Tungsten Carbide Grains Research Articles

Extrusion-Based Additive Manufacturing of WC-10Co Cemented Carbide Produced with Bimodal Ultrafine/Micron WC Particles

This article researches the effect of ultrafine (submicron) tungsten carbide powder addition on the microstructure and mechanical properties of WC-10Co cemented carbide produced by the extrusion of a highly filled polymer. This addition aims to develop a material with a good combination of toughness, hardness, and yield strength. The results demonstrate that increasing the ratio between ultrafine and micron WC particles from 0/100 to 45/55 in the initial powder results in successive decreases in average grain size from 2.61 µm to 1.75 µm. When 45% of ultrafine powder is introduced into the mixture, a high number of fine tungsten carbide grains is produced. This promotes inter-grain contact and reduces the free path of the binder phase, which results in a more rigid structure and in the material becoming more brittle. The best mechanical characteristics are achieved in WC-10Co cemented carbide with 15% content of ultrafine powder in the total weight of WC. Here, a microstructure with a bimodal distribution of tungsten carbide grains in a virtually non-intermittent cobalt phase was formed. This allowed us to achieve a compressive strength of 2449 MPa at the deformation of 6.69%, while the modulus of elasticity was 38.8 GPa. The results indicate a good combination of strength and ductility properties in the developed cemented carbide.

A new process for preparing ultrafine WC-Co cemented carbide by doping yttrium within the ammonium metatungstate solution

Ultrafine WC-Co cemented carbide has superior performance of high strength and high hardness, which is widely used in industrial fields. In the traditional process, high temperature carburization method is used to prepare tungsten carbide, and solid-phase mechanical milling method is used to mix grain growth inhibitor (Cr3C2) and tungsten carbide, which easily lead to large WC particle size and uneven WC grain size distribution in WC-Co cemented carbide, thus affecting mechanical properties of the alloy. In the new process, based on the genetic relationship between the particle size of ammonium paratungstate and tungsten carbide, ultrafine ammonium paratungstate uniformly doped with yttrium was firstly obtained by adding a certain amount of ammonia and yttrium oxide into the ammonium metatungstate solution. Then the ammonium paratungstate was calcined to obtain yttrium-doped tungsten trioxide, which was then converted into yttrium-doped ultrafine tungsten carbide powders by introducing carbon monoxide at a low temperature. Finally, the ultrafine WC-Co cemented carbide was prepared by pressure sintering. During the neutralization and crystallization process of ammonium metatungstate solution, the yttrium-doped ultrafine ammonium paratungstate (Fischer particle size 8.4 μm) with narrow particle size distribution and regular morphology was prepared. The yttrium-doped ammonium paratungstate was calcined at 500 °C for 90 min in air atmosphere to obtain yttrium-doped tungsten trioxide powder with a Fischer particle size of 4.5 μm and narrow size distribution. Then the yttrium-doped tungsten trioxide and carbon monoxide gas were reacted at 920 °C for 3h to obtain yttrium-doped ultrafine tungsten carbide powder with a Fischer particle size of 0.32 μm and a specific surface area of 4.44 m2/g, and ultrafine WC-Co cemented carbide with tungsten carbide grain size of 0.28 μm was obtained by pressure sintering. The yttrium uniform distributed effectively inhibited the abnormal growth of tungsten carbide grains. Compared with the WC-Co cemented carbide prepared by solid-phase mechanically mixing tungsten carbide powder and chromium carbide, the yttrium-doped WC-Co cemented carbide had a smaller average tungsten carbide grain size and a more homogeneous microstructure. The prepared yttrium-doped WC-Co cemented carbide had a hardness (HRA) of 94.6, a bending strength of 4841 M, and a coercive force of 42.3 KA/c.

