SIMS Studies of Alumina Growth at 1200°C

Abstract

This paper considers the mechanism of growth of α-Al 2 O 3 on β-NiAl at 1200°C, and the influence of yttrium and zirconium alloying additions on the transport processes. Scales have been formed in oxidation experiments using 16 O 2 and 18 O 2 , and the various isotopic species have been located using high-resolution (0.1μm lateral resolution) secondary ion mass spectrometry (SIMS). Supplementary information on oxide morphologies and structures has been obtained by scanning electron microscopy (SEM). SIMS images indicate the regions in the scale where oxidation has taken place predominantly by cation or anion diffusion at different stages of the growth process. α-Al 2 O 3 scales are shown by SIMS to develop by both outward transport of aluminum and inward transport of oxygen, with the latter predominating. The major effect of the “reactive element” additions is to limit outward aluminum transport.