High Velocity Oxy-fuel Thermal Spraying Research Articles

CoCrFeMnNi0.8V/Cr3C2-Ni20Cr High-Entropy Alloy Composite Thermal Spray Coating: Comparison with Monolithic CoCrFeMnNi0.8V and Cr3C2-Ni20Cr Coatings

High-entropy alloys (HEAs) are revolutionizing the field of surface engineering, challenging traditional alloy frameworks with their superior mechanical attributes and resistance to corrosion. This investigation delves into the properties of the CoCrFeMnNi0.8V HEAs, both as a standalone material and when blended with Cr3C2-Ni20Cr, to evaluate their efficacy as cutting-edge surface treatments. The addition of vanadium to the CoCrFeMnNi0.8V alloy results in a distinctive microstructure that improves hardness and resistance to abrasion. The incorporation of Cr3C2-Ni20Cr particles enhances the alloy’s toughness and longevity. Employing high-velocity oxy-fuel (HVOF) thermal spray methods, these coatings are deposited onto steel substrates and undergo detailed evaluations of their microstructural characteristics, abrasion, and corrosion resistance. Findings reveal the CoCrFeMnNi0.8V coating’s exceptional ability to withstand corrosion, especially in environments rich in chlorides. The hybrid coating benefits from the combination of the HEA’s inherent corrosion resistance and the enhanced wear and corrosion resistance provided by Cr3C2-Ni20Cr, delivering comprehensive performance for high-stress applications. Through the fine-tuning of the application process, the Cr3C2-Ni20Cr reinforced high-entropy alloy coating emerges as a significant advancement in protective surface technology, particularly for use in marine and corrosive settings. This study not only highlights the adaptability of HEAs in surface engineering but also prompts further investigation into innovative material pairings.

An HVOF-Sprayed (Cr3C2-NiCr+Co) Composite Coating on Ductile Cast Iron: Microstructure, Mechanical Properties, and Scratch Resistance.

High-velocity oxy-fuel (HVOF) thermally sprayed Cr3C2-NiCr coatings have been shown to be effective in shielding important machinery and equipment components from wear in harsh, high-temperature conditions. In this investigation, the HVOF thermal spray coating technique was used to deposit Cr3C2-NiCr powder with 10% Co particles onto ductile cast iron. The effect of the Co particles on the mechanical, tribological, and microstructure characteristics of a Cr3C2-NiCr/ductile cast iron system was investigated. The microstructure analysis employed various techniques, including light microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Scratch tests were applied to analyze the coating quality and adhesion. The coatings created using the HVOF spray method with Cr3C2-NiCr powders mixed with Co particles exhibited a dense structure containing large Co particles, partially melted, and very fine Cr3C2 particles embedded into the NiCr alloy matrix. Additionally, they possessed high hardness and excellent adhesion to the substrate. The results of bending strength tests were also presented, together with information on the coating's microhardness and fracture toughness. These included an analysis of the cracks and delamination in the Cr3C2-NiCr/ductile cast iron system. It was observed that the addition of Co particles significantly increased the resistance to cracking and wear behavior in the studied system.

A Comparative Study between a Thermal Spray CoCrFeMnNi0.8V/WC-Co High Entropy Alloy Composite Coating and Plain CoCrFeMnNi0.8V and WC-Co Thermal Spray Coatings

