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Microstructure Influence on Corrosion Resistance of Brazed AISI 304L/NiCrSiB Joints
Milena Penyaz,Johannes L. Otto,Nikita Popov,Alexander Ivannikov,Anke Schmiedt‑Kalenborn,Frank Walther,Boris Kalin 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10
The characterization of corrosion resistance, which is essential to estimate the lifetime of brazed joints in corrosive environments,is of central importance for many industrial applications and a basic requirement for the reliable and economicoperation of brazed components. High temperature vacuum brazing with thin amorphous-crystalline foils is used for numerousapplications such as exhaust gas heat exchangers. In this study one industrial BNi-5a® and two experimental rapidlysolidified filler metal foils of Ni7Cr7.5Si4Fe1.5B and Ni20Cr7.5Si4Fe4Mo1.5B wt% were used to braze joints of AISI304L. In addition, two holding times at 1160 °C were chosen to investigate the effect of the resulting microstructural differenceson corrosion resistance. Especially the amount and distribution of borides and silicides within the brazing seamcould be changed by the time-dependent diffusion processes, as could be shown by metallographic cross sections. Acceleratedintercrystalline corrosion tests were carried out to evaluate the influence of the microstructure on the corrosion depthand damage mechanisms. Additionally, potentiodynamic polarization measurements in synthetic exhaust gas condensate asan application-oriented corrosion medium were performed for a comparative evaluation of corrosion properties and rate. The combination of high chromium-containing filler metal and increased holding time, which led to a more homogeneousmicrostructure, resulted in a more than five times improved corrosion resistance within both investigations.