Effect of binder phases on the microstructure and sliding wear properties of HVOF-sprayed WC-based coatings

This study aimed to evaluate the microstructure and wear properties of WC-10Co-4Cr, WC-12Co, and WC-17Co coatings on TC4 titanium alloy. The coatings were deposited using high velocity oxygen-fuel (HVOF) technique. To analyze the influence of binder phases, the coatings were thoroughly examined using scanning electron microscopy, X-ray diffractometer, microhardness tester, and friction and wear tester. The analysis of the results reveals that the primary phases in all three coatings consist mainly of WC, with smaller quantities of W2C and amorphous phases present. The WC-10Co-4Cr powder demonstrates a relatively even particle size distribution, high degree of sphericity, and rough porous surface, allowing for efficient heat absorption and uniform heat distribution, resulting in a dense coating. Notably, the WC-10Co-4Cr coating exhibits significantly smaller tungsten carbide grain size compared to the other coatings. Moreover, the microhardness of the WC-10Co-4Cr coating, measured at 1377.8 HV0.05, is significantly higher than that of the WC-12Co and WC-17Co coatings, which measured at 1258.8 HV0.05 and 1182.4 HV0.05, respectively. Additionally, the WC-10Co-4Cr coating demonstrates low friction coefficient and wear volume, indicating excellent wear resistance. Subsequently, a comprehensive analysis was conducted to determine the reasons for the relative enhancement in binder performance.

Hybrid composite with WC/Y–TZP–Al2O3 ceramic matrix and dispersed Hadfield steel particles

Low-temperature and short-time sinter-forging has been used to obtain a dense WC/Y–TZP–Al2O3 hybrid ceramic–matrix composite with dispersed Hadfield steel with high fracture toughness. The hardness and К1С fracture toughness were 13.7 ± 0.3 GPa and 7.4 ± 0.4 MPa m1/2, respectively. The composite contained phases such as Y–TZP–Al2O3 eutectics and hypereutectic grains, WC agglomerates, γ-Fe particles as well as small amounts of Al2(WO4)3 and MnFe2O4. No t-ZrO2→m-ZrO2 transformational toughening occurred during mechanical loading so that enhanced fracture toughness resulted from forming a dense microstructures with ductile metallic interlayers between ceramic and tungsten carbide grains.

Wear of Carbide Plates with Diamond-like and Micro-Nano Polycrystalline Diamond Coatings during Interrupted Cutting of Composite Alloy Al/SiC

The complexity of milling metal matrix composite alloys based on aluminum like Al/SiC is due to their low melting point and high abrasive ability, which causes increased wear of carbide tools. One of the effective ways to improve its reliability and service life is to modify the surface by plasma chemical deposition of carbon-based multilayer functional layers from vapor (CVD) with high hardness and thermal conductivity: diamond-like (DLC) or polycrystalline diamond (PCD) coatings. Experiments on an indexable mill with CoroMill 200 inserts have shown that initial tool life increases up to 100% for cases with DLC and up to 300% for multilayered MCD/NCD films at a cutting speed of 800 m/min. The primary mechanism of wear of a carbide tool in this cutting mode was soft abrasion, when wear on both the rake and flank surfaces occurred due to the extrusion of cobalt binder between tungsten carbide grains, followed by their loss. Analysis of the wear pattern of plates with DLC and MCD/NCD coatings showed that abrasive wear begins to prevail against the background of soft abrasion. Adhesive wear is also present to a lesser extent, but there is no chipping of the base material from the cutting edge.

Empirical Study on the Effect of Tungsten Carbide Grain Size on Wear Resistance, Cutting Temperature, Cutting Forces and Surface Finish in the Milling Process of 316L Stainless Steel

Empirical Study on the Effect of Tungsten Carbide Grain Size on Wear Resistance, Cutting Temperature, Cutting Forces and Surface Finish in the Milling Process of 316L Stainless Steel

Molecular Dynamics Study on Adding Tungsten‐Carbide Grains to 304 Stainless Steel Polycrystals

