Ultrafine WC Research Articles

Kinetic study of electroless cobalt deposition on WC particles

The cobalt coating with an average thickness of 15–20 nm was uniformly plated on the surface of ultra-fine WC powders by electroless plating in the present work. The effects of electroless plating condition parameters on the deposition rate were studied. It was found that the deposition rate increased with the increase of CoSO4·7H2O content, pH value, complexing agent concentration, and bath temperature, while decreased with the increase of reducing agent (NaH2PO2·H2O) concentration. Furthermore, the cobalt deposition rate empirical equation and activation energy were determined. The results show that the activation energy (Ea) for the electroless cobalt on WC substrates is approximately 54.65 kJ/mol.

Effect of Ultra-fine WC Particles on Microstructural Evolution and Wear Behavior of Ni-Based Nano-CeO2 Coatings Produced by Laser

The wear behavior and microstructure of CO 2 laser cladded Ni-based alloy coatings with 1 wt% nano-CeO 2 and 20 wt% WC addition (CeO 2 /Ni) was compared with Ni-based coatings with 1 wt% nano-CeO 2 addition (WC-CeO 2 /Ni). Both coatings were cladded on 30CrMnSiNi2A steel with good metallurgical bounding to substrate. The influence of ultra-fine carbide WC on the microstructure of WC-CeO 2 /Ni alloy composite coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA). WC addition increased M 23 C 6 content, but decreased the M 7 C 3 . The comparison of comprehensive mechanical properties between coatings with and without fine WC particles was conducted on Vickers hardness and wear-resistance test system. Results indicate that the performance of WC-CeO 2 /Ni is better than that of CeO 2 /Ni metal matrix composition (MMC). Few hot cracks appeared in Ni-based WC-CeO 2 MMC production, which were investigated by SEM and EDS. The crack mechanism can be claimed as Fe dilution and coefficient of thermal expansion for WC-CeO 2 /Ni MMC differed from that of base material 30CrMnSiNi2A steel.

Influence of Micron WC Addition on the Microstructure and Mechanical Properties of Ultrafine WC–Co Cemented Carbides at the Elevated Temperature

In this paper, the influence of micron-grained WC additions with the different grain sizes on the microstructure and hardness of ultrafine WC–Co cemented carbides at the elevated temperature were investigated by the scanning electron microscope and mechanical properties test. The Vickers hardness and transverse rupture strength of hardmetals were measured at temperatures ranging from room temperature to 800°C. The results show that the addition of micron-sized WC particles can lead to the increase of fracture toughness and slow the decreasing of hardness at the elevated temperature.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ УЛЬТРАДИСПЕРСНЫХ ЧАСТИЦ МОНОКАРБИДА ВОЛЬФРАМА НА СТРУКТУРУ НАПЛАВЛЕННОГО МЕТАЛЛА

Statement of problem (relevance): the paper describes the problem of structure formation in welding low-carbon low-alloy steels. The weld metal structure forms in a complex thermal environment that predetermines the operating performance of the metal. Emergence of large columnar crystals in welds poses a potential hazard, as such structures may under certain conditions concentrate the tension and trigger destruction. The paper dwells upon the possibility of controlling the primary structure of welded metal by injecting nano- and ultrafine particles of a refractory material into the weld pool. The objective is to study how nano- and ultrafine particles of tungsten monocarbide WC) affect the structure of welded metal. Methods used: the researchers have carried out a laboratory experiment consisting in making electrodes with a coating containing a varying amount of ultrafine WC powder, then making welded-metal samples and studying the samples by optical microscopy (a Micromed-Met microscope) as well as measuring the Vickers hardness (a HV-1000 device). The novelty of this research consists in gathering new data on how the concentration of ultrafine WC powder in the electrode coating affects the structure of welded metal. The results: the structure of metal welded by electrodes with a coating containing 0, 0.02, or 0.2 % of WC powder (% of drymix weight) features columnar crystals surrounded by a grid of peripheral ferrite formed along the primary-grain boundaries. Needle-like inclusions of Widmanstatten ferrite sprouting from the crystal edges to the crystal center are observed along with bainitic structures. Electrodes with a coating containing 0.4% of WC powder produce welded metal of a finer cellular structure in the form of equiaxed crystals. The hardness of the welded-metal samples is within 184 to 189 HV. Practical significance: the research has produced data necessary for creating new coated electrodes for welding and surfacing low-carbon low-alloy steels.

