Tungsten Carbide-cobalt Research Articles

Effect of Cobalt Content on Microstructures and Wear Resistance of Tungsten Carbide–Cobalt-Cemented Carbides Fabricated by Spark Plasma Sintering

We researched tungsten carbide–cobalt (WC–Co)-cemented carbides without binder and with little binder and sintered by spark plasma sintering with 0 wt. %, 0.2 wt. %, 0.5 wt. % and 0.8 wt. % Co at different temperatures. The microstructures, hardness, fracture toughness and wear resistance of the WC–Co-cemented carbides were investigated by scanning electron microscopy and mechanical property tests. The wear resistance of WC–Co-cemented carbides with little to no binder is acceptable and it decreases with increase in Co content. There is no significant difference in wear resistance at 0 wt. % and 0.2 wt. % Co content. By analysing the friction and wear mechanism, it can be concluded that because the Co phase was extruded first, the stability of the WC hard base was disrupted, the WC phase desquamated and abrasion occurred. WC-cemented carbide with 0.2 wt. % Co is the most suitable material. The best results were achieved at 1680°C with 2333 HV30 and 6.82 MPa.m1/2

Nanoindentation Evaluation of Suspension Thermal Sprayed Nanocomposite WC-Co Coatings

The aim of this paper is to evaluate the microstructural and nanohardness characteristics of tungsten carbide-cobalt (WC-Co) cermet coatings deposited by liquid suspension spraying. Commercially available WC-Co coating powder was milled and water based suspension was produced as feedstock for the thermal spray coating process. Microstructural evaluations of WC-Co cermet coatings included XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscopy). Post spraying nanomechanical evaluations were conducted using a Berkovich nanoindenter. Results indicated relatively higher modulus but lower hardness of suspension coatings. The load displacement curves during nanoindentation were characteristic of the complex coating microstructure showing signs of microcracking and pile-up.

Effect of substrate bias on the tribological behavior of ta-C coating prepared by filtered cathodic vacuum arc

Tetrahedral amorphous carbon (ta-C) films were coated on the tungsten carbide cobalt by using filter cathodic vacuum arc (FCVA). All the specimens were coated at different bias voltage, such as 0 V, 40 V, 80 V, 120 V, and 160 V. The tribological behavior of all these specimens were evaluated by using a ball-on-disc type of tribo-test. Raman analysis was used in this research for investigating the bond structure in the coating films. From the experiment result shown the variation of the bias voltage of the ta-C coating do not bought to the change of the mechanical properties. As well as for the tribological aspect. Whereas, it only bought to the influence of the wear properties. The lowest wear rate result were found from the ta-C film that coated under 40V. This was due to the surface contact area and the surface roughness properties different at the different bias voltage.

Nanoparticles of WC-Co, WC, Co and Cu of relevance for traffic wear particles – Particle stability and reactivity in synthetic surface water and influence of humic matter

Studded tyres made of tungsten carbide cobalt (WC-Co) are in the Northern countries commonly used during the winter time. Tungsten (W)-containing nano- and micron-sized particles have been detected close to busy roads in several European countries. Other typical traffic wear particles consist of copper (Cu). The aims of this study were to investigate particle stability and transformation/dissolution properties of nanoparticles (NPs) of WC-Co compared with NPs of tungsten carbide (WC), cobalt (Co), and Cu. Their physicochemical characteristics (primarily surface oxide and charge) are compared with their extent of sedimentation and metal release in synthetic surface water (SW) with and without two different model organic molecules, 2,3- and 3,4-dihydroxybenzoic acid (DHBA) mimicking certain sorption sites of humic substances, for time periods up to 22 days. The WC-Co NPs possessed a higher electrochemical and chemical reactivity in SW with and without DHBA molecules as compared with NPs of WC, Co, and Cu. Co was completely released from the WC-Co NPs within a few hours of exposure, although it remained adsorbed/bonded to the particle surface and enabled the adsorption of negatively charged DHBA molecules, in contrast with the WC NPs (no adsorption of DHBA). The DHBA molecules were found to rapidly adsorb on the Co and Cu NPs. The sedimentation of the WC and WC-Co NPs was not influenced by the presence of the 2,3- or 3,4-DHBA molecules. A slight influence (slower sedimentation) was observed for the Co NPs, and a strong influence (slower sedimentation) was observed for the Cu NPs in SW with 2,3-DHBA compared with SW alone. The extent of metal release increased in the order: WC < Cu < Co < WC-Co NPs. All NPs released more than 1 wt-% of their metal total mass. The release from the Cu NPs was most influenced by the presence of DHBA molecules.

