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7155 |
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Wednesday, June 22, 2022, Saal Brüssel 10:40 AM Industrial application of brazing and diffusion bonding |
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Justification for replacing BAu-4 precious metal braze filler metal with Pal 30 Ni-based braze filler metal for dissimilar stainless steel joints |
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Warren Miglietti* / Miglietti and Associates, United States Michael Graham / Prince and Izant Company, USA |
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In the manufacture of fuel nozzle components of some industrial gas turbine engines used for power generation, a variety of stainless steel materials are utilized. There are often dissimilar metal joints brazed with precious metal Au-based filler metals, which although allow the braze joint to be easily X-Rayed for defects, are indeed very expensive. BAu-4 is one such braze filler metal of a nominal 82% Au – 18% Ni eutectic composition, is often utilized in production. With the increasingly high price of Au, there has been a demand for the usage of a less expensive braze filler metal. In this study, three Au-free braze filler metals were evaluated with the objective of replacing the expensive BAu-4 braze namely: 1) Pal 30 (contains Pd, no Au) 2) Pal 36 (contains Pd, no Au) 3) BNi-2 (contains no Pd or Au) The preceding braze filler metal candidates and BAu-4 were brazed to the following dissimilar stainless steel (SS) material combinations: a) 304 SS to 410 SS b) 301 SS to 17-4PH SS c) 410 SS to 17-4PH SS Tensile tests were carried out at 20oC and 538oC on all combinations listed above. In addition, low cycle fatigue tests were also carried out at 343oC. The resultant data showed that the BAu-4 brazed joints had the best properties at 20oC, but the Pal 30 braze joint had the best tensile and fatigue strength at elevated temperature, making it a viable candidate for cost reduction, i.e., to replace the expensive Au based BAu-4 filler metal. It is evident that there is a mechanical strength advantage to replacing BAu-4 with Pal 30 braze filler metal; however, the replacement comes with a potential loss in corrosion resistance if inappropriate braze parameters are utilized. Plans to mitigate this undesirable phenomena will be discussed. |