Suppression of diamond tool wear in machining of tungsten carbide by combining ultrasonic vibration and electrochemical processing

As an important ceramic material, tungsten carbide (WC) is utilized as the typical mold in precision glass molding, which has replaced conventional grinding and polishing to provide a highly replicative process for mass manufacturing of optical glass components. Ultra-precision grinding, which is time consuming and has low reproducibility, is the only method to machine such WC molds to high profile accuracy. Although diamond turning is the most widely used machining method for fabrication of optical molds made of metals, diamond turning of WC is still considered challenging due to fast abrasive wear of the diamond tool caused by high brittleness and hardness of WC. Ultrasonic vibration cutting has been proven to be helpful in realizing ductile-mode machining of brittle materials, but its tool life is still not long enough to be utilized in practical diamond turning of optical WC molds. In the current study, a hybrid method is proposed to combine electrochemical processing of WC workpiece surface into the diamond turning process. Cutting tests on WC using poly-crystalline diamond tools were conducted to evaluate its effect on improvement of tool wear and surface quality. Validation cutting tests using single crystal diamond tools has proven that the proposed hybrid method is able to significantly reduce the diamond tool wear and improve the surface quality of machined ultra-fine grain WC workpiece compared to ultrasonic vibration cutting without electrochemical processing.

Annealing effect on the mechanical properties of ultrafine WC–Co materials

In dry machining, the tool-chip interface temperature is a critical factor affecting the engineering performance of WC–Co tools. As the temperature variation of the cutting tool in dry machining is similar to that in annealing process, the effect of tool-chip interface temperature on the mechanical properties of cutting tool materials in dry machining can be studied by means of annealing experiment. In this paper, a series of annealing experiments of ultrafine-grained WC–Co materials were conducted, and the effects of the annealing temperature and holding time on the mechanical properties of WC–Co materials, including flexural strength, hardness and fracture toughness, were investigated. The results show that under the experimental conditions, the annealing temperature dominates the mechanical properties of WC–Co materials. The flexural strength and fracture toughness of the ultrafine-grained WC–Co materials decrease in different extent with increasing of annealing temperature, whereas the hardness does not change obviously. The measurements of the microstructures and residual stresses revealed that the deterioration of mechanical properties of WC–Co materials after annealing can be attributed to the relaxation of compressive residual stress.

Fine platelet-like grained WC–Co cemented carbides: Preparation, characterization, properties and application in PVD coating substrates

Strengthening of the adhesion strength and its stability of PVD coated cemented carbides has always been the focus of attention. Commercial ultrafine WC–12Co composite powder by spray conversion processing was used as the raw material. WC–12Co–0.05La2O3, WC–12Co–0.9Cr3C2–0.05La2O3, WC–12Co–0.5Cr3C2–0.4VC–0.05La2O3 and WC–12Co–0.9Cr3C2–0.4VC–0.05La2O3 alloys were prepared by a conventional long-time ball-milling. The results show that fine platelet-like grained WC–12Co–0.9Cr3C2–0.4VC–0.05La2O3 alloy is characterized with a homogenous microstructure, the best property combination of high strength, high hardness and high toughness and the highest WC (0001) texture coefficient. By using fine platelet-like grained WC–Co cemented carbides as the substrates, larger than 100N adhesion strength expressed by critical load LC2 for AlCrN, AlTiN and (AlCrSiWN+AlCrN) PVD coatings is achieved. The related strengthening mechanisms are discussed.

