Cemented Tungsten Carbide Research Articles

Nanosecond Laser Ablation Assisted Precision Grinding of WC/Co Cemented Tungsten Carbide

Nanosecond Laser Ablation Assisted Precision Grinding of WC/Co Cemented Tungsten Carbide

Температуры окисления инструментальных вольфрамокобальтовых твердых сплавов

Introduction. Products containing WC-Co cemented tungsten carbides are commonly used in various industries. It is often operates at elevated temperatures, at which, as noted in the literature, tungsten carbides are susceptible to severe oxidation in air. However, no sufficiently accurate values of oxidation temperatures and dependence of these temperatures and the oxidation rate of tungsten carbides on the cobalt content with its wide variation have been established. The subject of the study is the oxidation process of WC-Co cemented tungsten carbides. The purpose of the work is to obtain the oxidation temperatures of WC-Co cemented tungsten carbides with different cobalt content by weight in the range of 3–20 %. Methods. The dynamics of oxidation was studied in air. Specimens of the same length were heated to a temperature of 850 °C and cooled at the same rate in the furnace of a push-rod dilatometer Netzsch 402 PC while its expansion was simultaneously recorded. The oxidation rate of the specimens was determined by the difference in its length before heating and after cooling. The values of oxidation temperatures were obtained by mathematical analysis of relationships of the expansion on temperature. Results and discussion. Experimental dependences of expansion of WC-Co cemented tungsten carbides on temperature in the range from 20 to 850 °C, and for WC-8Co – up to 1,150 °C, were obtained. The oxidation rate of WC-Co cemented tungsten carbides increased linearly with increasing concentration of tungsten carbides (decreased with increasing cobalt content). During heating, two characteristic temperatures were identified: the onset of oxidation (631±4 °C) and the transition to active oxidation (804±11 °C). The established temperatures were the same for different ratios of tungsten carbides and cobalt. The results can be used when choosing temperature conditions for products made from WC-Co cemented tungsten carbides.

The Influence of Residual Stresses Induced by Grinding on the Fracture Toughness of Cemented Tungsten Carbide

The Influence of Residual Stresses Induced by Grinding on the Fracture Toughness of Cemented Tungsten Carbide

Physical properties of radiation dense reactive sintered borides

Reactive Sintered Borides (RSBs) were fabricated to investigate the effects of carbon and chromium content producing a series of samples referred to as Gen 2 RSBs. These RSBs were tested and evaluated for various mechanical (bulk moduli, fracture toughness, nano and micro-hardness) and microstructural properties. It is the first time when the correlation between different RSB phases and mechanical properties are understood in detail, along with the CALPHAD assessment of RSBs. CALPHAD was used to investigate the effect of sintering pressure and composition on melting point and liquid volume at sintering temperature and was critical in understanding of phase differences in Gen 1 and Gen 2 RSBs. Effects of carbon and chromium addition on mechanical and microstructural properties of RSBs were also investigated. Optimal second generation RSBs have fracture toughness of 7–10.1 MPa m0.5 and hardness of 15.9–19.1 GPa. RSBs with relative sintered density >98 % were achieved in this work. Combined X-ray diffraction and EBSD-EDX techniques were used to determine and confirm phase presence in RSBs. This work has demonstrated tractability and reproducibility of RSB materials with suitable mechanical properties for potential applications in spherical tokamaks alongside existing cemented tungsten carbides.

Disappearance of cobalt particles above nanocrystalline diamond films by HF-CVD on cemented tungsten carbide

Abstract In this study, the possibility of the disappearance of Co particles on the surface of nanocrystalline diamond (NCD) films with large thicknesses was examined. It is shown that the number of Co particles decreased clearly with larger thicknesses. In the thickest case, the Co particles disappeared almost completely. Investigation with energy-dispersive spectroscopy for the cross section of the NCD films suggested that the Co particle was embedded during the growth of the NCD film. Our observations will contribute to depositing smooth NCD films on tools without the embrittlement of substrates by Co etching.

