Mechanical Alloying Effects in Ball-Milled Tungsten-Copper (W-Cu) Composites

Abstract

Fine-grained, high-density (97%+ of theoretical density [TD]), 80 tungsten-20 copper weight-percent (80W-20Cu [58W-42Cu atomic-percent]) composites have been prepared using nonconventional alloying techniques. The W and Cu precursor powders were combined by high-energy ball milling in air. A second set of W+Cu mixtures was prepared in hexane to reduce contamination of the powders. The mechanically alloyed W+Cu powder mixtures were then coldpressed into green compacts and sintered at 1,250 °C. The effects of varying the milling medium and milling time were examined with density measurements. Longer milling increased product densities with a concomitant order-of-magnitude decrease in grain size; air was found to be a more effective medium than hexane. Residual impurities were identified with energy-dispersive x-ray spectroscopy (EDS), and their effects on sample properties were evaluated with microhardness measurements. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses demonstrated that the as-milled W-Cu alloy structures were metastable, decomposing into the starting W and Cu components upon heating at or above 450 °C. AcknowledgmentsThe authors gratefully note the contributions of Mr. Daniel Snoha for his careful review of the manuscript and his comments regarding the deterrnination and sources of baU-milling-induced lattice strain. m INTENTIONALLY LEFT BLANK. IV

The Effects of Composition on Solid State Sintering of Tungsten-Brass Composites

“…This is due to mutual insolubility or negligible solubility of copper and tungsten [10-11, 3, 4], in both solid and liquid states. This leads to lack of solution-precipitation, which causes restrictions in achieving full density in W-Cu systems [12][13]. The W-Cu phase diagram shows that the two metals are completely immiscible in both liquid and solid state [14].…”