Properties Of Tungsten Heavy Alloys Research Articles

Effect of nickel to cobalt ratio on mechanical properties of tungsten heavy alloys

The present study investigates the effect of Ni and Co on the mechanical properties of the W-Ni-Co alloy system. The alloys, based on 90 % W with varying Ni: Co ratios of 6:4, 7:3 and 8:2 (90W-6Ni-4Co, 90W-7Ni-3Co and 90W-8Ni-2Co) were processed through liquid phase sintering followed by a cyclic heat treatment (6 cycles). Thermomechanical treatment was carried out to improve strength and toughness levels. Quantitative metallography was employed to extract microstructural parameters including the volume fraction of the matrix phase, tungsten particle size, precipitate volume fraction and the contiguity of the W particles. The microstructural details at a finer scale were studied using scanning and transmission electron microscopy. Mechanical properties, such as tensile strength, elongation, hardness and impact toughness were also evaluated. The study shows that increasing the Ni: Co ratio decreases the precipitation of W in the matrix, which affects the mechanical behaviour of the alloys. The alloys having 7:3 and 8:2 Ni to Co ratio were additionally processed with an increased number of cycles (8 cycles) in the cyclic heat treatment to enhance the precipitation of fine W particles in the matrix. Since the alloy 6:4 showed brittle behaviour, it was not included for 8 cycles heat treatment study. The alloy with Ni to Co ratio of 8:2 resulted in superior combination of mechanical properties.

Effects of in situ phase reaction of η M12C and M6C on microstructure and mechanical properties of tungsten heavy alloy via spark plasma sintering

Spark plasma sintering (SPS) which densifies metallic or ceramic powders in few minutes can reduce sintering temperature, increase relative density, and inhibit grain growth in the consolidated materials. The phase reaction during the short SPS process is often ignored. In this work, a very important tungsten heavy alloy (WHA), 90 W − 7Ni − 3Fe (wt%) alloy, is taken as a typical example to demonstrate how in situ formation of η M12C or M6C influences the microstructural evolution and mechanical strength of the alloys SPSed at 1000–1200 °C through experimental characteristics combined with first−principles calculation. The results show that the in situ phase reaction from η M12C to M6C carbides plays a key role in the mechanical properties of WHAs, or oven more important than the relative density and grain size. The phase reaction from η M12C to M6C not only alters the phase composition of WHAs, but also lead to distinct interface relationship among matrix W, binder γ − (Ni, Fe) and η carbide phases. A maximum bending strength of 1268 ± 73 MPa was achieved after the phase reaction at 1200 °C, despite the lower relative density (95.8 ± 0.7%), smaller Young's modulus (209 ± 11 GPa) and bigger grain size (2.6 ± 1.0 μm).

Microstructure and Mechanical Properties of Tungsten Heavy Alloy Prepared Using Tungsten Metal Powder Produced from Heavy Alloy Scrap

Tungsten metal powder, using a hydrometallurgical route, was extracted from tungsten heavy alloy scrap that was generated during machining of penetrator cores for the manufacture of Fin Stabilised Armour Piercing Discarding Sabot (FSAPDS). The powder was subjected to extensive characterisation that included physical property evaluation and analysis of the alloy chemistry in order to assess its suitability for the preparation of tungsten heavy alloys with enhanced mechanical properties. Subsequently, a tungsten heavy alloy based on W-Ni-Co was consolidated using this powder through liquid phase sintering followed by heat treatment and swaging operations to realize long rods (~500 mm). This was followed by a detailed characterisation that included microstructure and mechanical property. The mechanical properties of these rods are promising, exhibiting a good balance of tensile and impact properties, which in turn underscores the potential of these recycled powders in the production of premium quality heavy alloy long rods for stringent applications such as kinetic energy penetrators.

