Abstract
Cr and Cr-bearing alloys possess satisfactorily good oxidation resistance at high temperatures, but they sulfidize catastrophically in sulfur-bearing environments which are encountered frequently in energy conversion systems and in petrochemical industries. Nb, on the other hand, has good sulfidation resistance but poor oxidation resistance at high temperatures. A combination of Cr and Nb is shown to improve the corrosion resistance at high temperatures in oxidizing and sulfidizing environments. Kinetic and microstructural studies of oxidation and sulfidation of Cr-40wt%Nb alloys were preformed at 1173 K in sulfur vapor ( P ~ , = 0.74 atm) . This two phase alloy consists of an fcc CrsNb intermetallic phase and small amount of Cr base alloy and shows very good oxidation resistance and appreciable sulfidation resistance in comparison with Fe-45Cr, pure Nb and Fe-40Mo. The dominant oxidation product is Cr203, while the sulfidation products are rhomobohedral Cr2S3 as an external scale and a Nb sulfide inner scale between the Cr2S3 and substrate.
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