Metal/Metal Nanocrystalline Cellular Composites
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Metal/Metal Nanocrystalline Cellular Composites Brandon A. Bouwhuis, Eral Bele, and Glenn D. Hibbard Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, ON, M5S 3E4, Canada
ABSTRACT Nanocrystalline electrodeposition can be used to reinforce conventional metallic microtruss materials and conventional metal foams, creating new types of metal/metal cellular hybrids in which the mechanical performance is controlled by an interconnected network of nanocrystalline tubes. This approach takes advantage of the large strength increase that can be obtained by grain size reduction to the nm-scale and the fact that the electrodeposited material is optimally positioned away from the neutral bending axis of the composite cellular struts or ligaments. This article presents an overview of the potential for structural reinforcement of bending-dominated and stretching-dominated cellular architectures by nanocrystalline electrodeposition.
INTRODUCTION New regions of material property space can be accessed by combining microstructural design at the nm-scale with architectural design at the µm- or mm-scale. In the first case, large strength increases associated with grain size reduction to below 50 nm have driven extensive research efforts into the development of nanocrystalline materials [e.g. 1-3]. For many potential structural applications, however, the density of a nanocrystalline material is just as important as its strength. In fact, reducing the density is more important than increasing the strength for certain weight specific materials performance indices, and it is especially critical for applying structural nanomaterials in the aerospace and automotive sectors. We have developed a new type of structural nanomaterial wherein the effective density of the parent metal is reduced by more than an order of magnitude by incorporating an internal periodic cellular architecture of open space. In one example a low density cellular nanocrystalline material was created by electroforming nanocrystalline Ni around a rapid-prototyped acrylic photopolymer micro-truss [4]. Micro-truss materials have periodic cellular architectures that are specifically designed to undergo stretching-dominated deformation as opposed to the bending-dominated deformation in conventional open cell metal foams [5-7]. This new cellular nanocrystalline hybrid material combined the structural efficiency of micro-truss architectures with the ultra-high strength that can be achieved by grain size reduction to the nm-scale. Although it played a critical role as a cathode support during the initial stages of nanocrystalline electrodeposition, the polymer core did not contribute significantly to the inelastic buckling resistance of the composite metal/polymer struts and it may therefore be desirable to remove it post deposition by means of chemical dissolution or thermal decomposition [4]. Nanocrystalline electrodeposition can also be used to reinforce cellular metals, creating new types of cellular composites
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