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Ceramic/metal interpenetrating network structure has been proved to have a significant effect on decreasing the coefficient of thermal expansion (CTE) of the metal matrix. In our study, a AgCuTi/SiC interpenetrating network structural composite (ASINC) was fabricated through a melt infiltration method. During the infiltration process, the AgCuTi filler melted and infiltrated into a porous SiC ceramic. Wetting behavior of the AgCuTi on the porous SiC ceramic was studied. Microstructure of the ASINC was characterized. The synthesized ASINC was fabricated as an interlayer to prepare a ZrB 2 –SiC–C ceramic/AgCuTi/ASINC/AgCuTi/GH99 brazed joint. Typical microstructure of the joint brazed at 860 °C for 10 min was investigated. The effect of holding time on the microstructure and the room-temperature shear strength of the brazed joints was studied. The maximum shear strength increased by 161% compared with the case brazed with a single AgCuTi interlayer. Microstructure evolution and mechanical strengthening mechanisms of the brazed joints were discussed in detail. [ABSTRACT FROM AUTHOR]

A novel Ag–Nb 2 O 5 braze filler is developed and successfully tested as a sealant candidate for solid oxide cells. The resultant AgNbO 3 by the reaction between Ag and Nb 2 O 5 at high temperatures turns out to be the key to enable a desirable wetting of the YSZ by the braze filler. Typical interfacial microstructure of the YSZ/AISI 310s brazed joints are characterized by a scanning electron microscopy (SEM) and a transmission electron microscopy (TEM) with an energy dispersive spectroscopy (EDS). Effects of Nb 2 O 5 contents and joining parameters on the microstructural evolution and mechanical performance of the joints are investigated. Joints with a maximum average strength of 100–110 MPa are achieved when bonding at 1150 °C/30 min with 5 mol.% Ag–Nb 2 O 5. The long-term stability of the YSZ/Ag–Nb 2 O 5 /AISI 310s joints are evaluated in air for over 350 h at 800 °C and no cracks or cell degradation are found in the joints after the aging process, indicating that the new-developed Ag–Nb 2 O 5 is a promising candidate as the sealant for the SOFC stacks. [ABSTRACT FROM AUTHOR]

Abstract To address the thermal stress issue in the brazed SiO 2f /SiO 2 -Invar joints, a novel nano-TiO 2p (p: particle) modified braze filler was developed. Wetting of the SiO 2f /SiO 2 composite by AgCuTi-based composite braze filler with different TiO 2p contents were conducted first and a TiO 2p content lower than 5 wt% was fixed. Then the microstructure evolution and mechanical performance of the SiO 2f /SiO 2 -Invar joints brazed with different TiO 2p additions and different brazing parameters were discussed. The highest shear strength of 30 ± 8 MPa was obtained at 910 °C/10 min. After using the TiO 2p modified braze filler, the fracture probability of the SiO 2f /SiO 2 -Invar joints dropped down by 75% (Taking 22 MPa as an example). Finally, a FEM was employed to get an in-depth understanding of the stress relief effects when using a TiO 2p modified braze filler. Results show that the compressive stress on the SiO 2f /SiO 2 side dropped down by 30% after using a 2 wt% TiO 2p modified braze filler. The in-situ formed Cu x Ti 6-x O (x = 2, 3) phases played a key role in relieving the residual stress of the brazed joints. The development of the novel TiO 2p modified braze filler was particularly suitable for the joining of the oxide ceramics and oxides-based composites. [ABSTRACT FROM AUTHOR]

Abstract For active brazing, excessive formation of brittle intermetallics in the brazed seam is always a big issue, which has an adverse effect on the joint property. Herein, an innovative vertical few-layer graphene (VFG) buffer layer was directly grown on the Invar surface prior to brazing. SiO 2 -BN ceramic and the Invar alloy with and without the VFG were first brazed using a Ag-Cu-Ti braze alloy. Interfacial microstructure and fracture morphologies of the brazed joints were then put into comparison. Results show that there is a 20% increase in shear strength after the VFG modification. To further discuss the effect of the interfacial microstructure variation on the joint property, Invar alloy was self-brazed. The fracture path and the tensile-shear strength of the Invar/Invar joints were discussed. Finally, the interaction between the VFG and Ti was characterized and the controlling mechanism of the intermetallic compounds formation by the VFG was proposed. This novel surface modification approach reported in this paper was promising particularly for the active brazing associated with the brittle IMCs formation issue. [ABSTRACT FROM AUTHOR]

