics (IMCs) layer in the brazing seam inevitably, embrittling the brazed joint. In this study, Nb element was added into Ti25Zr25Ni25Cu25 amorphous HEA filler to improve the microstructure of Ti3SiC2/GH3536 brazed joint, promoting the application of Ti3SiC2 and GH3536 in the aerospace industry. After detailed characterizations, the strengthening effect of Nb in the brazed joint was unveiled. The formation of Nb-base solid solution in the brazing seam was achieved owing to the addition of Nb, which effectively inhibited the generation of large brittle IMCs bulk. Moreover, the Nb-strengthened ZrSi2 and Ni2Ti phases were generated in the reaction zone, which was also favor in promoting the mechanical properties of brazed joints. When Ti25Zr25Ni25Cu25 amorphous HEA filler with 20 vol% Nb was applied to braze Ti3SiC2 to GH3536, a maximum value of 85.36 ± 2.39 MPa for shear strength was achieved. This study illustrates the optimization mechanism of Nb in Ti25Zr25Ni25Cu25 +Nb composite filler and promotes the further application of Ti25Zr25Ni25Cu25 in brazing system.

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.

Achieving high-thermal-conductivity brazed joint between carbon-based composites and Mo-Cu alloys by increasing the heat transfer area

Carbon-fiber-reinforced carbon matrix (Cf/C)-Mo30Cu brazed joints play an important role in the cooling systems of thermonuclear reactors. However, the limited contact area of heterogeneous interfaces severely limits the heat transfer efficiency. To overcome this drawback, we prepare three-dimensional porous interfaces by pre-oxidizing the Cf/C composite. Results show that circular gaps are formed between the carbon fibers and the pyrolyzed carbon after pre-oxidization at 600 °C in air. Fster braze penetration in the Cf/C composite is achieved, and the heat-transfer area across the interface is dramatically increased. The room-temperature thermal conductivity of the joints reaches a maximum value of 146 W·m−1·K−1 at a pre-oxidation time of 2 min; this value is 30 % higher than that obtained without treatment. The enhancement in thermal conductivity is mainly attributed to the increased contact area at the interface between the brazing seam and the Cf/C matrix, which provides more channels for heat transfer. This method of significantly improving the thermal conductivity is an important guide for the thermal management of thermonuclear reactors.

Joint Microstructure and Performance of Brazing Si3N4‐MoSi2 Composites to Nb with AgCuTi and AgCuTi+MoSi2p Active Fillers

MoSi2 particle (MoSi2p), the component of Si3N4‐MoSi2 composites, is added into an AgCuTi filler to strengthen the interface bonding without bringing new elements into the Nb/Si3N4‐MoSi2 brazed joint. In this new brazing system, microstructure evolution and strength of Nb/Si3N4‐MoSi2 joints as a function of brazing temperature and holding time, as well as MoSi2p content, are investigated. With an AgCuTi filler, the reaction of active Ti and Si3N4‐MoSi2 forms a composite layer consisting of Mo5Si3, TiN, and Ti5Si3 at the interface. The extensive growth of the layer is observed from 1.9 μm at 860 °C to 5.0 μm at 920 °C, and from 1.3 μm for 5 min to 4.6 μm for 20 min as the chemical reactions between Ti and Si3N4‐MoSi2 are more sufficient. Adding 6 wt% MoSi2p to the filler, the joints exhibit a peak shear strength of 154 MPa, an increase of 20% over that of a commercial AgCuTi filler, with the fracture path changing from the Si3N4‐MoSi2 to the brazing seam. The enhancement of the joint is attributed to the reinforcement of the seam by in situ reaction of the dispersed MoSi2p with Ti, refining the microstructure and reducing the thickness of the Mo5Si3+TiN+Ti5Si3 reaction layer.

Obtaining in-situ reacted Fe–W–Ni–Cr–Cu high-entropy alloy within the interlayer of dissimilar Cf/SiC-GH3536 joint by designing non-high-entropy Cu–Ti–W composite filler