Microstructure and mechanical properties of hot isostatic pressed tungsten heavy alloy with FeNiCoCrMn high entropy alloy binder

Microstructural development and mechanical properties of tungsten heavy alloy, WHA, with FeNiCoCrMn high entropy alloy, HEA, binder were investigated and compared to conventional WHA using Fe–Ni binder. Both WHAs, with HEA and conventional Fe–Ni binders, were fabricated by hot isostatic pressing at a temperature of 1450 °C in an argon environment. Scanning electron microscopy revealed that WHA with HEA and conventional binders possessed uniform and well-refined microstructures. Energy dispersive spectroscopy and X-ray diffraction, XRD, spectroscopy validated the formation and composition of HEA, existing as a skeletal network surrounding tungsten grains. HEA binder exhibited an overall increase of 42% in micro Vickers hardness values. Furthermore, hardness values of the tungsten heavy alloy were also seen to rise when fabricated with HEA binder. However, WHA sample with HEA binder was seen to undergo faster strain hardening and a premature failure, leading to lower values of ultimate strength and reduced ductility.

The Influence of Co Addition on the Structure and Mechanical Properties of Tungsten Heavy Alloys.

This study shows the results of Ni replacement with Co in a W-Ni-Co-type tungsten heavy alloy (WHA) in terms of the structure and mechanical properties. Five alloys containing 92 wt. % of tungsten plus Ni and Co changing in the proportions (Co:Ni) of 1:9, 2:8, 3:7, 4:6, and 5:5 were prepared using liquid phase sintering (LPS). The specimens were studied directly after sintering and after solution heat treatment. The tensile strength, yield strength, and elongation were evaluated. The results of tensile tests were supplemented with microhardness measurements of tungsten grains and matrix. Light microscopy was used for the microstructure, and a scanning electron microscope (SEM) equipped with an EDS attachment was applied for the assessment of the fracture mode and chemical microanalysis. It was concluded that the replacement of Ni with Co led to a tensile property increase that was accompanied by a gradual decrease in elongation that started to be critical for a Co:Ni ratio higher than 4:6.

The effect of fine W particles in matrix phase on mechanical properties of tungsten heavy alloys

Tungsten heavy alloys 90W-7Ni-3Co (WNC) and 89.6W-6.2Ni-1.8Fe-2.4Co (WNFC), produced using liquid phase sintering followed by thermo-mechanical processing, were investigated for microstructure and mechanical properties. 90W-7Ni-3Co alloy processed following a cyclic heat treatment showed fine tungsten particles in the matrix. The alloy, when heat treated at a temperature 850°C (the lower temperature of cyclic treatment), formed a W-rich intermetallic phase in the matrix that subsequently dissolved during high temperature (1150°C) solution treatment leaving behind fine W particles. On the other hand, the matrix phase of the alloy, 89.6W-6.2Ni-1.8Fe-2.4Co showed a clean structure devoid of any such precipitates. Both the alloys were subjected to a thermomechanical treatment that included two stage swaging with intermediate heat treatments. 90W-7Ni-3Co alloy exhibited superior strength, but lower elongation to failure and impact toughness as compared to 89.6W-6.2Ni-1.8Fe-2.4Co alloy. Microstructure-property correlation was undertaken in order to elucidate the effect of enhanced W dissolution and fine W precipitates (in the matrix) on mechanical behaviour of the alloys investigated.

Preliminary Study of the Rhenium Addition on the Structure and Mechanical Properties of Tungsten Heavy Alloy.

The results of structure and mechanical property investigations of tungsten heavy alloy (THA) with small additions of rhenium powder are presented. The material for the study was prepared using liquid phase sintering (LPS) of mixed and compacted powders in a hydrogen atmosphere. From the specimens, the samples for mechanical testing and structure investigations were prepared. It follows from the results of the microstructure observations and mechanical studies, that the addition of rhenium led to tungsten grain size decreasing and influencing the mechanical properties of W-Ni-Fe-Co base heavy alloy.

Effect of Heat Treatment Process and Composition on Deformation and Damage Behavior of WHA under Detonation Loading

The excellent material properties of tungsten heavy alloy (WHA) make it widely used in the military field. When used as killing elements of weapons, its dynamic mechanical properties under detonation loading directly determine the damage effect of weapons, which makes the research on its mechanical behaviors under high pressure and high strain rate loads such as detonation loading of great significance. In this paper, several WHAs with different compositions and processes are selected, and the mechanical properties and deformation and damage behavior under static explosion test are analyzed by combining macro and micro study, so as to provide guidance for the subsequent optimization of the performance design of WHA.

