Abstract
The lifetime under thermal cycling of a system consisting of an air plasma sprayed
thermal barrier coating (TBC) deposited on a metallic bondcoat (BC) is determined by the subcritical
growth of micro-cracks near the interface between both coatings. This growth mainly occurs
during the cooling down phase, as shown by the acoustic emission monitoring during the thermal
cycling. The factors controlling the stress level leading to the crack growth are the local curvature
of the metallic-ceramic interface, the growth of an oxide scale (TGO) at such interface and the
sintering of the TBC, the two last processes occurring during the high temperature cycle phase.
Implementing all these factors, a model based on Finite Element Method (FEM) calculations is
presented where growing cracks are incorporated by assigning soft properties to the FEM cells
occupied by the cracks. Determining the growth direction for the maximum energy release rate at
every cooling down step, the current crack extension during the cycling is tracked until it reaches a
characteristic length corresponding to the TBC failure. The influence by the metallic-ceramic
interface roughness and by the temperature gradient across the TBC is discussed.