Thermally Stable Nanometals by Predictive Atomic Scale Interfacial Energy Reduction

Report No. ARL-TR-5490
Authors: Dr. Kris Darling, Dr. Laszlo Kecskes, Professor Zi-Kui Liu, Professor Elizabeth Dickey, and Dr. Jing Li
Date/Pages: March 2011; 28 pages
Abstract: Nanocrystalline iron (Fe) alloys doped with 1 at.% zirconium (Zr), tantalum (Ta), and nickel (Ni), produced through high energy mechanical alloying, were investigated for microstructural stability. The results were consistent with theoretical predictions, indicating a decrease in stability with solute type in the following order: Zr, Ta, and Ni. Preliminary transmission electron microscopy (TEM) investigations of the most stable system, Fe-Zr, revealed the presence of 2.5 at.% Zr within the grain boundaries of the sample, confirming a thermodynamic tendency for stability. More specifically, Zr segregation was found to be inhomogenously distributed between grain boundaries of nanostructured regions. Such a distribution accounts for and provides a potential mechanism for the appearance of abnormal grain growth at elevated temperatures. Additional compositional profiling uncovered a new FCC phase, within the abnormally grown grains. This phase is coherent with the BCC Fe substrate matrix and has a lattice parameter of 8.5 ¿.
Distribution: Approved for public release
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Last Update / Reviewed: March 1, 2011