Ag-Cu Filler Research Articles

Microstructure and Mechanical Property of Titanium Film-Modified Sapphire/High Nb-TiAl Alloy Joints Using Ag-Cu Filler by Vacuum Brazing

Microstructure and Mechanical Property of Titanium Film-Modified Sapphire/High Nb-TiAl Alloy Joints Using Ag-Cu Filler by Vacuum Brazing

Ag-based filler metal wetting behavior and brazed joint performance on SLMed Ti/TiB2 substrate

PurposeThis study aims to investigate the wetting behavior of AgCuTi and AgCu filler metals on selective laser melting (SLMed) Ti/TiB2, and to analyze the microstructure and fracture characteristics of SLMed Ti/TiB2/AgCuTi or AgCu alloy/SLMed Ti/TiB2 brazed joints. The wetting behavior of AgCuTi and AgCu filler metals on the selective laser melted (SLMed) Ti/TiB2 has been studied. The analysis of microstructures and fracture characteristics in vacuum-brazed SLMed Ti/TiB2 substrate, using AgCuTi and AgCu filler metals, has been conducted to elucidate the influence of brazing temperature and alloy composition on the shear strength of the brazed joints.Design/methodology/approachBrazing SLMed-Ti/TiB2 in a vacuum using AgCuTi and AgCu filler metals, this study aims to explore the optimal parameters for brazed joints at various brazing temperatures (800°C−950°C).FindingsThe findings suggest that elevated brazing temperatures lead to a more extensive diffusion region in the joint as a result of the partial melting of the filler metal. The joint composition changes from distinct Ti2Cu layer/TiCu layer/filler metal to a-Ti (ss) + ß-Ti (ss)/TiCu. As the brazing temperature increases, the fracture mode shifts from brittle cleavage to ductile fracture, mainly attributed to a decrease in the CuTi within the brazed joint. This change in fracture behavior indicates an improvement in the ductility and toughness of the joint.Originality/valueThe originality of this study lies in the comprehensive analysis of the microstructure and shear strength of vacuum brazing SLMed Ti/TiB2 using AgCuTi and AgCu filler metals.

Microstructure, mechanical properties and hermeticity of W-Cu/HTCC brazed joints with surface metallization

WCu alloy and high temperature co-fired ceramic (HTCC) were metallized through electroless nickel plating, then one series of W-Cu/Ni/AgCu/Ni/HTCC joints were successfully brazed with AgCu filler. The microstructure, mechanical properties, and hermeticity of W-Cu/HTCC joints were systematically investigated, and the fracture paths of the joints were summarized. The results revealed that the interface microstructure of the joints consisted of Ni(Cu)-W, Ni3P, CuNi, Cu(s,s), and Ag(s,s) phases. As the brazing temperature increased, Ni atoms gradually diffused from the NiP layer into the filler layer and substrate. At 900 °C, the NiP layer dissolved, and Cu atoms from the WCu alloy diffused into the solder layer, leading to a sharp growth in joint thickness. The shear tests indicated that the promotion of Cu content in the filler layer effectively alleviated the residual stress in the joints, resulting in higher joint strength. The maximum shear strength of 73.57 MPa was reached when the joints brazed at 840 °C. The hermeticity measurement results showed that the joints brazed at 900 °C for 10 min exhibited exceptional hermeticity, with a helium leakage rate of 2.51 × 10−11 Pa·m3/s. This work provided a reference for the connection of metal packaging materials with high temperature co-fired ceramics.

Metallurgical aspect of a joint made of Inconel 718 and CuCrZr brazed with Ag-Cu eutectic filler

The realization of bimetallic structures is one of the major challenges of manufacturing industry, to this aim different technologies are employed, among these vacuum brazing presents some advantages: this technology, in fact, is relatively easy to use and the relative low temperature and low process time employed, avoid the formation of brittle intermetallics and thermally affected zones. An application of vacuum brazing technology is the realization of regenerative thrust chamber for rocket engines where cooling channels of CuCrZr are joined to Inconel 718 combustion chamber. In this work the critical metallurgical aspects occurring during brazing of Inconel 718 and CuCrZr using eutectic Ag-Cu filler are described in detail. These aspects include the formation of two distinct metallurgical zones inside the filler and an interdiffusion zone with Kirkendall porosity at the interface Inconel 718-Brazing Alloy. The analysis of fracture surface after tensile tests indicates that the interdiffusion zone is the weak point of the joint.

