High-Temperature Resistant Coatings for Strategic Aero-space Applications

Abstract

The aerospace components operating in hot sections of aero-engines and combustors experience extreme environments. Typically, the components are subjected to high service temperatures exceeding 1100°C and oxidizing conditions. Protective coatings are essential for preventing oxidation-induced dimensional degradation of the components and enhancing their high temperature capability as well as durability. Defence Metallurgical Research Laboratory (DMRL) has developed a variety of metallic and ceramic thermal barrier coating (TBC) systems for Ni-base superalloys, and refractory Nb-alloys for strategic aerospace applications involving ultra-high temperatures and high flow velocities. These coatings have demonstrated significant effectiveness against thermal degradation at temperatures as high as 2000 °C during oxidation in static air as well as in dynamic conditions involving high flow velocities (Mach > 2). The present article provides an overview of the advanced oxidation resistant and thermal barrier coatings developed in DMRL. The effectiveness of the TBCs in preventing dimensional degradation of the metallic and composite substrate materials has been evaluated at the laboratory scale. The developed TBCs have the potential for use in aero-engines and propulsion systems of hypervelocity vehicles.


Typical aero-gas turbine engine.
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(a) Cross-section microstructure showing the various constituents of thermal barrier coating (TbC) ensemble, and (b) cyclic oxidation behavior of CMSX-4 superalloy applied with various coatings. The superior oxidation resistance of Pt-aluminide coating is evident from its low and steady weight gain over prolonged durations exceeding 700 h. The oxidation tests were carried out at 1100 °C in air and each cycle comprised 45 min. heating followed by 15 min. cooling.
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Processing sequence and microstructure evolution of Pt-aluminide (Pt-Al) bond coat.
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Photographs of Pt-aluminide bond coated components: (a) low pressure turbine blades (lPTbs), (b) high pressure turbine blades (HPTbs), (c) low pressure turbine vanes (lPTVs), and (d) high pressure turbine vanes (HPTVs).
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