Effect of direct current patterns on densification and mechanical properties of binderless tungsten carbides fabricated by the spark plasma sintering system

Binderless tungsten carbide materials (bWCs) were fabricated by the spark plasma sintering (SPS) system. Ultrafine WC powders with adjusted oxygen contents and C/W atomic ratios were used as raw materials. Constant and pulsed direct current patterns (constant DC and pulsed DC) were chosen as the power supplies. The results indicate that for WC starting powders with either low (0.31%) or high (0.95%) oxygen contents, a relative density larger than 99.0% can be reached by pulsed DC at 1820°C. Nevertheless, the severely oxidized WC powders cannot be well-densified by constant DC. A high degree of densification of bWCs facilitates the collaborative improvement of the toughness and hardness. The existence of W2C facilitates the improvement of the hardness at the high expense of the toughness. The existence of graphite phase is substantially detriment to the toughness. The grain coarsening facilitates the improvement of the toughness with sacrificed hardness. The related mechanism is discussed.

Ultrafine WC nanoparticles anchored on co-encased, N-doped carbon nanotubes for efficient hydrogen evolution

The high-activity electrocatalysts for the hydrogen evolution reaction (HER) are highly desired to replace precious Pt, but difficult to achieve. Herein, we report the loading of ultrafine tungsten carbide (WC) nanoparticles (NPs) on cobalt-embedded, bamboo-like, nitrogen-doped carbon nanotubes (WC/Co@NCNTs) with high-level N doping via a one-step strategy, leading to a desirable multicomponent nanocomposite with superior activity and stability when used as the HER electrocatalyst. The optimized WC/Co@NCNTs showed a very low onset overpotential (Uonset) of ~18 mV, a small Tafel slope of 52 mV dec−1, a small η10 of only 98 mV to reach a current of 10mAcm−2, and a large exchange current density (j0) of 0.103mAcm−2, which also retained its high activity for at least 12.5h operation in acidic electrolyte. The DFT calculations revealed an important role of the N dopants in the HER as well as a favorable ΔGH* for the adsorption and desorption of hydrogen derived from the synergistic effects between WC NPs and Co@NCNTs.

Analysis on Calcination Process of WC–Co Precursor Powder

In this paper, calcination of WC–Co precursor powders with different Co contents prepared by solution technique was investigated. Thermal analysis was carried out. The precursor powders after calcination process were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). A mechanism of calcination of the precursor powder was proposed and substantiated by the experimental data. The mechanism was that carbon in Sample C (WC–3 wt.% Co) after calcination was provided only by the pyrolysis of soluble starch, while carbon in Sample A (WC–12 wt.% Co) was provided not only by the pyrolysis of soluble starch but also by the pyrolysis of methyl in acetate cobalt. The main phase after calcination was the mixture of WO3, CoO, and C. Moreover, ultrafine WC–Co composite powder was obtained after fast reduction–carbonization treatment. The morphology of WC–Co powder is hollow spherical granular structure where individual particles are cemented in the form of agglomerated ball and the mean particle size is 177 nm.

Defect structure evolution and abnormal grain growth during spark plasma sintering of nano WC–Si powders

Abstract

EFFECT OF COARSE-TO-FINE WC GRAIN RATIO ON MECHANICAL PROPERTIES AND ABRASIVE WEAR OF WC-8Co CEMENTED CARBIDES

This study performs a comprehensive analysis concerning the amount of fine tungsten carbide (WC) grains needed for the appropriate reinforcement of the cobalt (Co) metallic binder in WC-8Co cemented carbides. The goal is to investigate the balance of coarse-to-fine grain distribution to achieve overall improvement of the material’s mechanical and wear properties. All samples possessed the same WC-8Co binder content, therefore, allowing the role of grain size distribution to be tested. It was found that a ratio of 8:1 wt% of coarse to ultrafine grain WC yielded an appropriate balance between material hardness, fracture toughness, and rupture strength. Upon adding grain growth inhibitors vanadium carbide (VC) and chromium carbide (Cr3C2), the overall wear resistance is further improved compared to undoped composites when samples are tested under abrasive wear conditions.

