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̈ler, C. Chr. Schu; Stuck, A.; Beck, N.; Keser, H.; ̈ck, U. Ta

doi:10.1023/a:1008942502309

Cited by 42 publications

(27 citation statements)

References 10 publications

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“…The standard filler metals are alloys of the Ag-CuO system which was early investigated for the purpose of RAB. [1,2] Reactive air brazing has been investigated for the use in innovative and challenging applications in the energy generation such as gas separation tubes and solid oxide fuel cells (SOFC). In both applications, ceramic and metallic parts have to be joined.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Reactive Air Brazed Ceramic/Metal Joints with Unadapted Thermal Expansion Behavior

et al. 2014

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Reactive air brazing (RAB) is a promising and economic method for joining ceramic to metal as well as ceramic to ceramic. Hybrid joints gain importance in the field of challenging applications such as gas separation or solid oxide fuel cells. While the ceramic partner is often directly chosen due to its functionality, the metallic partner needs to be chosen carefully in order to avoid high residual stresses due to the differences in the thermal expansion coefficients. This leads to the restriction of the usage of a significant number of potential joining partners. Ceramic/metals components with unadapted thermal expansion behavior (Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-d /Crofer 22 H and 3YSZ/AISI 314) were joined by RAB. Cu-containing as well as Cu-free Ag-based filler metals were used. Analysis of the cross-section of brazed samples showed that the microstructure of the samples depends especially on the used filler metal. The melting process as well as the exothermic reactions leading to a distinct reaction zone could be observed in the differential scanning calorimetric measurements. While the microstructure of the joints is not significantly influenced by the base material, the strength of the BSCF/Crofer 22 H specimens is nearly four times lower than the strength of the specimens with the adapted thermal expansion coefficients (BSCF/AISI 314 and 3YSZ/Crofer 22 H). The reasons are residual stresses caused by the different thermal expansion coefficients. Finite element simulations assuming a viscoplastic material model show that an amount of stress can be reduced by relaxation within the silver based braze. But the volume of the high residual stresses is still larger in the BSCF/Crofer 22 H joints than that of the BSCF/AISI 314 joint resulting in a lower fracture strength.

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Section: Introductionmentioning

confidence: 99%

Characterization of Reactive Air Brazed Ceramic/Metal Joints with Unadapted Thermal Expansion Behavior

et al. 2014

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“…[1,2] These alloys differ from most braze filler metals in that (1) they readily wet a wide variety of ceramics, (2) brazing can be conducted directly in air without an inert cover gas or use of surface reactive fluxes, and (3) the resulting joint is inherently resistant to oxidation at high temperature. [3][4][5][6][7] The latter issue is a particularly significant challenge in high-temperature devices. Recent studies on the oxidation behavior of commercial active metal brazes, such as Nioro ABA and Gold ABA (Wesgo Metals), have shown that they are unreliable at temperatures beyond 500°C, due to oxidation along the interface between the filler metal and ceramic substrate.…”

Section: Introductionmentioning

confidence: 99%

Effect of Filler Metal Composition on the Strength of Yttria Stabilized Zirconia Joints Brazed with Pd-Ag-CuO x

Darsell

Weil

2008

Metall Mater Trans A

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Various compositions in the Ag-CuO x system are being investigated as potential filler metals for use in air brazing high-temperature electrochemical devices such as solid oxide fuel cells and gas concentrators. Prior work has shown that the melting temperature, and therefore the potential operational temperature, of these materials can be increased by alloying with palladium. The current study examines the effects of palladium addition on the joint strength of specimens prepared from yttria stabilized zirconia (YSZ) bars brazed with three different families of filler metals: Ag-CuO, 5Pd-Ag-CuO, and 15Pd-Ag-CuO. In general, it was found that palladium leads to a small-to-moderate decrease in joint strength, particularly in low copper oxide containing filler metals. However, the declination in strength is likely an acceptable trade-off for increased use temperature. In addition, a critical composition was observed for each filler metal series at which the mechanism for joint failure underwent a transition, typically from ductile to brittle failure. In each case, this composition corresponds approximately to the silver-rich boundary composition of the liquid miscibility gap in each system at the temperature of brazing.

