Tungsten Carbide-cobalt Research Articles

Wear resistance and microstructural properties of Ni–Al/h-BN/WC–Co coatings deposited using plasma spraying

Hexagonal boron nitride (h-BN) and tungsten carbide cobalt (WC–Co) were added to nickel aluminum alloy (Ni–Al) and deposited as plasma sprayed coatings to improve their tribological properties. The microstructure of the coatings was analyzed using a scanning electron microscope (SEM). Following wear test, the worn surface morphologies of the coatings were analyzed using a SEM to identify their fracture modes. The results of this study demonstrate that the addition of h-BN and WC–Co improved the properties of the coatings. Ni–Al/h-BN/WC–Co coatings with high hardness and favorable lubrication properties were deposited.

Apoptosis induced by tungsten carbide-cobalt nanoparticles in JB6 cells involves ROS generation through both extrinsic and intrinsic apoptosis pathways

In this study, apoptosis and related signaling induced by WC-Co nanoparticles were investigated in JB6 cells and rat lung macrophages. Electron spin resonance (ESR) and fluorescent staining indicated that both WC-Co nanoparticles and fine particles stimulated reactive oxygen species (ROS) generation. Catalase exhibited an inhibitory effect on WC-Co nanoparticle-induced ROS as well as mitochondrial membrane permeability damage. Further study indicated that WC-Co nanoparticles elicited higher cytotoxicity and apoptotic induction than fine particles. Western blot analysis showed activation of proapoptotic factors including Fas, Fas-associated protein with death domain (FADD), caspase 3, 8 and 9, BID and BAX. In addition, both cytochrome c and apoptosis-inducing factor (AIF) were upregulated and released from mitochondria to the cytoplasm. Our findings demonstrate that, on a mass basis, WC-Co nanoparticles exhibit higher cytotoxicity and apoptotic induction than fine particles. Apoptosis induced by WC-Co nanoparticles and fine particles involves both extrinsic and intrinsic apoptosis pathways.

Lead zirconate titanate coating of tungsten carbide-cobalt to enable smart coatings

Smart coatings enable sensing and actuation functionality to be added to materials. Piezoelectric coatings, especially lead zirconate titanate (PZT), have been used on a wide range of metallic and semiconducting substrates. Tungsten carbide-cobalt (WC-Co) is extensively used in the metal processing industry due to its hardness and abrasion resistance. The ability to apply piezoelectric coatings close to a metal cutting edge would enable improved control of the cutting process resulting in improved quality and reduced power consumption in the manufacturing process. However, the WC is sensitive to oxidation at typical PZT processing temperatures presenting a challenge to the development of functional PZT films for this application.This paper reports the use of a low temperature solution–gelation (sol–gel) process to deposit high quality crystalline PZT (Pb0.52Zr0.48TiO3) film onto a WC-Co substrate. Laser Doppler vibrometry showed significant piezoelectric activity with an effective d33 coefficient of 19pC/N. Both the dielectric constant and piezoelectric coefficient were lower than expected due to the formation of an insulating PbWO4 oxide interlayer between the conducting WC-Co substrate and PZT. Accounting for this layer indicated a d33 piezoelectric coefficient for the PZT of 85pC/N.

Influence of copper content on the microstructure and hardness of copper-doped tungsten carbide–cobalt bulk at the elevated temperature

Ultrafine WC–Co cemented carbides doped with 0, 0.5, 1, 1.5 and 2wt.% Cu were fabricated by the sintering/hot isostatic pressing (sinter–HIP) process for the mixed WC and chemical precipitated Co–Cu powders. The Vickers hardness of cemented carbides was measured at temperatures ranging from room temperature to 800°C. The Cu-doped WC–Co alloys with the higher proportion of WC hard phase and finer microstructure of the average grain size of 590nm exhibit the higher hardness at the elevated temperature of 800°C. The Cu-doped WC–Co cemented carbides have a potential application in machining.

