High-temperature Brazing Research Articles

Ultra-high temperature brazing of C/C using a simplified FeNiCrCu high-entropy alloy as filler

To increase remelting temperature of C/C brazed joint, a simplified FeNiCrCu high-entropy alloy (HEA) filler was designed in high-temperature brazing (HTB). The joint formation mechanism and fracture behavior were studied. The eutectic reaction of FeNiCrCu HEA with C/C could not occur, helping increase joint remelting temperature over HEA melting point (1334 °C). For the recommended parameter 1350 °C-2 min, dissolution of C/C occurred well, and no defect was observed both at interface and within bond seam. The maximum shear strength was 24.2 MPa due to the high strength in-situ (Cr,Fe)3C2 reinforced the high plastic Cu-Ni-Fe(S.S.) matrix and intimate wavy interface. Cr existed only in M3C2 in bond seam, reducing both carbon content and CTE of bond seam. For higher temperature and longer time, excessive dissolved carbon content resulted in the presence of large solidified carbon with defect at interface, joint shear strength decreased dramatically. These results provide a unique braze system for brazing carbon-based materials.

High temperature brazing of C/C using Hastelloy C-276 as filler and joint formation mechanism

To increase servicing temperature of brazed C/C joint, a commercial Hastelloy C-276 (Ni-15.5Cr-16Mo-5Fe-4W, wt. %) with high melting point was used as filler in high-temperature brazing (HTB). The fast HTB process with a soaking time of 2 min was performed at four levels 1250 °C, 1300 °C (bellow solidus), 1350 °C and 1400 °C (over liquidus). Joint shear strength of 23.5 MPa (under 1400 °C) and 20 MPa (under 1250 °C) were obtained due to significant dissolution of C/C, dense interface, infiltration, and MC in-situ reinforced C-rich Ni-based bond seam. Joint microstructure evolution examination indicated that carbon could rapidly diffuse into C-276, inducing segregation of the active elements Cr and Mo at C-276 grain boundaries, triggering C-(Ni, Fe)-(Cr, Mo) eutectic reaction in the grain. All joints fractured mainly within infiltrated zone. The study demonstrated that using Ni-based alloy containing Cr and Mo as filler was feasible.

Effect of a High Temperature Brazing Thermal Cycle on the Microstructure and Mechanical Properties of Fe–Cr–Mn–Ni–C Stainless Steel

Effect of a High Temperature Brazing Thermal Cycle on the Microstructure and Mechanical Properties of Fe–Cr–Mn–Ni–C Stainless Steel

Vacuum High-Temperature Brazing of 3003 Aluminum Alloy

Brazing filler metals based on the Al-Si system are widely used for brazing aluminum alloys. Their melting point is 577 °С (eutectic). It is necessary to conduct comprehensive studies of the technological properties of experimental filler metals and brazed joints to create a brazing filler metal with a reduced melting temperature for vacuum brazing of thin-walled aluminum products made of alloy 3003. The paper presents the research results on high-temperature vacuum brazing of aluminum alloy 3003 with Al-Cu-(Si, Mg) filler metal. It was determined that the amount of magnesium in the filler should be limited due to the risk of porosity formation associated with magnesium vaporization. It was identified that reducing the magnesium content increases the liquidus temperature above 530–550 °C. Therefore, experimental alloys require additional alloying with depressant elements, particularly silicon, to achieve the required melting temperature level. The chemical inhomogeneity of the filler in the initial state (after rapid solidification from the liquid state) and the structure of the brazed joints were investigated using micro-X-ray spectral analysis. Through empirical means, it was determined that a magnesium content of 1.5 % by weight in the filler allows for producing high-quality brazed joints without visible defects. In this case, shear strength is in the range of 0.6–0.7 of the strength of the base material. Tests of brazed joints for three-point bending resulted in an angle close to 180°, which indicates the promising use of experimental brazing filler metal in vacuum brazing of aluminum alloy 3003.