Effect of tungsten tantalum pre-alloying on the sintering structure of 90(W-Ta)-Ni-Fe alloy

The intrinsic brittleness of tungsten limits the improvement on the comprehensive mechanical properties of tungsten alloys. Starting from the perspective of solid solution toughening, this study innovatively used tungsten-tantalum particles instead of tungsten particles as the sintered core to prepare 90(W-Ta)-Ni-Fe alloy. Tantalum forms a BCC solid solution with tungsten in the process of high-energy ball milling. During the vacuum sintering process, tantalum precipitated and reacted with the matrix to form acicular phase. This precipitation process reduces the liquid phase sintering temperature of the tungsten alloy and refine the tungsten particles. The microstructure of the sintered alloy is composed of tungsten particles, matrix phase, intermediate phase, acicular precipitated phase and oxides. The solid solution of tantalum increases the hardness and reduces the modulus of the tungsten particles. The hardness and modulus of the matrix phase are increased due to the influence of the acicular precipitation phase. These findings indicate that the solid solution of tantalum has the potential to improve the comprehensive mechanical properties of tungsten heavy alloys.

Effects of Co and Co + Mo additions on tensile properties of tungsten heavy alloys: first-principles study and experimental investigations

ABSTRACT The present work illustrates the deformation behaviour of tungsten heavy alloys (WHAs) using first-principles calculation under tensile stress of three virtual alloy systems comprising the matrix phase and a W-grain along with two fcc–bcc interfaces. The energy values of the alloy systems decrease with the additions of Co and Co + Mo in the ternary alloy (W–Ni–Fe). The experimental lattice parameters of the matrix phase of alloys are in good agreement with those of the alloy systems calculated using the first-principles calculation. The lattice constants, yield strength and strength at 20% strain increase with the additions of Co and Co + Mo. The nature of theoretical stress–strain curves of systems is similar to those of the experimental stress–strain curves of typical alloys. The nitty-gritty of virtual alloy systems and the interrelated consequences resulting in closer to real alloys in terms of tensile flow curves have been discussed.

Microstructures and properties of 90W-4Ni-6Mn alloy prepared by vacuum sintering

Tungsten-nickel-manganese alloy is an excellent potential replacement of depleted uranium alloy for kinetic energy penetrator (KEP) due to its high self-sharpening effect. In this work, the 90W-4Ni-6Mn alloy was prepared by vacuum sintering, and the effects of the sintering temperature and oxygen content on its microstructure and properties were discussed. Sintering temperature had a great influence on the properties of tungsten heavy alloy. The optimal properties of 90W-4Ni-6Mn with the relative density of 99.43%, the W grain size of 3.80 μm, and the compressive strength of 2790 MPa were obtained at the sintering temperature of 1125 °C for 60 min under a vacuum of 10−2∼10−3 Pa. With the increase of oxygen content, the densification of powders became more difficult, and the microstructure homogeneity and mechanical properties of sintered samples decreased accordingly. The results provide a new effective way to prepare W–Ni–Mn alloy with high performance.

Effect of Fe Addition to Binder Phase on Mechanical Properties of Tungsten Heavy Alloy

In the present work, tungsten heavy alloys (WHA) in two different compositions (92 wt% W–2:1 wt% Ni/Co and 92 wt% W–2:1:1 wt% Ni/Co/Fe) were synthesized through liquid phase sintering followed by swaging and thermal treatment. Microstructure and mechanical properties were analyzed to study the effect of the binder composition on the WHA. The W–Ni–Co alloy has lower matrix volume fraction, finer tungsten particle size and low contiguity when matched to the W–Ni–Co–Fe alloy. Mechanical investigations such as tensile, Charpy and hardness were tested and were correlated with the microstructural features. W–Ni–Co alloy showed higher strength, hardness and impact due to more solubility of tungsten in the binder and low contiguity. Hence, Fe addition to binder has resulted in degradation in required properties. For further enhancement in strength, aging has been carried out at 500 °C for 1 h and improved strength is obtained at the marginal expense of ductility. W–Ni–Co alloy has a much higher Charpy impact value of 127 J when compared to alloy with Fe addition (55 J) due to lower dissolution of tungsten into the binder matrix.

