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I. INTRODUCTION

TUNGSTEN copper (W/Cu) composite materials are used today in a variety of applications where the thermal and electrical properties of copper, as well as the very low expansion characteristics of tungsten, can be advantageously combined. The combination of these two elements leads to the optimization of other alloy properties such as ductility, mechanical strength, corrosion, and wear resistance at elevated temperatures. Primary applications for W/Cu composite materials are electrical contacts and electrodes, welding and electroforging dies, heat sinks, and packaging materials. As both tungsten and copper, however, show an extremely limited solid solubility, only a few processes are known to be commercially successful.[1–4] The most common methods for the fabrication of W/Cu are the infiltration process, where liquid copper is filled in a cold-pressed porous tungsten skeleton, and liquid phase sintering of hot pressed blends of copper and tungsten powders.[5–12] In many studies, the mechanical alloying process have been used to synthesis W/Cu powders. Unfortunately, during this process, impurities introduced into the system from milling jars and balls after hours of milling, end up in the final W/Cu material. Even if mechanical alloying in many cases has produced nanocomposite powders, the process is time-consuming and has only been a success in small-scale productions.[9,13–15] The hydrogen reduction of metal oxides is a promising process route for composite materials and it represents a direct method for the production of metal composite powders with uniform composition. This route offers a unique advantage because the materials produced, under well-defined conditions, have enough active centers to achieve good chemU. TILLIANDER, Postdoctoral Student, R.E. AUNE, Associate Professor and Research Fellow, and S. SEETHARAMAN, Professor, are with Materials Process Science, Royal Institute of Technology (KTH), SE-10044 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted March 10, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS B

ical bonding between the dispersed material and the matrix during the production process itself. Because the numbers of unit processes are kept to a minimum and no environmentally dangerous effluence occurs in the process, the hydrogen reduction process offers a green route toward the production of alloy powders and intermetallics. The reduction route of composite materials has, over the years, been seriously investigated at the present laboratory at the Royal Institute of Technology (KTH, Stockholm). As a result, a number of transition metal intermetallics have been produced by the hydrogen reduction method. Basu et al.[16,17] have prepared various copper-tungsten oxide mixtures that could be precursors for the direct production of W/Cu powders of unusual morphologies for the ultimate manufacture of W/Cu electrical contact material. They have also presented results obtained on the kinetics of the reduction of copper tungstate in dry hydrogen at various te