Coating of MoSi2 healing particles for self-healing thermal barrier coatings

Abstract

To increase lifetime of the protective thermal barrier coatings (TBC) in jet engines and other gas turbines, a self-healing approach based on MoSi2 healing particle addition is considered. However, due to rapid oxygen transport in yttria-stabilized zirconia (YSZ), a common TBC material, premature oxidation is a major problem. This thesis investigates the feasibility of coating MoSi2 sacrificial particles with a protective Al2O3 shell to prevent this oxidation, while still retaining particle availability upon damage. Two different chemical methods, namely a sol-gel procedure and atomic layer deposition with residual chemical vapor deposition were successfully utilized to coat MoSi2 healing particles. The microcapsule composition and integrity has been investigated by means of scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The results demonstrate that after calcining at 1200 °C for 1h in argon ?-Al2O3 shell can be formed and the shell remains intact. Subsequently the heat treated encapsulated particles were embedded in YSZ matrix followed by healing tests at 1100 and 1200 °C. The crack-healing tests proved that the shells produced by both methods remain intact at high temperatures, but also the coatings have a protective effect compared to uncoated MoSi2. Moreover, the embedded particles show a crack healing effect, indicating the feasibility of this self-healing concept.