ABSTRACT
The morphology of the scales resulting from hot corrosion reactions should be different from that associated with simple oxidation of a metal/alloy in a single oxidant environment because oxidation and sulfidation commonly occur simultaneously. Investigations related to fundamentals of hot corrosion on pure metals, binary, and ternary alloys (mostly Ni-and Co-based) have revealed widely different scale morphologies due to varying experimental conditions [50]. Even case histories of commercially used Ni-and Co-based alloys that have suffered such damage under different operating conditions are reported to have revealed various types of scale morphologies [55]. In most service cases the general consensus is that a layer of sulfide particles forms beneath a region of porous oxide. The sulfides have often been identified as chromium-rich, even though nickel sulfides have also been reported in certain cases. Furthermore, the extent of internal sulfide layer can vary considerably depending on the service/test conditions. At times the sulfide layer appears to be virtually nonexistent, or it may appear as a very thin band of fine discrete sulfide particles or even as a large band of interconnected sulfide particles.
