Ja. Thompson et Tw. Clyne, The effect of heat treatment on the stiffness of zirconia top coats in plasma-sprayed TBCs, ACT MATER, 49(9), 2001, pp. 1565-1575
Thermal barrier coating (TBC) specimens have been prepared by plasma sprayi
ng. A vacuum plasma spray (VPS) MCrAlY bond coat and atmospheric plasma spr
ay (APS) zirconia top coat were deposited onto a nickel superalloy substrat
e. The stiffness of detached top coats was measured by cantilever bending a
nd also by nanoindentation procedures. Measurements were made on specimens
in the as-sprayed state and after various heat treatments. Significant chan
ges 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 influences the stress state i
n the coating. A previously-developed numerical model has been modified in
order to incorporate the effects of top-coal 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 drivi
ng force for debonding at the interface between the top coat and the bond c
oat. This effect may be at least partly responsible for the spallation of t
op coats which commonly afflicts TBCs after periods under service condition
s. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All lig
hts reserved.