Papers by Keyword: Tungsten Heavy Alloy

Abstract: Due to the excellent physical and chemical characteristics and mechanical properties of the tungsten heavy alloy (WHA), the WHAs have been widely applied in many areas of the national economy. In this paper, the concept of the WHA is introduced briefly, and the preparation process and properties of the WHAs are summarized. Compared with depleted uranium alloy, the WHA shows broad application prospects in the field of kinetic energy projectile.

Abstract: The microscopic analysis of 93W-4.9Ni-2.1Fe (wt. %) tungsten heavy alloy by hot-hydrostatic extrusion with severe plastic deformation strengthening were experimentally investigated mainly by transmission electron microscopy. Due to the profound differences in hardness of the tungsten particles and the NiFeW matrix a special TEM specimen preparation method had to be employed.It was shown that the microstructure of the as-extruded alloy was characterized by elongated tungsten particles with refinement cellular sub-structures consisting of high-density dislocations embedded in a binding Ni-Fe-W matrix phase with fine dynamically re-crystallized grains.

Abstract: Present work describes the evolution of microstructure and texture in W-26Ni-26Fe-13Co and W-28Ni-12Fe-10Co alloys during cold rolling. These alloys consist of two phases i.e. W-base (bcc) and matrix (fcc) in sintered and cold rolled conditions. Microchemistry obtained by electron Probe Micro Analyser (EPMA) clearly indicates that the extent of alloying is very less in W phase. The matrix phase mainly consists of Ni, Fe Co and W. The development of texture in both the W and matrix during cold rolling has been described in terms of α, γ and β fibres for bcc and fcc phases, respectively.

Abstract: This paper presents numerical analysis on the penetration into a semi-infinite Rolled Homogeneous Armor(RHA) steel target by a medium-caliber projectile at the velocity range from 900m/s to 1000m/s. The projectile was made of a 93% tungsten heavy alloy(WHA) having a diameter of 18mm. LS-DYNA, an explicit non-linear finite element analysis code, was used for the numerical analysis. This kind of penetration problem is generally accompanied by large deformation, high strain rate and thermal softening, accordingly the Johnson-Cook constitutive models combined with Johnson-Cook fracture model and Mie-Gruneisen equation of state were employed to describe the RHA target and the WHA projectile, respectively. Due to the lack of the parameters of the Johnson-Cook failure model of RHA, the corresponding data of 4340 steel were applied for RHA inevitably. Here, two different failure strains for 4340 steel from the literatures were substituted in for RHA and their effects on the numerical analysis results were discussed and compared to the test results in terms of penetration efficiency(P/L) and crater hole shape. A quarter parts of the semi-infinite RHA target and the WHA projectile were only modeled considering the symmetric configuration of the problem for the analysis.

Abstract: Spark plasma sintering (SPS) method was used to consolidate ultra-fine and mixed 93W-5.28Ni-1.32Fe-0.4Y2O3 (wt pct) powders, and the effects of sintering parameters on the densification degree and the performance of the as-sintered materials were investigated. Results showed that the SPS densification process could be divided into four stages. Compacts were densified rapidly at the stage III and a proper holding time promoted W diffusing into fcc-type Ni-Fe based solution. Heating rate and sintering time had a great influence on densification. When the powders were heated at a rate of 100°C/min to 1230°C and then held for 5min, the density, hardness and transverse rupture strength of the as-sintered material reached the optimum, being 17.18×103kg/m3, 41.4HRC and 935.1MPa, respectively. Its corresponding fracture morphology was characterized as intergranular rupture of W-W, and accompanied with some transgranular cleavage of tungsten grain.

Abstract: Tungsten heavy alloys are particle composites; they occupy a unique position in materials because of their combination of high density, strength and ductility. The main focus of this study was to examine the effect of sintering conditions (temperature and time) on the microstructural parameters of tungsten heavy alloys. Alloys composed of 88%, 93% and 95% wt. of tungsten and either Ni: Fe (in the ratio of 7:3) or Ni: Co (in the ratio of 7:3) were consolidated into green compacts. Samples of each of the six resulting alloys were sintered in hydrogen atmosphere at different temperatures for different sintering holding times. The microstructural parameters of both types were found to be roughly similar at each temperature and holding time. At higher sintering temperature and longer sintering holding times there was a matrix gradient and the formation of FeNi intermetallic phases at tungsten matrix interfaces. The microstructural parameters showed that the W-Ni-Co alloys may have some advantage as a result of their small tungsten grains and the lower contiguity.

Abstract: The goal of present work was to study the possibility to produce bars from heavy alloys based tungsten through rotary forging. For the experiment there were selected two compositions from the system W-Ni-Fe (90, respectively 93 %W/wt., Ni/Fe ratio = 7/3). From the two compositions there were prepared samples by conventional route of liquid phase sintering, followed by thermal treatment in a neutral atmosphere (N2, Ar) and by rotary forging with different reduction degree.

Abstract: In this research, the effect of microstructure on the mechanical properties of tungsten heavy alloys is discussed. The tensile properties of tungsten heavy alloys are found to be dependent on volume fraction of W, contiguity and grain size of W particle. The ductility is found to be influenced by contiguity and connectivity. The volume fraction of matrix increases sharply with the increase in rare metal oxide impurity, which adversely affects the mechanical properties of tungsten heavy alloys.

Abstract: In this study, the effect of various binders’ compositions on the feedstock of pre-alloyed tungsten heavy alloys (WHAs) powders has been investigated. Four kinds of wax-based binders were prepared from paraffin wax (PW), high-density polyethylene (HDPE), polypropylene (PP) and stearic acid (SA), and the characteristic of each feedstock was investigated at various temperatures and shear rates. It was found that all the feedstocks exhibited pseudoplastic flow behavior. Feedstock having multi-polymer components showed better rheological properties than those having mono-polymer because of good wettability between powder and binder, and less sensitivity to temperature and shear rates. This could be due to the molecular weight and length of molecular chain of PP and HDPE.

Abstract: The high temperature mechanical properties of dual phase heavy metal of 95W-3.5Ni-1.5Fe alloy were investigated in tension. The specimens were prepared by liquid phase sintering. Yield strength decreased and ductility increased as the testing temperature was increased to 300°C, reached a plateau at between 300 and 500°C and then decreased considerably. The fracture modes of alloys when deformed at room temperature were a mixture of intergranular fracture and transgranular cleavage. As the temperature was increased, the percentage of intergranular cleavage increased, although transgranular fracture also remained. At higher temperatures, substantial reduction in ductility and in yield strength was a result of loss of bonding strength between tungsten grains and matrix phase.