Transient Oxidation of a γ-Ni–28Cr–11Al Alloy

• Published in: Oxidation of metals Vol. 73; no. 1-2; pp. 275 - 288
• Main Authors: Hu, L., Hovis, D. B., Heuer, A. H.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.02.2010; Springer
• Subjects: ALLOYS; Aluminum oxide; Applied sciences; Chemistry and Materials Science; Chromium oxides; Corrosion; Corrosion and Coatings; Corrosion environments; Evolution; Exact sciences and technology; HEATING; Inorganic Chemistry; MATERIALS SCIENCE; Metallic Materials; Metals. Metallurgy; Nickel base alloys; OPTICAL MICROSCOPY; Original Paper; OXIDATION; OXIDES; Scale (corrosion); TRANSFORMATIONS; TRANSIENTS; Tribology; Hot stage; Optical microscopy; Transient oxidation; Layered TGO; γ-NiCrAl; Nickel base alloys; Corrosion; Oxidation; Transients
• ISSN: 0030-770X; 1573-4889
• DOI: 10.1007/s11085-009-9179-5

γ-NiCrAl alloys with relatively low Al contents tend to form a layered oxide scale during the early stages of oxidation, rather than an exclusive α-Al 2 O 3 scale, the so-called “thermally grown oxide” (TGO). A layered oxide scale was established on a model γ-Ni–28Cr–11Al (at.%) alloy after isothermal oxidation for several minutes at 1100°C. The layered scale consisted of an NiO layer at the oxide/gas interface, an inner Cr 2 O 3 layer, and an α-Al 2 O 3 layer at the oxide/alloy interface. The evolution of such an NiO/Cr 2 O 3 /Al 2 O 3 layered structure on this alloy differs from that proposed in earlier work. During heating, a Cr 2 O 3 outer layer and a discontinuous inner layer of Al 2 O 3 initially formed, with metallic Ni particles dispersed between the two layers. A rapid transformation occurred in the scale shortly after the sample reached maximum temperature (1100°C), when two (possibly coupled) phenomena occurred: (i) the inner transition alumina transformed to α-Al 2 O 3 , and (ii) Ni particles oxidized to form the outer NiO layer. Subsequently, NiO reacted with Cr 2 O 3 and Al 2 O 3 to form spinel. Continued growth of the oxide scale and development of the TGO was dominated by growth of the inner α-Al 2 O 3 layer.