In aerospace applications, the development of high-entropy alloys (HEAs) filler is an effective strategy to obtain reliable Cf/SiC nozzles and GH3536 thrust chambers components. Considering the high costs and extended preparation times with HEA fillers, utilizing non-HEA fillers to generate HEAs within brazing seam offers significant advantages. This study successfully joined Cf/SiC with GH3536 using a non-HEA Cu–Ti–W composite filler that facilitated the in-situ formation of Fe–W–Ni–Cr–Cu HEA during the brazing process. Furthermore, the formation and accompanying martensite phase transformation were revealed. The microstructure characteristic of W reinforcements/HEA/Cu(s,s) was ultimately formed in the brazing seam. The atomic structure of the HEA, confirmed to be hexagonal close-packed, was elucidated using spherical aberration-corrected transmission electron microscopy. Additionally, a martensite phase transformation was observed in the HEA, involving two adjacent layers of (0 0 0 1) atomic planes that sheared and move a3 distance alon g [10–10] in opposite directions, resulting in the formation of M-HEA. The inclusion of HEA and M-HEA in the Cf/SiC-GH3536 joint, brazed with Cu–Ti–W composite filler, increased its shear strength to 84.8 MPa, which was 2.15 times higher than that of joints without the W reinforcements. This study offers new insights into the design of composite fillers and the application of HEAs.

Specially Structured AgCuTi Foil Enables High-Strength and Defect-Free Brazing of Sapphire and Ti6Al4V Alloys: The Microstructure and Fracture Characteristics.

A novel AgCuTi brazing foil with a unique microstructure was developed, which could achieve strong vacuum brazing of Ti6Al4V (TC4) and sapphire. The brazing foil was composed of Ag solid solution (Ag(s,s)), Cu solid solution (Cu(s,s)), and layered Ti-rich phases, and had a low liquidus temperature of 790 °C and a narrow melting range of 16 °C, facilitating the defect-free joining of TC4 and sapphire. The sapphire/TC4 joint fabricated by using this novel AgCuTi brazing foil exhibited an outstanding average shear strength of up to 132.2 MPa, which was the highest value ever reported. The sapphire/TC4 joint had a characteristic structure, featuring a brazing seam reinforced by TiCu particles and a thin Ti3(Cu,Al)3O reaction layer of about 1.3 μm. The fracture mechanism of the sapphire/TC4 joint was revealed. The crack originated at the brazing seam with TiCu particles, then propagated through the Ti3(Cu,Al)3O reaction layer, detached the reaction layer from the sapphire, and finally penetrated into the sapphire. This study offers valuable insights into the design of active brazing alloys and reliable metal-ceramic bonding.

Microstructure and properties of YIG/YIG magnetic homogenization joint fabricated by a novel Bi2O3–B2O3–NiO–Fe2O3 magnetic glass

Aiming at mechanical and electromagnetic demands for yttrium iron garnet ferrite (YIG) integrated structure, a novel Bi2O3–B2O3–NiO–Fe2O3 (BBNF) low-melting magnetic glass braze was designed. Nearly magnetic homogenization YIG/YIG joints were fabricated successfully. In-situ magnetic microcrystalline phases NiFe2O4 and Ni2FeO4 with good mechanical property precipitated in the brazing seam. The magnetization performance of YIG/YIG joints was significantly promoted. Merely 10 % difference of the magnetization strength per unit mass of the joints to YIG base materials was achieved. The joint shear strength reached its maximum of 79 MPa due to the enhancement of the microcrystalline phases. It is significant for improving both structural stability and functional reliability of the microwave devices for long-term service.

Elimination mechanism of voids caused by density differences in high crystallinity alumina/alumina joints bonded with dysprosium aluminum silicate glass ceramic filler

In this work, the Dy2O3-Al2O3-SiO2 (DASN) and Dy2O3-Al2O3-SiO2-TiO2 (DAST) glass fillers were used for joining alumina ceramic. During the cooling process of the alumina/DASN/alumina joints, Dy2Si2O7 and Al2O3 were precipitated simultaneously and gradually grown. As a result, voids were formed due to the poor flowability of the glass ceramic filler and the large density difference between the glass filler and Dy2Si2O7 crystals. On the contrary, the addition of TiO2 altered the sequence of the crystalline phase precipitation during the cooling process. During cooling from the joining temperature (1450 °C) to 1100 °C, only Dy2Si2O7 was formed in the brazing seam. Simultaneously, the flowing glass phase was able to fill the spaces caused by the density differences. When the growth of Dy2Si2O7 phase ceased, the Al2O3 phase began to precipitate. Therefore, the voids caused by density differences can be eliminated in the alumina/DAST/alumina joints with high crystallinity. The optimal flexural strength of alumina/DAST/alumina joints tested at room temperature and 1000 °C reached 350 MPa and 158 MPa, respectively.

