Active Brazing Research Articles

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)

Active metal brazing of silicon nitride ceramics using a Cu-based alloy and refractory metal interlayers

Silicon nitride/silicon nitride joints with refractory metal (W and Mo) interlayers were vacuum brazed using an active braze, Cu-ABA (Cu–3Si–2Al–2.25Ti, wt%), and two interlayer arrangements in a double-lap offset configuration: Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 and Si3N4/Cu-ABA /Si3N4. Titanium segregated at the Si3N4/Cu-ABA and Mo/Cu-ABA interfaces, but not at the W/Cu-ABA interface. The room-temperature compression-shear strength values of Si3N4/Cu-ABA/Si3N4 and Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints were 118±24MPa and 22±5MPa, respectively. Elevated-temperature compression tests showed that Si3N4/Cu-ABA/Si3N4 joints had strength of 31±6MPa at 1023K and 17±3MPa at 1073K. Likewise, Si3N4/Cu-ABA/W/Cu-ABA/Mo/Cu-ABA/Si3N4 joints had strength of 19±4MPa at 1023K and 13±3MPa at 1073K. Knoop microhardness profiles revealed hardness gradients across the joints. The effect of joint microstructure and test configuration on the mechanical behavior is discussed.

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.

On the Challenges of Reducing Contact Resistances in Thermoelectric Generators Based on Half-Heusler Alloys

A method using fast hot pressing to join half-Heusler (HH) thermoelectric materials directly to an electrical current collector (Ag electrode) without using a third filler material is introduced. The compositions of the HH alloys used are Hf0.5Zr0.5CoSn0.2Sb0.8 and Ti0.6Hf0.4NiSn for p- and n-type, respectively. Using this method, the quality of the HH–electrode contacts is improved due to their low electrical contact resistance and less reaction–diffusion layer. The microstructure and chemical composition of the joints were examined using a scanning electron microscope equipped with energy-dispersive x-ray analysis. The electrical characteristics of the interfaces at the contacts were studied based on electrical contact resistance and Seebeck scanning microprobe measurements. In this paper, we show that joining the HH to a Ag electrode directly using fast hot pressing resulted in lower contact resistance and better performance compared with the method of using active brazing filler alloy.

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.

Microstructural evolution and characterisation of interfacial phases in Al2O3/Ag–Cu–Ti/Al2O3 braze joints

Alumina ceramics with different levels of purity have been joined to themselves using an active braze alloy (ABA) Ag–35.3Cu–1.8Tiwt.% and brazing cycles that peak at temperatures between 815°C and 875°C for 2 to 300min. The microstructures of the joints have been studied using scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy. A limited number of joints prepared with the ABA Ag–26.7Cu–4.5Tiwt.% have also been studied. In terms of characterising the interfacial phases, efforts were made to understand the interfacial reactions, and to determine the influence of various brazing parameters, such as the peak temperature (Tp) and time at Tp (τ), on the microstructure. In addition, the extent to which impurities in the alumina affect the interfacial microstructure has been determined.Ti3Cu3O has been identified as the main product of the reactions at the ABA/alumina interfaces. At the shortest joining time used, this phase was observed in the form of a micron-size continuous layer in contact with the ABA, alongside a nanometre-size layer on the alumina that was mostly composed of γ-TiO grains. Occasionally, single grains of Ti3O2 were observed in the thin layer on alumina. In the joints prepared with Ag–35.3Cu–1.8Tiwt.%, the interfacial structure evolved considerably with joining time, eventually leading to a high degree of inhomogeneity across the length of the joint at the highest Tp. The level of purity of alumina was not found to affect the overall interfacial microstructure, which is attributed to the formation of various solid solutions. It is suggested that Ti3Cu3O forms initially on the alumina. Diffusion of Ti occurs subsequently to form titanium oxide at the Ti3Cu3O/alumina interface.

Research and Preparation of Silver Free Amorphous Active Brazing Alloy

A silver free amorphous Cu-35Ti-12Ni active brazing alloy was successfully prepared in this work. The crystallinity, microstructure, and chemical composition were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive spectrometry (EDS), respectively. A typical characteristic peak of amorphous material was observed in the XRD pattern. The microstructures and chemical compositions of the silver free amorphous alloy were uniform. Differential scanning calorimetry (DSC) result shows that the amorphous silver free brazing alloy has higher melting temperature than commercial silver brazing alloy (Ag-26.5Cu-1.5Ti). Wetting contact angle and spreading area on Si3N4 ceramic substrate were used to evaluate the wetting ability of brazing alloy. The wetting angle was smaller than 5o, and the spreading area was 141.6 mm2 at 1100°C. The bending strength of silver free brazing alloy/Si3N4 was also carried out. The mechanical test shows that the amorphous Cu-35Ti-12Ni/Si3N4 has higher joint strength (304.7MPa) than the crystal Cu-35Ti-12Ni/Si3N4 (294.7MPa) at room temperature.