Effect of processing parameters on microstructure and properties of tungsten heavy alloys fabricated by SLM

Selective laser melting (SLM) was used to fabricate tungsten heavy alloy (WHA) with a nominal composition of W-7Ni-3Fe (wt%). Depending on the processing parameters (laser power, scanning speed, preheating, etc.), three different bonding mechanisms were observed, i.e., liquid phase sintering, partial melting and complete melting. The difference in applied energy density also reflected in a variation of the final composition, amount of W dendrites in γ-phase and the W grain contiguity. High density materials (>95%TD) were produced under optimal processing conditions. The effect of the as-built microstructure and post-process heat-treatment on the properties of WHA processed by SLM was evaluated. In the as-built condition, the WHA exhibited an UTS of 871 ± 30 MPa with a brittle fracture behaviour regardless of the applied processing parameters. With a suitable post-process heat-treatment, a material with a more optimal microstructure was obtained, with properties comparable to those of WHAs produced by conventional powder metallurgy (UTS of 850 ± 21 MPa with an elongation of 10.2 ± 1.0%).

Development of tungsten heavy alloy reinforced by cubic zirconia through liquid-liquid doping and mechanical alloying methods

A new tungsten heavy alloy, which is characterized by fine yttria stabilized cubic zirconia (c-ZrO2(Y)) particles dispersed in the alloy, was developed by an ion-level liquide-liquid (L-L) doping technique combined with mechanical alloying. The microstructure and mechanical properties of tungsten heavy alloy were investigated, and the formation process and role of zirconia were discussed. Results show the zirconium element transforms in an order of Zr4+ to Zr(WO4)2 or 2Zr(WO4)2 nH2O to m-ZrO2 in the preparation process of powders. Finally, the c-ZrO2(Y) particles with size of 200–1000 nm are obtained in tungsten heavy alloy during sintering at 1520 °C for 90 min. Most of c-ZrO2(Y) particles are distributed within tungsten grains, and some c-ZrO2(Y) particles tend to be dispersed at the interfaces of tungsten grains, while a small number of c-ZrO2(Y) particles are dispersed in γ(Fe, Ni, W) matrix. The compressive strength of new alloy is improved approximately 8.2% than that of 93 W-4.9Ni-2.1Fe. This attributes to c-ZrO2(Y), which refines tungsten grain, lowers W-W contiguity and strengthens tungsten and γ(Fe, Ni, W) grains.

Effect of composition, heat treatment and deformation on mechanical properties of tungsten heavy alloys

Five different compositions of tungsten heavy alloy with Ni, Fe, Co and Mo were prepared through powder metallurgy route using liquid phase sintering. Three alloys were based on quaternary W-Ni-Fe-Co (with varying Ni to Fe ratio and Co content) and the other two quinary systems with Mo addition. The sintered alloy blanks (cylindrical cross section) were subjected to a thermo-mechanical treatment, which comprised three vacuum heat treatments (at 1100 °C for 1.5 h followed by oil quenching) before and in between multiple swaging operations (at 500 °C) with a total deformation of 53%. This was followed by a detailed evaluation of different microstructural parameters in all compositions. Mechanical properties such as tensile strength, % elongation and impact were evaluated at the final stage (26 mm dia and 600 mm length). Increase in Co content resulted in better strength and elongation with marginal loss in impact values. The alloy containing 0.25 wt% Mo showed the best combination of tensile and impact properties. Further increase in Mo concentration to 0.5 wt% resulted in marginal increase in strength value but rapid deterioration in elongation and impact values. Scanning electron microscopy, electron probe micro analysis, quantitative metallography and fractography were carried out to establish an inter-relationship between microstructure, properties and fracture behaviour of the alloys investigated.

