Effects of Si, Al and Ti on corrosion of Ni-20Cr and Ni-30Cr alloys in Ar-20CO_2-20H_2O gas at 700 °C

摘要

Model alloys Ni-(20, 30)Cr with 1 Si, 1.5 Al or 2 Ti (all in wt.%) were exposed to Ar-20CO(2)-20H(2)O (in vol%) at 700 degrees C. Alloy specimens were electropolished before reaction to avoid cold working effects on alloy diffusion. The Ni-(20, 30)Cr alloys formed a NiO scale and an internal oxidation zone, together with NiO rods on the sample surface. The oxidation resistance of Si and Al bearing alloys was improved by the formation of additional protective layers of SiO2 or Al2O3. The addition of Ti promoted chromia growth. All alloys formed intergranular Cr-rich carbide precipitates beneath their scales.