Low Energy Fabrication Methods for Refractory High Entropy Alloys

Development of advanced, high temperature materials and components is critical for the fielding of hypersonic vehicles (HVs) and advancing gas turbines.  The harsh combustion environment in gas turbines and extreme aerothermal environment encountered by HVs poses significant challenges for material selection.  This is particularly true for leading edges and control surfaces which can reach temperatures in excess of 2000°C, as well as combustor and high pressure turbine regions. Furthermore, while the aeroshell and structure components may not reach as high of temperatures, they must provide mechanical integrity in the 1,000-1,500°C range.  For many traditional materials and structures traditionally used in aerospace applications, the heat fluxes, temperatures, and stresses encountered in HV applications make them unfit for service on these platforms.  Refractory high-entropy alloys (RHEAs) are an excellent option in this space as they offer exceptional mechanical properties and thermal properties due to their multi-component composition enabling high fracture resistance, high strength at elevated temperature, improved strength to weight ratio, and tailorable thermomechanical behavior. However, current manufacturing methods require melting leading to difficulties and uniformity and unwanted segregation. Moreover, the presence of refractory materials forces this melt to be very energy intensive and presents further disparity between the constituents. Therefore, a solution is needed that improves homogeneity of the produced parts.  This work focuses on utilizing enthalpy assisted hydrogen reduction to produce metallic RHEA powders which can be subsequently utilized in solid-state manufacturing processes.  Three manufacturing techniques will be explored to demonstrate the viability of this approach: binder-jetting (BJAM), direct ink writing, and cold spray additive manufacturing (CSAM).