Brazing copper and alumina metallized with Ti-containing Sn0.3Ag0.7Cu metal powder

A Sn-based metallization layer was successfully prepared on the surface of alumina at 900 °C by using Ti-containing Sn0.3Ag0.7Cu (SAC, wt.%) metal powder. Reliable alumina/copper joints were obtained by brazing pre-metallized alumina and copper using SAC filler at 580–660 °C for 5 min. The typical interfacial microstructure of brazed joint was copper/Cu₃Sn layer/Cu₆Sn₅ layer/β-Sn layer containing Ti₆Sn₅ phase and Al₂O₃ particles/alumina. As brazing temperature increased, the Cu–Sn intermetallic layers thickened rapidly and the amount of β-Sn phase reduced. When brazing temperature exceeded 640 °C, Kirkendall voids and microcracks formed at copper/Cu₃Sn interface. The joints brazed at 580–620 °C possessed high shear strength and the highest average shear strength of 32 MPa was achieved when brazed at 620 °C. Fracture analyses indicated that the joints mainly fractured inside of the Cu₆Sn₅ layer and β-Sn layer. The joints brazed above 620 °C demonstrated low shear strength due to the formation of Kirkendall voids which caused the joints fractured along the Cu/Cu₃Sn interface.     

Ultrasound-assisted brazing of Cu/Al dissimilar metals using a Zn–3Al filler metal

Ultrasound-assisted brazing of Cu/Al dissimilar metals was performed using a Zn–3Al filler metal. The effects of brazing temperature on the microstructure and mechanical properties of Cu/Al joints were investigated. Results showed that excellent metallurgic bonding could be obtained in the fluxless brazed Cu/Al joints with the assistance of ultrasonic vibration. In the joint brazed at 400 °C, the filler metal layer showed a non-uniform microstructure and a thick CuZn₅ IMC layer was found on the Cu interface. Increasing the brazing temperature to 440 °C, however, leaded to a refined and dispersed microstructure of the filler metal layer and to a thin Al_4.2Cu_3.2Zn_0.7 serrate structure in the Cu interfacial IMC layer. Further increasing the brazing temperature to 480 °C resulted in the coarsening of the filler metal and the significantly growth of the Al_4.2Cu_3.2Zn_0.7 IMC layer into a dendrite structure. Nanoindentation tests showed that the hardness of the Al_4.2Cu_3.2Zn_0.7 and CuZn₅ phase was 11.4 and 4.65 GPa, respectively. Tensile strength tests showed that all the Cu/Al joints were failed in the Cu interfacial regions. The joint brazed at 440 °C exhibited the highest tensile strength of 78.93 MPa.     

Effect of mechanical milling on Ni–TiH2 powder alloy filler metal for brazing TiAl intermetallic alloy: The microstructure and joint's properties

A TiH₂–50 wt.% Ni powder alloy was mechanically milled in an argon gas atmosphere using milling times up to 480 min. A TiAl intermetallic alloy was joined by vacuum furnace brazing using the TiH₂–50 wt.% Ni powder alloy as the filler metal. The effect of mechanical milling on the microstructure and shear strength of the brazed joints was investigated. The results showed that the grains of TiH₂–50 wt.% Ni powder alloy were refined and the fusion temperature decreased after milling. A sound brazing seam was obtained when the sample was brazed at 1140 °C for 15 min using filler metal powder milled for 120 min. The interfacial zones of the specimens brazed with the milled filler powder were thinner and the shear strength of the joint was increased compared to specimens brazed with non-milled filler powder. A sample brazed at 1180 °C for 15 min using TiH₂–50 wt.% Ni powder alloy milled for 120 min exhibited the highest shear strength at both room and elevated temperatures.     

