Synthesis and characterization of particle-reinforced Ni/Al 2 O 3 nanocomposites
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C.L. Chien Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218
P.C. Searson and R.C. Cammarata Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (Received 5 February 2002; accepted 18 March 2002)
Nanocomposite Ni/Al2O3 films were electrodeposited from a suspension of Al2O3 nanoparticles in aqueous nickel sulfamate solution. The volume fraction of particles incorporated increased with electrode rotation rate and decreased with deposition current density. The composition, microstructure, hardness, and magnetic properties of these nanocomposite films were characterized. The mechanical strengthening due to particle dispersion in the films was interpreted by considering an Orowan dislocation bowing mechanism. The coercivity of the films increased with increasing particle concentration in the film. The saturation magnetization showed a weak dependence on particle concentration.
I. INTRODUCTION
The addition of nanometer-sized particles to a host matrix can be used to modify the properties of the matrix material. For properties that depend on the particle spacing, such as magnetic1– 4 and mechanical5–9 properties, deviations from bulk properties can often be obtained at relatively low particle volume fractions. The fabrication of nanocomposites provides a method for synthesizing materials with properties tailored for specific applications. The fabrication of nanocomposite thin films can be achieved by codeposition of nanometer-sized particles during electrodeposition of the matrix material. Since materials that can be electrodeposited include metals, alloys, oxides, semiconductors, and electrically conducting polymers, this approach can be used to synthesize a wide range of nanocomposite materials. Applications include wear-resistant coatings,10–12 corrosion-resistant coatings,13 self-lubricating films,14 and thermally graded structures.15,16 The strengthening of the nanocomposites due to particle incorporation was characterized by microhardness measurements. The nanocomposites displayed significant hardness enhancements relative to single-phase
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J. Mater. Res., Vol. 17, No. 6, Jun 2002 Downloaded: 07 Jan 2015
nickel films. The hardness enhancement of the nanocomposite films can be attributed to both a rule of mixture effect as well as a dislocation pinning effect. The magnetic properties of the Ni/Al2O3 composites were also characterized. The magnetic moment of the nickel matrix decreased slightly due to the presence of the particles, and the magnetic coercivity increased as a function of particle density in the films. This is attributed to magnetic domain wall pinning by the Al2O3 nanoparticles. II. EXPERIMENTAL
Ni/Al2O3 composite films were electrodeposited from a suspension of Al2O3 nanoparticles (300 or 50 nm in diameter, Buehler Ltd.) in an aqueous nickel sulfamate solution. The compositi
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