Tungsten Grades Research Articles

Production and research of tungsten carbide powder from VA grade tungsten metal waste in aviation kerosene

Purpose. Obtaining and studying the composition, structure and properties of tungsten carbide powder from VA grade tungsten metal waste in aviation kerosene. Methods. Tungsten carbide powder from tungsten metal waste of the VA brand was obtained in the following sequence. The reactor was filled with a working medium – aviation kerosene of the TS-1 brand, the waste was loaded into the reactor. Electrodes were mounted from the same waste tungsten of the VA brand. The mounted electrodes were connected to a pulse generator. The necessary electrical parameters of the installation were set: the capacitance of the condensers is 42.0–43.5 UF; the voltage on the electrodes is from 115–120 V; the pulse repetition rate is 50–55 Hz. The resulting tungsten powder was studied using: a scanning electron microscope QUANTA 600 FEG; a particle size analyzer Analysette 22 NanoTec; an energy-dispersed X-ray analyzer from the company EDAX; X-ray diffraction on a diffractometer Rigaku Ultima IV. Results. Based on the conducted experimental studies, a new method for producing tungsten carbide powder has been developed, characterized in that the powder is obtained by electroerosive dispersion of tungsten metal waste of the VA brand in aviation kerosene at a capacitor capacity of 42.0–43.5 UF, an electrode voltage of 115–120 V and a pulse repetition frequency of 50–55 Hz. It has been experimentally established that spherical and elliptical particles of tungsten carbide powder W2C have sizes from 2.26 microns to 90.72 microns with an average volumetric diameter of 20.2 microns and contain carbon on the surface. Conclusion. The production of tungsten carbide suitable for industrial use at low energy costs from metal waste has shown high efficiency of the technology of electroerosion dispersion.

Microstructural changes induced in advanced tungsten grades under high temperature neutron irradiation

Recent studies addressing the change of mechanical properties after high temperature irradiation of tungsten have reported substantial increase of the ductile to brittle transition temperature as well as increase of the hardness. In this work, we performed microstructural analysis by means of transmission electron microscopy (TEM) on various tungsten grades earlier exposed to high temperature neutron irradiation at 1200 °C up to 1 dpa. The latter corresponds to the expected irradiation temperature on the surface of a tungsten monoblock during the steady state operation in ITER. TEM was applied to five tungsten (W) materials including ITER specification pure W and precipitate strengthened W alloys. The analysis of TEM data coupled with its discussion led to a number of important conclusions regarding the damage induced at 1200 °C neutron irradiation such as: (i) weak effect of recrystallization on the accumulation of the lattice damage; (ii) promising results on the tolerance of damage accumulation in W-Y2O3 grade and (iii) internal oxidation of TiC particles which may contribute to the huge increase of the irradiation induced hardening.

The effect of microstructure on recovery and recrystallization after annealing of two neutron irradiated ITER specification tungsten

The study of the recrystallization resistance of engineering grade tungsten (W) prior to and after neutron irradiation as well as subsequent thermal annealing provides valuable insight into neutron induced defect interactions and their kinetics as well as their correlation with recrystallization mechanisms. The outcome of such investigations would be of assistance for appropriate grade selection for a fusion reactor and the design of healing processes enabling the lifetime extension of fusion reactor components. Within this framework, samples from ITER specification W, forged bar and cold-rolled plate, were neutron irradiated to a dose of 0.18 dpa at 600 °C in the Material Test Reactor BR2, Mol, Belgium, and subsequently isochronally annealed from 700 to 1550 °C for 24 h with a 50 °C step with two non–irradiated counterparts. X-ray diffraction, optical microscopy and positron annihilation lifetime spectroscopy, combined with Vickers Hardness are used to correlate the recrystallization process and recovery mechanisms. It is found that the non-irradiated plate has a higher recrystallization resistance compared to that of the bar, with the former requiring 100 °C higher temperature for 24 h annealing time to recrystallize. Despite the irradiation induced dislocation loops and voids being of similar sizes and densities for both grades, the different initial microstructure affects the recrystallization process upon annealing, delaying it by 50 °C on the plate. Further in the plate a complete void dissolution is observed before recrystallization, which is not the case for the bar, for which the two effects occur at the same temperature.