Effect of brazing temperature on microstructure and mechanical properties of Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> joints brazed with Ag–Cu–Ti + Mo composite filler

Mo particles have been introduced into Ag–Cu–Ti brazing alloy for the joining of Si₃N₄ ceramic. Effect of brazing temperature on microstructure and mechanical properties of the joints were investigated. The result shows that a continuous reaction layer which is composed of TiN and Ti₅Si₃ was formed at the Si₃N₄/braze interface. The central part of the joint was composed of Ag-based solid solution, Cu-based solid solution, Mo particles, and Cu–Ti intermetallic compounds. By increasing the brazing temperature, both the thickness of the reaction layer and amount of Cu–Ti intermetallic compounds in the joint increased, being beneficial for the joint strength. Whereas, the reaction between Ti and Si₃N₄ ceramic proceeded excessively and more Cu–Ti intermetallic compounds were precipitated in the joint while elevating the brazing temperature to 950 °C, leading to deterioration of the bending strength. The maximal bending strength reached 429.4 MPa at 900 °C for 5 min when the Si₃N₄ ceramic was brazed with Ag–Cu–Ti + Mo composite filler.     

Joining of Cf/SiBCN composite with CuPd-V filler alloy

Two compositions of CuPd-V system filler alloy were designed for joining the Cf/SiBCN composite. Their dynamic wettability on the Cf/SiBCN composite was studied with the sessile drop method. The CuPd-8 V alloy exhibited a contact angle of 57° after holding at 1170℃ for 30 min, whereas for CuPd-13 V alloy,a lower contact angle of 28°can be achieved after heating at 1200 ℃ for 20 min. Sound C_f/SiBCN joints were successfully produced using the latter filler alloy under the brazing condition of(1170-1230)℃for 10 min. The results showed that the active element V strongly diffused to the surface of Cf/SiBCN composite, with the formation of V_2 C/VN reaction layer. The microstructure in the central part of the joint brazed at 1200 ℃ was characterized by the V_2 C/VN particles distributing scatteringly in CuPd matrix. The corresponding joints showed the maximum three-point bend strength of 82.4 MPa at room temperature.When the testing temperature was increased to 600 0 C, the joint strength was even elevated to 108.8 MPa.Furthermore, the joints exhibited the strength of 92.4 MPa and 39.8 MPa at 800 ℃ and 900 ℃, respectively.     

Vacuum brazing of GH99 superalloy using graphene reinforced BNi-2 composite filler

A novel graphene reinforced BNi-2 composite filler was developed for brazing GH99 superalloy. The interfacial microstructure of brazed joints was analyzed by field emission scanning electron microscope and a transmission electron microscope. The effects of graphene addition on the microstructure evolution and mechanical properties of brazed joints were investigated, and the strengthening mechanism of graphene was analyzed. The results revealed that due to the addition of graphene, M₂₃(C,B)₆ compounds were synthesized in the γ solid solution and brittle boride precipitates near the brazing seam decreased. Graphene was effective in retarding solute atoms diffusion thus impeding the precipitation of borides. Furthermore, the low coefficient of thermal expansion (CTE) of graphene was conducive to relieve stress concentration of the brazed joints during the cooling process. The shear strengths of brazed joints were significantly improved by exerting the strengthening effect of graphene. The maximum shear strengths of the brazed joints were 410.4?MPa and 329.7?MPa at room temperature and 800?°C, respectively.     

Microstructure and strength of brazed joints of Ti3Al-base alloy with different filler metals

