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Abstract
Processing multiphase composite materials using the powder metallurgy approach is rapidly becoming an important fabrication route for advanced materials production. Powder metallurgy methods have expanded in recent years to include net-shape fabrication of tungsten-copper (W-Cu) composites. Fabrication of W-Cu net-shapes has become an important issue in recent years due to the unique properties of W-Cu composites which make them suitable for a wide variety of applications. However, because of the mutual insolubility of tungsten and copper and the high contact angle of liquid copper on tungsten, W- Cu system is difficult to sinter to high density.
The processing technique used to prepare W-Cu composite powders affects on the homogeneity and properties of sintered materials produced from these powders. In the present work, W-20 and 30wt.% Cu composite powders were prepared by electroless coating technique. The coated composite powders were consolidated by a liquid phase sintering in vacuum furnace for 1 hr at two sintering temperatures, namely; 1250 and 1400 °C. For comparison, second series of samples were prepared by ball milling process using a mixture of W and Cu powders (uncoated powders) and were consolidated under the same sintering conditions as those of coated powders. The prepared powders and sintered materials were investigated using scanning and optical microscopy. Properties such as density, electrical resistivity, coefficient of thermal expansion (CTE), hardness, compressive strength, and wear properties were measured. The results showed that sintered composites fabricated from uncoated powders exhibited inhomogeneous structure due to the formation of large globules of copper and W agglomerates, while the structure of coated tungsten composites reveal the existence of copper within the tungsten grains, forming uniform interconnected structure. In contrast to composites made from uncoated powders, the Cu coated W sintered composites exhibit higher relative densities. The coated composites achieved a density of 95.21% and 98.6% of theoretical density for both (W-20wt.%Cu) and (W-30wt.%Cu), respectively. The electrical resistivity and CTE of the sintered coated composites showed lower values than those of the uncoated composites, while the hardness, compressive strength, and
wear resistance of the coated composites exhibited higher values.
Keywords: W-Cu composites, Liquid phase sintering, Chemical coating, Powder metallurgy.