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MATERIALS RESEARCH

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Nanocrystalline nickel and nickel-copper alloys: Synthesis, characterization, and thermal stability H. Natter, M. Schmelzer, and R. Hempelmanna) Physikalische Chemie, Universit¨at des Saarlandes, Im Stadtwald, D-66123 Saarbr¨ucken, Germany (Received 24 April 1997; accepted 6 October 1997)

Pulsed electrodeposition is a simple, yet versatile method for the production of nanostructured metals. For n-nickel we determine the influence of the physical and chemical deposition parameters on the nanostructure of the deposits and demonstrate that the grain size can be tuned to values between 13 and 93 nm, with rather narrow grain size distribution. The thermal stability of our n-nickel as studied by x-ray diffraction and differential thermal analysispexhibits no detectable grain growth up to temperatures of about 380 K and an initial t behavior at 503 K followed by a regime of anomalous grain growth. For nanocrystalline Ni12x Cux (Monel-metalTM ) we demonstrate that alloy formation occurs at room temperature and that both chemical composition and grain size can be controlled by the pulse parameters and by appropriate organic additives.

I. INTRODUCTION

Since the introduction of nanostructured materials by Gleiter1 and Grandqvist and Buhrman,2 the most common preparation techniques for metals and alloys are inert gas condensation (IGC)3,4 and ball milling (BM).5 The disadvantages of IGC are small sample amounts, large sample porosity, and a high cost of the preparation equipment. BM produces samples with a large amount of elastic lattice distortion and a high impurity content (abrasion from the vial set). The profitable properties of some nanostructured materials, e.g., enhanced hardness of n-Pd6 and toughness of n-WC/Co,7 the softmagnetic properties of FINEMETTM ,8 and the corrosion resistance of n-Ni9 promise industrial applications. Actually, n-nickel has already been commercially applied for the in situ repair of nuclear steam generators in the so-called ElectrosleeveTM process.10,11 Generally for industrial applications cost-efficient, versatile, and reliable large scale preparation techniques are required, such as pulsed electrodeposition (PED). This technique is not new. Already in 1837, by means of electrolysis with a modulated current, de la Rive12 prepared deposits with special properties. In 1893, using electrolysis with rectangular current pulses, Coehn13 produced Zn coatings which exhibit enhanced brightness and hardness. In 1896 the pulse reverse technique was introduced by Rosing.14 Over the last 15 years a kind of renaissance of the pulse plating techniques can be observed.15,16 Recently we have reported about n-Pd17 and n-Cu18 deposits prepared by pulsed electrodeposition, in particular with regard to the relation between nanostructure and deposition parameters. a)

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http://journals.cambridge.org

J. Mater. Res., Vol. 13, No. 5, May 1998

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Nanocrystalline Ni has electrochemically bee