WC-Co Coatings Research Articles

Structure and electrochemical behavior of coatings from complex concentrated alloys deposited by Metco Triplex Pro-210 gun

Complex concentrated alloys (CCAs) have gained a significant attention in the engineering and research community due to their unique phase structure and exceptional properties. CCAs are usually comprised of five or more principal alloying elements mixed in near-equimolar or equimolar ratio, which can derive their qualities from multiple principal elements owing to cocktail effect. In this study, atmospheric plasma spraying system equipped with a Metco Triplex Pro-210 gun was used to deposit CCAs designed coating compositions onto SS-316L steel substrate. The microstructure, mechanical and electrochemical behavior of the developed (CoCrFeNiMnx) CCAs were analyzed and compared to commercially used WC-17Co (Diamalloy 2005NS) and NiCr-75Cr2C3 (Metco 81NS) coatings deposited by APS Metco Triplex Pro-210 cascading arc plasma spray gun. The experimental results confirm that using Metco Triplex Pro-210 it is possible to manufacture a CCA coating layers with lower porosity, excellent phase stability in compare to conventional thermal spray processes. Coating characterization also reveals that the CCA coating’ grains experienced a significant amount of grain refinement as compared to those in as-received CCA feedstock powder materials due to the occurrence of shot peening effect and dynamic recrystallization caused by highly deformed splat boundaries during spraying process. The electrochemical results indicates that the CCA coatings have a lower corrosion rate in compare to its plasma sprayed counterparts.

The aqueous corrosion and wear responses of HVOF-deposited TiC-Ni3Al, WC-Co, and WC-CoCr coatings on AISI 4130 steel substrates

In prior studies, TiC-Ni3Al cermets have shown an excellent combination of corrosion and wear resistance in comparison to WC-Co, while exhibiting <50 % of the mass. Consequently, it is attractive to assess these materials in coating form. The aqueous corrosion and wear performance of TiC-Ni3Al cermet coatings, deposited by high-velocity oxy-fuel (HVOF) thermal spray onto AISI 4130 steel substrates, is examined in the present work. Two powder feedstock formats were investigated. The first is a conventional agglomerated and sintered powder, which is then compared to a micro-composite powder feedstock fabricated via a novel gelation technology. The HVOF coatings were subsequently examined in terms of their microstructure, corrosion, and wear behaviours. The potentiodynamic polarisation responses of the cermet coatings were assessed in a simulated sea water environment (deaerated H2O with 3.5 wt% NaCl). The reciprocating sliding wear responses were also examined, against a WC-Co counter-face sphere. The post-corrosion and worn surface morphologies were subsequently investigated with optical microscopy, scanning electron microscopy, and associated energy dispersive X-ray analysis, with focused ion beam milling used to evaluate the wear track cross-sections. The TiC-Ni3Al HVOF sprayed cermet coatings demonstrate a combination of high wear and corrosion resistance in comparison to conventional WC-Co and WC-CoCr cermet coatings that were also HVOF deposited and tested under similar conditions.

Erosion Behavior of Stellite-6 and WC-12Co Coatings on SA213-T22 Boiler Steel

At Mae-Moh power plant, Thailand, superheater tubes, which are exposed to a fly ash environment, often degrade due to solid particle erosion. To extend the service lifetime of the superheater tubes, the high velocity oxy-fuel (HVOF) thermal spray technique is used to deposit a protective coating on the material, SA213-T22 steel. In this work, the solid particle erosion of Stellite-6 and WC-12Co coatings was investigated using erodent particle impingement at angles of 30 and 90°. This was carried out with an average particle size of 60 μm. The erosion behavior of SA213-T22 with and without Stellite-6 and WC-12Co coatings was examined using ductile and brittle erosion modes. The erosion testing resulted in the brittle mode for both Stellite-6 and WC-12Co coatings, while the SA213-T22 without coating indicated the ductile mode. On investigation of the surface morphology, the SA213-T22 steel showed ploughing and microcutting. The Stellite-6 coating showed some evidence of ductile erosion such as lips on the coating surface, different from the WC-12Co coating which showed microcracks and deep cavities. The erosion resistance of the Stellite-6 coating was higher than the WC-12Co coating. This was due to the strength and toughness of the metal matrix composite structure and the low porosity of the coating.

