WC Nanopowders Research Articles

Rheology and thermomechanical evaluation of additively manufactured acrylonitrile butadiene styrene (ABS) with optimized tungsten carbide (WC) nano-ceramic content

Tungsten carbide (WC), a superhard and thermally stable ceramic, is widely used in several industries. Its exceptional features portray WC as a promising reinforcement and stabilizing agent for popular polymeric matrices deployed in material extrusion (MEX) 3D-Printing, such as Acrylonitrile Butadiene Styrene (ABS). This potential was investigated in depth and is presented herein. ABS/WC nanocomposite filaments were prepared by melt extrusion and tested. A filler loading of 0 wt % up to 10 wt % WC, in 2 wt % steps were fabricated. The impact of the WC nanopowder content on the structural, rheological, thermal, mechanical, and morphological characteristics of nanocomposite filaments and 3D printed samples was investigated with the aid of fifteen (15) different tests. The experiments revealed excellent thermal stability of the developed nanocomposites, as well as non-Newtonian shear thinning behavior of their melts, which is encouraging for their processability. WC nanoparticles impressively upgraded the mechanical capacity of the optimized nanocomposites in comparison to that of pure ABS. ABS with 4.0 wt % WC grade exhibited a noticeable increase in most of the mechanical characteristics; Compressive, flexural, and tensile strength all rose by 25.9%, 29.4%, and 20.9% respectively, while the microhardness increased by 100.3%, showing potential for use in applications requiring high wear resistance. The findings of the current research indicate that novel cost-effective ABS/WC composites have high potential and industrial merit for a variety of demanding applications with ABS-based composites.

Influence of Powder Charge Composition on the Structure and Properties of T15K6 Hard Alloy

The purpose of the study is to determine the effect of nanosized additives on the structure and properties of the T15K6 hard alloy.Methods. These studies were carried out using an S-3400N electron microscope. The mechanical and physical properties of the structure of a hard alloy of the WC-TiC-Co system were studied using the example of T15K6 when nanosized tungsten powder and nanosized tungsten carbide powder with cobalt deposited on it were introduced into the initial charge using an optical and electron microscope; An X-ray spectrum analysis of the obtained samples of the T15K6 hard alloy was carried out on a DRON-4 X-ray diffractometer.Results. A hard alloy of the WC-TiC-Co system was studied with the introduction of nanosized tungsten powder into the initial charge, as well as with the introduction of nanosized tungsten carbide with cobalt deposited on its surface.In the work, the used powders of tungsten, nano-tungsten, cobalt, titanium carbide, tungsten carbide, nano-powder of tungsten carbide were studied, and the microstructure of the obtained hard alloys was also studied. It is shown that the coercive force of the T15K6 alloy depends on the size of the cobalt phase regions in the alloy; measuring its value makes it possible to judge the size of carbide grains. To improve the strength properties of hard alloys of the WC-TiCCo system, it is recommended to introduce nanosized WC additives or WC nanopowder with deposited cobalt.Conclusion. To improve the strength properties of hard alloys of the WC-TiC-Co system, it is recommended to introduce nanosized WC additives or WC nanopowder with deposited cobalt. The introduction of these additives into the composition of the powder charge of the T15K6 hard alloy leads to an increase in the ultimate bending strength by 15%. The introduction of nanosized WC additives or WC nanopowder with deposited cobalt makes it possible to obtain a fine-grained structure with a grain size of no more than 4–6 μm.

Microstructure and phase composition of hard alloys produced from nanocrystalline powder mixture WC-6wt.%Co with C, Al and ZrC additives

