Chronological evaluation of interfacial damage in TBC due to thermal cycling

A two layer electron beam-physical vapor deposited (EV-PVD) thermal barrier coating (TBC) on a single crystal superalloy (Rene N5) substrate was characterized prior to and after thermal cycling at 2, 18, 25, 44, 50, 75, 100, 110, 150, and 175 cycles in between 200 C-1177 C. Optical microscopy, scanning electron microscopy, and thermal wave imaging techniques were used to characterize the interfacial damage. Pt-Al was used as bond coat and 8 wt % YSZ was used as outer top layer. Interfacial cracking was observed even at two thermal cycles. Thermally grown oxide (TGO) layer increased with the number of thermal cycles. After numerous cycles over 100, interfacial separation was observed to be higher at the middle than at the edges of the sample. This observation is consistent with buckling induced delamination-a possible mechanism for spallation. (C) 1999 Kluwer Academic Publishers.