WC 10Co Research Articles

Slurry erosion behaviour of HVOF sprayed coatings on hydro turbine steel: A review

Slurry erosion is one of the unavoidable problems in the operation of hydro power stations all over the world. Erosion mainly depends on the surface properties of the hydro turbine material and the different level of operating parameters like impact angle, impact velocity, slurry concentration, particle size and shape. Thermally sprayed hard metal coatings are widely used to protect components and surfaces against erosion wear in various applications. This study focuses on the slurry erosion behaviour of high velocity oxy-fuel (HVOF) sprayed coatings on hydro turbine steel. The HVOF sprayed coatings such as WC-CoCr, Cr3C2-NiCr, Al2O3, stellite, Cr2O3, Cr3C2–NiCr, NiCrSiB–35wt%WC–Co, WC–10Co– 4Cr and WC-12Co results in high bond strength, lower porosity and high resistance to slurry erosion. In this review paper, comprehensive and significant investigation has been made on existing literature of HVOF sprayed coatings on the material of hydro turbine components. The reported research work reveals that the predominant causes of slurry erosion of the uncoated hydro turbine steel include micro-cutting, micropores, cracks, craters, microchipping, pullout, de-bonding and spalling which can be effectively minimize by applying HVOF sprayed coatings.

Influence of thermal cycling modes on VK8 hard alloy mechanical and tribological properties

Hard alloys are popular materials widely used in the toolmaking industry. Refractory carbides included in their composition make carbide tools very hard (80 to 92 HRA) and heat-resistant (800 to 1000 °С) so as they can be used at cutting speeds several times higher than those used for high-speed steels. However, hard alloys differ from the latter by lower strength (1000 to 1500 MPa) and the absence of impact strength, and this constitutes an urgent problem. We studied the influence of thermal cycling modes on the mechanical and tribological properties of VK8 (WC–8Co) hard alloy used in the manufacture of cutters and cutting inserts for metal working on metal-cutting machines. As the object of study, we selected 5×5×35 mm billets made of VK8 (WC–8Co) alloy manufactured by powder metallurgy methods at Dimitrovgrad Tool Plant. The following criteria were selected for heat treatment mode evaluation: Vickers hardness, flexural strength, and mass wear resistance (as compared to the wear of asreceived samples that were not heat treated). Plates in the initial state and after heat treatment were subjected to abrasion tests. Wear results were evaluated by the change in the mass of plates. Regularities of the influence of various time and temperature conditions of heat treatment on the tribological properties of products made of VK group tungsten hard alloys were determined. An increase in the number of thermal cycling cycles improved such mechanical properties of the VK8 hard alloy as strength and hardness. When repeating the cycles five times, an increase in abrasive wear resistance was obtained compared to the initial nonheat-treated sample. The elemental composition of the VK8 hard alloy changed insignificantly after thermal cycling, only a slight increase in oxygen was observed on the surface of plates. The grain size after thermal cycling increased in comparison with the initial VK8 hard alloy. It was found that VK8 hard alloy thermocyclic treatment leads to a change in the phase composition. X-ray phase analysis showed the presence of a large amount of α-Co with an hcp-type lattice on the surface of a hard alloy and a solid solution of WC in α-Co. A change in the cobalt modification ratio causes a decrease in microstresses. An analysis of the carbide phase structure state showed that the size of crystallites and microstresses changed after thermal cycling. The lattice constant of the cobalt cubic solid solution decreased, which may indicate a decrease in the amount of tungsten carbide and carbon dissolved in it. Statistical processing of experimental results included the calculation of the average value of the mechanical property, its dispersion and standard deviation in the selected confidence interval.

