Reactive Air Brazing Research Articles

Reactive air brazing of Al2O3 ceramic with Ag-CuO-Pt composite fillers: Microstructure and joint properties

The effect of Pt content dispersed in Ag-CuO fillers on the interfacial microstructure and properties of Al2O3 ceramic joints brazed in air was investigated. Pt addition did not influence the variety of phases formed during reactive air brazing of Al2O3 joints. The position and morphology of CuO phase changed with Pt content which varied from 0 to 13.6 wt. %. Pt dissolved into Ag matrix completely. The typical interfacial sequence of brazed joints was Al2O3/CuAl2O4/CuO/Ag(s, s)/CuO/CuAl2O4/Al2O3. The addition of Pt to the Ag-CuO filler enhanced significantly the strength of Al2O3 joint from room temperature and up to 600℃. The joints brazed with Ag-CuO-9.0 wt. % Pt had the highest average strength at room temperature and at 600℃. The strength increased by 17 % and almost 100 %, respectively, compared with the Pt-free joint.

Microstructure and Mechanical Properties of Reactive-Air-Brazed 3YSZ/Crofer 22 APU Joints at Ambient Temperature

The growth of inventive high-temperature electrochemical devices such as solid oxide fuel cells constitutes a major task in brazing technology of ceramic–metal joints. In this work, reactive air brazing was used and the joining characteristics of 3YSZ with Crofer 22 APU have been systematically analyzed for three different brazing temperatures (1000, 1050 and 1100 °C) and two dwell times (5 and 30 min). The joints have been brazed successfully using the Ag–4CuO filler alloy. This braze filler metal was manufactured by an arc PVD (physical vapor deposition) process. Further, sufficient wetting of the zirconium oxide was achieved. The morphology of the oxide reaction layer at the steel side had a major influence on the shear strength of the brazed joints. A maximum average shear strength of 101 ± 4 MPa was obtained for a temperature of 1050 °C and a dwell time of 5 min.

Mechanical behavior of reactive air brazed (RAB) Crofer 22 APU-Al2O3 joints at ambient temperature

The evolution of innovative high-temperature electrochemical devices, such as high temperature solid oxide fuel cells (SOFCs), gas separators and gas reformers, consisting of metal–ceramic-joints is challenging. The seals have to be stable and gastight in isothermal high-temperature as well as in thermo-cyclic operation. Here, the reduction of porosity is the primary aim, to obtain air brazed joints with a long lifetime. In the last years, reactive air brazing (RAB) has gained rising interest for the joining of ceramic–ceramic and ceramic–metal compounds. In this paper an alternative brazing filler metal manufacturing process employing (physical vapor deposition (PVD)) is applied and its feasibility for the production of metal–ceramic composites has been investigated for Ag–4 wt%CuO. For RAB aluminum oxide with ferritic high chromium steel Crofer22APU have been joined. The pore formation in subordination of the braze and base materials can be monitored after brazing. By modifying the brazing process, the pore formation in the joints can be avoided. The microstructure of brazed joints with the developed braze foils is studied. Discussion of the results focuses on the influence of microstructural evolution on mechanical properties, the pore formation in the brazing seam and failure behavior of the brazed joints. A correlation between the process parameters brazing temperature and holding time and the achieved compound properties could be derived. Further, excellent wetting of the ceramic was obtained. The highest shear strength with 123 MPa was measured for a temperature of 1000 °C and 5 min, using the Ag4CuO alloy.

Reactive air brazing of the YSZ/AISI 310s couples using a novel Ag–Nb2O5 sealant

A novel Ag–Nb2O5 braze filler is developed and successfully tested as a sealant candidate for solid oxide cells. The resultant AgNbO3 by the reaction between Ag and Nb2O5 at high temperatures turns out to be the key to enable a desirable wetting of the YSZ by the braze filler. Typical interfacial microstructure of the YSZ/AISI 310s brazed joints are characterized by a scanning electron microscopy (SEM) and a transmission electron microscopy (TEM) with an energy dispersive spectroscopy (EDS). Effects of Nb2O5 contents and joining parameters on the microstructural evolution and mechanical performance of the joints are investigated. Joints with a maximum average strength of 100–110 MPa are achieved when bonding at 1150 °C/30 min with 5 mol.% Ag–Nb2O5. The long-term stability of the YSZ/Ag–Nb2O5/AISI 310s joints are evaluated in air for over 350 h at 800 °C and no cracks or cell degradation are found in the joints after the aging process, indicating that the new-developed Ag–Nb2O5 is a promising candidate as the sealant for the SOFC stacks.