A large specific surface area of WC nanopowder determines its high chemical activity and makes it very sensitive to various impurities, among which oxygen is most harmful and unavoidable. During heating, oxygen interacts with carbon of WC being removed in the form of CO/CO2, which finally leads to the appearance of embrittling η-phases in the hard alloy, abnormal growth of WC grains, and formation of a porous microstructure. To prevent heavy decarburization of WC during vacuum sintering of hard alloy from a nanocrystalline powder mixture WC-6wt.%Co, in this work we compared three methods: addition of extra carbon to compensate for carbon loss as a result of decarburization; addition of Al to bind impurity oxygen into Al2O3 before it interacts with carbon of WC; and addition of ZrC to compensate for carbon loss and bind impurity oxygen into ZrO2. Nanocrystalline powder mixtures based on WC-6 wt.%Co with and without additions of C, Al, and ZrC were prepared from microcrystalline powders of WC, Co, Al, ZrC, and carbon black by high-energy milling, then they were compacted in a cylindrical mold by uniaxial pressing at a pressure of ~460 MPa and sintered in graphite crucibles for 15 min at 1380 °C in vacuum of ~10-2 Pa. The heating rate to the temperature of sintering was 10 °C/min. The initial powders, powder mixtures prepared therefrom, and sintered hard alloys were certified using X-ray diffraction, chemical analysis, scanning electron microscopy, BET adsorption method, helium pycnometry, and Vickers method. The studies performed showed that the average particle size in all the prepared powder mixtures does not exceed 100 nm, and the content of impurity oxygen in them varies from 3.3 to 4.3 wt.% depending on the additives. It was established that only a part of oxygen contained in the powder mixtures is in the chemisorbed state and takes part in the decarburization of WC during vacuum sintering. The Al additive is completely oxidized during milling of the powder mixture and transforms into nanocrystalline Al2O3, which only aggravates carbon loss during sintering and results in the formation of a multiphase and relatively porous microstructure of the hard alloy. On the contrary, using carbon and ZrC additives we managed to prevent the decarburization of WC during sintering of the hard alloy and to form a less porous microstructure in it. It was shown that the presence of ZrO2 inclusions does not impede intensive growth of WC grains during sintering, but rather promotes it. Carbon deficit slightly suppresses intensive WC grain growth during sintering of hard alloy leading to the formation of η-phases and to an increase in the density and microhardness, but the presence of oxide inclusions Al2O3 and ZrO2 in the microstructure reduces the values of these properties.

Obtaining fine-grained hard alloys homogeneous in carbide grain

The actual task of this work is to obtain homogeneous hard alloys with fine carbide grains, combining high hardness and strength. Studies were carried out to establish the most favorable phase compositions of hard alloys and the most rational technical methodology for their production. In this research work, a nanostructured WC-TiC-Co powder charge was obtained by mechanochemical synthesis. Nanosized WC powder and nanopowder with precipitated Co were added to the hard alloy charge by mixing in a ball planetary mill. The process of pressing the powder charge at a pressure of 100-1000 MPa, as well as the sintering process at a temperature within the range of 1450-1600℃ was applied. The chemical-metallurgical method of deposition of metal layers from salt solutions was applied to obtain the WC-Co hard alloy. X-ray structural analysis and scanning electron microscopy were applied. The effect of the preparation method on the phase composition of WC-TiC-Co consolidated samples was studied. In the microstructure of these hard alloys, intercrystalline particles of (Ti,W)C are observed, and the presence of the liquid phase can lead to a rounded shape. It was found that the addition of nano-sized WC powder leads to an increase in pressed density. It was revealed that the addition of WC nanosize additives or WC nanopowder with deposited cobalt makes it possible to obtain a fine-grained structure with a grain size of not more than 4-6 microns. It was found that the addition of WC nanopowder with precipitated cobalt to the alloy has the highest Brinell hardness values; in addition, it leads to an increase in the bending strength.

