WEB Corrosion resistance of a Ni-based brazing alloy in a marine atmospheric exposure
The corrosion behaviour of a Ni-based brazing alloy after a seven-month exposure in a marine atmospheric test site was investigated. The Ni-20Cr-5.6Fe-5.4-B filler metal was deposited by brazing on a superduplex stainless steel. “Real” marine exposure provides more realistic conditions than traditional salt spray or humidity conditions, including both wet and dry environments.
Unexpected pitting corrosion was observed in the Ni-based filler metal. The microstructure of the Ni layer was analysed by optical and SEM microscopy, carrying out EDS analyses of the variety of phases with different morphologies and compositions generated by the brazing process. A significant corrosion damage was detected across certain acicular phases enriched in silicon and with a significant chromium depletion (about 5 wt. %), responsible for the decrease of the pitting corrosion resistance of these phases. It is not discarded also the formation of galvanic microcells between the Cr-depleted anodic zone and the surrounding uncorroded cathodic zone, enriched in chromium.
It was concluded that the brazing process produces a microstructure susceptible to pitting corrosion in the marine atmospheric environment.
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