Electronic Structure Basis for Solubility and Phase Stability in Metal Alloys
Abstract
This proposal aims to provide a quantitative basis for predicting phase stability and solubility limit in metallic alloys. Traditionally, the empirical Hume-Rothery rules are used to estimate the solubility limits in metallic alloys. The conditions are based on (1) size misfit (2) difference in electronegativity and (3) valence electron concentration. In addition, topological criteria, based on atomic sizes, are used to quantify the lattice stability of metallic alloys. The validity of size factor depends on the exact atomic sizes, which are difficult to define. The central hypothesis of this proposal is that the atomic volumes and the electronic charge distribution, in a metallic alloy, are related. Such a relationship implies that these quantities can be tuned by alloying. To test this hypothesis, electronic structure calculations will be performed to establish a relationship between local strain and the valence electron density. Three cases will be studied: (i) Ti ? ? ? phase transformation, (ii) decreasing the miscibility gap in binary Ti-V alloys by addition of Al and (iii) phase change in AlxCoCrCuFeNi alloy by tuning Al concentration. Furthermore, the question of formation of stable multicomponent solid solutions is particularly timely due to the emergence of “High-entropy” alloys. We propose that formation and stability of these alloys can be analyzed in the context of supersaturated solid solutions. Supersaturated solutions are formed as the result of a competition between a mixing driving force and the thermally activated diffusive phase separation. Our hypothesis is that favorable alloying provides the driving force for mixing. However, the stability of this phase is governed by low kinetic rates, which trap the alloy in its metastable phase. Vacancy formation and migration energies will be computed to calculate the diffusion rates. The outcome of this work is a predictive means to design alloys with tailored properties.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 02, 2017
- Source ID
- FA95501710168
Entities
People
- Maryam Ghazisaeidi
Organizations
- Air Force Office of Scientific Research
- Ohio State University
- United States Air Force