Active Brazing Alloy Research Articles

Influence of brazing parameters and alloy composition on interface morphology of brazed diamond

Active brazing is an effective technique for joining diamond or cBN grit to metallic substrates. This technique is currently used to manufacture superabrasive, high-performance tools. The investigation of interface reactions between diamond and active brazing alloys plays an important role in understanding and improving the brazing process and the resultant tool performance. Focused ion beam (FIB) milling enabled the high resolution investigation of these extremely difficult to prepare metal–diamond joints. The interfacial nanostructure is characterized by the formation of two layers of TiC with different morphologies. First a cuboidal layer forms directly on the diamond and reaches a thickness of approximately 70 nm. Then a second layer with columnar TiC crystals grows on the first layer into the brazing filler metal by a diffusion-controlled process. The combined thickness of both TiC layers varies between 50 nm and 600 nm depending on the brazing temperature and holding time.

Details on the Formation of Ti2Cu3 in the Ag-Cu-Ti System in the Temperature Range 790 to 860 °C

Silver-copper-titanium (Ag-Cu-Ti) ternary alloys are often used as active braze alloys for joining ceramics to metals at temperatures ranging from 780 °C (the melting point of the Ag-Cu eutectic) up to 900 °C. When Ti/Ag-Cu joints are brazed at low temperature (near 800 °C), the intermetallic compound Ti2Cu3 (tetragonal, P4/nmm, a = 0.313 nm, c = 1.395 nm) is systematically missing from the interface reaction layer sequence. An experimental investigation based on isothermal diffusion experiments in the Ag-Cu-Ti ternary system has then been undertaken to clarify the issues of thermal stability and formation kinetics of this compound. Evidence has been found for the stability of Ti2Cu3 at temperatures ranging from 790 to at least 860 °C. By heat treating Ag-Cu-Ti powder mixtures at 790 °C for increasing times, it has moreover been shown that Ti2Cu3 forms at a much slower rate than the two adjacent Ti-Cu compounds: TiCu4, the first phase to form, and Ti3Cu4. This explains why although thermodynamically stable, Ti2Cu3 is not obtained when temperature is too low or reaction time too short.

Joining CoSb<sub>3</sub> to Metal Surface of FGM Electrode for Thermoelectric Modules by SPS

The fabrication of electrodes is one of the key techniques in constructing thermoelectric elements for the practical applications. In this work, the commercial active brazing alloy “Incusil-ABA” was used for the joining of CoSb3 to the Cu surface of the graded electrode materials (Cu/AlN/Cu) by using spark plasma sintering (SPS). The bonding was performed in vacuum at temperatures 500°C for 10min. The brazing and diffusion bonding process were investigated by analyzing the crystal structure and microstructure of the bonding interface using X-ray diffraction and scanning electron microscopy, and its composition distribution was also analyzed by energy dispersive X-ray.

Wetting behaviour of Cu based active brazing alloys on siliconised graphite

The effects of Al and silicon additions to Cu based brazing alloy and the surface free silicon on siliconised graphite substrate on the wetting behaviour of the siliconised graphite by Cu–Al–Si–Ti alloys were investigated using the sessile drop technique at 1100°C. The contact angles were measured and the interfacial reactions were analysed. It was shown that surface free Si on siliconised graphite had a great positive effect on the contact angle. Furthermore, interfacial reactions could be controlled by adjusting the contents of Si and Al in brazing alloys.

Joining of CBN abrasive grains to medium carbon steel with Ag [sbnd]Cu/Ti powder mixture as active brazing alloy

In order to develop new generation brazed CBN grinding wheels, the joining experiments of CBN abrasive grains and medium carbon steel using the powder mixture of Ag Cu alloy and pure Ti as active brazing alloy are carried out at elevated temperature under high vacuum condition. The relevant characteristics of the special powder mixture, the microstructure of the interfacial region, which are both the key factors for determining the joining behavior among the CBN grains, the filler layer and the steel substrate, are investigated extensively by means of differential thermal analysis (DTA), scanning electron microscope (SEM) and energy dispersion spectrometer (EDS), as well X-ray diffraction (XRD) analysis. The results show that, similar to Ag Cu Ti filler alloy, Ag Cu/Ti powder mixture exhibits good soakage capability to CBN grains during brazing. Moreover, Ti in the powder mixture concentrates preferentially on the surface of the grains to form a layer of needlelike Ti N and Ti B compounds by chemical metallurgic interaction between Ti, N and B at high temperature. Additionally, based on the experimental results, the brazing and joining mechanism is deeply discussed in a view of thermodynamic criterion and phase diagram of Ti B N ternary system.