High entropy alloys (HEAs) have emerged as a frontier in surface engineering, challenging the status quo of traditional alloy systems with their exceptional mechanical properties and corrosion resistance. This study investigates the CoCrFeMnNi0.8V HEA, both as a standalone alloy and in a composite with WC-Co, to evaluate their potential as innovative surface coatings. The CoCrFeMnNi0.8V alloy, enriched with vanadium, demonstrates a unique microstructure with enhanced hardness and wear resistance, while the addition of WC-Co particles contributes to improved toughness and durability. By employing High Velocity Oxy-Fuel (HVOF) thermal spray techniques, coatings are deposited onto steel substrates and subjected to rigorous microstructural characterization, wear, and corrosion resistance testing. The results reveal that the CoCrFeMnNi0.8V coating exhibits impressive corrosion resistance in chloride-rich environments. The composite coating leverages the synergy between the HEA’s inherent corrosion resistance and WC-Co’s wear resistance, striking a balance that suits demanding applications. With optimized processing conditions, the composite WC-Co-reinforced high entropy alloy coating could offer a significant advancement in protective coatings technology, especially for maritime and other corrosive settings. This work not only underscores the versatility of HEAs in surface engineering applications but also opens avenues for the development of new material mixtures.

Electrochemical Metallization for Enhancing the Quality and Performance of Electric Motor

The present research aimed to evaluate the effect of nickel-based electrochemical metallization (EMNi) on the quality and performance of electric motor components, compared to high-velocity oxy-fuel (HVOF) thermal spray coating, the most widely used coating in the mining industry. The experiment was conducted using motor components comprised of 4340 VCN steel, 4140 VCL steel, 1045 steel, and stainless steel, which underwent both treatments. The surface temperature of the components was monitored during the processing stage, followed by evaluations of their Rockwell hardness (HRC) and surface characteristics (taper, ovality, parallelism, finish, wear) at the onset (day 0) and after 2 years of use the results indicate that EMNi delivers electric motor components with superior finishes and extended warranty and service life in comparison to HVOF.

Parametric optimization corrosion erosive wear and XPS response of FeCrCoAlTiB and FeCrCoNiSiB coatings on Q235 steel substrate by HVOF spraying using taguchi method

In the study high-velocity oxy-fuel thermal spraying to create Fe32Cr21Co21Al16Ti5B5 and Fe43Cr16Co12Al14Ti5B10, Fe32Cr21Co21Ni16Si5B5 and Fe43Cr16Co12Ni14Si5B10 coatings on Q235 steel substrates. Jet-type testing is used to examine the coatings’ resistance to slurry wear. Researchers examined the surface to learn more about the erosion process. Taguchi analysis and a wear model confirm the significance of the selected important factors. The wear model’s proposed mechanism shows remarkable agreement with the data. Coating loss may be attributed to several causes, including mixed ploughing, and cutting, platelet development, abrasion grooves, and cracking. The outcomes showed that the effect speed was the main contributing variable, the contribution ratio reached 65% to 70%, for the impact velocity of coating no 1 to 4. In contrast, it is recognized that impact velocity > impingement angle > erodent feed rate > erodent size is the most important sequence. Micro-cutting, mixed cutting, and ploughing were the essential disintegration systems for all coatings at low impingement points. In contrast, platelets were detected under normal impingement angles, as confirmed by SEM analysis. Both coatings seem to form passivation films, as shown by their greater Ecorr values relative to the substrate. Fe, Co, Cr, Al, and O all show up as peaks in XPS analyses.

Tribological and corrosive degradation of differently surface engineered 17-4 PH steel

In the present work, a high-velocity oxy-fuel (HVOF) thermal spray process was used to deposit ceramic coatings containing alumina (Al2O3)− 0.8 wt% ceria (CeO2)− 0.2 wt% reduced graphene oxide (rGO) on 17–4 PH steel. The results were compared with the nitrided 17–4 PH (N17–4 PH) steel. The mechanical characteristics of the bare substrate, nitrided substrate, and coating were evaluated regarding micro (Vickers) hardness, scratch hardness, nanoindentation, and high-temperature nanoindentation (300 °C). The tribological behavior of all the specimens mentioned earlier was studied in a universal mechanical tester in a ball on flat reciprocating wear test mode for different loads. Electrochemical responses regarding corrosion properties in 3.5 wt% aqueous salt solution were recorded and analyzed. The results showed that the ceramic coating performed better than the other two specimens regarding mechanical, tribological, and electrochemical properties. For example, the coating was nearly ten and six times more wear resistant than 17–4 PH steel and N17–4 PH steel, respectively, at 50 N load. The performance enhancement in the coating was ascribed to the coating hardness, dense microstructure, and introduction of rGO in the coatings, which participate in the tribological process. Further detailed analysis of the bare steel, ceramic coating, and the nitrided steel properties reveals that the nitriding process can be replaced with the proposed ceramic coating through the HVOF technique for tribological, corrosive, and extreme environmental applications for 17–4 PH steel.