For the active brazing of ceramic/metal couples, formation of brittle intermetallics in the brazed seam is often a big issue that needs to be addressed. Herein, a novel vertical few-layer graphene (VFG) modified Cu-23Ti braze filler was developed to join the SiO 2f /SiO 2 composite and the Invar alloy. Microstructures of the wetting interfaces and the SiO 2f /SiO 2 -Cu23Ti-Invar brazed joints with and without the VFG modification were put into comparison. Results show that the formation of intermetallics in the brazed seam are greatly suppressed and the joint strength improves by 2 times after using a VFG-modified Cu-23Ti braze filler. Typical microstructure of the SiO 2f /SiO 2 -Invar joint brazed using a VFG-modified Cu-23Ti braze filler was characterized and the joint formation mechanism was proposed finally. [ABSTRACT FROM AUTHOR]

In order to improve the ZrC-SiC and TC4 brazed joint property, functionally graded material (FGM) layers (two SiC particles reinforced TC4-based composite layers) were designed to relieve the residual stress in the ZrC-SiC and TC4 brazed joint. The FGM layers were fabricated on the TC4 surface using laser additive manufacturing technology before the brazing. Then the TC4 coated with the FGM layers and ZrC-SiC ceramic were brazed using Ti-15Cu-15Ni (wt%) filler. According to the SEM and TEM results, the volume fractions of SiC particles in the FGM layers could reach 20% and 39% respectively. Ti from the braze filler and TC4 reacted with the ZrC-SiC ceramic to form TiC and Ti 5 Si 3 adjacent to the ZrC-SiC ceramic. The shear test results indicate that the adoption of the FGM layers and the brazing temperature both affected the joint property significantly. The FGM layers could benefit the mitigation of coefficient of thermal expansion (CTE) mismatch between the ZrC-SiC and TC4, so that the residual stress caused by the CTE mismatch in the joint was relieved and the joint strength increased. The brazing temperature would affect the microstructure of the brazing seam and then control the joint strength. When the ZrC-SiC ceramic and TC4 coated with the FGM layers were brazed at 970 °C for 10 min, the maximum shear strength could reach 91 MPa, and cracks propagated in the ZrC-SiC ceramic substrate during the shear test. [ABSTRACT FROM AUTHOR]

A novel composite interlayer with a reinforced network was designed using a SiC ceramic with a network structure and Ti-Ni-Nb composite filler foils, to which the Nb and BN-SiO 2 ceramic were successfully brazed under vacuum. For a brazing temperature of 1160 °C and holding time of 10 min, the interfacial microstructure of the Nb/BN-SiO 2 ceramic joint was Nb/(βTi,Nb)-TiNi eutectic structure+(βTi,Nb) 2 Ni+SiC+TiC/TiN+Ti 2 N+TiB+Ti 5 Si 3 +TiO/BN-SiO 2 ceramic. In addition, the shear strength and nano-hardness were analyzed to evaluate the effect of the composite interlayer with a network reinforcement architecture on the mechanical properties of the joint. During brazing, the Ti-Ni-Nb filler metal infiltrated and reacted with the SiC to form the network reinforcement architecture, resulting in the residual stress being relieved and the mechanical performance of the joint being significantly improved. A maximum shear strength of 102 MPa was achieved, which was 60 MPa (142%) higher than that of the joint brazed without the network reinforcement architecture. A reduction in the residual stress on the BN-SiO 2 ceramic side from 328 MPa to 210 MPa was observed with the network reinforcement architecture, and the fracture path of the joint changed from the surface of the BN-SiO 2 ceramic to the interfacial reaction zone. [ABSTRACT FROM AUTHOR]

In this study, Ag–Cu–Ti/Cu mesh/Ag–Cu–Ti composite foils were designed to braze ZrB 2 –SiC–C (ZSC) ceramic and GH99 superalloy, and sound brazed joints were obtained. The interfacial microstructure and mechanical properties of the brazed joints were investigated. By comparing joints brazed with Ag–Cu–Ti filler alloy and Ag–Cu–Ti/Cu foil/Ag–Cu–Ti composite foils, the mechanism by which Ag–Cu–Ti/Cu mesh/Ag–Cu–Ti composite foils improves the shear strength of the joint was assessed. Due to the application of a Cu mesh, a reticular braze seam with enhanced ductility was fabricated, which can inhibit the formation of Ti–Cu intermetallic compounds in the braze seam and decrease the thickness of the Ti 3 SiC 2 layer adjacent to ZSC. As a result, the residual stress concentration in a brazed joint can be reduced. Using Ag–Cu–Ti/Cu mesh/Ag–Cu–Ti composite foils, the maximum shear strength of the brazed joints increased to 121 MPa, which is 560% of the joints brazed with Ag–Cu–Ti filler alloy (21 MPa). [ABSTRACT FROM AUTHOR]