MPEX High Heat Flux Plasma Dump Design, Manufacture, and Articles Test

The Material Plasma Exposure eXperiment (MPEX) device is a steady-state linear plasma device currently in the final design phase at the Oak Ridge National Laboratory. This device will reach ion fluences up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{31}\,\,\text{m}^{-2}$ </tex-math></inline-formula> and will be used to expose neutron-irradiated materials to divertor-relevant plasmas and to study the effects of plasma-material interactions. These studies will elucidate the complex effects of plasmas with divertor candidate materials capable of withstanding high heat flux and high fluences for next-generation fusion devices. Bidirectional plasma will be generated using a high-power (200 kW) helicon source. Plasma will be confined by superconducting magnets. The last plasma-facing component on the upstream side of the MPEX device is the dump, which has been designed to intercept plasma and energetic particles. The dump will have a total heat load of 9.2 kW. A copper alloy (Glidcop AL-15) was selected for use in the water-cooled flange design because of its high thermal conductivity, its retaining strength at elevated temperatures, and its ability to be used in the high-temperature braze joints used in this application. Titanium-zirconium-molybdenum (TZM) tiles are brazed to the Glidcop AL-15 flange using high-temperature braze alloy. External water-cooling channels are used on the dump flange to prevent water leakage inside the vacuum space. This article discusses the details of the high heat flux dump design, including the computational fluid dynamics (CFD) and structural analyses performed to validate the design to meet the operational requirements of the MPEX device.

Material Plasma Exposure eXperiment (MPEX) High Heat Flux Bellows for Component Alignment in High Microwave Environment

The Material Plasma Exposure eXperiment (MPEX) device is a linear plasma device developed to perform plasma material interaction experiments under the conditions prototypic of a fusion reactor divertor. MPEX has multiple systems that must be precisely aligned to the plasma axis, including an electron cyclotron heating system that emits up to 400 kW of microwave power into the vacuum vessel. Five distinct systems require precise alignment on the MPEX device, thus requiring four bellows, all of which are adjacent to the plasma at a relatively high heat flux of approximately 47 kW/m2 and microwave power regions. The MPEX high heat flux bellows (HHFB) is designed to deliver 6 degrees of freedom positioning. The HHFB includes titanium–zirconium–molybdenum (TZM) inserts that are brazed into a Glidcop AL-15 body using a high-temperature braze alloy, thus blocking direct line of sight to an edge-welded bellows from the plasma and microwave screen to block microwaves from the bellows. A custom ConFlat knife edge is machined into the Glidcop AL-15, so the vacuum flanges do not need a braze or weld joint on the vacuum interface. Fingerstock or copper mesh is used to restrict microwave power from entering the interstitial space between the water-cooled Glidcop AL-15 body and edge-welded bellows. Glidcop AL-15 was selected as the material of choice for the water-cooled body because it can maintain mechanical integrity at elevated temperatures, and it also allows for a high-temperature braze. TZM was selected for its machinability and compatibility with vacuum and plasma requirements. A test article is also being considered for a similarly shaped component, the MPEX limiter, that will demonstrate the integrity of the braze joint under high thermal load. Results from this testing will be extrapolated to deduce the lifetime and integrity of the HHFB design.

Microstructure and shear property of high-temperature brazing of TiAl alloy and 316L stainless steel with a Ni-based amorphous filler

High-quality joining of TiAl alloy to stainless steel is of great significance to the aerospace field. However, the hybrid structure of TiAl and 316L always suffers from insufficient strength when serving at elevated temperatures. In this work, a high-melting-point quaternary Ni-Nb-Zr-Ti amorphous alloy was applied as the filler metal to braze the two alloys at different temperatures. The microstructure and mechanical properties were studied in detail, and the results indicated that the joint was divided into three different regions and various reaction products were formed after brazing. The shear strength of the joint tends to first increase and then decrease with increasing brazing temperature. A satisfactory joint was obtained at 1090°C, and the highest shear strength reached 290 MPa and 180 MPa at room temperature and 750°C, respectively. Shear fracture indicates that there were obvious cleavage steps and some secondary cracks on the fracture surface, indicating that a high-melting-point quaternary Ni-Nb-Zr-Ti amorphous alloy is useful to improve the shear strength of TiAl alloy and 316L stainless steel, but it is difficult to effectively improve the plasticity. The fracture occurred on the TiAl interfacial region, and the phase causing microcrack initiation and propagation was AlNiTi.