The molecular dynamics method is conducted to study the mechanical properties and plastic deformation mechanism of composite materials ASSN‐WC with tungsten carbide (WC) grains added to 304 austenitic stainless steel nanopolycrystals (ASSN) during uniaxial tensile process. The results indicate that the overall strength of ASSN with void defect is decreased, and because of the larger shear model of WC crystal, the overall strength of ASSN‐WC material is improved, and its toughness is not significantly reduced. In the plastic deformation process, under low strain conditions, the main deformation mechanism inside polycrystals is dislocation slip. The slip of dislocations forms extended dislocations and stacking faults, which makes the grains deform. As the strain increases, the dislocation slip inside the grains becomes more intense, and deformation twins appear. The interaction between slip dislocations and grain boundaries makes the grain boundaries hinder the further deformation of the grains, and the strengthening effect on the local area of the material becomes more obvious. Meanwhile, in the process of strain increase, the WC grains do not rotate and deform. This can also effectively hinder the deformation of other grains on the adjacent edges and improve the stiffness of the composite material.

Topology of WC/Co Interfaces in Cemented Carbides.

WC-Co cemented carbides build one of the important classes of metal matrix composites. We show in this paper that the use of machine vision methods makes it possible to obtain sufficiently informative statistical data on the topology of the interfaces between tungsten carbide grains (WC) and a cobalt matrix (Co). For the first time, the outlines of the regions of the cobalt binder were chosen as a tool for describing the structure of cemented carbides. Numerical processing of micrographs of cross sections of three WC-Co alloys, which differ in the average grain size, was carried out. The distribution density of the angles in the contours of cobalt "lakes" is bimodal. The peaks close to 110° (so-called outcoming angles) correspond to the contacts between the cobalt binder and the WC/WC grain boundaries. The peaks close to 240° (or incoming angles) correspond to the WC "capes" contacting the cobalt "lakes" and are determined by the angles between facets of WC crystallites. The distribution density of the linear dimensions of the regions of the cobalt binder, approximated with ellipses, were also obtained. The distribution density exponentially decreases with the lengths of the semi-axes of the ellipsoid, approximating the area of the cobalt binder. The possible connection between the obtained data on the shape of cobalt areas and the crack trajectories in cemented carbides is discussed.

Characterization of ultrafine grain tungsten carbide tool and its wear investigation in friction stir welding of HSLA steel

In this work, cemented carbides with different cobalt content were developed by using medium and ultrafine tungsten carbide grains. The GGI, (Cr3C2), was added in small amount (0.5 wt. %) to restrict the grain growth. The effect of particle size, reinforcement content and sintering temperature on metallography, densification and mechanical properties is investigated. At 1680 ºC, Co phase was uniformly distributed at WC interface by particle rearrangement and resulted in fully dense microstructure. The fine particle enhanced the sintering rate due to large specific surface area and surface energy. The developed tool was used to join 4 mm thick high strength low alloy steel plates without severe wear and degradation of the tool. Tool oxidation and interface degradation associated to extreme tribological welding condition is observed.

Performance evaluation and failure analysis of conical picks used in a Botswana (Ngwato) mine

A coal mine in the central district of Botswana is experiencing premature failure of conical picks which mine 150–350 tons of coal/ pick rather than 400 tons/pick specification. This has adverse implications on business productivity and profitability due to the need to replace the picks with new ones. This study employed physical observation of mining operation; macroscopic and microscopic examinations; weight loss analysis; micro-hardness, and fractography analyses of one hundred and ninety-three (193) worn-out and five (5) new picks to investigate root causes of its failure and failure mechanisms with a view to identifying mitigation measures to avoid recurrent failure. It was observed that the picks situated at the extreme right and left ends of the cutter drum failed most frequently. Common modes of failure discovered for Botswana coal mine picks include one-sided wear of the pick body, pull-out of pick’s carbide tip, slimming steel body and even wear of carbide tip, and carbide tip deformation. Furthermore, cracking and crushing of tungsten carbide (WC) grains, cavity formation and pitting, coal intermixing, abrasion wear, long and deep cracks, rock channel formation, and corrosive degradation were identified as the failure mechanisms. Recommended mitigation measures to avoid repeated failures include the use of structurally stable materials at elevated temperature and characterised with improved hardness, toughness and wear resistance for pick manufacturing; exploring manufacturing technology that imparts improved bonding in the constituent materials without degrading material properties; redesigning of pick’s flange; and inspection of pick’s free rotation of the pick before starting any shift.