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“…[6,7] In recent years, a new method, so called "Reactive Air Brazing" RAB, for ceramic/ metal joining has been introduced into solid oxide fuel cell stack design. Originally developed for semiconductor packaging, [8] its newly proposed applications range from sealing of solid oxide fuel cells [7,9,10] to oxygen concentrators. [11] Brazing is performed in air without any inert cover atmosphere, what makes the process cost-effective in mass production.…”

mentioning

confidence: 99%

“…[11] Brazing is performed in air without any inert cover atmosphere, what makes the process cost-effective in mass production. [12] Reactive air brazed joints prove to be suitable for isothermal solid oxide fuel cell operation for more than 5 000 h. [5] The chemical composition of the braze/interconnect and braze/ceramic interfaces as well as their changes during stack operation have important influence on the mechanical properties of the entire joint. In ref., [5] it has been demonstrated that joints undergo microstructural changes during the isothermal operating periods at the envisaged service temperatures (700-850°C), which play an important role for mechanical durability.…”

mentioning

confidence: 99%

Mechanical Properties of Reactive Air Brazed (RAB) Metal/Ceramic Joints. Part 2: Tailored Microstructure for Thermal Cycling Resistance

Skiera

Brandenberg

et al. 2014

Adv Eng Mater

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Improvement of electrochemical performance and reduction of power degradation processes during operation are typical key issues of SOFC-stack development. With the envisaged application of SOFCs in automotive applications [1,2] mechanical integrity under fast thermal cycling is a new key condition for safe stack operation and thus mechanical strength and durability a gaining concern. [1,3,4] SOFCs of the planar type are ceramic multi-layer compounds comprising of anode, electrolyte, and cathode layers. An automotive lightweight stack concept described in detail in ref. [5] integrates the cells into metallic cell frames (upper manifolds, manufactured from, e.g. Crofer 1 22APU or Crofer 1 22H, Figure 1) which are laser-welded to the interconnect sheets (lower manifolds, Figure 1). Multiple repeating units are piled to build a stack of technically utilizable voltage. Ductile metal-based seals are considered to better suit the specific requirements of automotive application, especially long-term integrity under repeated start-stop cycles than brittle glass-ceramics. [6,7] In recent years, a new method, so called "Reactive Air Brazing" RAB, for ceramic/ metal joining has been introduced into solid oxide fuel cell stack design. Originally developed for semiconductor packaging, [8] its newly proposed applications range from sealing of solid oxide fuel cells [7,9,10] to oxygen concentrators. [11] Brazing is performed in air without any inert cover atmosphere, what makes the process cost-effective in mass production. [12] Reactive air brazed joints prove to be suitable for isothermal solid oxide fuel cell operation for more than 5 000 h. [5] The chemical composition of the braze/interconnect and braze/ceramic interfaces as well as their changes during stack operation have important influence on the mechanical properties of the entire joint. In ref., [5] it has been demonstrated that joints undergo microstructural changes during the isothermal operating periods at the envisaged service temperatures (700-850°C), which play an important role for mechanical durability.Fast heating and cooling induces challenging temperature gradients and transients into the joints. As a consequence mechanical stresses are generated. Additional stresses emerge from different coefficients of thermal expansion of the joining partners.The mechanical loading situation is thus suited to cause cyclic deformation of the metallic braze matrix which is hard to be estimated from the mechanical and microstructural data published so far. [5,10,[14][15][16][17][18] In particular, detailed information on thermal cycling resistance and associated failure mechanisms as well as their relationship to the morphology of the interfaces are still limited.

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Cited by 42 publications

References 10 publications

Characterization of Reactive Air Brazed Ceramic/Metal Joints with Unadapted Thermal Expansion Behavior

Characterization of Reactive Air Brazed Ceramic/Metal Joints with Unadapted Thermal Expansion Behavior

Effect of Filler Metal Composition on the Strength of Yttria Stabilized Zirconia Joints Brazed with Pd-Ag-CuO x

Mechanical Properties of Reactive Air Brazed (RAB) Metal/Ceramic Joints. Part 2: Tailored Microstructure for Thermal Cycling Resistance

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