Transient alumina transformation on a sputtered K38G nanocrystalline coating

A K38G superalloy nanocrystalline coating was produced by magnetron sputtering deposition and its transient oxides formation in the early stage of oxidation (from 5 to 1200 min) was characterized by SEM, XRD, TEM and Photo Stimulated Luminescence Spectroscopy (PSLS). During this early period of oxidation, a series phase transformation occurred and the metastable θ-Al2O3 finally transformed to stable α-Al2O3. The features of the transient θ-Al2O3 were detected by PSLS, XRD and TEM. The results indicate that transient alumina formation can not be avoided even with the nanocrystalline structure and the formation of these metastable alumina may contribute to the exclusive α-Al2O3 development on nanocrystalline materials.