Effect of binder phases on the cavitation erosion behavior of HVOF sprayed WC-based coatings

In order to address the issue of cavitation erosion (CE) damage in marine mechanical components, WC-10Co4Cr (WCC), WC-10Co (WC1) and WC-17Co (WC2) coatings were prepared on the surface of 316L stainless steel using high-velocity oxygen-fuel (HVOF) spraying technique. The study investigated the microstructures, phases, mechanical properties and CE behavior of the coatings with different binder phases. The effects of the type and content of binder phase on the CE resistance and mechanism of the coatings were studied by compared the differences of volume loss rate (VLR) and eroded surface morphologies between the coatings. It was observed that all three coatings were dense and tightly bonded to the substrate. The primary phases identified in the coatings were WC, W2C and Co3W3C. Compared with the WC1 and WC2 coatings, the WCC coating demonstrated superior CE resistance with the lowest volume loss rate (VLR). The VLR of the WC1 and WC2 coatings was approximately four times higher than that of the WCC coating. The binder phase of Co-Cr improved the mechanical properties and the bonding strength of hard and binder phase, which reduces the brittle detachment of WC particles. In addition, the WCC coating had high microhardness and elastic modulus (E), H/E and H3/E2, which hindered the initiation and propagation of fatigue cracks. The initiation of CE damage occurred at the original defects, such as pores, cracks. The primary CE mechanism of the coatings was the interlinking of cavitation craters, lamellar spalling caused by the fatigue cracks propagation along the interlayer. The brittle detachment of WC hard particles also occurred significantly in WC1 and WC2 coatings due to loss of the binder phase. It was concluded that the binder phase markedly influenced the CE resistance and mechanism of the coatings, the addition of Cr showed the most pronounced effect.

Структура и свойства покрытий WC-10Co4Cr, полученных высокоскоростным плазменным напылением

Introduction. Carbon steel is often used for the manufacture of various machine parts, but its operation in aggressive conditions (operation of steel parts under conditions of wear, high temperatures and aggressive corrosive environments) contributes to an extreme decline in properties, up to failure. To solve this problem the modification of the working surfaces of steel parts can be used. It increases its wear resistance, corrosion resistance, and service life. Metal-ceramic coatings based on WC are often used to improve the hardness, wear resistance and corrosion resistance of steel parts. The work purpose is to study the effect of high velocity atmospheric plasma spraying (HV-APS) modes on the structure, phase composition and properties of WC-Co coatings. Materials and methods. 86% WC-10% Co-4% Cr coatings were deposited on a mild steel substrate with help of the HV-APS method. The structure and phase composition of the coatings were analyzed using optical microscopy, scanning electron microscopy, and X-ray phase analysis. In addition, the results of measurements of porosity, microhardness, wear resistance, as well as a qualitative assessment of the adhesion are shown in this paper. Results and discussion. It is shown that all coatings are characterized by high density, absence of cracks and oxide films. Using the SEM and XRD methods, it is found that the coatings contain WC and W2C particles uniformly distributed in the metal matrix. The matrix is an amorphous or nanocrystalline supersaturated Co(W,C) solid solution. The maximum amount of carbides (49%) is observed in coatings obtained by deposition from a distance of 170 mm, arc current — 140 A; the minimum (25%) is observed in coatings obtained by deposition from a distance of 250 mm, arc current — 200 A. The coatings with the maximum amount of carbides have the maximum values of microhardness (1,284 HV0.1) and wear resistance. It is established that all coatings are characterized by high adhesion.