Properties of WC–Co hardmetals as a function of their composition and microstructural parameters

Research into WC–Co submicron hardmetals involving measurement of hardness, coercivity and microstructural characterization, as well as analysis and comparison of results from recent literature led to the development of a unified constitutive expression for Vickers hardness in a form that separates the effects of the tungsten carbide grain size from those of the cobalt binder volume fraction. With the proposed expression for HV one may recalculate and compare hardness values for hardmetals featuring the same average grain size but differing in the binder matrix content. The paper shows that, in contrast to the Lee-Gurland model, the proposed constitutive expression framework treats the hardmetal hardness as a function of the carbide skeleton hardness (HWC) and contiguity (C) described as HV = CHWC. The carbide skeleton hardness depends on the WC grain size only, and it is described by the Hall-Petch equation. The results of parallel hardness and coercivity measurements led to an empirical equation relating Hc to the WC grain size and the Co volume fraction. Based on the complete experimental data, the relationship between the coercivity and Vickers hardness was explored, and a simplified relationship between these physical values was proposed to carry out the primary HV evaluation based on the measured coercivity values. As noted in the paper, the above equations are valid for relatively narrow WC grain size distributions with a maximum coefficient of variation of 0.5.

Study of the growth kinetics of in situ WC grains in tungsten carbide layers produced by a diffusion-controlled reaction

To refine the microstructure, the growth behaviour of ceramic grains in tungsten carbide cemented layers produced by diffusion-controlled in situ reactions at 1000 °C, 1050 °C and 1100 °C for 1–5 h was investigated in the solid-state. The cemented layers were etched in a 25% hydrochloric acid solution for 36 h until the substrates were dissolved. Hence, ceramic grains adhered to the thin tungsten plate were obtained. The phase composition, microstructure and three-dimensional morphology of tungsten carbide ceramic were characterized by utilizing X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS). The indexed phase structure for the ceramic grains consists mainly of W2C and WC, and a transformation of W2C into WC occurred with the elevated temperature. The presence morphology of platelet and triangular prism and hexagonal prism plays a dominant role in tungsten carbide grains. The average value of basal plane radii (r) and prismatic plane length (L) were counted by means of the three-dimensional shape and size of grains. The growth kinetics and growth mechanism of ceramic grains were evaluated based on the classical power law. The in situ tungsten carbide grains grown exhibit a grain growth exponent equal to 3, and the growth rates increase with temperature. The calculated growth activation energy for the basal plane radii has a value of 554.64 kJ/mol, which is greater than the values obtained under liquid phase sintering because the inhibition effect of the precipitated phase may reduce the grain growth driving force, indicating that the growth of WC grains has difficulty overcoming the large energy barrier. The grain growth mechanism was determined to be grain boundary migration controlled by the volume diffusion of W and C elements.

Relaxation time shift of Cobalt related internal friction peak in WC-Co cemented carbide

Cemented carbides are widely used in the cutting tools industry for their mechanical properties. They are composite materials made of hard tungsten carbide grains jointed together by a ductile cobalt binder. Due to the extreme conditions of use of the tools, understanding the evolution of the microstructure of the two phases is essential. This evolution can be followed by Mechanical Spectroscopy, either as a function of the temperature, or of the frequency. A general overview of the spectrum reveals three mechanical loss peaks. The second peak presents a transition in its Arrhenius plot at 1140 K, when measured in isothermal frequency scans. The temperature of this transition corresponds with the Curie temperature of the cobalt in WC-Co. However, temperature scans do not reveal any shift in the Arrhenius plot. This result shows how the presence of a phase transition leads to the measurement of apparent activation energies when a relaxation peak is measured in out-of-equilibrium conditions.

