Effects of Si, Al and Ti on corrosion of Ni-20Cr and Ni-30Cr alloys in Ar-20CO2 at 700 °C

Model alloys Ni-(20, 30)Cr (wt.%) with (0.1, 1)% Si, 1.5% Al or (1, 2)% Ti were exposed to Ar-20CO2 at 700 °C. Samples were electropolished before reaction to avoid cold working effects on alloy diffusion. The Ni-20Cr alloy formed a thick NiO scale and an internal oxidation zone, whereas Ni-30Cr formed a duplex scale of NiO and Cr2O3 layers. The Si and Al additions increased the oxidation resistance by forming additional protective layers of SiO2 or Al2O3. Titanium accelerated chromia growth, promoting alloy surface coverage with protective oxide. All alloys formed intergranular Cr-rich carbide precipitates beneath their scales.