Tungsten Heavy Alloy Powders Research Articles

Binder jet printing of tungsten heavy alloy

Tungsten heavy alloy powder was processed to make it flowable and of a suitable high apparent density for additive manufacturing (AM). The powder was successfully binder jet printed and sintered to high density. Material in the as-sintered condition was tested and passed all requirements of the ASTM B777 specification for tungsten heavy alloy. Specimens were binder jet printed and an initial assessment of the dimensional capabilities of the process was performed.

Sintering of a nano-crystalline tungsten heavy alloy powder

A nano-crystalline Tungsten heavy alloy powder was obtained by mechanical alloying of elemental powders in a jar mill with a high ball to powder ratio. The chemical composition of the primary powder was 93 W-4.9Ni-2.1Fe (wt%). The mechanically alloyed powder had 22 nm sized tungsten crystallites distributed in an amorphous nickel base phase. Mechanical alloying reduced particle size of powders and also yielded to more uniform particles size distribution. Sintering behavior and microstructural development of that powder were studied and compared with a conventionally mixed powder. Mechanically stored energy and better distribution of primary elements in Nano-crystalline powder had decreased motivation energy of sintering and that powders showed more densification at relatively lower sintering temperatures. Sintering at low temperatures can depress grain growth during sintering and provide desirable properties. A transient intermetallic phase was formed in the nano-crystalline powder during sintering that has not been seen in conventionally mixed powders.

Synthesis and Characterization of High-Energy Ball-Milled Tungsten Heavy Alloy Powders

Mechanical alloying has been utilized extensively to produce non-equilibrium microstructure with a high degree of homogeneity. In the present work, different compositions of elemental powders of W, Ni and Fe were mixed in a high-energy vibratory type ball-milling machine. The morphology of the mechanically reacted powders varied as a function of milling time and these differences were observed by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It was found that elemental powders were progressively transformed into solid solution. The end product of the milled powder was uniform in size and homogeneous in shape. These results demonstrate that the mechanical alloying process can provide a powerful tool for the fabrication of tungsten heavy alloy powders at room temperature.

Fabrication and Characterization of Tungsten Heavy Alloys Using Chemical Reduction and Mechanical Alloying Methods

A novel reduction technique has been developed to synthesize nano-sized tungsten heavy alloys powders and compared with the same powders processed by mechanical alloying technique. In the first method, nano-sized tungsten heavy alloys powders have been obtained by reduction of precursors obtained by spray drying of several appropriate aqueous solutions, which were made from salts containing tungsten, cobalt, and nickel. By adjusting the stoichiometry of the component of the solutions, it is possible to obtain the desired chemical composition of the tungsten heavy alloys powders. In the second method, highly pure elemental powders of tungsten heavy alloys have been mechanically alloyed in a tumbler ball mill for different milling time. The investigated tungsten heavy alloy powders with the composition (95%W-3.5%Ni-1.5%Fe), (93%W-4.5%Ni-1.0%Fe-1.5%Co), and (90%W-6%Ni-4%Cu) have been prepared using both methods. The prepared powders have been compacted at 70 bar (200 MPa) and sintered in vacuum furnace at 1400℃. Vacuum sintering was carried out to achieve full densification of the produced tungsten heavy alloys. The investigated materials were going to be evaluated the physical and mechanical properties of the sintered parts such as density; electrical conductivity, hardness, and transverse rupture strength. The results reveal that, the grain size of alloys fabricated by chemical reduction technique (53.1 - 63.8 nm) is smaller than that fabricated by mechanical alloying technique (56.4 - 71.4 nm).

신공정에 의한 초미립 텅스텐계 복합분말 제조

A novel chemical method was evaluated to fabricate the ultrafine tungsten heavy alloy powders with bater-base solution made from the ammonium metatungstate (AMT), iron(II) chloride tetrahydrate (<TEX>$FeCl_2{\cdot}4H_2O$</TEX>), nickel(II) chloride hexahydrate (<TEX>$NiCl_2{\cdot}6H_2O$</TEX>) as source materials and the sodium tungstate dihydrate (<TEX>$NaWO_4{\cdot}2H_2O$</TEX>) as Cl-reductant. In the preparation of mixtures the amounts of the source components were chosen so as to obtain alloy of 93W-5Ni-2Fe composition(wt.%). The obtained powders were characterized by X-ray diffraction, XRF, field-emission scanning microscope (FESEM), and chemical composition was analyzed by EDX.

Preparation of Ultrafine Tungsten-Based Alloy Powders by GNP-Reduction Method

A novel glycine-nitrate process (GNP)-reduction method has been developed to fabricate ultrafine tungsten heavy alloy powders, with ammonium metatungstate (AMT), iron nitrate nonahydrate (Fe (NO3)3·9H2O), nickel nitrate hexahydrate (Ni (NO3)2·6H2O) as raw materials and gylcine as a complexant and incendiary agent. Precursor powders were obtained by self-propagation reaction in a suspension containing above materials. The precursor powders were then hydrogen-reduced to obtain composite powders with 90W-7Ni-3Fe composition (wt.%). Phase constitution and morphology of the precursor powders and the reduced powders were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Chemical composition of resultant powders was analyzed by energy dispersive spectrometer (EDS) analysis. It was shown that the GNP-reduction method produces ultrafine 90W-7Ni-3Fe powders with particle size of about 200 nm and highly dispersion of the composition.

Fabrication of ultrafine tungsten-based alloy powders by novel soda reduction process

A novel reduction method has been developed to fabricate ultrafine tungsten heavy alloy powders, with ammonium metatungstate (AMT), iron(II) chloride tetrahydrate (FeCl 2·4H 2O), nickel(II) chloride hexahydrate (NiCl 2·6H 2O) as source materials and sodium tungstate dihydrate (Na 2WO 4·2H 2O) as a reductant. In the preparation of mixtures the amounts of the source components were chosen so as to obtain alloy of 93W–5Ni–2Fe composition (wt.%). The obtained powders were characterized by X-ray diffraction, XPS, field-emission scanning microscope (FESEM), and chemical composition was analyzed by EDX.

Morphology and microstructure characterization of 95W-3.5Ni-1.5Fe powder prepared by mechanical alloying

The mechanism of mechanical solid-state reactions for formation of tungsten heavy alloy powder was discussed. A high-energy ball mill operating at room temperature was used for preparing tungsten heavy alloy powders, starting from elemental tungsten (W), nickel (Ni), and iron (Fe) powders. X-ray diffraction (XRD), particle size analyzer, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to follow the progress of the mechanical solid-state reaction of W, Ni, and Fe powders. These morphological studies revealed three stages in the milling process. In the first stage, the particle deformation changes the irregular structure of the as-received powder particles to flattened morphology, and the average particle size increases. In the second stage, the powder is sufficiently deformed and the tendency to fracture predominates over welding, and the particle size decreases. With continuous milling, the system reaches steady state, and relatively small and uniform particle size distribution is obtained after 20 h of milling.

Mechanically activated sintering of a tungsten heavy alloy powder : E. Gaffet et al (Inst. Polytechnique de Sevenans, Belfort, France)

Mechanically activated sintering of a tungsten heavy alloy powder : E. Gaffet et al (Inst. Polytechnique de Sevenans, Belfort, France)