Corrosion and Carburization Behaviour of Ni-xCr Binary Alloys in a High-Temperature Supercritical-Carbon Dioxide Environment

Abstract

Pure Ni and Ni-xCr (x = 7, 14, 22 and 27 wt%) binary alloys were exposed to supercritical-carbon dioxide environment at 600 °C and 20 MPa for 200 h. For pure Ni, a thick NiO layer was formed on the surface. Meanwhile, for Ni-7Cr alloy, an inner oxide layer consisted of rather irregular chromia and NiO was formed below the outer NiO layer. When Cr content was greater than 14%, a continuous chromia layer was formed, resulting in much lower weight gain and oxide thickness. However, amorphous carbon layers had developed along the oxide–matrix interface when chromia was formed. The presence of the carbon layer was explained in view of the high C activity corresponding to the low equilibrium oxygen potential of chromia.