Studies of Corrosion Resistance of Aluminized Coatings in Metal Dusting Environments

Metal dusting corrosion is a catastrophic degradation phenomenon for alloys in chemical process equipment at elevated temperature under carburizing atmospheres, typically synthesis gas (CO/H2/CO2/H2O). It starts by formation of solid carbon on the alloy surface, and proceeds with the gradual breakdown of the metallic matrix into fine particles. It is kinetically controlled when the constituents of high temperature alloys, i.e. Fe and Ni, also catalyze carbon formation. In this work, the coatings have been studied in modeling metal dusting conditions at 550-750oC and 20 bars compared to uncoated as-received or oxidized Ni-based alloys. The coatings consisted of aluminide layers, while some of them had an additional thin oxide layer above the aluminide layers, were obtained through the thermal diffusion process. They demonstrate superior performance with respect to carbon formation despite small structural changes in the surface under severe conditions; the forming stable oxide layer provides additional protection.