Next-generation Enabling, eXtreme Temperature RDRE

Quadrus Corporation’s Advanced Manufacturing Division (AMD) and our STTR partner University of Alabama in Huntsville (UAH) is pleased to present this proposal for demonstrating feasibility in an advanced rotating detonation rocket engine (RDRE) we call the Next-generation Enabling, eXtreme Temperature RDRE (NEXT-RDRE). NEXT-RDRE uses a clever combination of rhenium, C103, and Ti-6Al-4V to enable a lightweight chamber design that can operate with exceedingly high local wall temperatures. Rhenium is used in the hottest portions of the centerbody, outer body, and cowl/nozzle, because its melting point is 3,182°C (5,759°F). Even though rhenium is extremely strong at elevated temperatures, it is also extremely dense; being just over 21 g/cm3, it is more than 2-1/2 times denser than Inconel 718. Thus, NEXT-RDRE uses rhenium only where necessary, transitioning first to C103 niobium alloy and then to Ti-6Al-4V, as wall temperatures and heat fluxes allow. The design takes advantage of our experience with bimetallic laser powder bed fusion (L-PBF), diffusion bonding of refractory metals, and lightweight lattice structures in a manner that makes it weight competitive with ceramic matrix composite (CMC) designs. Our Phase I focuses on enabling high temperature, multi-material manufacturing techniques, so that multiple material combinations can be used at various strategic locations in the RDRE geometry. Sensitivity to hot oxidizing species is nearly universal for materials, but especially for nearly all refractory materials, so NEXT-RDRE includes a proven next-generation environmental barrier coating (EBC) to protect the underlying substrate materials. Our EBC consists of a thin layer of ruthenium between the substrate and the outer layer of hafnia, HfO2. Since hafnia, which is nearly as refractory as rhenium itself (m.p. 2,758°C), is already in an oxidized state, it naturally protects the substrate from oxidizing combustion products like O2, O, CO, OH-, and H2O.