Self-organized multilayer structure in magnetron sputtered Si[sbnd]Pt reservoirs on γ-TiAl alloy induced by high-temperature annealing and oxidation

Abstract

The development of oxidation-resistant coatings has been stimulated by the needs of the aerospace industry, in particular following the introduction of the ɣ-TiAl alloys in turbofan engines; however, oxidation resistance at high temperatures (>750 °C) is still a significant challenge. In the present work, the influence of Si-Pt-based coatings on a Ti-48Al-2Cr-2Nb alloy is evaluated when exposed to isothermal oxidation in a high-temperature environment (900 °C). The coatings were deposited by magnetron sputtering using different Si (63–80 at.%) and Pt (20–37 at.%) concentrations as well as varied thicknesses (6.8–12.2 μm). The evolution of the microstructure of the as-deposited SiPt layers has been tuned by vacuum annealing (10−6 Torr) at 750 °C for 16 h, followed by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) analyses. After vacuum annealing, the formation of a multilayer microstructure composed of intermetallic (PtxSiy, PtxAly, and TixSiy) sublayers has been identified. Influenced by the different SiPt reservoirs (thickness and the compositional Si/Pt ratio), the sublayers exhibited different morphologies; for the samples with a high Pt concentration, the growth of a columnar microstructure was observed. After oxidation at 900 °C for 100 h, the analyses indicated microstructural evolution, mostly related to the continued solid-state diffusional transport of the main elements (Ti, Al, Pt, Si, and O) and solid-state boundary reactions. The presence of oxygen was confirmed in all oxidized samples, but it was restricted to the top zone of the multilayer system primarily associated with the growth of mixed SiO2 and Al2O3 compounds.