The interfacial microstructure and properties of brazed joints of a Ti₃Al-based alloy were investigated in this paper to meet the requirements of the use of Ti₃Al-based alloy in the aeronautic and space industries. The effects of different brazing fillers on the interfacial microstructure and shear strength were studied. The relationship between brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. The brazed joints were qualitatively and quantitatively analyzed by means of EPMA, SEM and XRD. The results showed that using a AgCuZn brazing filler, TiCu, Ti(Cu,Al)₂ and Ag[s,s] were formed, the shear strength of the joint was decreased because of the formation of TiCu and Ti(Cu,Al)₂; using a CuP brazing filler, Cu₃P, TiCu and Cu[s,s] were formed at the interface of the joint, the former two intermetallic compounds decreased the shear strength. The analysis also indicated that using the TiZrNiCu brazing filler, the optimum parameters were temperature T=1323 K, joining time t=5 min, and the maximum shear strength was 259.6 MPa. For the AgCuZn brazing filler, the optimum parameters were joining temperature T=1073 K, joining time t=5 min, and the maximum shear strength was 165.4 MPa. To the CuP brazing filler, the optimum parameters were joining temperature T=1223 K, joining time t=5 min, and the maximum shear strength is 98.6 MPa. Consulting the results of P. He, J.C. Feng and H. Zhou [Microstructure and strength of brazed joints of Ti₃Al-base alloy with NiCrSiB, Mater. Charact., 52(8) (2004) 309–318], relative to the other brazing fillers, TiZrNiCu is the optimum brazing filler for brazing Ti₃Al-based alloy.     

Intermetallic compounds formed during brazing of titanium with aluminium filler metals

The effect of aluminium filler metal composition on the formation of AI-Ti intermetallic compounds was investigated in brazed aluminium-to-titanium (Al/Ti) joints and titanium-totitanium (Ti/Ti) joints. The clearance filling ability was also studied. In Ti/Ti joints, the thickness of the intermetallic compound layer was strongly dependent on the aluminium filler metal composition, whereas the clearance filling ability was independent of the composition. The maximum intermetallic compound layer thickness was observed in 99.99% highly pure aluminium filler metal; therefore all additional elements reduced the layer thickness. Above all, the addition of 0.8% Si greatly reduced the thickness. After brazing at 680° C for 3 min, the intermetallic compound formed by Al-0 to 0.8% Si filler metal was found to be of type Al₃Ti. Other compounds, of types Ti₉Al₂₃ and Ti₇Al₅Si₁₂, were also found in joints brazed by Al-3 to 10% Si filler metals. AI-0.8% Si filler metals maintained a higher joint strength than pure aluminium filler metal under brazing conditions of high temperature and long heating time. In Al/Ti joints, AI-Cu-Sn and AI-Cu-Ag filler metal mainly formed Al₃Ti, and Al-10Si-Mg filler metal mainly formed Ti₇Al₅Si₁₂ at the brazed interface of the titanium side after brazing at 600 to 620° C.     

Microstructure and mechanical properties of MoSi2–MoSi2 joints brazed by Ag–Cu–Zr interlayer

The present work investigates joining of two MoSi₂ parts through Cusil/Zr/Cusil interlayer with Cusil being a commercial eutectic of Cu–Ag alloy. The joining operation was implemented in an inert gas tube furnace by brazing. The brazing temperature ranged from 800 to 930 °C while the operation lasted for 60 min. Evaluation of joints strength through shear loading identified the maximum strength 60.31 MPa for the brazed sample at 830 °C. Interfacial microstructure was studied by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) techniques. Applying the temperature of 830 °C was led to a uniform dense joint consisting of various phases with excellent bonding within the interfaces. XRD and EDS results revealed different phases such as Mo₅Si₃, Ag-rich solid solution and Cu₁₀Zr₇ at the interface. At higher brazing temperatures the amount of intemetallic compounds and residual stresses increased and therefore, mechanical properties of the joint degraded. The fracture analysis by SEM revealed various fracture path and morphology for different brazing temperatures.     

Microstructure and brazing mechanism of porous Si3N4/Invar joint brazed with Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler

