In order to make advances in hypersonic flight, nuclear fusion, ballistic impact protection, and concentrated solar power, materials are needed that can withstand temperatures far above the melting point of typical high performance materials. This project investigates the effects of composition and microstructure on the properties of complex transition metal boride ceramics which have melting temperatures above 3000 C and are among the highest melting points for any known materials. This class of materials is known as ultra-high temperature ceramics. Entropy stabilization, a concept whereby at least four other elements in approximately equal ratios are added to a binary compound, has been used to produce stable, high entropy borides. Initial studies using this approach focused on synthesis and densification without analyzing properties. Hence, this research addresses a gap in knowledge of fundamental composition-microstructure-property relationships for boride ceramics. The scientific outcomes of the project will include identification of relationships among processing conditions, microstructures, and properties to enable design selection of compositions and microstructures that will yield properties desired for demanding applications. The broader impacts will include increased inter-campus collaboration between a doctoral university with higher research activity and a public university that offers terminal M.S. degrees. This collaboration will include expanding distance methods to extend curricular offerings at both schools, and establishing stronger research links between both to enhance student recruitment and increase access to research infrastructure.
The research will use an integrated experimental and computational approach to provide an unprecedented level of knowledge about the atomic structure, microstructure development, and composition-microstructure-property relationships for boride ceramics containing multiple transition metals. The main goals of the project are to: 1) utilize the entropy stabilization effect to produce new boride compositions containing metals that do not typically form borides; 2) control microstructure development by manipulating densification kinetics through changes in composition; and 3) establish ultra-high temperature structure-property relationships in this emerging class of materials. Computational methods will be used to investigate solution formation behavior, thermodynamic properties, and defect formation energies. Complementary experimental studies will focus on processing and properties of entropy stabilized boride ceramics. Reactive hot pressing will be used to produce ceramics with controlled compositions ranging from highly pure borides with containing one transition metal to entropy-stabilized compositions containing five transition metals in roughly equal proportions. In addition, reactive hot pressing offers the ability to control microstructure development to enable studies of microstructure-property relationships. The project will utilize advanced characterization tools to quantify metal distributions in boride ceramics with complex compositions, which will help elucidate densification kinetics, and measure intrinsic mechanical, thermal, and electrical properties of high entropy boride compositions. This project will lead to unprecedented knowledge of the thermochemical stability and inherent properties of entropy stabilized ceramics.
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.