X-ray Fluorescence Analysis of the Elemental Composition of Tungsten, Nickel and Copper

The purpose of this work was to conduct an X-ray fluorescence analysis of the elemental composition of tungsten, nickel and copper metal waste using an Olympus Delta portable spectrometer.Methods. To determine the chemical composition of raw materials, samples of metal waste in the form of copper rods, tungsten rods of various diameters and scraps of nickel plates intended for recycling were examined. To determine the elemental composition of metal waste, the method of X-ray fluorescence analysis (XFA) was chosen. The X-ray fluorescence method is based on the ratio of the intensity of X-ray fluorescence to the concentration of elements in the sample. Samples irradiated with powerful X-ray tube radiation, in response, emit characteristic fluorescent radiation of atoms proportional to their concentration in the sample. This method allows us to qualitatively assess the elemental composition of complex samples without violating their physico-chemical properties with minimal time costs. The Olympus Delta spectrometer was used as an express analyzer of metals and alloys, with the help of which experimental data on the composition of metal waste of tungsten, nickel and copper were obtained.Results. Based on the conducted studies aimed at X-ray fluorescence analysis of the elemental composition of tungsten, nickel and copper metal waste using the Olympus Delta portable spectrometer, it was found that the samples of the studied metal waste correspond to the following grades of alloys: tungsten rod made of tungsten grade VA; nickel plate made of nickel grade PNK-0T1; copper rod made of copper grade M3r.Conclusion. The results obtained will allow further research on their processing by the method of electroerosive dispersion and reuse in the production of heavy tungsten alloys. Renovation of metal waste, including tungsten, nickel and copper metal waste, will contribute to resource conservation, import substitution and ensuring the technological sovereignty of the Russian Federation.

THE EFFECT OF BROACHING TOOL CUTTING EDGES POLISHING ON PROCESS FORCES AND TEMPERATURE

In the industrial field, the search for improving the performance of machining tools considering their geometry, manufacturing, material, and coatings is a priority. This research focuses on optimizing the cutting edge for broaching Inconel 718. Drag-finishing was used to round and polish the cutting edge of a K10-Co 7% grade tungsten carbide roughing tool. The results reveal that increasing the cutting-edge radius affects the process forces increasingly, especially the thrust force. From the minimum tested radius of 5 micrometers to the maximum radius of 35 micrometers, the cutting and thrust force doubles at uncut thicknesses (RPT) of 75 and 100 micrometers. The plowing force is hardly affected. The shear coefficient Kcc also shows growth as the radius of the cutting-edge increases. The temperature increases proportionally with the radius, and in addition, the simulations show a change of the temperature distribution in the cutting profile with the change of the cutting-edge radius. Thus, the preparation of the cutting-edge could be crucial in the performance of the broaching process.

Grain boundary softening from stress assisted helium cavity coalescence in ultrafine-grained tungsten

The formation of helium cavities in coarse-grained materials produces hardening proportional to the number density and size of the cavities and due to the interaction of dislocations with intragranular helium defects. In nanostructured metals containing a high density of interfacial sinks, preferential cavity formation in the grain boundaries instead produces softening that is often attributed to enhanced interfacial plasticity. Employing two grades of ultrafine-grained tungsten, we explore this effect using targeted implantation studies to map cavity evolution as a function of the irradiation conditions and quantify its impact on the mechanical response through nanoindentation. Softening is reported at implantation temperatures above the threshold for preferential grain boundary cavity formation but at a sufficiently low fluence prior to the growth of intragranular cavities. Collective changes in the mean cavity size, density, and morphology beneath a residual impression on an implanted surface indicate that cavity coalescence accompanied the reduction in hardness. Complementary atomistic simulations demonstrate that, in tungsten grain structures exhibiting softening, grain boundary bubble coalescence is driven by stress concentrations that further act to localize strain in the grain boundaries through cooperative deformation processes involving local atomic shuffling and sliding, dislocation emission, and even the nucleation of unstable twinning events.

