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Isotopic Diffusion Databases for Magnesium Integrated Computational Materials Engineering (Mg-ICME)
The objective of this project is to create an isotopic (tracer) diffusion database in the Mg-rich phases of the Mg-Al-Zn-Mn system. This database and a thermodynamic database that is being continuously updated will be provided to participants involved in various tasks in the Mg-ICME program. This website represents efforts in progress toward gaining critical diffusion data.
Principal Investigator: Nagraj Kulkarni, Oak Ridge
Industrial Partners: U.S. Automotive Materials Partnership Integrated Computational Materials Engineering (ICME) Team, Magnesium Elektron North America
Oak Ridge National Laboratory
Bruce Warmack, (865) 574-6202; e-mail: firstname.lastname@example.org
Balasubramaniam Radhakrishnan, (865) 241-3861; email@example.com
Ethan Ambroziak [gb diffusion in thin films, summer 2012]
Peter Todd [retired]
Argonne National Laboratory
John Mundy [retired]
Jerry Hunter, e-mail: firstname.lastname@example.org
University of Central Florida
Yongho Sohn, email@example.com
Kevin Coffey, firstname.lastname@example.org
University of Newcastle, Australia
Graeme Murch, e-mail: email@example.com
Irina Belova, e-mail: firstname.lastname@example.org
Magnesium Elektron North America
The approach for measuring the tracer diffusion coefficient is based on the thin-film approach. The procedure first requires the preparation of homogeneous single phase alloy samples in the desired Mg-Al-Zn-Mn system. This is followed by deposition of stable isotopes or radioisotopes of these elements in the form of thin films on the sample surfaces. After diffusion annealing at various temperatures below the melting temperatures of these alloy samples, the isotopic diffusion depth profiles in these samples are measured using SIMS. Analysis of the diffusion depth profile data using the thin-film solution provides the tracer diffusivity for the selected sample composition at the annealing temperature. At higher temperatures the tracer diffusion in polycrystalline alloy samples is likely to be dominated by volume diffusion, while at lower temperatures there will likely be an additional contribution from grain boundary diffusion. The SIMS diffusion data will be analyzed to extract both types of diffusion contributions, though in this FY we have focused on volume diffusion measurements in large-grained samples. By repeating such measurements for different compositions and temperatures, a significant amount of tracer diffusion data for Mg and Zn in the single phase Mg-Al-Mn-Zn system is obtained. Since Al and Mn are monoisotopic elements, their tracer diffusivities will be computed indirectly using diffusion theory (Darken-Manning relations) that connects interdiffusion coefficients (obtained from diffusion couples) with tracer diffusion coefficients and thermodynamics. The collection of tracer diffusion data for all the components in the Mg-Al-Zn-Mn system will be then fitted using suitable functions to generate the tracer diffusion database.
U.S. Department of Energy Assistant Secretary for Energy Efficiency and Renewable Energy Office of Vehicle Technologies as part of the Automotive Lightweight Materials Program under contract DE-AC05-00OR22725 with UT-Battelle, LLC.
Special thanksJohn Allison and Bob McCune: Mg-ICME Program
Carol Schutte (Team Lead) and William Joost (Materials Engineer): Vehicle Technologies Program, DOE
Joe Carpenter: Former program manager, Automotive Lightweight Materials Program, DOE
Phil Sklad, Dave Warren: Automotive Lightweight Materials Program, ORNL
Example of diffusion at 350°C for one hour of 25Mg tracer isotope into a single Mg grain. Nonlinear fitting of the data is used to measure the diffusion coefficient.
Arrhenius plot of non-linear fit data shown at left, including Shewmon's 1954 radio-
nuclide results on polycrystalline samples. The straight line is a fit to the entire data set.
For details, see Mg Self-Diffusion Summary.