Utilization of Alumina Scale Formation by Ni-Base Alloys for High-Temperature Oxidation and Corrosion Resistance in Harsh Environments

High-temperature alloys rely on the formation of a protective oxide scale to resist high-temperature oxidation and corrosion attack, and chromia is the most common oxide to provide this function in commercial alloys. However, certain harsh environments require alloys that utilize the formation of even more protective oxide films to provide improved performance and longer lifetime. In these cases, an alumina scale becomes a viable solution to protect high-temperature alloys. This paper summarizes high-temperature oxidation and corrosion behaviors of several high-temperature Ni- and Co-base alloys tested under various high-temperature conditions, including short-term and long-term oxidation, cyclic oxidation, dynamic (burner rig) oxidation, water vapor oxidation, nitridation, and carburization at temperatures ranging from 871 to 1093 °C (1600–2000°F). The oxidation and corrosion behaviors are compared between the alumina-forming and chromia-forming alloys, and the results show that the alumina-forming alloys were significantly superior to the chromia-forming alloys for high-temperature oxidation and corrosion resistance in terms of oxidation and corrosion rate reduction, scale stability and adhesion, mass penetration suppression, etc. Based on the extensive tests, alumina scales were highly effective in resisting oxidation, nitridation, and carburization attacks, especially under severe oxidation and corrosion conditions. To further demonstrate the benefits of an alumina scale, an alumina-forming alloy with pre-oxidation heat-treatment was also studied in the nitridation test.