Dual Atmosphere Isothermal Aging and Rapid Thermal Cycling of Ag-Ni and Ag-CuO Stainless Steel to Zirconia Braze Joints

Silver—copper oxide brazes are commonly used to bond zirconia to stainless steel (SS) for Solid Oxide Fuel Cell (SOFC) and other high temperature joining applications. In fact, conventional Ag-CuO compositions (where Cu segregates to the surface, oxidizes, and reduces the silver wetting angle on zirconia from ∼85 to ∼40°) allow brazing to be performed in air. Unfortunately, the relatively high ∼40° wetting angles of these reactive air brazes, and the ability of SOFC anode gases to reduce the CuO in them, produce pores during SOFC manufacturing and operation that reduce joint strength, impermeability, and longevity. Recently, Ag brazes utilizing transient porous nickel layers, instead of CuO additions, have been shown to produce high quality braze joints between SS and yttria stabilized zirconia (YSZ). Here, the microstructural and compositional evolution of SS|Ag-3CuO|YSZ and SS|Ag-Ni|YSZ braze joints exposed to air on one side and humidified 4%H2-96%N2 on the other side for either ∼300 hours of ∼750°C aging or ∼300 25°C/min 35–830°C rapid thermal cycles are compared. While both brazes display considerable microstructural and compositional evolution, only the Ag-Ni brazes remain pore free and well bonded, indicating that Ag-Ni brazes may be more suitable for long term SOFC operation.

Efficacy of Ag–CuO Filler Tape for the Reactive Air Brazing of Ceramic–Metal Joints

Efficacy of Ag–CuO Filler Tape for the Reactive Air Brazing of Ceramic–Metal Joints

Computational design of metal oxides to enhance the wetting and adhesion of silver-based brazes on yttria-stabilized-zirconia

Ag–CuO is a broadly used reactive air brazing (RAB) system for effectively bonding ceramics and metal interfaces, especially for sealing yttria-stabilized zirconia (YSZ) to metals in solid-oxide fuel cells (SOFCs). To understand the superior performance of this braze, density functional theory (DFT) calculations were employed to investigate two mechanisms that can potentially increase the work of adhesion (Wadh) and hence reduce the wetting angle of Ag on YSZ. It was found while the formation of Ag–dissolved O clusters at the Ag–YSZ interface can promote wetting, a much greater wetting angle reduction comes from the formation of CuO interlayers between Ag and YSZ. Further, the Wadh of an Ag/CuO and CuO/YSZ interface was found to be significantly higher than that of an Ag/YSZ interface. Based on simulation-obtained insights into metal to oxide bond formation, a simple descriptor was developed to predict the Ag/oxide interface energies, the Ag/oxide Wadh, and to search for potential oxide interlayers capable of promoting the wetting and adhesion of Ag on YSZ. Many simple metal oxides (single cation) were examined, however their Wadh with Ag were less than that of an Ag/CuO interface. Expanding the search to multi-cation oxides led to several promising candidates, such as CuAlO2, CuGaO2, and Cu3TiO4; all of which are also stable in the reducing SOFC conditions. Depending upon their solubility in molten Ag, these newly-identified oxides could either be pre-applied as wetting promoting interlayers or directly incorporated into Ag to form new reactive air brazes.

Transient porous nickel interlayers for improved silver-based Solid Oxide Fuel Cell brazes

Silver-copper oxide reactive air brazes are the most widely used Solid Oxide Fuel Cell (SOFC) brazes. However, the conventional Ag-4 wt.% Cu composition has a high wetting angle of ∼40° in air on yttria-stabilized-zirconia (YSZ) that leads to manufacturing defects (denoted as Type I pores). Also, many elements that oxidize during brazing to promote braze wetting (such as Cu) are easily reduced by SOFC fuels. This results in Type II pores that decrease the braze interfacial strength and provide a quick path for hydrogen permeation into the braze (where the hydrogen reacts with diffused oxygen to form gaseous water pockets, denoted as Type III pores). The present work demonstrates that transient porous nickel interlayers, instead of reactive element additions, can be used to promote Ag wetting on YSZ and produce high-quality YSZ-stainless steel braze joints. Mechanical tests on these reactive-element-free, silver-based SOFC braze joints, both before and after 500 h of 750 °C oxidation in air, show that the braze and braze interface strengths are higher than the underlying YSZ|NiO-YSZ substrate. The elimination of Type I and Type II porosity enabled by this new technique should result in improved braze lifetimes for SOFC and other ceramic-to-metal sealing applications.