Carbides of transition metals: Properties, application and production. Review. Part 1. Titanium and vanadium carbides

The properties, application, and methods for producing titanium and vanadium carbides are considered. These carbides are oxygen-free refractory metal-like compounds. As a result, they are characterized by high values of thermal and electrical conductivity. Their hardness is relatively high. Titanium and vanadium carbides exhibit significant chemical resistance in aggressive environments. For these reasons, they have found application in modern technology. These carbides are used as surfacing materials for the application of wear-resistant coatings to steel products. It is possible to use them as catalysts in organic synthesis. Titanium carbide is used in tungsten-free hard alloys, carbide steels. Due to its high hardness, it is used as an abrasive and as a component of ceramic cutting tools. Vanadium carbide serves as an inhibitor of the growth of tungsten carbide grains in hard alloys. The properties of refractory compounds depend on the content of impurities and dispersion (particle size). To solve a specific problem associated with the use of refractory compounds, it is important to choose the right method for their preparation and to determine the permissible content of impurities in the initial components. This leads to existence of different methods for the synthesis of carbides. The main methods for their preparation are: synthesis from simple substances (metals and carbon), metallothermal and carbothermal reduction. Plasma-chemical synthesis (vapor-gas phase deposition) is also used to obtain carbide nanopowders. A characteristic is given to each of these methods. Information on the possible mechanism of the processes of carbothermal synthesis is presented.

Studies on the phase formation of cobalt contacted with zinc vapour

In cemented carbides cobalt serves as a binding agent between tungsten carbide grains. The zinc process exhibits an important technique to recycle these materials. The decomposition takes place at temperatures of 900–1000 °C and the role of gaseous zinc in this process is poorly investigated. A specific experimental set-up was used to ensure that only gaseous zinc reacts with solid cobalt. By varying the temperatures, times and Zn:Co ratios, it was possible to ensure the formation of intermetallic phases. According to the binary CoZn phase diagram, phases of different composition are formed, depending on temperature and pressure. It was found that not all of the indicated phases occur simultaneously, but several do. With the support of the findings from the layer evolution between two solid as well as solid and liquid substances, it is explained which layers may form in the CoZn system. The multiple phase formation depends on diffusitivity and other factors such as the different melting points, the atomic radii and the occurrence of cracks. Of these, the occurrence of cracks across or between two layers represents the most likely reason.

Impact of cobalt content and grain growth inhibitors in laser-based powder bed fusion of WC-Co

Processing of tungsten carbide‑cobalt (WC-Co) by laser-based powder bed fusion (PBF-LB) can result in characteristic microstructure defects such as cracks, pores, undesired phases and tungsten carbide (WC) grain growth, due to the heterogeneous energy input and the high thermal gradients. Besides the processing conditions, the material properties are affected by the initial powder characteristics. In this paper, the impact of powder composition on microstructure, phase formation and mechanical properties in PBF-LB of WC-Co is studied. Powders with different cobalt contents from 12 wt.-% to 25 wt.-% are tested under variation of the laser parameters. Furthermore, the impact of vanadium carbide (VC) and chromium (Cr) additives is investigated. Both are known as grain growth inhibitors for conventional sintering processes. The experiments are conducted at a pre-heating temperature of around 800 °C to prevent crack formation in the samples. Increasing laser energy input reduces porosity but leads to severe embrittlement for low cobalt content and to abnormal WC grain growth for high cobalt content. It is found that interparticular porosity at low laser energy is more severe for low cobalt content due to poor wetting of the liquid phase. Maximum bending strength of σB > 1200 MPa and Vickers hardness of approx. 1000 HV3 can be measured for samples generated from WC-Co 83/17 powder with medium laser energy input. The addition of V and Cr leads to increased formation of additional phases such as Co3W3C, Co3V and Cr23C6 and to increased lateral and multi-laminar growth of the WC grains. In contrast to conventional sintering, a grain growth inhibiting effect of V and Cr in the laser molten microstructure is not achieved.

