Impact of iron and chromium on coal ash corrosion behavior of Ni-Cr-Co based alloy for advanced ultra-supercritical power plants

The influence of alloyed iron and chromium on the coal ash corrosion behavior of Ni-Cr-Co based alloy was investigated at 800°C to 850°C. Results show that the alloyed iron accelerates the corrosion and alters the oxide scales by favoring the formation of Fe₂O₃ scale and the internal sulfides. As a contrast, the iron-free alloys grow mainly a Cr₂O₃ layer exhibiting lower corrosion rates. The temperature rising from 800°C to 850°C leads to the acceleration of corrosion in all cases. The increase in Cr content to 23 wt% is advantageous for the preferential oxidation of Cr and the retarding of Co and Al oxidation, which has a stronger impact at an elevated temperature of 850°C.