HVOF Spray Performance Optimization Analysis and Experimental Research of WC–12Co Coating on Ti Alloy

HVOF Spray Performance Optimization Analysis and Experimental Research of WC–12Co Coating on Ti Alloy

Study of the flexural behaviour and bonding strength of WC-Co metal matrix composite coatings produced by Laser Directed Energy Deposition

Surface coatings enable more durable and sustainable solutions to face the degradation of the functional surfaces of high-added-value components. Particularly, metal matrix composites (MMC) are known to mitigate friction efficiently. However, the bonding strength of MMCs severely limits their durability. Hence, it is not sufficient to focus on wear performance. In this work, the flexural strength and interfacial bonding of Stellite 6/WC MMCs produced by Laser Directed Energy Deposition were investigated. The manufactured coatings exhibited a strong bond to the substrate regardless of the WC content, as no delamination was observed. Additionally, all MMC coatings produced under different processing conditions and with the same composition showed similar elastoplastic behaviour, while specimens containing a higher WC% failed prematurely. This was ascribed to the local embrittlement of the reaction layer surrounding the WC particles, which were found to be crack initiation sites.

The Effect of High-Velocity Air-Fuel WC-12Co Coatings on the Wear and Corrosion Resistance of TC18 Titanium Alloy

TC18 titanium alloy is an essential material for aircraft landing gear. To reveal the wear and corrosion mechanisms of landing gear in service, a WC-12Co coating on a TC18 substrate was prepared by High-Velocity Air-Fuel (HVAF) spraying based on optimized process parameters, and an analysis of the microscopic characterization results for the materials involved was performed. Based on the computational fluid dynamics (CFD) method, the combustion reaction and discrete phase models of HVAF spraying were established. The flame characteristics under compressible turbulence and the flight temperature and velocity of particles were calculated. The effect of the spraying parameters on the flight temperature and velocity of particles was evaluated based on the response surface method (RSM) through multiple groups of orthogonal experiments, and the optimized process parameters were determined. The mass flow rate of reactants was 0.051 kg/s, the oxygen/fuel ratio was 2.83, the mass flow rate of the nitrogen was 0.000325 kg/s, the pressure of oxygen and fuel inlet was 1 MPa, the pressure at the particles inlet was 0.6 MPa and the maximum temperature and velocity of spraying particles were 1572 K and 417 m/s, respectively. The coatings prepared with the optimized process were subjected to the Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), wear, hardness, artificial seawater soaking and neutral salt spray experiments. The results showed that the mean hardness of the TC18 substrate was 401.2 HV0.3, the mean hardness of the WC-12Co coating was 1121 HV0.3, the friction coefficient between the TC18 substrate and the Si3N4 ceramic ball was 0.55 and the friction coefficient between the WC-12Co coating and the Si3N4 ceramic ball was 0.4. Compared to the TC18 substrate, the hardness of the WC-12Co coating was increased by 720 HV0.3, the friction coefficient with the Si3N4 ceramic ball decreased by 0.11, the corrosion resistance significantly improved and the maximum depth of the corrosion pits was 5 μm. The properties of the TC18 titanium alloy were effectively improved by the WC-12Co coating. The results of this study provide guidance for surface protection technologies of aircraft landing gear.

Tribocorrosion Performance of WC-12Co HVOF-Sprayed Coatings Reinforced with Carbon Nanotubes

WC-12Co HVOF-sprayed coatings (~400 µm in thickness) reinforced with multiwalled carbon nanotubes (MWCNTs), were deposited on a steel substrate. The aim of this work is to provide and analyze data from HVOF WC-12Co sprayed coatings, concerning the influence of the addition of MWCNTs on their tribocorrosion performance, in a 3.5% NaCl electrolyte. Electrochemical data (current density and corrosion potential from potentiodynamic polarization curves) and wear data (coefficients of friction, coating volume losses and wear constants) are reported for the coatings, with and without the addition of MWCNTs (labeled WCCNT and WCAS-RECEIVED, respectively), considering the synergistic effects of wear and corrosion coupling. Scanning electron microscopy (SEM) and profilometry are used to explain both the wear and corrosion mechanisms that account for each coating’s performance in this environment. During the tribocorrosion tests, similar wear constants, of the order of approximately 10−12 m3/Nm, were found for all samples, with an increase of ~20% due to the MWCNTs presence. However, for the coatings reinforced with MWCNTs, a remarkable increase in icorr, representing almost 3 times the icorr of the WCAS-RECEIVED coating, was determined. The above results illustrate the complex mechanisms that occur when these coatings are tested under tribocorrosion conditions, which give rise to concurrent interacting phenomena, involving both electrochemical and mechanical responses.

