High Velocity Oxy-fuel Thermal Spraying Research Articles

Resistance to slurry erosion by WC-10Co-4Cr and Cr3C2 − 25(Ni20Cr) coatings deposited by HVOF stainless steel F6NM

Hydroelectric turbine machinery experience extreme wear and tear due to slurry erosion and is one of the leading causes for the unplanned shutdown of hydro power plants. The coatings produced by High-velocity oxy-fuel (HVOF) thermal spray process on different hydro-turbine parts is known for improving wear resistance. In the present study, WC-10Co-4Cr and Cr3C2 − 25(Ni20Cr) coatings were sprayed by HVOF process on F6NM stainless steel of Dul-Hasti hydro-power plant turbine material. The slurry erosive wear studies of developed coatings was performed using high speed slurry erosive wear tester. Sediments collected from Dul-Hasti power plant dam site was taken as erodent material. The effect of four parameters specifically rotational speed (500–1250 rpm), slurry concentration (25–40 wt%), sand particle size (125–425 μm), and test duration (450–900 min) on slurry erosion of coated materials was studied. It was observed that among all the developed three coatings, the WC-10Co-4Cr coated samples has shown superior erosion resistance compared to Cr3C2 − 25(Ni20Cr) coated samples due to its improved micro-hardness. Both the developed coatings were observed to be useful in enhancing the erosion resistance of F6NM steel significantly. Erosion mechanism were studied in detail using SEM. The properties such as hardness and porosity were also examined.

Mechanical and microMechanical and microstructural characterization of yttria-stabilized zirconia (Y2O3/ZrO2; YSZ) nanopartstructural characterization of yttria stabilized zirconia (Y2O3/ZrO2; YSZ) nanoparticles reinforced WC-10Co-4Cr coated turbine steel

The aim of this paper is to investigate the WC-10Co-4Cr coatings reinforced with 5 % and 10 % of yttria-stabilized zirconia (Y2O3/ZrO2; YSZ) nanoparticles deposited on the CA6NM turbine steel by using the high-velocity oxy-fuel (HVOF) thermal spraying technique. In the HVOF technique, the hot jet of the semi-solid particles strikes against the workpiece and creates a layer of coating of varying thickness on the substrate material. The coatings fabricated with HVOF were analyzed by scanning electron microscope (SEM) / energy-dispersive x-ray spectroscopy (EDS). The phase identification of a crystalline material was made with the x-ray diffraction (XRD) technique. The mecha­nical properties in terms of porosity, surface roughness and microhardness of the nanocomposite coatings were also evaluated. The SEM/EDS analysis showed that dense and homogeneous coatings were developed by the reinforcement of YSZ nanoparticles. The peaks of XRD graphs of WC-10Co-4Cr coating reinforced with 5 and 10 % of YSZ nanoparticles revealed that the WC was present as a major phase and W2C, Co3W3C, Co, Co6W6C, Co6W and Y2O3/ZrO2 nanoparticles were observed as a minor phase. The porosity level decreased up to 42 and 56 % by the addition 5 and 10 % of YSZ nanoparticles as compared with conventional WC-10Co-4Cr coating. The surface roughness values for WC-10Co-4Cr conventional coating, 95 % (WC-10Co-4Cr) + 5 % YSZ and 90 % (WC-10Co-4Cr) + 10 % YSZ nanocomposite coated samples were found to be 5.03, 4.89 and 4.28 respectively. The nanocomposite coatings reinforced with 10 % YSZ nanoparticles exhibited the highest microhardness value (1278 HV). The WC-10Co-4Cr coatings reinforced with 10 % of YSZ nanoparticles resulted in low porosity, low surface roughness and high microhardness. During the coating process, the nanoparticles of YSZ flow into the pores and are dispersed in the gaps between the micrometric WC particles and provide a better shield to the substrate material. The WC-10Co-4Cr with 10 % of YSZ nanoparticles showed better results in terms of mecha­nical and microstructural properties during the investigation.

