Design of oxide precipitates in nanostructured materials

Nanocrystalline materials are very interesting for fundamental study and engineering applications due to their superior mechanical properties. Severe plastic deformation has received considerable interest as an essential technique for producing bulk nanocrystalline materials. However, the microstructure instability of nanocrystalline materials is the primary concern since it significantly influences the resulting mechanical properties. Alloying addition is one practical solution. It is recognized that non-metallic Oxygen can be used to tailor material`s microstructures and attendant properties. However, Oxygen`s exact role for improving the thermal stability of nanocrystalline materials remains unclear. The presence of oxygen atoms can change local bonding in materials. The fundamental question is how the oxygen atoms change local bonding in materials. Could we design the stabilized nanostructures by tailoring the oxygen level? Although some experimental studies about oxygen effects in nanocrystalline materials exist, the underlying physical mechanism of the oxygen effect is still poorly understood. Furthermore, oxygen atoms are inevitably involved in the powder processing procedure during mechanical alloying, and there is an urgent requirement to clarify the oxygen effects in nanocrystalline. To address these issues, in this project, we will develop an effective route to control oxygen levels incorporation in bulk nanocrystalline materials. As an example, we select pure Cu and Ta metals and CuTa alloy, introduce different amounts of oxygen contents, and deform them by high-pressure torsion. We study the detailed microstructure and mechanical properties, and then further establish a relationship between the structure and property. The experimental methods include advanced electron microscopy, real- time observations, mechanical properties tests, and theoretical calculations. The originality of this proposal is to cover controllable oxygen concentration, oxygen atoms imaging and their distributions, how oxygen atoms interact with defects, and oxygen tuning mechanical properties and thermal stability of nanocrystalline materials. The study will provide the basis for developing novel nanocrystalline by ubiquitous oxygen atoms.