Effect of Yttrium Oxide Dispersion on the Microstructure and Properties of Tungsten Heavy Alloys

<p>Tungsten heavy alloys are considered as two phase composites with 88 to 97 wt% tungsten interspersed in a matrix of relatively low melting elements such as nickel, iron and cobalt. The mechanical properties of these alloys are greatly influenced by the microstructural features such as tungsten grain size, tungsten-tungsten contiguity and matrix volume fraction. Oxide dispersion strengthening (ODS), refinement of tungsten grain size, cyclic heat treatment, addition of alloying elements like Cr, Mo, and Co are some of the methods investigated to improve the microstructural features and thereby the mechanical properties of tungsten heavy alloys. Among these methods ODS has been considered as a promising processing technique since the tungsten grain size observed in ODS alloys is finer compared to the conventional alloys and more importantly the dynamic fracture mode changes from adiabatic shear band to brittle fracture. The present study is mainly focused on investigating the effect of 0.3 wt% yttrium oxide (Y2O3) dispersion on the microstructure and consequently the tensile properties of 90W-6Ni-2Fe-2Co alloy. With 0.3 wt%Y2O3, the ODS alloy (89.7W-6Ni-2Fe-2Co-0.3Y2O3) is processed by two-stage sintering with subsequent thermo-mechanical treatment which includes vacuum heat treatment and swaging. ODS alloy and the conventional alloy (without oxides) are compared based on the microstructures and tensile properties obtained after liquid phase sintering and after final processing.</p>

Effect of swaging and aging heat treatment on microstructure and mechanical properties of tungsten heavy alloy

In the present study, a 90W-6Ni-2Fe-2Co (Wt.%) tungsten heavy alloy was processed through liquid phase sintering route, followed by vacuum heat treatment and swaging. Further, ageing was carried out at 700° C for three different time period, in order to improve mechanical properties. Microstructural analysis showed decrease in contiguity levels from sintered to swaged condition. Swaging improved the tensile strength of the alloy at the expense of ductility and impact. Aging of the swaged alloys showed further improvement in yield, tensile strength and hardness of the alloy with concomitant loss of ductility and impact toughness. The fracture surface of sintered alloy exhibited brittle failure features consisting of tungsten-matrix and tungsten-tungsten failure. However, the heat treated alloy showed lesser intergranular failure indicating higher ductility. The swaged alloy exhibited relatively higher fraction of transgranular cleavage features. The study shows that the heat treatment (that includes solution heat treatment and ageing) and swaging can be used judiciously to tailor the final mechanical properties of the tungsten heavy alloys.

Effect of Effect of Cold Isostatic Pressing on the Physical and Mechanical Properties of Tungsten Heavy Alloys

Abstract: The objective of this experimental study is to investigate the effect of cold isostatic pressing (CIP) on the density, mechanical properties and microstructure of 93%W-4.9%Ni-2.1%Fe alloy. Also, to compare between the effect of uni-axial pressing and cold isostatic pressing on the alloy properties.Elemental powders were mixed using double cone mixer for 2 hours. Cold Isostatic Pressing was applied for consolidation of metal powders into green compacts to obtain cylindrical tensile and impact specimens under different pressures using rubber molds. Finally, the specimens were sintered under vacuum atmosphere at 1470oC for 90 minutes. The results of density, tensile strength, ductility, hardness and impact resistance obtained from the produced specimens were compared with those obtained using uni-axial compaction. Moreover, the values of the isostatic compaction pressure were varied in order to study their effect on the mechanical properties and to determine the optimum value providing the highest properties. The microstructure analysis indicates that uni-axial compaction can provide a structure with lower contiguity, and a grain size relatively course, while isostatic pressing provides a structure with fine grains and higher contiguity. The obtained results of all measured mechanical properties prepared by cold isostatic pressing showed higher values than those measured on specimens uni-axially compacted, for all values of pressure. We can, also, notice that the relative green density is higher, in case of applying CIP technique, for all values of compaction pressure. It can be concluded that cold isostatic pressing leads to a sensible improvement in alloy properties.

Effect of Applying Hot Isostatic Pressing on the Microstructure and Mechanical Properties of Tungsten Heavy Alloys

Effect of Applying Hot Isostatic Pressing on the Microstructure and Mechanical Properties of Tungsten Heavy Alloys

Effect of Applying Hot Isostatic Pressing on the Microstructure and Mechanical Properties of Tungsten Heavy Alloys

Effect of Applying Hot Isostatic Pressing on the Microstructure and Mechanical Properties of Tungsten Heavy Alloys