Porous Si_3N_4 was brazed to Invar alloy in this study, and Ag-Cu-Ti/Cu/Ag-Cu multi-layered filler was designed to inhibit the formation of Fe_2Ti and Ni_3Ti intermetallic compounds. The effects of the brazing temperature and the thickness of Cu interlayer on the microstructure and mechanical properties of brazed joints were investigated. The typical microstructure of the joint brazed with multi-layered filler was porous Si_3N_4/TiN + Ti_5Si_3/Ag-Cu eutectic/Cu/Ag-Cu eutectic/Cu-rich layer + diffusion layer/Invar. When the brazing temperature increased, the reaction layer at the ceramic/filler interface grew thicker and the Cu interlayer turned thinner. As the thickness of Cu interlayer increased from 50 to 150μm, the joint strength first increased and then decreased. In this research, the maximum shear strength(73 MPa) was obtained when being brazed at 1173 K with a 100μm Cu interlayer applied in the filler, which was 55% higher than that brazed with single Ag-Cu-Ti brazing alloy and had reached 86% of the ceramic. The release of residual stress and the barrier effect of Cu interlayer to inhibit the formation of Fe_2Ti and Ni_3Ti intermetallics played the major role in the improvement of joint strength.     

Silicon nitride-stainless steel braze joining with an active filler metal

Hot-pressed Si₃N₄ was brazed to 410-stainless steel using a Ag-Cu-Ti alloy foil in a vacuum. The occurrence of cracking due to processing was examined by systematically varying the brazing temperature and time between 840 and 900 °C and 6 and 60 min, respectively. Cracks were found in Si₃N₄ parallel to the bonding interface when the braze joints were processed at the lower temperatures (for all processing times at 840 °C and for times of 6 and 12 min at 860 °C). A reaction layer was observed to develop in the filler metal adjacent to Si₃N₄, rich in Ti and containing some Si. The thickness of this layer depended on brazing temperature and time. Microcracks were found in the reaction layer normal to the bonding interface in the joints processed at higher brazing temperatures (880 °C for 60 min and at 900 °C for 30 and 60 min). The low temperature cracks occurred, apparently, as a result of the incomplete relaxation of thermal stresses due to the presence of a hard continuous titanium strip in the filler metal; the high temperature microcracks seemed to be affected by the increase in thickness of the reaction layer and by the precipitation of intermetallic compounds. The compressive shear strength of the braze joints were evaluated and correlated with the cracking behaviour and microstructure changes in the joint. A strong braze joint was obtained when the reaction layer was relatively thin and no cracks were present in either the reaction layer or the Si₃N₄.     

Interface and Bond Strength of Brazing Cemented Carbide K20 to Alloy Steel AISI 4140 by High-Frequency Induction

High-frequency induction brazing of cemented carbide (WC–Co, K20) and alloy steel (AISI 4140) using Cu–Zn base filler metal was carried out. The relationship between microstructure and performance of the welding joint was investigated. It was found that the filler metal exhibited excellent wettability and metallurgical bond in the welding surface. As the heating rate reduced, welding joint appeared smooth without any visible crack. In the diffusion layer, some intermetallic compounds were observed, which were produced by the reaction of diffusion atoms. The microhardness in the middle of the welding seam was 168 Hv and it increased gradually when approaching to the edge of welding seam. With brazing temperature increased or heating rate decreased, the shear strength of welding joint increased first and then decreased. The machining test clearly revealed that the cutting temperature and the flank wear increased with the cutting speed rose. The welding joint had good shear strength when the temperature was below 500°C and the shear strength decreased seriously when the temperature exceeded 500°C.     

Microstructure of brazed joints between mechanically metallized Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and stainless steel

Brazing has been increasingly used to join metals to advanced ceramics. Brazing covalent materials requires either the use of active filler alloys or the previous metallization of the surface. To that end, a new and simple mechanical technique has been applied to metallize advanced ceramics, thus avoiding the use of costly Ti-based active filler alloys. The mechanical metallization of Si₃N₄ with Ti was employed as an alternative route to deposit active metallic films prior to brazing with stainless steel using 72% Ag--28% Cu or 82% Au—18% Ni eutectic alloys. The brazing temperatures were set to 40°C or 75°C above the eutectic temperature of each filler alloy. Ti-films of average thickness 4 μm produced adequate spreading of both filler alloys onto Si₃N₄ substrates, which were subsequently brazed to stainless steel. The interface of Si₃N₄/310 stainless steel basically consisted of a reaction layer, a precipitation zone and an eutectic microconstituent. Mechanically sound and vacuum-tight joints were obtained, especially upon brazing at relatively lower temperatures. Increasing the brazing temperature resulted in thermal cracking of the Si₃N₄, possibly due to increased thermal stress.     

