Defect-Electron Interaction at Ambient Temperature in Metallic Materials

Non-technical Summary

High temperature has been used to process metallic materials since prehistoric times. The intense heat moves out the otherwise immobile internal defects and thus improves the properties. The same principle is used today. For example, steel processing requires temperatures in excess of 800 C applied for many hours. This research project aims to transform the current state-of-the-art by asking the question, can metals be processed at room temperature? The hypothesis is that, by passing high current - but not allowing the temperature to rise, a purely mechanical force can be generated inside the material. This force can make the defects mobile without raising the temperature and in a timeframe of minutes only. Accordingly, the objective of this research is to understand how the electrons (from current flow) interact with the defects, and how the elimination or rearrangement of defects is different from conventional heat treatment. These experiments are performed inside high magnification microscopes to develop fundamental insights of the proposed process. Accomplishment of this project will give a new alternative to the metallic processing industry, which consumes a big portion of US energy (and carbon) footprint. The new science can also be employed in other systems where current can be passed, like electronics. By bypassing high temperature, this new process may impact the economy of manufacturing industry. The immediate impact is education and training of graduate and undergraduate students, while promoting diversity. The project involves student from middle school to enhance awareness of the carbon economy of manufacturing, and underlying science, to the next generation.

Technical Summary

Defect and microstructural control in metals and alloys require very high temperature (comparable to melting point) and long times (from few hours to days). In this project, the PIs propose a non-thermal force to achieve the same effects in minutes. Here, electrical current is passed through the specimen, while controlling its temperature to the ambient. Whenever the electrons collide with defects and grain boundaries, they lose the momentum – generating the 'electron wind force' (EWF). The hypothesis is that the EWF dissociates immobile and complex defects species to create very high density of disentangled and mobile dislocations. This allows the EWF to impart high mobility to the defects without raising the temperature. The specific objectives of this project are to (a) provide direct evidence of defect and microstructural control by performing fundamental experiments inside microscopes with near-atomic resolution and (b) investigate the electron-defect interaction to predict the evolution of various defect species (vacancies, partials, dislocations, twins) and correlate that to the microstructural changes. The transformative aspect of this project is the departure from centuries-old heat treatment techniques to the proposed non-thermal process. It explores the atomic to grain level fundamentals of defect-EWF interaction, which remain mostly unknown. The research is integrated with undergraduate education through Senior Capstone design course to train the next generation with emerging manufacturing technology. A student recruitment is through the Penn State Minority/Women in Engineering program. A unique outreach program, Print with Metals, is developed for Middle school students. These activities are complemented by the Manufacturing Day event to draw high and middle school students towards engineering, and specifically next generation manufacturing careers.

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.