High temperature (900 °C) sliding wear of CrNiAlCY coatings deposited by high velocity oxy fuel thermal spray

Nickel based superalloy are in demand for high temperature applications and their corrosion, erosion and wear resistance have been investigated for a long time. Nickel chromium (NiCr) alloys are widely used for corrosion resistant coatings, while chromium carbide nickel chromium (CrC-NiCr) alloys are preferred for wear resistant coatings at high temperature. In this study CrNiAlCY coatings were deposited via a liquid fuelled high velocity oxy fuel (HVOF) thermal spray using two spray parameters and tested as wear resistant coatings. Effects of processing parameters on microstructure and mechanical properties of the coatings were investigated. Results showed that higher oxygen flow rates are critical for obtaining coatings with lower porosity and higher microhardness. Coating with lower porosity and higher hardness was chosen for both room temperature (~24 °C) and high temperature (900 °C) unlubricated sliding wear tests in a ball on disc setup. The coating was tested against alumina counterbody under 3 different loading conditions (10, 30 and 60 N). The wear rate of the coating was directly proportional to the applied load at room temperature. In the room temperature tests, wear debris was produced, which then oxidised and pushed away to the edges of the wear track. On the other hand, wear debris was smeared on the wear surface at high temperature tests. The surface was oxidised into Cr 2 O 3 at high temperatures, which acted as a protective layer. Although thermal softening took place at higher temperatures, wear rates under 10 and 30 N were similar to room temperature values due to the protective oxide layer formed on the top surface; however, the oxide layer under 60 N could not withstand the load, started to crack and lost its protective ability. • CrNiAlCY coatings have been produced using a liquid-fuelled HVOF thermal spray. • Effects of spray parameters on the microstructure and hardness studied. • Wear performance was investigated against the alumina counter body. • 2 Different temperature settings were used during the wear tests.

Development of FeV-WC Ni Cr B Si coating on Stainless steel using HVOF process

In the present investigations, 50% Fe V + 50% (WC Ni Cr B Si) Coating is developed on SS304 Substrate with High-Velocity Oxy-Fuel (HVOF) thermal spray process. SS304 substrate is commonly used for the plant machinery process vessels which are affected by moderate corrosion and wear applications. This investigation aims to study the performance of the developed coating. The Feedstock powders are characterized by various characterization methods such as SEM, EDS, and XRD, while the as-sprayed coating is characterized by SEM and XRD. The vicker hardness testing technique is used to identify the hardness of the coating. Present research work represents that developed coating improvises average microhardness of substrate from 185 to 205 HV0.1 to 340–680 HV0.1 and thus improves the wear resistance.

Solution precursor thermal spraying of gadolinium zirconate for thermal barrier coating

Gadolinium zirconate (GZ) is an attractive material for thermal barrier coatings (TBCs). However, a single layer GZ coating has poor thermal cycling life compared to Yttria Stabilized Zirconia (YSZ). In this study, Solution Precursor High Velocity Oxy-Fuel (SP-HVOF) thermal spray was used to produce a double layer GZ/YSZ TBC and compared the thermal cycling performance with the single layer YSZ TBC. The temperature behaviour of the solution precursor GZ was studied, and single splat tests were carried out to obtain an optimised spray parameter. In thermal cycling tests, the single-layer YSZ reached 20 % failure at 85 ± 5 cycles, whereas the double-layer GZ/YSZ was at 70 ± 15 cycles. The single-layer failed at the topcoat/TGO interface, whereas the double-layer failed at GZ/YSZ interface and topcoat/TGO interface. Moreover, Gd diffusion occurred near the GZ/YSZ interface, resulting in porosities in the GZ layer.

Mechanical properties and tribological performance of A356/Cr3C2-NiCr surface composite developed by high-velocity oxy-fuel and post friction stir processing treatment

High-velocity oxy-fuel thermal spraying and post friction stir processing (FSP) techniques were utilized to fabricate a new lightweight metal matrix composite for industrial application in which A356 aluminum (Al) cast alloy and Cr3C2-NiCr were the matrix and reinforcements, respectively. The microstructure of the BM, friction stir processed samples, and composites were evaluated using optical microscopy and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy. The investigations demonstrated that the coarse eutectic silicon blades were crushed to fine particles after FSP and the Cr3C2-NiCr coating were uniformly dispersed into the base metal (BM). The hardness of the samples was measured via microhardness and nanoindentation tests, which indicated a significant improvement (about twice the BM) in the hardness of the 4-pass friction stir processed composite. Considering the results of the uniaxial tensile test, the FSP enhanced the yield strength (YS) and ultimate tensile strength (UTS) of the samples. The YS and UTS of the 4-pass friction stir processed composite were nearly 53 and 22% higher than those of the BM, respectively. To study the tribological performance of the samples, the dry sliding wear test was conducted on the samples using a reciprocal wear machine. The results showed that the wear and friction performances of the composites improved dramatically (∼98% and 61% decrease in the wear rate and friction coefficient, respectively). Finally, the SEM investigations from the fracture surfaces, worn surfaces, and debris resulting from the wear tests were conducted on the samples to understand the fracture and wear mechanisms.