Brazing of silicon nitride ceramic composite to steel using SiC-particle-reinforced active brazing alloy

Silicon carbide particles have been introduced as reinforcements in a commercially available active metal braze filler alloy (Incusil ABA, Wesgo Metals) used for the joining of ceramic-to-metal. The effect of particle reinforcement of the braze filler on the flexural strength of ceramic to metal joints has been investigated at room temperature and at elevated temperatures. An average four point flexural strength of nearly 400 MPa is achieved at room temperature when using Incusil ABA + 30 vol.% SiC (sandwich foil system) compared to 330 MPa with Incusil ABA alone. At a test temperature of 250 °C relaxation of residual stresses in the joints results in an average flexural strength of approximately 520 MPa when using Incusil ABA + 10 vol.% SiC. These values compare with an average room temperature flexural strength of nearly 800 MPa for the ceramic composite. The reaction products of the braze alloy at the joint interface were identified by SEM.

Nanocrystalline phases and epitaxial interface reactions during brazing of diamond grits with silver based Incusil-ABA alloy

The commercial active brazing alloy “Incusil-ABA” was used for the bonding of diamond grits in order to assess their suitability for high performance machining tools. It was found that the microstructure of the brazing alloy matrix consisted of primary precipitates of Cu in a Ag–Cu eutectic matrix and an additional Cu–In–Ti rich intermetallic phase. Interface characterisation revealed the presence of a Ti-rich interfacial layer between the diamond and the alloy matrix. Therefore, good wettability was obtained for the embedded diamond grit particles. This intervening layer comprised nanosized cuboidal TiC which seemed to have acted as a precursor to its formation and fine metastable needles that were identified as cubic Ti 3InC. Furthermore it was demonstrated that a three phase crystallographic orientation relationship had been obeyed at the interfacial region between the diamond, TiC and Ti 3InC.

Infrared brazing of Ti 50Ni 50 shape memory alloy using two Ag–Cu–Ti active braze alloys

Microstructural evolution, shape memory effect and shear strength of infrared brazed Ti 50Ni 50 shape memory alloy using Cusil-ABA ® and Ticusil ® active braze alloys are investigated. The Ag–Cu eutectic braze alloy can readily wet Ti 50Ni 50 substrate by minor titanium additions. The brazed Ti 50Ni 50/Cusil-ABA ®/Ti 50Ni 50 joint is mainly comprised of Cu-rich, Ag-rich and CuNiTi phases. On the other hand, the brazed Ti 50Ni 50/Ticusil ®/Ti 50Ni 50 joint consists of Ag-rich, Cu-rich and TiCu 2 phases. Because the chemical composition of Ticusil braze alloy is located inside the huge miscibility gap, the molten braze tends to be separated into two liquids during brazing. One is rich in Ag, and the other is rich in both Cu and Ti. The Ag-rich liquid does not react with Ti 50Ni 50 substrate. In contrast, the copper content is depleted from the matrix of brazed joint due to the formation of interfacial TiCu 2 phase. The TiCu 2 phase is less detrimental to the shape memory effect than CuNiTi phase during the shape recovery bending test. Shear strength of brazed joints exceeds 200 MPa for both braze alloys if the brazing time exceeds 180 s. However, thick interfacial CuNiTi and TiCu 2 layers can deteriorate the shear strength.

Behavior of titanium in the interfacial region between cubic BN and active brazing alloy

In the present investigation, the diffusion behavior of the element titanium in the interfacial region between Ag-based active brazing alloy and cubic BN grain was investigated by scanning electron microscope and energy dispersion spectrometer, as well X-ray diffraction. Meanwhile, the growth mechanism and activation energy of the reaction layer was also deeply studied from the viewpoint of kinetics. The result showed that the active element Ti concentrated to and reacted with the grain crystal to form TiB 2 and TiN to join hard grains and tool substrate. Furthermore, the calculated activation energy value indicated that the width of the interfacial reaction layer was mainly depended on the TiN layer in the special growing process of brazing temperature 880–920 °C and dwell time 300–1200 s.

