OXIDIZING-SULFIDIZING CORROSION OF Ni-xCr-10Al ALLOYS AT 700-800 °C

The corrosion behavior of Ni-10Al and Ni-xCr-10Al (x=3, 5, 10) alloys at 700-800 degrees C in H(2)-H(2)S-CO(2) mixtures was studied. The addition of Cr resulted in a significant reduction of the corrosion rate of the Ni-10Al alloy: at 700 degrees C the corrosion of Ni-10Al alloy showed a linear kinetic law, but Ni-xCr-10Al followed the multi-stage parabolic rate law; at 800 degrees C the corrosion of all the alloys followed a quasi-parabolic rate law. Ni-10Al alloy formed a complex scale of Ni(3)S(2) and Al(2)O(3), whereas Ni-3Cr-10Al formed an irregular scale of Al(2)O(3) with a CrS inner corrosion region, and a thin layer of Al(2)O(3) formed on Ni-5Cr-10Al and Ni-10Cr-10Al alloys. The equilibrium partial pressures of oxygen and sulfur in the mixed gases were calculated to estimate the possible reactions between the alloy components and the gaseous atmosphere, and the corrosion mechanisms were also discussed.