Electroforming of oxide-nanoparticle-reinforced copper-matrix composite
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Yasuhiro Sakamoto Research Organization for the 21st Century, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
Hiroyuki Inoue and Akihiro Iwase Department of Materials Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
Naoya Masahashi Kansai Center, Institute for Materials Research, Tohoku University, Sakai, Osaka 599-8531, Japan (Received 9 June 2014; accepted 12 November 2014)
A method based on the electroforming technique has been proposed for the fabrication of nanoparticle-reinforced copper-matrix composites using an electrolyte of copper sulfate–sulfuric acid solution containing 1 cm3/L of the nanoparticles without surfactants. Of the tested nanoparticles such as Al2O3, SiO2, TiO2, ZrO2, and CeO2, whose sizes ranged from 10 to 30 nm, only TiO2 nanoparticles were successfully embedded in the copper matrix during electroforming, owing to their positive charge in the electrolyte solution. It should be noted that there was very little contamination in the copper matrix, because surfactants were absent during electroforming. Therefore, the electrical conductivity of the specimen that was electroformed in the electrolytes with TiO2 nanoparticles was not significantly different from that of pure copper. Nevertheless, the hardness, yield, and ultimate tensile strength were significantly improved by a small amount (0.3 mass%) of TiO2 nanoparticles primarily because of strengthening by Orowan mechanics. The electroforming process is thus a promising means to prepare copper-matrix composites with an excellent balance of electrical conductivity and mechanical strengths.
I. INTRODUCTION
The use of copper in power-supply interconnections such as electric cables and connectors requires not only excellent electrical conductivity but also good mechanical properties. The mechanical properties of soft copper are typically improved through alloying with metallic elements and thermomechanical processing, as this leads to solid-solution and age-precipitation strengthening. However, even just a small amount of solid-solution metal alloying significantly increases the electrical resistivity of copper.1–3 There is, therefore, a need for new techniques and processes to improve the mechanical properties of copper without degrading its electrical conductivity. An attractive solution to this problem lies in pure copper-based composites that are strengthened by a fine dispersion of hard and inert particles. Since the copper matrix retains essentially the same electrical conductivity as that of the pure metal, the decrease in conductivity of the composite is limited to just a few percent by virtue of the Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.401 J. Mater. Res., Vol. 30, No. 4, Feb 28, 2015
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small volume fraction of added particles. Moreover, the mechanical properties are enhanced by the hard nanoparticles, ideally measuring several tens of nanometers in diameter
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