Wear and corrosion behaviour of the cryogenically treated tungsten carbide coatings

ABSTRACT The WC–12Co coatings were deposited on SS 410 substrates using a high-velocity oxygen fuel (HVOF) process and the coatings were heat-treated at 750°C for 1 h in argon environment. Further, the coatings were subjected to cryogenic treatment for 1, 2, 8 and 24 h, and its influence on the reciprocating sliding wear and corrosion characteristics was studied. The structural changes in the coatings after post-treatment were assessed by X-ray diffraction analysis and Raman spectroscopy. Microhardness was improved for cryogenically treated coatings due to the α-Co transformation into ϵ-Co. Cryogenic treatment duration was not having a significant effect on the microhardness values. However, the specific wear rate was influenced by the cryogenic treatment duration. Also, corrosion resistance was increased with the increased cryogenic treatment duration. The protective layers consisting of WO3 and Co3O4 phases formed during the cryogenic treatment are attributed to the improved corrosion resistance of the coatings.

Properties of WC-Co coatings with Al2O3 addition

Abstract Properties of WC-Co coatings with Al2O3 addition on the C45 mild steel surface in acidic chloride solution were examined. The WC-Co-Al2O3 coatings on steel surfaces were deposited by an electro-spark (ESD) technique. The anti-corrosion properties of the coatings were mainly investigated by electrochemical methods. Moreover, the scanning electron microscope (SEM) was employed for the observation of the surface of materials. The structure of coatings depended on the composition of electrospark electrodes. In the WC80-Co5-Al2O315 coating, the largest corrosion resistance was shown. The corrosion rate of the specimen was approximately eight times smaller than the coating without of Al2O3 addition. The aim of the research was to obtain, by adding alumina, an improvement in the functional properties of WC-Co coatings produced by the ESD method. Due to the original features of ESD coatings, they can be used in sliding friction pairs and as anti-wear coatings on cutting tools.

Experimental investigation of WC-12Co cold sprayed: Substrate hardness, bonding mechanism, powder type

Effects of substrate hardness and particle type on a single WC-12Co (Tungsten carbide cobalt) particle's deposition behavior during the cold spray process was investigated in this study. SEM was used to analyze the surface and cross-sections of the deposited particles to determine their morphology. It was discovered that the deposition behavior of WC-12Co particles changed with increasing substrate hardness, going from fully embedding into soft substrate to partially flattening and even rebounding from the hard substrate. Spherical microstructured WC-12Co particles sustained more severe deformation than other types of powder because of the smaller WC size. The porosity value of WC-12Co coatings is lower, at 1.18 %. WC-12Co particles bulk properties remained unchanged since there were no microstructural changes, decarburization, or the formation of fragile phases.

Tribological Characteristics of WC-12Co Coatings Sliding Against SiC and Si3N4 Counter Balls

Tribological Characteristics of WC-12Co Coatings Sliding Against SiC and Si3N4 Counter Balls

Effect of inert environment on the sliding wear behaviour of the HVOF sprayed WC-12Co coating

The reciprocating sliding wear behaviour of high velocity oxy-fuel sprayed WC-12Co coatings in the inert environment at room temperature, and 300 °C temperature with varying load conditions was investigated. The worn-out coatings and the debris were analyzed by scanning electron microscopy and Raman spectroscopy. From the wear test data, the coefficient of friction was measured as lower in the air environment at both room temperature and 300 °C, compared with the argon environment due to the development of self-lubricating tribo-oxide layers. The development of CoWO4 phases at the surface decreases friction and wear and allows the coating to uphold the tribological properties at higher temperatures. Higher loads mechanically damage the coatings and quickly remove the protective oxide layer compared with the lower loads. In the protective environment, abrasive wear and adhesive wear mechanisms were observed to be played predominant role, whereas, in the air environment, the oxidative wear mechanism was found to be significant.