Environmental benefits of coatings based on nano-tungsten-carbide cobalt ceramics

Engineered nanomaterials (ENMs) offer improved or novel technical properties and, consequently, are increasingly being used in various applications. Furthermore, ENMs may contribute to a higher eco-efficiency compared to conventional technologies due to decreased materials and energy requirements. Thus far, only a few studies into the environmental performance of ENMs have been conducted and these have mainly focused on the production stage and have not considered a full life cycle thinking approach. Nano-WC-Co coatings are featured to have an improved wear resistance and require less material compared to conventional hard chromium coatings for the same performance in the application. Here, we perform a life cycle assessment to compare the environmental performance of two alternative ceramic coatings for conveyer rolls: novel tungsten-carbide cobalt nanoparticles (nano-WC-Co) and conventional hard chromium. The results of the cradle-to-grave life cycle assessment of nano-WC-Co application showed an overall reduced environmental impact in the main impact categories compared to hard chromium coatings. The most considerable reduction was observed in the categories metal depletion (−98%), water depletion (−91%), agricultural land occupation (−83%). Likewise, the categories human toxicity (−73%) and fresh water eutrophication (−79%) showed a reduced environmental impact. The results were evaluated by a sensitivity analysis and two particularly influential parameters were identified: the efficiency of thermal spraying process, and the extended product lifespan. Overall, it has been shown that nano-WC-Co coatings contribute to a higher eco-efficiency in every sensitivity variation and can offer more sustainable solutions compared to the conventional technology.

Braking performance and noise in excessive worn brake discs coated with HVOF thermal spray process

In this paper, two excessive worn brake discs of a light commercial vehicle were coated with High velocity oxygen fuel (HVOF) thermal spray process for reuse. The coated discs were compared with uncoated Original equipment manufacturer (OEM) D1 disc in terms of braking performance and noise. The D2 disc was coated with tungsten-carbide-cobalt (88 %WC-12 %Co) powder and NiCr (80/20) binder, and 500 Gm thick coating was obtained. The D3 disc was coated with Colmonoy-88 (Ni-W-Cr-B-Si) powder and NiCr (80/20) binder and 600 Gm thick coating was obtained. Several test procedures (e.g. bedding, vibration, and structural-strength tests) was applied to three discs using inertia brake dynamometer. Results showed that coated D2 disc with tungsten carbide cobalt provided lower brake noise and higher brake performance compared with OEM disc. Considering the coefficient of friction and temperature, coated D3 disc has approximately equal braking performance with OEM D1 disc despite the high braking noise value.

Enhanced mechanical properties and oxidation resistance of tungsten carbide-cobalt cemented carbides with aluminum nitride additions

Tungsten carbide-cobalt cermets respectively doped with 0, 0.5, 1.0, 1.5 and 2wt% aluminum nitride were fabricated by the sintering process at 1400°C. The existence of aluminum nitride in the binder phase could refine tungsten carbide grains and reinforce the obtained cermets. The cermets with 1.0wt% aluminum nitride exhibited the higher hardness of 17.1GPa and transverse rupture strength of 3120MPa, compared with 15.6GPa and 2500MPa of the pure cermets. Owing to the addition of aluminum nitride, a high oxidation resistance was measured in cermets with 2.0wt% aluminum nitride, which is nearly 1.9 times than that in the pure cermets.