Interfacial microstructure and shear strength of reactive air brazed oxygen transport membrane ceramic–metal alloy joints

To fabricate a multi-layered structure for maximizing oxygen production, oxygen transport membrane (OTM) ceramics need to be joined or sealed hermetically metal supports for interfacing with the peripheral components of the system. Therefore, in this study, Ag–10 wt% CuO was evaluated as an effective filler material for the reactive air brazing of dense Ce0.9Gd0.1O2–δ–La0.7Sr0.3MnO3±δ (GDC–LSM) OTM ceramics. Thermal decomposition in air and wetting behavior of the braze filler was performed. Reactive air brazing was performed at 1050 °C for 30 min in air to join GDC–LSM with four different commercially available high temperature-resistant metal alloys, such as Crofer 22 APU, Inconel 600, Fecralloy, and AISI 310S. The microstructure and elemental distribution of the ceramic-ceramic and ceramic-metal interfaces were examined from polished cross-sections. The mechanical shear strength at room temperature for the as-brazed and isothermally aged (800 °C for 24 h) joints of all the samples was compared. The results showed that the strength of the ceramic-ceramic joints was decreased marginally by aging; however, in the case of metal-ceramic joints, different decreases in strengths were observed according to the metal alloy used, which was explained based on the formation of different oxide layers at the interfaces.

Evolution behavior of Al2O3 nanoparticles reinforcements during reactive air brazing and its role in improving the joint strength

Nanoparticles have not been employed as reinforcements of composite filler for reactive air brazing (RAB) until now. It is crucial to investigate the evolution behavior and the strengthening mechanism of nanoscale reinforcements during RAB. In this study, the Al2O3 nanoparticle reinforced Ag-CuO-Al2O3 composite filler developed before was used to reactive air braze YSZ ceramic. Al2O3 nanoparticles were sintered together during RAB, forming microscale particles. TEM observations discovered that some Al2O3 reinforcements still remained at nanoscale. Fine crack bifurcations were readily formed between nanoscale and microscale Al2O3 particles during crack propagation. This process absorbed more fracture energy than the case of only microscale Al2O3. Higher brazing temperature reduced the viscosity of braze melt, which facilitated the mobility of Al2O3 particles. Therefore, the aggregation of Al2O3 nanoparticles was enhanced. So that fewer nanoscale Al2O3 reinforcements remained in the joint. Consequently, the joint properties would be weakened. The maximum shear strength (62MPa) was obtained when the joints were brazed at 1050°C for 30min. High-temperature oxidation test (800°C for 100h and 150h) showed that the morphology and distribution of Al2O3 reinforcements underwent few changes. These joints still maintained the high-temperature (800°C) shear strength above 38MPa.

Reactive-Element-Free, Silver-Based Brazes for SOFC Applications

The current go-to braze for SOFC applications is the Ag-CuO reactive air braze (RAB). As with other RAB brazes, the ability to use this braze with ceramic materials (such as yttria stabilized zirconia (YSZ) and oxide-protected stainless steel (SS)) is enabled by a braze component (in this case Cu) reacting with the brazing atmosphere to form a surface oxide that facilitates wetting. [1-3]. Although Ag-CuO provides an easy way to join YSZ and SS for SOFC applications, the insufficient ~45° wetting angle of the conventional Ag-4 wt.% Cu braze [1, 2] often leads to braze joint manufacturing defects (Type I pores). Further, the reduction of CuO during dual atmosphere (H2/O2) SOFC operation results in porosity (Type II pores) that: i) mechanically weaken the braze/SS and braze/YSZ interfaces and ii) facilitates H2invasion into the center of the braze, which in turn, hastens the development of gaseous water pockets within the braze (Type III pores) caused by dissolved oxygen and hydrogen meeting. This poster will present a new method for silver brazing YSZ and SS without the need for reactive air elements. As shown in Figure 1, this procedure (which is performed under SOFC electrode compatible oxygen partial pressures ≥ 1x10-10atm) produces a braze that wets both the YSZ and SS. In addition, this procedure also produces Ag-YSZ bonding which has been shown by Kuhn et. al [4] to have a fracture energy two times higher than conventional Ag-CuO braze joints. It is expected that the elimination of Type I and Type II pores enabled by this new brazing method will increase SOFC braze joint lifetimes.

