Beyond Ni-based superalloys: Coatings for novel materials in H2 turbine engines

Abstract

As aviation strives to reduce its carbon footprint, hydrogen-powered engines have emerged as a promising technology, albeit presenting new materials challenges. Traditional Ni-based superalloys are increasingly being replaced by lightweight alternatives such as intermetallic γ-TiAl alloys and SiC-based ceramic matrix composites (CMCs). These materials offer the advantages of reduced weight and improved thermal efficiency, but their performance in harsh high-temperature environments, particularly in the presence of water vapor, remains a significant challenge. As a result, protective coatings have become essential to ensure the longevity and reliability of engine components under extreme conditions. For γ-TiAl alloys, alumina-forming coatings such as Ti-Al-Cr have shown promise in protecting the base material by forming a dense Al2O3 scale [1]. However, the brittle nature of these coatings compromises mechanical properties. Novel approaches, such as the use of MAX phase coatings (e.g. Ti2AlC, Cr2AlC), offer improved mechanical strength due to their unique nanolaminate structure [2]. In this study, the coatings were tested in laboratory air and water vapor conditions to compare their oxidation kinetics and phase formation at 850 °C. SiC/SiC CMCs require advanced environmental barrier coating (EBC) systems to protect against water vapor degradation. Multilayer EBC systems, consisting of an Si-based bond coat, followed by rare earth disilicate and monosilicate layers, such as Yb2Si2O7 and Yb2SiO5, show promising results in maintaining phase stability and resistance under cyclic oxidation and water vapor exposure [3,4,5]. In this study, the durability of these coatings under extreme conditions at 1200 °C is presented. In particular, the morphological- and phase stability of the silicates, as well as the oxidation kinetics of the bond coat, are addressed for long-term reliability and compared under different atmospheres. Advances in coating technologies are critical to the success of these novel materials in hydrogen-fueled turbine engines, pushing the boundaries of aerospace materials performance in high temperature, high humidity environments.