Interfacial microstructure and mechanical properties of Ti3SiC2 ceramic and TC11 alloy joint diffusion bonded with a Cu interlayer

Reliable joints of Ti₃SiC₂ ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti₂Cu + TiCu/Ti₅Si₄ + TiSiCu/Cu(s, s)/Ti₃SiC₂. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti₃SiC₂/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti₅Si₄ and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti₃SiC₂ substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti₃SiC₂ ceramic.     

Microstructure evolution and mechanical property of ZrC-SiC/Ti6Al4V joints brazed using Ti-15Cu-15Ni filler

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.     

Interfacial microstructure and mechanical properties of ZTA/ZTA joints brazed with Ni-Ti filler metal

The reliable brazing of the ZTA ceramic joints was successfully obtained using Ni-Ti filler metal. The microstructure and mechanical properties of the joints brazed at different temperatures were investigated. During the process of brazing, both Al₂O₃ and ZrO₂ in the ZTA reacted with the Ni-Ti filler, resulting in the formation of the AlNi₂Ti + Ni₂Ti₄O reaction layer adjacent to the ZTA substrate when brazed at 1350 °C for 30 min. NiTi and Ni₃Ti compounds precipitated at the center of brazing seam. When the brazing temperature increased from 1320 °C to 1380 °C, the thickness of AlNi₂Ti + Ni₂Ti₄O layer increased gradually. As the brazing temperature varied from 1400 °C to 1450 °C, TiO was formed adjacent to the ZTA substrate, along with the reduction of Ni₂Ti₄O. AlNi₂Ti distributed at the interface and center of brazing seam. The maximum shear strength of 152 MPa was obtained when brazed at 1420 °C for 30 min.     

Microstructure and mechanical properties of BN-Si3N4 and AlON joints brazed with Ag-Cu-Ti filler alloy

AlON was successfully brazed to BN-Si₃N₄ using a Ag-Cu-Ti filler alloy. SEM, TEM and XRD studies revealed that a TiN + TiB₂ + Ti₅Si₃ reaction layer formed adjacent to the BN-Si₃N₄ while a (Cu,Al)₃Ti₃O layer formed adjacent to the AlON. In addition, Ag-Cu eutectic, Cu(s,s) and AlCu₂Ti were observed in the brazing filler. The effect of brazing temperature on the microstructure and mechanical properties of the joints was investigated. As the brazing temperature increased, the reaction layers became thicker, while the thickness of the brazing seam decreased. Meanwhile, the amount and the size of AlCu₂Ti intermetallic compounds decreased. The shear strength of the joints first increased and then dropped with increasing the brazing temperature. A joint with a maximum strength of 94 MPa was obtained when it was brazed at 850 °C for 15 min.     

Microstructure evolution of Si3N4/Si3N4 joint brazed with Ag–Cu–Ti + SiCp composite filler

The Si₃N₄ ceramic was brazed by Ag–Cu–Ti + SiCp composite filler (p = particle) prepared by mechanical mixing. Effects of the content of Ti and SiC particles on microstructure of the joint were investigated. A reliable Si₃N₄/Si₃N₄ joint was achieved by using Ag–Cu–Ti + SiCp composite filler at 1173 K for 10 min. A continuous and compact reaction layer, with a suitable thickness, forms at the Si₃N₄/braze interface. The SiC particles react with Ti in the brazing layers, forming Ti₃SiC₂ thin layers around the SiC particles themselves and Ti₅Si₃ small particles in the Ag[Cu] and Cu[Ag] based solid solution. The higher content of SiC particles in the filler (≥10 vol%) depresses interfacial bonding strength between the Si₃N₄ substrate and composite brazing layer due to the thinner reaction layer and the bad fluidity of the filler. The Ti₃SiC₂ → TiC + Ti₅Si₃ reaction occurs when Ti concentration around SiC particles in the filler increases.     