Defect evolution of neutron irradiated ITER grade tungsten after annealing

The microstructural evolution of neutron irradiated tungsten (W) after annealing and its correlation with the corresponding mechanical properties provides valuable insight on the defect interactions and their annihilation processes. This would result in the identification of recovery mechanisms, leading to the design of healing processes and thus, enabling the lifetime extension of fusion reactor components. Within this framework, samples from ITER specification forged W bar were neutron irradiated to a dose of 0.2 displacements per atom (dpa) at 600 °C in the Belgian Material Test Reactor (BR2) and subsequently annealed at 800 and 1000 °C. The evolution of the irradiation induced defects after annealing has been assessed by transmission electron microscopy (TEM), positron annihilation lifetime spectroscopy and electrical resistivity and its effect on the mechanical properties are discussed in terms of Vickers hardness. Neutron irradiation results in the formation of dislocation loops and voids. TEM observations show an increase in the size of both defect types after post irradiation (PI) annealing at both temperatures, accompanied by an initial increase in their density after PI annealing at 800 °C, followed by a subsequent decrease after PI annealing at 1000 °C. The presence of TEM-irresolvable defects of both types is revealed in the as-irradiated state, which is evidenced by the evolution of Vickers hardness, resistivity and positron lifetimes and their correlation after the PI annealing. In the as-irradiated state, as well as after PI annealing at both temperatures, the hardening is dominated by voids.

A novel fine gangue depressant: Metal ions-starch colloidal depressant and its effect on ultrafine chlorite

The flotation of chlorite is entrainment of foam under Pb-BHA collector systems, influencing the flotation indexes. And the entrainment of chlorite is an inevitable phenomenon without any depressant. In this study, flotation test reveals that the entrainment of fine chlorite significantly decreases the tungsten grade and the selective index, and metal ions-starch colloidal depressant can improve the tungsten grade of concentrate, whose selectivity is greater than that of caustic starch. X-ray photoelectron spectroscopy measurement confirms both caustic starch and metal ions-starch can chemisorb on the chlorite surface, which change repulsive interaction force to attractive interaction force, agglomerating chlorite to form the clusters and increase the size of chlorite particles. Furthermore, metal ions-starch cannot adsorb on the surface of scheelite and change the interaction force between chlorite and scheelite to make an agglomeration, whereas the caustic starch can. Meanwhile, the selectivity of metal ions-starch is better than that of caustic starch, mainly because the functional group of -CH2-O-Me is superior to that of hydroxy. Therefore, this study provides a new depressant to inhibit the entrainment of chlorite and achieve the improvement of grade on concentrate.

Fracture-mechanical behaviour of ITER grade tungsten subjected to three different rolling processes

We investigated the fracture-mechanical behaviour of three ITER grade tungsten plates subjected to different rolling processes. One plate was uniaxially rolled at a normal rolling ratio. The two other plates were subjected to cross rolling processes at normal and high rolling ratios. Two of the three plates were characterized for L-T and T-L orientations, whereas the plate subjected to the cross rolling at a normal rolling ratio was tested in the L-T orientation only. The DBTTs of the investigated plates determined via fracture-mechanical experiments were near 300°C, irrespective of the specimen machining directions. Marginally better fracture-mechanical behaviour was observed in the L-T orientation compared to T-L orientation for the uniaxially rolled plate. The plate subjected to the cross rolling process at the normal rolling ratio was found to have inferior fracture-mechanical behaviour. This manifested in the form of steep load drops in load-displacement curves, which persisted even at the highest test temperature of 800°C. Fractographic investigations revealed the governing failure modes of the investigated materials.

