New frontiers in synthesis of high-entropy transition metal borides enabled by microwave-induced plasma

University Of Alabama At Birmingham, Birmingham AL

Investigators

Abstract

NON-TECHNICAL SUMMARY The significance of this project is that it addresses the need for advanced ceramics as a key enabling technology for many applications in aerospace, defense, power generation, and processing industries having significant national impact. The study of materials designed for operation under harsh conditions is essential to meet a range of challenges—from creating better turbines, reactors, and batteries to developing future energy systems. The experimental and computation components of this project help support the goals of the National Materials Genome Initiative (MGI) in the effort to discover, manufacture, and deploy advanced materials faster and with less cost than ever before. The class of materials known as high-entropy ceramics developed in this project extends the range of high temperatures and resistance to rusting as needed for advanced material systems, such as hypersonic vehicles. The investigations involve understanding how these new materials form, along with their mechanical and rust resistance. The materials are processed using a highly efficient technique based on a state of matter known as plasma; a processing approach not yet explored in this field. Both experimental and computational methodologies are employed to provide new knowledge about how these materials can be synthesized, characterized, and modeled. The community are engaged about the wonders of plasma technology through involvement with a local science center, with aim for a broad viewing audience including the general public and K-12 students. TECHNICAL SUMMARY This project investigates a novel approach for synthesis of high-entropy transition metal borides enabled by microwave-induced plasma. Compared to conventional processes that rely primarily on convection, the advantages of this approach include: enhanced diffusion, reduced energy consumption, very rapid heating rates and considerably reduced processing times, decreased sintering temperatures, and improved physical and mechanical properties. The plasma discharge is highly efficient in promoting microwave heating and chemical reactions via highly active species such as electrons, ions and radicals. This synthesis route is yet unexplored for high-entropy ceramics and presents opportunity to study the mechanisms contributing to formation of this relatively new class of materials. The kinetics and reaction pathway leading to complete phase transformation via this unique approach is investigated, along with characterization of structure, hardness and oxidation resistance. The computational effort guide component selection by computing entropy forming ability with partial occupation method, predict oxidation resistance using CalPhad to couple thermodynamics with phase diagrams, and model mechanical properties with special quasi-random structures. Outcomes from this project include: new understanding of how microwave-induced plasmas affect and enhance reaction pathways/kinetics toward high-entropy boride formation and development of new models for mechanical and oxidation resistance properties along with validation from experiment. Community outreach in this project focuses on the wonders of plasma technology for a broad viewing audience including the general public and K-12 students. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.