High-temperature friction behavior of amorphous carbon coating in glass molding process

In the glass molding process, the sticking reaction and fatigue wear between the glass and mold hinder the service life and functional application of the mold at the elevated temperature. To improve the chemical inertness and anti-friction properties of the mold, an amorphous carbon coating was synthesized on the tungsten carbide-cobalt (WC–8Co) substrate by magnetron sputtering. The friction behavior between the glass and carbon coating has a significant influence on the functional protection and service life of the mold. Therefore, the glass ring compression tests were conducted to measure the friction coefficient and friction force of the contact interface between the glass and amorphous carbon coating at the high temperature. Meanwhile, the detailed characterization of the amorphous carbon coating was performed to study the microstructure evolution and surface topography of the amorphous carbon coating during glass molding process by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ramon spectroscopy, and atomic force microscope (AFM). The results showed that the amorphous carbon coating exhibited excellent thermal stability, but weak shear friction strength. The friction coefficient between the glass and coating depended on the temperature. Besides, the service life of the coating was governed by the friction force of the contact interface, processing conditions, and composition diffusion. This work provides a better understanding of the application of carbon coatings in the glass molding.

Effect of the combined addition of TaC and NbC on the dispersity of cubic phase in ultra-fine WC–10Co–0.5Cr cemented carbides

TaC and NbC have different effects on the dispersity of precipitated cubic phase, which acts as an important role in regulating the mechanical properties of ultra-fine cemented carbides. In this work, the influence of the combined addition of TaC and NbC on the microstructure evolution and mechanical properties in ultra-fine WC–10Co–0.5Cr cemented carbides was systematically investigated through the thermodynamic calculations and experiments. With the guide of thermodynamic calculations, the ultra-fine WC–10Co–0.5Cr cemented carbides with the combined addition of TaC and NbC were prepared. By replacing TaC with NbC, the dispersity of cubic carbides can be improved significantly from large-size honeycombed to small-size isolated cubic particles, which is explained by thermodynamic calculations. The brittle cubic phase results in the degradation of crack propagation resistance, and thus deteriorates the mechanical properties. Therefore, both the hardness and fracture toughness increase with the improvement of dispersity of cubic phase in cemented carbides.

The Study of Microstructure and Mechanical Properties of Diesel Engine Piston Coated with Carbide Composites by Using HVOF Method

Thermal barrier coating (TBC) materials inside the cylinder in diesel vehicles are used to increase the reliability, durability, engine efficiency and performance of the hot parts of metal components in the engine. For this reason, as the researches on TBC in diesel engines increase day by day, new thermal researches of barrier coating material inside cylinders are proceeding. Therefore, in this study, Cr3C2–25(NiCr), WC–10Co–4Cr and WC–12Co powders were coated on a piston of a diesel engine surface (AlSi12CuNi) by using HVOF method. The SEM images of coating layers were taken, and EDS and XRD analyses were done. Additionally, adhesion resistance, microhardness and surface roughness measurements of materials were done. In XRD studies, in Cr3C2–25(NiCr) coating layers, Cr3C2 and Cr7C3 composites, and in WC–10Co–4Cr and WC–12Co coating layers, WC, W2C and Co3W3C composites were found. The best adhesion resistance, maximum hardness value and minimum roughness value were detected on the samples that were coated with WC–12Co powder.

Erosion performance of detonation gun deposited WC–12Co, Stellite 6 and Stellite 21 coatings on SAE213-T12 steel

ABSTRACT Thermal spray coatings are used to improve the erosion resistance of boilers and turbine components for power plants and other industries. In this work, detonation gun spraying method is used to deposit WC-12Co, Stellite 6 and Stellite 21 coatings on SAE213-T12 boiler steel. The coatings were characterized using microhardness tester, scanning electron microscope (SEM), optical microscope and X-ray diffractometer (XRD). The solid particle erosion behaviours of the coatings were evaluated at 30° and 90° impact angles using an air jet erosion test rig. The erosion rates of Stellite 6 and Stellite 21 coatings are found approximately 60% and 50% respectively higher than WC–Co coating, which might be attributed to the respective hardness of the coatings. Cobalt content in the coatings played an important role on the erosion behaviour of the coatings. The erosion mechanisms of the coatings involved micro-ploughing, micro-cutting along with some micro-cracking and hard phase pull-outs.

