Scale Evolution During Early Oxidation Stages of Polycrystalline β-NiAl at 1100°C and the Effect of Implanted Yttrium

Abstract

The development of scales at early oxidation stages was studied in terms of the evolution of their morphology and phase composition on unmodified and Yttrium-implanted β-NiAl intermetallic compound at 1100°C in air for exposure periods from 3 min up to 24 hours and Scanning Electron Microscopy, Low-Angle X-ray Diffraction and Photoluminescence Spectroscopy. Similar consecutive stages of the scale evolution were found on both materials and implanted yttrium retarded the rate of this process which manifested itself mainly in impeding the phase transformation of transient aluminium oxides into α-Al₂O₃, the required protective layer. The scale evolution had a local nature and under the same oxidation conditions the regions sometimes co-existed, exhibiting different stages of the evolution. No unambiguous relationship was found between the scale morphology and its phase composition.