Effect of nano yttria stabilized zirconia on corrosion behaviour of chromium oxide coatings on boiler steel

In this research work, 5 wt.% nano yttria-stabilized zirconia (YSZ) reinforced chromium oxide-based nanocomposite coatings were prepared and successfully deposited on ASME-SA213-T-22 (T22) boiler tube steel substrates using high-velocity oxyfuel (HVOF) thermal spraying method. The corrosion behaviour of composite coating has been compared with that of conventional chromium oxide coating. All the coatings were analysed by scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray diffraction. It was found that the addition of 5 wt.% YSZ in the Cr2O3 matrix results in the reduction of the porosity of the coating and an increase in hardness. During corrosion investigations, it was found that YSZ-reinforced Cr2O3 nanocomposite coating on T22 provides better corrosion resistance than conventional Cr2O3 coating in the molten salt environment at 900 °C. The inclusion of YSZ has reduced porosity by filling in the gaps in the chromium oxide coating, causing particle interlocking, and preventing the entry of corroding species.

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.

SiC/YAG composite coatings by a novel liquid fuelled high velocity oxy-fuel suspension thermal spray

Despite recent advances in suspension-based thermal spray techniques, there is still a need to widen the capability of available thermal spray setups to handle suspension to explore new compositions and improve the properties and performance of existing ones. In this work, a novel setup for injecting liquid-based feedstock in a liquid-fuelled high velocity oxy-fuel (HVOLF) thermal spray torch is proposed, involving a new hardware (“Hybrid Nozzle”) capable of injecting suspension radially and protecting the thermal spray flame from the environmental oxygen by inert gas shrouding. The new setup was used to deposit SiC/YAG composite coatings with 85 wt% SiC content, and their wear performance was evaluated. An oxygen deficient environment was provided to the HVOLF flame, ensuring that no or minimal (<2 wt%) SiO2 was formed in the coating during the spray, as confirmed by XRD. A good wear performance was observed at low load below 20 N, with a specific wear rate < 5 × 10−5 mm3/Nm, with the onset of wear mechanisms characteristic of ceramic wear in the brittle regime between 20 and 30 N. The future applicability of this novel setup to a range of oxidation- and heat-sensitive materials and composites offers the opportunity for new coating materials to be explored with suspension and solution precursor-based HVOLF thermal spray.

Dry sliding wear behaviour of suspension HVOF thermal sprayed Al2O3-MoS2 and Al2O3-BN nanotube coatings

In our present work, alumina/BNNTs and alumina/MoS2 coatings were deposited onto stainless steel substrates by solution precursor high velocity oxy-fuel thermal spraying. The phase evolution, microstructure and tribological properties of the two kinds of coatings were studied. Investigation of the phased content showed that Al2O3, BN and MoS2 survived in the coatings after being sprayed with SHVOF technology. Cross-section images of the coatings showed that the interface between the coating and the substrate was well bonded, and there were no obvious particle inclusions and defects at the interface. The top morphology of the coatings exhibited certain degree of particle deformation, which was conducive to the formation of a more compact coating with less porous and better bonding strength with the substrate. Dry sliding tests showed that alumina/BNNTs and alumina/MoS2coating improved the tribological properties of the samples and they were suitable for low load friction conditions (5 and 10 N). A crack evolution model was proposed to analyze the failure of coatings. This work could provide a reference for the application of the two coatings in the field of friction and wear.

