THE EFFECT OF HEAT TREATMENT ON THE STIFFNESS OF ZIRCONIA TOP COATS IN PLASMA-SPRAYED TBCs
J. A. THOMPSON, T. W. CLYNE
ACTA MATERIALIA
abstract:Thermal barrier coating (TBC) specimens have been prepared by plasma spraying. A vacuum plasma spray (VPS) MCrAlY bond coat and atmospheric plasma spray (APS) zirconia top coat were deposited onto a nickel superalloy substrate. The stiffness of detached top coats was measured by cantilever bending and also by nanoindentation procedures. Measurements were made on specimens in the as-sprayed state and after various heat treatments. Signicant changes were detected in the Young s modulus of the top coat as a result of the heat treatments. The rate of sintering was found to be a function not only of the temperature but also of whether or not the coating was attached to the substrate during the heat treatment. This inuences the stress state in the coating. A previously-developed numerical model has been modied in order to incor- porate the effects of top-coat stiffening on the development of stress within the TBC system during exposure to high temperature. It is expected that sintering of the top coat will lead to increases in the driving force for debonding at the interface between the top coat and the bond coat. This effect may be at least partly responsible for the spallation of top coats which commonly aficts TBCs after periods under service con- ditions. 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
keywords:Plasma spray; Thermal barrier coatings (TBCs); High temperature
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