Atmospheric Plasma Spraying of Self-Healing Thermal Barrier Coatings

The state-of-the-art material for the topcoat of thermal barrier coatings (TBCs) is yttria stabilized zirconia (YSZ). Due to induced stresses while thermal cycling, cracks develop near the thermally grown oxide layer (TGO), which can cause delamination. In the described approach a self-healing TBC will be created by embedding MoSi₂ in the topcoat. The developed cracks will be refilled due to oxidation and the accompanying volume expansion. By this the lifetime of TBCs can be improved. As the topcoat still consists of YSZ the TBC is expected to have the advantages of the state-of-the-art material and the described self-healing ability. The processing parameters to produce composite YSZ/MoSi₂ coatings by atmospheric plasma spraying (APS) have been studied. A major challenge are the different characteristics of MoSi₂ and YSZ in terms of melting temperature and oxidation behavior. The quality of the coatings has been evaluated by X-ray powder diffraction and scanning electron microscopy.