Zifeng Wang
Advisor: Prof. Ting Zhu
will propose a doctoral thesis entitled,
Atomic-Scale Investigation of Deformation Mechanisms in BCC Metals
On
Tuesday, December 3rd at 10:30 a.m.
MRDC 4115
and/or
Virtually via Zoom
https://gatech.zoom.us/j/9177065615?pwd=UE43WEZBZDZ6SmQ3eHhwRE1yUGF6dz09
Committee
Prof. Ting Zhu – George W. Woodruff School of Mechanical Engineering (advisor)
Prof. Naresh N. Thadhani – School of Materials Science and Engineering
Prof. David L. MacDowell – School of Materials Science and Engineering
Prof. Joshua P. Kacher – School of Materials Science and Engineering
Prof. Oliver N. Pierron – George W. Woodruff School of Mechanical Engineering
Abstract
Body-centered cubic (BCC) crystals, known for their high strength at elevated temperatures, are crucial in extreme environments,. These properties make BCC metals, particularly refractory metals like molybdenum, tungsten, and niobium, valuable in aerospace and nuclear applications. However, they also exhibit brittleness at low temperatures due to limited dislocation mobility, a phenomenon driven by the ductile-to-brittle transition temperature (DBTT) and high Peierls stress, which inhibits dislocation motion.
In this proposal, in-situ high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) simulations are combined to study three key deformation mechanisms in BCC metals. First, we explore anomalous twinning in tungsten, revealing unexpected twin nucleation on the {112} twin plane with lower resolved shear stresses rather than the {112} anti-twin plane. Second, we investigate superplastic deformation in tungsten nanostructures, observing over 100% elongation at room temperature due to dislocation-grain boundary interactions. Finally, we examine fracture behavior in single-crystal molybdenum across temperatures up to 1100°C, identifying various crack propagation modes, involving dislocation activity, cleavage, and phase transitions from the initial BCC structure to the newly formed FCC and HCP structures. Understanding these mechanisms is crucial for guiding the design of materials that combine high strength and ductility, improving the mechanical performance of BCC metals across a range of temperatures, and enhancing their applications in industries such as aerospace and nuclear energy.