Reactive air brazing of YSZ-electrolyte and Al2O3-substrate for gas sensor sealing: Interfacial microstructure and mechanical properties

A YSZ/Al2O3 layered structure was successfully reactive air brazed using AgCuO fillers. The interaction mechanism between the filler and ceramics was systemically analyzed. The effects of filler composition on the interfacial microstructure and joint properties were investigated. AgCuO fillers possessed good wettability on the YSZ and Al2O3 ceramics. Ag had diffused into the ceramic substrates, but the width of the diffusion layer at the YSZ interface (∼10 nm) was narrower than that at the Al2O3 substrate (∼20 nm). Further HRTEM observations confirmed interatomic bonding between the CuO and the ceramics. The lattice mismatches at the Al2O3/CuO and YSZ/CuO interfaces were 0.98% and 2.97%, respectively. The filler alloy composition had a major influence on the microstructure and shear strength. The CuO phase preferentially precipitated at the Al2O3 interface. Consequently, the continuous CuO and CuAl2O4 layers gradually formed at the Al2O3 interface with increasing CuO content in the filler. The maximum shear strength (∼45 MPa) was obtained when the composition was Ag-8mol%CuO.

Reactive air brazing of YSZ ceramic with novel Al2O3 nanoparticles reinforced Ag-CuO-Al2O3 composite filler: Microstructure and joint properties

The YSZ ceramic coated with a copper layer (~5μm) was successfully reactive air brazed using novel Al2O3 nanoparticles (NPs) reinforced Ag-CuO-Al2O3 composite filler. The effects of Al2O3 NPs content on the interfacial microstructure and joint properties were investigated. When the content of Al2O3 NPs was 8wt.%, YSZ joints obtained fine interfacial microstructure and optimal mechanical properties. The coefficient of thermal expansion of composite filler was calculated to be 16.26×10−6K−1, presenting a decline of 12.1% compared to that of Ag-CuO base filler. The hardness and modulus values of braze joint slightly increased to 2.6GPa and 164GPa, respectively, possessing a better ability to resist deformation. Consequently, the YSZ joint possessed a maximum shear strength of 60MPa, which was 25MPa (~71%) higher than that of the joints brazed using Ag-CuO base filler. The leakage rate of YSZ-tube/AgCuO-8Al2O3/YSZ-block samples was measured to be 3.2±0.9×10−10Pam3s−1, which met the leakage rate requirements for vacuum tight components (less than 10−9Pam3s−1). It implied that this novel method was an effective way to obtain hermetic YSZ joints.

Interfacial reaction and microstructural evolution of Ag-Cu braze on BaCo0.7Fe0.2Nb0.1O3-δ at high temperature in air

Based reactive air brazing technique, interfacial reaction and microstructure formation of Ag-6.6mol% Cu wetting on BaCo0.7Fe0.2Nb0.1O3-δ(BCFNO) membrane in air were investigated. The interfacial microstructural analysis revealed that at high temperature Ag-Cu alloy transformed into Ag-Cu-O braze in air and the liquid braze penetrated into BCFNO matrix along the grain boundaries. Cu-O in the liquid braze reacted with BCFNO to form CoCuO2 and Ba2Cu3O5+x confirmed by XRD. Ridge formed quickly at the triple line as a result of the migration of the interfacial reaction products and in response to the vertical component of force from surface tension. The rapid interfacial reaction and ridging at the spreading front actually stalled the spreading of the liquid braze, rather than a continuous layer of smoother, barrier-free reaction phase forming and driving accompanied spreading. Low macroscopic contact angles between the braze and BCFNO substrate were observed due to the evolution of the ridge composed of the interfacial reaction products near the tripe line.

