Overview on Recent Developments of Bondcoats for Plasma-Sprayed Thermal Barrier Coatings
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REVIEW
Overview on Recent Developments of Bondcoats for PlasmaSprayed Thermal Barrier Coatings D. Naumenko1 • R. Pillai1 • A. Chyrkin1 • W. J. Quadakkers1
Submitted: 1 March 2017 / in revised form: 21 September 2017 Ó ASM International 2017
Abstract The performance of MCrAlY (M = Ni, Co) bondcoats for atmospheric plasma-sprayed thermal barrier coatings (APS-TBCs) is substantially affected by the contents of Co, Ni, Cr, and Al as well as minor additions of Y, Hf, Zr, etc., but also by manufacturing-related properties such as coating thickness, porosity, surface roughness, and oxygen content. The latter properties depend in turn on the exact technology and set of parameters used for bondcoat deposition. The well-established LPPS process competes nowadays with alternative technologies such as HVOF and APS. In addition, new technologies have been developed for bondcoats manufacturing such as high-velocity APS or a combination of HVOF and APS for application of a flashcoat. Future developments of the bondcoat systems will likely include optimization of thermal spraying methods for obtaining complex bondcoat roughness profiles required for extended APS-TBC lifetimes. Introduction of the newest generation single-crystal superalloys possessing low Cr and high Al and refractory metals (Re, Ru) contents will require definition of new bondcoat compositions and/or multilayered bondcoats to minimize interdiffusion issues. The developments of new bondcoat compositions may be substantially facilitated using thermodynamic–kinetic modeling, the vast potential of which has been demonstrated in recent years.
& D. Naumenko [email protected] 1
Forschungszentrum Ju¨lich GmbH, Institute for Energy and Climate Research (IEK): Microstructure and Properties of Materials (IEK-2), 52425 Ju¨lich, Germany
Keywords interdiffusion MCrAlY bondcoats oxidation thermal barrier coatings thermal spraying thermodynamic–kinetic modeling
General Remarks The operating temperatures of components in gas turbines and aircraft engines increased considerably in the recent years. The turbine inlet temperatures are comparable with the solidus temperatures of cast, directionally solidified, and single-crystal Ni-base superalloys typically used for manufacturing of the components in the hottest turbine sections. To prevent overheating, the components are internally cooled and additionally protected by ceramic thermal barrier coatings (TBCs). The TBCs, mostly consisting of yttria-stabilized zirconia, are commonly applied on the structural components in aircraft engines by electron beam-assisted vapor deposition (EB-PVD). In contrast, in land-based power-generating turbines, thermal spraying, especially air plasma spraying (APS), is frequently used to deposit the TBC. A metallic bondcoat (BC) between the zirconia-based TBC and the nickel-base alloy provides oxidation resistance for the base material and adherence of the ceramic coating (Ref 1, 2). Its physical and mechanical properties, in particular coefficient of thermal expansion (CTE) as w
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