Microstructure and performance of glass fiber metal composite-bonded diamond segment with Cu-Sn-Ti alloy

To develop metal-bonded diamond tools without dressing during machining, a novel glass fiber metal composite bonding agent with Cu–Sn–Ti alloy was proposed. The three-point bending strength of the diamond segments and the Vickers microhardness of the solidified composite bonding agents were tested. The microstructures of the diamond segments were investigated and the wear tests were performed for each group of diamond segments. The results showed that diamond segments with glass fiber content of 1.55 wt % - 6.89 wt % exhibited lower bending strength (declined by 36.4%–80.4%) and smaller microhardness (reduced by 16.0%–87.9%), compared to those of the diamond segment with no glass fiber addition. Good bonds were formed among the Cu–Sn–Ti alloy, glass fibers, and diamond grits. Chemical reactions occurred between the Cu–Sn–Ti alloy and glass fibers during high-temperature brazing, forming new intermetallic compounds such as Ti5Si3, Ti2O3, and Ti(Cu, Al)2, which improved the bonding strength. With an increase in the glass fiber content, fractures were more likely to occur in the glass fibers than in the diamonds, resulting in the bending strength decreasing more and more slowly. The wear resistance of the diamond segments decreased gradually with increasing glass fibers weight content. The diamond segment with 4.98 wt % glass fibers exhibited the best and most stable wear performance.

Investigation of microstructure evolution and strength mechanism of the Cu coated BNi-7 core-shell structure filler metal

In this paper, a novel method of using the Cu coated BNi-7 core-shell structured composite filler metals to braze was adopted to alleviate the residual thermal stress in the joints of Inconel 718. A pure Cu layer coated with the BNi-7 powders was successfully prepared by electroless plating to fabricate ductile filler metal with excellent mechanical properties. The obtained BNi-7 powders with 2 μm thick Cu coating exhibit dense and uniform structure through the elemental mapping analysis of the composite filler metal. The thickness and the content of the Cu layer could be determined by electroless plating time and the pH value of the plating solution. Meanwhile, the thermal physical parameters of the obtained composite filler were characterized by DSC analytical method, and the result indicated that the melting point was higher than the BNi-7 filler metal. The Inconel 718 were brazed without any defects using the composite filler metal in a vacuum. Compared to the BNi-7 filler metal, the Cu coated BNi-7 composite filler metal could form plenty of uniform reticular solid solutions during the high-temperature brazing process instead of acicular eutectic compounds. When adding the Cu powders mechanically into the original BNi-7 filler metals, voids and cracks could be found through the joints due to the uneven distribution of the Cu. The typical interfacial sequence of the joints was Inconel 718/Ni(Cu)ss+ σ-FeCr/Ni5P2 + Ni3P + Ni(Cr)ss + Ni2Cr + Ni(Cu)ss + σ-FeCr + Ni(Cu, Cr, Fe)ss/Ni(Cu)ss+ σ-FeCr/Inconel 718. The formation of the reticular Ni(Cu, Cr, Fe)ss phase released the stress in the brittle phase adjacent leading to the increasing ductility of the joints. The addition of the Cu-coated layer significantly enhanced the strength of the joint at room temperature, and the strengthening mechanisms were proposed.

Characterization of Ag-Based Filler for Electrolyte/Metallic-Interconnect Joint in Metal-Supported Solid Oxide Fuel Cells Applications

Metal-supported solid oxide fuel cells (MS-SOFCs) exhibit better electrochemical performance than conventional ceramic-supported cells at lower temperature due to their exceptional thermal, electrical, and mechanical properties. MS-SOFCs can withstand rapid thermal cycling operation and make it practical for mobile applications. A reliable seal is essential for electrolyte/metallic interconnect joint in MS-SOFC applications. In the present study, we proposed an Ag-Ge alloy filler as a high-temperature brazing sealant for use in MS-SOFCs. Commercial ferritic stainless steel (Crofer22H) and La1-XSrXGa1-yMgyO3- δ (LSGM) substrate were employed as metallic interconnect and electrolyte for this study, respectively. The adhesive and hermetic characterization for the electrolyte/metallic interconnect joint joined by the Ag-Ge alloy filler were examined by using high-temperature leak test at elevated temperatures. Results showed that the leak rate of LSGM/Crofer22H coupon is 5 x 10-4 mbar∙l/s/cm after aging at 750 °C for 90 hours in He/air. In addition, SEM/EDS analyses also revealed that Ge element in the Ag-Ge filler was prone to diffuse toward Crofer22H and LSGM side, and thus improved the interfacial adhesion of the LSGM/Crofer22H joint.

