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Rhenium alloys exhibit a unique combination of chemical, physical, and mechanical properties that makes them attractive for a variety of applications. Herein, we present atomic-scale structural and atomic part-per-million level three-dimensional (3D) chemical characterization of a Re-Ni coating, combining aberration-corrected scanning transmission electron microscopy (STEM) and atom-probe tomography (APT). A unique combination of a columnar and multilayer structure is formed by singlebath dc-electroplating and is reported here for the first time. Alternating thicker Re-rich and thinner Ni-rich layers support a mechanism in which Ni acts as a reducing agent. The multilayers exhibit hetero-epitaxial growth resulting in high residual shear stresses that lead to formation of corrugated interfaces and an outer layer with mud-cracks. IntroductionRhenium (Re) is a refractory metal with a unique combination of chemical, physical, and mechanical properties that makes it attractive for high-temperature, catalytic, energy, electrical, biomedical, and other applications, in spite of its high cost. [1,2] Interest in electroless deposition [3,4] and electrodeposition [5][6][7][8][9][10][11][12][13][14][15][16] of Re and its alloys has recently emerged. Electroplating of pure Re yields poor deposition results. The addition of salts of the iron-group metals (Ni, Fe, and Co) to the plating bath improves, however, the coating dramatically, allowing deposition of thick layers of the

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Rhenium (Re) is a promising refractory metal that has unique combination of properties. Compared to other refractory metals, Re has the greatest tensile strength and excellent creep resistance over a wide range of temperatures (up to ~2000°C). Pure Re does not have a ductile-to-brittle transition temperature. Moreover, unlike other refractory metals, Re does not form stable carbides. Thus, it is potentially attractive coating on different carbon material. Electroless plating is relatively simple method for generating thin metallic and metal alloy films on conductive and nonconductive surfaces. The ability of electroless plating to coat the inside of holes and recesses without using external current source or vacuum technology equipment makes it an ideal coating technology for many applications. In this study, high Re content (more than 65 at.%) Re-Co coatings were prepared by electroless deposition. The pH dependence of process kinetics, film microstructure and composition was studied. The obtained films were characterized by HRSEM, AFM, XPS and XRD methods. It was shown that as deposited films have amorphous structures with microhardness value of 600 - 620 HV. Crystalline hcp structure of Re-Co coating was detected only after annealing at 550 oC. Thin coatings (250-500 nm) have demonstrated good corrosion protection of copper in salt medium reducing corrosion current at list by one order of magnitude. The annealed deposits have shown improved mechanical and electrical properties. Such films exhibit ferromagnetism and could be applied in mobile magnetic components where soft-magnetic response combined with mechanical stability is required (MEMS devices).