The hardness variation of two kinds of alloys with 36 wt pct W content and 7/3, 9/1 Ni-to-Fe ratios during strain aging at 800℃ was studied. The microstructures of the aged alloys were analyzed by X-ray diffraction a...The hardness variation of two kinds of alloys with 36 wt pct W content and 7/3, 9/1 Ni-to-Fe ratios during strain aging at 800℃ was studied. The microstructures of the aged alloys were analyzed by X-ray diffraction and TEM. The results show that the strain aging hardness of W-Ni-Fe ternary alloy with 7/3 Ni-to-Fe ratio decreases monotonically with the increase of aging time. Under the same conditions, the hardness of 9/1 Ni-to-Fe ratio alloy decreases in the initial aging stage, but then increases as aging process goes on. X ray diffraction and TEM analysis show that there is not any precipitation depositing from the alloy with 7/3 Ni-to-Fe ratio during aging. The monotonic decrease in hardness of this alloy during aging process results from the recovery, recrystallization and solid solubility declining. In the alloy of 9/1 Ni-to-Fe ratio, the fine β phase precipitates dispersively during aging which hardens the alloy. The two different kinds of mechanisms (the softening one and the hardening one) decide the hardness variation of the alloy with 9/1 Ni-to-Fe ratio mentioned above.展开更多
In this study, Cu was added as the third additive to lower the sintering temperature of W-Ni-Fe alloy. By adding 2 wt pct Cu, a dense 93W-3.5Ni-l.5Fe-2.0Cu tungsten alloy was obtained by hot-pressing at a low temperat...In this study, Cu was added as the third additive to lower the sintering temperature of W-Ni-Fe alloy. By adding 2 wt pct Cu, a dense 93W-3.5Ni-l.5Fe-2.0Cu tungsten alloy was obtained by hot-pressing at a low temperature of 1573 K which is a process of liquid-phase sintering. As a result, the morphology of W-Ni-Fe alloy changed obviously after the addition of Cu and the alloy had-higher relative density and rupture strength. The mechanism of the densification of W-Ni-Fe-Cu alloy at the low temperature.was then mainly investigated. It was found that, part sintering activators Ni and Fe could exist in liquid form at 1573 K due to the addition of Cu, which made it easy for Ni and Fe to dissolve W and thus the full densification of W-Ni-Fe-Cu alloy at the low temperature was realized.展开更多
Spark plasma sintering method （SPS） was used to consolidate mixed W-5.6Ni-1.4Fe （mass fraction, %） powders from commercial fine elemental powders, and both the densification behavior and microstructure evolution i...Spark plasma sintering method （SPS） was used to consolidate mixed W-5.6Ni-1.4Fe （mass fraction, %） powders from commercial fine elemental powders, and both the densification behavior and microstructure evolution in sintering were investigated at different heating rates. The results show that the SPS densification process can be divided into three stages. At the initial unshrinking stage, fast heating generates instantaneous discharge and locally inhomogeneous temperature distribution in solid-state powder particles, enhancing later densification; during the intermediate solid state sintering stage, diffusion is more sufficient in the slow-heated SPS process; at the final transient liquid-phase sintering stage, tungsten grains become sphered and coarsen rapidly, but fast heating helps maintain rather small grain sizes.展开更多
MA W-Ni-Fe alloyed powder compact was sintered by microwave technology, and the influence of microwave sintering on consolidation of W-Ni-Fe alloy was studied. The fracture morphology and microstructure of alloys were...MA W-Ni-Fe alloyed powder compact was sintered by microwave technology, and the influence of microwave sintering on consolidation of W-Ni-Fe alloy was studied. The fracture morphology and microstructure of alloys were measured by SEM and metallurgical microscope. The experimental results showed that microwave sintering promoted the densification of MA W-Ni-Fe alloyed powder quickly with the higher heating rate. The density of the sintered samples increased with the increase of sintering temperature, and significant densification shrinkage occured at 1300 ~ 1400°C. The tungsten grain grew rapidly at 1450°C. When the alloy was microwave sintered at 1550°C, the inner structure of alloy is more homogeneous, the average W grain size is about 15 μm, and the relative density of sintered specimen is 99%.展开更多
基金This work was supported by the National Natural Science Foundation of China under grant No.59971007.
