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Molecular Dynamics Simulations on Nanocomposites Formed by Intermetallic Dispersoids of B2 Structure and Aluminum Matrices

M. Namkung, S. Paik and R. A. Wincheski
NASA Langley Rsearch Center, US

Keywords: nanocomposites, dispersoids, aluiminides and interfaces

Abstract:
Molecular dynamics simulations were performed in order to characterize the local lattice structure in the vicinity of the interfaces between nanosized B2 intermetallic aluminide dispersoids and aluminum matrices. The dispersoid materials selected for the present study are NiAl and FeAl. The former was one of the materials included in our previous study which concluded that the formation of a stable B2 type dispersoid in an FCC matrix is not a simple task [1]. The interest of the latter is that it is nonmagnetic when perfectly ordered but becomes ferromagnetic when the lattice is disordered making it a good candidate for local damage indicating material [2]. In the present study, we modified the initial configuration of the system and constructed stable B2 dispersoids in aluminum matrices. The results for both systems, i. e., NiAl and FeAl embedded in aluminum matrices, show that the presence of misfit dislocations at the interface is necessary to form stable nanocomposite systems due to a substantial difference in the lattice constants of the matrix and the dispersoid. Besides having misfit dislocations, lattice distortion is present in the interface region when the dispersoid lattice is oriented parallel to that of matrix. Misfit dislocations are present but the matrix lattices in the interface region are seen noticeably disordered when the dispersoid lattice is rotated with respect to that of matrix for both systems. Regardless of the relative orientation of the dispersoid with respect to that of matrix, the density of matrix atom is slightly lower in the interface region at room temperature. Elevated temperatures, however, are seen to equalize the densities of matrix atoms in the interface and bulk regions. Therefore, the results of the present study fully describe the entire processes of composite fabrication, i. e., compaction of mixture between dispersoid and matrix materials, and densification of the compacts by sintering. No major noticeable difference was found in the results of the two composite systems investigated in the present study. The next steps of simulations will investigate the effects of deformation and fracture of these composites on the lattice structures of dispsersoids which are in parallel with the experimental study that is currently in progress. [1]. Min Namkung, Sun M. Paik, and Buzz Wincheski, On-line Proc. International Conference on Computational Nanoscience (San Juan, Puerto Rico, April 22 – 25, 2002) [2]. A. Arrott, Private communication

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