A Novel Approach to the Rapid in situ Synthesis of Tungsten Carbide Nanopowder by Plasma Milling and Carbothermal Reduction

This work prepares nanocrystalline tungsten carbide (WC) powder using conventional ball milling or plasma milling (P‐milling) to process tungsten trioxide (WO3)–carbon (C) mixtures, with subsequent carbothermal reduction. The aim is to assess the effects of a discharge plasma on the microstructure of these materials. The results indicates that WC powders with particle sizes of less than 100 nm could be fabricated through heating at a relatively low temperature of 1150 °C for 1 h under vacuum after P‐milling. This process is found to allow a lower processing temperature and provided more complete carburization in comparison with conventional ball milling. P‐milling is determined to produce more loosely adhering WO3 nanoparticles and a higher surface area, resulting in more reactive sites and a larger contact area between WO3 nanoparticles and C atoms. This technique simultaneously generates more oxygen vacancies and defects on the surfaces of the WO3 and C, respectively, based on the use of a plasma discharge. It is evident that this new technology permits nanocrystalline WC to be readily obtained from WO3 and C in a reduced time span and at a lower cost and greater efficiency. This technique could also be used to fabricate WC nanopowders on an industrial scale.

Changes in Mechanical Characteristics of HPC Samples Modified with WC and WO<sub>3</sub> Nanopowder Agglomerates

The paper presents the results of tests of HPC (high performance composites) samples consisting of aramid and glass fabrics modified by agglomerates of WC and WO3 nanopowders. According to the test results, introduction of WC and WO3 powders into the composite plate structure makes it more rigid and elastic, increasing its ability to dissipate energy.

Determination of changes in the mechanical properties of polymer composites with the addition of agglomerates of WC nanopowder

Recently, there has been a growing interest in the development of new composite materials with improved characteristics. The article presents the results of tests of composite specimens based on aramid fabrics modified with WC nanopowder agglomerates obtained from carbide manufacturing waste. The following mechanical characteristics were investigated: transverse bending resistance, fracture resistance and energy absorption during contact with a physical body at high speed. According to the results, the transverse bending resistance increased by 35% at a WC concentration of 5%. When 3% WC powder was added to the matrix composition, the total crack length after impact was almost halved. The largest increase in energy absorption of the samples was about 30% at 1% additive concentration. The significant increase in the investigated parameters can be explained by the complex morphology of the embedded particles. In further investigations it is planned to study in detail the mechanism of distribution of nanodispersed WC powder additive in the volume of the modified material.

Analysis of the Electroconsolidation Process of Fine-Dispersed Structures Out of Hot Pressed Al2O3–WC Nanopowders

Fabrication of alumina–tungsten carbide nanocomposite was investigated. Characteristics of the densification and sintering were analyzed considering both the nano-size particle starting powders and the processing stages. Different heating rates were generated during densification and consolidation with a maximal load was applied only after a temperature of 1000 °C was reached. Due to the varying dominance of different physical processes affecting the grains, appropriate heating rates and pressure at different stages ensured that a structure with submicron grains was obtained. With directly applied alternating current, it was found that the proportion Al2O3 (50 wt.%)–WC provided the highest fracture toughness, and a sintering temperature above 1600 °C was found to be disadvantageous. High heating rates and a short sintering time enabled the process to be completed in 12 min, saving energy and time.

ВЛИЯНИЕ АГЛОМЕРАТОВ НАНОПОРОШКА КАРБИДА ВОЛЬФРАМА НА СВОЙСТВА ЦЕМЕНТА

The object of the research is cement samples modified by agglomerates of tungsten carbide nanopowders obtained from carbide waste. The paper considers the influence of tungsten carbide nanopowder on the change in the main cement characteristics (density, water demand, setting time, kinetics of strength gain, compressive strength, bending strength). The optimum additive content in cement materials is 3%. This parameter is estimated by the maximum growth of compressive and flexural strength at all stages of hardening. The effect of WC powder additive on the structure of the cement matrix has been shown. Due to the high dispersibility of WC nanopowder, its particles act as additional crystallization centers, fill in the micropores of the cement stone and create a denser and stronger structure. The results of studying the microstructure of the cement stone with additions of WC powder indirectly confirm the results of strength characteristics. The cement-sand samples with the modifier are found to have a denser crystallized cement-sand stone compared to the control sample (without WC powder addition). The conducted researches have shown perspectivity of application of WC nanoparticles agglomerates as modifying additives for cement materials, which can be used in production of special purpose concrete (hydraulic, radioprotective, etc.). The economic effect of the use of WC nanoadditives obtained from hard-alloy production wastes can be obtained due to a reduction in costs at the stages of construction and operation of structures, buildings, structures based on it.

