External α-Al2O3 scale on Ni-base alloy 602 CA. – Part I: Formation and long-term stability

• Published in: Corrosion science Vol. 124; pp. 138 - 149
• Main Authors: Chyrkin, A., Pillai, R., Galiullin, T., Wessel, E., Grüner, D., Quadakkers, W.J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.08.2017; Elsevier BV
• Subjects: Alloys; Alumina; Aluminum oxide; Chromia; Chromium oxides; Internal oxidation; Ni-base alloy; Nickel base alloys; Oxidation; Oxidation resistance; Oxide scale; Pre-oxidation; Scale (corrosion); Stability; Studies; Oxide scale; Oxidation resistance; Ni-base alloy; Chromia; Internal oxidation; Alumina; Pre-oxidation
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2017.05.017

•A procedure to promote external alumina scaling on Ni-base alloy 602 CA at 1100 and 1200°C.•Multi-step pre-oxidation treatments at lower temperatures.•Pre-oxidised specimens showed improved oxidation resistance at 1100 and 1200°C.•The mechanism of healing of the external alumina after spallation was explained.•Good adherence, long-term stability and healing capability of the external alumina scale. A multi-step oxidation treatment was developed for the NiCrAl-base alloy 602 CA to promote the growth of protective α-Al2O3 scales during exposure at 1100–1200°C in air. Above 1000°C, the alloy forms external chromia scales accompanied by internal alumina precipitation. On the other hand, external alumina grows on alloy 602 CA surface at 800–900°C. The alloy specimens were pre-oxidized at 800°C to form the external α-Al2O3 scale and further exposed at 1100 and 1200°C. The resulting oxide scales were characterized with SEM/EDX, EBSD, and TEM. The pre-grown alumina scale demonstrated good adherence, long-term stability and healing capability.