Thermophysical and Thermal Cycling Properties of Multi-element Rare Earth Doped YSZ Thermal Barrier Coatings
The rare earth oxide ceramic designed as 4.5wt.%Gd2O3-5.5wt.%Yb2O3-10.5wt.%Y2O3-79.5wt.%ZrO2(GdYbYSZ)is a candidate material for thermal barrier coatings(TBCs),which will be suitable for application at higher temperatures.GdYbYSZ ceramic powders and bulks are fabricated by solid-state synthesis at temperatures above 1 300℃,and the powders have no phase transformation and exhibit excellent thermal stability despite long-term calcination at 1 100℃和 1 300℃.The averaged thermal diffusivity and thermal conductivity of GdYbYSZ ceramics are approximately 2.1%and 5.1%lower than those of the conventional YSZ bulk respectively.The GdYbYSZ ceramic coatings are directly manufactured on the surface of(Ni,Pt)Al bond coat by means of electron beam physical vapor deposition(EB-PVD),whose phase structure consists primarily of cubic phase with co-existing of excess Y2O3 and ZrO2.Meanwhile,elemental compositions of Y and Zr within as-deposited ceramic topcoats are higher than those in the ingot,and the constituents of Gd and Yb elements in these two types of specimens tend to be similar.A large number of regularly distributed"mud-like"microcracks appear on the surface of GdYbYSZ ceramic coating after the long-term alternating thermal cycling at 1 100℃.The transverse microcracks originating in the ceramic topcoat have elongated to the interface of ceramic coating and TGO layer that further cause the degeneration and separation of the interface.The spalling location of the GdYbYSZ ceramic coating mainly occurs at the upper and lower adjacent interfaces of the TGO layer.The serious rumpling,undulation,cross-linking,stress accumulation and rapid relaxation at the convex tip exist in the TGO layer are the critical factors to accelerating interfacial delamination and spallation failure of GdYbYSZ/(Ni,Pt)Al TBCs.
electron beam physical vapor depositionthermal barrier coatingthermophysicalthermal cyclingspallation failure
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