Nanostructured Tungsten Carbide Research Articles

Comprehensive behavior of reduced graphene oxide (rGO) reinforced plasma sprayed nanostructured WC–Co coatings

The effects of reduced graphene oxide (rGO) as an additive on the microstructure, mechanical properties, and tribological behavior of air plasma sprayed (APS) nanostructured tungsten carbide–cobalt (WC-25 wt.%Co) coatings were studied. The rGO was added in three distinct weight percentage proportions of 0.5, 1, and 1.5 wt.%. The microhardness and surface roughness of the APS sprayed nanostructured WC-25 wt.%Co coatings reinforced with rGO were changed significantly. Microstructural alterations in the coatings were also noticed with the addition of additives. Gluing of rGO amid coating splats was also seen in the microstructure of the coatings. The coatings’ microstructure revealed the presence of tungsten (W), tungsten carbide (WC), and semi-tungsten carbide (W2C) as the primary phases. The existence of the W2C phase in the microstructure of the coatings was mostly due to the decarbonization of WC at higher temperatures during plasma spraying. It was also found that the amount of wear of the coatings was exceptionally low because the rGO could not be extracted from the 1.5 wt.% rGO-reinforced coatings particularly. The wear degradation in the 0.5 and 1.0 wt.% rGO added coatings was mostly due to delimitation and the subsequent pulverization, notably at loads and sliding speeds of 1.5 kgf and 0.17 m/s.

Metallic hierarchical structures uniformly covered with WC@PDMS composite coatings toward comprehensively durable superhydrophobic surfaces

Superhydrophobic surface is one of the most promising materials for the prevention and elimination of ice in daily lives but its durability remains a tremendous problem. Inevitable deterioration on the low-free-energy coating caused by harsh environment restrains their potential applications. Icephobic polymers are more durable than mostly used fluorosilanes for their higher thickness and cohesive strength but difficult to be uniformly modified on rugged micro-nanostructures. In this study, a nanostructured tungsten carbide doped PDMS layer was uniformly covered on aluminum microcones via a hybrid fabrication process combining nanosecond and femtosecond laser ablations and a rotational homogenization process. The prepared superhydrophobic surfaces exhibited excellent water repellency and anti-icing properties in icing-deicing cycles, water flow impacting and freezing-melting cycles. Multiple mechanical/chemical damage tests were performed to test their durability comprehensively. In mechanical tests, the surfaces could withstand linear abrasion length of 240 cm under 5.2 kPa pressure, impacting sand amount of at least 80 g or tape peeling for at least 200 cycles. The chemical durability was elucidated in −40 to 200 °C cycles, 2-day ultraviolet exposure and immersion in different liquids. The proposed hybrid method to form homogenous, ductile and durable superhydrophobic coatings could yield a prospective candidate for applications in anti-fouling and anti-icing.

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.

Influence of heating rate on formation of nanostructured tungsten carbides during thermo-chemical processing

The structure, morphology and growth mechanism of nanostructured W-C phases during its synthesis by thermo-chemical processing at different heating rates was investigated. Higher heating rates of 8 and 4 K/min led to the formation of core–shell type nanoparticles via sequential formation of the trigonal ε-W2C (Space group:P3¯m1) followed by the hexagonal α-WC layer (Space group: P6¯m2). It appears that the formation of the core–shell possibly initiates by the nucleation of metastable W2C to form octahedral core, which subsequently act as the nucleation site for the growth of the lower order α-WC from the surface layer. The surface layer encapsulating the metastable phase possibly restricts the coarsening of the particles to a size less than 100 nm. Slow heating rate of 1 K/min, on the other hand, leads to the formation of single phase ε-W2C with abnormal particle size growth and epitaxial morphology along (001) crystallographic plane. This observation confirms that the anisotropic lattice volume expansion in the crystalline ε-W2C induced diffusion of carbon leading to abnormal particle coarsening.

Multigenerational Exposure to WCCo Nanomaterials-Epigenetics in the Soil Invertebrate Enchytraeus crypticus.