Characterization of Ag-Based Filler for Electrolyte/Metallic-Interconnect Joint in Metal-Supported Solid Oxide Fuel Cells Applications

Metal-supported solid oxide fuel cells (MS-SOFCs) exhibit better electrochemical performance than conventional ceramic-supported cells at lower temperature due to their exceptional thermal, electrical, and mechanical properties. MS-SOFCs can withstand rapid thermal cycling operation and make it practical for mobile applications. A reliable seal is essential for electrolyte/metallic interconnect joint in MS-SOFC applications. In the present study, we proposed an Ag-Ge alloy filler as a high-temperature brazing sealant for use in MS-SOFCs. Commercial ferritic stainless steel (Crofer22H) and La1-XSrXGa1-yMgyO3- δ (LSGM) substrate were employed as metallic interconnect and electrolyte for this study, respectively. The adhesive and hermetic characterization for the electrolyte/metallic interconnect joint joined by the Ag-Ge alloy filler were examined by using high-temperature leak test at elevated temperatures. Results showed that the leak rate of LSGM/Crofer22H coupon is 5.0 x 10-4 mbar∙l/s/cm after aging at 750°C for 100 hours in He/air. In addition, SEM/EDS analyses also revealed that Ge element in the Ag-Ge filler is prone to diffuse toward Crofer22H and LSGM side, and thus improves the interfacial adhesion of the LSGM/Crofer22H joint.

Repairability analysis of the energy gas turbine rotor blade second stage shroud by high-temperature brazing

The article considers the repair of the energy gas turbine rotor blade second stage shroud. The paper presents an analysis of the possibility of the repair consisting of the replacement of both labyrinth and honeycomb seals by the high-temperature brazing process. All the steps of the repair process were discussed and the results of microscopic metallographic evaluation using a light microscope and a scanning electron microscope were presented. Several advantages related to the use of this technology were indicated.

Nanojoining with Ni Nanoparticles for Turbine Applications.

Thermal joining can lead to high thermal stresses, undesired structural changes, and the associated loss of properties. In the turbine industry, monocrystalline materials are often used to take advantage of their high creep resistance and heat resistance. For process-related reasons, components are mechanically machined, and the contours usually have slightly work-hardened areas due to the mechanical processing. Downstream thermal processes at temperatures above 1100 °C can lead to recrystallization (Rx) at these areas, so that the properties are negatively affected. Usually, the joining temperatures for high-temperature brazing are in the range of 1200 °C, both in new installations and in the case of repairs. It is therefore desirable to reduce the joining temperature without changing the choice of filler material, which can lead to susceptibility to corrosion and oxidation. According to investigations of the last years, nanojoining with nanoparticles offers great potential. The joining temperature can be lowered due to the “surface effect.” A considerable reduction in the size of the particles leads to a significant increase in surface atoms and thus in the specific surface area. The connection of the materials occurs predominantly due to sintering processes. After the joining process, the properties of a bulk material are available again. Mechanical properties comparable to those of brazing have already been achieved with silver nanoparticles (Hausner in WWA 56, 2015). Up to now, publications on the topic of nanojoining have largely referred to silver nanoparticles/silver sintering. Due to the temperature application range, silver filler material cannot be used in gas turbines. Therefore, the first results of nickel nanoparticles for joining of the nickel-based superalloy PWA 1483 using induction heating are described in this paper. During joining, the parameters brazing temperature, holding time and the surface treatment of the base materials were varied. It becomes clear that the microstructure of the joint is dependent on temperature and holding time. Moreover, if the temperature is too low and holding time too short, only insufficiently sintering occurs, which leads to sample failure during the metallographic preparation. On the other hand, samples with a tensile shear strength of up to 165 MPa can be achieved with convenient joining conditions.

