Potential influences of bond coat impurities and void growth on premature failure of EB-PVD TBCs

The influences of void growth and bond coat impurities on premature failure of electron beam-physical vapor deposition (EB-PVD) thermal barrier coatings (TBC) were studied. Results show that numerous fine voids were present beneath alumina scales that formed on as-deposited commercial CVD NiPtAl bond coat surfaces during EB-PVD of YSZ. Voids were not observed beneath scales that formed on grit-blasted NiPtAl surfaces. The benefits of grit-blasting primarily involved prevention of void growth. Surface treatments that remove S and/or accelerate alpha alumina formation without roughening the bond coat surface will likely extend the ultimate durability of state-of-the-art EB-PVD TBC.