Evaluation of the residual stress of HVOF sprayed carbon coating after wear testing conditions using ANN coupled Taguchi approach

The as deposited carbon coating was successfully synthesized from agricultural waste using High Velocity Oxy-fuel (HVOF) thermal spray deposition technique. The surface topography of as deposited carbon coating, confirms the presence of molten, semi-molten, and un-melted grains along with the formation of lamellae. Taguchi L9 orthogonal Array (OA) and Artificial Neural network (ANN) models were used to predict and optimize the process parameters for residual stress after wear testing conditions. The estimated mean (μ) obtained from optimal responses is 11 MPa. Three confirmation tests of as-deposited carbon coating for residual stress after wear testing conditions were conducted for optimal level of parameters at level 3 of Temperature (250 °C), level 3 of sliding velocity (0.3 m s−1), and level 3 of load (80 N). The percentage (%age) contribution of as-deposited carbon coating for residual stress after wear testing conditions from Analysis of Variance (ANOVA) prediction was highest for temperature (51.23%), followed by 32.8% of sliding velocity, and 12.5% for a load.

Quasicrystalline Coatings Exhibit Durable Low Interfacial Toughness with Ice.

Ice accretion can adversely impact many engineering structures in commercial and residential sectors. Although there are many reports of low-ice-adhesion-strength materials, a scalable and durable deicing solution remains elusive, as ice detachment is dominated by interfacial toughness for large interfaces. In this work, durable metallic coatings based on Al-rich quasicrystalline alloys were prepared and applied on aluminum substrates using high-velocity oxyfuel thermal spray. X-ray diffraction patterns confirmed the quasicrystalline phases of the coating, and its large-scale deicing capability was studied by evaluating the coating's ice detachment mechanics using long lengths of ice. A toughness-controlled regime of interfacial fracture was observed for ice lengths longer than ∼2 cm, and a low shear strength of ∼30 kPa was achieved for a 20 cm ice length. The metallic coatings exhibited excellent ice repellency even after being abraded, scratched, heated, UV-irradiated, and exposed to chemical contaminations, demonstrating promising durability for real-world, large-scale ice removal.

Large-scale manufacturing route to metamaterial coatings using thermal spray techniques and their response to solar radiation

Metamaterials, an artificial periodic two- or three-dimensional configuration, can change propagation characteristics of electromagnetic waves (i.e., reflection, transmission, absorption). The current challenges in the field of metamaterial coatings are their manufacturing in a large-scale and large-length scale. There is a clear need to enhance process technologies and scalability of these. Thermal spraying is a method used to deposit small- to large-scale coatings where the sprayed layer is typically formed by the successive impact of fully or partially molten particles of a material exposed to various process conditions. This work aims to investigate the feasibility to manufacture large scale metamaterial coatings using the thermal spray technique and examine their response to solar radiation. Two types of coatings namely, Cr2O3 and TiO2, were deposited onto various substrates (e.g., steel, aluminium, glass, indium tin oxide (ITO)–coated glass) with a fine wire mesh (143 µm and 1 mm aperture sizes) as the masking sheet to manipulate the surface pattern using suspension high-velocity oxy-fuel thermal spraying (S-HVOF) and atmospheric plasma-sprayed (APS) methods, respectively. Post deposition, their responses subjected to electromagnetic wave (between 250 and 2500 nm or ultraviolet (UV)-visible (Vis)-infrared (IR) region) were characterised. The additional microstructural characterisation was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), three-dimensional profilometry, and optical spectroscopy. It is demonstrated that through novel application of thermal spray techniques, large-scale manufacturing of metamaterial coating is possible, and such material can affect electromagnetic wave propagation. Comparison between Cr2O3 and TiO2 coatings on aluminium substrates showed reduced three orders of reduced reflectance for Cr2O3 coatings (for 1-mm aperture size) throughout the spectrum. It was concluded that for a similar bandgap, Cr2O3 coatings on aluminium substrate will yield improved optical performance than TiO2 coating, and hence more useful to fabricate opto-electronic devices.Graphical abstract

Investigation on Microstructure, Mechanical and Wear Properties of HVOF Sprayed Composite Coatings (WC-Co + CR) On Ductile Cast Iron.