Hermetic diamond capsules for biomedical implants enabled by gold active braze alloys

As the field of biomedical implants matures the functionality of implants is rapidly increasing. In the field of neural prostheses this is particularly apparent as researchers strive to build devices that interact with highly complex neural systems such as vision, hearing, touch and movement. A retinal implant, for example, is a highly complex device and the surgery, training and rehabilitation requirements involved in deploying such devices are extensive. Ideally, such devices will be implanted only once and will continue to function effectively for the lifetime of the patient. The first and most pivotal factor that determines device longevity is the encapsulation that separates the sensitive electronics of the device from the biological environment. This paper describes the realisation of a free standing device encapsulation made from diamond, the most impervious, long lasting and biochemically inert material known. A process of laser micro-machining and brazing is described detailing the fabrication of hermetic electrical feedthroughs and laser weldable seams using a 96.4% gold active braze alloy, another material renowned for biochemical longevity. Accelerated ageing of the braze alloy, feedthroughs and hermetic capsules yielded no evidence of corrosion and no loss of hermeticity. Samples of the gold braze implanted for 15 weeks, in vivo, caused minimal histopathological reaction and results were comparable to those obtained from medical grade silicone controls. The work described represents a first account of a free standing, fully functional hermetic diamond encapsulation for biomedical implants, enabled by gold active alloy brazing and laser micro-machining.

Processing of metal-diamond-composites using selective laser melting

Purpose – The purpose of this paper is a feasibility study that was performed to investigate the basic processability of a diamond-containing metal matrix. Powder-bed-based additive manufacturing processes such as selective laser melting (SLM) offer a huge degree of freedom, both in terms of part design and material options. In that respect, mixtures of different powders can offer new ways for the manufacture of materials with tailored properties for special applications such as metal-based cutting or grinding tools with incorporated hard phases. Design/methodology/approach – A two-step approach was used to first investigate the basic SLM-processability of a Cu-Sn-Ti-Zr alloy, which is usually used for the active brazing of ceramics and superhard materials. After the identification of a suitable processing window, the processing parameters were then applied to a mixture of this matrix material with 10-20 volume per cent artificial, Ni-coated mono-crystalline diamonds. Findings – Even though the processing parameters were not yet optimized, stable specimens out of the matrix material could be produced. Also, diamond-containing mixtures with the matrix material resulted in stable specimens, where the diamonds survived the layer-wise build process with the successive heat input, as almost no graphitization was observed. The diamond particles are fully embedded in the Cu-Sn-Ti-Zr matrix material. The outer part of the diamonds partly dissolves in the matrix during the SLM process, forming small TiC particles and most likely a thin TiC layer around the diamond particles. Originality/value – The feasibility study approved the SLM processing capabilities of a metal-diamond composite. Although some cracking phenomena sill occur, this seems to be an interesting and promising way to create new abrasive tools with added value in terms of internal and local lubrication supply, tooling temperature control and improved tooling durability.

Microstructure and Mechanical Performance of Cu-Sn-Ti-Based Active Braze Alloy Containing In Situ Formed Nano-Sized TiC Particles

A Cu-Sn-Ti-based active brazing filler alloy was in situ reinforced with nanosized TiC particles by adding different amounts of a cellulose nitride-based binder. The TiC particles emanate from a reaction of the Ti within the filler alloy with the carbon from the binder that does not decompose completely during heating. The correlation between the microstructure and mechanical performance was studied. In addition, the effect of different binder amounts on the shear strength and cutting performance of brazed diamond grains was studied in shear tests and single grain cutting tests. The results clearly show that the mechanical performance of the brazed diamond grains can be improved by the formation of TiC particles. This is attributed to particle strengthening of the filler alloy matrix as well as to the decreasing grain size and more homogeneous distribution of the (Cu,Sn)3Ti5 phase with increasing amount of binder.