Ni-Ta-Si Brazes for Planar Solid Oxide Fuel Cell Applications

Introduction Solid oxide fuel cells (SOFC) are high efficiency devices for converting the chemical energy from a wide range of fuels and energy-carriers directly into electricity [1]. One of the major challenges for the viability of commercial SOFC devices is the development of suitable sealing technologies to prevent air and fuel crossover at SOFC operating temperatures of ~750⁰C. Today, reactive air brazing (RAB) of Ag-based brazes is commonly used for this purpose. Unfortunately, due to the high diffusivity of both H and O in silver, diffusing H and O react to form micro-pores in silver-based brazes which eventually develop into a porous structure that degrades the seal, reduces the mechanical robustness of the joint, and limits the lifetime of commercial SOFC devices to ~10,000 hours [2]. The present work reports on a new, computationally identified family of Ni-Ta-Si brazes developed to replace conventional Ag-based brazes in SOFC applications. Experimental Methods Here, Thermo-Calc© software was used to identify candidate alloy systems with a melting range suitable for SOFC brazing applications. To limit the number of candidate alloy systems, radioactive, toxic, prohibitively expensive, and chemically unstable elements were eliminated from consideration. Ni-based alloy systems with all possible combinations of the remaining 25 elements from the periodic table were then studied to find alloys with a melting range between 900 and 1000°C. Of the 276 possible ternary alloy combinations, Thermo-Calc© analyses were performed on 172 systems, 104 systems remained unanalyzed because of a lack of Thermo-Calc© data, and 19 Ni-based candidate systems were proposed for experimental investigation. These candidate alloys were physically fabricated using arc-melting in suitable atmospheres and characterized using differential scanning calorimetry (DSC) to determine liquidus and solidus temperatures, thermogravimetric analysis (TGA) to determine the high temperature oxidation resistance, and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) to determine the microstructural and compositional stability. Results and Discussion Of the 19 systems, Ni-Ta-Si alloys with and without boron melting point suppressant additions displayed promising ductility, melting, and high temperature oxidation resistance behavior. Specifically, the liquidus and solidus temperatures for Ni20Ta7Si and Ni20Ta7Si1B (the boron percentage is a nominal composition which may be an overestimate of the actual boron composition due to boron vaporization during alloy fabrication) are 1163.1°C/1122.9°C and 1017.0°C/1065.8°C, respectively, showing that minor boron additions lowers the Ni20Ta7Si melting range by ~100°C. This melting range is comparable to that of the commercial braze BNi2 (Ni82.4Cr7Si4.5B3.1Fe3), which is 1000°C/970°C. Further, the low melting range of Ni20Ta7Si1B occurs in an alloy that does not contain Cr (Cr has been shown to poison SOFC electrodes) [3]. Figure 1 shows TGA results for different Ni-Ta-Si(B) samples as well as a commercial BNi2 braze at 750°C in air. The Ni20Ta7Si1B sample shows good oxidation resistance similar in magnitude to that of BNi2. Figure 1 also shows that, in addition to lowering the Ni-Ta-Si melting point, 1 wt.% of boron significantly modifies the Ni-Ta-Si microstructure (and presumably the oxidation mechanism) through the formation of a Ta enriched surface reaction zone, and a compositionally homogenized surface reaction zone. Conclusions Here a systematic computational-experimental approach was developed to search for, fabricate, and characterize new braze candidates for future SOFC application.Surprisingly, alloys systems with 20 wt.% of Ta (Ta has a melting point of 3020°C) still melt at temperatures as low as 1065⁰C. Boron additions into the Ni-Ta-Si system further reduce the alloy melting point, alter the oxidation mechanism, and improve the oxidation resistance.Although additional wetting, joint strength, and thermal cycling experiments are needed, the Ni-Ta-Si(B) system may be a promising new family of brazes for SOFC or other applications. Acknowledgements This material is based upon work supported by the Department of Energy under Award Number DE-FE0023315.

Reactive air brazing of GDC–LSCF ceramics using Ag–10 wt% CuO paste for oxygen transport membrane applications

This paper reports the effectiveness of a Ag–10wt% CuO braze filler for the joining of dense Ce0.9Gd0.1O2–δ–La0.6Sr0.4Co0.2Fe0.8O3–δ (GDC–LSCF) dual-phase ceramics for the oxygen transport membrane applications. Brazing was performed at 1050°C for 30min in air. The microstructure of the ceramic-filler-ceramic interfaces of the polished cross-sectional areas and the elemental distribution were examined. The results indicated that the Ag–10wt% CuO braze filler ensured reliable and compact joining without the formation of cracks and voids at the joining interface. The room temperature mechanical shear strengths were 59.3 and 40.2MPa for the as-brazed and isothermally aged joints at 800°C for 24h in air, respectively.