Development of irradiation tolerant tungsten alloys for high temperature nuclear applications

Development of refractory metals for application as plasma-facing armour material remains among priorities of fusion research programmes in Europe, China and Japan. Improving the resistance to high temperature recrystallization, enhancing material strength to sustain thermal fatigue cracking and tolerance to neutron irradiation are the key indicators used for the down selection of materials and manufacturing processes to be applied to deliver engineering materials. In this work we investigate the effect of neutron irradiation on mechanical properties and microstructure of several tungsten grades recently developed. Neutron irradiation campaign is arranged for screening purposes and therefore is limited to the fluence relevant for the ITER plasma facing components. At the same time, the neutron exposure covers a large span of irradiation temperatures from 600 up to 1000 °C. Four different grades are included in the study, namely: fine-grain tungsten strengthened by W-carbide (W–4wt.% W2C), fine-grain tungsten strengthened by Zr carbides (W–0.5% ZrC), W alloyed with 10 at.% chromium and 0.5 at.% yttrium (W–10Cr–0.5Y) and technologically pure W plate manufactured according to the ITER specification by Plansee (Austria). The strengthening by W2C and ZrC particles leads to an enhanced strength, moreover, the W–0.5ZrC material exhibits reduced DBTT (compared to ITER specification grade) and is available in the form of thick plate (i.e. high up-scaling potential). The W–10Cr–0.5Y grade is included as the material offering the self-passivation protection against the high temperature oxidation.

TEM investigation of neutron irradiated and post irradiation annealed tungsten materials

In this paper, we present a transmission electron microscopy study of three tungsten grades subjected to neutron irradiation and post-irradiation annealing. The irradiation was performed at 600 °C up to 0.2 dpa and the microstructure was investigated after the irradiation, reported in a previous publication, as well as after the annealing at 800 °C and 1000 °C. The evolution of the radiation induced defects is characterized and the overall microstructural features are compared in three states: virgin-as irradiated – as annealed after irradiation. The annealing at 800 °C causes an increase in the loop and void densities and moderate increase in the mean sizes. An increase of the annealing temperature to 1000 °C causes a reduction of the loop density, while the loop size increases. Also the void density reduces, but not necessarily the void fraction. The peak of the void volume fraction is found around 800 °C, which coincides with the earlier reported experimental data on the void swelling peak under neutron irradiation.

Positron annihilation spectroscopy investigation of defects in neutron irradiated tungsten materials

The identification of defects in neutron damaged materials is essential for elucidating the correlation between the microstructure and the properties of a material. Positron annihilation spectroscopy (PAS) is very sensitive in open volume defects and thus a useful tool for the investigation of the radiation damage in matter. Tungsten is a critical material for the first wall and divertor of fusion reactors. In the current work, the evolution of the open volume defects in tungsten (W) materials neutron irradiated to 0.12 displacements per atom (dpa) and in the temperature range from 600 to 1200 °C in the Belgian Material Test Reactor BR2 is investigated by positron annihilation lifetime and coincidence Doppler broadening spectroscopy. Three tungsten grades were studied: W(100) single crystal, ITER grade forger bar and heavily deformed “cold”-rolled sheet. PAS results show that the neutron irradiation results in the formation of dislocations and voids of size larger 1 nm at all irradiation temperatures and in all W grades. The dislocation and void density decreases with increasing irradiation temperature. Moreover, the void size increases with the increase of the irradiation temperature.

Irradiation hardening of advanced tungsten grades: An experimental and inverse finite element method study

The effect of neutron irradiation on mechanical properties of various advanced W grades (pure, doped by K, alloyed by Re) was assessed by means of mechanical testing using miniaturized tensile and sub-miniaturized three-point bending (3PB) specimens. Different irradiation conditions in terms of temperature (400, 600, 800 and 1100 °C) and irradiation dose (0.2–0.25 dpa, 1.0–1.1 dpa) were considered. In order to extract the yield stress from the flexural load-displacement data, the empirical correlation between the flexural stress at a specific reference point on the flexural stress-strain curve and uniaxial tensile yield stress was established. The empirical ratio identified can be applied for the 3PB testing in a wide range of temperatures and plastic properties of un-irradiated and irradiated W alloys. The accuracy of the yield stress determination deduced using the empirical correlation from the 3PB tests was compared with the inverse FEM modelling procedure applied to the 3PB tests carried along with reference data extracted from the dedicated tensile tests. The information on the tensile yield stress and work hardening rate of all studied materials at different irradiation conditions was summarized and discussed in the view of the irradiation hardening.

