Lifetime study of sputtered PtAl coating on γ-TiAl with and without TBC topcoat at high temperatures

Abstract

In this study, a PtAl based coating was tested under high temperature conditions at 900 °C and 1000 °C. The composition of Pt-53Al was chosen because of its excellent results in previous studies at another temperature. Due to the formation of a thin continuous alumina layer on top and the phase stability of the oxidation resistant coating, a lifetime of 1500 1 h-cycles was achieved.Depending on the testing temperature and time, the coating underwent an evolution of different Ti-Pt-Al phases due to the outward diffusion of Ti and Nb from the substrate and inward diffusion of Pt. The oxidation resistance decreases with a continued interdiffusion and a decreasing Pt content in the Ti-Pt-Al phases.Additionally, the Pt-53Al coating was successfully deposited with a Thermal Barrier Coating top coat by EB-PVD. The oxidation test at 1000 °C also revealed a lifetime up to 1500 cycles without failure, particularly based on the good adhesion between the TGO and TBC.Mass gain measurements were done at each temperature and for all coating systems. Further microstructural examination methods to study the coating evolution, such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffractometry (XRD) for phase analysis, were used.