Recent work indicates that the high-velocity oxy-fuel (HVOF) thermal spraying WC–Co coatings have been used to enhance the wear resistance of various engineering components in a variety of industrial environments. In the present work, WC–Co powder, containing Cr particles in an amount of 10%, was deposited on ductile cast iron with the HVOF thermal spray coating technique. An investigation was conducted to determine the role of Cr particles in the WC–Co coating produced with the HVOF technique on microstructure, mechanical, and wear properties in a system of type: WC-Co coating/ductile cast iron. The microstructure of the HVOF-sprayed WC–Co + Cr coating was characterised by light microscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy-dispersive X-ray spectroscopy (EDS). The analysis of the microstructure showed the formation of a coating with low porosity, compact structure, and good adhesion to the substrate with a typical lamellar structure composed of fine molten Cr particles and finely fragmented WC grains embedded in a Co matrix, reaching the size of nanocrystalline. The scratch test was applied for the analysis of the adhesion of coatings to the substrate. The erosion behaviour and mechanism of material removal was studied and discussed based on microstructural examinations. Moreover, the results were discussed in relation to the bending strength test, including cracks and delamination in the system of the WC–Co + Cr/ductile cast iron, as microhardness and erosion resistance of the coating. It was found that the addition of Cr particles to the WC–Co powder, which causes hardening of the binder phase is a key influence on increased mechanical and wear properties in the studied system. Additionally, due to the construction of nanostructured coatings, suitable proportion of hard and soft phases, the technique sprayed HVOF coatings have advantageous properties such as high density and good slurry erosion resistance.

YAG thermal barrier coatings deposited by suspension and solution precursor thermal spray

Yttrium aluminium garnet (YAG) is a promising topcoat material for thermal barrier coatings due to its high temperature stability and better CMAS (calcium-magnesium-alumino-silicate) resistance. YAG topcoats were deposited by suspension and solution precursor high-velocity oxy-fuel (HVOF) thermal spray. The relationships between processing, microstructure and final properties were studied through a range of characterization techniques and thermal cycling tests. The microstructure of the as-sprayed YAG topcoat from stoichiometric solution precursor (SP-YAG) had distributed pores and inter-splat boundaries, while the as-sprayed topcoat produced from suspension (S-YAG) had vertical and branched micro cracks, pores, and inter-splat boundaries. Both as-sprayed coatings were composed of amorphous phase, hexagonal yttrium aluminium perovskite (YAP) and cubic YAG. In thermal cycling tests, 20% of SP-YAG failure was reached after the 10th cycle; whereas, S-YAG reached the failure criteria between the 60th and 70th cycle. The failure of both the SP-YAG and the S-YAG topcoats occurred due to thermal stresses during the thermal cycling.

Evolution of porosity in suspension thermal sprayed YSZ thermal barrier coatings through neutron scattering and image analysis techniques

Porosity is a key parameter on thermal barrier coatings, directly influencing thermal conductivity and strain tolerance. Suspension high velocity oxy-fuel (SHVOF) thermal spraying enables the use of sub-micron particles, increasing control over porosity and introducing nano-sized pores. Neutron scattering is capable of studying porosity with radii between 1 nm and 10 μm, thanks to the combination of small-angle and ultra-small-angle neutron scattering. Image analysis allows for the study of porosity with radii above ∼100 nm. For the first time in SHVOF 8YSZ, pore size distribution, total porosity and pore morphology were studied to determine the effects of heat treatment. X-ray diffraction and micro-hardness measurements were performed to study the phase transformation, and its effects on the mechanical properties. The results show an abundant presence of nano-pores in the as-sprayed coatings, which are eliminated after heat treatment at 1100 °C; a transition from inter-splat lamellar to globular pores and the appearance of micro-cracks along with the accumulation of micro-strains associated with the phase transformation at 1200 °C.

Influence of carbon nano tube additions on coating characteristics of WC-Co/Cr3C2-NiCr on T12 substrate

The outstanding properties such as good mechanical, thermal and electrical properties exhibited by CNT’s have influenced it to be one of the contender reinforcements for the composite material. The present work aims to characterize ASTM-SA213-T12 thermal power plant boiler tube steel substrate coated using High Velocity Oxy-fuel (HVOF) thermal spray process with mixture of WC-Co/Cr3C2-NiCr alloy along with different variations of Carbon Nanotubes (CNT). The CNT content is varied by 3, 5 and 7 wt%. The coating deposits are then characterized. Uniform dispersion of CNT and denser structure due to the filling of voids, resulted in the increase of hardness and decrease in the amount of porosity. The corrosion rate was found to be decreased with increased addition of CNT content in CNT-WC-Co/Cr3C2-NiCr powder combination mainly due to the interlocking of particles inhibiting the penetration of corrosion species.

