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Wide gap active brazing of ceramic-to-metal-joints for high temperature applications

K. Bobzin,L. Zhao,N. Kopp,S. Samadian Anavar

《机械工程前沿（英文）》 2014年第9卷第1期页码 71-74 doi: 10.1007/s11465-014-0291-0

摘要：

Applications like solid oxide fuel cells and sensors increasingly demand the possibility to braze ceramics to metals with a good resistance to high temperatures and oxidative atmospheres. Commonly used silver based active filler metals cannot fulfill these requirements, if application temperatures higher than 600°C occur. Au and Pd based active fillers are too expensive for many fields of use. As one possible solution nickel based active fillers were developed. Due to the high brazing temperatures and the low ductility of nickel based filler metals, the modification of standard nickel based filler metals were necessary to meet the requirements of above mentioned applications. To reduce thermally induced stresses wide brazing gaps and the addition of Al₂O₃ and WC particles to the filler metal were applied. In this study, the microstructure of the brazed joints and the thermo-chemical reactions between filler metal, active elements and WC particles were analyzed to understand the mechanism of the so called wide gap active brazing process. With regard to the behavior in typical application oxidation and thermal cycle tests were conducted as well as tensile tests.

关键词： wide gap active brazing nickel filler metals high temperature application WC Al₂O₃

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Application of cold spraying for flux-free brazing of aluminium alloy 6060

Kirsten BOBZIN, Lidong ZHAO, Thomas SCHLAEFER, Thomas WARDA,

《机械工程前沿（英文）》 2010年第5卷第3期页码 256-260 doi: 10.1007/s11465-010-0095-9

摘要： In the present study, samples of aluminium alloy 6060 were coated by cold spraying with a powder of brazing alloy Al12Si. The influence of the process gas temperature on particle velocities and coating build-up was investigated. The coated samples were heat-treated in air and under argon atmosphere to investigate the wetting behaviour of the deposited Al12Si and the diffusion processes between Al12Si coatings and substrates. Coated samples were brazed flux-free under argon atmosphere by an induction heating system. The microstructure of the coated, heat-treated, and brazed samples was investigated. The shear strength of the brazed joints was determined. The results show that the brazing alloy Al12Si could be very well deposited on the substrate by cold spraying. The particle velocity increased with increasing process temperature. Correspondingly, the thickness of Al12Si coatings increased with increasing process temperature. The heat treatments showed that a very good metallurgical bond between the Al12Si coatings and the substrate could be realized by the deposition using cold spraying. The coated samples could be well brazed without fluxes. The coating thickness and overlap width influenced the shear strength of the brazed joints. The highest shear strength of brazed joints amounts to 80 MPa.

关键词： aluminium alloy flux-free brazing cold spraying shear strength

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Influence of the filler materials on flux-free brazing of pure aluminium (1050)

Kirsten BOBZIN, Lidong ZHAO, Thomas SCHLAEFER, Thomas WARDA,

《机械工程前沿（英文）》 2010年第5卷第1期页码 47-51 doi: 10.1007/s11465-009-0079-9

摘要： In the present study, samples of pure aluminium (1050) were deposited by cold spraying with filler materials such as Al12Si, Al7Si, Al12Si-4%Cu, and the Al-Si-based filler material A, which was especially developed for flux-free brazing by the Surface Engineering Institute. Besides, pure Si powder was also sprayed. The coated samples were heat-treated under different conditions and were brazed under an argon atmosphere without fluxes or with the flux Nokolok by an induction heating system. The shear strength of the brazed joints was determined. The results show that the filler materials could be well deposited by cold spraying. A thin layer of brittle Si could also form due to the strong deformation of the substrate surface. The heat treatments showed that a very good metallurgical bond between the filler materials and the substrate could be realized by the deposition by cold spraying. The Al7Si deposited samples could not be brazed without fluxes under the given conditions. The samples deposited with other filler materials could be brazed without fluxes. The in-situ diffusion process made it possible to braze the Si-deposited samples at 580°C. The joints of the samples deposited with the filler material showed the highest shear strength of 41 MPa, whereas the values of the Al12Si and Si deposited samples were less than 20 MPa. The employment of the flux Nikolok significantly increased the shear strength of the Al12Si deposited samples to more than 53 MPa.

关键词： aluminium flux-free brazing cold spraying shear strength

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Flux-free brazing of Mg-containing aluminium alloys by means of cold spraying

BOBZIN Kirsten, ZHAO Lidong, ERNST Felix, RICHARDT Katharina

《机械工程前沿（英文）》 2008年第3卷第4期页码 355-359 doi: 10.1007/s11465-008-0055-9

摘要： In the present study, AlSi12 and AlSi10Cu4 were deposited onto Mg-containing aluminium alloys 6063 and 5754 by cold spraying. The influences of the two brazing alloys and spray parameters on coating formation were investigated. The microstructure of the coatings was characterized. Some coated samples were heat-treated at 590°C and 560°C in air to investigate the effect of the rupture of oxide scales on the diffusion of elements during heat-treatment. Some coated samples were brazed under argon atmosphere without any fluxes. The results show that AlSi12 had much better deposition behaviour than AlSi10Cu4. Due to the rupture of oxide scales, Cu and Si diffused into the substrate and a metallurgical bond formed between the brazing alloys and the substrates during heat-treatment. The coated samples could be brazed without any fluxes. Because the oxide scales prevented the formation of a metallurgical bond locally, the brazed samples had relatively low shear strengths of up to 43 MPa.

