Growth study of nanocrystalline Ni and Ni 3 Al using molecular dynamics
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Growth study of nanocrystalline Ni and Ni3Al using molecular dynamics Z. Y. Zhang1, X. K. Meng1, J. Wang2, Hanchen Huang2, and X.-Y. Liu1,3 1 Department of Materials Science and Engineering, Nanjing University, Nanjing, 210093, China, People's Republic of 2 Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY, 12180 3 Ames Laboratory, Iowa State University, Ames, IA, 50011 ABSTRACT The growth of nanocrystalline materials has received much attention recently due to its importance in nanocrystalline thin film properties and fabrications. Research studies of this subject have so far focused on the face-centered-cubic metals. Two mechanisms, grain-rotation induced grain coalescence and curvature-driven grain-boundary migration are considered as the dominant mechanisms in the nanograin growth. In this work, we use molecular dynamics method to simulate the growth of Ni and Ni3Al alloy. We find the above mechanisms can describe the growth behavior well. A detailed comparison of the nanograin growth between the two systems is discussed in terms of grain rotation and grain sliding. We also study the temperature effect and the size effect in the nanograin growth. The tendency of twinning in the nanograin growth is discussed. INTRODUCTION Recently, the growth of nanocrystalline materials has been a focus of investigation because it directly influences the properties and application of nanocrystalline materials. The studies on grain growth have mainly focused on the face-centered-cubic (fcc) metals. Up till now, many simulations of grain growth have revealed that in addition to the conventional mechanism of grain growth by curvature-driven grain-boundary (GB) migration, grain rotations induced grain coalescence plays an equally important role [1]. These two mechanisms can trigger each other and the interplay between them leads to grain growth. In this paper, we use molecular dynamics (MD) simulations to study the mechanism of grain growth in nanocrystalline Ni metal and Ni3Al alloy. We focus our study mainly on two aspects, i.e., temperature effect and size effect. To the authors’ knowledge, modeling study of alloy nanocrystalline growth has not been done. Here we pay more attention to the research results of Ni3Al alloy, comparing the nanograin growth mechanism with that of Ni in terms of grain rotation and grain sliding. METHOD We use embedded atom method (EAM) [2] to describe the atomic interactions. The Voter and Chen EAM potential [3] is used in our simulations. This potential has been used successfully before to study Ni and Ni3Al alloy properties including those of grain-boundaries [3]. In the present study, the initial microstructures are generated using a Voronoi construction [4]. A set of grain centres are chosen at random. And the part of space closer to a given centre than to any other centre is filled with atoms in an fcc lattice with a randomly selected crystallographic
orientation. For the sake of simplicity and clarity, eight or fewer nanograins
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