In-vitro cell interaction and apatite forming ability in simulated body fluid of ICIE16 and 13-93 bioactive glass coatings deposited by an emerging suspension high velocity oxy fuel (SHVOF) thermal spray

ICIE16 and 13-93 bioactive glasses have been proposed as alternative chemically stable compositions in physiological fluid keeping bioactivity comparable to Bioglass®. ICIE16 and 13-93 bioactive glasses coatings were produced via an emerging suspension high-velocity oxy-fuel (SHVOF) thermal spraying technique. Suspensions of ICIE16 and 13-93 with 10 wt% solid loading in isopropanol (IPA) and water were used to produce coatings on AISI304 stainless steel using a flame power of 50 kW and 75 kW. For both glass formulations, the coatings deposited at a lower flame power were more porous, less hard, and less rough (~6% porous and 242 HV) than the coatings obtained at a higher flame power (~4% porosity and 300 HV). ICIE16 coatings showed more dissolution in SBF (simulated body fluid) than the 13-93 coatings. Moreover, the 13-93 glass coating sprayed at 75 kW showed the highest stability in SBF since only 2% of the coating was resorbed in SBF after 7 days of immersion and revealed apatite precipitation after 7 days. In-vitro cell tests, using MG63 cells, showed good cell attachment and proliferation on the surfaces of the coatings, revealing good cytocompatibility. The 13-93 coating sprayed at 75 kW revealed the highest cell proliferation after 7 days of incubation. This can be attributed to the higher surface roughness of the coating (Ra = 6.5 ± 0.6 μm).

Mechanical and wetting properties of 25%NiCr-75%Cr2C3 cermet coated on low carbon steel using HVOF thermal spray technique

The hydrophobic ceramic–metal composites with enhanced mechanical properties will have longer durability because of the embedded liquid-repellent properties, with low water and salt absorption. In this work, the 25%NiCr-75%Cr2C3 cermet powder has been coated on low carbon steel substrate, using High Velocity Oxy-fuel thermal spray technique. The SEM is employed to analyse the morphological characterization of the coating. The mechanical properties of the 25%NiCr-75%Cr2C3 coating is evaluated using the Vickers micro-indentation technique. The micro-hardness, fracture toughness and brittleness index of the coatings are obtained. Also, the wetting property of the coating in 3.5% NaCl salt solution is investigated using the contact angle measured by sessile drop method. The contact angle of the coating is observed to be hydrophobic in nature with a contact angle of 98.14⁰. Thus, 25%NiCr-75%Cr2C3 hydrophobic coatings helps in the improvement of brittleness, fracture toughness, and the microhardness.

Isothermal and Cyclic Oxidation Behavior of HVOF-Sprayed NiCoCrAlY Coatings: Comparative Investigations on the Conventional and Nanostructured Coatings

Conventional and nanostructured NiCoCrAlY coatings were deposited using the high-velocity oxy-fuel thermal spraying technique. The nanostructured NiCoCrAlY powder feedstock for the coatings was produced by the ball-milling method. The microstructures of the as-received and nanostructured powders as well as their developed coatings were investigated by x-ray diffraction, a field-emission scanning electron microscope equipped with energy-dispersive x-ray spectroscopy, and a transmission electron microscope. Williamson–Hall measurements were also carried out to estimate the crystalline size of the powders and coatings. For the evaluation of the oxidation kinetics, the free-standing coating specimens were subjected to short- and long-term isothermal and cyclic oxidation at 1000 and 1100 °C, respectively, under a laboratory air atmosphere. The results indicated that the as-received NiCoCrAlY coating had parabolic oxidation behavior in short- and long-term exposure tests. For the nanostructured NiCoCrAlY coating, in contrast, the long-term oxidation kinetics deviated from parabolic behavior and showed instead sub-parabolic rate behavior. The obtained results also revealed that the nanostructured NiCoCrAlY coating had greater oxidation resistance to both isothermal and cyclic conditions on account of the formation of a dense and slow-growing Al2O3 layer on the coating surface.

