Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was successfully designed to braze porous Si3N4 and Invar alloy. To further reduce the CTE mismatch between the porous Si3N4 and brazing filler, Mo particles were introduced into Ag-Cu-Ti. The effects of the Mo addition on the microstructure and mechanical properties of the brazed joints were studied. The results showed that, the addition of Mo particles into Ag-Cu-Ti lowered the CTE mismatch and improved the joint strength to a certain degree. However, an excessive content was harmful. The Mo particles could absorb Ti at high temperature, causing Ti shortage in the reaction with the ceramic. When cooling down, the absorbed Ti was released. The released Ti could react with Cu to generate Cu-Ti phase. So, additional Ti was adopted in the brazing filler as a supplement. When the Ti content was 5 wt%, the reaction layer on the ceramic interface was too thin to transfer enough load. However, when it reached 15 wt%, the Cu interlayer dissolved completely and Fe-Ti and Ni-Ti phases appeared. The maximum joint shear strength (83 MPa) was obtained with 10 wt% Ti and 5 vol% Mo, which had exceeded 90% of the porous Si3N4 and was 56% higher than the joint brazed without Mo particles.

Brazing of Ti2AlC ceramics has been successfully performed using a pure Al filler metal, in the temperature range 1023 K–1173 K and with holding time ranging from 0 to 30 min. The microstructure of the Ti2AlC joints was studied, and the mechanical properties of the joints were evaluated by shear strength test. It is observed that the Al filler has weak effect on the stability of Ti2AlC substrate, and only a small amount of decomposition products including the TiCx and TiAl3 compounds can be observed in the joints. In addition, the formation of an inter-diffusion layer in the Ti2AlC substrate is considered as the major brazing mechanism. The maximum shear strength of the Ti2AlC joints using the pure Al filler metal is 95 MPa, with an electrical conductivity of 2.21×106 S m−1, after holding the sample at 1123 K for 10 min.

Silicon nitride-based composite ceramics with different contents of magnesium titanate have been fabricated via gas pressure sintering method. The phase compositions, microstructure, mechanical performances and dielectric properties of the composite ceramics were investigated. The density of the Si3N4-based composite ceramics firstly increased with additive of magnesium titanate powder up to 5 wt% and then gently decreased, and the mechanical properties firstly increased and then declined. Besides, the dielectric constant and dielectric loss increased with the increase of magnesium titanate contents. For the Si3N4-based composite ceramics with 5 wt% magnesium titanate powders, the flexural strength, elastic modulus, dielectric constant and dielectric loss reached 451 MPa, 274 GPa, 7.65, 0.0056, respectively. These results suggested that the magnesium titanate was beneficial for the improvement of mechanical performances and dielectric constant of Si3N4-based composite ceramics.

The brazing of the Ti2AlC ceramic to nickel has been successfully performed using nickel based filler alloy, to extend high temperature applications of Ti2AlC ceramic. The interfacial morphology was observed by SEM, and the phases in the joint were characterized by EDS and XRD. During the brazing process, the diffusion of Ni from filler alloy to the Ti2AlC substrate was discovered. Afterwards, the diffusion kinetics were studied by measuring the thickness of the ‘interaction zone’, and the activation energy was calculated to be 152 kJ/mol. In addition, the effect of brazing parameters on shear strength was studied. The results revealed that increasing thickness of the ‘interaction zone’ and ‘filler zone’ was favorable for relieving the thermal stress in the joint, led to an improvement in mechanical properties. Finally, the maximum shear strength of the Ti2AlC/Ni brazed joints was measured to be 193 MPa, obtained at 1100 °C for 30 min.