Electrochemical response and passivation affinity of Fe-based amorphous HVOF coatings prepared from pig iron on mild steel

The present work discusses the passivation tendency and corrosion resistance of a novel Fe66.59C11.70P7.58Mn0.37Si2.86Cr1.72Mo0.92B8.26 amorphous coating prepared from pig-iron deposited on mild steel using a high-velocity oxy-fuel (HVOF) thermal spray process. A quantitative assessment of the micromorphological features developed on each coating after the fabrication has been provided. The polarization response, current-transient at the potential in the passive zone, and gravimetric evaluations after 30 days of the salt-fog test using 3.5 w/v % NaCl solution were recorded to understand the overall corrosion behavior of the HVOF coatings. A steady-state electrochemical impedance measurement was also performed. The spectroscopic examination of the corrosion product was performed to understand the nature of passivation, and it revealed the formation of protective iron-chromate and phosphate phases on all the coatings. The synergistic effect of these protective phases and iron-based protective rust phases is believed to be the primary reason for the strong passivation of the coatings. Also, it has been proposed that the corrosion rates calculated from dynamic polarization response should not be considered as final assessment for corrosion resistance of the coatings. Rather, long term corrosion assessment is important to understand the benefit of amorphous coatings with lean chemistry of passive elements, like Cr.

Effects of HVOF spray parameters on porosity and hardness of 316L SS coated Mg AZ80 alloy

High velocity oxy-fuel (HVOF) coatings are becoming more popular in a variety of applications that demand a dense surface with strong wear and corrosion resistance. The HVOF thermal spray technique was used to deposit 316L stainless steel on the magnesium alloy (AZ80). Response surface methodology (RSM) was used to optimize the following HVOF spray parameters to achieve higher hardness and reduced porosity: flow rate of oxygen (O), flow rate of LPG (L), feed rate of powder (F), spray distance (S), and flow rate of carrier gas (C). ANNOVA was performed to develop empirical relations between process variables and measured results. A sensitivity analysis was also carried out to determine the most critical parameter. Correlation plots revealed an inverse relationship between porosity volume percentage and microhardness (R2 = 0.92). 257 lpm (O), 61 lpm (L), 38 gpm (F), 231 mm (S), and 16.50 lpm (C) were identified to be the parameters related to the minimal porosity volume percentage (0.21 ± 0.013 vol%) and the maximum microhardness (367 ± 4 HV0.3).

Corrosion behaviour OF HVOF deposited Zn–Ni–Cu and Zn–Ni–Cu–TiB2 coatings on mild steel

Abstract In this study, Zn–Ni–Cu and Zn–Ni–Cu–TiB2 coatings were deposited using high-velocity oxy-fuel (HVOF) thermal spray technique on a mild steel substrate. Corrosion tests like neutral salt spray (NSS) following (ASTM B-117) standard and immersion cycle test following ASTM G-31, ASTM G1-03, standards were carried out for Zn–Ni–Cu and Zn–Ni–Cu–TiB2 coated mild steel along with uncoated mild steel acting as a control. Both Zn–Ni–Cu and Zn–Ni–Cu–TiB2 coated mild steel were corrosion resistant as compared to uncoated mild steel. Raman analysis following the immersion cycle test inferred that uncoated mild steel had all forms of rust. While Zn–Ni–Cu and Zn–Ni–Cu–TiB2 coated mild steel developed very little rust. The characterization helped to understand the changes in the surface before and after tests. It was observed that both Zn–Ni–Cu and Zn–Ni–Cu–TiB2 coated mild steel had little corrosion degradation of surface as compared to uncoated mild steel. Suggesting that both coatings performed significantly better compared to uncoated mild steel in corrosive environments. Polarization and EIS tests of both coated and uncoated mild steel in a 3.5% NaCl medium helped to understand the behaviour of coatings over a range of frequencies. Both coated samples had high polarization potential E corr values and lower polarization current I corr values as compared to uncoated mild steel. Inferring better performance of coatings in corrosive environments as compared to uncoated mild steel.