It has become clear how important it is to assess longer term effects of (nano) materials in the environment given the current evidence showing how epigenetics drives response mechanisms. Here we studied global DNA methylation in standard soil invertebrate Enchytraeus crypticus over 224 days when exposed to nanostructured tungsten carbide cobalt (WCCo nanomaterials (NMs)) and to cobalt (CoCl2) in a multigenerational experiment. In order to assess the transgenerational effect, we used a multigenerational (MG) test design consisting of four generations in spiked soil followed by two generations in clean soil. Results showed that MG exposure to WCCo NMs caused global DNA methylation to increase, which continued in unexposed generations and was associated with an increase in reproduction (phenotypic effect). In general, WCCo NMs caused more (and more consistent) methylation than CoCl2.

The influence of carbides on the microstructure, grain growth, and oxidation resistance of nanostructured carbides-strengthened cobalt-based multi-track laser-cladding layers

Cladding layers were prepared on carbon steel using nanostructured carbide-strengthened cobalt (Co)-based alloy (using nanostructured tungsten carbide as hard phases) as a deposited material by multi-track laser cladding. In addition to Co-based alloy, the deposited materials contained nanostructured chromium carbide (Cr3C2), vanadium carbide (VC), or Cr3C2 and VC. Compared with the substrate, all cladding layers had an improved oxidation resistance with an increased time (0–50 h) at 800 °C. Cr2C3 had a higher oxidation-resistance performance than VC and the mutual reaction of Cr2C3 and VC. The constitution and phases of the cladding layers indicated hexagonal-close-packed-α and body-centered-cubic-β cobalt and hard carbides, such as CoCx, V8C7, and Cr3C2, and some decarburization as Co3W3C and WC1-x. Elemental inter-diffusion occurred between the different phases as indicated by transmission electron microscopy and electron backscattered diffraction. Mixed carbide has a larger misorientation than the cobalt matrix, and electron backscattered diffraction has considerable potential to evaluate plastic deformation. The average grain size of the hard carbides was much larger than that of the original deposited material. The carbides grew rapidly through interfacial diffusion, boundary migration, and coalescence, which followed the Kirkendall effect and Ostwald-coarsening mechanism. This research helps to understanding the microstructure, oxidation resistance, grain growth, and interfacial behavior in multi-track laser-cladding layers.

Synthesis of Nanostructured Tungsten Carbide (WC) from Ammonia Paratungstate-APT and its Characterization by XRD and Rietveld Refinement

The carbides of refractory metals like tungsten carbide (WC), tantalum carbide (TaC) and niobium carbide (NbC), has been extensively studied due to their applications in several areas of industry, because of their specific properties; such as high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The tungsten carbide, particularly, is generally used at hardmetal industries due to its high hardness and wear resistance. New synthesis techniques have been developed to reduce the synthesis temperature of refractory metal carbides using more reactive precursors and gas-solid reactions for carbon reduction. The result is producing pure carbides suitable properties for production of high quality cemented carbides and more selective catalysts. In this work, pure and nanostructured WC was obtained from the ammonium paratungstate hydrate (APT), at low temperature and short reaction time. Hydrogen (H2) and methane (CH4) were used as a reducing gas and carbon source, respectively. The precursor and obtained product were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained by diffraction of X-rays showed that complete reduction and carburization of APT have been took place resulted in pure WC formation. The average crystallite size was in nanometer order reaching values of approximately 20.8 nm and a surface area (BET) of 26.9 m2/g.

Non-Noble Metal Oxygen Reduction Reaction Catalysts Based on Tungsten Carbide Supports and Fe-N Structures: Rrde Studies in Acid and Alkaline Media