•Composition of 42CrMo/filler reaction layer was determined to be TiC by TEM.•A nanometer thin layer of TiN1−x was formed at the surface of the TiN particles.•Ti in the filler diffused towards and enriched around TiN particles.•Equilibrium of the TiNx with Ag–Cu–Ti as a function of Ti content was calculated.•Formation mechanism of Si3N3/42CrMo joint brazed with Ag–Cu–Ti + TiNp was analyzed.Ag–Cu–Ti filler alloy incorporated with TiN particles was used to join the Si3N4 ceramic to 42CrMo steel, and the formation mechanism of the joint was revealed using SEM, EDS, XRD and TEM investigations. Microstructural examination showed that TiN + Ti5Si3 reaction layer is adjacent to the Si3N4 ceramic, whereas randomly oriented TiC with grain sizes ranging from 50 to 100 nm form in the 42CrMo/filler reaction layer. The Ag–Cu–Ti brazing alloy exhibits intimate bonding with TiNp, as Ti diffuses towards and enriches around TiNp. A nanometer thin layer of hypostoichiometric TiN1−x is formed at the surface of the particles. Only a small amount of Cu–Ti intermetallic compounds is found in the seam brazed with composite filler of lower TiNp content, whereas various and numerous Cu–Ti intermetallic phases precipitate at higher TiNp content.

A novel high-temperature filler alloy, Co42.5Ti42.5Nb15 (at%) developed with which Cf/SiC–Nb joints were successfully obtained at 1553–1613 K for 10 min. The effects of brazing temperature on the microstructure and mechanical properties of the joints were investigated. The results show that the typical Cf/SiC and Nb joint consist of Cf/SiC composite/(Ti,Nb)C reaction layer/(Ti,Nb)2Co layer/Nb[Ti,Co]+(Ti,Nb)Co eutectics with some CoNb4Si compounds/Nb substrates. With increasing the brazing temperature, both the thickness of the reaction layers and the content of CoNb4Si in the brazing layer increased, whereas the thickness of the brazing layer reduced. The shear strength presented a peak value of 187 MPa from a brazed at 1593 K.

A novel Ni–Cr–P–Cu filler alloy was designed to join graphite and copper at 1173–1253 K for 10 min, and the effects of brazing temperature on the microstructure and mechanical properties of the joints were investigated. The typical microstructure of the joints was as follows: graphite/Cr3C2+Cr7C3 reaction layer/Ni3P+Cu-based solid solution+chromium carbide reaction phases/Cu. On increasing the brazing temperature, the thickness of the brazing layer was reduced, whereas the thickness of the reaction layer at the graphite/filler alloy interface was increased. However, the reaction layer was formed discontinuously at the graphite/filler alloy interface while increasing the brazing temperature to 1253 K, at which the crack propagation mode was through the interface of the graphite/filler alloy. The shear strength first increased then decreased with the increase of brazing temperature, and the maximal shear strength of the joint could reach 60 MPa when the brazing temperature was 1223 K.

The composite filler shows more advantages than traditional brazing alloys, and has been widely introduced into joining ceramics or ceramics to metals. However, the underlying formation and strengthening mechanisms remained uncertain in the joint. In current research, SiCp (p = particle) was incorporated in Ag–Cu–Ti brazing alloy for joining Si3N4 ceramic. Nanoindentation method was introduced for probing the mechanical properties of reaction phases between the brazing alloy and SiCp. A novel formation mechanism model was thus proposed. In addition, optical microscope (OM) in conjunction with digital image correlation (DIC) techniques has been first applied to elucidate the deformation mechanism in the joint with and without SiC incorporation. The following reasons were believed to strengthen the brazed joint: load-transfer ability of SiCp, plastic relaxation in the brazing layer and CTE reduction of the composite filler.

