Oxidation Behavior of Ni–Cr Alloys in CO2 at 700 °C

Abstract

Model alloys Ni–(5, 10, 20, 25, 30 wt%)Cr were exposed to Ar–20CO2 and Ar–20O2 at 700 °C. Samples were electropolished before reaction to avoid cold-working effects and, as a result, to reveal the effect of alloy bulk diffusion. All alloys underwent breakaway oxidation in CO2, forming an external Ni-rich oxide scale and other oxides internally. In oxygen, the Ni–(5, 10, 20)Cr alloys formed a nonprotective Ni-rich scale plus an internal oxidation zone, but Ni–(25, 30)Cr formed a protective Cr2O3 scale. Carbide precipitates were found in Ni–20Cr reacted in CO2. It is shown that Wagner’s diffusion theory accounts satisfactorily for the difference in alloy scaling behavior in the two gases.