A thermal barrier coating (TBC) made of porous ZrO2 ceramic was formed on a nickel-based single crystal
superalloy (NSA) by plasma electrolytic oxidation (PEO). An oxidation barrier coating (OBC) made of Al2O3
based ceramics was created between the TBC and NSA substrate by coating the NSA with aluminum before
the PEO treatment that oxidized it into Al2O3. The keyfinding of this study is that ZrO2-based TBC can be
formed by PEO of an OBC-coated NSA in a K2[Zr(CO3)2(OH)2] solution. The TBC contained monoclinic-,
tetragonal- and cubic-ZrO2 crystals and had a unique gradient porous texture. Relatively large pores existed
nearthe interface between OBC and TBC,and the numberand sizeofporesintheTBC decreasedwithincreasing
distance from the interface. The TBC had ZrO2 grains with a diameter of about 300 nm. The TBC shows a low
thermal conductivity equivalent to that of conventional TBCs owing to this porous texture withfine grains.
The bond strength between the PEO coating and substrate was 26.8 ± 6.6 MPa, which is close to that of
conventional TBCs.
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