Thermally Stability of Nanostructures - An Experimental and Modeling Investigation
EMSL Project ID
49175
Abstract
The goal of this proposal is to develop nanostructured alloys that can be fabricated in bulk form (>1 cm3) without compromising their nanostructure, either during the fabrication process or during service at elevated temperatures. Thus, the three main objectives of this project are: (i) Design alloy compositions with the potential to form thermally stable nanostructures, (ii) develop techniques for rapid validation of alloy compositions predicted to form thermally stable nanostructures, and (iii) develop techniques for rapid optimization of alloy compositions that have been validated to form thermally stable nanostructures. These objectives will be achieved through a combination of experiments and atomistic simulations with the help of EMSL’s experimental and computational resources, respectively. In parallel, thermodynamic modeling will be performed in collaboration with university partners to identify compositions with the potential to yield nano-grained materials that do not coarsen at elevated temperatures.Traditionally, nanostructures are generated by severe mechanical deformation e.g. ball milling, severe plastic deformation, etc. However, in this project, the fundamental behavior of nanostructures will be studied by taking advantage of EMSL’s magnetron sputtering capability that is capable of depositing clean, nano-grain, electron transparent, thin films of controlled composition. We will focus on Mg-, Al- and Fe-Si based alloys. The Mg- and Al-based alloys compositions are targeted for lightweight structural applications while the Fe-Si alloys are meant for soft magnets. The choice and concentration of solutes for the Mg- and Al-alloy systems will be guided by thermodynamic modeling. High-throughput sputtering techniques will be developed to produce a range of compositions in a single run. The as-sputtered thin films will be heated in-situ in the S/TEM and characterized with respect to the kinetics of solute segregation, grain-growth and precipitate formation. Compositions that are resistant to thermal coarsening will be identified and further investigated using atom probe tomography (APT) to quantify the solute’s propensity for segregation to the grain-boundaries. The experimental effort will be complemented by atomistic simulation methods, such as Monte Carlo (MC) and molecular dynamics (MD). Interatomic potentials for binary alloys will be obtained from the literature, and new ones will be developed if necessary. An on-lattice self-learning kinetic Monte Carlo (KMC) code developed at PNNL will be used to simulate solute diffusion to the grain boundaries. Thus, the modeling effort will enable a fundamental understanding of the role of solutes, grain-boundaries, temperature and solute concentration in influencing the thermal stability of nano-sized grains.
In summary, this research will provide valuable insights into the influence of solutes in controlling the thermal stability of nano-grained alloys. Successful development of nanostructured materials, enabled by this research, will allow one to fully utilize the unique functional performance only evident at nanoscale.
Project Details
Start Date
2015-11-23
End Date
2016-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members