TRANSPORT IN ALPHA-AL2O3 SCALES ON FE-AL AND NI-AL ALLOYS AT 1100-DEGREES-C

The nature of transport processes occurring during the growth of oxides at 1100-degrees-C on Fe-25 wt% Al and Ni-32 wt% Al has been investigated, Both materials develop protective alpha-Al2O3 scales which have been characterized by SEM, RHEED and Auger electron spectroscopy. Two-stage oxidation experiments have been conducted using O-16(2) and O-18(2) gases: imaging SIMS (secondary ion mass spectrometry) has been used to locate the different isotopic species. The SIMS data (profiles from areas as small as 3.5 mum X 3.5 mum, and images with 0. 1 mum lateral resolution) illustrate the complexity of the growth processes, and indicate areas where scale growth has taken place predominantly by cation or oxygen ion diffusion.