Micro-texturing of a WC–10Co–4Cr-Coated ASTM A479 Steel to Form a Super-Hydrophobic Surface

Super-hydrophobic (SH) surfaces mostly motivated by the primordial surface designs considerably increase the life of the substrate. In the present work, effort has been made towards rational development of the SH surface on ASTM A479 steels substrates coated with WC–10Co–4Cr using high-velocity oxy-fuel. Distinct coating configurations have been investigated to analyse the effect of circular texturing patterns using nanosecond laser fibre texturing machine for the development of SH surfaces. Here, a freshly prepared solution of Hexafor 644-D/PFOA/Al2O3 nanoparticles was utilized for simple HVLP spraying and dip coating methods to formulate SH coatings on untextured and textured surfaces. The developed SH surfaces were characterized by field emission scanning electron microscope, X-ray diffraction, energy-dispersive spectroscopy and surface roughness tester. Water repellency of fabricated SH surfaces and its durability were studied by measuring the water contact angle (WCA), sliding angle, sandpaper abrasion test, tape peeling tests and water impact tests. All the configurations of the developed SH surfaces were found to be sustainable against the different wear tests performed during the study and exhibited excellent repellence to water and ink droplets. The highest WCA and sliding angle for textured and dip-coated SH surface (configuration—C 2.1) were found to be 162.6° and 10°, respectively. Further, it was found that during the sandpaper abrasion test, and the configuration corresponding to textured surfaces after thermal spray coating sustained super-hydrophobicity up to 30 cycles. Because of simple steps and the desired properties obtained by proposed methods, the coatings may be used for producing SH surfaces in apt industrial applications.

Study of the effects of the laser remelting process on the microstructure and properties of the WC–10Co–4Cr coating sprayed by HVOF

The laser remelting technique is considered a promising and effective method for improving the surface of thermally sprayed coatings, eliminating microstructural defects such as pores and cracks, increasing the life of parts and equipment by increasing microhardness and increasing anchoring force between coating and substrate. In the present work, tungsten carbide alloy (WC–12Co–4Cr) coatings were deposited on properly prepared SAE 1016 substrates using the high velocity oxy-fuel technique. An ytterbium fiber laser was used to remelt the surface of the coating by accurately varying the scanning speed and laser beam power to achieve a pore and crack-free coating and better metallurgical anchorage to the substrate through the optimization of the studied parameters. The samples were characterized by scanning electron microscopy and microhardness. The results show that it is possible to obtain higher hardness coatings after the laser remelting process, free of pores or pronounced imperfections and metallurgically bonded to the substrate. We also found a processing range for the ytterbium laser remelting of the WC–12Co–4Cr coating aiming at high productivity and microstructural optimization of the coating for different thicknesses.

Microstructure and mechanical property of WC-10Co/RM80 steel dissimilar resistance spot welding joint

In this work, resistance spot welding (RSW) was used to weld dissimilar metals of cemented carbide (WC–10Co) and high strength steel (RM80). The mechanical property and microstructure of welded joints were analyzed by shear test, scanning electron microscopy and micro X-ray diffraction, establishing the corresponding relationship between the mechanical property of welded joints and microstructure. The results show that with the increase of welding current, the shear strength of welded joints first increased and then decreased, the maximum of which under the optimal welding process was 924 MPa. The characteristics of five interface bonding types were clarified, whose proportion under different welding currents was calculated, and the contribution of each interface bonding type to the performance of welded joints was studied based on the mechanical property and fracture mechanism.