Induction brazing of NdFeB magnet with PVD-deposited AgCu alloy

The NdFeB magnets service in high-power electric-mechanical conversion devices sometimes endure high stress and high-temperature impact, and adhesion of these magnets using glue cannot ensure the reliability. In this study, the NdFeB was induction brazed with physical vapor deposition (PVD)-deposited Ag72Cu28 alloy layer, then the microstructure, mechanical properties and magnetic properties of the brazed joints were characterized, and effects of the filler metal thickness and the induction heating time were analyzed. The results show that the PVD coating can effectively prevent the surface oxidation of the NdFeB. The AgCu filler metal penetrates into the NdFeB and is partly mixed with the liquefied Nd-rich intergranular phase of the NdFeB, forming a good metallurgical bonding. The thickness of the penetration layer increases obviously with increase of the heating time and filler metal thickness. The bonding strength of the NdFeB brazed joint increases firstly and then decreases with increasing heating time, and a peak bending strength of 196.94 MPa was obtained. Fracture of the brazed joint occurs inside the NdFeB substrate close to the penetration layer. After a further annealing, the coercivity of the brazed NdFeB sample is a little higher than that of the un-brazed sample, and the squareness decreases by only a little. Properties of the brazed joints might be further improved by optimizing the amount of filler metal and the induction heating parameters.

Brazing SiC ceramic to Al0.3CoCrFeNi high‐entropy alloy using Ag–Cu filler metal

AbstractRealizing the joining of SiC ceramic to Al0.3CoCrFeNi high‐entropy alloy is a technical interest for aviation, aerospace, and nuclear energy industry. In this study, the reliable brazing of SiC and Al0.3CoCrFeNi high‐entropy alloy was realized by inactive AgCu filler, which lays the foundation for the following research on ceramic‐high‐entropy alloy dissimilar joining. The interfacial microstructure was characterized by a scanning electron microscope and transmission electron microscope in detail, and the influence of Al0.3CoCrFeNi dissolution on interfacial reactions was studied. The effect of brazing temperature on microstructure evolution and mechanical properties was discussed. The results indicated that elements Ni, Fe, Co, and Cr from Al0.3CoCrFeNi were crucial for the joint formation. (Ni, Fe, Co)2Si + graphite + Cr23C6/(Cr, Fe)23C6 + (Ni, Fe, Co)2Si formed adjacent to SiC and (Fe, Co, Cr, Ni)–Si silicide + Cu(s,s) + Cu–Ni–Al‐rich phase formed next to Al0.3CoCrFeNi. The reaction layers on SiC side thickened and the morphology of (Fe, Co, Cr, Ni)–Si‐ and Cu–Ni–Al‐rich phase experienced distinct changes with the increasing temperature. The highest strength of ∼32.2 MPa was obtained at 850°C for 10 min.

Characterization of ZTA Composite Ceramic/Ti6Al4V Alloy Joints Brazed by AgCu Filler Alloy Reinforced with One-Dimensional Al18B4O33 Single Crystal

Al18B4O33 whiskers were used as a reinforcer to study the effect of one-dimensional single crystal on the quality improvement of ZTA composite ceramic/Ti6Al4V alloy joints brazed by AgCu alloy. The microstructure of the joint with whisker additions was characterized in detail. The effects of brazing temperature on the microstructure and shear strength of the brazed joints were investigated. The results showed that the whiskers reacted with the liquid alloy during the brazing process and continuous (Cu,Al)3Ti3O layers were formed in contact with the residual whiskers. The addition of 2 wt.% Al18B4O33 whiskers into AgCu filler alloy can delay the growth of the (Cu,Al)3Ti3O layer on the ZTA side, and can significantly restrain the growth of the Ti-Cu compound region over a brazing temperature range of 800~875 °C. Because of the one-dimensional reinforcement, the temperature window for obtaining ZTA/Ti6Al4V joints with shear strength values higher than 50 MPa was extended, and the maximum shear strength of the joints reached 56 MPa.

Microstructure evolution and joining strength of diamond brazed on Ti-6Al-4V substrates using Ti-free eutectic Ag-Cu filler alloy

In this study, strong bonding of vacuum brazed synthetic diamond and Ti-6Al-4V substrates joints was achieved using a Ti-free eutectic AgCu filler alloy. It was found that the brazing temperature remarkably influenced the interfacial microstructures, and hence affected the bonding strength of brazed diamond joints. Thermodynamic calculation and TEM microstructural characterization revealed that the rapid adsorption and dissolution of Ti in molten filler alloy is responsible for the preferential precipitation of TiCu and/or Ti2Cu IMCs on the brazed diamond surface and the excessive formation of TiCu IMCs, which largely impaired the bonding strength of brazed Ti-6Al-4V/diamond joints. An evolution model exploring the microstructure and mechanical properties of the brazed joints on Ti-6Al-4V substrates was proposed, by taking the behavior of Ti adsorption into account. The underlying mechanism to gain a reliable bonding between Ti-6Al-4V substrate and diamond in this work is therefore of essential implications for the understanding of microstructure and bonding strength of other hard-to-wet materials on Ti-based substrates.

