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Due to native character of thermal expansion coefficient (CTE) mismatch between Cf/SiC and GH3536, achieving high strength joint was a huge challenge for Cf/SiC-GH3536 joints. Herein, a composite filler metal of Ag-Cu-Ti + Sc2(WO4)3 was developed to join Cf/SiC and GH3536. This work introduced Sc2(WO4)3 to Ag-Cu-Ti system as a negative thermal expansion (NTE) reinforcing phase to release joint residual stress. Sc2(WO4)3 was evenly distributed in the brazing seam and reacted with Ti to form Ti3O5 reaction layer. The results of finite element analysis showed that the residual stress of the joints was effectively released by introducing Sc2(WO4)3 reinforcing phase, and the mises stress was decreased from 447 to 401 MPa. The maximum shear strength of the Cf/SiC-GH3536 joint brazed with Ag-Cu-Ti + 6 vol% Sc2(WO4)3 filler alloys was 64 MPa, which was about 2.6 times higher than that of Ag-Cu-Ti alloys. The results of this study provide a promising strategy for the introduction of new Sc2(WO4)3 reinforcing phase in Ag-Cu-Ti system, and improve the reliability and feasibility of composite brazing alloy in brazing filed.

The AgCuSnTi filler was designed to braze Gr/2024Al composite and Ti6Al4V titanium alloy through investigating the effect of Sn and Ti addition in AgCuSnTi filler on the microstructure and mechanical property of the joint. The results showed that Sn and Ti addition decided the distribution of compounds (Al2Cu and Al5CuTi2 phases) in the brazing seam. The increasing of Sn content could enhance the flowability of brazing alloy, and promote the compounds to be dispersive in the brazing seam. Ti in the filler induced the formation of Al5CuTi2 phase instead of Al2Cu phase. When the Gr/2024Al and Ti6Al4V were brazed using the AgCuSnTi filler with 3 wt.% Ti and 27 wt.%Sn at 680℃ for 10 min, the Al2Cu and Al5CuTi2 phases were dispersed in the brazing seam. The maximum shear strength of the brazed joint was 17 MPa and cracks propagated in the Gr/2024Al substrate. In addition, Ni/Nb/Ni composite interlayers were designed to strengthen the Gr/2024Al composite and Ti6Al4V titanium alloy joint, and the joint strength increased to 24 MPa owing to the adoption of the interlayers.

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 ZrB2–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.

For the first time, the wetting behavior of SiC ceramics modified by ion bombardment was studied and the interfacial microstructure was characterized. An amorphous layer was formed on the SiC surface, which has significant influence on the wetting behavior and the interfacial microstructure of SiC/AgCu–Ti wetting system. The interfacial reactions were accelerated when filler melted on the bombarded SiC surface, and the spreading on the bombarded SiC ceramics was controlled by interfacial reactions firstly and then by diffusion. The spreading rates, kr, were denoted as kr,i = 42.28exp (-456.2/RT) for bombarded SiC, and kr,0 = 28.62exp (-329.9/RT) for the original one. Ion bombardment improved the bonding quality of ceramics/droplet interface effectively, a mixed reaction layer containing TiC and Ti5Si3 was formed and no reactant stratification was occurred at the interface of SiC/droplet.

Ar ion bombardment was conducted to modify the SiC surface microstructures, which had a vital effect on the interfacial microstructure and shear property of brazing joints. The amorphous layer with thickness of ∼120 nm was formed on the bombarded surface, accompanied with plenty of dislocations and twins beneath the amorphous layer. Reliable SiC/AgCu-Ti/SiC joints were brazed in vacuum at 900 °C for 10 min, and the interfacial microstructure was investigated by SEM, EDS and TEM in detail. When the ion bombarded SiC was used as substrates, the microstructure of brazing beam was optimized as SiC / Ti5Si3 + TiC mixed layer / Ag(s,s) + Cu(s,s) containing TiCu / Ti5Si3 + TiC mixed layer / SiC, in which the interfacial stratification was eliminated compared to the conventional SiC brazing. The shear strength was improved to 30.9 MPa with ion bombardment, which was ∼72.6 % higher than that of the original SiC joints without ion bombardment. The proposed Ar ion bombardment method provides a novel way to modify the brazability of ceramics.

Transition metal oxides show great potential as electrocatalysts, owing to the low cost and rich chemical states. However, the limited surface areas, low intrinsic activity and poor hydrogen evolution reaction (HER) activity greatly restrict the application for overall water splitting. Herein, we have constructed S doped NiCo2O4 nanosheet arrays by Ar plasma (Ar-NiCo2O4|S) to enhance active sites and boost catalytic kinetics. Consequently, the Ar-NiCo2O4|S shows the improved performances for HER and oxygen evolution reaction (OER). Further, as bifunctional electrocatalysts, Ar-NiCo2O4|S exhibit a voltage of 1.63 V at 10 mA cm−2, as well as good stability.