Investigation on the role of Nb in strengthening Ti3SiC2/Ti25Zr25Ni25Cu25 + Nb/Ti60 brazed joint

Ti25Zr25Ni25Cu25 amorphous high-entropy alloy (HEA) filler has been proved to be an excellent filler in acquiring the ceramic/metal brazed joint with thin brittle diffusion and reaction zone (DRZ). However, due to the high content of active Ti element, excessive intermetallics (IMCs) is generated in the brazing seam inevitably, which significantly deteriorates the mechanical properties of brazed joint. Therefore, it's urgent to improve the composition of Ti25Zr25Ni25Cu25 amorphous HEA filler to avoid the generation of excessive IMCs, contributing to its further application. In this study, the Ti25Zr25Ni25Cu25 amorphous HEA filler was proposed to be modified with Nb element and applied to achieve the Ti3SiC2/Ti60 brazed joint, which is a promising candidate brazed joint in the aerospace industry. According to the detailed characterization on the microstructure and mechanical properties, the role of Nb in strengthening brazed joint was clarified. The addition of Nb contributed to the generation of more ductile (Nb, β-Ti) (s, s), β-Ti (s, s) and less brittle IMCs. As a result, the brazing seam was strengthened and was not the weak area anymore during the shear test. When 20 vol% Nb was added into the HEA filler, the shear strength of Ti3SiC2/Ti60 brazed joint reached to a maximum value of 90.65 ± 3.15 MPa. This study provides a potential method to improve the composition Ti25Zr25Ni25Cu25 amorphous HEA filler and promotes its further application.

Brazing of high-nitrogen steel to Al0·3CoCrFeNi using a BNi-2 filler: Microstructure, mechanical properties, and corrosion resistance

Studies that focus on brazing high-nitrogen steel (HNS) to high-entropy alloys (HEAs) are currently limited. In this study, the HEA Al0·3CoCrFeNi was successfully brazed to HNS using a commercial BNi-2 filler at 1080–1140 °C. The microstructure and shear strength of the Al0·3CoCrFeNi/HNS brazed joints were observed and evaluated. The typical microstructure of the brazed joint was HNS/infiltration layer/reaction layer/Ni(s,s) (containing NiAl3)/reaction layer/infiltration layer/Al0·3CoCrFeNi. The higher brazing temperature and longer holding time promoted the diffusion of B as a brazing seam with homogeneous Ni(s,s), and more intergranular Cr-rich borides formed in the base materials. The optimized shear strength attained 549.2 MPa after the joint brazed at 1120 °C for 15 min, and ductile fracture occurred in the reaction zone. The insufficient and excessive diffusion of B resulted in residual Cr–B compounds in the brazing seam and excess borides in the HNS, respectively, which negatively affected shear strength. All the joints showed poor corrosion resistance following immersion in a 3.5 wt% NaCl solution because the excess Cr-rich compounds resulted in decreased Cr content in the surrounding matrix. Therefore, Ni-based fillers without B were more suitable for obtaining Al0·3CoCrFeNi/HNS joints with a favorable corrosion resistance.

Homogenization treatment-induced reduction of brittle intermetallic compounds in Ti2AlNb/Ti60 brazed joints: Effect on microstructure and mechanical properties

The microstructure evolution and mechanical properties of Ti2AlNb/Ti-36.5Zr–10Ni–15Cu-0.5Co-0.5Nb/Ti60 brazed joints before and after homogenization treatment were comprehensively evaluated. Initially, the joints brazed at 900 °C for 15 min exhibited a continuous coarse strip network of Ti2Cu, Ti2Ni, Zr2Cu and Zr2Ni brittle intermetallic compounds in the central region of the braze seam, which detrimentally affecting the mechanical properties. Subsequent homogenization at 600 °C for 1 h, the amount of continuous brittle intermetallic compounds significantly decreased through sufficient atomic diffusion. Concurrently, the inadequately transformed eutectic β-Ti within the intermetallic compounds underwent an active eutectoid reaction. This structural transformation established a coherent interface with elastic distortion between the α-Ti and intermetallic compounds, effectively minimizing the lattice mismatch. Thus, a widmanstatten structure (i.e., acicular intermetallic compounds within a eutectoid microstructure matrix) with improved mechanical properties was formed. Consequently, a mean shear strength of 350.3 MPa was attained after treatment at 600 °C for 1 h, marking a substantial 206 % increase compared to that before homogenization treatment. This finding underlines the pivotal role of homogenization treatment in optimizing the performance of aeroengine components.

