Effect of Zr addition on alumina scale formation during oxidation of high purity FeCrAlY-alloy

Abstract

Additions of reactive elements (Y, Zr, La, Ce, Hf, etc.) modify the high temperature oxidation performance of alumina-forming alloys by improving the scale adhesion, changing the scale growth mechanism and oxidation kinetics. The RE-effect has been commonly studied on model alloys containing only one RE. In contrast, commercial alloys normally contain several RE’s, but in addition a number of impurities unavoidable in the large scale production. This causes difficulties in attributing the observed effects to a particular RE. In this work the effect of Zr on oxidation of FeCrAlY-alloys has been studied using high purity model materials. The oxidation kinetics obtained during thermogravimetric experiments are complemented by extensive characterisation studies of the oxidised specimens. The results show that during high temperature exposure Zr rapidly diffuses into the oxide scale. Upon its incorporation into the scale, Zr changes the oxide microstructure and phase composition resulting in an improved scale spallation resistance and consequently in alloy lifetime extension.