Active Brazing Alloy Research Articles

Specially Structured AgCuTi Foil Enables High-Strength and Defect-Free Brazing of Sapphire and Ti6Al4V Alloys: The Microstructure and Fracture Characteristics.

A novel AgCuTi brazing foil with a unique microstructure was developed, which could achieve strong vacuum brazing of Ti6Al4V (TC4) and sapphire. The brazing foil was composed of Ag solid solution (Ag(s,s)), Cu solid solution (Cu(s,s)), and layered Ti-rich phases, and had a low liquidus temperature of 790 °C and a narrow melting range of 16 °C, facilitating the defect-free joining of TC4 and sapphire. The sapphire/TC4 joint fabricated by using this novel AgCuTi brazing foil exhibited an outstanding average shear strength of up to 132.2 MPa, which was the highest value ever reported. The sapphire/TC4 joint had a characteristic structure, featuring a brazing seam reinforced by TiCu particles and a thin Ti3(Cu,Al)3O reaction layer of about 1.3 μm. The fracture mechanism of the sapphire/TC4 joint was revealed. The crack originated at the brazing seam with TiCu particles, then propagated through the Ti3(Cu,Al)3O reaction layer, detached the reaction layer from the sapphire, and finally penetrated into the sapphire. This study offers valuable insights into the design of active brazing alloys and reliable metal-ceramic bonding.

Experimental study on manufacturing of vacuum-brazed grinding tools with diamond grains

AbstractThis work provides an experimental study on manufacturing methods for vacuum-brazed diamond grinding for edge machining of carbon fiber-reinforced polymers (CFRP). Therefore, various methods for applying active brazing alloys and diamond grains were investigated. The application methods were evaluated regarding practicability and the possibility of automation. Additionally, the samples were examined after vacuum brazing and brazing results were compared concerning method, amount and type of brazing alloy, diamond grains and binding agent. It was found that the best results could be achieved by using fluidized bed coating for diamond application and a brazing alloy containing a 15% binding agent. The method and brazing alloy were then used to produce cylindrical mounted points for grinding tests. It was possible to show that vacuum-brazed tools performed as good as commercially available electroplated tools.

Study on the Effect of "3D-rGO" Buffer Layer on the Microstructure and Properties of SiO2f/SiO2 and TC4 Brazed Joint.

Brazing a SiO2f/SiO2 composite with metals is often faced with two problems: poor wettability with the brazing alloy and high residual stress in the joint. To overcome these problems, we report a combined method of selective etching and depositing reduced graphene oxide (rGO) on the surface of a SiO2f/SiO2 composite (3D-rGO-SiO2f/SiO2) to assist brazing with TC4. After the combined treatment, a "3D-rGO" buffer layer formed on the surface layer of the SiO2f/SiO2, and the contact angle was reduced from 130° to 38°, which meant the wettability of active brazing alloy on the surface of SiO2f/SiO2 was obviously improved. In addition, the "3D-rGO" buffer layer contributed to fully integrating the brazing alloy and SiO2f/SiO2; then, the infiltration of the brazing alloy into the surface layer of the SiO2f/SiO2 was enhanced and formed the reduced graphene oxide with a pinning structure in the three dimensional ("3D-pinning-rGO") structure. Moreover, the joining area of the brazing alloy and SiO2f/SiO2 was expanded and the mismatch degree between the SiO2f/SiO2 and TC4 was reduced, which was achieved by the "3D-pinning-rGO" structure. Furthermore, the concentration of the residual stress in the SiO2f/SiO2-TC4 joints transferred from the SiO2f/SiO2 to the braided quartz fibers, and the residual stress reduced from 142 MPa to 85 MPa. Furthermore, the 3D-pinning-rGO layer facilitated the transfer of heat between the substrates during the brazing process. Finally, the shear strength of the SiO2f/SiO2-TC4 joints increased from 12.5 MPa to 43.7 MPa by the selective etching and depositing rGO method.