Higher entropy-induced strengthening in mechanical property of Cantor alloys/Zr-3 joints by laser in-situ eutectic high-entropy transformation

To effectively regulate the grain boundary infiltration in CoCrFeMnNi high-entropy alloy (Cantor alloys, HEA) caused by the violent atomic interdiffusion, the higher configuration entropy on Cantor alloys surface was designed and realized via eutectic high-entropy (EHEA) transformation. Meanwhile, to effectively alleviate the residual stress caused by the notable difference in the thermal expansion coefficient (CTE) between Cantor alloys and Zr-3 alloys, a cladding layer was applied to the HEA surface using laser cladding technology of Nb, followed by brazing to Zr-3 alloys with Zr63.2Cu filler. The cladding layer's microstructure comprised Nbss and FCC+(Co,Ni)2Nb eutectic structure, resulting from an in-situ reaction between Cantor alloys and Nb. The Nbss and FCC demonstrated good plasticity, and the (Co,Ni)2Nb Laves phase provided increased strength, endowing both good plastic deformation ability and strength of the cladding layer. Notably, the existence of EHEA in the laser cladding layer made the Cantor alloy entropy from 1.61 R to 1.77 R, greatly enhancing its thermal stability and suppressing the grave grain boundary infiltration. Joints produced via laser cladding with Nb-assisted brazing exhibited a complex microstructure (HEA/Nbss + FCC + (Co,Ni)2Nb/(Zr,Nb)(Cr,Mn)2 + (Zr,Nb)ss/(Zr,Nb)2(Cu,Ni,Co,Fe) + (Zr,Nb)(Cr,Mn)2 + (Zr,Nb)ss/Zr-3 and a significantly improved shear strength of 242.8 MPa at 1010 °C for 10 min, 42.4 % higher than that of directly brazed joints. This improvement was attributed to reduced grain boundary infiltration, alleviated residual stress due to CTE disparity, and eliminated micro-cracks in the brazing seam. This study presents an effective solution for reducing residual stresses and achieving reliable bonding between Cantor alloys and Zr-3 alloys, with potential applications in brazing CoCrFeNi-based HEA and Zr-3 due to the beneficial eutectic reaction between CoCrFeNi and Nb.

Microstructure and mechanical properties of Al0·3CoCrFeNi high-entropy alloy joints brazed using a FeCoCrNiCu/Ti composite interlayer

This study introduces a brazing technique for joining Al0·3CoCrFeNi high-entropy alloy (HEA) utilizing a FeCoCrNiCu/Ti composite interlayer. The primary objectives of this investigation encompass an examination of the microstructure of the Al0·3CoCrFeNi joint, as well as an evaluation of the shear strength of the brazed joints under diverse brazing parameters. The characteristic microstructure of the Al0·3CoCrFeNi brazing seam is comprised of Ti (s, s), Cu (s, s) from the FeCoCrNiCu interlayer, and face-centered cubic (FCC) phases containing more than five elements. When the brazing temperature increases from 1100 °C to 1180 °C, there is a gradual augmentation in the diffusion of Ti element and subsequent reactions involving Cu, Ti, and Ni. Furthermore, the impact of holding time on the brazing seam is investigated. The findings suggest that prolonging the holding time has a relatively negligible effect on the reaction layer formed by the Ti foil. However, it does lead to a reduction of the Cu (s, s) content within the FeCoCrNiCu interlayer. Notably, the highest shear strength reaches up to 280 MPa when the joint brazed at 1160 °C for 10 min. In addition, the shear strength did not decrease below 800 °C. During the shear test, ductile fractures are observed in the joint, indicating favorable mechanical properties. Overall, this study successfully demonstrates the potential of the proposed brazing technique employing a FeCoCrNiCu/Ti composite interlayer for the effective joining of Al0·3CoCrFeNi HEA. By optimizing the brazing parameters, it is possible to achieve robust joints with exceptional mechanical characteristics.

Improved the mechanical properties of SiCf/SiC-GH536 joints by in-situ introducing better toughness MoNiSi phase to the brazing seam

Brazing, a crucial technology for connecting composites with metals, emerges as an effective solution to the intricate challenges posed by alternative joining methods. This investigation employs foam Ni and MoNi as intermediary layers to establish connections between silicon carbide reinforced silicon carbide composites (SiCf/SiC) and GH536 superalloy. The diverse joint structures, scrutinizing their intricate impact on the mechanical properties of the brazed joints are systematically explored in this study. Findings reveal distinctive characteristics depending on the intermediary layer: Ni foam widens the brazing seam, with a significant portion of Ni elements in the nickel foam adopting the Ni(s, s) form within the brazing seam. Meanwhile, MoNi foam as the intermediary layer prompts the in-situ formation of a substantial MoNiSi phase within the brazing seam. The alternation between the MoNiSi and FCC phases contributes to a harmonized internal stress state within the joint, resulting in an impressive strength of 106.7 MPa. This study delineates a novel technical trajectory for the practical engineering application of SiCf/SiC composites.