Shock compression of cemented tungsten carbides to 100 GPa: Structure of shock waves, Hugoniot relations, and strength

Plate impact experiments are conducted on cemented tungsten carbides (WC) with a 3.7 and 6.0 wt. % cobalt binder to better understand their dynamic, high-pressure response to 100 GPa. The measured wave profiles show propagation of steady structured waves. Standard impedance matching procedures are used to determine the Hugoniot relations in the shock velocity–particle velocity (Us−vp) and Hugoniot stress–specific volume (P−V/Vo) planes. The Hugoniot elastic limit of the samples is controlled by ductility of the Co binder and is determined to be 4.45 ± 0.29 GPa for cemented WC with 3.7 wt. % cobalt and 3.72 ± 0.24 GPa for a 6.0 wt. % cobalt binder. Both grades show a non-linear Us–vp relationship depending on whether the particle velocity is in the strength dominated or hydrodynamic regime. In the strength dominated regime, a non-linear decrease in Us is observed as vp increases from ambient to the material’s hydrodynamic limit. In the hydrodynamic regime, the Us–vp Hugoniot is linear and is determined to be Us=4.97(±0.006)+1.446(±0.018)vp km/s for WC with 3.7 wt. % Co and Us=4.93(±0.006)+1.463(±0.017)vp km/s for 6 wt. % Co. Both WC grades indicate shear-stress hardening with mean stress immediately after yield, followed by pressure softening, and then a sharp fall in stress carrying capacity as the mean stress is increased to ≈70 GPa (hydrodynamic limit) and beyond. This behavior is in contrast to pure WC ceramics, which show continued shear-stress hardening with mean stress to ≈80 GPa.

Enhancing machining performance of EN24 steel with CVD diamond coated tool and minimal quantity lubrication

The research aims to investigate the effect of chemical vapour deposition (CVD) diamond coatings on cemented tungsten carbide (WC-Co) inserts when machining EN24 steel. In addition to the diamond coating, the research also incorporates the use of minimal quantity lubrication (MQL) technique during the machining process. The research involves experimental studies to evaluate the machinability characteristics of EN24 steel using tungsten carbide cutting inserts with diamond coatings and MQL. Diamond-coated tools are extremely effective in machining EN24 steel, particularly in applications requiring high precision, wear resistance, and long tool life. They are commonly used in industries such as aerospace, automotive, and manufacturing, where quality and durability of the machined components are critical. L12 orthogonal array was used to design experiments with the type of cutting insert used, test condition and cutting speed as control factors. Various parameters such as tool wear, cutting temperature and surface roughness were measured and compared with conventional machining techniques. The results reveal that average flank wear of cutting inserts decreased by 67.4% as a result of MQL when compared with dry machining conditions. Average flank wear decreased by 77.6% after diamond coating were applied compared with uncoated inserts. Diamond coated inserts subjected to MQL exhibit largest percentage reduction of 74.11% for surface roughness when compared to uncoated inserts. The average cutting temperature decreased by 53.09% due to MQL compared to dry machining.

Laser micromachining of bionic transport structures on cemented tungsten carbide for passive directional transport of lubricants

Several 10 ℓ/min of cooling lubricants are used to cool and lubricate the cutting edges during conventional mechanical milling of lightweight metals. Different concepts of minimum quantity lubrication (between 5 mℓ/h and 50 mℓ/h) have been developed in the past since the recycling and disposal of the cooling lubricants is energy-intensive and costly. One promising approach for minimum quantity lubrication during milling processes with closed cutting edges is the passive directional transport of the lubricant along the chip guiding surfaces to the milling area.Laser micromachining with ultrashort laser pulses was used for the fabrication of bionic transport structures on tools made from cemented tungsten carbide. An analytical model for the prediction of the dimensions of the transport structures was derived and experimentally verified. The microscopic surface structures that form on the surface of the transport structures were investigated and their wetting behavior for different lubricants and deionized water was characterized by contact angle measurements. A low contact angle <6° was achieved with laser wavelength-sized ripples on the surface. Finally, passive directional transport of lubricants on tools made from cemented tungsten carbide could be demonstrated with bionic transport structures over a distance of up to 60 mm.

Simultaneous micromachining with beam splitting of ultrashort laser pulses at high average power for the productive fabrication of microchannels

Laser micromachining with ultrashort laser pulses is a promising approach for the generation of small geometries in the micro-meter scale, such as microchannels for passive fluid transport. The ablation of small structures with high average laser power still poses a challenge when high surface quality is required. In this work, beam splitting with a diffractive optical element (DOE) was used to divide the laser beam of a high-power ultrafast laser into an array of 1x15 spots on the workpiece. Fast scanning of up to 20 m/s perpendicular to the orientation of the array using a Galvanometer-scanner allowed for simultaneous micromachining of multiple microchannels with high surface quality on cemented tungsten carbide. The high average laser power of 160 W in combination with the adapted processing strategy enabled the simultaneous and productive fabrication of 15 microchannels with a low surface roughness of Sa < 1.5 µm along the channel wall.