Влияние механической активации порошка вольфрама на структуру и свойства спеченного материала SN-CU-CO-W

Introduction. One of the methods for improving the properties of sintered materials is mechanical activation of powders. It ensures milling the powders, changing its energy state, intensifying the sintering of powder materials, and forming a fine-grained structure in it. When tungsten powders are mechanically activated in planetary centrifugal mills, nanoparticles can be formed, which have a high reactive power. The objective of the paper is to study the effect of mechanical activation of tungsten particles on the structure and properties of the sintered Sn-Cu-Co-W powder material. Research technique: Mechanical activation of W16,5 grade tungsten powder is carried out in a planetary centrifugal ball mill AGO-2U for 5…120 minutes with carrier speeds of 400…1,000 rpm. The mixture of tungsten, tin, copper, and cobalt powders are compacted by static pressing in molds and then sintered in vacuum at 820 °C. The morphology and size of powder particles, as well as the structure of the sintered samples, are studied by scanning electronic microscopy, X-ray microanalysis, and optical metallography. Porosity of the sintered samples is identified by the gravimetric method. Microhardness of the structural constituents and macrohardness of the sintered materials are measured, too. Results: in the modes under study, mechanical activation is accompanied by the formation of tungsten nanoparticles with the minimum size of 25 nm. Alongside this, the powder is exposed to cold working, which hinders further milling. Tungsten nanoparticles, characterized by high surface energy, have a significant effect on the dissolution-precipitation of cobalt during liquid-phase sintering of Sn-Cu-Co-W powder material. Addition of nanodispersed tungsten into the material slows down the growth of cobalt particles during sintering and contributes to the formation of a fine-grained structure. The sintered Sn-Cu-Co-W material, containing mechanically activated tungsten, features higher hardness of 105…107 HRB, which is explained by cold working of tungsten particles and dispersion hardening. The results can be applied for improving mechanical properties of Sn-Cu-Co-W alloys used as metallic binders in diamond abrasive tools.

Damage behaviors in microstructures and mechanical properties of pure tungsten induced by repetitive thermal loads

Damage behaviors of ITER grade tungsten (W) induced by repetitive thermal loads have been investigated using an electron beam device EBMP-30. The metallographic observation, backscattered electron scanning electron microscopy, electron backscattered diffraction, atomic force microscopy analysis and tensile tests were carried out after the repetitive heat loads. Results indicate that there are negligible effects on the microstructures, surface morphologies and mechanical properties with the absorbed power densities (APD) lower than 10 MW/m 2 . While serious damages including the severe surface roughness with protruding structures along grain boundaries, and significant grains coarsening with the evolution of the grain shape occur undesirably due to the full recrystallization during the repetitive 30 MW/m 2 heat loads. Furthermore, after exposed to an APD of 30 MW/m 2 with 50 heat loads, the tensile properties deteriorate dramatically, resulting in a limited ultimate tensile strength of only 328 MPa and even a zero total elongation at 300 °C. The relationships between the thermal loads, microstructures evolution and degradation of mechanical properties have been analyzed.

Recent progress in the assessment of irradiation effects for in-vessel fusion materials: tungsten and copper alloys

The present contribution highlights results of the recent irradiation campaigns applied to screen mechanical properties of advanced tungsten and copper-based materials—main candidates for the application in the plasma-facing components (PFC) in the European DEMO, which has also been presented at 28th IAEA fusion energy conference. The main challenges in the formulated irradiation programme were linked to: (I) assessment of the ductile-to-brittle transition temperature of newly developed tungsten-based materials; (ii) investigation of an industrial pure tungsten grade under high temperature irradiation, reflecting operational conditions in the high flux divertor region; (iii) assessment of the high temperature strength of CuCrZr-based alloys and composites developed to enable the extension of the operational window for the heat sink materials. The development and choice of the advanced materials is driven naturally by the need to extend the operation temperature/fluence window thereby enlarging the design space for PFCs. The obtained results helped identifying the prospective tungsten and copper-based material grades as well as yielded a number of unexpected results pointing at severe degradation of the mechanical properties due to the irradiation. The results are discussed along with the highlights of the microstructural examination. An outlook for near future investigations involving in-depth post-irradiation examination and further irradiation campaigns is provided.