Brazing continuous carbon fiber reinforced Li2O–Al2O3–SiO2 ceramic matrix composites to Ti–6Al–4V alloy using Ag–Cu–Ti active filler metal

C_f/LAS composites and TC4 alloy were brazed successfully by vacuum brazing using Ag–Cu–Ti active filler metal. The interfacial microstructure was characterized by a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction. The effects of brazing temperature on the interfacial microstructure and joint properties were investigated in details. Various phases including TiC, TiSi₂, Ti₃Cu₄, Cu (s,s), Ag (s,s), TiCu and Ti₂Cu were formed in the brazed joints. Interfacial microstructure varies greatly with the increase of brazing temperature, while the amount of Ti₂Cu reduced, but no new phase is generated. The optimal shear strength of the joint is 26.4 MPa when brazed at 890 °C for 10 min. Shear test indicated that the fracture of the brazed joints went through the TiSi₂ + TiC layer close to the C_f/LAS composites interface.     

Effect of in situ synthesized TiB whisker on microstructure and mechanical properties of carbon–carbon composite and TiBw/Ti–6Al–4V composite joint

Carbon–carbon composite (C–C composite) and TiB whiskers reinforced Ti–6Al–4V composite (TiB_w/Ti–6Al–4V composite) were brazed by Cu–Ni + TiB₂ composite filler. TiB₂ powders have reacted with Ti which diffused from TiB_w/Ti–6Al–4V composite, leading to formation of TiB whiskers in the brazing layer. The effects of TiB₂ addition, brazing temperature, and holding time on microstructure and shear strength of the brazed joints were investigated. The results indicate that in situ synthesized TiB whiskers uniformly distributed in the joints, which not only provided reinforcing effects, but also lowered residual thermal stress of the joints. As for each brazing temperature or holding time, the joint shear strength brazed with Cu–Ni alloy was lower than that of the joints brazed with Cu–Ni + TiB₂ alloy powder. The maximum shear strengths of the joints brazed with Cu–Ni + TiB₂ alloy powder was 18.5 MPa with the brazing temperature of 1223 K for 10 min, which was 56% higher than that of the joints brazed with Cu–Ni alloy powder.     

Vacuum brazing of sapphire with Inconel 600 using Cu/Ni porous composite interlayer for gas pressure sensor application

In this research, sapphire as a ceramic was brazed to Inconel 600 as a metal with a commercially available Cusil ABA (63Ag–1.75Ti–35.25Cu) filler foil as braze alloy where Cu/Ni porous composite introduced as an interlayer so it could be used in a particular gas pressure sensor application. Several brazing processes were carried out in a high vacuum furnace in order to investigate the effects of brazing parameters on the joint interface and mechanical properties. The common brazing temperature and time were in the ranges of 830–900 °C and 15–30 min respectively, while vacuum pressure was remained constant at 1 × 10⁻⁴ Pa. SEM-EDS and XRD analyses of the joint microstructure and interface composition revealed five distinct phases; Ni₃Ti, AlNi, Cr_1.97Ti_1.07, Fe_0.2Ni_4.8Ti_5, (TiO_1.06)_3.32. The brazing area formed two “ocean” structures near to Inconel and sapphire interfaces whereas a reaction layer was developed at the surface of Inconel 600. Under the mechanical property analyses the brazed joint at 900 °C for 30 min obtained the maximum shear strength of 58.5 MPa which is adequate for particular gas pressure sensor application.     