Tungsten carbide (WC) has been receiving considerable attention in recent years due to its interesting properties, such as, a Pt-like catalytic behavior, [1] high electrical conductivity, chemical stability in acidic electrolytes, and much lower cost compared to platinum. [2] Non-noble catalysts of the type Fe-N/C (iron atoms coordinated to nitrogen atoms in a graphene packed structure) have also been considerably studied given their high catalytic activity toward the oxygen reduction reaction in both, alkaline and acid electrolytes. In this work, Fe-N structures were incorporated into various tungsten carbide nanostructures and their catalytic activities toward the oxygen reduction reaction are assessed in both, acid and alkaline media. Nanostructured tungsten carbides supported on carbon (WC(20, 30, 40%)/C) were prepared by depositing suitable amounts of WO3 on the Vulcan XC72R carbon black, followed by a thermal treatment at 850 0C for 4 hours in a controlled CH4/H2 atmosphere with a subsequent passivation step in a Ar/O2 (99%/1%) atmosphere for 12 hours at 25 oC. The Fe-N structure precursor was obtained by complexing an iron salt ((NH4)2Fe(SO4)2 x 6 H2O) with a nitrogen ligand (2,4,6-Tris(2-pyridyl)–1,3,5–Triazina), followed by deposition on the various WC/C supports with a subsequent pyrolysis step at 700 0C or 800 0C for 2 hours in a controlled N2 atmosphere. The electrocatalysts were physically characterized by X-ray Diffraction, X-ray Photoelectron Spectroscopy and Energy-dispersive X-ray spectroscopy. XRD spectra revel that the WC(30%)/C presents the highest WC proportion among the different supports, while the deconvoluted XPS spectra (W4f peak) evidence the presence of W+6, W+4 and W+2 at the surface of the material, with a much higher proportion of W+2 compared to insignificant amounts of W+6 and W+4. In contrast, when Fe-N structures are prepared on the WC(30)/C support, a higher proportion of W+6 is observed. The catalytic activity of these composites were assessed through cyclic voltammetry on a thin catalyst layer rotating ring-disk electrode, where the durability of the catalysts were conducted, followed with EDX analyses of the thin layer. Considering the ORR electrocatalytic activity, as a trend, it was seen that the Fe-N/WC/C catalyst presents higher activity compared to the support itself (WC/C) in both acidic and alkaline media with a prevalence of the direct 4e- reaction pathway. Further results for the dissolution of Fe upon accelerate durability test revels loss of metal along the cycling, and this information was important for the understanding of the ORR characteristics in these hybrid nanomaterials. Acknowledgements: Authors acknowledge the São Paulo Research Foundation (FAPESP - Procs. 2013/16930-7, 2016/07848-3), Brazil, for financial supports. The authors also wish to thank Brazilian Nanotechnology National Laboratory (LNNano) for assisting with the XPS measurements.

Spark plasma sintering of tungsten carbide nanopowders obtained through DC arc plasma synthesis

Abstract The paper dwells on the research conducted into high-rate consolidation of pure tungsten carbide (WC) nanopowders using the Spark Plasma Sintering technology. Studies included the effect that the original size of WC nanoparticles and their preparation modes have on density, structure parameters, and mechanical properties of tungsten carbide. Samples of high-density nanostructured tungsten carbide characterized by high hardness (up to 31–34 GPa) and improved fracture toughness (4.3–5.2 MPa m 1/2 ) were obtained. It has been found that materials that show abnormal grain growth during sintering have lower values of sintering activation energy as compared to materials the structure of which is more stable during high-rate heating. A qualitative model is proposed that explains this effect through the dependence of the grain boundary diffusion coefficient on the grain boundary migration rate.

Hydrogenation Properties of Nanostructured Tungsten Carbide Catalysts in a Continuous‐Flow Reactor

AbstractTungsten monocarbide (WC) obtained through a urea glass route showed a high activity and chemoselectivity for the continuous‐flow reduction of a variety of nitro compounds under milder conditions than those reported previously. The favorable effect of the nanostructure was shown by comparison with other commercially available WC materials. Moreover, WC functioned as an efficient support for Ni nanoparticles. This expanded its range of applicability and led to a bimetallic Ni@WC composite characterized by a high activity for the hydrogenation of cardanol, a phenolic lipid obtained from cashew nut shells.

Nano-Structured Tungsten Carbide Coating Reduces Wear of Tooling for Extrusion and Abrasive Materials Forming

This paper presents the applications of advanced CVD Tungsten Carbide coating to extend the life of tooling used for forming abrasive and corrosive materials.Hardide nanostructured Tungsten Carbide coating combines high hardness (70-77Rc) with excellent toughness. Unlike other hard coatings Hardide can produce a conformal coating layer on complex-shaped tools, including internal surfaces of extrusion die cavities and moulds. In ASTM G65 test the Hardide coating abrasion resistance exceeded WC/Co (9%) cemented carbide by a factor of 4X, and D2 tool steel by 10X. Thus the coating can significantly increase the life of D2 steel tooling used for forming abrasive materials and by maintaining better dimensional tolerances and surface finish of the tool it will manufacture better quality products.The Hardide coating has enhanced resistance to corrosion and aggressive media, including acids; this makes the coating especially suitable for the tooling used in forming uPVC, PTFE and other corrosive materials.The Hardide coating has been tested on extrusion and pelletizing dies processing abrasive and corrosive slurries and typically showed a 3X increase in the life of the tooling. Similar results were achieved by the coating of powder compaction punch/die sets for pharmaceuticals tableting.

