Stabilising thermal barrier coatings with ytterbium
Thermal barrier coatings (TBCs) safeguard metallic components from the effects of high temperature in aeronautics and other demanding fields. TBCs reduce the threat of thermal fatigue and can therefore significantly extend the expected lifetime of the parts they protect. An extensive investigation of TBCs was carried out in the context of an RTD project entitled HIPERCOAT. Material scientists with the University of California, Santa Barbara in the United States evaluated the stability of zirconia-based TBCs doped with several different metals, including scandium (Sc), yttrium (Y) and ytterbium (Yb). The behaviour of the TBCs varied considerably depending on the choice of doping material. In the case of Y, the advantage of non-transformability, which is crucial for applications involving cyclic thermal loading, was lost. This was contrary to the latest published research. In fact, the best results were observed for Yb. Thermodynamic modelling was subsequently employed to determine which of the doping materials delivered the greatest toughness, another key TBC parameter. Yet again, Yb proved to be several times stronger than the other alternatives. Finally, experiments with co-doping indicated that durability could be improved when Y was paired with lighter elements. These findings will be exploited by the organisations participating in HIPERCOAT in the development of next generation TBCs.