Induction of miR-21-PDCD4 Signaling by Tungsten Carbide-Cobalt Nanoparticles in JB6 Cells Involves ROS-Mediated MAPK Pathways

Tungsten carbide-cobalt (WC-Co) nanoparticle composites have wide applications because of their hardness and toughness. WC-Co was classified as "probably carcinogenic" to humans by the International Agency for Research on Cancer (IARC) in 2003. It is believed that the toxicity and carcinogenesis of WC-Co is associated with particle size. Recent studies demonstrated that the tumor suppressor gene programmed cell death 4 (PDCD4) and its upstream regulator miR-21 have been considered as oncogenes for novel cancer prevention or anticancer therapies. The present study examined the effects of WC-Co nanoparticles on miR-21-PDCD4 signaling in a mouse epidermal cell line (JB6 P+). The results showed that (i) exposure of JB6 cells to WC-Co stimulated a increase of miR-21 generation; (ii) WC-Co also caused inhibition of PDCD4, a tumor suppressor protein and downstream target of miR-21, expression in JB6 cells; (iii) inhibition of ERKs with ERK inhibitor U0126 significantly reversed WC-Cominus;induced PDCD4 inhibition, but inhibition of p38 with p38 inhibitor SB203580 did not; and (iv) ROS scavengers, N-acetyl-L-cysteine and catalase, blocked the inhibitory effect of WC-Co on PDCD4 expression, while superoxide dismutase promoted the inhibitory effect. These findings demonstrate that WC-Co nanoparticles induce miR-21 generation, but inhibit PDCD4 production, which may be mediated through ROS, especially endogenous H2O2, and ERK pathways. Unraveling the complex mechanisms associated with these events may provide insights into the initiation and progression of WC-Co-induced carcinogenesis.

Predicting Surface Roughness of WEDMed Wc-Co Composite Using Box-Behnken Response Surface Method

Wire electro discharge machining is vital to cut electrically conductive, hard, tool-die Composite materials. Optimization of WEDM involves thermo, electric, material and mechanical parameters. Achieving best possible output is one of the challenges of research and manufacturing community. Box-Behnken is a response surface methodology that can reach objective function in as few as 15 experimental runs. The present work discusses RSM as applied to wedm of tungsten carbide cobalt metal matrix composite. Selected input parameters were, on-time, off-time and wire tension. Design of experiments was used, Mathematical models were developed and the effects investigated for the response of surface roughness. Response contours been utilized to find optimum conditions and correlations developed were verified. The error established was 4.6% and a high coefficient of determination R sq (97%) promises satisfactory performance.

Statistical Modeling and Optimization of Process Parameters in Electro-Discharge Machining of Cobalt-Bonded Tungsten Carbide Composite (WC/6%Co)

In this paper, attempts have been made to model and optimize process parameters in Electro-Discharge Machining (EDM) of tungsten carbide-cobalt composite (Iso grade: K10) using cylindrical copper tool electrodes in planing machining mode based on statistical techniques. Four independent input parameters, viz., discharge current (A: Amp), pulse-on time (B: μs), duty cycle (C: %), and gap voltage (D: Volt) were selected to assess the EDM process performance in terms of material removal rate (MRR: mm3/min), tool wear rate (TWR: mm3/min), and average surface roughness (Ra: μm). Response surface methodology (RSM), employing a rotatable central composite design scheme, has been used to plan and analyze the experiments. For each process response, a suitable second order regression equation was obtained applying analysis of variance (ANOVA) and student t-test procedure to check modeling goodness of fit and select proper forms of influentially significant process variables (main, two-way interaction, and pure quadratic terms) within 90% of confidence interval (p-value≤0.1) It has been mainly revealed that all the responses are affected by the rate and extent of discharge energy but in a controversial manner. The MRR increases by selecting both higher discharge current and duty cycle which means providing greater amounts of discharge energy inside gap region. The TWR can be diminished applying longer pulse on-times with lower current intensities while smoother work surfaces are attainable with small pulse durations while allotting relatively higher levels to discharge currents to assure more effective discharges as well as better plasma flushing efficiency. Having established the process response models, a multi-objective optimization technique based on the use of desirability function (DF) concept has been applied to the response regression equations to simultaneously find a set of optimal input parameters yielding the highest accessible MRR along with the lowest possible TWR and Ra within the process inputs domain. The obtained predicted optimal results were also verified experimentally and the values of confirmation errors were computed, all found to be satisfactory, being less than 10%. The outcomes of present research prove the feasibility and effectiveness of adopted approach as it can provide a useful platform to model and multi-criteria optimize MRR, Ra, and TWR during EDMing WC/6%Co material.