CaO-Al2O3-SiO2(CAS) glass ceramics were designed and prepared using a melt-quench approach. The coefficient of the thermal expansion (CTE) of the synthesized CAS (4.12 × 10−6 K−1) matched perfectly with that of the SiC ceramic (4.01 × 10−6 K−1). Thermal analysis of the CAS was conducted. Then the joining of the SiC ceramics by the CAS glass ceramics under various process parameters were conducted. The bonding temperature affects the fluidity of the CAS glass and the oxidation of the SiC substrate. The holding duration decides the infiltration of the CAS glass into the SiC substrate. The optimal bonding parameter is 1400 ℃/10 min and the corresponding highest shear strength of the SiC/CAS/SiC bonded joints in average was 56 MPa. Fracture observation was also conducted to help analyze the relationship between the interfacial microstructure and the joint strength. Finally, the formation mechanism of the SiC/CAS/SiC bonded joints was proposed.

Due to the poor wettability of the AgCuTi alloy on the quartz fiber reinforced composite (QFSC), a reliable joining of the QFSC to itself or to other metals can be hardly achieved. In this study, vertically aligned carbon nanotube (VA-CNT) composed of multi-wall carbon nanotube (MWCNT) was synthesized on the QFSC surface by a plasma enhanced chemical vapor deposition method. As a result, the final contact angle decreased from 96.5° (without VA-CNT modification) down to 30.6° (with VA-CNT modification) at 870 °C with 10min holding duration. Besides, the reaction layers at the AgCuTi/QFSC interface transformed into continuous ones and the infiltration effects became more obvious after the VA-CNT modification. Finally, a possible mechanism how VA-CNT enhanced the wettability of the AgCuTi alloy on the QFSC surface was proposed. Defective sites on the MWCNT surface with a high chemical reactivity and the nanoscale capillary structure of the VA-CNT turned out to be the essential factors to promote the wetting process. This novel surface modification approach can offer new insights on addressing the wetting issues in composites preparation, brazing and soldering, etc..

AA2219-T87 alloy was self-reacting friction stir welded at different traverse speeds. Joints produced at low traverse speed exhibit tunnel defects. The tunnel defects can be avoided by higher trave...

Graphene nanosheets (GNSs) had been considered as the potential reinforcements of the composites. In this study, sponge-like graphene was used as a reinforcement to enhance the dispersity of GNSs in the metal matrix. AgCuTi alloy was melted and infiltrated into the sponge-like graphene, which led to the reaction between the GNSs and the AgCuTi alloy. The microstructure on the interface of the GNSs and AgCuTi alloy was characterized. The GNSs reinforced AgCuTi based composite was utilized as an interlayer to braze graphite and Cu, and the dispersity of the GNSs in the brazing seam was discussed. Comparing with the pure AgCuTi interlayer, the shear strength of the graphite and Cu joint was increased by 75% when the GNSs reinforced AgCuTi based composite interlayer was used.

Brazing C/SiC composites to Ti6Al4V alloy is associated with the problem of high residual stress inducing low joining strength. To overcome this problem, negative thermal expansion Zr2P2WO12 (ZWP) nanoparticles were introduced into AgCu brazing alloy to obtain robust C/SiC-Ti6Al4V joints. Microstructures and mechanical properties of the joints brazed with different ZWP contents were investigated. Results indicated that 3 wt% ZWP nanoparticles dispersed homogeneously among brazing seam and compatible with brazing alloy. The width of reaction layer at C/SiC side was reduced sharply. Meanwhile, the finite element analysis showed that residual stress was reduced by 52.9 MPa and stress concentration among reaction layer was eliminated. The average shear strength of the joints brazed with AgCu + 3 wt% ZWP increased to 146.2 MPa, which was 70.8% higher than that of joints brazed without ZWP.

AZ31B magnesium alloy and 6061 aluminum alloy were welded by the longitudinal magnetic field hybrid cold metal transfer (CMT) welding process. Three magnetic pole structures were designed and the distributions of magnetic field were simulated. The results show that the platform-shaped magnetic pole structure can improve the longitudinal direction of magnetic field in weld zone, which was suitable to redistribute welding heat source and decrease welding spatters. With the applied magnetic oscillation the welding width increased, the welding penetration and wetting angle decreased, meaning the wetting behavior of molten metal improved. The welding pores in the weld zone were suppressed with the increase of coil currents. The magnetic oscillation obviously reduced the thickness of Mg2Al3 layer and dispersed the distribution of strengthening phases Mg2Si that can prevent the crack propagation. The microhardness value at the interface layer was increased and the shear strength of the Al/Mg joints reached a maximum of 1411 N with magnetic oscillation, increasing by 30% compared to the normal welded joint. Fracture of the Al/Mg lap joints occurred at the Mg2Al3 layer/weld interface and Al side around the fusion line.