Improvement for Ti3SiC2/Cu joint brazed using composite fillers with abnormal expansion ceramic particulates

Reducing the residual stresses and improving the mechanical strength of large-scale ceramic/metal brazing joints is an important problem that must be solved for its practical engineering application. Using composite filler with solid-state phase transformation ceramic particulates, it is theoretically feasible to relieve the residual stress and improve the mechanical properties of ceramic/metal brazed joints. In this study, Cu mesh, Ag–28Cu–2Ti (wt.%), and yttria-stabilized zirconia (0.6 mol.% YSZ solid-state phase transformation ceramic particulates) composite power fillers were used in the brazing of Ti₃SiC₂ ceramic and pure copper. The microstructure of joints and YSZ particulates in the interface was investigated and confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM), and transmission electron microscopy (TEM). In addition, the effect of YSZ particulates content on the mechanical properties of joints was investigated and evaluated by the shear strength. The results show that the interfacial phases were mainly Ti₅Si₃, TiC, Ti_xCu, Ag (s, s), Cu (s, s), and YSZ particulates. Moreover, most of YSZ particulates undergo the solid-state phase transformation from tetragonal zirconia (t-ZrO₂) to monoclinic zirconia (m-ZrO₂) during the cooling process of brazing. The abnormal volume expansion of the solid-state phase transformation reduced the thermal mismatch between Ti₃SiC₂ ceramic and filler, thereby reducing the residual stress in the interface of joint. When using composite filler with 6 wt.% YSZ particulates, the shear strength of Ti₃SiC₂/Cu joint reached the maximum. The maximum average shear strength of the joints was 80.2 MPa, which was about 103.6% more than the joint without YSZ particulates.     

Interfacial microstructure and mechanical properties of porous-Si3N4 ceramic and TiAl alloy joints vacuum brazed with AgCu filler

Porous Si₃N₄ ceramic was firstly joined to TiAl alloy using an AgCu filler alloy. The effects of brazing temperature and holding time on the interfacial microstructure and mechanical properties of porous-Si₃N₄/AgCu/TiAl joints were studied. The typical interfacial microstructure of joints brazed at 880 °C for 15 min was TiAl/AlCu₂Ti/Ag-Cu eutectic/penetration layer (Ti₅Si₃+TiN, Si₃N₄, Ag (s, s), Cu (s, s))/porous-Si₃N₄. The penetration layer was formed firstly in the brazing process. With increasing brazing temperature and time, the thickness of the penetration layer increased. A large amount of element Ti was consumed in the penetration layer which suppressed the formation and growth of other intermetallic compounds. The penetration layer led the fracture to propagate in the porous Si₃N₄ ceramic substrate. The maximum shear strength was ~13.56 MPa.     

Microstructure evolution and bonding strength of the Al2O3/Al2O3 interface brazed via Ni-Ti intermetallic phases

In this study, Al₂O₃ workpieces were vacuum brazed by using Ni-45Ti binary alloy. The interfacial microstructure evolution of the joints obtained at different brazing temperatures was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The bonding strength of the joints was measured by shear testing. The results indicated that Ni₂Ti₄O and AlNi₂Ti were the main reaction products in the joint areas. Moreover, the Ti₂Ni intermetallic compound formed in the brazing seam. The typical layer structure of the brazed joints was Al₂O₃/AlNi₂Ti/Ni₂Ti₄O/Ti₂Ni + NiTi/Ni₂Ti₄O/AlNi₂Ti/Al₂O₃. With the brazing temperature increasing, the thickness of the Ni₂Ti₄O reaction layer adjacent to the Al₂O₃ substrate increased significantly, while the AlNi₂Ti phase had a tendency to dissolve with the brazing temperature increasing. The mechanism for the microstructure evolution was also discussed. The maximum shear strength of 125.63±4.87 MPa of the joints was obtained when brazed at 1350 °C for 30min. The fracture occurred hardly in the interface between Al₂O₃ and Ni-45Ti filler alloy.     

Strengthening the ZrC-SiC ceramic and TC4 alloy brazed joint using laser additive manufactured functionally graded material layers

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.     

