Thermal Barrier Coatings for Cryogenic Rocket Engines

This paper summerizes the last three years of research and development of thermal barrier coating (TBC) at the German Aerospace Center (DLR) for applications in cryogenic liquid rocket engines. Preliminary screening tests of different sub-layers and coating techniques were performed at low pressure conditions (< 1 MPa). The purpose of these tests was to identify the most suitable combination of thermal barrier coating technique and bonding layer structure. Coatings which had successfully passed this first screening phase were then qualified further in a second test campaign, in which samples of the coated elements underwent cyclic testing by subsequent exposure into baths of boiling nitrogen and water in order to check their stability against temperature shocks at cryogenic temperatures. Having passed this second screening test campaign, the best combination of thermal barrier coating and bonding layer was further tested using a sub-scale combustion chamber at pressures (10 MPa) and temperatures similar to real rocket engines. While a first series was performed with water as the coolant medium, a second test camping utilizing liquid hydrogen was employed for the final qualification of the technique.