Investigation of a brazed joint EK-181/V/W obtained by Cu-Sn and Cu-Ti amorphous foils

The work presents the results of high temperature brazing of reduced activated ferritic martensitic steel EK-181 with pure tungsten, which is essential for DEMO fusion reactor. Vanadium interlayer was used to reduce thermal stresses. Brazing alloys to be used were rapidly quenched into ribbons Cu-12Sn, Cu-20Sn, Cu-12Sn-0,4P for EK-181/V, Cu-50Ti for V/W. Microstructure investigations, mechanical and thermocycling test were carried out.

Joining tungsten with steel for DEMO: Simultaneous brazing by Cu-Ti amorphous foils and heat treatment

Abstract Development of a reliable technology to join tungsten with steel is essential for DEMO application; however, it is difficult due to large differences in their physical properties. To solve this problem, high-temperature brazing was carried out. Cu-Ti brazing alloys, which were rapidly solidified into foil, were used together with a compensating vanadium interlayer, so the EK-181 steel/Cu-28Ti/V/Cu-50Ti/W and EK-181/Cu-50Ti/V/Cu-50Ti/W brazed joints were obtained. The microstructures of the seams were investigated by optical microscopy, SEM (EDX, EBSD) and synchrotron XRD. Thermocycling and shear strength tests showed that Cu-28Ti wt. % brazing alloy ensures a firmer joint compared to Cu-50Ti wt. %. The Cu-28Ti wt. % brazing alloy was used to perform high-temperature brazing in the brazing mode equivalent to traditional EK-181 steel heat treatment. It showed that every step of the heat treatment affected the microstructures and the shear strength.

Interfacial reaction and brazing behaviour of SiCf/SiC with Cf/C composites using Si-10Zr alloy at high temperatures

A Si-Zr eutectic alloy was employed as a high-temperature braze filler to join SiCf/SiC composites with Cf/C composites. The interfacial microstructure and bonding mechanism on the side of the SiCf/SiC composites were studied for the first time. The results showed that SiC reaction layers formed between the Si-Zr filler and both substrates. The SiC layer resulted from the chemical reaction between Si and C at the filler–Cf/C interface. In contrast, at the filler–SiCf/SiC interface, coarse-SiC crystals only precipitated on the SiC fibre bundles, and there was only non-reactive bonding between the filler and the SiC matrix. In addition, the reactive infiltration process between the liquid Si alloy and the porous substrates contributed to the formation of infiltration structures, including Cf/C–SiC and SiCf/SiC–Si-ZrSi2, resulting in the reinforcement of the substrates and the joint. Finally, a favourable shear strength of 38 MPa was achieved.

Effect of high-temperature brazing with a nickel-based STEMET 1301A brazing alloy on the unbrazing temperature of 12Kh18N10T steel joints

The challenges facing the creation of brazed joints of 12Kh18N10T (AISI 321) austenitic stainless steel with high unbrazing temperatures for extreme working conditions in aerospace appliances are considered in this study. An amorphous-nanocrystalline nickel–based foil, Ni-7Cr-4.5Si-3.5Fe-2.6B, wt.%, is used for brazing the steel. Experiments on brazing regimes with various temperatures (1070–1160 °С) and times of exposition (15–80 min) are carried out. The formation of Ni-based solid solutions with different Cr, Fe, Mn, Si, and Ti contents in the brazed seam is detected for all brazing regimes. Using Thermo-Calc software, the liquidus temperature located in a range between 1268 and 1388 °С is calculated. To verify the calculated values, the unbrazing temperature is experimentally determined for specimens, with a composition of the solid solutions, formed in the center of the brazed seam during brazing at 1160 °С/15 min, 1070 °С/15, and 1160 °С/80 min. The experimental results deviate from values computed by Thermo-Calc by no more than 54 °С. The experimental samples obtained using the 1070 °C/40 min and 1100 °C/80 min regimes demonstrate high unbrazing temperatures equal to 1303 °C and > 1330 °C, respectively, which corresponds to the calculations with an accuracy of 2.5%. Taking into account the combination of properties (strength and unbrazing temperature), brazing regimes of heating to 1070–1100 °C and an exposure time for 15–40 min can be recommended for the production of high-strength joints with high unbrazing temperatures.