Sparking plasma sintering of tungsten carbide nanopowders

Spark Plasma Sintering studies of the high-speed consolidation of pure tungsten carbide WC nanopowders have been carried out. The influence of the initial size of the WC nanoparticles and modes of their receiption the density, structural parameters, and mechanical properties of tungsten carbide are studied. Samples of high-density nanostructured tungsten carbide with high hardness (up to 31–34 GPa) and an increased crack resistance (4.3–5.2 MPa m1/2) are obtained. It is found that the effect of accelerating tungsten carbide nanopowder sintering under conditions of high-speed heating is associated with the acceleration of diffusion along grain boundaries in the sintered material. It is shown that the nonmonotonic dependence of the optimal sintering temperature on the initial grain size is caused by a change in grain-boundary diffusion coefficient in conditions of abnormal grain growth. It is found that the size of abnormally large grains in spark plasma sintering depends on the volume fraction of particles of the nonstoichiometric phase.

Nanostructured tungsten carbide synthesis by carbothermic reduction of scheelite: A comprehensive study

Mixtures of scheelite and graphite or carbon black, with different CaWO4:C weight ratios, have been mechanically milled for 24h. One mixture was mechanically milled for 8h to assess the role of a shorter milling time. The resulting powders have been studied by thermal analysis, isothermal annealing at different temperatures (1100–1400°C), X-ray diffraction (XRD) and scanning electron microscopy (SEM) to determine the effect of temperature and content of carbon on microstructure and phase purity of tungsten carbide formed by carbothermic reduction of scheelite (CaWO4+4 C→CaO+WC+3 CO). The experimentally observed reduction reaction sequence showed the formation of the intermediate phases Ca3WO6, W and W2C. A thermodynamic analysis proved that tricalcium tungstate (Ca3WO6) is a stable phase that forms independently of the partial pressure of CO, and that – under inert gas flow – the reaction can take place at temperatures as low as 700°C. However, the onset of the reaction was affected by the carbon content and heating rate, and therefore kinetics effects determine the temperature at which the reaction occurs.All powders subjected to 1h isothermal annealing exhibited micrometer-sized CaO particles and submicrometer-sized WC aggregates consisting of crystallites with an average size ranging between 40 and 90nm, depending on carbon content and annealing temperature.A shorter milling time did cause a small increase of residual W2C in the powder after heat treatment.A slight stoichiometric excess of carbon black was sufficient to ensure complete reduction of scheelite and formation of high phase purity WC, with very small amounts of W2C. After leaching with diluted HCl, the obtained powder is suitable for manufacturing ultra fine grained cemented carbides tools and wear parts.

Metallurgical characteristics and machining performance of nanostructured TNN-coated tungsten carbide tool

Abstract The effect of depositing Nb-rich Ti1–x Nb x N coatings on the metallurgical characteristics and machining performance of tungsten carbide tools is investigated. The direct current reactive magnetron sputter deposited Ti1– x Nb x N thin film was crystalline in the as-deposited state. The surface of the film is characterized by a dense granular structure with very few voids and lower roughness than the pristine tungsten carbide surface. Nanoindentation studies revealed that the Ti1–x Nb x N coating enhanced the hardness and Young's modulus of the tungsten carbide tool to 35 GPa and 703 GPa, respectively, as compared to 20 GPa and 550 GPa respectively, for the uncoated tool. Scratch tests showed that the Ti1–x Nb x N coating increased the adhesion strength on the tungsten carbide tool. Similarly, the tool wear, surface roughness and cutting force in turning an EN24 alloy steel component displayed significant improvement due to the Ti1–x Nb x N coating. The minimum surface roughness, minimum tool flank wear and minimum cutting forces were predicted for Ti1–x Nb x N coated tools based on the Taguchi experimental design.