A novel composite interlayer composed of Ti-40Ni-20Nb/Nb/Ni-19Cr-10Si was designed. By using that, a reliable C/SiC-GH99 brazed joint was successfully obtained at 1200 °C for 20 min. Results demonstrated that the composite interlayer could relieve the residual stress. Practically, the diffusion of Ni was drastic inhibited at the GH99 side. The formation of brittle Ni-Si intermetallics at the C/SiC side was thus greatly decreased. The effects of the Nb foil thickness in the composite interlayer on the interfacial microstructure were studied. When the original thickness of the Nb foil was larger than 100 μm, the residual Nb foil could inhibit the diffusion of Ni and optimize the interfacial microstructure. A desirable interfacial microstructure composed of (Ti, Nb)Ni, (Ti, Nb)C and NiNbSi was obtained. The optimal shear strength at room temperature was 123 MPa. The high temperature shear strength was 88 MPa, 75 MPa and 57 MPa at 400 °C, 600 °C and 800 °C, respectively.

To address the thermal stress issue in the brazed SiO2f/SiO2-Invar joints, a novel nano-TiO2p (p: particle) modified braze filler was developed. Wetting of the SiO2f/SiO2 composite by AgCuTi-based composite braze filler with different TiO2p contents were conducted first and a TiO2p content lower than 5 wt% was fixed. Then the microstructure evolution and mechanical performance of the SiO2f/SiO2-Invar joints brazed with different TiO2p 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 TiO2p modified braze filler, the fracture probability of the SiO2f/SiO2-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 TiO2p modified braze filler. Results show that the compressive stress on the SiO2f/SiO2 side dropped down by 30% after using a 2 wt% TiO2p modified braze filler. The in-situ formed CuxTi6-xO (x = 2, 3) phases played a key role in relieving the residual stress of the brazed joints. The development of the novel TiO2p modified braze filler was particularly suitable for the joining of the oxide ceramics and oxides-based composites.

To study the effects of melting point depressants (MPD), i.e., boron and silicon, on the microstructural evolution of the joints, transient liquid phase (TLP) bonding of GH3039 and IC10 single crystal was carried out using Ni-Cr-Si-B interlayers with different silicon and boron contents. The microstructural evolution of TLP bonded joints was studied by regulating the silicon and boron contents in the interlayer. It was confirmed that boron showed a much stronger impact on depressing melting point compared with silicon. A completely isothermal solidified GH3039/IC10 joints were obtained with a Ni-10Cr-5Si-3B interlayer under 1200 ℃ for holding 2 h. Finally, the effects of holding duration on the microstructural evolution and mechanical properties of the joints were studied in detail. Under 1200 ℃, a complete isothermal solidification was achieved when the bonding duration was extended to 2 h with BNi2 interlayer. The corresponding highest mean tensile strength was 730 MPa.

Fused silica was root cause of poor wettability of SiO2f/SiO2. SiO2f/SiO2 was composed of SiO2 in different states, which mean crystallized SiO2 formed fused silica and amorphous SiO2 formed quartz fibers. Wetting results show with holding time increasing, wetting angle of AgCuTi-crystallized SiO2 decreased from 137° to 87°, meaning poor wettability. Besides, Ti3O5 and Ti2O3 particles formed. While, wetting angle of AgCuTi-amorphous SiO2 decreased from 110° to 43°, indicating good wettability. Cu3Ti3O reaction layer formed. Thus, the crystal structure of SiO2 determined reaction product in wetting interface, which was a dominating influence on the wettability of AgCuTi SiO2f/SiO2 system.

Carbon fiber reinforced carbon matrix (C f /C) composite and Ni base superalloy were brazed in vacuum using MBF 20 filler. By varying brazing temperatures and holding times, the effects of brazing parameters on the microstructure as well as its evolution and mechanical properties of the joints were investigated. The results show that the microstructural evolution of joints experiences three stages. With the rising of brazing process parameters, the dissolution of C f /C turns strong, leading to the formation of rough composite/filler interface and the increasing of amount of Cr 7 C 3 and MC complex metal carbides. The residual stress concentration in joint changes consequently. The maximum shear strength of the joint can reach 35 MPa (which is up to 92% of the shear strength of C f /C substrate), 15 MPa and 9 MPa at room temperature, 800 °C and 1000 °C, respectively. The fracture initiates and propagates in C f /C composite.

