Effects of wet and dry milling conditions on properties of mechanically alloyed and sintered W–C and W–B 4 C–C composites

Abstract

Tungsten based W–1C and W–2B₄C–1C (wt-%) powders synthesised by mechanical alloying (MA) for milling durations of 10, 20 and 30 h, in wet (ethanol) and dry conditions, were characterised. X-ray fluorescence spectroscopy investigations revealed Co contamination which increased with increasing milling time during wet milling. X-ray diffraction investigations revealed the presence of W and WC phases in all powders, Co₃C intermetallic in the wet milled W–1C powders and W₂B intermetallic phase in both wet and dry milled W–2B₄C–1C powders. As blended and MA processed powders were consolidated into green compacts by uniaxial cold pressing at 500 MPa and solid phase sintered at 1680°C under hydrogen and argon atmospheres for 1 h. X-ray diffraction investigations revealed the presence of W₂C intermetallic phase in sintered composites produced from both wet and dry milled W–1C powders and the W₂B intermetallic phase in sintered material from the wet milled W–2B₄C–1C powder. Sintered composites from wet milled powders showed relative densities >91%, with the maximum density of 99·5% measured for the sintered 30 h wet milled W–2B₄C–1C composites. Microhardness values for the wet milled W–1C and W–2B₄C–1C composites were 2–2·5 times higher than those for dry milled composite powders. A maximum hardness value of 23·7±2·1 GPa was measured for the sintered W–2B₄C–1C composite wet milled for 20 h.