SURFACE EROSION PERFORMANCE OF YTTRIUM OXIDE BLENDED WC-12CO THERMALLY SPRAYED COATING FOR MILD STEEL

This study is conducted to examine the tribological performance of WC-12Co coating and WC-12Co mixed with yttrium oxide coating applied on mild steel. Mild steel machinery is usually used for hydropower generation but the sediments present along with the river water cause wear on the machinery surface. DUCOM slurry pot tester setup was used for the experiments. This study was based on the coatings of WC-12Co as well as the mixing of yttrium oxide with WC-12Co powder in various proportions ranging from 1–3% by weight on mild steel. The high-velocity oxygen fuel thermal spray coating process was used to deposit a microlayer coating on the mild steel. It is observed that the microhardness of the coatings increases with the addition of yttrium oxide. The experiments were carried out varying the concentration, rotational speed, and test duration in the range of 10–40% by weight, 750–1500[Formula: see text]rev/min, and 30–120[Formula: see text]min duration, respectively. It is observed that the WC-12Co+2%Y2O3 coating has a higher erosion resistance.

Promising WC-30WB-10Co Cemented Carbide Coating with Improved Density and Hardness Deposited by High Velocity Oxy-Fuel Spraying: Microstructure and Mechanical Properties

WC-Co coatings sprayed by HVOF attracted much attentions, benefiting from the satisfactory wear resistance and high bonding strength to the steel substrates. Nevertheless, high density of conventional coatings required excessive Co binder, which decreased the hardness and operation life. Based on this, a strengthened WC-30WB-10Co coating was developed with both high density and improved hardness, using high-qualified thermal sprayed composite powders. Comparison between the phase composition, microstructure, interfacial bonding strength and properties of the newly developed coatings and WC-12Co conventional coatings was clarified in detail. Compared to WC-12Co powders, spherical WC-30WB-10Co powders showed higher apparent density and flowability, due to the in situ formed CoWB and CoW2B2 phases during the accelerated metallurgy reaction. Oxidation and decarburization were confirmed during HVOF spraying with the formation of W2C, Co3W3C and Co6W6C phases in both coatings. Attracting WC-30WB-10Co coating with microhardness of 1639HV0.3 and relative density of 99.44% was achieved, higher than those of 1222 HV0.3 and 99.27% of WC-12Co. This was attributed to the formation of the ternary compounds and the consumption of the ductile Co binder in the WC-30WB-10Co coatings. The hard alloy coatings are expected to be well applied in aggressive wear and corrosion environments due to the high hardness and low metal phase content.

Effects of 3D Roughness Parameters of Sandblasted Surface on Bond Strength of HVOF Sprayed WC-12Co Coatings

This work aims to reveal the effects of 3D roughness parameters of sandblasted surfaces on bond strength between thermal spray coatings and substrates. The investigation was carried out on the surface of AISI 4140, which were pretreated with automatic-sandblasting system. 3D topography and roughness parameters were analyzed by a 3D optical profiler. The bond strength of WC-12Co coatings was measured using a pull-off test method. Scanning electron microscope revealed that the morphology of the surface after sandblasting was rough. Furthermore, the surface topography was characterized by several irregular peaks and pits with different directions and no fixed orientation randomly distributed on sandblasted surface. The average values for surface roughness Sa = 4.84 ± 0.34 μm and bond strength = 32.8 ± 2.8 MPa were obtained. In terms of 3D roughness parameters, Sa, Sdr, Sdq and Sq were found to have more significant impact on affecting the bond strength, showing a nonlinear regression relationship. Furthermore, bond strength was positively correlated with Sa, Sdr and Sdq, while inversely proportional to Sq. This confirmed that a greater surface roughness of a sandblasted surface was not more conducive to the improvement of bond strength. The influence mechanism of each parameter was discussed, which was consistent with the regression mathematical model.