In this study, the SiBCN ceramic and TC4 alloy were successfully brazed using TiB2 reinforced AgTi composite filler in a vacuum furnace. The typical interfacial microstructure of the joint and the reaction products were identified through EDS, SEM and XRD. The effect of the TiB2 content and brazing temperature on the joint microstructure and property were investigated. During the brazing process, the filler reacted with the SiBCN to form TiC + TiB + TiN + Ti5Si3 reaction layer adjacent to the SiBCN. With the increase of the TiB2 content in the composite filler, the diffusion of Ti in the brazing seam was restrained, and the reaction layer became thinner. Meanwhile, the TiB2 volume fraction in the brazing seam increased. The increase of the brazing temperature promoted the reaction of the braze filler and the base materials. Thick reaction layer adjacent to the SiBCN and lots of Ti (s.s) and Ti2Ag in the brazing seam were obtained at high brazing temperature. When the SiBCN and TC4 were brazed using 6 wt% TiB2 reinforced AgTi composite filler at 980 °C for 10 min, the maximum shear strength of the joint reached 32 MPa.

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 SiO2f/SiO2 composite and the Invar alloy. Microstructures of the wetting interfaces and the SiO2f/SiO2-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 SiO2f/SiO2-Invar joint brazed using a VFG-modified Cu-23Ti braze filler was characterized and the joint formation mechanism was proposed finally.

Wetting behavior of AgCu filler on chromium film-deposited Al2O3 ceramics was studied by sessile drop method under vacuum, and brazing of chromium-deposited alumina using AgCu was carried out. Cr film can improve the wettability of AgCu filler on alumina ceramics, and the contact angle decreased dramatically. However, with further increase in temperature and extension of wetting time, Cr atom might diffuse excessively to molten alloy or substrate leading to thinned or disappeared Cr film on alumina; thus, the contact angle of AgCu on alumina increased. The reliable alumina joint was obtained via chromium deposition using AgCu filler brazed at 900 °C for 10 min, and no hard or brittle intermetallic compounds formed in the brazed joint. The maximum shear strength of 16.8 MPa was achieved when the thickness of deposited chromium film was 2 μm.

To improve the strength of a ceramic (ZrC-SiC) and a titanium alloy (TC4) brazed joint, laser deposited functionally graded material layers (FGM layers) between ZrC-SiC and TC4 were designed to reduce the residual stress in the brazed joint. A simulation model of the brazed joint was created to investigate the mechanism of residual stress reduction due to FGM layers. The results show that the residual stress component in the normal direction of the brazing interface (normal stress) is tensile at the ZrC-SiC edges and the in-plane residual stress component on the brazing interface is compressive in the ZrC-SiC adjacent to the brazing seam. The adoption of the FGM layers significantly reduces both the normal residual stress and in-plane residual stress. During the shear test, the normal stress concentrates at the ZrC-SiC edges near the brazing seam. By applying fracture forces 645 N and 1365 N measured in shear experiments to the ZrC-SiC/TC4 joint model and ZrC-SiC/TC4-FGM joint model respectively, the local fracture stress in the normal direction is identified to be 648 MPa and 671 MPa from both models, respectively. Although the fracture force for both models are quite different due to the difference of residual stress produced by brazing, the identified local fracture stress is close each other. The predicted cracking initial position is around the corner of the ZrC-SiC close to the brazed zone which is the same as observed in experiments.

Joining of graphite materials is problematic primarily due to the poor wettability of non-active filler metal on these materials. In an attempt to overcome this problem, magnetron sputtering deposition of Cr film on graphite was performed to modify the surface of the graphite. The wetting and brazing of graphite are carried out using non-active AgCu eutectic filler metals after deposition. The results indicated that surface modification enables wetting and joining of graphite with non-active filler. Cr film reacted with graphite forming Cr-C interfacial reaction layer, which resulted in the decrease of contact angle. Reliable graphite/graphite joints were obtained at temperature from 1113 K to 1233 K for 10 min. The typical interfacial microstructure of the brazed joint is graphite/Cr-C layer/Ag(s,s) + Cu(s,s) eutectic phase/Cr-C layer/graphite. The optimal shear strength of the joint was 13.6 MPa when the brazing parameters were 1173 K for 10 min.

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 Ti5Si3 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.

The wettability of zirconia with Sn0.3Ag0.7Cu-Ti (SAC-Ti) alloys was investigated via the sessile drop method with the increase of temperature. Zirconia, pre-metallized with SAC-Ti metal powder at 900 °C, was brazed to copper using an SAC solder paste at the low temperature of 250 °C. The active element Ti reduced the contact angle as the temperature increased. The lowest contact angle of 8° was obtained with SAC-4 wt% Ti which possessed sufficient Ti and appropriate fluidity. When zirconia was pre-metallized with SAC-4 wt% Ti alloy, the typical microstructure of the copper/SAC/zirconia joint was copper/Cu6Sn5 layer/β-Sn layer containing Ti3Sn and Ti6Sn5 phases/Ti3Sn layer/TiOx layer/zirconia. As the Ti content increased, more Ti-Sn intermetallic compounds remained in the seam, and the shear strength increased first and thereafter decreased. The highest shear strength of 19.1 MPa was achieved as zirconia was pre-metallized with SAC-4 wt% Ti. Fracture analyses indicated that brittle fracture was initiated at the reaction layers adjacent to zirconia and propagated in the seam during shear test.