Finite element based 3-D modelling of residual stress in high vacuum actively brazed diamond/Ni-Cr filler/C45 steel joint

In active brazing of diamonds, high brazing temperature and difference in the thermo-mechanical properties of the diamond grain, filler alloy, and substrate lead to the development of unfavorable residual stresses in the bonding region. This residual stress can potentially cause initiation of cracks within the interfacial reaction layer formed between diamond and filler-alloy, weakening the joint. Since the diamond particles used in diamond grinding tools are micro-sized and complex in shape, it is experimentally difficult to measure residual stress at the grit-filler interface. In the present investigation, a coupled thermo-mechanical three-dimensional finite element model has been developed to predict, map, and analyse the formation of residual stresses in diamond-bond-substrate systems. The presented model uniquely differs from those in literature, which are mostly 2-D type and did not consider the presence of interfacial reaction layer between diamond and filler. A Ni-Cr-Fe-B active brazing alloy has been selected as the filler and C45 steel as the substrate in the current simulation. Chromium carbide has been considered to be the interfacial compound. The numerical simulation suggests that the maximum value of residual stresses, predominantly tensile in nature, gets shifted from the diamond to the intermetallic zone at the bond level when the interfacial reaction compound is introduced between the diamond and filler. It also establishes that orientations of diamond during its placement on substrate for brazing have significant influence on the magnitude of induced residual stress. Approximately 40 % reduction has been observed in case of hexagon-base brazed diamonds when compared to that (1620 MPa) developed on square-base brazed diamonds. Raman spectral analysis of brazed specimen was conducted to experimentally validate the numerical simulation results. Residual stress was estimated from the peak shift of D-band in the spectra. The numerically computed residual stresses were found to deviate within the range of 3–15 % of the experimentally determined values.

Improved wetting of gold active braze alloy on diamond for use in medical implants

Medical implants containing active electronics must have a leak-proof encapsulation to be certified as safe for human use. Implantable devices made from diamond demonstrated exceptionally long implantation lifetimes due to the outstanding biostability and biocompatibility of the material. However, since diamond does not melt and is therefore not weldable, forming joints between diamond components or embedding metallic wires and bonding pads within diamond is challenging. One method consists of using active braze alloys to bond diamond surfaces together. These active brazes comprise a precious metal alloy containing a carbide forming element that chemically bonds to the diamond as the braze metal melts. Silver-based active braze alloys are used successfully for brazing diamond in industrial applications, but silver is toxic to living tissue and, therefore unsuitable for use in implants. Gold active braze alloys (Au-ABA) are biocompatible but exhibit very poor wetting on the diamond. Here we demonstrate the use of molybdenum (Mo) and niobium (Nb) interlayers including single layers of Mo, Nb or Mo/Nb bilayer thin films as a solution to improve the wetting of Au-ABA on diamond surfaces. Theses interlayers provide for excellent penetration of the braze into the grooves and crevices in the diamond surfaces. We report on optimum recipes for the interlayer, both for the fabrication of weld lines and for the formation of smaller complex micro-structures and hermetic electrical feedthroughs.

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.

Nd:YAG pulsed laser brazing of cBN to steel matrix with Zr modified Ag–Cu–Ti active brazing alloy

The study was to investigate the modifying effect of the active element Zr on the properties of mechanical alloyed (MA) AgCu28–4.5Ti brazing alloys, especially the joint performance of cubic boron nitride (cBN)/45 steel brazed with AgCu28–4.5Ti–4Zr active brazing alloy. The brazing process was carried out using an Nd:YAG pulsed laser device under a high purity argon atmosphere. The granularity distribution and composition analysis of the MA brazing alloys, microstructural examinations and phase analysis were performed using a laser granularity analyzer, scanning electron microscopy (SEM) equipped with energy dispersion spectrometry (EDS), and X–ray diffraction (XRD) techniques. The results indicate that the alloy particles are refined, sizes are uniform, and the formation of the hard-brittle phase is reduced owing to the addition of the active element Zr. The wettability of the brazing alloy containing Zr is enhanced. The reaction of the active element Zr with Ag or Cu inhibits the combination of Ti with Ag or Cu under rapid laser heating and cooling, and further promotes the generation of TiB and TiN compounds. The joining mechanism is derived from the formation of a continuous reaction layer between cBN and the brazed alloy, containing a sub-outer structure of TiB, TiB2, TiN, ZrB2, and an outer structure consisting of AgZr2, Cu10Zr7. This multi-layered structure, which is from cBN to 45 steel, realizes the metallurgy combination of the brazing alloy and cBN particles. The friction and wear tests indicate that the reliable connection of cBN to steel is realized.