최신의 고능률 브레이징 기술개발 동향

Recent developing tendency for technologies of high efficient brazing are studied by searching of NDSL, Science Direct, KIPRIS, PCT and so on. Active metal brazing, arc brazing, fluxless brazing, brazing with low melting point, reactive air brazing, laser brazing, laser droplet brazing are investigated. By optimal selecting of the above mentioned technologies, it needs to investigate an economical metallurgical design and the advanced brazing methods. To improve the embrittlement of intermetallic compound at brazing interface, it must be studied the inexpensive variant metals including nonmetals and the heat sources(MIG, TIG, Laser) by hybrid techniques. Key words: Brazing, fluxless brazing, Laser brazing, Active metal, Laser droplet, Intermetallic compound

New SOFC‐Stack Design with Parallel‐Connected Cells – Basic Concept and Joining Aspects

AbstractSolid oxide fuel cells (SOFC) technology still suffers from problems like high costs and insufficient lifetime, partly caused by the traditional serial‐connected stack design. To overcome some of these issues a new design with parallel‐connected cells is proposed. The concept is based on a cartridge designed repeating unit consisting of two cells, electrically connected in parallel. Stack modules with 50 to 60 W can be built up by stacking and interconnect these basic units, likewise in a parallel mode. Finally, several stack modules can be connected in serial configuration to supply reasonable terminal voltage and power. Different design options for the twin cell unit were evaluated by flow field simulations and with respect to their producibility. Both, metallic and ceramic concepts for the cell frames are considered. Glass seals are completely avoided to improve durability. Reactive air brazing (RAB) is used for mounting the cells in the frames. The concept with metallic cell frames additionally uses pulsed laser welding to seal the gas compartments. Preliminary tests on welding and brazing show the general feasibility of these joining technologies and disclose a way to mass production of twin cells as basic repeating units. Flow field simulations assist the dimensioning to assure homogeneous distribution of reactants.

Aging Behavior of Reactive Air Brazed Seals for SOFC

AbstractIn this study the gas‐tightness of reactive air brazed YSZ‐steel joints and their long‐term stability at high temperatures in air and dual atmospheres are investigated. Silver‐based braze compositions like Ag‐4CuO are used for reactive air brazing of gas‐tightness samples. During aging in air at 850 °C for 800 h all tested samples remained hermetic. However, microstructural analysis reveals the formation of voids within the brazing zones and severe changes of the interfacial oxide layers. It is shown, that due to the diffusion of chromium and manganese from the steel substrate the thickness of the reaction layers increases and the phase composition changes. Furthermore, in previous work a decrease of the bending strength of reactive air brazed YSZ‐steel joints due to the microstructural changes is observed. In contrast, the aging in dual atmospheres at 850 °C causes strong degradation and the total loss of gas‐tightness. Reducing atmospheric conditions lead to different reactions profiles of the silver based brazes in contact with the YSZ electrolyte. Complex reaction products are identified and reported.

Results for a New SOFC-Stack Design with Parallel-Connected Cells

The TU Clausthal and CUTEC institute have teamed up to design, build and test a new stack architecture, based on repeating units with cells connected in parallel. This approach allows the use of electrically conducting seals like brazes and can be realized without any glass sealing. Unlike conventional (serially connected) stacks, where all cells operate at the same current but individual voltage, in this setup each cell contributes as much current as possible at a common voltage. Thereby accelerated degeneration caused by undervoltage and the associated oxidation of the nickel catalyst can be completely overcome. The concept uses two cells in electrical parallel connection with the anodes facing each other to form a repeating unit. Two designs have been realized: An all ceramic housing made from 3YSZ, sealed with reactive air brazing (RAB) and a metallic one with a Crofer 22 APU housing, joined by laser beam welding. The housing materials have been chosen with respect to their thermal expansion coefficient (TEC) matching the TEC of the used ESC cells. Special interconnectors have been produced via hydroforming to create an even flow field while providing sufficient contact area. The paper will focus on the test results of the repeating units under various operation conditions and the analysis of the degradation of components and joints. Polarization curves for the twincell repeating unit and the individuell cells under H2 and air at 880°C are depicted in figure one. Figure 1