Brazing SiO 2 -BN ceramic to Ti6Al4V is often associated with the problem of brittle continuous phases and high residual stress at the reaction layer of SiO 2 -BN, inducing low joining strength. To overcome these problems, SiO 2 -BN ceramic modified with in situ synthesized carbon nanotubes (CNTs) were joined to Ti6Al4V by TiZrNiCu alloy. Results show that CNTs can improve the wettability of TiZrNiCu on SiO 2 -BN rapidly, and break the continuous reaction layer of SiO 2 -BN into fine sizes. Residual stress can also be reduced by low CTE of CNTs and fine size phases among reaction layer. The shear strength of SiO 2 -BN/Ti6Al4V joints with CNTs modified is 35.3 MPa at 970 °C for 10 min, which is 3 times higher than that of the joints without CNTs modified.

In this study, the microstructure and mechanical properties of Cu6Sn5 and Cu3Sn intermetallic joints, formed by the transient liquid phase (TLP) soldering process with and without the assistance of ultrasonic waves (USWs), were compared. After the application of USWs in the TLP soldering process, Cu-Sn intermetallic compounds (IMCs) exhibited a novel noninterfacial growth pattern in the molten solder interlayer. The resulting Cu6Sn5 and Cu3Sn joints consisted of refined equiaxed IMC grains with average sizes of 3 and 2.3 µm, respectively. The Cu6Sn5 grains in the ultrasonically soldered intermetallic joints demonstrated uniform mechanical properties with elastic modulus and hardness values of 123.0 and 5.98 GPa, respectively, while those of Cu3Sn grains were 133.9 and 5.08 GPa, respectively. The shear strengths of ultrasonically soldered Cu6Sn5 and Cu3Sn joints were measured to be 60 and 65 MPa, respectively, higher than that for reflow-soldered intermetallic joints. Ultrasonically soldered Cu6Sn5 and Cu3Sn joints both exhibited a combination of transgranular and intergranular fractures during shear testing.

TZM alloy and ZrC particle reinforced W composite (ZrCp-W) were vacuum brazed using Ti-61Ni eutectic brazing alloy. The typical interfacial microstructure of the brazed joint consisted of three zones: a Mo solid solution layer, a brazing seam consisting of TiNi phase, TiNi3 phase and (Ti, Zr)Ni2 phase, and a diffusion layer composed of W particles, (Ti, Zr)C particles and (Ti, Zr)Ni2 phase. The results revealed that brazing temperature affected the interfacial morphologies of the joint, the phase constituents of the brazing seam, the element contents of these phases and the mechanical properties of the brazed joint. The optimal shear strengths at room temperature and at 800 °C reached 124.8 MPa and 82.3 MP respectively when brazed at 1240 °C for 10 min. Meanwhile, the fracture paths located at the TZM substrate and the fracture surface exhibited inter-granular fracture characteristics.

In this study, transparent alumina and TiAl alloy were successfully brazed at 860°C-940 °C using Ag-21Cu-4.5Ti (wt%) filler metal. The microstructure and mechanical properties of the joints were investigated. SEM and TEM analysis showed the typical interfacial microstructure of the joints brazed at 900 °C for 5min was TiAl/β-Ti + AlCuTi/AlCu2Ti + AlCuTi/AlCu2Ti + Ag(s,s) + Cu(s,s)/(Cu,Al)3Ti3O/transparent alumina. The effects of brazing temperature and holding time on the microstructure and mechanical properties of TiAl/transparent alumina joint were studied. In addition, the effects of the dissolution and diffusion of TiAl on the microstructural evolution of the brazing seam were discussed. Shear strength analysis reveals that the shear strength of the joint increases at first and then decreases when brazing temperature rises. The maximum shear strength is 49 MPa when the joint is brazed at 900 °C for 5 min.

An AgCu-4.5 wt.%Ti/W/AgCu-1 wt.%Ti composite interlayer was designed to braze the Invar-SiO2f/SiO2 joints. Ti contents in the interlayer between the tungsten foil and the Invar alloy was optimized. The effects of the tungsten-foil thickness on the microstructure, elemental distribution and mechanical properties of the brazed joints were investigated. Compared with a single AgCu-4.5 wt.%Ti interlayer, a sufficient metallurgical reaction happened on the SiO2f/SiO2 composite side and the formation of Fe2Ti, Ni3Ti compounds which are detrimental to the joint properties, was greatly inhibited by using a low-expansion composite interlayer (LECI). The tungsten interlayer can reduce the CTE (coefficient of thermal expansion) mismatch in the Invar-SiO2f/SiO2 joint. The highest shear strength of joints brazed with an LECI was 33 MPa, which was 1.75 times higher than the joints brazed with a single AgCu-4.5 wt.%Ti interlayer.