Modeling and Analysis of MRR in WEDMed WC-CO Composite by Response Surface Methodology

Wire electro discharge machining (WEDM) was applied to machine tungsten carbide-cobalt (WC-CO) metal matrix composite. It finds increasing application in auto, aeronautical and oil drill application. The material is extremely hard, brittle and tool grade. The present work is undertaken on 10% cobalt, 90% tungsten grade in which keen study is lacking. Amongst many variables, On-time, Off-time and ignition current were shortlisted as critical input parameters. The goal is to identify the input parameter level that maximizes the material removal rate. The input parameters for the experiments were selected after considering previous related work, manufacturer's catalog and industrial expert's opinion. From Taguchi L27 experimental plan, the Box-Behnken trials for 14 experiments were derived in order to model and to predict the output response with good accuracy. The investigation was carried out on the high speed Sodick machine so that it aligns with industry requirement of higher productivity. Response surface modeling and regression analysis was done. Analysis of variance was used to isolate parameters that are critical from pooled data. The experimental results were verified by running at recommended setting of the findings. The outcome was encouraging. Output response improves with on-time at 8 μ- Sec, off -time 15 μ- Sec and ignition current of 16 amperes. It was found that overall metal removal rates increased by 13%, to 17.42 mm3/min from the process average rate of 15.15 mm3/min. A mathematical equation was derived to predict performance. Surface, response contour plots were utilized to analyze performance. The validity of derived model was verified. Since error obtained was 4.5%, higher coefficient of determination is 87% and adequate precision was >4, the model is valid.

Modeling and Analysis of MRR in WEDMed WC-CO Composite by Response Surface Methodology

Wire electro discharge machining (WEDM) was applied to machine tungsten carbide–cobalt (WC-CO) metal matrix composite. It finds increasing application in auto, aeronautical and oil drill application. The material is extremely hard, brittle and tool grade. The present work is undertaken on 10% cobalt, 90% tungsten grade in which keen study is lacking. Amongst many variables, On-time, Off-time and ignition current were shortlisted as critical input parameters. The goal is to identify the input parameter level that maximizes the material removal rate. The input parameters for the experiments were selected after considering previous related work, manufacturer’s catalog and industrial expert’s opinion. From Taguchi L27 experimental plan, the Box-Behnken trials for 14 experiments were derived in order to model and to predict the output response with good accuracy. The investigation was carried out on the high speed Sodick machine so that it aligns with industry requirement of higher productivity. Response surface modeling and regression analysis was done. Analysis of variance was used to isolate parameters that are critical from pooled data. The experimental results were verified by running at recommended setting of the findings. The outcome was encouraging. Output response improves with on-time at 8 μ- Sec, off -time 15 μ- Sec and ignition current of 16 amperes. It was found that overall metal removal rates increased by 13%, to 17.42 mm3/min from the process average rate of 15.15 mm3/min. A mathematical equation was derived to predict performance. Surface, response contour plots were utilized to analyze performance. The validity of derived model was verified. Since error obtained was 4.5%, higher coefficient of determination is 87% and adequate precision was >4, the model is valid. Keywords: WEDM, material removal rate, WC-CO, response surface, regression analysis

Modelling and experimental investigation of process parameters in WEDM of WC-5.3 % Co using response surface methodology

