Composition, Structure and Properties of Electroless Deposited Rhenium-Rich Re-Co Thin Films

Abstract

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).