In order to improve the ZrC-SiC ceramic and TC4 brazed joint property, graded double-layered SiC particles (SiCp)-reinforced TC4-based composite structure (named as GLS for convenience) was designed to relieve the residual stress in the joint. The GLS was successfully fabricated on TC4 substrate by double-layered laser deposition technology before the brazing process. The investigation of the GLS shows that the volume fraction of SiCp in the two composite layers was graded (20 and 39 vol pct, respectively). Ti5Si3 and TiC phases formed in the GLS due to the reaction of SiCp and TC4. The laser power-II (the laser power for the second deposition layer) affected the microstructure of the GLS significantly. Increasing the laser power-II would promote the reaction between the SiCp and TC4. But the high laser power-II made the layer I remelt completely and the two layers became homogeneous rather than graded structure. In the ZrC-SiC and TC4 brazed joint, the CTE (coefficient of thermal expansion) was graded from the TC4 to the ZrC-SiC due to the GLS, and the strength of the joint with the GLS (91 MPa) was higher than that without the GLS (43 MPa).

ZrC-SiC ceramic and TC4 alloy were successfully brazed using a self-prepared Ti-15Cu-15Ni filler. The microstructure and mechanical property of the joints obtained at different brazing temperatures were investigated. The results indicated that Ti from the Ti-15Cu-15Ni and the TC4 reacted with the ZrC-SiC to form TiC phase adjacent to the ZrC-SiC ceramic. In the brazing seam, Ti2(Ni, Cu) intermetallic compounds zone (IMCs Zone), Hypoeutectic Zone and Hypereutectoid Zone formed. The brazing temperature affected the dissolution of TC4 into the braze filler significantly, and then determined the microstructure of the joint. The formation of α-Ti in the brazing seam could decrease the hardness and the brittleness of the brazing seam, which was beneficial to the property of the brazed joint. The joint strength reached a maximum value of 43 MPa when the joint was brazed at 970 °C and cracks propagated in the ZrC-SiC substrate near the brazing seam.

Homogeneous (Cu, Ni)6Sn5 intermetallic compound (IMC) joints were rapidly formed in asymmetrical Ni/Sn/Cu system by an ultrasound-induced transient liquid phase (TLP) soldering process. In the traditional TLP soldering process, the intermetallic joints formed in Ni/Sn/Cu system consisted of major (Cu, Ni)6Sn5 and minor Cu3Sn IMCs, and the grain morphology of (Cu, Ni)6Sn5 IMCs subsequently exhibited fine rounded, needlelike and coarse rounded shapes from the Ni side to the Cu side, which was highly in accordance with the Ni concentration gradient across the joints. However, in the ultrasound-induced TLP soldering process, the intermetallic joints formed in Ni/Sn/Cu system only consisted of the (Cu, Ni)6Sn5 IMCs which exhibited an uniform grain morphology of rounded shape with a remarkably narrowed Ni concentration gradient. The ultrasound-induced homogeneous intermetallic joints exhibited higher shear strength (61.6 MPa) than the traditional heterogeneous intermetallic joints (49.8 MPa).

The 5-mm-thick AZ61 magnesium alloy was friction stir welded by using the specially designed bobbin tool with various rotation speeds. Defect-free welds were successfully obtained with rotation spe...

Plasma bombardment was applied to remove the surface oxide film of 7075 alloy and the deposited Cu layer with thickness of ∼20 μm was attached closely to the surface of 7075 alloy by magnetron sputtering process. The brazing of 7075 alloy using Cu foil was carried out at 580 °C as the contrast test. The results showed that the brazed joints using deposited Cu layer have better microstructure and higher mechanical properties than that of using Cu foil. As brazing temperature increased to 570 °C, the deposited Cu layer was dissolved into the substrate gradually and formed intermetallic compounds. Further increasing brazing temperature, the intermetallic compounds were reduced and the homogenization of microstructure of brazed joints was enhanced. The shear strength of brazed joints increased firstly and then decreased with the increasing of brazing temperature. The maximum shear strength of 38.7 MPa was obtained when brazing temperature was 600 °C.