Electrochemical corrosion behavior of HVOF sprayed WC–12Co coating on H13 hot work mould steel

Purpose This study aims to investigate the electrochemical corrosion performance of high velocity oxygen fuel (HVOF) sprayed WC–12Co coating in 3.5 Wt.% NaCl solution, which provided a guiding significance on the corrosion resistance of H13 hot work mould steel. Design/methodology/approach A WC–12Co coating was fabricated on H13 hot work mould steel using a HVOF, and the electrochemical corrosion behaviors of WC–12Co coating and substrate in 3.5 Wt.% NaCl solution was measured using open circuit potential (OCP), potentiodynamic polarization curve (PPC) and electrochemical impedance spectroscopy (EIS) tests. Findings The OCP and PPC of WC–12Co coating positively shift than those of substrate, its corrosion tendency and corrosion rate decrease to enhance its corrosion resistance. The curvature radius of capacitance curve on the WC–12Co coating is larger than that on the substrate, and the impedance and polarization resistance of WC–12Co coating increase faster than those of substrate, which reduces the corrosion process. Originality/value The electrochemical corrosion behaviors of WC–12Co coating and substrate in 3.5 Wt.% NaCl solution is first measured using OCP, PPC and EIS tests, which improve the electrochemical corrosion resistance of H13 hot work mould steel.

Effect of Heat Treatment on the Cavitation Erosion Performance of WC–12Co Coatings

WC–12Co coatings were deposited on 16Cr5Ni stainless steel substrate by high-velocity oxygen fuel (HVOF) process, followed by a one-hour heat-treatment in a tube furnace with a nitrogen atmosphere at 650, 800, 950, and 1100 °C, respectively. The influence of heat-treatment temperature on properties and cavitation erosion resistance of as-sprayed and heat-treated WC–12Co coatings was studied. The cavitation erosion test was carried out with ultrasonic cavitation erosion equipment. The porosity, microhardness, phase composition, as well as surface and cross-section morphology of the coatings were characterized. The coating heat-treated at 800 °C showed three typical cavitation erosion stages and exhibited the best cavitation erosion resistance. The cavitation erosion resistance was closely related to the coating microstructure and heat-treatment process. 3D optical microscopy was used to analyze the eroded surface of the coatings. The cavitation erosion mechanism of the coatings was discussed.

Corrosion Behavior of WC–10 wt % Ni3Al Composite in Acidic Media

The room temperature corrosion behavior of WC–10 wt % Ni3Al composite and WC–8 wt % Co hardmetal in various acidic solutions (1 M H2SO4, 1 M HCl and 1 M HNO3) were compared and investigated utilizing immersion test, electrochemical measurement and surface analytical techniques. The results show that in H2SO4 solution WC–10Ni3Al composite has a nobler free corrosion potential, lower corrosion current density (Icorr) values and intrinsically better corrosion resistance than WC–8Co. Notably, pseudopassivity was observed in the polarization curves of WC–10Ni3Al in both HCl and H2SO4 solutions. In addition, although WC–10Ni3Al is corroded much faster in HNO3 solution than in the other two mediums, it exhibits a superior corrosion resistance compared to WC–8Co. The corrosion mechanism of WC–10Ni3Al composites is dominated by Ni dissolution.

The Distribution of Carbon in a Tungsten–Cobalt Alloy during Heat Treatment in a Gaseous Medium of Carbon Oxides

Investigations of composition, structure, and hardness of ultrafine-grained solid alloy WC–8Co–0.4VC–0.4Cr3C2 after treatment in a gaseous mixture of CO + CO2 of compacts with a lack of carbon for 50 min at a temperature 650°C on the initial stage of liquid-phase sintering. It was found that at CO content of 72.5% in the gas mixture, conditions are created for replacing the initial carbon deficiency (about 0.3%) and obtaining two-phase ultrafine-grained carbide of stoichiometric composition, in which carbon and hardness are uniformly distributed over the depth of the samples. This alloy has the lowest porosity (2.5%) and the highest hardness (HV1941). It was found that an increase of up to 80% or a decrease of up to 0% of the CO content in a gas mixture leads to the formation of a lack of carbon (1.0%) or an excess of carbon (4.5%) on the surface of the samples. This leads to a significant decrease in hardness. It is shown that the change in the carbon content and hardness in the depth of the samples is much less than on the surface.

