The ceramic top coat of the as-received sample has uniform columnar grains with less spacing between columns. X-ray diffraction analysis showed the top coat retains a tetragonal phase and <200> texture after thermal cycling. After 251 cycles, the thermal barrier coating failed with spallation occurring along the yttria-stabilized zirconia (YSZ)/thermally grown oxide (TGO) interface and within the TGO. One sample failed prematurely after 20 cycles with monoclinic zirconia observed on the bottom of the spalled YSZ. Further study of microstructural changes during cyclic oxidation is ongoing.

1. As Received Doosan-EBPVD SEM Images of the YSZ Surface The ceramic top-coat is has typical uniform columnar grains with less inter-column spacing. YSZ YSZ

2. YSZ top-coat has tetragonal t’ phase and is textured along <200>. XRD YSZ Top-Surface (As Received) (111) (200) (220) (311) (222) (400) (004) (204) (420) ť ZrO 2

3. Cross-sectional Back Scattered Electron Micrographs (As Received) epoxy YSZ Bond coat ~ 151µm ~ 64µm The bond-coat is rich in Co, hence it is CoCrAlY.

4. Failed Sample ť ZrO 2 Lifetime ~ cycles YSZ YSZ After thermal cyclic oxidation the ceramic coating retains t’ phase and texture along <200>.

5. Back-Scattered Microcraphs of Spalled YSZ Bottom Surface and Top-Surface of Bare Bond Coat Spalled YSZ Bottom Surface Top-Surface of Bare Bond Coat The nature of spallation is mixed i.e. it occurred along YSZ/TGO, Bondcoat/TGO and within TGO. ť ZrO 2 YSZ TGO TGO Bond Coat

6. Cross-sectional Backscattered Electron Micrographs TGO Thickness Tortuosity L/L 0 epoxy YSZ Bond coat YSZ TGO Bond coat epoxy Bond coat YSZ

7. Premature TBC Failure Lifetime ~20 Cycles Significant monoclinic ZrO 2 was observed on the bottom surface of the spalled YSZ. ť ZrO 2 m ZrO 2 F,T(111) M M(111)