Laser welding-brazing process was developed for joining 5052 aluminum alloy and H62 brass in butt configuration with Zn-15%Al filler. Effect of welding speed on microstructural characteristics and mechanical properties of joints were investigated. Acceptable joints without obvious defect were obtained with the welding speed of 0.5–0.6 m/min, while lower and higher welding speed caused excessive back reinforcement and cracking, respectively. Three reaction layers were observed at welding speed of 0.3 m/min, which were Al 4.2 Cu 3.2 Zn 0.7 (τ′)/Al 4 Cu 9 /CuZn from weld seam side to brass side; while at welding speed of 0.4–0.6 m/min, two layers Al 4.2 Cu 3.2 Zn 0.7 and CuZn formed. The thickness of interfacial reaction layers increased with the decrease of welding speed, but varied little at different interfacial positions from top to bottom in one joint. Tensile test results indicated that the maximum joint tensile strength of 128 MPa was obtained at 0.5 m/min, which was 55.7% of that of Al base metal. All the joints fractured along the weld seam/brass interface. Some differences were found regarding fracture locations with three and two reaction layers. The joint fractured between Al 4 Cu 9 and τ′ IMC layer when the interface had three layers, while the crack occurred between CuZn and τ′ phase in the case of two layers.

The multilayer Ti and Ni foils were designed to braze SiO 2 -BN diphase ceramic with Nb at 1140 °C for 5min. The interfacial microstructure was examined using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM) and X-ray diffraction (XRD) methods, respectively. Experimental results and thermodynamical calculations showed that the interfacial microstructures between Nb and SiO 2 -BN ceramic were (βTi,Nb)-TiNi eutectic structure/TiNi + TiNi 3 /TiN + Ti 3 O 5 + TiB 2 + Ti 5 Si 3 . The effects of the Ti content in the Ti-Ni braze alloy on the microstructures of the joints were investigated. With the increase of the Ti content, less Ni 3 Nb formed in the joint and TiNi 3 phase successfully turned into TiNi and Ti 2 Ni. The effects of the Ti content in the Ti-Ni braze alloy on the shear strength of the joints showed that the optimum thickness of the TiN + Ti 3 O 5 + TiB 2 + Ti 5 Si 3 reaction area was about 13 μm and the maximum shear strength of 52 MPa was achieved when the Ti content was 45 wt.%.

Reliable brazing of TZM alloy and ZrC particle reinforced (ZrC p ) W composite was achieved in this study by using Ti-28Ni eutectic brazing alloy. The typical interfacial microstructure of TZM/Ti-28Ni/ZrC p -W brazed joint consisted of a Ti solid solution (Ti(s, s)) layer, a continuous Ti 2 Ni layer and a diffusion layer mainly composed of W particles and (Ti, Zr)C particles. With an increase of brazing temperature, more ZrC particles and W particles entered the molten brazing alloy, which broadened the brazing seam and diminished the Ti 2 Ni layer, resulting in the disappearance of the Ti 2 Ni layer eventually. Meanwhile, more Ti(s, s) stripes were observed on the TZM side. The presence of continuous Ti 2 Ni intermetallic phase and Ti(s, s) stripes structure in joints deteriorated the joining properties, which resulted in the formation of brittle fracture under shear test. In addition, the fracture path was related to the brazing temperature, and cracks initiate and propagate in the continuous Ti 2 Ni layer at lower temperatures. However, the fracture path tended to be located at the TZM substrate close to the interface between TZM and the brazing seam when the brazing temperature exceeded 1040 °C. The optimal room temperature shear strength reached 120.5 MPa when brazed at 1040 °C for 10 min and the fracture surface exhibited cleavage fracture characteristics, and the shear strength at high temperature of 800 °C for the specimens with highest shear strength at room temperature reached 77.5 MPa.

SiO 2 –BN ceramic and Ti plate were joined by active brazing in vacuum with Ag–Cu–Ti + BN composite filler. The effect of BN content, brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated. The results showed that a continuous TiN–TiB 2 reaction layer formed adjacent to the SiO 2 –BN ceramic, whose thickness played a key role in the bonding properties. Four Ti–Cu compound layers, Ti 2 Cu, Ti 3 Cu 4 , TiCu 2 and TiCu 4 , were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag. The central part of the joint was composed of Ag matrix, over which some fine-grains distributed. The added BN particles reacted with Ti in the liquid filler to form fine TiB whiskers and TiN particles with low coefficients of thermal expansion (CTE), leading to the reduction of detrimental residual stress in the joint, and thus improving the joint strength. The maximum shear strength of 31 MPa was obtained when 3 wt% BN was added in the composite filler, which was 158% higher than that brazed with single Ag–Cu–Ti filler metal. The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content, brazing temperature and holding time. Based on the correlation between the microstructural evolution and brazing parameters, the bonding mechanism of SiO 2 –BN and Ti was discussed.