Effect of grinding on surface characteristics of HVOF-sprayed WC–10Co–4Cr coatings

ABSTRACT The aim of this research was to investigate the effect of the grinding depth of cut on surface quality and corrosion behaviour of WC–10Co–4Cr cermet coatings. Accordingly, a WC–10Co–4Cr coating with 400 μm thickness was deposited on the carbon steel substrate using a High-Velocity Oxygen Fuel (HVOF) process. Consequently, the effect of different depths of cut on the coating properties was evaluated. Porosity, surface roughness and microhardness of as-sprayed and ground coatings were measured in order to investigate the effect of grinding on the coating characteristics. The corrosion behaviour of the coatings was evaluated using open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarisation tests. The results indicated that after grinding, the porosity and microhardness of the coatings were increased and the surface roughness was decreased. Furthermore, the increase in the depth of cut increased the coating porosity and microcracks. Therefore, the corrosion resistance of the coating was decreased.

Fabricating Ultrathin Plate-Like WC Grains in WC–8Co Hardmetals by Increasing Discharge Intensity During Plasma-Assisted Ball Milling

The effects of plasma discharge intensity on the microstructure evolution of ball-milled tungsten (W)–carbon (C)–cobalt (Co) mixtures and the formation mechanism of ultrathin plate-like tungsten carbide (WC) grains prepared by ball milling with and without plasma discharge were investigated. It was found that increasing the plasma discharge intensity during ball milling obviously promoted the formation of a thin flake-like W phase because of the electroplasticity effect and simultaneously lowered the carburization temperature between W and C. A combination of high hardness and transverse rupture strength of 92.9 HRA and 3659 MPa, respectively, was obtained for the WC–8Co alloy fabricated by plasma milling at a gas pressure of 5 × 103 Pa with a dielectric barrier discharge layer thickness of 3 mm. These properties were mainly attributed to the markedly lowered activation energy of the WC phase and generation of highly oriented ultrathin plate-like WC grains by plasma milling. The combination of the flake-like structure of the plasma-milled W aggregate and high specific interfacial area and short diffusion distance of W/C were readily inherited by the ultrathin plate-like WC grains in the sintered WC–Co hardmetals.

Comparison of abrasive wear by rice husk of an HVOF WC–Co–Cr-based coating and an electric arc sprayed coating based on Fe–Cr–B–Si

The effect of abrasive wear is particularly relevant in the industrial areas of agriculture, mining, mineral processing and earth moving. Wear problems occur in mills and silos where grain is stored and moved in large quantities through the process of agro-processing. Machines and equipment that work under direct contact with the grain suffer from severe three-body abrasive wear from the rice husks. The main objective of this study was to investigate the abrasive wear behavior of an Fe–29Cr–4B–1.75Si coating sprayed by electric arc and a WC–10Co–4Cr coating applied by the high-velocity oxygen fuel (HVOF) methods. Both coatings used SAE 1016 carbon steel as the substrate. A dry-sand, rubber wheel abrasion test was performed using ASTM G65 standard that employs sand as an abradant. It was compared to a variation on that test that employed rice husk as the abradant. The coatings were characterized by scanning electron microscopy, X-ray diffraction and microhardness. The microhardness values for coatings and substrate were measured using a microhardness Vickers tester equipped with a diamond pyramid indenter. The results showed that the mechanisms of wear differ by the change of abrasive, characterizing a wear by scratches when using the sand, and by microcutting, ledges and cracks when the rice husk is used as an abradant. The WC–10Co–4Cr deposition by HVOF showed satisfactory performance under abrasive wear with rice husk demonstrating a potential for application in agricultural implements working in the rice culture.