The correlation between tribological properties of nanostructure TiN coatings and deposition process parameters in PACVD system

Titanium base coatings are being used extensively for improving wear characteristics at the surface of different parts. Titanium nitride was deposited by Plasma Assisted Chemical Vapor Deposition (PACVD) techniques with purpose improve interface with substrate, as this can increase wearing of the entire part in spite of desirable wear behavior of TiN. Samples from H13 steel were prepared and they experienced plasma nitriding (PN) prior to TiN deposition. TiN coatings were deposited in different conditions of temperature (475, 500 and 525°C) and duty cycle (33, 40 and 50%). Topographic studies were preceded by Atomic Force Microscope (AFM). Surface hardness was evaluated using Vickers's micro-hardness test. In order to study the wear behavior, pin-on-disc test was chosen which included examining the sample's resistance against pins from steel and tungsten carbide-cobalt. Based on the results obtained it can be observed that increasing the deposition temperature from 475 to 525°C will lead to higher values of hardness, thus the obtained weight loss from samples decreased from 2.1 to 0 mg. In addition to that, with increasing the duty cycle of system from 33 to 50%, weight loss of the TiN coating has increased from 0 to 2mg due to an increase in the value of surface roughness.

Nanotoxicity: emerging concerns regarding nanomaterial safety and occupational hard metal (WC-Co) nanoparticle exposure.

As the number of commercial and consumer products containing engineered nanomaterials (ENMs) continually rises, the increased use and production of these ENMs presents an important toxicological concern. Although ENMs offer a number of advantages over traditional materials, their extremely small size and associated characteristics may also greatly enhance their toxic potentials. ENM exposure can occur in various consumer and industrial settings through inhalation, ingestion, or dermal routes. Although the importance of accurate ENM characterization, effective dosage metrics, and selection of appropriate cell or animal-based models are universally agreed upon as important factors in ENM research, at present, there is no “standardized” approach used to assess ENM toxicity in the research community. Of particular interest is occupational exposure to tungsten carbide cobalt (WC-Co) “dusts,” composed of nano- and micro-sized particles, in hard metal manufacturing facilities and mining and drilling industries. Inhalation of WC-Co dust is known to cause “hard metal lung disease” and an increased risk of lung cancer; however, the mechanisms underlying WC-Co toxicity, the inflammatory disease state and progression to cancer are poorly understood. Herein, a discussion of ENM toxicity is followed by a review of the known literature regarding the effects of WC-Co particle exposure. The risk of WC-Co exposure in occupational settings and the updates of in vitro and in vivo studies of both micro- and nano-WC-Co particles are discussed.

In vitro inflammatory effects of hard metal (WC-Co) nanoparticle exposure.

Identifying the toxicity of nanoparticles (NPs) is an important area of research as the number of nanomaterial-based consumer and industrial products continually rises. In addition, the potential inflammatory effects resulting from pulmonary NP exposure are emerging as an important aspect of nanotoxicity. In this study, the toxicity and inflammatory state resulting from tungsten carbide–cobalt (WC–Co) NP exposure in macrophages and a coculture (CC) of lung epithelial cells (BEAS-2B) and macrophages (THP-1) at a 3:1 ratio were examined. It was found that the toxicity of nano-WC–Co was cell dependent; significantly less toxicity was observed in THP-1 cells compared to BEAS-2B cells. It was demonstrated that nano-WC–Co caused reduced toxicity in the CC model compared to lung epithelial cell monoculture, which suggested that macrophages may play a protective role against nano-WC–Co-mediated toxicity in CCs. Nano-WC–Co exposure in macrophages resulted in increased levels of interleukin (IL)-1β and IL-12 secretion and decreased levels of tumor necrosis factor alpha (TNFα). In addition, the polarizing effects of nano-WC–Co exposure toward the M1 (pro-inflammatory) and M2 (anti-inflammatory) macrophage phenotypes were investigated. The results of this study indicated that nano-WC–Co exposure stimulated the M1 phenotype, marked by high expression of CD40 M1 macrophage surface markers.