The present study investigated the effect of brazing temperature and holding time on the microstructure and mechanical properties of Ti2AlC-copper joints brazed with Ag-Cu filler alloy at 800–900 °C for 10 min and held for different times at 850 °C. The representative structure of the joints was Ti2AlC/interaction area in the Ti2AlC substrate/brazing layer/diffusion area of the copper substrates/Cu. The brazing layer was composed of Cu-rich phases, AlCu2Ti intermetallic compounds and Ag[Cu] solid solutions. With increasing brazing temperature, more filler alloy was infiltrated into the ceramic substrate and reacted with Ti2AlC, accelerating the decomposition of Ti2AlC and the formation of Ti3AlC2, TiC and AlCu2Ti reaction phases. Moreover, more copper substrate was dissolved into the filler alloy; thus, more Cu-rich phase and AlCu2Ti were produced in the brazing layer. Moreover, the width of the brazing layer was reduced, while the widths of both the interaction area and diffusion area increased. As the brazing temperature was increased, the shear joint strength increased and then decreased. By prolonging the holding time, the widths of both the interaction area and the diffusion area were increased, while the width of the brazing layer was held constant at approximately 50 μm. Neither the structure nor the shear strength of the joints was influenced by the holding time. The optimum brazing parameters for joining Ti2AlC ceramic to copper with Ag-Cu filler alloy were 850 °C for 40 min. The joints obtained exhibit a maximum shear strength of 203.3 MPa.

The composite filler has been widely introduced for joining ceramic. However, the underlying formation and strengthening mechanisms in the joint remain uncertain. In this study, a commercial Ag–Cu–Ti brazing alloy with Mo particles reinforcement has been introduced for joining Si3N4 ceramic and the effect of Mo particles on the microstructure and flexural strength of the joint was investigated. Nanoindentation was employed to characterize the mechanical properties for reaction phases in the joints. The modulus and hardness values for Cu–Ti intermetallics and brazing alloy in the joint were first reported, providing a strong evidence to elucidate the strengthening mechanism. In addition, the strength was increased from 200 MPa, with Ag–Cu–Ti alone, to a maximum of 429 MPa while using Ag–Cu–Ti + 5 vol.% Mo composite filler. We are convinced that, for a well-bonded joint, the thermal expansion mismatch between the joined materials and the plastic deformation in the brazing alloy determined the joint strength.

Si3N4 ceramics were brazed using Au–Ni–V metal foils at 1423 K for different holding times. Effect of holding time on microstructure and mechanical properties of the joints was investigated. The results indicate that a reaction layer of VN exists at the interface between Si3N4 ceramic and filler alloy. With increasing holding time from 0 to 90 min, thickness of the VN reaction layer increases from 0.4 to 2.8 μm, obeying a linear relation. Mechanism of the interfacial reaction was discussed by calculating the formation of free energy of VN. No specific orientation relationship exists between VN reaction layer and Si3N4 ceramic. In addition, Ni3Si intermetallic compound appears in the joint when the holding time increases to 90 min, resulting in the deterioration of the joint strength.

Capillary infiltration and an in situ reaction between filter papers and zirconia powders were employed to synthesize laminated C/ZrC composite via vacuum impregnation and hot-pressing sintering at 1700 °C for 90 min under a pressure of 30 MPa. The microstructures and mechanical properties of the laminated C/ZrC composite were characterized via XRD, SEM, TEM analyses and the three-point bending test. The results indicated that the obtained composite exhibited a distinct laminar structure with alternating carbon and zirconium carbide layers. The composite had a bulk density of 1.89 g/m3, an open porosity of 21.6%, and a bending strength of 128 MPa. Typical non-brittle fracture behaviors are observed, and the composites show an elastic deformation at the beginning of the test, exhibiting a zigzagging rise until the maximum stress is reached.

Reliable brazing of carbon fiber reinforced SiC (Cf/SiC) composite to Nb-1Zr alloy was achieved by adopting a novel Ti45Co45Nb10 (at.%) filler alloy. The effects of brazing temperature (1270–1320 °C) and holding time (5–30 min) on the microstructure and mechanical properties of the joints were investigated. The results show that a continuous reaction layer (Ti,Nb)C was formed at the Cf/SiC/braze interface. A TiCo and Nb(s,s) eutectic structure was observed in the brazing seam, in which some CoNb4Si phases were distributed. By increasing the brazing temperature or extending the holding time, the reaction layer became thicker and the amount of the CoNb4Si increased. The optimized average shear strength of 242 MPa was obtained when the joints were brazed at 1280 °C for 10 min. The high temperature shear strength of the joints reached 202 MPa and 135 MPa at 800 °C and 1000 °C, respectively.