Microstructure and mechanical behavior of Pt-modified NiAl diffusion coatings

The performance of thermal barrier coatings (TBCs) in jet engines is strongly influenced by thermal and mechanical properties of the bond coat. In this investigation two different types of Pt-modified diffusion coatings developed for application as oxidation protection or as a bond coat in TBC systems were studied with respect to their microstructure and mechanical properties. The microstructural analyses based on different microscopy techniques and X-ray diffraction measurements revealed distinct differences between the two coatings: the coating aluminized by a gas phase process consisted solely of a (NiPt)Al phase, while the coating fabricated by pack-cementation consisted mainly of the two phases (NiPt)Al and Al 2 Pt, leading to a higher strength in comparison with the single-phase coating. In contrast, the ductility determined with 3-point bend tests between room temperature and 700 °C was clearly better for the single-phase coating. Additionally, the substrate curvature of coated sheets was measured to gain some information about coating stresses.