Enhanced mechanical properties and consolidation of the ultra-fine WC–Al2O3 composites using pulsed current activated heating

The rapid sintering of ultra-fine WC–Al2O3 composites in a short time was investigated with a focus on the mechanical properties and consolidation using pulsed current activated sintering. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanomaterials. The addition of Al2O3 to WC can facilitate consolidation and improve mechanical properties. The hardness and fracture toughness of WC–Al2O3 composites outperform those of monolithic Al2O3.

Electromechanical Hardening of Nanostructured Alloy Layers Applied in Surfacing

Electromechanical hardening of applied surface layers of thermostable and wear-resistant iron and ferronickel alloys modified by ultrafine TiCN and WC particles is considered; the ferronickel alloy contains γ′-Ni3Al phase. The dependence of the microhardness and the depth of the hardened layer on the current is established.

Effect of the Cubic Phase Distribution on Ultrafine WC–10Co–0.5Cr–xTa Cemented Carbide

The (Ta, W)C cubic phase distribution plays a key role in the microstructure and mechanical properties of ultrafine WC–Co–Cr3C2–TaC cemented carbides. By integration of thermodynamic calculations and key experiments, the influence of the cubic phase distribution in ultrafine WC–10Co–0.5Cr–xTa cemented carbides was systematically investigated. A series of ultrafine grained cemented carbides were designed and fabricated through ball‐milling and vacuum sintering at 1410°C for 1 h. The microstructure was investigated using scanning electron microscopy (SEM). The electron backscattered diffraction (EBSD) was used to measure the orientation and size of cubic phase segregation. The results indicate that the cubic phase in the microstructure distributes more heterogeneously in the range of 0.2 to 0.7 wt% Ta addition, but finally the isolated cubic phase is homogeneously distributed with a Ta content from 0.7 to 1 wt%. Combining the thermodynamic calculation with the experiment, the mechanism for the microstructure evolution has been revealed. The mechanical properties of alloys substantially depend on the cubic phase distribution in the microstructure. A synergetic correlation between the transverse rupture strength (TRS) and Rockwell hardness was observed. The homogeneity of cubic phase can be designed and controlled effectively via the present approach.

High-quality cemented carbides on the basis of near-nano and coarse-grain WC powders obtained by self-propagating high-temperature synthesis (SHS)

In the present paper cemented carbides with different grain sizes produced with WC powders obtained by the self-propagating high-temperature synthesis (SHS) were examined. Morphology, particle size distribution and chemical composition and of the SHS-powders were studied in detail. Microstructures of a submicron grade with 5% Co made from the near-nano WC powder obtained by the SHS and a standard submicron grade are similar with slightly more large WC grains in the sample made from the SHS WC powder. The mechanical properties of the ultrafine WC–5% Co grade made from the near-nano WC powder obtained by the SHS and its wear-resistance are comparable with those of the standard ultrafine grade. The microstructure of a medium-coarse WC–6% Co grade made from the medium-coarse SHS WC powder and its properties are comparable with those of the convenient medium-coarse carbide grade for percussive drilling. Results of laboratory performance tests on percussive drilling of the medium-coarse WC–6% Co grade obtained from both the SHS WC powder and conventionally fabricated WC powder indicate that their wear-resistance and performance toughness are very similar. Thus, it is established that high-quality WC–Co cemented carbides with different WC grain sizes varying from submicron to medium-coarse can be produced from the SHS WC powders.

