The wire and powder fed process makes metal composite printing feasible however, the printed part has limited dimensional accuracy and high surface roughness. 17 demonstrated the deposition of various metal carbides, such as titanium carbide, tungsten carbide, and silicon carbide into a titanium alloy matrix via a process whereby titanium wires and the metal carbide powder are fed into a melt pool formed by a laser. In the vast majority of these cases only a single material is used however there are current research efforts to expand metal 3D printing to include multi-material capabilities. Here, the main technologies include: direct metal laser sintering 13, electron beam melting 14, directed energy deposition 15 and FDM using a metal filled polymer filament 16. However, there has been increased uptake of metal based AM as the technology transitions from being primarily used as a prototyping tool to making end products 1. ![]() Early applications of AM focused on the use of polymers due to the ease of consolidation, either through a photo-polymerisation (stereolithography) 11 or thermal process (fused deposition modelling (FDM)) 12. ![]() Due to the design flexibility that AM offers, there has been considerable industrial uptake in fields such as: aerospace 2, automotive 3, medical 4, 5, 6 and energy 7, 8, 9, 10 to name but a few. The potential of this novel low-cost multi-metal 3D printing approach is demonstrated with the thermal actuation of an electrical circuit and a range of self-assembling structures.Īdditive manufacturing (AM), which is also commonly known as 3D printing, fabricates complex 3D geometries by sequentially joining material together layer-by-layer 1. Electrical conductivity measurements show that the bimetallic structures have a conductivity between those of nanocrystalline copper (5.41 × 10 6 S.m −1) and nickel (8.2 × 10 5 S.m −1). Analysis of the thermo-mechanical properties of the printed strips shows that mechanical deformations can be generated in Cu-Ni strips at temperatures up to 300 ☌ which is due to the thermal expansion coefficient mismatch generating internal stresses in the printed structures. Scanning electron microscopy, X-ray computed tomography and energy dispersive X-ray spectroscopy shows that bimetallic structures with a tightly bound interface can be created, however convex cross sections are created due to uneven current density. Improvements in deposition speed (34% (Cu)–85% (Ni)) are demonstrated with an electrospun nanofibre nib compared to a sponge based approach as the medium for providing hydrostatic back pressure to balance surface tension in order to form a electrolyte meniscus stable. The concept is demonstrated through a meniscus confined electrochemical 3D printing approach with a multi-print head design with nickel and copper used as exemplar systems but this is transferable to other deposition solutions. Here, we present a novel multi-metal electrochemical 3D printer which is able to fabricate bimetallic geometries and through the selective deposition of different metals, temperature responsive behaviour can thus be programmed into the printed structure. ![]() However, the vast majority of 4D printing approaches use polymer based materials, which limits the operational temperature. 4D printing has the potential to create complex 3D geometries which are able to react to environmental stimuli opening new design possibilities.
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