Comparative study on the joining performance of TiH2 and ZrH2 modified AgCu28 brazing alloys with pulsed laser welding-brazing

Brazed alloys between cubic boron nitride (cBN) grits and matrix extremely affect the service life of the grinding wheel. The aim of this study was to investigate the addition of elemental Zr to improve the connection effect of alloys. The plates of pure titanium (Ti) Gr. 1 and AISI 1045 steel had been applied to conduct the welding-brazing experiments with active brazing alloys of AgCu28-4.5Ti and AgCu28-4.5Ti-4Zr. Brazing alloys was heated with an Nd:YAG pulsed laser welding-brazing system under inert argon gas atmosphere. Transition zones between the brazed alloys and matrices were investigated with scanning electron microscope (SEM), energy dispersion spectrometer (EDS), and X-ray diffraction (XRD) analyses. In addition, hardness of the brazed layer was analyzed as well as tribology. The results showed that the active element, zirconium (Zr), significantly accelerated the bidirectional diffusion and improved the gradient evolution of the main elements in the transition zones. Compared to Zr-free brazing alloys, the active element, Zr, inhibited the overproduction of the hard-brittle phase of Cu3Ti and formed other intermetallic compounds, such as AgZr2 and Cu10Zr7, which were beneficial to the metallurgical joint. A brazed layer with a lower friction coefficient, a more uniform hardness distribution, and better ductility was obtained, though the wear resistance slightly decreased. A solid solution product of Zr-Cu was formed during laser welding-brazing process, which strengthens the brazed layer and improves its overall performance.

Formation of Interfacial Reaction Layers in Al2O3/SS 430 Brazed Joints Using Cu-7Al-3.5Zr Alloys

The formation of interfacial reaction layers was investigated in an α-Al2O3/430 stainless steel (SS430) joint brazed using a Cu-7Al-3.5Zr active brazing alloy. Brazing was conducted at above its eutectic temperature of 945 °C and below liquidus 1045 °C, where liquid and solid phases of the brazing alloys coexists. At 1000 °C, the liquid phase of the brazing alloy was wet onto the α-Al2O3 surface. Zr in the liquid phase reduced α-Al2O3 to form a continuous ZrO2 layer. As the dwell time increased, Zr in the liquid phases near α-Al2O3 interface was used up to thicken the reaction layers. The growth kinetics of the layer obeys the parabolic rate law with a rate constant of 9.25 × 10−6 cm·s−1/2. It was observed that a number of low yield strength Cu-rich particles were dispersed over the reaction layer, which can release the residual stress of the joint resulting in reduction of crack occurrence.

Active metal brazing of Al2O3 to Kovar® (Fe–29Ni–17Co wt.%) using Copper ABA® (Cu–3.0Si–2.3Ti–2.0Al wt.%)

The application of an active braze alloy (ABA) known as Copper ABA® (Cu–3.0Si–2.3Ti–2.0Al wt.%) to join Al2O3 to Kovar® (Fe–29Ni–17Co wt.%) has been investigated. This ABA was selected to increase the operating temperature of the joint beyond the capabilities of typically used ABAs such as Ag–Cu–Ti-based alloys. Silica present as a secondary phase in the Al2O3 at a level of ~5 wt.% enabled the ceramic component to bond to the ABA chemically by forming a layer of Si3Ti5 at the ABA/Al2O3 interface. Appropriate brazing conditions to preserve a near-continuous Si3Ti5 layer on the Al2O3 and a continuous Fe3Si layer on the Kovar® were found to be a brazing time of ≤15 min at 1025 °C or ≤2 min at 1050 °C. These conditions produced joints that did not break on handling and could be prepared easily for microscopy. Brazing for longer periods of time, up to 45 min, at these temperatures broke down the Si3Ti5 layer on the Al2O3, while brazing at ≥1075 °C for 2–45 min broke down the Fe3Si layer on the Kovar® significantly. Further complications of brazing at ≥1075 °C included leakage of the ABA out of the joint and the formation of a new brittle silicide, Ni16Si7Ti6, at the ABA/Al2O3 interface. This investigation demonstrates that it is not straightforward to join Al2O3 to Kovar® using Copper ABA®, partly because the ranges of suitable values for the brazing temperature and time are quite limited. Other approaches to increase the operating temperature of the joint are discussed.

Wireless induction coils embedded in diamond for power transfer in medical implants.