Joining of Cf/SiC composite to Ti-6Al-4V with (Ti-Zr-Cu-Ni)+Ti filler based on in-situ alloying concept

In this paper, a novel brazing process based on in-situ alloying concept was carried out to join C_f/SiC composite to TC4 alloy at 940 °C for 20 min. Mixed powders of Ti-Zr-Cu-Ni alloy and pure Ti metal were used as interlayer. In the process, Ti-Zr-Cu-Ni alloy melted and then dissolved pure Ti metal via liquid-solid reactions, achieving in-situ alloying of the interlayer. The interfacial microstructure and formation mechanism of the brazed joints were investigated. The effect of Ti powder content on the microstructure and the mechanical properties of joints were analyzed. The results showed that: the maximum lap-shear strength of the in-situ alloying brazed joints was 283±11 MPa when using (Ti-Zr-Cu-Ni)+40 vol% Ti composite filler, and this value was 79% higher than the mechanical strength when using Ti-Zr-Cu-Ni alone. A reaction layer of (Ti,Zr)C+Ti₅Si₃ formed near C_f/SiC composite side, while a diffusion layer of Ti₂Cu+Ti(s,s) formed near Ti-6Al-4V side. In the interlayer, lots of Ti(s,s) were distributed uniformly and few of Ti-Cu compounds were found, contributing to the plasticity of joints. Adding moderate Ti powder was beneficial for improving the interfacial reaction between C_f/SiC composite and filler material, which affected the lap-shear strength of joints.     

Brazing SiC ceramic using novel B4C reinforced Ag–Cu–Ti composite filler

The development of new composite fillers is crucial for joining ceramics or ceramics to metals because the composite fillers exhibit more advantages than traditional brazing filler metal. In this research, novel B₄C reinforced Ag–Cu–Ti composite filler was developed to braze SiC ceramics. The interfacial microstructure of the joints was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of B₄C addition and brazing temperature on the microstructure evolution and mechanical properties of the joints was analyzed. The results revealed that TiB whisker and TiC particles were simultaneously synthesized in the Ag-based solid solution and Cu-based solid solution due to the addition of B₄C particles. As the brazing temperature increased, the thickness of Ti₃SiC₂+Ti₅Si₃ layers adjacent to SiC ceramic increased. Desirable microstructure similar to the metal matrix reinforced by TiB whisker and TiC particles could be obtained at brazing temperature of 950 °C. The maximum bending strength of 140 MPa was reached when the joints brazed at 950 °C for 10 min, which was 48 MPa (~52%) higher than that of the joints brazed using Ag–Cu–Ti filler.     

Microstructural evolution and mechanical properties of TiB2-TiC-SiC ceramics joint brazed using Ti-Ni composite foils

A novel TiB₂-based ultra-high-temperature ceramic containing 60 vol.% TiB₂, 20 vol.% TiC, and 20 vol.% SiC was fabricated by hot pressing and subsequently joined using the brazing technique. Ti-based filler was used as the brazing alloy by taking advantage of the reaction between Ti and TiB₂-TiC-SiC. The effects of the brazing temperature on the microstructure and mechanical properties of the brazed joint were investigated. The results showed that Ti in the filler reacted with the TiB₂-TiC-SiC ceramics and formed a reaction layer I that comprised TiB and TiC. The brazing seam was composed of TiB, TiC, Ti₅Si₃, Ti₂Ni, and TiNi. When the brazing temperature was increased, the reaction between TiB₂-TiC-SiC ceramics and the filler was observed to become vigorous; this led to an increase in the growth of the reaction layer I. Meanwhile, the continuous Ti₂Ni layer in the brazing seam gradually disappeared; it was replaced by TiB and Ti₅Si₃. The room temperature shear strength reached a maximum value of 168 MPa when the joint was brazed at 1040 °C for 30 min; while it was 104 and 81 MPa at test temperature of 600 °C and 800 °C, respectively. In addition, the effects of TiB whiskers on the coefficient of thermal expansion of the brazing seam and fracture of the brazed joint were discussed.     