Microstructure and wear performance of alumina/graphene coating on textured Al2O3/TiC substrate composites

The incorporation of graphene-based nanodispersoids in ceramic coatings is known to enhance the wear behavior of these materials. In this study, for the first time, alumina/graphene nanoplatelets (GNPs) coatings were deposited through Suspension High Velocity Oxy-Fuel (SHVOF) thermal spray on Al2O3/TiC substrate composites, which were laser microtextured with grid and line surface patterns. Dense coatings with around 8−10 μm thickness were obtained by spraying alumina suspension containing 1 wt. % GNPs. The tribological performance of the alumina/GNPs coatings on the Al2O3/TiC substrate composites was evaluated using ball-on-disc sliding wear tests. The alumina/GNPs coated Al2O3/TiC substrate composites textured with grid pattern showed the best tribological performance reaching a steady coefficient of friction (CoF) at lower sliding distances and presenting the lowest wear rate of the Al2O3/TiC substrate composites and the counterbody.

A suspension high velocity oxy-fuel thermal spray manufacturing route for silicon carbide – YAG composite coatings

Silicon carbide (SiC) coatings obtained through thermal spraying represent a major engineering challenge due to the high tendency of SiC to decompose during the spraying process. In order to avoid this decomposition, suspension high velocity oxy-fuel (SHVOF) thermal spray was used in combination with a novel SiC powder modified by addition of yttrium aluminium garnet (YAG) as the feedstock. The colloidal stability of the feedstock in water was optimised in order to obtain stable and well-dispersed suspensions suitable for SHVOF spraying. Dense SiC-YAG coatings with ~80 μm thickness were obtained and the coatings showed promising results in terms of porosity, microstructure, phase distribution and mechanical properties. Energy dispersive X-ray spectroscopy and X-ray diffraction showed a lack of degradation of the SiC phase in the coatings, thanks to the formation of a molten YAG phase during the spray process, which prevents SiC decomposition.

Mechanistic insight into the role of amorphicity and porosity on determining the corrosion mitigation behavior of Fe-based amorphous/nanocrystalline coating

Fe-based in-situ amorphous/nanocrystalline composite coatings were prepared from an amorphous/crystalline powder (Fe63Cr9P5B16C7) using high velocity oxy-fuel thermal spraying of optimized parameters. To investigate the individual effects of amorphicity and porosity on corrosion performance, two melt spun ribbons with no porosity having different amorphous content viz. (i) fully amorphous (FA-Rib) and (ii) partially amorphous (PA-Rib) structure with similar amorphicity as that of the coatings, were synthesized. Potentiodynamic polarization and electrochemical impedance spectroscopy studies revealed a greater influence of the reduced amorphicity on the increased passive current density and decreased polarization resistance, than that of the porosity in the fully amorphous matrix. Besides, extent of pitting increased, whereas fraction of protective phases (chromium oxide and Cr substituted hematite) in the corrosion products of post-polarized samples decreased gradually in the order of FA-Rib to PA-Rib to the coating. Moreover, results of Auger electron spectroscopy revealed that depletion of Cr and thinning of passive film increased significantly with crystallization of amorphous structure, compared to additional porosity effect. These results confirmed that corrosion mitigation ability of the coating was primarily affected by reduced amorphicity. Role of both these microstructural features in governing the corrosion mechanism of the amorphous coating was elucidated.

Effect of WC Grain Size and Abrasive Type on the Wear Performance of HVOF-Sprayed WC-20Cr3C2-7Ni Coatings

In order to investigate the effect of WC grain size on coatings’ properties and abrasive wear performance, a few WC-20Cr3C2-7Ni coatings with three different WC grain sizes were deposited by the high-velocity oxy-fuel (HVOF) thermal spray process. The phase compositions, microstructures, and mechanical properties of the coatings were investigated. Furthermore, the two- and three-body abrasive wear performances of the three coatings were tested by using SiC and SiO2 abrasives, respectively. The results show that all the three coatings were composed of WC, Cr3C2, and the Ni binder as well as the (W,Cr)2C phase. The abrasive wear resistance of the WC-20Cr3C2-7Ni coating monotonously increased with increasing WC grain size when the SiC abrasive was used in the two- and three-body abrasive wear tests. However, the wear resistance trend was reversed when the SiO2 abrasive was used in the three-body abrasive wear test. The specific wear rate of the WC-20Cr3C2-7Ni coating exposed to the SiC abrasive under the two-body abrasive wear test was the largest. The wear resistance of the coatings was more significantly affected by the hardness of the abrasive particles than the size of carbides present within the coating. The high hardness of SiC can cut both the carbide and the binder phase of the WC-based cermet coatings, resulting in a high wear rate, whereas the low hardness of SiO2 cuts and/or scratches the binder initially, and then it dislodges the carbides from the matrix. The dislodged carbides which were subsequently pulled out from the matrix by the repeated impact of the SiO2 abrasives result in a milder wear rate.