Mechanical evaluation of WC-Co materials with varying microstructures

Tungsten carbide‑cobalt materials are useful in a variety of extreme applications due to a desirable blend of properties, yet the technology has not significantly changed since their initial development in the 1920s. The mechanical properties of this class of materials is highly dependent on two variables, the size of the tungsten carbide grains, and the amount of binder phase present in the final body. In this study, the amount of binder phase is isolated across three commercial materials from the same manufacturer with three different grain sizes to investigate the effect on mechanical properties. The mechanical properties investigated are indentation hardness, flexure and tensile strength, as well as fracture toughness. In general, an increase in hardness and tensile strength with decreasing grain size was observed, while the fracture toughness showed the opposite trend with toughness increasing with increasing grain size. The flexure strength results did not show a correlation to grain size. Fractographic analysis identified the dominant strength-limiting flaw for each sample, which largely were in the form of porosity. Other flaws types, such as inclusions from the milling process, clusters of large grains, and machining cracks from the surface finishing process, were also identified. Weibull analysis was performed and deemed appropriate for analysis of these materials, but strength-size scaling was not conducted due to the variability in the strength-limiting feature between the different specimen geometries.

DEVELOPING A TECHNOLOGY FOR OBTAINING COMPOSITE MATERIALS BY HOT PRESSING WITH METALLIZED DIAMOND GRAINS

A new technology has been developed for the manufacture of diamond tools with a bond of 34% Fe+6% Ni+32% Cu+8% Sn+10% WC+10% Сч18 and with titanium metallized diamond grains of HSD90 (АС200) grade, including the processes of manufacturing a composite mixture, cold pressing, sintering, hot pressing and machining. Optimal sintering and hot pressing regimes were selected and substantiated: sintering temperature: 800 ± 200C, holding time: 0,75...1,0 hour, hot pressing temperature: 850 ± 100C, holding time: 25...30 minutes, specific pressure: 80...100 MPa, in this case the hardness of the composite is 60...102 HRB, impact strength KCU 2...36 kJ/m2, shear strength is 23...160 MPa. It is shown that the composite material has a heterogeneous structure: the matrix is mainly a mixture of α (hard alloy of tin in copper - with a 13,5% tin content) and δ phases (Cu31Sn8), in which solid solutions of α iron and nickel, as well as intermetallic phases with tin and copper, and fillers - grains of graphite and tungsten carbide, are seen as separate grains. At the same time, the presence of gray cast iron in the composite leads to the formation of free graphite, which improves the antifriction properties of the composite.

In situ synthesis of dicobalt phosphide on tungsten carbide-cobalt cemented carbide substrates as a hydrogen evolution reaction electrocatalyst

A new approach is proposed to recycle tungsten carbide-cobalt cemented carbides through fabricating dicobalt phosphide catalyst on the surface of cemented carbides for the hydrogen evolution reaction. tungsten carbide-cobalt cemented carbides with different tungsten carbide grain sizes were prepared via a powder metallurgy method. The three-dimensional cobalt skeletons with controlled pore structure on the surface of cemented carbides were obtained by etching tungsten carbide grains in alkaline solution. Dicobalt phosphide particles were synthesized on the cobalt skeleton via a phosphorization treatment. The increasing pore size of cobalt skeletons significantly improved the catalytic performance of phosphatized sample. The design and preparation of dicobalt phosphide catalyst can recycle waste cemented carbides.

Ultrafine Cemented Carbides with Cobalt and Iron Binders Prepared via Reactive <i>In Situ</i> Sintering

Reactive sintering of cemented carbides involves mechanical and thermal activation of precursor elemental powders, followed by in-situ synthesis of tungsten carbide. This approach promotes formation of ultrafine microstructure favored in many cemented carbide applications. Our study focuses on the effect of mechanical activation (high-energy milling) on the properties of powder and following thermal activation (sintering) on the microstructure characteristics and phase composition. Reactive sintering proved effective – an ultrafine grained microstructure of cemented carbides with Co and Fe binders was achieved. Formation of tungsten carbide grains was complete at low temperature during reactive spark plasma sintering, resulting in textured microstructure with anisotropic grain formation and growth.