PVD based coatings for high temperature applications in aircraft engines

Abstract

Protective coatings play a crucial role in extending service life of components employed in harsh environments as found in aircraft engines. Particularly, new technologies for reducing the CO2 footprint of aviation generate new material challenges. Lightweight materials, such as γ-TiAl-based alloys and SiC-based ceramic composites, are pivotal in the aviation industry, making protective coatings indispensable but generating new challenges in coating design and processing. Recent research demonstrates promising protection for γ-TiAl-based alloys through alumina-forming intermetallic coatings based on Ti-Al- Si [1] or Ti-Al-Cr [2] which are applied via physical vapor deposition. However, their brittle nature compromises mechanical properties. Sputter coatings made of MAX-phases like Ti2AlC or Cr2AlC show promise for protection in high-temperature environments, offering unique nanolaminate microstructures resulting in improved mechanical properties [3]. Future propulsion systems, like MTU's WET engine or systems using E-fuels based on electrolytically produced H2, pose additional material challenges due to the highly corrosive water vapor in exhaust gases. Multi-layered environmental barrier coating (EBC) systems, applied by reactive magnetron sputtering, offer a promising solution for sustainable use [4]. Figure 1 displays an exemplary multilayer coating with a Si-based adhesion bond coating for oxidation protection and Yb-silicate based top coating for corrosion protection in water vapor atmospheres. For achieving higher thermal efficiency, materials used in jet engines shall allow higher temperatures, necessitating novel alloys like Mo-Si-Ti. While these alloys provide high melting point and creep resistance, their poor oxidation behavior requires protective coatings. Silica-forming coatings, along with a CTE-matched graded Mo-Si interlayer, present an opportunity for improved oxidation resistance up to 1200°C [5]. Such multilayer and graded coating systems were processed at DLR with a multi-source magnetron sputtering system in a one-batch process. A combinatorial approach is facilitated by placing components at different positions in the coating chamber, promising rapid material development in the future. The presentation will give a focused overview on recent research in the development of new coating systems for materials in aero engines, addressing main material and processing issues and contextualizing achieved results.