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 i...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.展开更多
Fabrication of full-density W-brass composites is very difficult to achieve because of evaporation of zinc, insolubility of W and brass and compacts expansion. In this study, to achieve full-density W-brass composites...Fabrication of full-density W-brass composites is very difficult to achieve because of evaporation of zinc, insolubility of W and brass and compacts expansion. In this study, to achieve full-density W-brass composites, mechanical alloying (MA) and activated sintering process were utilized. Mechanical coating of W with Ni using high energy planetary ball mill was carried out. The milling was divided into two stages: to alloy and modify the surface of W with Ni for enhanced activation. The microstructure of the milled powders and sintered compacts, elemental composition and phases present were studied by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) respectively. As-received powder compacts was also sintered under the same condition for comparison purpose. The effects of milling time on the microstructure, sinterability and the hardness of the composites were investigated. It was observed that the samples produced from 8 h milled powder had the highest relative sintered density (98% TD) and microhardness (234 Hv). On the other hand, the samples from the as-received powders expanded and had a relative sintered density of (67% TD) and microhardness as low as 24 Hv. The significance of this study is the possibility of producing W-brass composites as a cheaper alternative to W-Cu composites.展开更多
Intergranular stress corrosion cracking (ISCC) of α-brass in neutral Mattsson's solution was found to be controlled by an unusual 'W'-shaped galvanic cell whose cathode is the grain boundary oxide film (G...Intergranular stress corrosion cracking (ISCC) of α-brass in neutral Mattsson's solution was found to be controlled by an unusual 'W'-shaped galvanic cell whose cathode is the grain boundary oxide film (G.B.0. film) and surface film and the anode is fresh metal at the cracked tip on both sides of the G.B.0. film. Redox reactions involved in the cell have been proposed here. According to this mdel, initidtion of ISCC is caused by the rupturing of surface film along grain boundaries, thus forming a galvanic cell. Propagation of ISCC resulted from alternate advances of G.B.0. film and dissolution on both sides of G.B.0. film caused by the effect of electrochemical reaction. This work developed an effective approach to investigate the embrittlement process at the tip of the crack, by increasing the length of the embrittlement region through constant strain test and distinguishing the morphology and the nature of the corrosion products by optical microscopy and scanning electron microscopy (SEH).展开更多
文摘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.
文摘Fabrication of full-density W-brass composites is very difficult to achieve because of evaporation of zinc, insolubility of W and brass and compacts expansion. In this study, to achieve full-density W-brass composites, mechanical alloying (MA) and activated sintering process were utilized. Mechanical coating of W with Ni using high energy planetary ball mill was carried out. The milling was divided into two stages: to alloy and modify the surface of W with Ni for enhanced activation. The microstructure of the milled powders and sintered compacts, elemental composition and phases present were studied by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) respectively. As-received powder compacts was also sintered under the same condition for comparison purpose. The effects of milling time on the microstructure, sinterability and the hardness of the composites were investigated. It was observed that the samples produced from 8 h milled powder had the highest relative sintered density (98% TD) and microhardness (234 Hv). On the other hand, the samples from the as-received powders expanded and had a relative sintered density of (67% TD) and microhardness as low as 24 Hv. The significance of this study is the possibility of producing W-brass composites as a cheaper alternative to W-Cu composites.
文摘Intergranular stress corrosion cracking (ISCC) of α-brass in neutral Mattsson's solution was found to be controlled by an unusual 'W'-shaped galvanic cell whose cathode is the grain boundary oxide film (G.B.0. film) and surface film and the anode is fresh metal at the cracked tip on both sides of the G.B.0. film. Redox reactions involved in the cell have been proposed here. According to this mdel, initidtion of ISCC is caused by the rupturing of surface film along grain boundaries, thus forming a galvanic cell. Propagation of ISCC resulted from alternate advances of G.B.0. film and dissolution on both sides of G.B.0. film caused by the effect of electrochemical reaction. This work developed an effective approach to investigate the embrittlement process at the tip of the crack, by increasing the length of the embrittlement region through constant strain test and distinguishing the morphology and the nature of the corrosion products by optical microscopy and scanning electron microscopy (SEH).