HVOF and HVAF Coatings of Agglomerated Tungsten Carbide-Cobalt Powders for Water Droplet Erosion Application

Water droplet erosion (WDE) is a phenomenon caused by impingement of water droplets of several hundred microns to a few millimeters diameter at velocities of hundreds of meters per second on the edges and surfaces of the parts used in such services. The solution to this problem is sought especially for the moving compressor blades in gas turbines and those operating at the low-pressure end of steam turbines. Thermal-sprayed tungsten carbide-based coatings have been the focus of many studies and are industrially accepted for a multitude of wear and erosion resistance applications. In the present work, the microstructure, phase analysis and mechanical properties (micro-hardness and fracture toughness) of WC-Co coatings are studied in relation with their influence on the WDE resistance of such coatings. The coatings are deposited by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) processes. The agglomerated tungsten carbide-cobalt powders were in either sintered or non-sintered conditions. The WDE tests were performed using 0.4 mm water droplets at 300 m/s impact velocity. The study shows promising results for this cermet as WDE-resistant coating when the coating can reach its optimum quality using the right thermal spray process and parameters.

Reinforcement of tungsten carbide grains by nanoprecipitates in cemented carbides

In contrast to the conventional method that obtains a high fracture strength of tungsten carbide–cobalt (WC–Co) cemented carbides by reducing WC grain size to near-nano or nanoscale, a new approach has been developed to achieve ultrahigh fracture strength by strengthening the WC grains through precipitate reinforcement. The cemented carbides were prepared by liquid-state sintering the in situ synthesized WC–Co composite powders with a little excess carbon and pre-milled Cr3C2 particles having different size scales. It was found that the nanoscale dispersed particles precipitate in the WC grains, which mainly have a coherent or semi-coherent interface with the matrix. The pinning effect of the nanoparticles on the motion of dislocations within the WC grains was observed. The mechanisms for the precipitation of nanoparticles in the WC grains were discussed, based on which a new method to enhance the resistance against the transgranular fracture of cemented carbides was proposed.

Finite Element Analysis of Particle Impact on Substrates Using HVOF Thermal Spray Coating

Lower flame temperature characteristics of high velocity oxygen fuel (HVOF) flame spray process favor several surface coating applications. Simulation of HVOF coating is extremely complex to analyze, since its properties and microstructure depend on numerous processing parameters. Finite element analysis (FEA) is used in this paper to analyze the influence of particle heat input and impact velocity on HVOF coating on various substrates. HVOF thermal spray coating conditions, Tungsten Carbide Cobalt (WC-Co) particles and steel substrate were modeled using ANSYS 14.5. Droplets of different size were considered as particles in the numerical analysis to study their impact on the substrate. Thermal and residual stress analysis was done on both the particle and substrate during different stages of the high velocity impact process. Both rigid and soft conditions of the particle and substrate were simulated. Thermal stress of both the particle and substrate were found to increase rapidly very close to the impact process. Smaller sized particles had higher plastic strain when compared to larger sized particles. However, the residual stress and plastic strain of the substrate increased when impacted by larger sized particles. Residual stress of both particle and substrate were found to be influenced by the impact and thermal stress of each other. Higher velocity of the flame spray showed improved plastic strain and stress on individual particles, which is a major reason for the dense pattern of coating.