Microstructure and properties of coarse-grained WC–10Co cemented carbides with different carbon contents during heat treatments

The effects of cryogenic treatment (CT) and tempering-cryogenic treatment (TCT) on the microstructure and properties of coarse-grained WC–10Co cemented carbides with different carbon contents were researched. The binder phase, WC mean grain sizes, W solubility in the binder, relative magnetic saturation, densities, hardness, wear resistance and second phase precipitation of cemented carbides with different heat treatments were discussed. The results show that there are significant changes of microstructure and properties in the samples with CT and TCT, especially due to the precipitation of metastable nanoparticles $${\text{W}}_{x} {\text{Co}}_{y} {\text{C}}_{z}$$ in the binder during the heat treatments of CT and TCT. With the simultaneous combination of microstructure and nanoparticle-reinforced binder, a dramatically improved combination of hardness and wear resistance of the samples after TCT has been achieved.

Features of Influence of Sintering Conditions of Fine-Grained WC—10Co Cemented Carbide on Its Structure, Physical-Mechanical and Operational Characteristics

The results of a study of the influence of the environment during sintering of fine-grained WC—10Co cemented carbide on its structural characteristics and physico-mechanical properties, as well as the operational durability and wear mechanisms of the cutting plates of this alloy in impact cyclic turning process of 40Kh steel parts are presented. It is shown that the sintering of a cemented carbide in vacuum as compared with sintering in a methane-hydrogen environment reduces the residual microporosity of its structure, improves the physico-mechanical properties and operational durability of the cutting plates made from it. A new phenomenon was found to be the formation of continuous chip in the conditions of discontinuous turning of 40Kh steel parts and the welding it to a working part of a cutting plate from WC-10Co cemented carbide sintered in vacuum, and the absence of such a phenomenon for an alloy sintered in a methane-hydrogen environment.

High temperature wear resistance and thermal fatigue behavior of Stellite-6/WC coatings produced by laser cladding with Co-coated WC powder

The Stellite-6/WC composite coatings were produced on AISI H13 hot work tool steel by laser cladding with mixture of Co-coated WC (WC-12Co) particles and Stellite-6 powder. The phase composition, microstructural characterization, high temperature wear resistance and thermal fatigue behavior of Stellite-6/WC coatings were investigated and compared with the properties of the coatings produced from mixture of WC particles and Stellite-6 powder. The results showed that using the WC-12Co particles alleviated the decomposition of WC and resulted in the weaker intensity of W2C, CoCx and Co6W6C peaks in the X-Ray Diffraction (XRD) patterns. Compared with using the WC particles directly as the coating material, using the WC-12Co particles could further improve the wear resistance of coatings according to the relative lower width and depth of wear scars at the same WC content. In addition, fewer fatigue cracks were observed on the surface of coatings made by adding WC-12Co particles under the same thermal fatigue conditions, which indicates that using WC-12Co is beneficial to extend the life of Stellite-6/WC coatings.

Electroless nickel–phosphorus plating on WC–Co powders using HVOF feedstock

ABSTRACTIn this study, electroless nickel–phosphorus plating was optimised for WC–Co powder using different bath loads and then subjected to a high-velocity oxygen fuel process. The produced Ni–P-coated WC–12Co powders were subsequently used as HVOF feedstock materials. Based on the SEM results, an increase in the bath load resulted in a decrease in the thickness of the Ni–P coating formed on the WC–12Co powders. Moreover, applying the HVOF process led to a lower porosity and roughness and a higher thickness of nickel coating, whereas applying a suitable thickness of this coating can prevent the destructive W2C phase. Finally, a bath load of 16 g L–1 was determined as the optimum value to achieve a proper thickness of the Ni–P, extremely low porosity (0.3%), good surface roughness (5 μm), and high microhardness (1112 Hv) in the produced coating.