Interfacial microstructure and mechanical properties of Ti–6Al–4 V/Cf/β–spodumene composites joints brazed by Ag–Cu eutectic brazing filler were investigated. The effects of brazing temperature and holding time on the interfacial microstructure and mechanical properties of Ti–6Al–4 V/Cf/β–spodumene composites joints were studied. The result indicated that the typical interfacial microstructure of the joint was Ti–6Al–4 V/Ti2Cu + α-Ti (s,s)/Ti2Cu/TiCu/Ag (s,s)/Cu (s,s)/Ti2Cu3/TiSi2 + TiC/Cf/β–spodumene composites. The thickness of the diffusion layer, Ti2Cu3 layer, and reaction layer on the interface of Cf/β–spodumene composites increased with the brazing temperature or holding time increasing, meanwhile, the thickness of Ti–Cu layers decreased. The diffusion of Ti in brazing seam, which was significantly determined by the brazing temperature and holding time, was a decisive factor on the interfacial microstructure and mechanical properties of brazed joints. The optimal shear strength of joint brazed at 880 °C for 10 min was 33.5 MPa. Further raising the brazing temperature or extending the holding time would reduce the shear strength of joints. Brazing specimens brazed at 880 °C and 910 °C for 10 min broke in form of cleavage fracture after shearing test. Moreover, the formation of excessive thickness of TiSi2 + TiC layer or Ti3Cu4 reaction layer was harmful to the mechanical property of the joint.

Laser welding-brazing of dissimilar metals 5052 aluminum alloy and H62 brass in butt configuration was performed with Zn-15%Al filler metal. Laser beam offset was defined as the deviation from the center of the laser beam to the butted joint face. Influence of laser offset (defined Al side (−) and brass side (+)) on microstructure and mechanical properties of welded-brazed joints were investigated. Satisfied and defect-free joints were obtained when laser beam was irradiated at Al side, while poor wetting at the bottom, interfacial cracks and lack of penetration occurred when laser offset was shifted to brass side. When the laser offset was −0.6–0 mm, the interfacial microstructure mainly consisted of serrated layer Al 4.2 Cu 3.2 Zn 0.7 adjacent to the weld seam and continuous layer CuZn close to the brass substrate. When the laser offset moved towards brass side (0.3 mm), Al 4 Cu 9 phase formed in between CuZn and Al 4.2 Cu 3.2 Zn 0.7, due to more melting and dissolution of brass. Tensile test indicated that joint strength increased first and then reduced with laser offset from Al side to brass side, and the maximum tensile strength of 128 MPa was obtained at laser offset of −0.3 mm, which was 55.7% of that of Al base metal. All the joints fractured along the bottom of brass side with brittle fracture surface and fracture location extended into the weld seam at the upper of the joints.

The wettability of graphite by SnAgCu-Ti alloys was investigated by sessile drop method in vacuum. Bonding of graphite to itself using SnAgCu-Ti alloys was carried out and the joint strength was evaluated by shear test. Active element Ti began to react with graphite at 600 °C and TiC interfacial reaction layer was formed, which resulted in the decrease of contact angle. It had a continuous decrease as temperature elevated. In isothermal process, a lower contact angle was obtained at a higher isothermal temperature resulting from the decrease of the stoichiometry of TiC x . The spreading activation energy of SAC-Ti on graphite surface was 182.66 kJ/mol. Desirable graphite/graphite joint was obtained by direct brazing using SnAgCu-Ti in vacuum. The typical microstructure of brazed joint was graphite/TiC/β-Sn containing Ti 6 Sn 5 /TiC/graphite. The shear strength of direct brazed joints varied from 17.6 to 20.6 MPa. Reliable joint was bonded without any filler metal in atmosphere at 250 °C after graphite metallized by SnAgCu-Ti. A favourable shear strength of 20 MPa was achieved. Pre-metallized graphite by SnAgCu-Ti decreased the bonding temperature and guaranteed the bonding strength.

A novel nano-Si3N4 particle reinforced AgCuTi composite filler (AgCuTiC) was used to braze Ti6Al4V and Si3N4 ceramic in the study and brazing cycles that peak at 880 °C for 0–20 min. Effects of holding time on interfacial microstructure and mechanical property were studied by scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy, and universal testing machine. TiN and Ti5Si3 were identified as the main product of the reaction between Si3N4 and Ti. The interfacial microstructure evolved considerably with joining time, eventually leading to a high degree of inhomogeneity across the length of the joint, and the maximal shear strength of 78.3 MPa was obtained when the joint was brazed at 880 °C for 10 min. A limited number of Si3N4/Si3N4 and Ti6Al4V/Ti6Al4V joints using AgCuTiC with different content of Ti particles were also studied to clarify the influences of diffusion and dissolution behaviors of element Ti on interfacial microstructure. In terms of characterizing the interfacial phases, efforts were made to understand the microstructural evolution mechanism of Si3N4/Ti6Al4V brazed joints.