Effects of Cu interlayers on the microstructure and mechanical properties of Al2O3/AgCuTi/Kovar brazed joints

Al₂O₃ ceramic and Kovar alloy brazed joints were achieved using three types of Ag-based interlayers: a AgCuTi foil, a AgCuTi/Cu foil/AgCuTi multi-interlayer and a AgCuTi/Cu foam/AgCuTi multi-interlayer. The effects of the addition of Cu interlayers on the interfacial microstructure and mechanical properties of Al₂O₃/AgCuTi/Kovar brazed joints were investigated. When Kovar alloy and Al₂O₃ ceramic were brazed with 50 μm Cu foil at 900°C for 10 minutes, the Cu foil was completely dissolved in the liquid filler. A nearly continuous Cu layer remained in the joint when the thickness of the Cu foil reached 100 μm under the same brazing conditions. With the increase in Cu foil thickness, the thickness of Ti–O compounds + Ti₃Cu₃O reaction layer formed nearby the Al₂O₃ ceramic first increased and then remained the same. The Al₂O₃/Kovar joints brazed with 100 μm Cu foil at 900°C for 10 minutes showed a maximum shear strength of 138 MPa. A low brazing temperature was beneficial to maintain the original structure of the Cu foam. Furthermore, when the joints were brazed at 880°C for 10 minutes, the average shear strength of the Al₂O₃/AgCuTi/Cu foam/AgCuTi/Kovar joints was 140 MPa, which was 30 MPa higher than that of a single AgCuTi interlayer.     

Microstructure and mechanical properties of porous Si3N4/Invar joints brazed with Ag-Cu-Ti+Mo/Cu/Ag-Cu multi-layered composite filler

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 porous Si3N4 ceramic to Invar alloy with a novel Cu–Ti filler alloy: Microstructure and mechanical properties

Porous Si₃N₄ (P–Si₃N₄) ceramic was successfully joined to Invar alloy using a Cu–Ti active brazing alloy for the first time. The interfacial reactions between the Cu–Ti filler and two dissimilar substrates were studied. The influence of brazing process on the microstructure evolution of the joint was revealed, along with the formation of an infiltration layer that permitted the bonding of P–Si₃N₄ substrate. Ti reacted with Si₃N₄ to form TiN and Ti₅Si₃ compounds, resulting in the decomposition of Si₃N₄. In addition, the reaction and diffusion dual-layer formed at the Cu–Ti/Invar interface, which was attributed to the interaction of alloy elements between the braze filler and the Invar alloy. Fe–Ti and Ni–Ti intermetallics together with Cu solid solution (s,s) constituted the microstructure of the brazing seam. In addition, the optimal shear strength of the brazed joint was 20 MPa and the fracture propagation occurred in the P–Si₃N₄ ceramic substrate adjacent to the infiltration layer during the shearing tests.     

Graphene nanoplatelets reinforced AgCuTi composite filler for brazing SiC ceramic

Graphene nanoplatelets (GNPs) were used as reinforcement in AgCuTi filler for brazing SiC ceramic. Ti from the filler reacted with SiC ceramic to form TiC and Ti₅Si₃ adjacent to the SiC ceramic. According to the TEM and HRTEM results, TiC layer exhibited good lattice matching with SiC substrate. TiC particles synthesized by the reaction between Ti and GNPs in situ promoted the heterogeneous nucleation of TiCu and Cu(s,s), and contributed to the refinement of microstructure. Shear tests results indicated that the adoption of GNPs affected the joint property significantly. The TiC particles and an appropriate TiC + Ti₅Si₃ layer thickness both relieved the residual stress of the brazed joint and thereby increased the joint strength. The shear strength of the joint reached the maximum value of 38 MPa when using AgCuTi/GNPs (GNPs reinforced AgCuTi) composite filler containing 1% GNPs, which was ～139% higher than that of the joint brazed with AgCuTi filler.     

