Formation of an alumina layer on a FeCrAlY alloy by thermal oxidation for potential medical implant applications

Surface modification by thermal oxidation of oxide dispersion strengthened (ODS) aluminium-containing high temperature alloys generally involves the f ormation of a dense and adherent alumina layer, which protects the underlyi ng matrix against further degradation in aggressive environments at high te mperatures. It is also known that alumina is a material with good biocompat ibility and excellent wear behaviour. This combination makes this type of s urface treated alloys a choice for constructional materials fur high temper ature applications and also a potential candidate for room temperature appl ications, such as load-bearing surgical implants. In this study attention i s paid to the formation of alumina layers by high temperature oxidation, as a surface treatment, at 900, 1200 and 1400 degreesC in air on a commercial FeCrAlY-alloy PM 2000. Specimens originating from two different batches we re used to investigate the effect of differences in microstructure and mino r constituents on the oxidation kinetics, composition and structure of the oxide scale. The most obvious difference between these batches is the grain size. One batch corresponds with an average grain size smaller than 1 mum, whereas the other batch contains grain sizes being in the range of the spe cimen thickness (1-2 mm). Chemical analysis of these batches revealed also small differences between the minor constituents. Results showed that the m ass gain was slightly lower for the fine grained material, which correspond s well with the smaller thickness of the oxide scale formed on the fine gra ined material. In addition, after isothermal oxidation at 900 and 1200 degr eesC the total number of nodules found on the outer part of the oxide scale was higher for the coarse grained material. During oxidation at 1400 degre esC no differences occurred between the oxidation behaviour of specimens or iginating from both batches. Differences in the oxidation behaviour can be explained by differences in microstructure and minor constituents. However, from the presented results it was not possible to reveal the effect of eac h individual material parameter. (C) 2001 Elsevier Science B.V. All rights reserved.