Manufacturing and testing in reactor relevant conditions of brazed plasma facing components of the ITER divertor

A fabrication route based on brazing technology has been developed for the realization of the high heat flux components for the ITER vertical target and Dome-Liner. The divertor vertical target is armoured with carbon fiber reinforced carbon and tungsten in the lower straight part and in the upper curved part, respectively. The armour material is joined to heat sinks made of precipitation hardened copper–chromium–zirconium alloy. The plasma facing units of the dome component are based on a tungsten flat tile design with hypervapotron cooling. An innovative brazing technique based on the addition of carbon fibers to the active brazing alloy, developed by Ansaldo Ricerche for applications in the field of the energy production, has been used for the carbon fiber composite to copper joint to reduce residual stresses. The tungsten–copper joint has been realized by direct casting. A proper brazing thermal cycle has been studied to guarantee the required mechanical properties of the precipitation hardened alloy after brazing. The fabrication route of plasma facing components for the ITER vertical target and dome based on the brazing technology has been proved by means of thermal fatigue tests performed on mock-ups in reactor relevant conditions.

Joining Method of Silicon Nitride to Carbon Steel

We investigated the method of joining silicon nitride having on its surface a thin layer of active silicon metal to carbon steel. The active silicon layer is formed through the thermal dissociation of silicon nitride (Si3N4) into silicon (Si) and nitrogen gas (N2). The active silicon layer is directly joined to carbon steel via an induced eutectic melting reaction between the silicon and iron (Fe) found in carbon steel, or via brazing of two materials using general brazing metal such as Ag-Cu alloys. This joining process does not require the use of expensive active brazing alloys such as Ag-Cu-Ti alloys or a sputtering method designed to coat the active metals on surface of silicon nitride.

Microstructural characterization of SiC ceramic and SiC–metal active metal brazed joints

SiC ceramic is joined to itself, to stainless steels and to Inconel 718 using indigenously developed active brazing alloys. Detailed interfacial product analysis by scanning electron microscopy, electron probe microanalysis and X-ray diffraction revealed that the interfacial reactions are dependent on Ti concentration and the composition of the metal member in the ceramic–metal couple.

Fabrication of a composite powder and its application as an active brazing alloy

A copper-based active brazing alloy containing a high titanium content was produced by an electroless coating technique. Particles with a narrow density distribution were produced by deposition of nano-copper on a fine titanium powder. Both conventional titanium powder and sponge titanium were studied. The effects of pH and time on copper deposition were investiguated.

Brazing of Mo and Nb using two active braze alloys

The brazing of molybdenum and niobium using two active braze alloys, 63Ag–35.25Cu–1.75Ti and 68.8Ag–26.7Cu–4.5Ti, has been extensively evaluated. Both infrared and traditional vacuum furnace brazing are included in the experiment. Two active braze alloys demonstrate excellent wettability on Mo and Nb substrates, especially upon increasing the test temperature from 900 to 950 °C. For 63Ag–35.25Cu–1.75Ti braze alloy, the brazed joint primarily consists of Ag-rich and Cu-rich phases. Because the Ti is completely miscible with Mo and Nb, there is no reaction product at the interface among the braze alloy and two substrates. Accordingly, dimple-dominated fracture is extensively observed in the brazed joint. The brazed Mo/68.8Ag–26.7Cu–4.5Ti/Nb joint primarily consists of Ag-rich, Cu-rich and Nb-rich phases. A few Cu–Ti intermetallics are found in the brazed joint due to higher Ti content in the braze alloy. However, the presence of Cu–Ti intermetallic phases demonstrates little effect on the shear strength of the brazed joint. Dimple-dominated fracture is observed for the 900 °C brazed joint. The Nb-rich phase is found in both brazed joints, and its amount is increased with increasing brazing temperature and/or time. Accordingly, the growth of the Nb-rich phase is greatly inhibited during rapid infrared brazing. The coarsening of the Nb-rich phase significantly deteriorates the shear strength of the brazed Mo/68.8Ag–26.7Cu–4.5Ti/Nb joint, and finally results in cleavage fracture of the brazed joint.

