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

Abstract

Surface modification by thermal oxidation of oxide dispersion strengthened (ODS) aluminium-containing high temperature alloys generally involves the formation of a dense and adherent alumina layer, which protects the underlying matrix against further degradation in aggressive environments at high temperatures. It is also known that alumina is a material with good biocompatibility and excellent wear behaviour. This combination makes this type of surface treated alloys a choice for constructional materials for high temperature applications and also a potential candidate for room temperature applications, such as load-bearing surgical implants. In this study attention is paid to the formation of alumina layers by high temperature oxidation, as a surface treatment, at 900, 1200 and 1400°C in air on a commercial FeCrAlY-alloy PM 2000. Specimens originating from two different batches were used to investigate the effect of differences in microstructure and minor 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 μm, whereas the other batch contains grain sizes being in the range of the specimen thickness (1–2 mm). Chemical analysis of these batches revealed also small differences between the minor constituents. Results showed that the mass gain was slightly lower for the fine grained material, which corresponds well with the smaller thickness of the oxide scale formed on the fine grained material. In addition, after isothermal oxidation at 900 and 1200°C 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°C no differences occurred between the oxidation behaviour of specimens originating 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 each individual material parameter.