Effect of tungsten nanoparticles on sintering of the Sn-Cu-Co-W powder material

The effect of tungsten nanoparticles on the kinetics of sintering of the Sn-Cu-Co-W powder material used as a binder in diamond tools was studied. The W16,5 grade tungsten powder was mechanically activated in the AGO-2U planetary centrifugal mill for 60 minutes at the carrier rotation frequencies of 800 RPM. The mixture of tungsten, tin, copper, and cobalt powders was compacted by static pressing in press dies and then sintered in vacuum at the temperature of 820°C. The morphology and sizes of powder particles, as well as the structure of the sintered samples, were studied by the methods of scanning electronic microscopy. It has been demonstrated that tungsten nanoparticles have a noticeable effect on the process of dissolution-reprecipitation of cobalt in liquid-phase sintering.

Neutron irradiation effects in different tungsten microstructures

In this work the correlation of the neutron radiation damage and tungsten (W) microstructure is investigated. Further, the modification of the structure as a result of the neutron irradiation is assessed and its effect on the mechanical properties is determined. Forged bar (ITER grade), cold rolled sheet, and single crystalline tungsten materials were neutron irradiated at 600 °C to a damage of 0.12 displacements per atom. Neutron irradiation results in the formation of voids of almost the same size (larger than 1 nm) and dislocations detected by positron annihilation lifetime spectroscopy. All W grades have similar total dislocation densities, in the range of (1.6–2.4)×1014 m−2, as determined by electrical resistivity measurements. After irradiation the hardness of all tungsten grades increases and the largest increase is that of the single crystal (47%), whereas the smallest that of the sheet (13%). Increase in the yield strength, correlated to the increase of the hardness, is also found. The largest increase is observed for the single crystal (25%) and the smallest for the sheet (6%). The different degrees of hardening and strengthening indicate that the microstructure of the different tungsten grades has a significant influence on their neutron radiation damage resistance.

Application of sub-miniaturized bending tests to extract tensile properties from neutron-irradiated metallic alloys

In this work, we demonstrate the applicability of sub-miniaturized three-point bending (3PB) testing for the extraction of tensile plastic properties of metallic materials, such as yield stress and work hardening rate. The approach is developed and validated on the example of tungsten. For this, dedicated finite element method (FEM) simulations are performed to reveal the correlation between the flexural stress-strain response in 3PB tests and yield stress in tensile tests. Furthermore, a dedicated inverse FEM procedure utilizing rate-sensitive isotropic physical model is developed to extract both yield stress and work hardening rate from the available set of bending tests. Both FEM-based approaches are first benchmarked on unirradiated materials and then validated using neutron-irradiated tungsten grades. The accuracy of the tensile properties extracted using both methods is discussed along with the estimation of a number of 3PB tests required to reach a target precision. The applicability of 3PB geometry for the extraction of tensile properties from unirradiated bending tests below ductile-to-brittle transition temperature (DBTT) is also addressed.

Removal of suspended solids from weathered tungsten-ore beneficiation wastewater by electroneutralization and chemical precipitation

The direct reuse of weathered tungsten-ore beneficiation wastewater (WTBW) in tungsten-flotation system seriously deteriorates the flotation index of tungsten because of its high content of suspended solids (SS). In the present study, an innovative technology using calcium chloride (CaCl2) to remove SS from WTBW was established based on the theory of electroneutralization and chemical precipitation. A series of laboratory tests was performed to determine the optimal conditions for SS removal from WTBW. Species-distribution calculation, zeta potential, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used to analyze the underlying mechanism. Results showed that the content of SS in WTBW decreased from 25.16×103 mg/L to 22.56 mg/L after CaCl2 treatment. A concentrate with tungsten grade and recovery of 1.93% and 74.81%, respectively, was obtained by reusing the treated wastewater in the tungsten-flotation system. Compared with untreated wastewater, the tungsten grade and recovery of concentrate increased by 0.45% and 12.20%, respectively. Moreover, the Ca2+ supplied by CaCl2 can neutralize the negative charge on SS surface and further react with CO32– and SiO32– in solution to form CaCO3(S) and CaSiO3(S), which explained why CaCl2 can promote the aggregation and sedimentation of SS.