Microwave assisted synthesis of WC nanopowder from nanosized multicomponent system W-C produced in thermal plasma reactor

The effect of processing multicomponent nanopowders of the W-C system obtained by plasma-chemical synthesis in a microwave electromagnetic field with a frequency of 24 GHz, generated by continuous gyrotron, has been experimentally studied. It was found that the formation of nanosized particles of tungsten carbide WC occurs during microwave treatment. The influence of the processing time, microwave power and the composition of the gas atmosphere on the phase composition of nanopowders, their morphology and specific surface area was investigated.It has been found that processing in a microwave field can reduce the time of chemical transformations, leading to the formation of tungsten monocarbide, by an order of magnitude compared to traditional heating in an electric furnace in a hydrogen environment. At the same time, the particle size is preserved in the nanometer range.

Feasibility of Cobalt-Free Nanostructured WC Cutting Inserts for Machining of a TiC/Fe Composite.

The paper presents results of investigations on the binderless nanostructured tungsten carbide (WC) cutting tools fabrication and performance. The scientific novelty includes the description of some regularities of the powder consolidation under electric current and the subsequent possibility to utilize them for practical use in the fabrication of cutting tools. The sintering process of WC nanopowder was performed with the electroconsolidation method, which is a modification of spark plasma sintering (SPS). Its advantages include low temperatures and short sintering time which allows retaining nanosize grains of ca. 70 nm, close to the original particle size of the starting powder. In respect to the application of the cutting tools, pure WC nanostructure resulted in a smaller cutting edge radius providing a higher quality of TiC/Fe machined surface. In the range of cutting speeds, vc = 15–40 m/min the durability of the inserts was 75% of that achieved by cubic boron nitride ones, and more than two times better than that of WC-Co cutting tools. In additional tests of machining 13CrMo4 material at an elevated cutting speed of vc = 100 m/min, binderless nWC inserts worked almost three times longer than WC-Co composites.

Investigation of the effect of tungsten carbide nanopowder additives on the strength properties of fiberglass, based on LAVESAN glass fabric and EPR 320 epoxy resin

The paper presents the results of tests for modulus of elasticity and tensile strength of fiberglass samples consisting of glass fiber Lavesan (Italy) and epoxy resin binder EPR 320 with hardener EPH 162, modified with WC tungsten carbide nanopowder, obtained from carbide waste. The positive effect of WC nanopowder on tensile strength and modulus of elasticity is shown. With the addition of nanoadditives in the mass concentration of 1 … 4% of the resin mass, the increase in tensile strength was more than 1.5 … 2.5 times, with no significant change in material elasticity.

Study on influencing factors and mechanism of high-quality tungsten carbide nanopowders synthesized via carbothermal reduction

In this study, high-quality WC powders with 100 nm were synthesized using a simple and efficient carbothermal reduction method. The effects of carbon source and temperature on the synthesis process, nucleation and growth mechanism of WC nanopowders were investigated in detailed. The results show that acetylene black with small particle size and good dispersion is the optimal carbon source to prepare WC nanopowders. The uniform precursor synthesized by acetylene black can significantly increase the contact probability of WO3 and C particles, greatly reduce the activation energy, and effectively improve the reaction efficiency during subsequent carbothermal reduction process. Moreover, the formation temperatures of WC are reduced to 1000 °C compared with other three carbon source. Further increasing carbothermal reduction temperature can provide the driving force of diffusing atoms, which promotes the carbothermal reduction reaction, but also significantly increases the diffusion rate of grain boundary resulting in rapid grain growth.