High-temperature erosion of Fe-based coatings reinforced with cermet particles

High-velocity oxy-fuel sprayed, iron alloy-based powder coatings, reinforced with tungsten carbide–cobalt (WC–Co) and titanium carbide–nickel molybdenum (TiC–NiMo) cermet particles, are compared under high-temperature abrasive–erosive wear conditions. Both WC–Co and TiC–NiMo particles underwent fracture, as well as dissolution, during the spraying process, but in the case of WC–Co particles this process was remarkably less intensive. Under the low impact angle conditions, the WC–Co particle-reinforced coating exhibited 1.1 times lower wear than the TiC–NiMo particle-reinforced coating because of the larger amount of the reinforcement remaining. Under the normal impact angle conditions, the WC–Co particle-reinforced coating showed 1.2 times lower wear than the TiC–NiMo particle-reinforced coating because of the resulting larger size of the WC–Co reinforcement and a more ductile matrix.

Cobalt extraction from tungsten carbide-cobalt (WC-Co) hard metal scraps using malic acid

Tungsten carbide-cobalt (WC-Co) hard metal scraps release toxic heavy metals into groundwater when they are buried underground after industrial use. Recovering abundant Co from WC-Co hard metal scraps helps protect the environment as well as urban mining of Co. In this study, we characterized Co extraction from WC-Co hard metal scraps in malic acid and other leachants based on process parameters. We also introduced Co dissolution by wet milling in malic acid. Initially, WC-Co scraps were oxidized to produce a mixture of WO3 and CoWO4 and then pulverized with a ball mill to increase their specific surface area for improving the reaction with malic acid. Co in the Co2+ oxidation state dissolved as Co-malate (Mal) complexes, Co(H2Mal)2, and finally CoHMal, from CoWO4 in malic acid. We studied the change in Co dissolution efficiency with varying concentration, dissolution time, temperature, and agitation rate. H2O2 at 2vol% was added to decompose a thin layer of insoluble tungstic acid (WO3⋅H2O) covering the CoWO4 surface, which is a byproduct of forming the Co-Mal complex, into soluble peroxotungstic acid (WO3⋅H2O2⋅H2O). However, the increase in Co dissolution by adding H2O2 was fairly minimal. When wet milling, which simultaneously pulverizes and dissolves oxidized WC-Co scraps, was used, Co dissolution efficiency increased substantially with dissolution time.

Abrasion resistant low friction and ultra-hard magnetron sputtered AlMgB14 coatings

Hard aluminum magnesium boride films were fabricated by RF magnetron sputtering from a single stoichiometric AlMgB14 ceramic target. X-ray amorphous AlMgB14 films are very smooth. Their roughness does not exceed the roughness of Si wafer and Corning glass used as the substrates. Dispersion of refractive index and extinction coefficient were determined within 300 to 2500 nm range for the film deposited onto Corning glass. Stoichiometric in-depth compositionally homogeneous 2 μm thick films on the Si(100) wafer possess the peak values of nanohardness 88 GPa and Young’s modulus 517 GPa at the penetration depth of 26 nm and, respectively, 35 GPa and 275 GPa at 200 nm depth. Friction coefficient was found to be 0.06. The coating scratch adhesion strength of 14 N was obtained as the first chipping of the coating whereas its spallation failure happened at 21 N. These critical loads and the work of adhesion, estimated as high as 18.4 J m−2, surpass characteristics of diamond like carbon films deposited onto tungsten carbide–cobalt (WC–Co) substrates.

Synchrotron-radiation-based X-ray micro-computed tomography reveals dental bur debris under dental composite restorations.

Dental burs are used extensively in dentistry to mechanically prepare tooth structures for restorations (fillings), yet little has been reported on the bur debris left behind in the teeth, and whether it poses potential health risks to patients. Here it is aimed to image dental bur debris under dental fillings, and allude to the potential health hazards that can be caused by this debris when left in direct contact with the biological surroundings, specifically when the debris is made of a non-biocompatible material. Non-destructive micro-computed tomography using the BioMedical Imaging & Therapy facility 05ID-2 beamline at the Canadian Light Source was pursued at 50 keV and at a pixel size of 4 µm to image dental bur fragments under a composite resin dental filling. The bur's cutting edges that produced the fragment were also chemically analyzed. The technique revealed dental bur fragments of different sizes in different locations on the floor of the prepared surface of the teeth and under the filling, which places them in direct contact with the dentinal tubules and the dentinal fluid circulating within them. Dispersive X-ray spectroscopy elemental analysis of the dental bur edges revealed that the fragments are made of tungsten carbide-cobalt, which is bio-incompatible.