Abstract. Tungsten carbide-cobalt (WC-Co) composite is a difficult-to-machine material owing to its excellent strength and hardness at elevated temperature. Wire electrical discharge machining (WEDM) is a best alternative for machining of WC-Co composite into intricate and complex shapes. Efficient machining of WC-Co composite on WEDM is a challenging task since it involves large numbers of parameters. Therefore, in present work, experimental investigation has been carried out to determine the influence of important WEDM parameters on machining performance of WC-Co composite. Response surface methodology, which is a collection of mathematical and experimental techniques, was utilised to obtain the experimental data. Using face-centered central composite design, experiments were conducted to investigate and correlate the four input parameters: pulse-on time, pulse-off time, servo voltage and wire feed for three output performance characteristics – cutting speed (CS), surface roughness (SR) and radial overcut (RoC). Using analysis of variance on experimental data, quadratic vs. two-factor interaction (2FI) models have been suggested for CS and RoC while two-factor interaction (2FI) has been proposed for SR. Using these mathematical models, optimal parameters can be determined easily for desired performance characteristics, and hence a trade-off can be made among different performance characteristics.

Material selection for the tool holder working under hard milling conditions using different multi criteria decision making methods

Nowadays machining of materials in their hardened state, also called hard machining, is a challenge in production of tools and molds. It has some advantages such as lower process time and lower manufacturing cost when compared to conventional machining. In machining of hard workpiece materials, however, very high stresses act on the tool holder through the cutting tool. These stresses necessitate the tool holder to have some specific properties. Especially in hard milling, the tool holder should have high stiffness and should be able to dissipate the energy generated during interrupted cutting. Material cost of the tool holder is also important since lower costs provide a competitive advantage for manufacturers. The material selection for the tool holder should be conducted considering aforementioned requirements. To tackle the difficulty of the material selection with specific properties from a large number of alternatives, multi-criteria decision-making (MCDM) methods have been used. In this paper a decision model including extended PROMETHEE II (EXPROM2) (preference ranking organization method for enrichment evaluation), TOPSIS (technique for order performance by similarity to ideal solution) and VIKOR (VIšekriterijumsko KOmpromisno Rangiranje) methods were used for the selection of the best material for the tool holder used in hard milling. The criteria weighting was performed by compromised weighting method composed of AHP (analytic hierarchy process) and Entropy methods. The candidate materials were ranked by using these methods and the results obtained by each method were compared. It was confirmed that MCDM methods can be used for the solution of real time material selection problems. Tungsten carbide–cobalt and Fe–5Cr–Mo–V aircraft steel were found as the best materials for the tool holder production. The obtained results are found to be rather satisfactory and can be used in design stage of hard machining operations.

Hard-metal (WC–Co) particles trigger a signaling cascade involving p38 MAPK, HIF-1α, HMOX1, and p53 activation in human PBMC

Hard-metals are made of tungsten carbide (WC) and metallic cobalt (Co) particles and are important industrial materials produced for their extreme hardness and high wear resistance properties. While occupational exposure to metallic Co alone is apparently not associated with an increased risk of cancer, the WC-Co particle mixture was shown to increase the risk of lung cancer in exposed workers. We have previously shown that WC-Co specifically induces a burst of reactive oxygen species (ROS) and in vitro mutagenic/apoptogenic effects in human peripheral blood mononucleated cells (PBMC) used as a validated experimental model. In the present study, PBMCs were treated during a short period (15 min) to focus on the very rapid ROS burst induced by WC-Co. We investigated by microarray the response to WC-Co versus Co(2+) ions (CoCl(2)) after 15 min exposure and found that the oxidative stress response HMOX1 gene was highly expressed in WC-Co-treated samples. This result was confirmed by qRT-PCR, and western blotting was carried out to analyze translational and post-translational regulation of genes belonging to the HMOX1 pathway. We show here that WC-Co, and metallic Co particles although with slower kinetics, but not CoCl(2) or WC alone, induced a temporally ordered cascade of events. This cascade implies p38/MAP kinase activation, HIF-1α stabilization, HMOX1 transcriptional activation, and ATM-independent p53 stabilization. These events, and in particular HIF-1α stabilization, could contribute to the carcinogenic activity of WC-Co dusts.