Diffusion brazing of Ti–6Al–4V and austenitic stainless steel using silver-based interlayer

In the present study, vacuum brazing was applied to join Ti–6Al–4V and stainless steel using AgCuZn filler metal. The bonds were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. Mechanical strengths of the joints were evaluated by the shear test and microhardness showed that shear strength decreased with increasing the brazing temperature and time. The results showed that the wettability of the filler alloy was increased by enhancing the wetting test temperature. It was shown that by increasing the brazing temperature various intermetallic compounds were formed in the bond area. These intermetallic compounds were mainly a combination of CuTi and Fe–Cu–Ti. The shear test results verified the influence of the bonding temperature on the strength of the joints based on the formation of different intermetallics in the bond zone. The fracture analysis also revealed different fracture footpath and morphology for the different brazing temperatures.     

Brazing parameters determine the degradation and mechanical behaviour of alumina/titanium brazed joints

The main aims of the present study are simultaneously to relate the brazing parameters with the correspondent interfacial microstructure, the resultant mechanical properties and the electrochemical degradation behaviour of commercially pure titanium/alumina brazed joints. A filler metal on the Ag-26.5Cu-3Ti system has been used. Three different brazing temperatures (850, 900 and 950°C) and three holding times (0.3, 1.2, 2.4 ks) were tested, in order to understand the influence of each combination of brazing temperature holding times, over the final microstructure and properties of the joints. The mechanical properties of the M/C joints were assessed on the basis of bond strength tests carried out using a shear solicitation scheme. The fracture surfaces were studied morphologically and structurally using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The degradation behaviour of the M/C joints was assessed by means of electrochemical techniques. It was found that a brazing temperature of 850°C and a holding time of 2.4 ks, produces the best results in terms of bond strength, 130 ± 16 MPa. The mechanical properties obtained could be explained on the basis of the different compounds identified on the fracture surfaces by XRD. On the other hand, a brazing temperature of 950°C produces the best results in terms of corrosion rates (lower corrosion current), 3.44 ± 0.73 A cm^–2. However, the joints produced at 850°C using a holding time of 1.2 ks present the best compromise between mechanical properties and degradation behaviour, 122 ± 12 MPa and 7.59 ± 1.47 A cm^–2 respectively. The role of Ti diffusion from the metallic Ti to the Al₂O₃ surface is fundamental in terms of the final value achieved for the M/C bond strength. On the contrary, the Ti distribution along the brazed interface does not seem to play any relevant role in the M/C joints electrochemical performance.     

Microstructural development of diffusion-brazed austenitic stainless steel to magnesium alloy using a nickel interlayer

The differences in physical and metallurgical properties of stainless steels and magnesium alloys make them difficult to join using conventional fusion welding processes. Therefore, the diffusion brazing of 316L steel to magnesium alloy (AZ31) was performed using a double stage bonding process. To join these dissimilar alloys, the solid-state diffusion bonding of 316L steel to a Ni interlayer was carried out at 900 °C followed by diffusion brazing to AZ31 at 510 °C. Metallographic and compositional analyses show that a metallurgical bond was achieved with a shear strength of 54 MPa. However, during the diffusion brazing stage B₂ intermetallic compounds form within the joint and these intermetallics are pushed ahead of the solid/liquid interface during isothermal solidification of the joint. These intermetallics had a detrimental effect on joint strengths when the joint was held at the diffusion brazing temperature for longer than 20 min.     

Effect of brazing temperature on the microstructure of martensitic–austenitic steel joints

Dissimilar joining of reduced activation ferritic–martensitic steel to AISI 316LN austenitic stainless steel is carried out by brazing in inert atmosphere at three different temperatures, i.e. 980, 1020 and 1040°C using AWS BNi-2 powder. The braze joints are characterised by scanning electron microscopy, X-ray diffraction, micro-hardness measurement. With increasing brazing temperature from 980 to 1040°C, the approximate width of the braze layer decreases from 350 to 80?µm and hardness reduces from 600 to 410?VHN. However, not much difference is found in microstructure and hardness between braze joints produced at 1020 and 1040°C. With increasing brazing temperature, morphology and volume fraction of intermetallics formed in the braze layer change, thereby reducing the hardness variation between the braze layer and the base metal.