Seeding ductile nanophase in ceramic grains.

Transgranular brittle fracture is the dominant failure mode of brittle materials, including ceramics and ceramic matrix composites. However, strengthening these materials without sacrificing their toughness has been a big challenge. In this study, an innovative approach is proposed to achieve coordinated strengthening and toughening of ceramics-based composites by introducing specific ductile coherent nanoparticles into ceramic grains. As an example, the WC-Co cemented tungsten carbides were used to demonstrate how this brittle material can achieve ultrahigh strength without losing toughness by seeding metallic nanoparticles inside WC grains. The mechanisms for inducing the formation and modulating the amount, size, and distribution of such nanophase within the ceramic grains were disclosed. The fraction of transgranular ruptures of the brittle ceramic phase was reduced significantly due to the presence of the ductile coherent in-grain nanoparticles. Both the strength and strain limit of the cemented carbides were remarkably increased compared to their counterparts reported in the literature. The coordinated strengthening and toughening strategy proposed in this work is applicable to a broad range of ceramics and ceramic matrix composites to obtain superior comprehensive mechanical properties.

Sinter-based additive manufacturing of hardmetals: Review

Hardmetals, commonly referred to as cemented tungsten carbide (WC) or simply tungsten carbide, is one of the oldest liquid phase sintered, two phase composite, powder metallurgical (PM) product. In fact, this year marks the 100th year since the first hardmetal patent was issued. The classic two-phase composite hardmetal structure typically consists of hard ceramic-like WC particles that are embedded in a softer matrix binder phase primarily consisting of cobalt (Co), sometimes in conjunction with other metals such as nickel and iron, that takes into solution some tungsten and carbon.Various shaping methods have been used to fabricate hardmetals into useful products. Traditional machining to shape hardmetal components was extremely difficult due to the high hardness of these materials (significantly harder than any steels used for cutting). Press and sinter was the process of choice for making relatively simple shapes from hardmetals and is still extensively used. To accommodate some shape complexity, die pressed or cold isostatically pressed “green” parts were machined followed by subsequent sintering to shape hardmetal components. Extrusion using organic polymers was another technique that was adapted to make hardmetal rods and bars. Using the powder injection molding (PIM) process to form more complex shapes from hardmetals was a natural evolution. However, the tooling cost and the typically low volume of parts required for many hardmetal applications was a major barrier. At the turn of the century, there was a rapid growth of the additive manufacturing (AM) sector that is capable of fabricating extremely complex shaped components without the use of any tooling. However, the early AM processes that gained commercial viability were founded on the melt-based techniques, which was generally not conducive to processing of hardmetals. Since 2015, a number of sinter-based AM technologies started to emerge and these technologies were found to be better suited for the processing of hardmetals into complex shapes in an economic manner. This paper will review the developments in the processing of hardmetals using some of the different sinter-based AM techniques.

Some aspects of solid solution grain growth inhibitors in cemented tungsten carbides

Cemented tungsten carbides are the materials of choice for applications requiring superior wear resistance with high strength and toughness. Recently, there has been a growing interest in using ultrafine-grained cemented carbides to exploit the benefits of superior properties and improved performance. Finer grain carbides, due to higher interface area, are more susceptible to grain growth, and processing of these carbides requires uniform distribution of the inhibitor phase(s) to promote a homogeneous microstructure.A new class of grain growth inhibitor alloys has been developed, which enables better control of WC particle coarsening during liquid phase sintering of WC-Co-based powder compacts. The new alloys are formulated as solid solutions of the selected inhibitor carbide phases (VC and/or Cr3C2) in the Co metal binder phase. The solid solution approach realizes a much more uniform dispersion of the inhibitor carbides in the green body, thereby ensuring more effective mitigation of WC grain growth during liquid phase sintering. A significant reduction in the melting point of the Co-rich matrix by the addition of the inhibitor phases contributes to the reduced WC coarsening rate. Another contributing factor, and possibly the most important mechanism, is the decrease of solubility and transport of W and C atoms from one grain to the adjacent one, thus, further restricting the WC coarsening rate. Examples of using the solid solution grain growth inhibitors and some of the related mechanisms of grain growth inhibition will be described in this paper.

