Understanding Grain Boundary Multiplicity and Its Role in Deformation Mechanisms of Nanocrystalline Metals

NON-TECHNICAL SUMMARY

A grain is a crystallite where the atoms are periodically arranged. The interface between differently oriented grains, i.e., grain boundaries, strongly influences, if not determine, many mechanical and physical properties of materials, such as strength, ductility (material’s ability to bend before breaking), and resistance to radiation damage. Increasing scientific data suggests that grain boundaries in metals can have many different kinds of atomic arrangements (also known as multiplicity), and the transition between them leads to significant property changes.

If we have a better understanding of grain boundary multiplicity and its structure-property relationship, scientists and engineers can devise synthesis strategies to tailor grain boundaries towards enhanced mechanical performance of nanostructured metals. In this project, Dr. Penghui Cao and Dr.

Huolin Xin at UC Irvine will use forefront computational modeling and electron microscopy tools to study grain boundary multiplicity at the atomic level and reveal its critical role in determining how nanocrystalline metals deform. A fundamental understanding of grain boundary multiplicity could facilitate the design of engineering metals with desirable mechanical properties for structural applications, such as aerospace and nuclear energy systems.

The project-based education plan aims to attract the participation of high school students from diverse backgrounds and thereby motivate and enable underrepresented minorities to pursue STEM careers. TECHNICAL SUMMARY

This project centers on revealing the 3D atomic structure of grain boundaries and fundamentally understanding how grain boundary structure multiplicity influences plastic deformation mechanisms of nanostructured metals. Scientifically, we hypothesize that the plastic deformation mechanisms in nanocrystalline metals can be tuned by tailoring grain boundary multiplicity.

To test this central hypothesis, we propose research tasks combining atomistic simulation, reaction pathway simulations, theoretical modeling, electron tomography, and in-situ transmission electron microscopy experiments. This integrated computational and experimental study aims to address four major questions: (1) How to determine the 3D atomic structure of grain boundaries, revealing boundary defects, structure units, and multiplicity? (2) How do grain boundary defects and multiplicity influence mobility and migration mechanisms of grain boundaries? (3) Is it possible to control plastic deformation by tailoring grain boundary state and structure multiplicity, which results in enhanced plasticity and ductility in nanocrystalline metals? (4) What are the new deformation mechanisms which can be enabled by defective grain boundary or transformed boundary?

The physical insights gained from this research will advance the exploitation of structure-property relationships in nanostructured metals, laying the groundwork for effective tailoring of mechanical behaviors through controlling structure, multiplicity, crystallographic distribution of boundaries.

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.