Direct Deposition of Cubic Boron Nitride Films on Tungsten Carbide–Cobalt

Thick cubic boron nitride (cBN) films in micrometer-scale are deposited on tungsten carbide-cobalt (WC-Co) substrates without adhesion interlayers by inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) using the chemistry of fluorine. The residual film stress is reduced because of very low ion-impact energies (a few eV to ∼25 eV) controlled by the plasma sheath potential. Two types of substrate pretreatment are used successively; the removal of surface Co binder using an acid solution suppresses the catalytic effect of Co and triggers cBN formation, and the surface roughening using mechanical scratching and hydrogen plasma etching increases both the in-depth cBN fraction and deposition rate. The substrate surface condition is evaluated by the wettability of the probe liquids with different polarities and quantified by the apparent surface free energy calculated from the contact angle. The surface roughening enhances the compatibility in energy between the cBN and substrate, which are bridged by the interfacial sp(2)-bonded hexagonal BN buffer layer, and then, the cBN overlayer is nucleated and evolved easier.

Influence of visco-elastic binder properties on ram extrusion of a hardmetal paste

The influence of the viscous and elastic components of a visco-elastic binder phase on the extrusion behaviour of a tungsten carbide–cobalt hardmetal paste was investigated by studying the paste over a range of temperatures, 30–42 °C, where the binder changed from a semi-solid gel to a viscous liquid. The extrusion behaviour of the paste was studied by ram extrusion and quantified by the Benbow–Bridgwater (BB) method. The elastic and viscous components of the binder were studied separately by means of oscillatory and steady shear techniques in a controlled stress rheometer using rough parallel plates. The paste behaviour fitted the four parameter BB model well: the initial bulk yield stress parameter, σ0, increased linearly with the binder elastic modulus, G′, while both the velocity dependence parameters α and β were linearly related to the binder steady shear viscosity. Analysis of paste-wall slip parameters gave estimated slip layer thicknesses of 2–5 particle diameters.

Phase transformation in tungsten carbide–cobalt composite during high temperature treatment in microwave hydrogen plasma

To study phase formation up to 2300K, tungsten carbide–cobalt (WC–Co) samples were exposed to concentrated solar radiation in hydrogen plasma. The reducing atmosphere was a non-equilibrium hydrogen plasma created in a microwave cavity at the nominal power of 1000W. The dissociation fraction of hydrogen molecules in plasma was of the order of 10% assuring for almost optimal reduction of any oxide that could be formed on the surface of samples due to the residual atmosphere. Micro-structural characterization was performed by XRD and AES depth profiling. The results showed the appearance of Co6W6C phase at the temperature of 1050±50K. This phase almost vanished at the temperature of 1300±90K and was replaced by the Co3W3C phase. This phase vanished at 1690±150K where only WC and Co peaks were detected by XRD. The AES depth profiles showed enrichment of the surface film with Co at elevated temperatures. At extremely high temperature of 2300K, the Co vanished from the surface layer but remained in crystalline form in the bulk material. SEM imaging showed an evolution of the material crystallinity up to perfectly recognizable crystals of the dimension of approx. 1μm at the maximum temperature. The results are explained by mobility of Co atoms, surface segregation and sublimation at very high temperature.

Influence of mechanical properties of tungsten carbide–cobalt thermal spray coatings on their solid particle erosion behaviour

The present investigation has been carried out in order to study the erosion wear behaviour of WC–Co base thermal spray coatings. WC–12Co and WC–10Co–4Cr coatings were deposited by means of high velocity oxygen fuel (HVOF) thermal spraying. The erosion tests were conducted at impact angles of 30 and 90° using SiC particles of ∼50 μm in diameter as erodent, at a velocity of 83·4 m s−1. It has been found that the erosion rate for both coated systems was higher when the test was carried out at an angle of 90°. The through-thickness residual stresses of the coatings, as well as the microstructural characterisation, allowed an explanation of the results and the erosion mechanisms in each case. It has been found that, under the experimental conditions carried out in the present study, the WC–10Co–4Cr coating exhibited a higher erosive wear resistance as compared to the WC–12Co coating.

