Effect of Damage Processes on Spallation Life in Thermal Barrier Coatings
Abstract
Thermal barrier coatings (TBCs) provide thermal insulation to high temperature superalloys. TBCs consist of an outer ceramic layer that provides good thermal insulation due to the low thermal conductivity of the ceramic used, and the inner metallic bond coat layer that provides needed oxidation resistance to the underlying superalloy. The microstructure of the bond coat changed from high aluminum concentration beta-(Ni, Pt)3Al phase, which has a very good oxidation resistance, to beta-(Ni, Pt)3Al plus gamma'-(Ni, Pt)3Al dual phase microstructure due to oxidation and interdiffusion between the bond coat and the substrate during the thermal test in air. The microstructure change influenced the oxidation behaviors of the bond coat. Less protective oxide (Ni-rich) formed on gamma-(Ni, Pt)3Al due to depletion of aluminum, and the oxide scale on gamma'-(Ni. Pt)3Al ha less adhesion to the bond coat. The TGO Layer and bond coat was subjected to high residual radial stresses during cool down from oxidation temperature du to the thermal expansion mismatch between the different layers. The high residual stress initiated the damages in TGO layer, the TBC/TGO interface and the TGO/bond coal interface as well. The evolution of the damages in TBCs resulted in local loss in adhesion of the coating during thermal cycling. The formation and evolution of micro-decohesion was the key failure mechanism of TBC for lone term thermal cycling. Thermal wave imaging technique as non-destructive and non-contact method was successfully used to monitor the health of TBC. The results reveal that there was no major delamination in TBC specimens during thermal tests.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 09, 2001
- Accession Number
- ADA397661
Entities
People
- Golam Newaz
Organizations
- Wayne State University