Unveiling the Toxicity of Fine and Nano-Sized Airborne Particles Generated from Industrial Thermal Spraying Processes in Human Alveolar Epithelial Cells.

High-energy industrial processes have been associated with particle release into workplace air that can adversely affect workers’ health. The present study assessed the toxicity of incidental fine (PGFP) and nanoparticles (PGNP) emitted from atmospheric plasma (APS) and high-velocity oxy-fuel (HVOF) thermal spraying. Lactate dehydrogenase (LDH) release, 2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) metabolisation, intracellular reactive oxygen species (ROS) levels, cell cycle changes, histone H2AX phosphorylation (γ-H2AX) and DNA damage were evaluated in human alveolar epithelial cells at 24 h after exposure. Overall, HVOF particles were the most cytotoxic to human alveolar cells, with cell viability half-maximal inhibitory concentration (IC50) values of 20.18 µg/cm2 and 1.79 µg/cm2 for PGFP and PGNP, respectively. Only the highest tested concentration of APS-PGFP caused a slight decrease in cell viability. Particle uptake, cell cycle arrest at S + G2/M and γ-H2AX augmentation were observed after exposure to all tested particles. However, higher levels of γ-H2AX were found in cells exposed to APS-derived particles (~16%), while cells exposed to HVOF particles exhibited increased levels of oxidative damage (~17% tail intensity) and ROS (~184%). Accordingly, APS and HVOF particles seem to exert their genotoxic effects by different mechanisms, highlighting that the health risks of these process-generated particles at industrial settings should not be underestimated.

Investigating the Water Jet Erosion Performance of HVOF-Sprayed WC-10Co Coatings on 35CrMo Steel Utilizing Design of Experiments

To enhance the surface of a material with the desired qualities for diverse applications in service, a variety of thermal and thermo-chemical surface treatment processes are used. Due to the high-velocity impact inherent in the process, high-velocity oxy-fuel (HVOF) spray is now frequently employed in industrial applications for its ability to generate a high-quality coating with appropriate hardness and low oxide content. In this investigation, a high-velocity oxy-fuel (HVOF) thermal spraying process was utilized to coat WC-10Co powders on a 35CrMo steel substrate. A water jet erosion test was also used to examine the substrate and coated samples’ erosion behavior. The erosion rate was systematically investigated using water jet variables such as the angle of impingement, water jet velocity, standoff distance, and erodent discharge. For the development of multiple regression models, experiments were performed utilizing the central composite rotatable design and the response surface methodology. The angle of impingement had the most impact on the rate of coating erosion, leading to the water jet velocity, standoff distance, and erodent discharge.

Mechanical and microstructural properties of yttria-stabilized zirconia reinforced Cr3C2-25NiCr thermal spray coatings on steel alloy

In this research work, nano yttria-stabilized zirconia (YSZ) reinforced Cr3C2-25NiCr compo­site coatings were prepared and successfully deposited on ASME-SA213-T-22 (T22) boiler tube steel substrates using high-velocity oxy-fuel (HVOF) thermal spraying method. Different nanocomposite coatings were developed by reinforcing Cr3C2-25NiCr with 5 and 10 wt.% YSZ nanoparticles. The nanocomposite coatings were analysed by scanning elec­tron microscope (SEM)/Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) technique. The porosity of YSZ- Cr3C2-25NiCr nanocomposite coatings was found to be decreasing with the increase in YSZ content, and hardness has been found to be increasing with an increase in the percentage of YSZ in the composite coatings. The coating of 10 wt.% YSZ-Cr3C2-25NiCr showed the lowest porosity, lowest surface roughness, and highest microhardness among all types of coatings. This may be due to the flow of YSZ nanoparticles into the pores and gaps that exist in the base coatings, thus providing a better shield to the substrate material.

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.