文摘The hardness variation of two kinds of alloys with 36 wt pct W content and 7/3, 9/1 Ni-to-Fe ratios during strain aging at 800℃ was studied. The microstructures of the aged alloys were analyzed by X-ray diffraction and TEM. The results show that the strain aging hardness of W-Ni-Fe ternary alloy with 7/3 Ni-to-Fe ratio decreases monotonically with the increase of aging time. Under the same conditions, the hardness of 9/1 Ni-to-Fe ratio alloy decreases in the initial aging stage, but then increases as aging process goes on. X ray diffraction and TEM analysis show that there is not any precipitation depositing from the alloy with 7/3 Ni-to-Fe ratio during aging. The monotonic decrease in hardness of this alloy during aging process results from the recovery, recrystallization and solid solubility declining. In the alloy of 9/1 Ni-to-Fe ratio, the fine β phase precipitates dispersively during aging which hardens the alloy. The two different kinds of mechanisms (the softening one and the hardening one) decide the hardness variation of the alloy with 9/1 Ni-to-Fe ratio mentioned above.
文摘In this study, Cu was added as the third additive to lower the sintering temperature of W-Ni-Fe alloy. By adding 2 wt pct Cu, a dense 93W-3.5Ni-l.5Fe-2.0Cu tungsten alloy was obtained by hot-pressing at a low temperature of 1573 K which is a process of liquid-phase sintering. As a result, the morphology of W-Ni-Fe alloy changed obviously after the addition of Cu and the alloy had-higher relative density and rupture strength. The mechanism of the densification of W-Ni-Fe-Cu alloy at the low temperature.was then mainly investigated. It was found that, part sintering activators Ni and Fe could exist in liquid form at 1573 K due to the addition of Cu, which made it easy for Ni and Fe to dissolve W and thus the full densification of W-Ni-Fe-Cu alloy at the low temperature was realized.
基金Project (2010CB635104) supported by the National Basic Research Program of ChinaProject (2007AA03Z112) supported by the National High-Tech Research and Development Program of China+2 种基金Project (9140A18040709JW1601) supported by the Advanced Research Fund of DOD, ChinaProject (2009ZZ0019) supported by the Fundamental Research Funds for the Central Universities, ChinaProject (NCET-10-0364) supported by the Program for New Century Excellent Talents in University, China
文摘Spark plasma sintering method （SPS） was used to consolidate mixed W-5.6Ni-1.4Fe （mass fraction, %） powders from commercial fine elemental powders, and both the densification behavior and microstructure evolution in sintering were investigated at different heating rates. The results show that the SPS densification process can be divided into three stages. At the initial unshrinking stage, fast heating generates instantaneous discharge and locally inhomogeneous temperature distribution in solid-state powder particles, enhancing later densification; during the intermediate solid state sintering stage, diffusion is more sufficient in the slow-heated SPS process; at the final transient liquid-phase sintering stage, tungsten grains become sphered and coarsen rapidly, but fast heating helps maintain rather small grain sizes.
文摘MA W-Ni-Fe alloyed powder compact was sintered by microwave technology, and the influence of microwave sintering on consolidation of W-Ni-Fe alloy was studied. The fracture morphology and microstructure of alloys were measured by SEM and metallurgical microscope. The experimental results showed that microwave sintering promoted the densification of MA W-Ni-Fe alloyed powder quickly with the higher heating rate. The density of the sintered samples increased with the increase of sintering temperature, and significant densification shrinkage occured at 1300 ~ 1400°C. The tungsten grain grew rapidly at 1450°C. When the alloy was microwave sintered at 1550°C, the inner structure of alloy is more homogeneous, the average W grain size is about 15 μm, and the relative density of sintered specimen is 99%.