Influence of oxygen on densification kinetics of WC nanopowders during SPS

The shrinkage of the WC nanopowders with increased oxygen content during Spark Plasma Sintering (SPS) was shown to be limited by the grain boundary diffusion with abnormally low activation energy. It was found that the reduction of the SPS activation energy may originate from the effect of oxygen on the diffusion permeability of the grain boundaries in tungsten carbide at the intensive compaction stage as well as from an abnormal grain growth at the high-temperature sintering stage. The kinetics of SPS of the WC-W2C–WO3–W nanopowders at the intense compaction stage is controlled by the sintering rate of the oxide particles with simultaneous transformation of these ones into the W2C particles and then, at the high-temperature sintering stage – by the plastic flow of the W2C particles in the presence of tungsten ones. The ceramic specimens with high density (98–99%) and ultrafine grained structure (mean grain size < 0.3 μm) having an increased hardness Hv = 30.5 GPa at minimum Palmquist fracture toughness ~ 6.5 MPa m1/2 were obtained by SPS.

The influence of the rotation frequency of a planetary ball mill on the limiting value of the specific surface area of the WC and Co nanopowders

An increase in the hardness and wear resistance of WC-Co alloys with a decrease in the grain diameter of WC and Co makes it relevant to search for methods for producing powders with a maximum specific surface area (SSA). SSA growth is limited even when milling powders of WC and Co in the most high-energy mills. Effect of increasing the rotation speed of a planetary ball mill on the limiting value of the SSA of obtained nano sized WC and Co powders is studied. According to the developed model, an increase in the rotational speed of the mill leads to an increase in the limiting value of SSA if the cause is particle hardening. If the cause is coalescence, an increase in frequency leads to a decrease in the limiting value of the SSA. It was determined that the limiting value of SSA of WC particles increases from 1.0⋅108 m2/m3 to 2.2⋅108 m2/m3 (Sauter average diameter decreases from 60 to 27 nm) with increase of mill rotation frequencies from 2.5 to 4.2 rps due to a decrease in the volume of “indestructible” particles. And the limiting value of SSA of WC particles decreases from 2.2⋅108 m2/m3 to 1.1⋅108 m2/m3 (Sauter average diameter increases from 26 to 55 nm) with increase of mill rotation frequencies from 5 to 6.7 rps due to the increase of the coalescence rate. The experiment showed that the limiting value of SSA for Co powder decreases from 1.0⋅108 m2/m3 to 1.1⋅106 m2/m3 with increasing of the rotational speed of the mill from 2.5 rps to 6.7 rps (Sauter average diameter increases from 60 to 5450 nm) due to the increase of the coalescence rate. Studies have shown that the growth of SSA of WC grains is limited by a certain value (11.5 nm).

Influence of additives and concentration of WC nanoparticles on properties of WC−Cu composite prepared by electroplating

Abstract The effects of additives (polyethylene glycol (PEG), sodium dodecyl sulfate (SDS)) and WC nano-powder on the microstructure, relative density, hardness and electrical conductivity of electroplated WC−Cu composite were investigated. The preparation mechanism was also studied. The microstructure of samples was analyzed by XRD, SEM, EDS, TEM and HRTEM. The synergistic effect of PEG and SDS made the WC−Cu composite more compact during the electroplating process. The hardness of WC−Cu composites increased with the increase in WC content, while the electrical conductivity decreased with the increase in WC content. The density of samples tended to increase initially and then decreased with increase in the additive content. When the electroplating solution contained 10 g/L WC nano- powder, 0.2 g/L PEG and 0.1 g/L SDS, the WC−Cu composite exhibited hardness of HV 221 and electric conductivity of 53.7 MS/m. Therefore, the results suggest that WC−Cu composite with excellent properties can be obtained by optimizing the content of additives and WC particles.

Synthesis of tungsten carbide nanopowders by direct carbonization of tungsten oxide and carbon: Effects of tungsten oxide source on phase structure and morphology evolution

