Ep. Busso et al., A mechanistic study of oxidation-induced degradation in a plasma-sprayed thermal barrier coating system. Part I: Model formulation, ACT MATER, 49(9), 2001, pp. 1515-1528
The effect of the oxidation induced degradation of a typical plasma-sprayed
thermal barrier coating (PS-TBC) system on the local ceramic-metal interfa
cial stresses responsible for the nucleation of mesoscopic cracks is invest
igated. A coupled oxidation-constitutive approach is proposed to describe t
he effect of the phase transformations caused by local internal and externa
l oxidation processes on the constitutive behaviour of the metallic coating
. The coupled constitutive framework is implemented into the finite element
method and used in parametric studies employing periodic unit cell techniq
ues. The effects of service, microstructural and ceramic-metal interface pa
rameters on the peak interfacial stresses during service and cooling to roo
m temperature are quantified. The results of the parametric unit cell FE an
alyses revealed a strong dependency of the local stresses responsible for m
esoscopic crack nucleation and growth on the local morphology of the oxidis
ed interface, the sintering of the ceramic coating, stress relaxation effec
ts due to creep, the thickness of the thermally grown oxide (TGO), and the
applied mechanical loads. When no mechanical straining of the TBC system is
considered, local tensile stresses normal to the coating surface within th
e ceramic top coating reach values of up to 330 MPa at room temperature for
a critical TGO thickness of approx. 3 mum. (C) 2001 Acta Materialia Inc. P
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