The making and performance of patterned-monolayer brazed diamond wheel produced with Ag-based novel active filler

Present paper delineates a novel route adopted for successfully manufacturing single layer brazed patterned diamond wheels with enhanced attributes. A pneumatic pick-drop methodology is used for placing the grits in a uniform and patterned manner. Instead of commonly used Ni-Cr alloys, a novel formulation of μ-TiC inoculated composite Ag-Cu-Ti filler has been preferred, which helped in arresting crack formation at the root of grit brazement and simultaneously ensured high bond wear characteristics. Addition of μ-TiC particles substantially improved wear characteristics of basic Ag-Cu-Ti alloy but tend to impair its wetting ability on diamond surface with increase in its wt% in the composition. Therefore, its presence in the filler was restricted to only 2 wt% to keep such compromise within acceptable level. Wheels developed using active Ag-Cu fillers were further subjected to performance evaluation by grinding of WC-Co cermets. The operating parameters were changed in such a way that wheels experienced increasing order of grinding-aggressiveness. The degree of aggressiveness in the grit-work interaction has been defined by a unifying scalar quantity, termed as “aggressiveness number”. No trace of wheel loading was observed even in the most aggressive condition due to uniformly spaced grits. The failure counts of diamond grits are also related to this scalar. A detailed analysis is presented to address the suitability of μ-TiC reinforcement in the formulation of active Ag-Cu filler in the light of the grinding force and grit retention ability of the wheels.

Electrical contacting of High-Velocity-Air-Fuel sprayed NiCr20 coatings by brazing

Thermally sprayed heater coatings can be used to control the surface temperature of parts and tools. A crucial point for such applications that has been neglected in the past is a reliable electrical contact with the power supply. One possible solution is the soldering or brazing of cables and cable connectors onto the heater coating. In this study, the possibility of brazing cable connectors to High-Velocity-Air-Fuel sprayed NiCr20 coatings was investigated to ensure electrical contact. The eutectic Ag-Cu filler was used for the vacuum brazing process. The insufficient wetting of the filler on the as-sprayed coating surface and the favored wetting of this filler on the copper cable connector led to low joint quality. This joint was improved by grinding the coating surface and changing the cable connector’s material. Furthermore, measurements of the heater coatings’ electrical resistance confirmed that electrical contacting by brazing is possible without significant influence on the heater coatings’ properties.

Design of multi-layered architecture in dissimilar ceramic/metal joints with reinforcements clustering away from both substrates

To combine the advantages of ductile fillers and composite fillers and alleviate residual stress in joints between ZrB2-SiC ceramics (ZS) and TC4-TiBw composites, a novel multi-layered joint architecture composed of a layer of clustering SiC at the center of the joint (L-C-SiC) and two ductile layers without SiC particles bordering both substrates (L-DS) was designed. To achieve this, SiC particle skeletons with continuous micro-channels (SSCC) were integrated with AgCu filler as an interlayer. The effects of SSCC porosity and brazing temperature on joint microstructure and mechanical properties were investigated. In particular, the braze/ZS and braze/SSCC interfaces were analyzed through X-ray diffractometry (XRD), transmission electron microscopy (TEM), and wavelength-dispersive spectroscopy (WDS). The residual stress was also evaluated. The results indicate that increasing the brazing temperate improved the infiltration into the SSCC and promoted the SSCC/braze interface reaction (was detrimental to the SiC particle skeleton). Reducing the SSCC porosity changed the thicknesses of the two L-DSs and enhanced the inhomogeneity of the SSCC/braze interface reaction (induced a shear stress in L-C-SiC). For brazing with an interlayer of 30% porosity at 820 °C, the joint shear strength reached a maximum of ~41.2 MPa, mainly due to the construction of the multi-layered joint architecture.