关键词： diffusion metallurgical substrate Mg-containing aluminium spraying

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Brazing of ceramic-to-ceramic and ceramic-to-metal joints in air

Kirsten BOBZIN, Thomas SCHLAEFER, Lidong ZHAO, Nils KOPP, Arne SCHLEGEL

《机械工程前沿（英文）》 2010年第5卷第2期页码 125-129 doi: 10.1007/s11465-010-0007-z

摘要： Reactive air brazing (RAB) is an emerging technology for the production of ceramic-to-ceramic and ceramic-to-metal joints. In this study, RAB was investigated with respect to the potential applications for solid oxide fuel cells (SOFCs) as one example of use. It was found that alumina could be well brazed by RAB with AgCu and AgCuTi brazes. Both braze composition and brazing temperature influenced significantly the wetting behavior and their mechanism of wetting. AgCu and AgCuTi braze alloys could also be used to produce brazed joints with the SOFC materials ceramic yttria stabilized zirconia and steel X1CrTiLa22. However, CuO reacts with the steel, forming a brittle oxide layer on the steel surface, which is undesirable for SOFC applications. The first trials with Ag0.5Al showed a promising solution.

关键词： reactive air brazing (RAB) X1CrTiLa22 Al₂O₃ yttria stabilized zirconia (YSZ) solid oxide fuel cell (SOFC)

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Influence of direct electric current on wetting behavior during brazing

Kirsten BOBZIN, Wolfgang WIETHEGER, Julian HEBING, Lidong ZHAO, Alexander SCHMIDT, Riza ISKANDAR, Joachim MAYER

《机械工程前沿（英文）》 2020年第15卷第3期页码 496-503 doi: 10.1007/s11465-019-0582-6

摘要： The wetting behavior of liquid metals is of great importance for many processes. For brazing, however, a targeted modification beyond the adjustment of conventional process parameters or the actual set-up was not possible in the past. Therefore, the effect of direct electric current along the surface of a steel substrate on the wetting behavior and the formation of the spreading pattern of an industrial nickel-based filler metal was investigated at a temperature above = 1000 °C in a vacuum brazing furnace. By applying direct current up to = 60 A the wetted surface area could be increased and the spreading of the molten filler metal could be controlled in dependence of the polarity of the electric current. The electric component of the Lorentz force is supposed to be feasible reasons for the observed dependence of the electrical polarity on the filler metal spreading direction. To evaluate the influence of the electric current on the phase formation subsequent selective electron microscope analyses of the spreading pattern were carried out.

关键词： brazing electric current assisted wetting Lorentz force

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Creep of brazed plate-fin structures in high temperature compact heat exchangers

Shantung TU, Guoyan ZHOU

《机械工程前沿（英文）》 2009年第4卷第4期页码 355-362 doi: 10.1007/s11465-009-0065-2

摘要： In recent years, the need for high temperature heat exchangers to improve the efficiency of power and chemical conversion systems has been growing. However, the creep design of the high temperature compact heat exchangers has been a primary concern because the working temperature can be well above the creep limit of the materials. To establish the high temperature design criterion for compact heat exchangers, creep behavior of the plate-fin structures and brazed joints are investigated in this paper. The time-dependent deformation and bending stress of the plate-fin structures are obtained analytically by simplifying the fins to elastic springs. The creep damage evolution inside the brazed joint is studied by coupling the finite element method with a damage constitutive equation. The significant effect of creep property mismatch in the brazed joint on the creep strength is demonstrated.

关键词： compact heat exchanger creep damage brazing joint

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ARC welding method for bonding steel with aluminum

Zhenyang LU, Pengfei HUANG, Wenning GAO, Yan LI, Hanpeng ZHANG, Shuyan YIN

《机械工程前沿（英文）》 2009年第4卷第2期页码 134-146 doi: 10.1007/s11465-009-0033-x

摘要： When welding steel with aluminum, the appearance of intermetallic compounds of Fe and Al will decrease tenacity and increase rigidity, which leads to bad joint performance. A new type of low energy input (LEI) welding technology is introduced which can be used to weld steel with aluminum. Using the technology, brazing was located on the steel side and arc fusion welding on the aluminum side. The less heat input reduces the thickness of intermetallic compounds to 3-4 μm. Tensile strength tests prove that the joint breaks at the heat-affected zone and the strength is higher than 70% of the aluminum’s. Thus, the method can lead to a good performance joint.

关键词： joining of steel and aluminum low energy input welding arc welding fusion welding – brazing