Excess Vacancy Enabled Transformations in Light Metal Alloys

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NON-TECHNICAL SUMMARYInnovating processes for lightweight metal alloy manufacture advances public welfare and secures the national defense by enabling efficient production of new materials that provide strength without adding weight in applications from vehicles and protective equipment to space exploration. This award supports basic scientific studies regarding how atomic structures respond to extreme conditions of temperature and strain that result in defects called vacancies, where atoms are missing from the metal’s crystal structure. This research advances the understanding of why and how vacancies cluster with solute atoms that differ from the primary metal, gathering into small bubbles called voids and encouraging the formation of strengthening particles.Multiple experimental techniques are used: positively charged particles are used to measure defects; atom probe reveals locations of different elements in the crystal structure; and electron microscopy images show larger scale features such as voids. Simulations predict how vacancies, solute and voids interact to better interpret the experimental data. These simulations also provide estimates of how the rate at which voids form, varies with temperatures, vacancy densities, and solute chemistries and densities. Experimental data are used to guide the choices of simulations and to check the validity of the simulations. In the process, this work advances simulation capabilities.This project engages undergraduates from Morgan State University, a nearby historically Black university, to foster the success of a newly emerging program that provides access to engineering degrees not currently offered at that university. The investigators also are planning to host an “Extreme Vacancy Engineering” workshop.TECHNICAL SUMMARYThe proposed research program aims to accelerate the development of new light alloys and processing routes by expanding our fundamental understanding of how vacancy supersaturation alters the thermodynamics of vacancy clustering, vacancy-solute complex formation, and void nucleation in ways that promote solute clustering and intermetallic precipitation. Alloys over a range of compositions are subjected to quenching and deformation to enhance vacancy densities in a controlled manner. Analysis is performed using an emerging computational methodology, transition interface sampling, coupled with targeted characterization using positron annihilation spectroscopy, atom probe tomography, and transmission electron microscopy in concert with molecular dynamics and Monte Carlo simulation. Experiments are leveraged to guide simulations and simulations to interpret experiments. The work aims to build a thermodynamic understanding for key processes in the form of free energy pathways that eschew classical nucleation theory assumptions in out-of-equilibrium systems.This research program engages undergraduates from Morgan State University, a nearby HBCU, to foster the success of a newly emerging 3+2 program that opens new pathways into materials-related engineering majors. A workshop on “Extreme Vacancy Engineering” is also anticipated to promote an emerging field of materials processing and designThis 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.