Controllable distribution of reinforcements for reducing the strain energy in dissimilar ceramic/metal joints

A novel design of a multi-layered joint architecture, characterized by the controllable spatial distribution of ceramic reinforcements, was obtained, when brazing ZrB2-SiC ceramics and Ti-6Al-4 V reinforced by TiB whiskers with AgCu filler. To induce SiC reinforcements to cluster together, within the center of the filler and especially away from the ZrB2-SiC, SiC was added into joint, in the form of a SiC interlayer featuring a 3D-bridged network structure with continuous micro-channels infiltrated by capillary force by liquid filler during brazing. Different SiC particles were connected together, by micro-bridges being not destroyed during brazing. The layer rich in SiC could reduce thermal expansion mismatch between different substrates, the AgCu next to the ZrB2-SiC could relax the strain energy by high plastic deformation. Compared to joint brazed with single AgCu, joint strain energy decreased from 10.8 × 10−6 J to 8.6 × 10−6 J, accordingly joint shear strength increased from ∼5.4 MPa to ∼41.2 MPa.

Self-propagating synthesis joining of Cf/Al composites and TC4 alloy using AgCu filler with Ni–Al–Zr interlayer

The successful joining of carbon fiber-reinforced aluminum matrix (Cf/Al) composites and TC4 alloy can produce composite structure and meet the demands of lightweight in aerospace field. Up to now, few experimental researches have been reported on the joining of Cf/Al composites and TC4 alloy. In this study, the AgCu foils and Ni–Al–Zr compact were designed for the self-propagating high-temperature synthesis joining of these two materials. Cf/Al composites were joined with a reactive Ti plated on its joining surface. The typical microstructure of TC4/(AgCu/Ni–Al–Zr/AgCu)/Ti/Cf/Al joint was analyzed, and the effects of joining condition on microstructural evolution of the SHS joint were investigated. A thin reaction layer of Ni–Al–Ti intermetallic compounds was formed adjacent to the TC4 alloy. As a result, AgCu foils could reduce the effect of reaction heat on the substrates and improve the joint shear strength. When the thickness of AgCu foils reaches 150 μm, the Ni–Al–Zr interlayer mainly acts as auxiliary heat source. High joining pressure caused the active elements to diffuse into Cf/Al composites and weakened the shear strength of the joint. Finally, the joint shear strength could reach 36.4 MPa when the AgCu foils were 50 μm and the joining pressure was 2 MPa.

Brazing of SiC ceramics pretreated by chromium coating using inactive AgCu filler metal

AbstractIn this work, chromium coating conducted by magnetron sputtering was introduced to braze SiC ceramics using inactive AgCu filler metal. The results showed that reliable metallurgical bonding of SiC ceramics was obtained at 900°C for 10 minutes. SEM, XRD, and TEM were used to identify the reaction phase in the joint, and the typical interfacial microstructure was SiC/mixed CrSi2 + Cr23C6 layer/CrSi2/Ag(s,s)+Cu(s,s)/CrSi2/mixed CrSi2 + Cr23C6 layer/SiC. The shear strength of SiC joint using chromium coating brazed with inactive AgCu filler metal was 29.6 MPa and the joint fractured at the SiC substrate entirely after shear test. The proposed active element coating method provides a feasible way to achieve the brazing of ceramics.

Vacuum brazing ZSCf composite ceramics to TC4 alloy with Ag-Cu filler

In this study, the carbon fiber reinforced ZrB2-SiC composite ceramic was joined to Ti6Al4V alloy with Ag-Cu eutectic alloy filler at varied holding time and a fixed temperature of 800℃. Interface microstructure and shear strength of brazing joints were studied. The brazed ZSCf ceramics/AgCu/TC4 alloy is endowed with good metallurgical bondings. A typical interfacial structure of joints brazed for 10min was found as ZSCf/TiC/Ti5Si3/Ag(s,s)/Cu(s,s)+TiC/TiCu/Ti2Cu/(TiC+TiCu)/TC4 alloy. Increase of holding time did not vary the precipitated phase of the joints but decreased thickness of the Ag(s, s) and Cu(s, s) reaction layer and gradually thickened the Ti-Cu reaction layer near the TC4 side. The formation process of reaction products was discussed in detail. The holding time substantially influenced shear strength of the joints. A maximum shear strength of 39MPa was reached at a brazing time of 20min.

Microstructure and Mechanical Properties of a SiO2 Ceramic and TC4 Alloy Joint Brazed with a Nanocomposite Filler

