The aim of this study is to evaluate the thermal lifetime properties of yttria-stabilized zirconia (YSZ) coatings with a columnar microstructure. YSZ suspensions were sprayed under different conditions in order to obtain a sample lot with columnar microstructures varying from well-separated to closely spaced. Thermo-cyclic fatigue (TCF) tests were performed at 1100 °C and the results are presented. Coatings with well-separated columns reached 2150 cycles prior to failure compared to 1300 cycles in the case of coatings with compact columns. The apparent lower TCF resistance is attributed to a loss of thermal compliance inducing the development of sharp intercolumnar cracks. Failures seem to be linked to debonding at the TGO-substrate interface. The bond coat and substrate surface roughness also play a role in such failures and their impact is discussed.

The aim of this work, devoted to yttria stabilised zirconia (YSZ) thermal barrier coatings, is to produce by DC plasma spraying a single thick pass macro cracked orthogonally to the substrate. YSZ was plasma sprayed in air atmosphere on Hastelloy X substrates, with a NiCrAlY bond coat. A three-zone microstructure is observed, where lamellae and columns are present. The measurements of deposition stresses during spraying allow explaining the macrocrack formation.

The isothermal oxidation of bond coats composed of vacuum plasma sprayed (VPS) MCrAlY (NiCoCrAlYTa and CoNiCrAlY) or palladium modified nickel aluminides (NiPd + APVS) was studied in several oxygen partial pressures (10 5 , 1 and 10 -5 Pa), with two heating rates (20 and 60K/min) at different temperatures (900, 1000 and 1100°C). For MCrAlY coatings, Arrhenius plots of the parabolic rate constants show a kinetic transition below 1000°C. This could be linked to a transition from Al 2 O 3 to Cr 2 O 3 scale growth. Lower oxygen partial pressures induce lower parabolic rate constants at 900°C. This leads to the assumption that scales grown at low oxygen partial pressures are still formed of alumina at 900°C. Nevertheless, these results could not be confirmed by chemical analysis (EDS, XPS). The two tested heating rates show no influence on the oxidation kinetics of both MCrAlY coatings. In the case of aluminide, for low oxygen partial pressures, the parabolic kinetics are reduced of one order of magnitude (for P O2 = 10 5 to 1 Pa) and correspond to a thinner scale of α-alumina. Also, the heating rate modifies the parabolic kinetics (i.e. after the transient stage) and the total weight gains for all oxidation temperatures, with higher parabolic rate constants after heating at slower rate.