Morphology studies of a W/Cu alloy synthesized by hydrogen reduction
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Because of the applications for W/Cu composite materials in high technology, the advantages of synthesizing this alloy by the hydrogen reduction route were investigated, with special attention to the properties of the product that was formed. Kinetic studies of reduction indicated that the mechanism changes significantly at 923 K, and the product had unusual properties. In the present work, morphological studies of the W/Cu alloy with 20 wt% Cu, produced at 923 K, were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W, forming a metastable solid solution in the nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence of two phases, pure W and pure Cu. The SEM results were in agreement with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes were about 20 nm. The structure of the W/Cu alloy produced in the present work was compared with those for pure Cu, produced from Cu2O produced by hydrogen reduction under similar conditions. This indicated that the presence of W hinders the coalescence of Cu particles, and the alloy retains its nano-grain structure. The present results open up an interesting process route toward the production of intermetallic phases and composite materials under optimized conditions.
I. INTRODUCTION
The demands for materials with unique properties are increasing in a number of high-technology areas, for example in electronics. Processing multiphase composite materials using the powder metallurgy approach is rapidly becoming an important fabrication route for advanced materials production. A promising process route for the production of alloys in powder form is hydrogen reduction of metal oxides. Because metal powders can be produced from the respective oxides by reduction using a suitable gaseous reductant, the alloy formation can be achieved at fairly low temperatures, resulting in fine-grained alloys or materialmatrix composites. In the present work, a hydrogen reduction route was used, and it represents a direct production of the W/Cu material of unusual morphologies and with uniform composition. This route offers a unique advantage as the
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0181 J. Mater. Res., Vol. 21, No. 6, Jun 2006
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materials produced under well-defined conditions have enough active centers to achieve good chemical bonding between the dispersed material and the matrix during the production process. As the number of unit processes is 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. Composite materials of W
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