Electrochemical Deposition of FeCo Alloys and FeCo/TiO 2 Nanocomposites
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Electrochemical Deposition of FeCo Alloys and FeCo/TiO2 Nanocomposites I. Shaoa, P. M. Vereeckena, R. C. Cammarataa, P. C. Searsona, and C. L. Chienb a
Department of Materials Science and Engineering The Johns Hopkins University, Baltimore, MD 21218 b Department of Physics and Astronomy The Johns Hopkins University, Baltimore, MD 21218 ABSTRACT Electrochemical deposition of FeCo alloys with 1:1 atomic ratio has proved difficult due to cracking from high stress. By using a sulfamate electrolyte and optimizing other deposition parameters, we successfully electrodeposited high quality FeCo films of 20-25 mm in thickness and 7 mm in diameter. Using a suspension of hard oxide nanoparticles (25 nm TiO2) in the electrolyte, we produced oxide-dispersion-strengthened FeCo/TiO2 nanocomposite films with large grains. Enhanced strength was observed from these nanocomposites relative to pure FeCo alloys as determined from Knoop hardness measurements. In order to further improve the ductility of the alloys, vanadium has been codeposited with FeCo. Some preliminary results of FeCoV alloy deposition are reported. INTRODUCTION Iron-cobalt alloys near the equiatomic composition have superior soft magnetic properties with a very high saturation magnetization (24 kG), high permeability at high magnetic flux density, and low D.C. coercivity. In the field of micro-devices, such as hard disk drives, microactuators and micro-inductors, thin film deposition processes have to be developed to generate desirable magnetic materials. Electrochemical deposition is an important processing technology for microfabrication due to its low cost, high yield, low energy requirements, and capability for generating high-aspect-ratio features. However, electrochemical deposition of FeCo alloys has been problematic over the years. Bulk FeCo alloys are primarily used in the manufacture of rotor and stator laminations in motors and generators for aircraft power generation applications. The inferior mechanical properties of these alloys, including low yield strength, low creep resistance, and poor ductility, inhibit many applications. Oxide dispersion strengthening can improve both yield strength and creep resistance. We have utilized electrochemical codeposition from an electrolyte containing a suspension of TiO2 particles (25 nm in diameter) to produce oxide dispersion strengthened FeCo/TiO2 nanocomposites. Large grain sizes of the order of 10 mm were observed for all these FeCo/TiO2 films. Composition, hardness and magnetic properties were tested for these films. EXPERIMENTAL FeCo alloy films were deposited from an aqueous sulfamate solution of 0.75 M cobalt sulfamate (IMC Americhem) + 0.5 M iron(II) sulfamate (Strem Chemicals) + 0.4 M boric acid + 0.25 M sodium chloride + 0.025 M sodium borate + 0.025 M vitamin C + 1 g/l saccharine + 0.5 vol.% aerosol DPOS 45 surfactant (Cytec Industries) + 0.4 mM ammonium metavanadate. A small amount of vanadium was added to enhance the ductility of the alloy. Although no vanadium was detected in the deposited films (the
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