Wireless power and data transfer to medical implants is a research area where improvements in current state-of-the-art technologies are needed owing to the continuing efforts for miniaturization. At present, lithographical patterning of evaporated metals is widely used for miniature coil fabrication. This method produces coils that are limited to low micron or nanometer thicknesses leading to high impedance values and thus limiting their potential quality. In the present work we describe a novel technique, whereby trenches were milled into a diamond substrate and filled with silver active braze alloy, enabling the manufacture of small, high cross-section, low impedance microcoils capable of transferring up to 10mW of power up to a distance of 6mm. As a substitute for a metallic braze line used for hermetic sealing, a continuous metal loop when placed parallel and close to the coil surface reduced power transfer efficiency by 43%, but not significantly, when placed perpendicular to the microcoil surface. Encapsulation of the coil by growth of a further layer of diamond reduced the quality factor by an average of 38%, which can be largely avoided by prior oxygen plasma treatment. Furthermore, an accelerated ageing test after encapsulation showed that these coils are long lasting. Our results thus collectively highlight the feasibility of fabricating a high-cross section, biocompatible and long lasting miniaturized microcoil that could be used in either a neural recording or neuromuscular stimulation device.

An investigation on joining of Al6061-T6 to AZ31B by microwave hybrid heating using active braze alloy as an interlayer

Active braze alloy is used as an interlayer material to join AZ31B to Al6061-T6 by microwave hybrid heating. The phase compositions of the reaction layer and the microstructure aspects are investigated using Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray spectroscopy (EDX) and X-ray diffraction (XRD). Intermetallic compounds of Aluminum, Magnesium, Silver and Oxygen i.e. Mg55Al40Ag5, Al60Mg38Ag2, MgAl2O4 and TiO were found to be formed in the reaction layer. Hardness of intermetallic towards the aluminum parent material is high i.e. 4.31GPa. This is due to the formation of intermetallic that are brittle and hard in nature. The tensile shear strength of the joint was evaluated. The formation of intermetallic compounds i.e. Al60Mg38Ag2, MgAl2O4 and TiO are responsible for the poor strength.

Evolution of the interfacial phases in Al2O3–Kovar® joints brazed using a Ag–Cu–Ti-based alloy

A systematic investigation of the brazing of Al2O3 to Kovar® (Fe–29Ni–17Co wt.%) using the active braze alloy (ABA) Ag–35.25Cu–1.75Ti wt.% has been undertaken to study the chemical reactions at the interfaces of the joints. The extent to which silica-based secondary phases in the Al2O3 participate in the reactions at the ABA/Al2O3 interface has been clarified. Another aspect of this work has been to determine the influence of various brazing parameters, such as the peak temperature, Tp, and time at Tp, τ, on the resultant microstructure. As a consequence, the microstructural evolution of the joints as a function of Tp and τ is discussed in some detail. The formation of a Fe2Ti layer on the Kovar® and its growth, along with adjacent Ni3Ti particles in the ABA, dominate the microstructural developments at the ABA/Kovar® interface. The presence of Kovar® next to the ABA does not change the intrinsic chemical reactions occurring at the ABA/Al2O3 interface. However, the extent of these reactions is limited if the purity of the Al2O3 is high, and so it is necessary to have some silica-rich secondary phase in the Al2O3 to facilitate the formation of a Ti3Cu3O layer on the Al2O3. Breakdown of the Ti3Cu3O layer, together with fracture of the Fe2Ti layer and separation of this layer from the Kovar®, has been avoided by brazing at temperatures close to the liquidus temperature of the ABA for short periods of time, e.g., for Tp between 820 and 830 °C and τ between 2 and 8 min.

A 3D lateral electrode structure for diamond based microdosimetry

A diamond based microdosimeter prototype featuring a 3D lateral electrode structure was created using laser ablation and active brazing alloys and characterised by means of ion beam induced charge collection measurements and finite element analysis, using Synopsys TCAD simulation package.