Investigations of cavitation erosion and wear resistance of cermet coatings manufactured by HVOF spraying

This work studies the effect of mechanical properties and microstructure on sliding wear and cavitation erosion behaviors of cermet coatings deposited via high velocity oxy-fuel (HVOF) spraying on AZ31 magnesium substrate. Cavitation tests indicated that WC-Co-Cr cermet had superior resistance to cavitation erosion than WC-Cr3C2-Ni, WC-Co coatings, and far better resistance than the AZ31 expressed by the volume material loss 3.74 mm3, 6.99 mm3, 10.30 mm3, and 108.82 mm3, respectively. WC-Co-Cr coating’s erosion mechanism exhibited uniform material removal, which slows the erosion rate. The CoCr binder prevented severe surface pitting and the detachment of the WC-Co-Cr cermet material in massive chunks which was observed for WC-Co and WC-Cr3C2-Ni coatings. Cermet coatings microstructure discontinuities such as pores and ceramic-metallic phase interfaces are the centers of material erosion. No clear correlation between the erosion behavior and mechanical properties of coatings was revealed. Contrary to that, sliding wear results were strongly related to the mechanical properties. The WC-Co-Cr and WC-Co samples exhibited higher hardness and higher values of Young’s modulus than the WC-Cr3C2-Ni one. The generated stresses with lower values of hardness and Young’s modulus for the WC-Cr3C2-Ni sample resulted in a higher wear factor, approx. 1·10−7 mm3·N−1·m−1. For the harder samples, which exhibited higher stiffness (WC-Co-Cr and WC-Co), this type of wear resulted in lower values of the wear factor: 6·10−8 mm3·N−1·m−1 and 9·10−8 mm3·N−1·m−1, respectively. Deposition of the cermet coatings effectively protected the magnesium substrate, which shows low resistance to cavitation erosion and sliding wear when uncoated.

High-Pressure Cold Spray Coatings for Aircraft Brakes Application

This paper addresses the potential use of high-pressure cold spray (HP-CS) technology to produce a film of friction material onto a low-carbon steel substrate to allow its use as potential composite material for the stators and rotors of aircraft brake units. Namely, WC-Cr3C2-Ni, WC-Ni, WC-Co-Cr, Cr3C2-NiCr and WC-Co coatings were deposited by using HP-CS, for the purpose of creating high friction and wear resistance composite coatings onto a low-carbon steel substrate. Tribological (friction coefficient and wear rate) and thermal properties as well as coating hardness and adhesion to the low-carbon steel substrate were evaluated to assess the potential use of the coatings as brake surface materials. The tribological and adhesion properties were evaluated by using a pin-on-disk high-temperature tribometer at 450 °C and a scratch test, respectively, whereas coatings hardness was evaluated with a Rockwell C hardness tester. Results obtained show that all coatings exhibit high friction coefficients and low wear rates compared to the low-carbon steel substrate, good adhesion, and elevated microhardness. Furthermore, the WC-Co coating shows better microhardness and thermal properties, while the WC-Co-Cr coating exhibited a better friction coefficient. Unfortunately, it was not possible to quantify the wear resistance due to the elevated roughness of the coatings, but from the analysis carried out on the alumina counterpart of the tribometer, it can be concluded that all the coatings exhibited a very low wear rate. In fact, after the tribological tests, it emerged that the alumina counterpart was more abraded than the investigated coatings.

Reciprocating sliding wear behavior of the heat-treated WC-12Co coatings

WC-Co coatings were produced on SS 410 plates and subjected to heat treatment at different temperatures (from 300 to 900 °C). The microstructural studies and structural analysis of the coatings before and after heat treatment were carried out by electron microscopy and X-ray diffraction analysis. From the Vickers indentation method, hardness values were measured, and higher microhardness was observed for the coatings after heat treatment. The sample that was heat-treated at 750 °C exhibited the highest hardness. From the sliding wear test results, the wear resistance of the coatings was observed as increased after the heat treatment. However, it was found that the heat-treated coatings at 600 °C exhibited higher wear resistance. Cracking and fracture were the dominant wear mechanisms observed for the heat-treated coatings, along with coating delamination and oxidation.