Three Dimensional Digital Alloying with Reactive Metal Inks

3D printing of multifunctional components using two or more materials is a rapidly growing area of research. Metallic alloy inks have been used with various 3D printing techniques to create functional components such as antennas, inductors, resistors, and biocompatible implants. Most of these printing techniques use premixed metallic alloy inks or nanoalloy particles with a fixed composition to fabricate the functional part. Since the properties of alloys vary with changes in the elemental composition, a printing process which could digitally dispense alloy inks having specific desired compositions would enable different functionalities and be highly desirable. Using the binary copper-nickel system as an example, the formation of alloy with metal precursor inks is presented. Since copper and nickel both have a face centered cubic (FCC) structure and show complete miscibility in each other, formation of their nanoalloy is, in theory, relatively easy. By printing metal precursor inks rather than nanoparticle suspensions, problems associated with the nanoparticle inks such as ink stability and nozzle clogging can be avoided. Copper and nickel precursor inks were formulated having rheological properties suitable for inkjet printing. Reduction of metal inks was studied under various conditions. The sintered metal and alloy structures were characterized using thermal analysis, infrared spectroscopy, energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction. Nickel, a ferromagnetic metal, showed novel microstructures such as aligned nanowires and nanowire grids when reduced in the presence of a magnetic field. These microstructures had enhanced anisotropic electrical and magnetic properties along the direction of the nanowire. The reduction of combined ink solutions (copper and nickel) showed formation of a two phase with copper as one phase and a nickel rich alloy as other. These structures demonstrated no change in electrical resistivity when exposed to an oxidation rich environment. To achieve a homogeneous alloy formation, the copper phase and the nickel rich phase were diffused together at high temperatures. Copper nickel alloy inks with ratios Cu30Ni70, Cu50Ni50, and Cu70Ni30 were formulated and reduced at 230 °C and later high temperature diffusion was achieved at 800 °C. The lattice parameter of the alloy phase for the inks with ratio Cu30Ni70 was 3.5533Å, Cu50Ni50 was 3.5658 Å, and Cu70Ni30 was 3.5921 Å. Using Vegard’s law, the composition of the alloy phases for the three samples were estimated to be Cu32Ni68, Cu46Ni54, and Cu75Ni25. This formation of the desired alloy composition can open the door to numerous applications in biomedical and electronics sectors, among others