Densification and structural change of mechanically alloyed W-Cu composites
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Fine-grained, high-density (97+ pct of theoretical density (TD)), 80W-20Cu wt pct (58W-42Cu at. pct) composites have been prepared using nonconventional alloying techniques. The W and Cu precursor powders were combined by a high-energy ball-milling procedure in air or hexane. The mechanically alloyed W+Cu powder mixtures were then cold pressed into green compacts and sintered at 1523 K. The milling medium and milling time were varied to increase product densities with a concomitant order-of-magnitude decrease in grain size. For densification, air was found to be a more effective medium than hexane. From microhardness measurements, it was concluded that the W-Cu alloys were dispersion and solution hardened, but were sensitive to entrapped residual impurities. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron micros-copy (SEM) analyses were used to demonstrate that the as-milled and sintered W-Cu alloy structures were metastable, decomposing into the starting W and Cu components upon heating at or above 723 K.
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