Enhancing the High Temperature Capability of Nanocrystalline Alloys: Utilizing Thermodynamic Stability Maps to Mitigate Grain Growth Through Solute Selection

Report No. ARL-TR-6743
Authors: Mark A. Tschopp, Kristopher A. Darling, Mark Atwater1, Brian K. VanLeeuwen, Mark A. Atwater, and Zi-Kui Liu
Date/Pages: December 2013; 46 pages
Abstract: Mitigating grain growth at high temperatures in binary nanocrystalline alloys is important for processing nanocrystalline alloy systems. The objective of this research is to develop a methodical design-based approach for selecting solutes in binary nanocrystalline alloys by revisiting grain boundary thermodynamics and the internal processes of grain growth and solute segregation in a closed system. In this work, the grain boundary energy is derived and systematically studied in terms of temperature, grain size, concentration, and solute segregation for binary systems of 44 solvents and 52 solutes, using readily-available elemental data, such as moduli and liquid enthalpy of mixing. It is shown that through solute segregation, the grain boundary energies of some binary systems can be reduced, resulting in thermodynamically stable grain structures and successful prediction of solutes that inhibit grain growth in some nanocrystalline alloys. Parametric studies reveal trends between equilibrium grain size, solute distribution and temperature for various binary systems culminating in the generation of nanocrystalline thermodynamic stability maps as a tool for solute selection in binary nanocrystalline alloys.
Distribution: Approved for public release
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Last Update / Reviewed: December 1, 2013