Prealloyed (PA) and premixed (PM) W-brass with the composition of 60 wt% W, 1 wt% Ni and 39 wt% brass was sintered at the temperature of 800˚C, 920˚C and 1000˚C each. As a result of difficulties in the densification of W-Cu and W-Cu alloys, mechanical alloying (MA) and activated sintering were combined. The powders were mechanically alloyed for 13 hours to produce nanosized W grains embedded in brass. The microstructure and properties of these composites with increase in sintering temperature has been studied. Both prealloyed and premixed composites sintered at 800˚C (solid state sintering) and 920˚C (sub-solidus state sintering) have lower sintered densities and hardness. The densification rate in the premixed composites was observed to be higher than that of the prealloyed composites. Their densification and properties increased with the increase in the sintering temperature. Premixed composite sintered at 1000˚C had 91.0% sintered density, 180 Hv microhardness against 76.0% and 133 Hv respectively for prealloyed composite at the same temperature. The values of electrical conductivity in both prealloyed and premixed composites increased with increase in temperature.
The effects of 1% tin (Sn) addition on the densification of pre-alloyed and pre-mixed W-brass composites were carried out. The green compacts were produced with the pressure of 350MPa and sintered at the temperature of 800°C, 920°C and 1000°C. The Sn addition is aimed at inhibiting the dezincification (selective removal of zinc from an alloy) of the brass component by the elimination of pores and enhances densification. The hardness of the composites increased with increase in temperature, the densification was low at both temperatures while the electrical conductivity remains constant as a result of constant composition in both pre-alloyed and pre-mixed composites. The microstructures revealed pores, which might be as a result of zinc evaporation.
The problem of lead poisoning resulting from the use of lead shot in hunting waterbirds and shooting sports has led to the partial ban, voluntary restriction and complete ban of lead shot in some countries. The ban resulted in the alternatives like copper shot, tungsten-tin shot, bismuth-tin, steel shot, etc. These alternatives are still expensive and other possible alternatives have not been explored up to date. There is therefore need to ban lead shot world-wide and step up research into the alternatives (green shot).
In this study, the effect of composition on solid state sintering of tungsten-brass was carried out. The densification of W-Cu has been a difficult problem to the materials engineers. However, the densification behaviour of tungsten-brass in the solid and liquid state is still not known. Tungsten-brass with the composition of 50W-brass, 60W-brass, 70W-brass and 80W-brass were sintered in a horizontal tube furnace under pure hydrogen environment at the temperature of 900°C and the relative sintered density, hardness, electrical conductivity and microstructural characterization was carried out. The relative sintered density and the electrical conductivity increase with the increase in the volume fraction of the matrix (brass) while the hardness decreases with the increase in the volume fraction of brass. The sample with the lowest volume fraction of W has the highest relative sintered density (71%) while the one with the highest volume fraction of W has the lowest relative sintered density (66%). The microstructure of the samples was not homogeneous due to mutual immiscibility between W and brass and lack of capillary force to enhance rearrangement and distribution of W and brass. It is obvious from the results that solid state sintering cannot give full densification of tungsten-brass composites.
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