Creep-Based Nanomanufacturing of Crystalline Metals and Alloys

Nanostructures of metallic materials are critical for meeting the growing demands in catalysis, energy storage, sensors, filtration, and drug-delivery. Manufacturing of metal nanostructures largely relies on expensive lithography and thin film deposition techniques. Molding is a high-throughput fabrication process for nanostructures, but the large crystal grains in metals hinder their flow at nanoscale. This grant supports fundamental research in high temperature plastic deformation of crystalline metals to advance molding-based scalable nanomanufacturing. The research enables fabrication of high aspect-ratio nanostructures of many metallic alloys including high surface-area porous metal nanostructures which are highly desirable for energy conversion and storage and biomedical applications. The manufacturing research in metal nanostructures benefits the economy and society by advancing technologies in energy, healthcare and other industrial sectors thus advancing US competitiveness and prosperity. The project provides education and hands-on training to students at all levels and prepares them for the growing industry in advanced manufacturing. The outreach activities in this project are designed to particularly inspire students with disabilities for careers in science and engineering fields. Nanostructures are routinely fabricated by templated molding of soft polymers and other glassy materials in their stable viscous state. A similar approach is however not directly applicable to crystalline metals due to their highly reactive liquid state and rigid microstructural features in the solid state. This project investigates creep-based plastic deformation of crystalline metals and alloys for controllable molding at different length scales. Creep in metals is generally considered detrimental for structural applications, but recent studies indicate its potential for controllable nanoforming. Molding experiments with systematic variation in processing conditions and feedstock material enable decoupling of different creep mechanisms and their role in governing nanoscale metal molding. The project studies size-dependent mechanisms, e.g., dislocation-mediated plasticity, Nabarro-Herring creep, and Coble creep, in thermomechanical nanomolding of metals and alloys and flow mechanisms in template filling as a function of mold size, processing time and atmosphere. The knowledge gained from molding of homogeneous materials is applied to multi-phase and porous metal alloys, including high-entropy and eutectic alloys. Quantitative descriptions of creep induced flow advances the understanding of atomic diffusion in complex alloys and porous structures. Besides novel manufacturing science, the project has the potential to contribute new fundamental knowledge in metallurgy and mechanics. 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.