Thermal barrier coatings with a double-layer bond coat on Ni3Al based single-crystal superalloy

Isothermal oxidation and hot corrosion behaviors of diffusion aluminide coatings deposited by chemical vapor deposition

“…A new continuous layer with some vertical or round pores and numerous irregular shape precipitates are also appeared within the interdiffusion zone. The numbers and width of pores arerelatively large as compared with those before oxidation testing as reported in our previous work[19]. The chemical compositions of the surface new layer, large grains in aluminide layer and continuous layer in the interdiffusion zone are almost identical inFig.…”

Thermal cycling behavior of EB-PVD TBCs on CVD platinum modified aluminide coatings

“…The TGO strain energy is sensitive to the stress value because it depends on the square of the stress. It is well known that the segregation of Er, Ti, W and other substrate elements at the TGO/ bond coat interface reduces the interface toughness dramatically, and depletion of Al in the bond coat leading to the formation of brittle oxides also results in a weak interface adhesion [4,34]. Because the stress in the TGO changes substantially with cycles, use of measured stress rather than calculated TGO stress for calculating strain energy release rate is recommended.…”

“…Both air plasma spray (APS) and electron-beam physical vapor deposition (EB-PVD) are suitable to produce YSZ coating in industry [3]. EB-PVD TBCs with columnar structure exhibit higher strain tolerance than APS coatings and receive great interest especially for coatings used in aero engine airfoils [4]. Since the YSZ top coat has high oxygen permeability at the use temperature of TBC systems, it is usual to apply a so-called bond coat before the deposition of the ceramic layer to provide oxidation protection for the system [5].…”

“…It is designed as an Al reservoir, enabling to form a dense, protective thermal grown oxide (TGO) scale of a-Al 2 O 3 at the surface of bond coat adjacent to the TBC [6]. There are two major categories of bond coat used in industry [4][5][6]: (1) the over-layered MCrAlYX (M = Ni, Co; X = Si, Hf) coatings, usually composed of the b-NiAl phase and either c-Ni 3 Al or c-Ni solid solution; (2) the diffusion coatings (b-NiAl, (Ni, Pt) Al, and et al), typically a single b-phase, produced by pack cementation or chemical vapor deposition (CVD) methods. The MCrAlYX coatings, which can be produced by various PVD methods and low-pressure plasma spray (LPPS), are also prevalent bond coats used in the aerospace industry [7].…”

“…However, the overlay process can only prepare external coatings, leaving internal surface of the vanes and blades being exposed to high temperature gas, which is not desirable for advanced turbine used in more aggressive environments. The lower amount of Al available in the coating ''reservoir'' for TGO formation is the other drawback of the MCrAlYX coatings [4,8].…”