| Thermal barrier coating systems (TBCs) are widely used in the turbine industry to protect air cooled super-alloy airfoils from direct exposure to the full gas temperature of the combustion gas. In aviation, TBCs are required to provide longer lifetime and more heat resistant performance.Pt is found useful to improve the stability of the TBC in many studies. The bond coat oxidizes to form a protective layer of Al2O3 on the top coat, and during subsequent exposure in service. Spallation of the YSZ top coat is often associated with eventual failure of the underlying Al2O3 layer. Thus, design of bond coats with optimized Al2O3 adherence is a clear path to improve TBC performance.On the basis of the material composition, density functional theory calculation is planned in this study.The study show that Al2O3 layer on NiCoCrAl+Y coatings has more holes for internal oxidation on account of the element Y diffusion and enrichment on the interface. In addition, steam can promote the internal oxidation. While a thinner and uniform alumina form on NiCoCrAl+Y(O) coatings because element Y is fixed by oxygen atoms during producing coatings. Water vapor present less influence to protective alumina formation on the NiCoCrAl+Y(O) coating. Therefore, oxidation behavior of NiCoCrAl coatings vary in composition and structure in different oxidizing atmosphere. Besides, Y and Y-enrichment oxides have important implications for the behavior.Pt could improve the thermal cycling stability performance of the bond coats in EB-PVD TBC System, the study partially explain that by calculation:Pt plays a great role in hindering the oxygen adsorption and aluminium segregation. Thus Pt can slow down the form of alumina on the top of BC. PtAl2 has the similar lattice constant as NiAl and is more stable than Ni3Al during forming Al2O3. So Pt can improve the bonding performance of Al2O3 and lifetime of thermal barrier coating.
|
PDF Full Text Request