Wetting of AgCu-Ti filler on porous Si3N4 ceramic and brazing of the ceramic to TiAl alloy

The effect of Ti content on the wettability of AgCu-Ti filler on porous Si₃N₄ ceramic was studied by the sessile drop method. AgCu-2 wt% Ti filler alloy showed a minimum contact angle of 14.6° on porous Si₃N₄ ceramic during the isothermal wetting process. The mechanism of AgCu-Ti filler wetting on porous Si₃N₄ ceramic is clarified in this paper. Porous Si₃N₄ ceramic was brazed to TiAl alloy using AgCu-xTi (x = 0, 2 wt%, 4 wt%, 6 wt%, 8 wt%) filler alloy at 880 °C for 10 min. The effect of Ti content on the interfacial microstructure and mechanical properties of porous-Si₃N₄/AgCu-xTi/TiAl joints are studied. The typical interfacial microstructure of p-Si₃N₄/AgCu-Ti/TiAl joint is p-Si₃N₄/penetration layer (Ag(s,s)+Si₃N₄+TiN+Ti₅Si₃)/Ag(s,s)+Cu(s,s)+TiCu/AlCu₂Ti/TiAl. The maximum shearing strength of the brazed joint was 14.17 MPa and fracture that occurred during the shearing test propagated in the porous Si₃N₄ ceramic substrate for the formation of the penetration layer.     

Microstructure and mechanical properties of the Si3N4/42CrMo steel joints brazed with Ag–Cu–Ti + Mo composite filler

The Si₃N₄ ceramic was joined to 42CrMo steel using Ag–Cu–Ti + Mo composite filler. Effect of Mo particles content on the microstructure and mechanical properties of the joints were investigated. Defect-free joints were received when the Si₃N₄/42CrMo steel joints were brazed with Ag–Cu–Ti + Mo composite filler. The results show that a continuous reaction layer which is composed of TiN and Ti₅Si₃ was formed near the Si₃N₄ ceramic. A double reaction layer which consists of Fe₂Ti and FeTi was also formed adjacent to 42CrMo steel, with Fe₂Ti being located near the steel. The central part of the joint is composed of Ag based solid solution, Cu based solid solution, Mo particles and some Cu–Ti intermetallic compounds. The maximal bending strength reached 587.3 MPa with 10 vol.% Mo particles in the joint, at which the joint strength was 414.3% higher than the average strength for the case without Mo particles addition.     

Effect of interfacial microstructure evolution on the peeling strength and fracture of silicon nitride/oxygen-free copper foil joints brazed with Ag-Cu-TiH2 filler

Gas-pressure sintered silicon nitride (Si₃N₄) ceramic was brazed to oxygen-free copper (OFC) foil using 20.22 ± 0.93 mg/cm² of Ag-Cu-TiH₂ filler at 875 ^◦C for 0.5 h. The effect of TiH₂ content on the 3D morphology, including the cross-section microstructure and etched surface morphology of Si₃N₄ ceramic/OFC foil joints, was analyzed. An evolution model of the interfacial microstructure for joints was proposed based on 3D morphological analysis. The reaction between the brazing alloy and Si₃N₄ ceramic formed the interfacial reaction layer and the inside reaction zones during brazing. The growth mechanism of the interfacial reaction layer was discussed in detail. The peeling test was used to evaluate the bonding strength of the Si₃N₄ ceramic/OFC foil joints, and the optimum peeling strength of 25.1 N/mm was achieved at 5 wt% TiH₂ content. The interfacial microstructure of the joints changed with TiH₂ content, leading to different main fracture mechanisms and corresponding peeling strengths.     

Reactive brazing of silicon nitride to Invar alloy using Ni foam and AgCuTi intermediate layers

Silicon nitride (Si₃N₄) ceramic and Invar alloy have been brazed by using AgCuTi active filler and the Ni foam was added to further improve mechanical properties of joints in this study. The microstructure of Si₃N₄/Invar brazed joint changed obviously after adding Ni foam with different thickness. Ni foam reacted with the AgCuTi active filler during brazing, but it did not completely disappear and still maintained the basic frame structure after brazing. The average shear strength of the brazed joints with 0.2 mm Ni foam could reach 180 MPa, and their thermal cycle lifetime also improved significantly. The addition of Ni foam shifted the fracture location of joints from Si₃N₄ ceramic to brazing seam. These results indicated that the Ni foam could act as a buffer layer to reduce the residual thermal stress, and improve the mechanical properties of Si₃N₄/Invar joint.