John Herbert Wood

High chromium cobalt-base coatings for low temperature hot corrosion☆

Abstract Accelerated oxidation tests have been conducted on a number of cast Co-Cr-Al alloys coated with a thin film of Na 2 SO 4 and exposed in an O 2 -0.15%(SO 2 -SO 3 ) gas mixture at 750°C. These tests show that the corrosion resistance of binary Co-Cr alloys increases with the chromium content of the alloys and that even small concentrations of aluminum have detrimental effects on their corrosion resistance. Tests on Co-Cr coatings on a Rene 80 substrate under the same conditions indicate that there is a transition from a high to a low corrosion rate at a chromium level of about 37.5 wt.%. These results can be explained on the basis of a mechanism that we have already proposed in the literature. Based on our laboratory studies, we have developed new Co-Cr coatings that provide excellent resistance to low temperature hot corrosion and are also acceptable for conventional, high temperature, hot corrosion.