Infrared Brazing of Ti50Ni50 Shape Memory Alloy and Inconel 600 Alloy with Two Ag-Cu-Ti Active Braze Alloys

Infrared brazing of Ti50Ni50 SMA and Inconel 600 alloy using Cusil-ABA and Ticusil filler metals has been investigated. The joints were dominated by Ag-Cu eutectic with proeutectic Cu in the Cusil-ABA brazed joint and with proeutectic Ag in the Ticusil one. A continuous curved belt composed of a Ni3Ti layer and a (Cu x Ni1−x )2Ti layer formed in the brazed Ti50Ni50/Ticusil/Inconel 600 joint. On the Ti50Ni50 SMA side, an intermetallic layer of (Cu x Ni1−x )2Ti formed in all joints, with x values around 0.81 and 0.47. Layers of (Cu x Ni1−x )2Ti, Ni3Ti, and mixed Ni3Ti and Ni2Cr intermetallics were observed next to the Inconel 600 substrate in the brazed Ti50Ni50/Cusil-ABA/Inconel 600 joint. The maximum shear strengths of the joints using the Cusil-ABA filler metal and the Ticusil filler metal were 324 and 300 MPa, respectively. In the Cusil-ABA brazed joint, cracks with cleavage-dominated fracture propagated along the (Cu x Ni1−x )2Ti interfacial layer next to the Ti50Ni50 SMA substrate. In the Ticusil brazed joint, ductile dimple fracture occurred in the Ag-rich matrix near the Inconel 600 alloy substrate. The absence of a detrimental Ti-Fe-(Cu) layer on the Inconel 600 substrate side can effectively improve the shear strength of the joint.

Microgalvanic Corrosion Behavior of Cu-Ag Active Braze Alloys Investigated with SKPFM

The nature of microgalvanic couple driven corrosion of brazed joints was investigated. 316L stainless steel samples were joined using Cu-Ag-Ti and Cu-Ag-In-Ti braze alloys. Phase and elemental composition across each braze and parent metal interface was characterized and scanning Kelvin probe force microscopy (SKPFM) was used to map the Volta potential differences. Co-localization of SKPFM with Energy Dispersive Spectroscopy (EDS) measurements enabled spatially resolved correlation of potential differences with composition and subsequent galvanic corrosion behavior. Following exposure to the aggressive solution, corrosion damage morphology was characterized to determine the mode of attack and likely initiation areas. When exposed to 0.6 M NaCl, corrosion occurred at the braze-316L interface preceded by preferential dissolution of the Cu-rich phase within the braze alloy. Braze corrosion was driven by galvanic couples between the braze alloys and stainless steel as well as between different phases within the braze microstructure. Microgalvanic corrosion between phases of the braze alloys was investigated via SKPFM to determine how corrosion of the brazed joints developed.

Investigation of brazing of Ba(Zn0.33Ta0.67)O3 ceramic with Ti6Al4V alloy

Feasibility of brazing Barium Zinc Tantalate (BZT) ceramics with Ti6Al4V alloy using active and non-active brazing alloy was investigated in the present study for high power RF window application. BZT ceramics were brazed successfully with Ti6Al4V alloy under high vacuum with active brazing alloy (Ticusil® (4.5%Ti) and Cusil-ABA® (1.5%Ti) at 850°C and non-active brazing alloy (BAg8) at 830°C. Micrographs at the interface of non-active brazed joints are free of interfacial micro-defects, and exhibit excellent physical contact and good metallurgical bonding with high diffusivity when compared to active-brazed joints. Ceramic-filler interfacial layer thickness is high for samples containing non-active filler (~25µm) compared to the samples containing active filler materials (~9µm and ~5µm). The average shear strength of BZT ceramics brazed with non-active brazing alloy BAg8 is higher (~45.5MPa) in comparison with active brazing alloys (~33MPa and ~31MPa). Fracture surface reveals that the failure is on ceramics side only indicating that the strength of non-active brazed joint is more compared to ceramics.

