Fabrication and deformation of aluminum-manganese microsandwich structure
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The combination of low areal density, high flexural rigidity, and open architecture makes metallic microsandwiching a promising candidate for structural frameworks in small-scale multifunctional devices. We demonstrate a one-step electrodeposition procedure to synthesize an aluminum–manganese (Al–Mn) microsandwich using a porous polycarbonate (PC) membrane template from room-temperature ionic liquid. Mn was added to refine the microstructure and increase the hardness of Al. A cyclic voltammogram study shows Mn codeposit with Al in an acidic chloroaluminate electrolyte. Increasing the MnCl2 concentration in the electrolyte from 0.05 to 0.25 M promoted a crystalline to amorphous phase transition of the deposited structures. Finally, mechanical properties and damage resistance of the microsandwiches were evaluated using nano- and micro-indentation tests as well as finite element methods.
I. INTRODUCTION
Microarchitectured materials including microlattices and microsandwiches have emerged recently as promising structural and functional frameworks for small-scale multifunctional devices.1–3 Their open architecture not only leads to low areal density and high damage tolerance, but also provides channels for heat/fluid flow, which is critical to multifunctional devices such as highcapacity batteries, insect-like robots, and microair vehicles.4–7 A sandwich structure exhibits higher bending rigidity than lattices by effectively redistributing the mass to the outer surfaces (instead of the core), similar to natural cellular materials found in insects and plants.1,8 The stiff face sheets carry bending and in-plane stresses during deformation, while the low-density core bears transverse shear stresses.9 Such superior property has led to extensive study on the structural design of sandwiches, mostly with core size above tens of millimeters. The damage tolerance of sandwiches is highly dependent on the density, strength, and geometry of the core.10 It was found that the periodic sandwich core can be optimized to sustain loads at much lower relative densities than stochastic foams.11 Further improvement of mechanical properties may also be achieved by hybridizing the core material.12 Existing fabrication procedures of large-scale sandwich structures typically involve welding or adhesive bonding of the face sheets and the core. These techniques become challenging as core size decreases to the nano- to
micro-meter scale. Recently, there have been several successful attempts to create microlattice and microsandwich structures from polymers,2 ceramics,13 and metals.7 Kolodziejska et al.2 demonstrated the synthesis of an ultrathin lightweight polymer micosandwich by using a self-propagating photopolymer waveguide. Meza et al.13 developed energy-absorbing ceramic microlattices with high compression ductility by combing photon lithography, atomic layer deposition, focused ion beam microscopy (FIB), and oxygen plasma etching. Recently, the same group7 combined the template fabrication procedure with aqueous electrodeposition (ED) to produce
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