TZM/graphite interface behavior in high-temperature brazing by Ti-based brazing filler materials

Graphite was successfully brazed to TZM alloy using the Ti-56Ni, Ti-8.5Si, Ti-33Cr and Ti-30V-3Mo brazing filler materials, respectively, and the corresponding brazing temperatures ranged from 1300 to 1700 °C. The results show that the microstructure of TZM/graphite braze metal was composed of NiTi and Ni3Ti compounds when using Ti-56Ni brazing filler, and the discontinuous TiC compounds were found at the Ti-56Ni/graphite side. When using the Ti-8.5Si, Ti-33Cr and Ti-30V-Mo brazing fillers, the metallurgical combination was obtained due to the formation of the Ti-Mo solid solution at the TZM/brazing filler side and the TiC reaction layer at the graphite/brazing filler side. The fracture was occurred at the interface of TiC/graphite during shear test, which indicated the poorer bonding strength between the graphite and granular TiC.

High Temperature Mechanical Properties of a Vented Ti-6Al-4V Honeycomb Sandwich Panel.

For aerospace applications, honeycomb sandwich panels may have small perforations on the cell walls of the honeycomb core to equilibrate the internal core pressure with external gas pressure, which prevent face-sheet/core debonding due to pressure build-up at high temperature. We propose a new form of perforation on the cell walls of honeycomb sandwich panels to reduce the influence of the perforations on the cell walls on the mechanical properties. In this paper, the high temperature mechanical properties of a new vented Ti-6Al-4V honeycomb sandwich panel were investigated. A vented Ti-6AL-4V honeycomb sandwich panel with 35Ti-35Zr-15Cu-15Ni as the filler alloy was manufactured by high-temperature brazing. The element distribution of the brazed joints was examined by means of SEM (scanning electron microscopy) and EDS (energy-dispersive spectroscopy) analyses. Compared to the interaction between the face-sheets and the brazing filler, the diffusion and reaction between the honeycomb core and the brazing filler were stronger. The flatwise compression and flexural mechanical properties of the vented honeycomb sandwich panels were investigated at 20, 160, 300, and 440 °C, respectively. The flatwise compression strength, elastic modulus, and the flexural strength of the vented honeycomb sandwich panels decreased with the increase of temperature. Moreover, the flexural strength of the L-direction sandwich panels was larger than that of the W-direction sandwich panels at the same temperature. More importantly, the vented honeycomb sandwich panels exhibited good compression performance similar to the unvented honeycomb sandwich panels, and the open holes on the cell walls have no negative effect on the compression performance of the honeycomb sandwich panels in these conditions. The damage morphology observed by SEM revealed that the face-sheets and the brazing zone show ductile and brittle fracture behaviors, respectively.

Current Review on the Research Status of Cemented Carbide Brazing: Filler Materials and Mechanical Properties

Cemented carbides have been widely applied in cutting tools and wear-resistant components due to their ultrahigh hardness and good wear resistance. However, the disadvantages of limited impact toughness and high cost have restricted their further application. Consequently, cemented carbides are usually joining with ductile steels to combine the advantages of both. Among various materials joining technologies, brazing have been an effective method to achieve high quality dissimilar cemented carbide joints. In this paper, the research status of cemented carbide brazing is reviewed. The materials utilized as brazing filler metal in cemented carbide brazing joints are summarized in detail. Researchers have done lots of works utilizing Cu based and Ag based brazing filler metals which are the most commonly used interlayers in brazed joints of cemented carbide and ductile steel. The effects of different filler metal on wettability, microstructure, phase constitution and mechanical properties of brazed cemented carbides joints are analysed. Besides, a series of newly developed brazing filler material such as nickel-based high temperature brazing filler metal, amorphous brazing filler metal and high entropy alloy brazing filler materials are also involved. These newly developed brazing filler metals have shown great potential in fabricating high quality joints. Finally, the current issues of cemented carbide brazing are reviewed and the develop trend is predicted.