Development Trends of Technology of Ultrafine and Nanosized Hard Alloys WC–Co The Overlook

There were considered the main methods of powders WC production: rapid carbothermal reduction (RCR), «calcination – reduction – carbidization» (CRC), reduction of tungsten oxide by carbon at rotary furnace, method of spray conversion process (SCP), self-propagating high-temperature synthesis (SHS), high energy milling and others. There was made analysis of impact of growth inhibition for carbide grain on structure of hard alloys. According to the data of some authors, optimal content of inhibitor is equal to 0,5–1,5 mas.%; in the case of its large quantity has place brittleness of alloy by means of formation of complex carbide phases. There was demonstrated that is impossible obtain nanosized hard alloys ( d WC < 100 nm) by means of traditional solid-state sintering of mixtures – it is need to use alternative solid phase consolidation. There was considered structure, properties and fields of application submicron and nano sized hard alloys, obtaining by means of hot pressing, high frequency induction pressing, electric discharge sintering during plasma pressure consolidation (PPC), spark plasma sintering (SPS) etc.

Microstructure and properties of ultrafine WC–Co–VC cemented carbides with different Co contents

Ultrafine WC–Co–VC cemented carbides are used extensively in a variety of industrial environments due to their excellent mechanical properties and outstanding wear resistance. Co content affects the service performance of the cemented carbides. In the present study, the influences of Co content on microstructure, physical, and mechanical properties were investigated systematically. Ultrafine WC–Co–VC cemented carbides with Co content varying from 4 wt% and 7 wt% and assistance of VC (0.35 wt%) as inhibitor of WC grain growth were prepared. The physical and mechanical properties were tested and the microstructure characteristics were observed by optical microscope (OM) and scanning electron microscopy (SEM). From the results, it is found that with Co content increasing, both the cobalt magnetism and bending strength increase, while the coercive force, Rockwell hardness, density, and abrasive wear resistance decrease. In addition, the OM and SEM results show that the increase of Co content in WC–Co–VC cemented carbides tends to reduce the quantity and size of micro-pores, and make the fracture mode change from brittle fracture to ductile fracture.

A new approach to control the segregation of (Ta,W)C cubic phase in ultrafine WC–10Co–0.5Ta cemented carbides

The dispersity of (Ta,W)C cubic phase in cemented carbides is crucial for controlling the microstructural homogeneity and improving the mechanical properties. An effective method for improving the segregation of (Ta,W)C phase is presented, with a guide from the thermodynamic calculation. Ultrafine WC–10Co–0.5Ta cemented carbides with different carbon contents were sintered at 1410 °C under a vacuum. With increasing carbon content, the (Ta,W)C phase segregation was gradually eliminated, and both transverse rupture strength and hardness increase.

Potentials of nanostructured WC–Co hardmetal as reference material for Vickers hardness

The potential of nanostructured WC–Co hardmetal as reference material for Vickers hardness was researched in this paper. Preliminary reference Vickers hardness blocks were developed from a WC 9–Co mixture. The WC powder used was nanoscaled and had a grain size of 150nm and a specific surface area of 2.5m2/g. Hardness blocks were consolidated using the Sinter-HIP process. Properties of the sintered material were obtained by using standard measurement techniques like magnetic properties or the SEM analysis of microstructure. Special emphasis was placed on hardness uniformity of the test surface as it is the most important property placed on reference hardness blocks. Hardness uniformity was tested by analysis of variance, ANOVA, for single factor in order to determine if significant hardness variations across the block surface were present. From the conducted research it was concluded that hardness distribution over the whole test surface was uniform. The achieved superior properties of the material, such as full densification, nanosized homogeneous microstructure, high hardness and good fracture toughness, influenced the metrological characteristics of the reference Vickers hardness block. Hardness non-uniformity is nearly two times lower when compared to commercially available standard reference material made of ultra-fine WC–Co. Material response does not involve chipping, cracking or any other imperfections. The research opens a new area of application for nanostructured WC–Co hardmetals as reference material for Vickers hardness for high hardness range.