In the paper, WC nanopowders are successfully prepared by carbothermal reduction method, and the effect of tungsten oxide source on the phase structure evolution and products properties of the as-synthesized WC nanopowders has been investigated. Four tungsten oxide powders are chosen as tungsten oxide sources, e.g., rods-like WO3 , WO3 nanopartiles, WO3 micro-particles and WO2.9 micro-particles. Compared with other three tungsten oxide sources, the WO3 micro-particles possesses small particle size, less agglomerates and good dispersity and the uniform tungsten oxide-carbon mixture after ball milling can be easily obtained. The appropriate tungsten oxide source can result in lower processing temperature (≤1200 °C) and shorter holding time (≤3 h). Single-phase WC powders with average particle size of 100 nm and uniform particle distribution can be achieved by micro-particle-like WO3 at 1100 °C for 3 h. The as-prepared WC products by other three tungsten oxide sources exhibit problems of more aggregates, non-uniform particle size and large particle size (250 nm), respectively. In addition, the method can provide a facile, low-cost, efficient, and industrially feasible pathway for large scale preparation of WC nanopowders.

Preparation and properties of the VC/Cr3C2/TaC doped ultrafine WC-Co tool material by spark plasma sintering

This work is focused on the preparation and properties of ultrafine WC-Co cemented carbides. Samples were prepared by spark plasma sintering technology using WC and Co nanopowders and different inhibitors such as VC, Cr3C2 and TaC. The influence of inhibitors on the microstructure and mechanical properties of cemented carbides was investigated by using separate addition of VC/Cr3C2/TaC (0, 0.4 and 0.8 wt%) and pairwise addition (VC-Cr3C2, VC-TaC and Cr3C2-TaC). The results showed that with the addition of VC/Cr3C2/TaC, the average WC grain size decreased and VC led to smaller grain size than Cr3C2 and TaC. WC grain morphologies of cemented carbides with VC were triangular prisms with multi-step structure, whereas tended to be round and blunt in cemented carbides with Cr3C2/TaC. Moreover, the addition of inhibitors caused hardness to increase and fracture toughness to decrease in various degrees. Transverse rupture strength (TRS) was affected by changes in grain size and WC/Co interfacial energy caused by inhibitors. The sample with 0.4 wt% VC-0.4 wt% Cr3C2 sintered at 1250 °C had comprehensive mechanical properties. Its relative density, average grain size, hardness, fracture toughness and TRS were 98.9%, 200 nm, 2110 kg/mm2, 10.4 MPa⋅m1/2 and 1990 MPa, respectively.

Hot Pressing of Tungsten Monocarbide Nanopowder Mixtures by Electroconsolidation

The paper presents theoretical and experimental results in the field of the manufacturing of cemented tungsten carbide materials. The important issue of avoiding any additional substances like plasticizers was challenged in order to reach the maximal possible density of sintered material while keeping its purity. To solve the problem, the electroconsolidation method of hot pressing supported by direct current was applied. The respective apparatus was constructed that enabled WC nanopowders to be sintered under pressure and high temperature during a very short time of ca. 3 minutes. In the experiments, because of the short heating time, grain size of the sintered bulk WC increased insignificantly, in general, remaining smaller than 1 μm. Similarly, sintering under hot pressing with direct current, a mixture of 3% by weight Y2O3 stabilized ZrO2 and 50% by weight WC, produced a fine structure with a uniformly distributed WC grains. The applied electric field led to the formation of a temperature gradient around the pores, with a favourable impact on the compaction of large pores and an increase in the final density of the bulk material. The experimental research confirmed that the main mechanism of the densification of nanodispersed powders of tungsten monocarbide was a locally inhomogeneous diffusion-viscous flow with intergranular slipping.

Synthesis of Nanostructured WC-Co Hardmetal by Selective Laser Melting

Selective laser melting is a layer-by-layer technique to form a solid part from powder. The thermal cycle of this process can be as short as one millisecond and less. This is why it is favorable to obtain nanostructured materials with advanced properties. Metal matrix composite WC-Co is studied. Micron-sized Co powder was mixed with WC nanopowder in a planetary ball mill to prepare uniform composite powder. Single remelted beads and monolayers were obtained from the composite powder on the substrates of sintered WC-Co. No cracks and good adhesion to the substrate are observed. The high cooling rate up to 106 K/s explains the fine microstructures. Increasing the scanning velocity is favourable because of refining the microstructure and decreasing the balling-effect. The attained values of surface roughness are as low as 1-2 μm.