Acrylamide route for the co-synthesis of tungsten carbide–cobalt nanopowders with additives

In this work, cemented tungsten carbide nano-particles were prepared by a chemical method called acrylamide gel. In this process, first, a xerogel containing tungsten and cobalt oxide particles was synthesized. Then, it was carburized by a hydrogen reduction heating process.Acrylamide and N, N-methylene-bis-acrylamide monomers were used as an in-situ carbon. Ammonium meta tungstate (NH4)6H2W12O40·xH2O, and cobalt nitrate Co(NO3)2·6H2O salts were used as the precursor.Both reduction and carburization reactions were carried out simultaneously and the formation of the intermediate phases of W2C, Co3W3C, and Co6W6C led to decrease in the activation barrier.Transactions of reduction and carburization processes were studied by X-ray diffraction analysis at various temperatures. Accordingly, tungsten carbide phase formation was completed at 1100°C. The formation of W–C and V–C bonds was verified by Raman spectroscopy. SEM images showed the average nano particle size of 50nm.

AlSiTiN and AlSiCrN multilayer coatings: Effects of structure and surface composition on tribological behavior under dry and lubricated conditions

Nanocomposite coatings have been widely studied over the last years because of their high potential in several applications. The increased interest for these coatings prompted the authors to study the tribological properties of two nanocomposites under dry and lubricated conditions (applying typical MQL media), in order to assess the influence of the surface and bulk properties on friction evolution. To this purpose, multilayer and nanocomposite AlSiTiN and AlSiCrN coatings were deposited onto tungsten carbide-cobalt (WC-Co) samples. Uncoated WC-Co materials were used as reference. Coatings were analyzed in terms of hardness and adhesion. The structure of the samples was assessed by X-ray diffraction (XRD), while the surface composition was studied by XPS analysis. Friction tests were carried out under both dry and lubricated conditions using an inox ball as counterpart. Both coatings showed high hardness and good adhesion to the substrate. As far as the friction properties are concerned, in dry conditions the surface properties affect the sliding contact at the early beginning, while bulk structure and tribolayer formation determine the main behavior. Only AlSiTiN coating shows a low and stable coefficient of friction (COF) under dry condition, while the use of MQL media results in a rapid stabilization of the COF for all the materials.

Enhancement of conventional WC-Co and Inconel 625 HVOF thermal spray coatings by the addition of nanostructured WC-Co for wear/corrosion applications in the oil/gas industry

Recently, economical and fast solutions for preventing failure due to wear and corrosion in oil and gas industries have been reduced through the deposition of cermets using HVOF thermal spray coatings especially tungsten carbide–cobalt (Diamalloy 2004) deposits to reduce wear effects and Inconel-625 (Diamalloy 1005) to prevent corrosion. The new research trend towards the development of bimodal (mixed of nano- and micro-size particle) feedstock powders, through the addition of nanostructured WC-Co, is showing promise and is under investigation in this research. A design-of-experiment software was implemented to study the influence of different powder percentage on the coating performance such as coating microstructure and coating mechanical performance, such as three-point bending tests and hardness measurement. Results show that hardness, bending and yield strength of the coating increased as the composition percentage of nanostructured WC-12Co mixed in with the Diamalloy 2004/1005 (WC-12Co micro/Inconel-625, respectively) composite increased due to the strong adhesion of WC nanosize grains at the substrate/coating interface through improved mechanical interlocking and reduce the possibility of cracks initiation. The results show promise in terms of the current maintenance challenges experienced by the oil/gas industry today, in terms of possibly extending the life of components, plus providing huge economic savings.