Damage caused during Laser Drilling of Thermal Spray TBCs on Superalloy Substrates
K.T. Voisey, J.A. Thompson, T.W. Clyne
Department of Materials Science & Metallurgy University of Cambridge
Abstract
Laser drilling is used to manufacture cooling holes in turbine blades. These blades, and other aeroengine components, are often protected by thermal barrier coatings (TBC). The TBC studied here was composed of a NiCrAlY bond coat (BC) and a partially stabilised ZrO2 top coat (TC), both plasma sprayed. Holes having diameters around 100 m were drilled through the coated superalloy, with a Nd:YAG laser. Subsequent deposition of a plasma sprayed over-layer (CoNiCrAlY) was use to promote spontaneous debonding at the BC/TC interface. A numerical model for prediction of residual stress development during plasma spraying was used to evaluate the strain energy release rate when debonding occurred (ie the fracture energy of the interface). Laser drilling was found to generate a significant increase in this fracture energy. This result is explained in terms of observed microstructural effects.
keywords:blades; TBCs; bond coat; thermal barrier; release rate; top coat; plasma spraying; Thermal Spray; spontaneous debonding
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