Stabilization and Strengthening of Nano-Crystalline Immiscible Alloys
Abstract
The technical objective of the proposed effort is to develop a fundamental understanding of the physical mechanisms responsible the thermal stability and strength of nanocrystalline immiscible alloys. The proposed effort seeks to achieve the stated technical objective through a four-stage approach. First, a rigorous thermodynamic theory will be developed for grain boundary (GB) segregation in multicomponent alloy systems subject to mechanical stresses to identify and enable prediction of the most critical thermodynamic parameters controlling the stability of nano-crystalline materials. Theory development will focus on the incoherent interface case and will derive the generalized adsorption equation (in the standard and Gibbs-Helmholtz forms) and the Maxwell relations and will require development of computational algorithms for thermodynamic integration to compute the GB free energy. Second, a new ADP potential will be developed for the Cu-Ta system, and a database offirst-principles DFT calculations will be generated. The DFT data will include binding relations (formation energy versus atomic volume) for a number of imaginary compounds with different crystalline structures and chemical compositions across the entire composition range from pure Cu to pure Ta. Third) atomistic calculations of segregation, free energy and other thermodynamic characteristics will be performed for a large set of individual GBs in Cu alloyed with different amounts of Ta. This set ofGBs will include symmetrical and asymmetrical tilt GBs, twist GBs, and a number of mixed tilt/twist misorientations representing general GBs in polycrystalline materials. And fourth, to address kinetic factors of thermal stability, atomistic simulations will be conducted to investigate the solute effect on the mobility of GBs driven by capillary forces or applied stresses. Several low-index orientations aligned parallel to the cylinder axis will be tested, including [001), [011], [111] and [211], and the size distributions of such clusters as functions of temperamre and alloy composition will be smdied systematically.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1510077
Entities
People
- Y. Mishin
Organizations
- Army Contracting Command
- George Mason University
- United States Army