Implantable diamond capsules for electro stimulation and recording

Event Abstract Back to Event Implantable diamond capsules for electro stimulation and recording Kumaravelu Ganesan1, 2, David J. Garrett1, Nick Opie2 and Steven Prawer1 1 University of Melbourne, School of Physics, Australia 2 SmartStent PTY LTD, Australia Introduction: Implantable electronic devices must necessarily adhere to a very strict set of standards before they can be approved for clinical use. One of these standards is the requirement that electronically active components such as microprocessors must be encapsulated hermetically to protect the body from the toxicity of conventional electronic components and as well as to protect the components from the harsh environment inside the body which leads to accelerated device failure. This article provides an overview of an all-diamond hermetic capsule for retinal as well as cortical implants for electrostimulation and recording. Materials and Methods: Diamond Microelectrode array: Diamond microelectrode array of 3-D surface electrodes as shown in fig1a and fig 1.b was fabricated using conventional as well as unconventional fabrication techniques. The microelectrodes are nitrogen incorporated unltrananocrystalline diamond and the body is polycrystalline diamond[1]. CMOS chip integration: Lithographically defined Indium bumps and flip chip bonding technique was used to bond the CMOS processor to the electrode to make one-to-one connection. Electrical feedthrough: An active braze alloy of 95% gold was brazed in vacuum environment to form the electrical feedthrough, electrical contacts as well as the braze line for final laser welding. Laser Microwelding : Pulsed Laser welding technique was used to join the two halves together hermetically. Fig. 1. (a) Components of the diamond/gold encapsulation with high-density diamond electrode array (2) flip-chip bonded to a 256 channel stimulator application specific integrated circuit (ASIC) (1) and a diamond box with integrated feedthroughs for power and data transfer (3). The two diamond components are sealed by welding around the outer edges of the braze seam (b).[2] (c)Diamond cortical implant for recording. This is approximately half the size of the retinal implant shown in (b) and has the dimension of 2X0.7X0.3mm. A receiver Rx coil in fabricated on the diamond body. Results and Discussion: An all diamond 256 channel retinal implant was fabricated and tested successfully. A cortical recording implant is under development with the wireless power and data transfer facilities. Conclusion: A new hermetic encapsulation paradigm for a medical implant , using polycrystalline diamond, was presented. The new packaging technology uses high-conductivity gold braze feedthroughs for power and data input and a laser welded seam of Gold-ABA braze joining the diamond shell components. This work was funded in part from Australian Research Council through its Special Research Initiative (SRI) in Bionic Vision Science and Technology grant to Bionic Vision Australia (BVA); ARC Linkage grant 2015(SMARTSTENT PTY LTD)

Interfacial reactions between sapphire and Ag–Cu–Ti-based active braze alloys

The interfacial reactions between two commercially available Ag–Cu–Ti-based active braze alloys and sapphire have been studied. In separate experiments, Ag–35.3Cu–1.8Ti wt.% and Ag–26.7Cu–4.5Ti wt.% alloys have been sandwiched between pieces of R-plane orientated sapphire and heated in argon to temperatures between 750 and 900 °C for 1 min. The phases at the Ag–Cu–Ti/sapphire interfaces have been studied using selected area electron diffraction, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy.Gradual and subtle changes at the Ag–Cu–Ti/sapphire interfaces were observed as a function of temperature, along with the formation of a transient phase that permitted wetting of the sapphire. Unequivocal evidence is shown that when the active braze alloys melt, titanium first migrates to the sapphire and reacts to dissolve up to ∼33 at.% oxygen, forming a nanometre-size polycrystalline layer with a chemical composition of Ti2O1–x (x ≪ 1). Ti3Cu3O particles subsequently nucleate behind the Ti2O1–x layer and grow to become a continuous micrometre-size layer, replacing the Ti2O1–x layer. Finally at 845 °C, a nanometre-size γ-TiO layer forms on the sapphire to leave a typical interfacial structure of Ag–Cu/Ti3Cu3O/γ-TiO/sapphire consistent with that seen in samples of polycrystalline alumina joined to itself with these active braze alloys. These experimental observations have been used to establish a definitive bonding mechanism for the joining of sapphire with Ag–Cu alloys activated by small amounts of titanium.

Plasma treatment on SiO2f/SiO2 composites for their assisted brazing with Nb

Brazing SiO2f/SiO2 composites with metals is often associated with the problems of poor wettability with active brazing alloy and poor mechanical properties of joints. To overcome these problems, we report the plasma treatment on SiO2f/SiO2 by PECVD for their assisted brazing with Nb. The O–Si–O bonding changed into Si–C bonding on the surface of SiO2f/SiO2 by the plasma treatment can improve the wettability of Ag–Cu–Ti brazing alloy on SiO2f/SiO2. Furthermore, SiO2f/SiO2 after the plasma treatment can contribute to the infiltration of brazing alloy into SiO2f/SiO2 to form the pinning structure and reducing the residual stress, which could strengthen the joint. The obtained joint has a high shear strength of 60.5 MPa, approximately 11 times higher than that without plasma treatment.