CONICET | Buscador de Institutos y Recursos Humanos

Surface modification by coatings has become an essential step to improve the surface properties of materials. Coatings can protect a substrate by providing a barrier between the metal and its environment. The nanostructured coatings have long been recognized to exhibit remarkable and technologically attractive properties due to their extremely fine microstructure. Nickel and tungsten (Ni-W) alloys are particularly interesting because they exhibit good corrosion resistance in different aqueous media, high hardness and ductility, catalytic and anisotropic magnetic properties. In this work nanocrystalline Ni-W alloys were obtained galvanostatically by pulse electroplating, this method was selected because it allows controlling the structure, morphology and size of the grains and chemical composition in the electrodeposits through the correct adjustment of the system variables (pH, concentration, temperature, pulse frequency). Here we have done an extensive characterization of an electrodeposited Ni-W coating by using surface techniques such as Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS), and bulk techniques such as energy dispersive X-ray Analysis (EDX), X-ray Diffraction (XRD), X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS), and High Resolution Transmission Electron Microscopy (HRTEM).The surface of the coating consists of 10-50 nm crystals forming a cauliflower-like structure protected by a mixture of nickel and tungsten oxides. The cauliflower structure is preserved into the bulk coating that exhibits an average composition 70 at% Ni-30 at% W. Two different phases are observed in the bulk structure: a W-rich amorphous phase (40 %) and a Ni-rich crystalline phase (60 %). Results from this extensive characterization shed light on some controversial points related to the chemical composition and structure of this interesting system