The effect of bond coating surface modification on the performance of atmospheric plasma spray thermal barrier coatings

Asperities in atmospheric plasma sprayed (APS) CoNiCrAlY bond coatings were observed to rapidly form spinel-type oxides growing into the APS yttria-stabilized zirconia (YSZ) top coating during isothermal exposures. To minimize these transient oxides, bond coatings were either lightly or heavily modified to remove asperities, prior to top coating deposition. After a 100 h isothermal exposure at 1100 degrees C in dry air, modified regions formed a thin, Al-rich thermally grown oxide (TGO) scale while unmodified regions formed Cr- and Ni-rich transient oxide. However, in 1-h furnace cycle testing (FCT) at 1100 degrees C, the modified bond coatings showed a reduced average lifetime compared to the specimens with unmodified bond coatings. The benefit of asperities may be to geometrically inhibit crack propagation, but the volume of transient oxide formed may also density the adjacent YSZ and further inhibit cracking.