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Thermal Stability of Nanostructures - An Experimental and Modeling Investigation


EMSL Project ID
50073

Abstract

The goal of this proposal is to develop nanostructured magnesium (Mg)-based 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 Mg-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 (using EMSL’s experimental resources) and thermodynamic modeling; the latter will be performed in collaboration with university partners to identify compositions with the potential to yield nano-grained Mg-alloys 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-based alloys that are targeted for lightweight structural applications. The choice and concentration of solutes will be guided by thermodynamic modeling. The as-sputtered thin films will be heated in-situ in the S/TEM or in the sputtering chamber and characterized with respect to solute segregation, precipitate formation and grain-growth. 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 and/or precipitation to the grain-boundaries.
In parallel, the experimental effort will be complemented by a modeling task that will be performed by our academic collaborator. The modeling effort will implement thermodynamic models, employing the Regular Nanocrystalline Solution (RNS) model combined with lattice Monte Carlo (LMC) simulations, to design Mg-based alloy compositions with the potential to form nanostructures that are stable against detrimental grain growth and phase segregation. The outcome of these predictions is the realization of thermodynamically (as opposed to kinetically) stable nanostructures.
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
2017-10-13
End Date
2018-09-30
Status
Closed

Team

Principal Investigator

Aashish Rohatgi
Institution
Pacific Northwest National Laboratory

Team Members

Arun Devaraj
Institution
Pacific Northwest National Laboratory

Libor Kovarik
Institution
Pacific Northwest National Laboratory

Related Publications

Devaraj A., W. Wang, V.R. Vemuri, L. Kovarik, X. Jiang, M.E. Bowden, and J.R. Trelewicz, et al. 2018. "Grain Boundary Segregation and Intermetallic Precipitation in Coarsening Resistant Nanocrystalline Aluminum Alloys." Acta Materialia. PNNL-SA-135423. [Unpublished]