Papers by Keyword: Tungsten Heavy Alloy

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Authors: Jae Hyun Joo, Chang Hyun Lee, Joon Hong Choi
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.
Authors: Zoran S. Nikolic, Masahiro Yoshimura
Abstract: In this paper, we investigated numerically gravity induced skeletal settling during liquid phase sintering. The microstructural evolution will be simulated by simultaneous computation of displacement of the center of mass and mass transport due to dissolution and precipitation at the interfaces between solid-phase and liquid matrix. Common to this study based on domain methodology for definition of regular multi-domain model will be the need to relate some diffusional phenomena to essential geometric and topological attributes of the W-Ni porous microstructure influenced by skeletal settling combined with extrication of some solid-phase domains during liquid phase sintering.
Authors: Woon Hyung Baek, Eun Pyo Kim, Heung Sub Song, Moon Hee Hong, Seong Lee, Young Moo Kim, Sung Ho Lee, Joon Woong Noh, Joo Ha Ryu
Abstract: A new tungsten heavy alloy with hybrid structure was manufactured for the kinetic energy penetrator. The tungsten heavy alloy is composed of two parts: core region is molybdenum added heavy alloy to promote the self-sharpening; outer part encompassing the core is conventional heavy alloy to sustain severe load in a muzzle during firing. The fracture surfaces of the specimen is observed after ballistic tests. The core region revealed brittle behavior with W/W inter-granular fracture which activates self-sharpening. On the other hand, outer part exhibited conventional ductile fracture mode. From ballistic test, it was found that the penetration performance of the hybrid structure tungsten heavy alloy is higher than that of conventional heavy alloy. This heavy alloy is thought to be very useful for the penetrator in the near future.
Authors: M. Premkumar, U. Ravikiran, M. Sankaranarayana, T.K. Nandy, A.K. Singh
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.
Authors: Woon Hyung Baek, Moon Hee Hong, Eun Pyo Kim, Joon Woong Noh, Seong Lee, Heung Sub Song, Sung Ho Lee
Abstract: This paper focuses on the variations of static and dynamic properties of tungsten heavy alloy with heat treatment. The matrix phase of 93W-4.9Ni-2.1Fe (weight percent) has been penetrated into W/W grain boundaries during a cyclic heat treatment which consists of repeated isothermal holdings at 1150 °C and water quenching between them. By applying the cyclic heat treatment, the impact energy of tungsten heavy alloy is increased about three times from 57 to 170 J. When the tungsten heavy alloy is cyclically heat treated at 1150 °C and then re-sintered at 1485 °C, W/matrix interface is changed from round to undulated shape. The irregularity of the interface is increased with increasing the number of heat treatment cycles. From the measurement of the residual stress of W grains by X-ray diffraction, it is found that the irregularity of the interface is closely related with strain energy stemmed from the difference of thermal expansion coefficient between W particles and matrix phase. From dynamic ballistic test, it is found that the tungsten heavy alloy with undulated W grains forms many narrow fracture bands which are preferential for the self sharpening effect, thus, for the improvement of the penetration performance.
Authors: Syed Humail Islam, M. Tufail, Xuan Hui Qu
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.
Authors: Syed Humail Islam, Xuan Hui Qu, Farid Akhtar, Pei Zhong Feng, Xin Bo He
Abstract: Mechanical properties of tungsten heavy alloys are dependent on many factors including the purity of the raw materials, their tungsten content, manufacturing parameters and the microstructure of the final compact. The main object of this research was to examine the effect of sintering conditions (temperature and time) on the microstructure of tungsten heavy alloys and how the resulting modification of the microstructure can be used to optimize their mechanical properties. Alloys composed of 88%, 93% and 95% wt. of tungsten with the balance of Ni: Fe in the ratio of 7:3 were consolidated into green compacts. Samples of each of the three resulting alloys were sintered at different temperatures (1350°C,1450°C and 1500 0C) for different sintering holding times (3 and 30 minutes) in hydrogen atmosphere. Standard metallographic procedures were used to obtain SEM micrographs. The mechanical properties of tungsten heavy alloys were found to be dependent on the microstructural parameters such as W particle size, solid volume fraction, connectivity and w-w contiguity. It was shown that the mechanical properties of the alloys, and especially their ductility, are harmed when tungsten grains are contiguous.
Authors: Farid Akhtar
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.
Authors: Syed Humail Islam, Xuan Hui Qu, M. Tufail
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.
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