Vacuum brazing of TC4 alloy and SiO2 ceramic was achieved using a nano-AgCuNi braze alloy. The melting temperature of nano-AgCu powders was analyzed by differential scanning calorimeter. Furthermore, the effects of the Ni content on the microstructure and mechanical properties of the joints were studied. The results showed that the melting temperature of the nano-AgCu filler was 774 °C. A decrease in the melting temperature of 6 °C was observed, compared with the general AgCu filler, and this decrease enabled the interfacial reaction of the joint to begin earlier. The typical interfacial microstructure of the TC4/nano-AgCuNi/SiO2 ceramic joint brazed at 950 °C for 10 min was TC4/α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectoid structure/Ti2(Cu,Ni) compound with α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure/Ti4O7 + TiSi2/SiO2 ceramics. The homogeneous microstructure of α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectoid structure primarily existed in the diffusion layer. Additionally, the refined α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure created via a eutectic reaction and Ti2(Cu,Ni) compound was distributed in the brazing seam. The Ni content could influence the formation of Ti-Cu-Ni ternary intermetallic compounds (IMCs). An increase in Ni led to an increase in the α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure in the brazing seam. The shear strength of the brazed joints first increased and then decreased with the increase in the nano-Ni content, and the optimal shear strength of 30.1 MPa was achieved at 10 wt.% Ni. The increase in the α-Ti + Ti2(Cu,Ni) + Ti2(Ni,Cu) hypereutectic structure and the decrease in brittle compounds enhanced the shear strength of the joint. Fracture analysis of the joints brazed at 950 °C for 10 min indicated that the cracks mainly occurred in SiO2 ceramic.

Wetting kinetics and interfacial structure of AgCu alloy spreading on TB8 substrates

AgCu filler metal spreading over TB8 substrate under a high-purity argon atmosphere was conducted at 920 °C. Effects of surface roughness and topography of the substrate on the wetting kinetics were investigated. The interfacial microstructures of AgCu eutectic alloy/TB8 substrate solidified couples was analyzed by optical microscope, scanning electron microscope, energy dispersive spectrometer and transmission electron microscope. Results revealed that the substrate surface roughness and topography had significant influences on the wetting kinetics and spreading process. The spreading was preferential when AgCu molten metal over an anisotropically microstructured surface. When the surface of the substrate was not anisotropic, the spreading morphology was almost a perfect circle. An additional capillary driving force exists when the molten metal flows on the rough surface, which leads to a better wettability. The interfacial microstructure of the resolidified AgCu on the TB8 substrate was Ag(ss)/ Ti3Cu4/Ti2Cu/ /Ti(ss) + Ti2Cu/TB8, and the spreading edge domain near the triple-line is rich in Ag.

Investigation on viscosity, surface tension and non-reactive wettability of melting Ag-Cu-Xwt%Ti active filler metals

The microstructure, viscosity and surface tension of melting Ag-Cu-Xwt%Ti active filler metals were researched, the influence mechanism of microstructure on the viscosity and surface tension was discussed, the non-reactive wetting behavior of melting Ag-Cu-Xwt%Ti filler metals on W substrate was investigated. The research results indicate that, the microstructure of Ag-Cu filler metal is composed by Ag86Cu14 phase and Ag56Cu44 phase, while after Ti element be added in the Ag-Cu-Xwt%Ti filler metal, Cu-Ti intermetallic compounds will be formed. The different microstructures of the Ag-Cu-Xwt%Ti filler metals, especially the difference between the amounts and kinds of the intermetallic compounds, lead to the various viscosity and surface tension. Viscosity of the Ag-Cu-Xwt%Ti filler metal can be divided into low temperature zone and high temperature zone. At the low temperature zone, the viscosity increases obviously with the increasing Ti content, while at the high temperature zone, the viscosity for the four melting Ag-Cu-Xwt%Ti filler metals show little difference. With increase of the temperature, surface tension for the four melting Ag-Cu-Xwt%Ti filler metals all decrease firstly and then increase, and the temperature for the lowest surface tension is 975 °C. Moreover, with increase of the Ti content, surface tension of the melting Ag-Cu-Xwt%Ti filler metal increases gradually at both low temperature zone and high temperature zone, but the difference among them at low temperature zone is larger than that at high temperature zone. The non-reactive wetting experimental result confirms this conclusion very well.

Wetting and Brazing of Chromium Film-Deposited Alumina Using AgCu Filler Metal

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.

Laser‐induced metallization of porous Si3N4 ceramic and its brazing to TiAl alloy

AbstractThe poor wettability of traditional brazing filler alloys on the surface of ceramics always lead to the formation of defects in the joints and weaken the bonding strength eventually, especially the porous ceramics. Metallization on ceramics is an effective way to improve the wettability. In this work, laser‐induced cladding process was applied to metalize the surface of porous Si3N4 ceramic, and the traditional AgCu eutectic filler alloy can wet on the metalized surface completely. The metalized porous Si3N4 ceramic brazed to TiAl alloy successfully using AgCu filler alloy. The interfacial microstructure and mechanical property of the porous Si3N4/TiAl alloy brazed joint was significantly improved by the novel laser‐induced metallization process.