Mechanical properties of cemented tungsten carbide with nanocrystalline FeNiZr binder

The use of cemented tungsten carbide (WC) spans numerous commercial applications. Due to the extreme hardness and high modulus provided by the WC phase combined with added plasticity and resulting toughness contributed by the cobalt (Co) binder, cemented WC-Co is a good candidate for cutting tools, machining tools, and mining equipment. Co has been identified as a strategic and critical material from the Department of the Interior (DOI) and is “anticipated to be a human carcinogen” by the US Department of Health and Human Services (HHS). Nanostructured FeNiZr is being evaluated as a plausible binder replacement to Co since it doesn't exhibit these concerns. Preliminary consolidations of WC-FeNiZr powders utilizing Field Assisted Sintering followed by Hot Isostatic Pressing have generated (near) fully dense samples with hardness and toughness values exceeding 16 GPa (1630 HV) and 13 MPa-m1/2 (11.83 ksi-in1/2) respectively. Electron Backscatter Diffraction and Transmission Electron Microscopy are used to explain the structure-property relationship.

Analysis on carbonization evolution behavior of tungsten carbide powders and its application in cutting tools

In this article, the microstructural evolution of tungsten carbide (WC) powder with coarse particle size was studied. The WC powders were prepared by directly carbonizing tungsten powders of 8.5 μm in Fisher sub-sieve size (FSSS) under various conditions. The sequence of chemical reactions was analyzed by calculating the Gibbs free energies, and the phase transition mechanisms of tungsten particles was studied by using characterization techniques including SEM and XRD. The experimental results showed that the phase transition process is dominated by carbon diffusion reaction, and the diffusion rate was studied by analyzing carbonized tungsten particles prepared at specific temperatures. The grain growth process and mechanism were also studied by analyzing the morphology and grain size of WC powders prepared at 1800 °C in different carbonization times, and the results are consistent with the recrystallization grain growth theory. Finally, technique of Electron Backscattered Diffraction (EBSD) was utilized to identify and measure the grain size of WC powders prepared from tungsten powder of 0.6 μm in FSSS. The cemented tungsten carbide substrate prepared from WC powder with higher average grain size exhibited higher performances in metal cutting application of turning and drilling.

Electrochemical separation technology and mechanism of tungsten and cobalt in Na2WO4-WO3-CoO molten salts

The separation and recovery of tungsten and cobalt from cemented tungsten carbide (WC-Co) scraps can be carried out by adding WO3 and CoO into the Na2WO4 molten salt to simulate the calcination of WC-Co scraps. The Raman spectra and the XRD patterns of the molten salts cooled naturally to room temperature, and the predominance diagram of Na-W-Co-O system, show that the addition of CoO reduced the concentration of Na2W2O7 in the molten salt. Molecular dynamics simulations based on first principles indicated the following reaction mechanism: WO42− + WO3 → W2O72−, W2O72− + O2– → 2WO42−. Electrochemical cyclic voltammetry (CV) and square wave voltammetry (SWV) were used to analyze the redox behaviors of tungsten and cobalt with different molar ratios of WO3 and CoO in the molten salts. The reduction of the tungsten ion was a two-step reaction, W6+ → W2+ → W, and the reduction of the cobalt ion was a one-step reaction, Co2+ →Co. On increasing the amount of added CoO, the deposition potential of tungsten ions shifted towards a more negative potential, while the deposition potential of cobalt ions remained unshifted. Therefore, W coatings, Co3W alloys and Co powders were obtained by selective electrodeposition.

Case study for the formation of a surface alloy on cemented tungsten carbide using ultrashort MHz to GHz burst-pulses

The authors of this paper report on the generation and utilization of high-frequency combined MHz- and GHz-bursts consisting of ultrashort laser pulses in order to form a surface alloy on the composite material cemented tungsten carbide. The resulting topographies, ablation depths and chemical compositions of the irradiated material surfaces were characterized with respect to the modification of the surface of a composite material whose elements tungsten carbide (WC) and cobalt (Co) permit the formation of a surface alloy only in a common meta-stable liquid phase. The results of this case study demonstrate that using high-frequency bursts of ultrashort laser pulses in the investigated parameter range, the formation of a surface alloy is possible without a tendency to change the chemical composition of WC and Co, and the depth of re-solidified material depends on the combination of MHz and GHz burst-pulses.