Joining silicon nitride ceramic using a composite powder as active brazing alloy

The aim of this study was to join silicon nitride ceramic using a Cu–Ti bi-metallic composite powder. The microstructure and mechanical properties obtained were similar to results obtained with conventional active brazing alloys but with different kinetics. The experimental results obtained show the potential in using the composite powder as a brazing alloy. The reaction layer produced at the ceramic/filler metal interface was composed mainly of TiN and Ti5Si3. Similar to many active ceramic brazing processes, the reaction layer was formed in two stages, where the initial step was controlled by a liquid/solid reaction, followed by diffusion controlled growth. Depending on the brazing parameter, the reaction layer thickness ranged between 4 and 12 μm. Reaction layer growth was modeled and the effective activation energy was found to be 64 kJ/mole. The four-point bending strength varied between 250 and 400 MPa, depending on joining conditions. The crack propagation mode was through the interface for low strength joints and through the ceramic for high strength joints.

Assessment of melting behavior of Cu-coated Ti powders using thermal analysis

Abstract The sequence of intermetallic formation and growth, and melting behavior of a Cu-coated Ti powder, used as active brazing alloy (ABA) for joining ceramic was studied. The experiments show that melting starts at around 885 °C, regardless of the heating rate. Prior to the onset of melting, a series of intermetallic layers was observed (Cu/TiCu 4 /Ti 3 Cu 4 /Ti 2 Cu 3 /Ti) with their relative thickness depending on the heating rate. A heating rate of 10 °C/min gives a final melting temperature of 900 °C as opposed to 915 °C for a sample heated at 40 °C/min. The utilization of N 2 as a “protective” gas has shown the instantaneous formation of TiN from the reaction between Ti and N 2 when the first liquid appears, indicating N diffusion through the copper shell. The remainder of the powder still contains Ti in copper as a TiN diffusion barrier was formed. Mixtures of ABA and Si 3 N 4 powder have demonstrated that the surface of the powder becomes liquid at 894 °C as an intense exothermic peak from the reaction between Ti and Si 3 N 4 is observed.

Brazing silicon nitride to an iron-based intermetallic using a copper interlayer

The effect of adding a copper interlayer to absorb the residual stresses produced during cooling of a silicon nitride (Si 3N 4) ceramic brazed to an iron aluminide alloy was demonstrated. Differential scanning calorimetry (DSC) results showed the positive influence of the copper interlayer in diluting the high-titanium content brazing alloy by decreasing the quantity of active brazing alloy (ABA) available for reaction. The reaction layer formation mechanism was investigated by low voltage line scan FESEM and was shown to consist of a growth competition between the TiN and Ti 5Si 3 layer. An activation energy of 137 kJ/mol for the reaction layer formation was calculated. A Fe/Cu–Ti alloy reaction at the interface between the Cu interlayer and the FA-129 was observed. This reaction zone extended up to 100 μm in thickness. The maximum bending strength obtained was 160 MPa. All fractures occurred at the Cu/Si 3N 4 interface, suggesting higher strengths for the FA-129/Cu interface.

Metal substrate effects on the thermochemistry of active brazing interfaces

This work investigates the effects of the metal substrate on the thermochemistry of active brazing alloys during ceramic/metal joining applications. The thermodynamics and kinetics of the interactions between the metal substrate and the braze alloy are examined. Numerical simulations are used to rationalize experimental observations reported elsewhere. It is shown that using Ni metal substrates at temperatures much higher than the liquidus of the brazing alloys can dramatically decrease the chemical activity of Ti in Cu-based brazing alloys. This effect is much less intense when Fe-metal substrates are in contact with the same active brazing alloy systems. It is additionally proven that the time scales necessary to observe such detrimental decrease in chemical activity are on the order of minutes.

Wetting behavior of Co based active brazing alloys on SiC and the interfacial reactions

The wetting behavior of Co-based alloys on silicon carbide (SiC) was investigated by the sessile drop method. In vacuum at 1493 K for 10 min, the CoFeNi(Si, B)–(8–15)Cr–(14–21)Ti alloy exhibits good wettability on SiC, but after cooling fracture occurred within the SiC. The interfacial reactions were studied. The newly designed CoNi(Si, B)–Cr–Ti alloy is a promising brazing alloy for SiC.

Utilisation of Field Emission Scanning Electron Microscopy to Characterise an Active Brazing Alloy (ABA) Produced by an Electroless Plating Technique

Utilisation of Field Emission Scanning Electron Microscopy to Characterise an Active Brazing Alloy (ABA) Produced by an Electroless Plating Technique