A Comprehensive Review of Thermal Barrier Coatings Microstructure with Different Platinum-Modified Aluminide Bond Coats

Thermal Barrier Coatings (TBCs) are used to protect the surface of hot components of gas turbines. TBCs usually have three layers and include a Top Coat (TC) ceramic layer, an intermediate metallic Bond Coat (BC) layer, and a Thermally Grown Oxide (TGO) layer. In the present study, a brief survey of the microstructure of the ceramic layer produced by Air Plasma Spray (APS) and Electron Beam Physical Vapor Deposition (EB-PVD) has been done. Due to the inherent microstructure of the top coat ceramic layer, Diffusion aluminide bond coats are widely used in thermal barrier coatings for oxidation and hot corrosion resistance of Ni-base superalloy components of advanced gas turbine engines. Modifying these coatings by Pt addition considerably improves their high-temperature oxidation resistance. This effect of Pt has prompted intense research on the microstructure and oxidation behavior of Pt-modified aluminide coatings (Pt-Al) over the past several decades. The present review is to collate the available information on the subject. The study includes traditional b-(Ni, Pt)Al bond coats as well as the Pt-modified g–g¢ type of bond coats that have gained prominence in more recent times. A brief description of typical process steps involved in the formation of Pt-aluminide coatings is provided followed by a detailed assessment of coating microstructures reported under various processing conditions. The influence of prior diffusion treatment, on the coating microstructure, is highlighted. The various mechanisms of the role of Pt in enhancing the oxidation and resistance of aluminide coatings, as suggested in the literature, are discussed.