Journal
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING
Volume 22, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0965-0393/22/2/025022
Keywords
Ni-Al; molecular dynamics; free energies
Funding
- US Department of Energy by Lawrence Livermore National Laboratory [DE-AC52-07NA27344]
- DOE Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering
- DOE's Early Career Research Program
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Metals that can form intermetallic compounds by exothermic reactions constitute a class of reactive materials with multiple applications. Ni-Al laminates of thin alternating layers are being considered as model nanometric metallic multilayers for studying various reaction processes. However, the reaction kinetics at short timescales after mixing are not entirely understood. In this work, we calculate the free energies of Ni-Al alloys as a function of composition and temperature for different solid phases using thermodynamic integration based on state-of-the-art interatomic potentials. We use this information to interpret molecular dynamics (MD) simulations of bilayer systems at 800K and zero pressure, both in isothermal and isenthalpic conditions. We find that a disordered phase always forms upon mixing as a precursor to a more stable nano crystalline B2 phase. We construe the reactions observed in terms of thermodynamic trajectories governed by the state variables computed. Simulated times of up to 30 ns were achieved, which provides a window to phenomena not previously observed in MD simulations. Our results provide insight into the early experimental reaction timescales and suggest that the path (segregated reactants)->(disordered phase)->(B2 structure) is always realized irrespective of the imposed boundary conditions.
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