Molecular Dynamics Simulations on Nanocomposites Formed by Intermetallic Dispersoids of L1 2 Type and Aluminum Matrices
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Molecular Dynamics Simulations on Nanocomposites Formed by Intermetallic Dispersoids of L12 Type and Aluminum Matrices Min Namkung, 1Sun Mok Paik, and Buzz Wincheski NASA Langley Research Center Hampton, VA 23681 1 Kangwon National University Chunchun, Korea ABSTRACT Molecular dynamics simulations were performed to characterize the lattice morphology in the region adjacent to the interfaces in nanocomposite systems of a Ni3Al dispersoid embedded in Al matrix (Ni3Al/Al) and an Al3Nb dispersoid embedded in aluminum matrix (Al3Nb/Al). A nearly perfect coherent interface is obtained in the Al3Nb/Al system with the lattice planes of dispersoid and matrix aligned parallel in all directions. The simulation results show the presence of the matrix atom-depleted regions near the dispersoid boundary for most cases. Detailed analysis revealed that certain sites immediately next to the dispersoid are energetically favored for the matrix atoms to occupy. The matrix atoms occupying these sites attract other atoms producing the depleted regions. In certain specific situations of Al3Nb/Al system, however, the wetting of a rotated dispersoid is overwhelmingly complete prompting the need of further study for better understanding. The order parameters of dispersoids calculated for Ni3Al in aluminum is nearly constant while that for Al3Nb in aluminum is rapidly decreasing function of temperature in the range of 300 to 1800K. INTRODUCTION Second phase particles that are mixed and uniformly distributed within a matrix are called dispersoids. By selecting appropriate type, size, morphology, and concentration of these dispersoids in a matrix, it may be possible to develop structural components that are capable of actively indicating their physical/chemical states and are optimized for best performance based on given application purpose. For example, the magnetic properties of Ni3Al particles can be affected by the local stress states that may be indicative of the changes in other material states. At the same time, when mixed with a substantial volume fraction, the small nearest neighbor distance between such densely populated dispersoids may prevent the dislocation loop formation while being highly resistant to cutting by dislocations [1]. The current series of investigation concentrates on the morphology of such composites to establish a foundation for systematic study on nanocomposite systems of damage indicating capabilities and prolonged service lives. Our previous study clearly showed that a Ni3Al dispersoid, which is coherent with the aluminum matrix, causes a substantial degree of local lattice distortion in the vicinity of matrix/dispersoid interface [2] that is known to enhance the strength of alloys [1]. An unresolved problem of the study was the appearance of lattice atom-depleted regions near the interface in the composite system with a rotated dispersoid and its origin was not well understood. Therefore, the purpose of the present study is to find ways of minimizing the
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regions of matrix atom depletion near
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