Amorphous carbon modified nano-sized tungsten carbide as a gas diffusion electrode catalyst for the oxygen reduction reaction

Nanostructured tungsten carbide is used as the catalyst in a gas diffusion electrode. The presence of the appropriate amorphous carbon is beneficial for improving the conductivity and dispersibility of the tungsten carbide catalyst.

High-speed electropulse plasma sintering of nanostructured tungsten carbide: Part 1. Experiment

The high-temperature consolidation of nanopowders of pure tungsten carbide by electropulse plasma sintering (spark plasma sintering) is investigated. The influence of the initial size of WC nanoparticles and their preparation modes on the density, structural parameters, and mechanical properties of tungsten carbide are investigated. Samples of high-density nanostructured tungsten carbide with high hardness (to 31 GPa) and crack resistance (5.2 MPa m1/2) are fabricated.

Research Progress of Tungsten Nanorods and Nanoplatelets

Because of the characteristics of both one dimensional nanostructure and excellent physical and chemical properties, the kinds of novel nanomaterials-tungsten carbide nanowires, have important academic significance and practical meaning. The research development of one-dimensional nanostructured tungsten carbide is reviewed. The production methods of one-dimensional nanostructured tungsten carbide, such as nanotubes, nanorods, nanowires and nanoneedles by thermal decomposition technique, vapour deposition technique, magnetron sputtering technique, Eruptive heating technique and template technique respectively are systematically introduced. This paper summarizes the growth mechanisms and the problems involved in the existing synthesis methods. The research tendency is also forecasted.

Synthesis of nanostructured tungsten carbide via metal-organic chemical vapor deposition and carburization process

Nanostructured tungsten carbide particles were successfully synthesized by metal-organic chemical vapor deposition in a spouted bed followed by carburization in CH4/H2 atmosphere in the temperature range 700–900°C. The carburization process was a little bit complex, which involved the coating of carbon on the outer surface of the decomposed W(CO)6 precursor particles and then followed by carbon diffusion into the particles, leading to the formation of nanostructured WC via an intermediate metastable phase W2C. The carbon deficient phase W2C was formed initially at lower carburization temperature and then transformed to stable WC phase by increasing the temperature and holding time.

The influence of dielectric media on nano-structured tungsten carbide (WC) powder synthesized by electro-discharge process

In this investigation, nano-structured tungsten carbide (WC) powder has been synthesized using electro discharge process with tungsten and graphite electrodes submerged in two different dielectrics (kerosene and deionized water). The effect of input parameters (current and pulse duration) in the electro discharge process on the amount of powder production, structure, phases, morphological properties, and size distribution of particles were studied. The obtained results illustrated that, in the majority of setup settings, the amount of nano-structured powder in the kerosene was noticed to be approximately four times greater than the amount of powder produced in deionized water dielectric. Furthermore, it was observed that the particle size in kerosene dielectric (10–30nm) was smaller than the particle size in deionized water (30–80nm). According to XRD patterns, WC1−x phase in kerosene and W2C phase in deionized water were the main phases of synthesized powder. After producing WC1−x and W2C, both powders were put into the carburization operation under the Nitrogen gas to produce WC phase.

A Novel Approach for Direct Synthesis of Nanocrystalline Tungsten Carbide from Milled Scheelite Ore

In recent years, nanostructured tungsten carbide (WC) has been synthesized mainly from precursors like WO3, W, WCl6, and WCl4. These pure precursors are obtained by multistep high temperature treatments from the ore. Single phase nanocrystalline WC has been synthesized for the first time from scheelite ore at significantly lower [923 K (650 °C)] temperature. The activated charcoal and Mg turnings have been used as carbon source and reducing agent, respectively. The effect of time and temperature on the reaction has been investigated. The reaction by-products and impurities were washed firstly with dilute HCl and then with dilute base. The powders were characterized by X-ray diffraction technique and high resolution transmission electron microscope. The XRD patterns were refined by Rietveld method. The WC crystallite size was observed to decrease with lowering of synthesis temperature. The average crystallite size of WC formed was 20 nm. This report presents an exclusive, straight forward, environment friendly, and reproducible method for synthesis of nanocrystalline WC directly from scheelite ore.