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Electron Beam-Physical Vapor Desposited Thermal Barrier Coatings (EB-PVD TBC) on the Ni-base superalloy IN 738LC were tested in respect to non-isothermal and cyclic oxidation resistance at 1100°C. Two types of MCrAlY's (M = Ni, Co), a Co-base and a Ni-base, were used as bond coats (BC) for the TBC's. Additionally, free standing MCrAlY specimens of 2 mm thickness were manufactured by vacuum plasma spraying. The results of the present studies strongly indicate, that an important life time governing factor of the TBC is the yttrium incorporation into the alumina based Thermal Grown Oxide (TGO) which results in an increase of the TGO growth rate and in parallel in a decrease of the yttrium concentration in the coating. If the yttrium concentration has been decreased beneath a critical level, its positive effect on TGO adherence is lost, resulting in TGO spallation. The time required for yttrium exhaustion will not only depend on the initial yttrium content but also on the yttrium reservoir, which is directly proportional to the BC thickness. The transport of yttrium into the TGO seems to occur slower in a Co-based than in a Ni-based coating, resulting in a longer life time for the TBC on the CoNiCrAlY-BC.

Zirconia doped with 3.2–4.2 mol% (6–8 wt%) yttria (3–4YSZ) is currently the material of choice for thermal barrier coating topcoats. The present study examines the ZrO2‐Y2O3‐Ta2O5/Nb2O5 systems for potential alternative chemistries that would overcome the limitations of the 3–4YSZ. A rationale for choosing specific compositions based on the effect of defect chemistry on the thermal conductivity and phase stability in zirconia‐based systems is presented. The results show that it is possible to produce stable (for up to 200 h at 1000°–1500°C), single (tetragonal) or dual (tetragonal + cubic) phase chemistries that have thermal conductivity that is as low (1.8–2.8W/m K) as the 3–4YSZ, a wide range of elastic moduli (150–232 GPa), and a similar mean coefficient of thermal expansion at 1000°C. The chemistries can be plasma sprayed without change in composition or deleterious effects to phase stability. Preliminary burner rig testing results on one of the compositions are also presented.

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