ORIGINAL PAPER Transient Oxidation of a c-Ni–28Cr–11Al Alloy L. Hu • D. B. Hovis • A. H. Heuer Received: 6 July 2009 / Revised: 14 September 2009 / Published online: 11 October 2009 Ó Springer Science+Business Media, LLC 2009 Abstract c-NiCrAl alloys with relatively low Al contents tend to form a layered oxide scale during the early stages of oxidation, rather than an exclusive a-Al 2 O 3 scale, the so-called ‘‘thermally grown oxide’’ (TGO). A layered oxide scale was established on a model c-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 a-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 dis- continuous 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 a-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 devel- opment of the TGO was dominated by growth of the inner a-Al 2 O 3 layer. Keywords c-NiCrAl Á Layered TGO Á Hot stage Á Optical microscopy Á Transient oxidation Introduction During the operation of gas turbine engines, a thermal protection system is necessary to protect the load-bearing Ni-base superalloy components. The thermal protection system usually comprises an outermost 7 wt% Y 2 O 3 -stabilized ZrO 2 L. Hu Á D. B. Hovis Á A. H. Heuer (&) Department of Materials Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue White 418, Cleveland, OH 44106, USA e-mail: heuer@case.edu 123 Oxid Met (2010) 73:275–288 DOI 10.1007/s11085-009-9179-5