DMREF: Discovery, Development, Design and Additive Manufacturing of Multi-Principal-Element Hexagonal-Close-Packed Structural Alloys

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Presently, the field of metallurgy is undergoing a renaissance spurred on by the realization that useful structural alloys can be formed by mixing many different types of atoms in roughly equal proportions. These materials are referred to as “multi-principal-element” alloys (MPEAs), and this approach has already given rise to the discovery of new strong and ductile alloys. However, these examples have been based on only a small subset of the atoms in the periodic table, and only a limited number of underlying crystal structures. The initial discoveries are encouraging, but the true potential of MPEAs is yet to be tapped. In this Designing Materials to Revolutionize and Engineer our Future (DMREF) project, advanced materials theory and high-throughput computation and experiments are combined with the tools of machine learning to accelerate the discovery and development of a relatively unexplored class of MPEAs in which the atoms of the alloy are arranged in a hexagonal pattern. This research area is ripe for transformative discoveries for targeted applications including the focus of this project: stronger and lighter alloys for low temperature structural applications inspired by the conditions encountered in space exploration. The project emphasizes alloys that can be fabricated through additive manufacturing, commonly referred to as metal 3D printing. Hence the alloys will be available for immediate technological applications because additive manufacturing offers great opportunities for rapid fabrication of components with complex geometries and tailored structures at the microscopic scale. These research goals will be achieved by harnessing the power of materials data while educating the next generation of materials researchers, and accordingly, the project is well aligned with the goals of the Materials Genome Initiative. In more detail, the project focuses on discovering and developing MPEAs crystallizing in the hexagonal-close-packed (HCP) structure. The initial focus is on alloys formed from the elements titanium, scandium, yttrium, zirconium, and hafnium. The composition space will be explored theoretically through computation of a set of identified descriptors including formation energies, lattice parameters, elastic constants, stacking fault and twin energies. The approach will leverage new classes of universal interatomic potentials for initial screening, with candidate systems investigated in more quantitative details using density functional theory based methods coupled with approaches designed to average over the wide variety of compositional arrangements encountered in MPEAs. Simultaneously, MPEAs will be synthesized using directed energy deposition laser systems and a concentration gradient approach that allows synthesis of a broad composition range within one sample. Ductility will be characterized using rapid nanoindentation screening and cryogenic micro-tensile testing. The resulting data will be used to develop and improve machine learning models that will, in turn, lead to suggestions for new materials. These materials will then be synthesized, and the process repeated. This iterative process will, ultimately, establish correlations between computable data and observable mechanical properties that enable the discovery and development of additively manufactured HCP MPEAs for low temperature applications. 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.