Optimization of the active element and reinforcement proportion for improving joint strength of brazed Si3N4/42CrMo

Micron-TiN particles and Ti powder were introduced into the AgCu powder filler to design a particle-reinforced composite filler. This TiN particle (TiNp) modified brazing material was adopted to reliably braze Si3N4 ceramics onto 42CrMo steel, and the ratio of active element Ti to TiNp reinforcement was optimized for joint strength improvement. The reaction layer’s thickness (TiN+Ti5Si3) adjacent to the ceramic decreased by introducing TiNp. Nevertheless, the reaction layer’s thickness (TiC) at the 42CrMo side did not vary too much. TiNp showed excellent wettability with Ag-Cu-Ti braze, and there was no obvious reaction at the interface. Cu-Ti intermetallic compounds were formed and randomly distributed in the brazing seam. When the TiNp content did not exceed 8 vol.%, the joints’ mechanical properties first sharply decreased and then remained basically unchanged when Ti increased. Raising the TiNp content to 10 vol.%, the joint strength showed the changing trends of first increasing and then dropping by increasing Ti content. The bending strength reached the maximum value of 396 MPa when 8 vol.% TiNp and 4 wt.% Ti were adopted.

Interfacial microstructure and mechanical properties of Si3N4/Invar joints using Ag–Cu–In–Ti with Cu foil as an interlayer

Abstract Si3N4 and Invar alloy brazed joints were achieved using two types of Ag-based interlayers: a Ag–Cu–In–Ti foil and a Ag–Cu–In–Ti/Cu/Ag–Cu multi-interlayer. The results showed that when only using a single Ag–Cu–In–Ti filler, the wave-shaped Fe2Ti + Ni3Ti intermetallic compounds are concentrated in the middle of the brazing seam. When adding Cu as the interlayer, the dissolution of the Cu interlayer formed a large number of Cu(s,s) blocks of different sizes in the brazing seam, which hindered the concentrated distribution of Fe2Ti + Ni3Ti intermetallic compounds in the brazing seam. As a result, Fe2Ti and Ni3Ti were dispersedly distributed in the brazing seam, increasing the shear strength of the brazed joint. The shear strength of brazed joints was increased by 82 % compared to joints brazed with a single Ag–Cu–In–Ti filler when the Cu interlayer was added.

Enhancing the high-temperature thermal evacuation of Cf/C-Mo30Cu joint via grooving 3D heat transfer interface

The joining of Cf/C composite to Mo30Cu alloy plays an important practical role in a bias filter for thermonuclear fusion. In this study, the Cf/C composite is joined to Mo30Cu alloy at 860 °C/10 min using AgCu4.5Ti braze after fabricating the three dimensional (3D) heat transfer interface along the Cf/C interface. The effect of interface grooving on the thermal conductivity of the joint is investigated and compared with the original brazed joint. The results demonstrate that the room temperature thermal conductivity of the joint reached a maximum of 132 W·m−1·K−1 at a grooving depth of 200 μm, which is 17.8 % higher than that of the original joint (112 W·m−1·K−1). The thermal conductivity of the joint is still as high as 100 W·m−1·K−1 at a temperature of 500 ℃. The excellent high-temperature thermal conductivity significantly reduces the Cf/C damage and extends the service life of the joint. And the shear strength of the joint has also been significantly increased by 252 % from 13.1 MPa to 33.1 MPa. Grooves prepared along the Cf/C interface provide channels for braze penetration, increasing the contact area between the brazing seam and the Cf/C matrix. Ultimately, the thermal evacuation performance of the joint is improved by increasing the heat exchange area across the joint. Also, grooves along the Cf/C interface enable mechanical interlocking with the brazing seam, achieving an enhanced joint strength. The heat transfer process of the brazed joint is simulated and analyzed by the finite element method. The analysis indicated that the thermal evacuation across the joint can be enhanced by pre-fabricating a 3D heat transfer interface in the joint. This research can provide a reference for solving the problem of heat accumulation in the first wall materials inside thermonuclear reactors.