Ultrasonic-assisted brazing of sapphire with high strength Al–4.5Cu–1.5Mg alloy

The method for joining alumina using high strength aluminum alloys as a filler metal has been desired for years because of the very limited strength of the joints using pure aluminum in the current methods. Here we show a novel ultrasonic-assisted brazing method for making sapphire (monocrystalline α-alumina) joints using a high strength aluminum alloy of Al–4.5Cu–1.5Mg as a filler metal. The bonding between the sapphire alloy and the Al–4.5Cu–1.5Mg was realized through an interfacial oxidation of metallic elements, resulting in formation of MgAl2O4 at the interface. Ultrasonic wave was used to promote the interfacial oxidation during brazing and an annealing heat treatment was used during cooling. Nominal shear strength of the joints made with Al–4.5Cu–1.5Mg was ~125MPa, 2.7 times higher than that made with pure Al. Finite element method (FEM) was used to study the difference on fracture behaviors of the joints made with the Al–4.5Cu–1.5Mg alloy and pure aluminum. The actual bonding shear strength at the sapphire/Al–4.5Cu–1.5Mg interface was estimated as high as 230MPa. Thus, a new technical route for joining ceramics with aluminum alloys is proposed, which is hopefully an alternative of conventional active brazing.

Interface reaction in ultrasonic vibration-assisted brazing of aluminum to graphite using Sn–Ag–Ti solder foil

The microstructures and formation mechanism of the interface between pure aluminum and graphite were studied when performed the active brazing in atmospheric conditions using assistive ultrasonic vibration. At the C/solder interface, the active component (Ti) in the Sn5Ag5Ti active solder can reduce the surface tension on the surface of graphite through the interface reaction between Ti and C atoms, which is the dominant driving force during wetting process on the surface of graphite; at the Al/solder interface, Ag and Al atoms can form a type of substitutional solid solution due to occupy the positions of diffused Al atoms and affect the diffusion path between Al and Ti atoms under the brazing temperature, which can reduce the surface tension, lowering the energy of whole system and improving the wetting behavior of the liquid solder on the aluminum surface. The application of ultrasonic vibration can remove the surface oxidation films of the base metals and molten solders; hence, ultrasonic vibration can enhance the wettability of liquid solder on the surface of the base metals and accelerate the element diffusion rates of interfacial reactions.

High Temperature Ultrasonic Transducer for Real-time Inspection

A broadband ultrasonic transducer with a novel porous ceramic backing layer is introduced to operate at 700°C. 36° Y-cut lithium niobate (LiNbO3) single crystal was selected for the piezoelectric element. By appropriate choice of constituent materials, porosity and pore size, the acoustic impedance and attenuation of a zirconia-based backing layer were optimized. An active brazing alloy with high temperature and chemical stability was selected to bond the transducer layers together. Prototype transducers have been tested at temperatures up to 700°C. The experiments confirmed that transducer integrity was maintained.

Active brazing of carbon fiber reinforced SiC composite and 304 stainless steel with Ti–Zr–Be

Abstract Carbon fiber reinforced SiC (C f /SiC) was successfully joined to 304 stainless steel with Ti–Zr–Be filler metal by vacuum brazing. The interfacial microstructure was investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), auger electron energy spectroscopy (AES) and X-diffraction (XRD). The mechanical properties of the brazed joints were measured by a mechanical testing machine. The results show that Ti and Zr elements in the interlayer can react with the brazed materials, the brazed joint mainly consists of Ti 5 Si 3 , TiSi, TiBe, TiFe and Zr(s,s) reaction products. The 304 stainless steel constantly dissolved and Ti, Be diffused into 304 stainless steel, which formed the diffusion layers between interlayer and 304 stainless steel. Ti and Be elements have an effect on promoting the formation of α-Fe layer. The maximum shear strength of 109.13±2.55 MPa is obtained at 950 °C with 60 min holding time.

Study on vacuum brazing of high purity alumina for application in proton synchrotron

The paper describes an experimental study to evaluate two different vacuum brazing processes to obtain high purity alumina (99.7%) joints suitable for application in rapid cycle proton synchrotron. Two different brazing routes, adopted for making alumina–alumina brazed joints, included (i) multi-step Mo–Mn metallization, followed by brazing with BVAg-8 alloy and (ii) advanced single-step active brazing with CuSil-ABA® alloy. Both the brazing routes yielded helium leak tight and ultra-high vacuum (pressure<10−9mbar) compatible joints. Active-brazed specimens exhibited tensile and mean flexural strengths of 62 and 110MPa, respectively. Metallized-brazed specimens, although associated with relatively lower tensile strength (35MPa) than the targeted value (>50MPa), displayed higher mean flexural strength of 149MPa. The results of the study demonstrated that active brazing is a simple and cost effective alternative to conventional multi-step metallization route for producing quality joints of high purity alumina for application in rapid cycle proton synchrotron machine.

