Microstructural evolution and microhardness in zirconia-based EB-PVD thermal barrier coatings

As-deposited and laboratory heat-treated ("aged") electron beam physical vapor deposited (EB-PVD) thermal barrier coating (TBC) samples were characterized microstructurally using SEM and TEM, particularly focusing on the sintering accompanying aging in the ZrO2-based top coat. Unusual but shallow surface microcracking occurred on first heating as deposited TBCs. The ZrO2 top coats of the TBCs were indented at two different loading rates between room temperature and 1204degreesC using a commercial hot hardness tester. The aged sample is harder than the as-deposited sample under all conditions. The faster loading rate decreased the apparent hardness for both samples, and revealed a previously unrecognized "dynamic" effect during microindentation. In the as-deposited TBC, delocalized damage associated with micro-hardness indents was confined to the area directly beneath the indenter, while in the aged TBC, the damage was less delocalized, some indent-induced microcracks having propagated into the surrounding material.