High Entropy Alloys via Powder Metallurgy

High entropy alloys (HEAs) have become one of the most promising class of materials for harsh environment applications. Their properties make them ideal for unique applications across various industries, such as high-temperature structural components and thermal protection systems for aerospace, components of nuclear reactors and gas turbines for the energy sector, and as armor and high-performance weapons in the Defense industry. Although many academic reports have validated their potential on a small scale, these materials have only received isolated attention in applied settings.Typical HEA compositions include four to six elements. Melt and cast techniques, including arc melting, are most commonly used to create HEAs. This approach requires melting all elements of the composition, which may require high temperature and can limit the choices of elements, especially refractory elements having drastically different melting points. In addition, compositional variations and coarse grain size of melt and cast materials require extensive thermo-mechanical treatment for homogenization of the microstructure to improve ductility. These problems are significantly amplified when preparing macroscopic specimens. As a result, two main problems have hampered the successful transition of these promising HEAs.Lab-based techniques or melt-centered approaches are not easily scalable. This makes HEA development cost prohibitive given that commercial entities would require minimum orders of multi-kilogram quantities to melt-cast any composition. A powder processing approach, such as powder metallurgy, offers an alternative which is applicable to all kinds of materials independent of their melting temperature. In addition, a powder-based approach provides ultrafine grain size, homogeneous microstructure and compositional flexibility in design. This scalable technology is thus perfectly suited for the development and transition of advanced refractory HEA materials.            Following on our precedents tailoring the properties of refractory HEAs by powder metallurgy (PM) methods, our proposed program aims at two complementary objectives: 1) demonstrate the generality of powder-based processing to enable the fabrication of macroscopic specimens of HEAs with defined properties, and 2) develop a process to reduce refractory oxide powders in order to increase the purity and properties of selected HEAs. This transformative program will not only have a high impact at the Navy, but across the DOD, DOE and commercial sector.