Interface Reaction Thermodynamics of AgCuTi Brazing Filler Metal and Alumina Ceramic

In this work, the interface reaction between Al2O3 ceramic and Ag70.5Cu27.5Ti2 brazing filler metal at 845-860°C was investigated. Based on the data of thermodynamics and kinetics, the Gibbs free energies of the main interface reactions in the real brazing system condition were calculated. But the values of normal equilibrium reaction condition and the real interface reaction brazing system were different; and the main influential factor was the brazing temperature, and the system vacuum of brazing condition can lead the change of equilibrium constant (Kα). The results revealed that the high temperature and vacuum active brazing is a non-equilibrium interface reaction especially to titanium alloy, the vacuum and alloy liquid solution are beneficial to the brazing process, and the by-product formation of titanium-oxygen are affected by the diffusion process.

An Innovative Joint Structure for Brazing Cf/SiC Composite to Titanium Alloy

In view of aerospace applications, an innovative structure for joining a Ti alloy to carbon fiber reinforced silicon carbide has been developed. This is based on the perforation of the CMC material, and this procedure results in six-fold increase of the shear strength of the joint compared to the unprocessed CMC. The joint is manufactured using the active brazing technique and TiCuAg as filler metal. Sound joints without defects are produced and excellent wetting of both the composite ceramic and the metal is observed. The mechanical shear tests show that failure occurs always within the ceramic material and not at the joint. At the CMC/filler, Ti from the filler metal interacts with the SiC matrix to form carbides and silicides. In the middle of the filler region depletion of Ti and formation of Ag and Cu rich regions are observed. At the filler/Ti alloy interface, a layered structure of the filler and Ti alloy metallic elements is formed. For the perforation to have a significant effect on the improvement of the shear strength of the joint appropriate geometry is required.

Examination of the Porosity in Reactive Air Brazed Joints by Ultrasonic Testing

Reactive air brazing (RAB) has been developed as a method to join ceramics and steel, using CuO as a reactive agent that interacts with the surface of the ceramic, enabling a wetting by the molten filler metal. A major benefit of this method is the fact that the joining process can be carried out in an ambient atmosphere, in contrast to active brazing processes, which need to be performed in a vacuum furnace. In the past, several investigations were conducted to improve the mechanical bonding properties for both methods. A sealed gas‐tightness is also important for innovative applications such as solid oxide fuel cells. In this regard, the reduction of porosity, which is necessary in order to achieve reproducible joints with a long lifetime, presents a challenge. Therefore, it is necessary to conduct fundamental analyses of the driving forces and mechanisms of the formation of voids in the interfacial area to guarantee a reliable joint quality. In this study, the authors used an ultrasonic testing method in the realm of the immersion technique to evaluate the porosity in brazements produced with varying process parameters. A major goal was to assess the influence of the cooling stage on the pore formation. The advantage of this non‐destructive method is the possibility to scan the entire joint area using just one scan. The investigations were flanked by SEM analyses on different cross‐sections.

Effect of brazing temperature on the shear strength of Inconel 600 joint

Inthisstudy, Inconel 600alloywasbrazedbyusing Cusil ABA which is an active filler alloy in a high-vacuum condition under a pressure of 1×10 �4 Pa. Three brazing temperatures (830, 865, and 900 °C) were chosen based on the solidus temperature of AgCuTi filler alloy in order to investigate the effects of these temperatures on the perfor- mance of the brazed joint. Brazing processes were carried out over a period of time (15 min) to ensure that the filler alloy was melted completely. The performance of the brazing process was evaluated in terms of bonding strength by shear test, whereas microstructural analysis was performed to inves- tigate the bonding morphology. The results revealed that a maximum value of shear strength (223.32 MPa) was obtained at a brazing temperature of 865 °C compared with other temperatures. It was also observed morphologically that the highest shear strength was influenced by the formation of two reactionlayersthat crossed in the center of the brazedarea due tointerdiffusioneffectofseveral constituentsfromthe Inconel 600 alloy and active brazing filler.

The influence of brazing temperature and surface roughness on the wettability of reactive brazing alloys

Abstract Using two active brazes based on silver–copper, the wetting behaviour was investigated on hard metals and diamond. Here, it was possible both to characterise the in-situ wetting angle as a function of temperature, the surface roughness and the time by using the flow rate and the wetting angle as well as to analyse the underlying mechanisms. A directly proportional relationship between temperature and the formed wetting angle was demonstrated during the tests up to a material dependent limiting value. Moreover, the wetting behaviour was shown to deteriorate with increasing surface roughness values. By means of investigating the diffusion zone between the carbide metal and the braze using scanning electron microscopy, it was possible to establish that the penetration depth of the active element titanium into the carbide metal increased with increasing brazing temperature.