Bending fatigue failure of atmospheric-plasma-sprayed CoNiCrAlYÂ +Â YSZ thermal barrier coatings

Bending fatigue failure of conventional atmospheric-plasma-sprayed CoNiCrAlY + ZrO2-8 wt.% Y2O3 thermal barrier coatings with/without the thermally grown oxide layer generated between the bond coat and the top coat was experimentally studied at room temperature. Microscopical and profilometrical characterization of as-received and fractured specimens and a simplified finite element study of cooling thermal stresses show that the same fatigue strength of both the as-coated and the oxidized specimens (i.e. its insensitivity to the presence of the thermally grown oxide) is most likely caused by a preferential through-the-thickness cracking of the thermally grown oxide layer. Moreover, the bond-coat/substrate interface is identified as the weakest part of the studied thermal barrier system under both low and high crack growth rates.