Mechanical properties and wear resistance of functionally graded WC–Co

Functionally graded tungsten carbide–cobalt (FG WC–Co) composites were fabricated using a carburization process that preferentially segregated cobalt away from the free surface, establishing a compositional gradient into the bulk of the material. The resulting surface, which is harder due to increased WC content, has potentially broad application in tools for rock drilling and metal machining. The microstructure and mechanical properties of FG WC-10wt.% Co and FG WC-16wt.% Co samples were compared to conventional WC–Co for hardness, wear, fracture toughness, transverse rupture strength (TRS), impact, compression strength, and compressive fatigue. The increased surface hardness of the functionally graded materials resulted in substantially improved wear resistance, from 40% to 80%, compared to their conventional homogeneous WC–Co counterparts at equivalent levels of hardness, strength, and fracture toughness. FG WC–Co also exhibited improved impact and compressive fatigue resistance in a cutting element with a dome-topped geometric shape.

Effect of active screen plasma nitriding pretreatment on wear behavior of TiN coating deposited by PACVD technique

Titanium based alloys are used extensively for improving wear properties of different parts due to their high hardness contents. Titanium nitride (TiN) is among these coatings which can be deposited on surface using various techniques such as CVD, PVD and PACVD. Their weak interface with substrate is one major drawback which can increase the total wear in spite of favorite wear behavior of TiN. Disc shaped samples from AISI H13 (DIN 1.2344) steel were prepared in this study. Single TiN coating was deposited on some of them while others have experienced a TiN deposition by active screen plasma nitriding (ASPN). Hardness at the surface and depth of samples was measured through Vickers micro hardness test which revealed 1810Hv hardness as the maximum values for a dual-layered ASPN–TiN. Pin-on-disc wear test was done in order to study the wear mechanism. In this regard, the wear behavior of samples was investigated against pins from 100Cr6 (Din 1.3505) bearing steel and tungsten carbide–cobalt (WC–Co) steel. It was evidenced that the dual-layer ASPN–TiN coating has shown the least weight loss with the best wearing behavior because of its high hardness values, stable interface and acceptable resistance against peeling during wearing period.

Induction of Apoptosis by Tungsten Carbide‐Cobalt Nanoparticles in JB6 Cells Involves ROS Generation through both ‘Extrinsic’ and ‘Intrinsic’ Apoptotic Pathways

Tungsten Carbide‐Cobalt (WC‐Co) nanoparticle composites have wide applications because of their hardness and toughness. In this study, apoptosis and related signaling induced by WC‐Co were investigated. Electron spin resonance (ESR) and fluorescent staining indicated that both WC‐Co nano‐ and fine particles stimulated reactive oxygen species (ROS) generation. Catalase inhibit WC‐Co‐induced ROS as well as mitochondrial membrane permeability damage, indicating that H2O2 may play an important role in the cytotoxicity induced by WC‐Co. Further studies indicated that WC‐Co nanoparticles elicited a higher cytotoxicity and apoptotic induction than fine particles. Western‐blot analysis showed an activation of proapoptotic factors including Fas, FADD, caspase 3, 8 and 9, BID, and BAX. Lamin A and beta‐actin were cleaved. Interestingly, WC‐Co particles also induced Bcl‐2, an anti‐apoptotic factor, up‐regulation. In addition, both cytochrome c and AIF were up‐regulated and released from mitochondria to the cytoplasm. The results demonstrate that apoptosis induced by WC‐Co involve both ‘extrinsic’ and ‘intrinsic’ apoptotic pathways and nanoparticles exhibit higher cytotoxicity and apoptotic induction than fine particles.

Investigation of atypical molten pool dynamics in tungsten carbide-cobalt during laser deposition usingin-situthermal imaging

An atypical “swirling” phenomenon observed during the laser deposition of tungsten carbide-cobalt cermets by laser engineered net shaping (LENS®) was studied using in-situ high-speed thermal imaging. To provide fundamental insight into this phenomenon, the thermal behavior of pure cobalt during LENS was also investigated for comparison. Several factors were considered as the possible source of the observed differences. Of those, phase difference, material emissivity, momentum transfer, and free surface disruption from the powder jets, and, to a lesser extent, Marangoni convection were identified as the relevant mechanisms.