Abstract
The study focused on dissimilar brazing of metallized YSZ (Yttria-Stabilized Zirconia) and Crofer alloy using BAg-8 (72Ag-28Cu, wt%) filler foil. The YSZ substrate was metallized by sequentially sputtering Ti (0.5/1 μm), Cu (1/3 μm), and Ag (1.5/5 μm) layers, and the Crofer substrate was coated with Ag layers with a thickness of 1.5 and 5 μm, respectively. The BAg-8 filler demonstrated excellent wettability on both metallized YSZ and Crofer substrates. The brazed joint primarily consisted of Ag-Cu eutectic. The metallized Ti layer dissolved into the braze melt, and the Ti preferentially reacted with YSZ and Fe from the Crofer substrate. The globular Fe2Ti intermetallic compound was observed on the YSZ side of the joint. The interfacial reaction of Ti was increased when the thickness of the metallized Ti layer was increased from 0.5 to 1 μm. Both brazed joints were crack free, and no pressure drop was detected after testing at room temperature for 24 h. In the YSZ/Ti(0.5μ)/Cu(1μ)/Ag(1.5μ)/BAg-8(50μ)/Ag(1.5μ)/Crofer joint tested at 600 °C, the pressure of helium decreased from 2.01 to 1.91 psig. In contrast, the helium pressure of the YSZ/Ti(1μ)/Cu(3μ)/Ag(5μ)/BAg-8(50μ)/Ag(5μ)/Crofer joint slightly decreased from 2.02 to 1.98 psig during the cooling cycle of the test. The greater interfacial reaction between the metallized YSZ and BAg-8 filler due to the thicker metallized Ti layer on the YSZ substrate was responsible for the improved gas-tight performance of the joint.
Highlights
To form a metallurgical bond between metal and ceramic materials has been a challenging task over the past 20 years [1,2,3,4,5]
Crofer waswas performed withwith the BAgDissimilar vacuum brazing brazingofofmetallized metallized
The YSZ substrate was metallized by sequentially sputtering Ti (0.5/1 μm), BAg-8 braze alloy
Summary
To form a metallurgical bond between metal and ceramic materials has been a challenging task over the past 20 years [1,2,3,4,5]. Many traditional braze fillers cannot wet the ceramic surface and achieve a reliable brazed joint [14,15,16,17,18]. Both issues must be considered before brazing metal and ceramic substrates. E.g., Ag-Cu-Ti fillers, have been widely studied in brazing metal and ceramic materials [6,22,23]. Some such applications are oxygen transport membranes, gas sensors and fuel cells [26,27,28] This investigation focused on brazing metallized YSZ and Crofer substrates using the BAg-8 braze alloy for gas-tight applications. The microstructural evolution of the brazed joints and correlations with pressure drop tests at 25 and 600 ◦ C were evaluated in the experiment
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