Oxidative Dissolution of Cemented Tungsten Carbides in Molten Sodium Carbonate by Addition of Copper(I) Oxide as Oxidizing Agent for Tungsten Recycling

Due to the monopolized supply of tungsten resource, it is important to efficiently recycle tungsten scrap for use as a secondary resource. The recycling of tungsten from cemented carbide tools by the molten carbonate method was investigated using simulated hard and soft scrap (carbide tool tips and WC powder, respectively). The oxidative dissolution of tungsten was examined in molten Na2CO3 under Ar–O2–CO2 atmospheres at 1173 K. Based on the immersion potentials of Cu, W, Co, C, and WC–Co, Cu2O was suggested to work as an oxidizing agent for tungsten dissolution. The oxidative dissolution rate for carbide tool tips with 12.8 mol% Cu2O addition reached 57 mg h−1 for the reaction time of 2.5 h, equivalent to 0.32 mm h−1. The decrease in the dissolution rate after 2.5 h was attributed to the decrease in the Cu(I) ion concentration in the melt and the inhibition of ion diffusion by the deposited metallic Cu. No violent reaction leading to explosion was observed, even for the oxidative dissolution of fine WC powder with a large surface area. Thus, this method provides significant safety improvements compared to the molten nitrate method.Graphical

Diamond grinding wheel wear characterization after finishing cemented tungsten carbide cutting inserts

Diamond grinding wheel wear characterization after finishing cemented tungsten carbide cutting inserts

Energetic characterization during plasma electrolytic polishing of cemented tungsten carbide

Electrical and thermal measurements were conducted during the plasma electrolytic polishing (PEP) of cemented tungsten carbide (WC-Co) materials to characterize energetic aspects of the process in relation to the temporal development of the gaseous layer near the workpiece. The power transferred to the workpiece is determined using a calorimetric probe and employing the time derivative of the temperature curve. It shows distinct heating phases due to the generation of the gaseous layer. At the beginning of the process, a typical power of 367 ± 17 W is transferred to the workpiece of a surface area of 14 cm2. At longer process times, a stabilized gaseous layer limits the power transferred to the workpiece to 183 ± 3 W. In an attempt to describe the heat transferred to the electrolyte, the electrolyte temperature was measured using a thermocouple situated 15 mm away from the workpiece. The local electrolyte temperature increases from 70 to 81 °C for an immersion depth of 20 mm. Moreover, the spatiotemporal development of the electrolyte temperature was obtained by 2D-hydrodynamic modeling using COMSOL Multiphysics®. The modeling results for the local temporal temperature development are in excellent agreement with the experimental values when the turbulent model is applied up to t = 65 s. Afterward, the laminar model leads to a better agreement. Furthermore, line scan x-ray photoelectron spectroscopy revealed that aliphatic carbon was preferentially removed. Only a slight compositional gradient in the vertical direction after the PEP process was observed.

Structural and Mechanical Properties of DLC/TiN Coatings on Carbide for Wood-Cutting Applications

In this work, the diamond-like carbon and titanium nitride (DLC/TiN) multilayer coatings were prepared on a cemented tungsten carbide substrate (WC—3 wt.% Co) using the cathodic vacuum arc physical vapor deposition (Arc-PVD) method and pulsed Arc-PVD method with a graphite cathode for the deposition of TiN and carbon layers, respectively. The structural and mechanical properties of the prepared coatings were studied, and different techniques, such as scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman spectroscopy, and microindentation techniques investigated their microstructure, composition, and phases. The prepared coatings had a multilayer structure with distinct phases of DLC, TiN, and carbide substrate. The potentiodynamic polarization method (PDP) was performed for the DLC/TiN multilayer coatings in 3% NaCl solution to evaluate the corrosion resistance of the prepared coatings. It has been shown that the DLC layer provided the coating with a polarization resistance of 564.46 kΩ. Moreover, it has been demonstrated that the DLC/TiN coatings had a high hardness of 38.7–40.4 GPa, which can help to extend the wood-cutting tools’ life.