High Velocity Oxy-fuel Coatings Research Articles

Studies on wear and microstructure assessment of WC-Co reinforced iron based HVOF coating

This research work uses a High-Velocity Oxy Fuel (HVOF) system to create a cermet based WC-10Co reinforced with a durable Iron-based (FeNiCrMo) advanced composite coating to resist high-temperature sliding wear on an ASTM-SA213-T11 steel substrate. Metco 41C (70%) + WC-10Co (30%) were mechanically blended. Then, feedstock was utilized by the HVOF system to create coatings. The base alloy and the coatings were subjected to various metallurgical and mechanical characterizations. Dry sliding wear test of base alloy and coating, were evaluated using the pin-on-disc device. The test was performed by varying parameters of load 10 N and 20 N with variable temperature of 200 °C, 300 °C and ambient conditions. SEM/EDS and XRD techniques were used to examine the worn samples and to identify the formation of new phases during wear test. The wear characteristics pertaining to wear rate, volume loss, and COF were computed. The coating exhibits both intermetallic phases, such as Mo2C and Co3W3C, and challenging stages, such as Cr3C2, Ni3C, W2C, Fe2C, and SiC. There has been a resultant improvement in wear resistance and hardness of coating relative to the base alloy.

High-velocity oxy-fuel and high-velocity air fuel sprayed WC-Co-Cr coatings on solution-treated 21-4N steel for slurry and corrosion resistance

This study aims to fabricate WC-Co-Cr coatings on the solution-treated 21-4N steel utilizing high-velocity oxy-fuel (HVOF) and high-velocity air fuel (HVAF) techniques. The microstructure, hardness, surface quality, porosity, slurry erosion, and corrosion resistance of HVOF and HVAF coatings on solution-treated 21-4N steel were investigated and compared. The HVAF sprayed WC-Co-Cr coating exhibited dense structure, more hardness (1582 HV), greater fracture toughness (5.69 MPa m1/2), less decarburization, and lower porosity (0.97 %) as compared to HVOF sprayed coating. Further, slurry jet erosion tests and electrochemical corrosion tests provide a comprehensive evaluation of the coating’s performance under erosive and corrosive conditions. Eventually, the conclusive results of the study affirm the exceptional performance of the high-velocity air fuel sprayed WC-Co-Cr coating, demonstrating its superiority in both erosion and corrosion resistance compared to the high-velocity oxygen fuel sprayed coating.

Erosion Prediction Gaussian Process Regression Algorithm for Alumina and Chromia Reinforced Nickel-Based High-Velocity Oxy-Fuel Coatings

Background:: Machine learning (ML) methodologies have demonstrated efficacy in the determination of erosion rates and material removal. In this context, a novel Erosion Prediction Gaussian Process Regression Algorithm (EPGPRA) was developed to predict the volumetric erosion in thermal spray coatings. Aim:: In this patent, a novel EPGPRA based model was developed to predict the volumetric loss of 30Al2O3 and 20Cr2O3 reinforced Ni-based coatings deposited using a high-velocity oxy-fuel (HVOF) process. Objective:: The objective of this patent is to develop a GPR model for the prediction of Ni-30Al2O3 and Ni-20Cr2O3 coatings. Methods:: Spraying powders were applied to the SS316L steel substrate in order to develop coatings. An erosion tester was used in order to investigate the wear resistance of HVOF-coated steel. The gathered experimental dataset is put to use in the construction of a powerful GPR model. The outcomes from GPR model were then measured against the values obtained from the experiments. To demonstrate the accuracy of the GPR model, the produced model is evaluated against various cutting-edge machine learning methods. Results:: This innovation was successful in terms of developing a new GPR model for wear prediction. The discrepancy between the actual and expected values is the smallest for Matern 5/2 (M5/2) GPR in the validation set. It was also lesser as compared to Ensemble Boosted Trees, Support Vector Machine, Linear regression, and Fine Tree. In terms of MSE, MAE, RMSE, and R2 the accuracy performance of the M5/2 GPR model was determined to be 9.8565×10-5, 0.0048884, 0.009928, and 0.93 correspondingly. Ni-Chromia coating performed better than the Ni-Alumina. Conclusion:: As per this patent, a novel EPGPRA-based model was developed, which is the better machine learning technique for wear prediction of Ni-based HVOF coatings.

Improvement in Corrosion Performance of ECAPed AZ80/91 Mg Alloys Using SS316 HVOF Coating.

Mg AZ80/91 alloys are highly popular due to their lightweight, high strength-to-weight ratio, and good machinability. However, their moderate mechanical properties and corrosion resistance have limited their use in the automotive, aerospace, and defense sectors. This study primarily aims to enhance the mechanical performance and corrosion resistance of Mg AZ80/91 alloys, making them more suitable for applications in the aerospace and automotive industries. Firstly, equal-channel angular pressing (ECAP) of Mg AZ80/91 alloys has been attempted to improve their mechanical properties. Secondly, a high-velocity oxy-fuel (HVOF) coating of SS316 was applied over the Mg AZ80/91 substrate to enhance its corrosion resistance. In the second step, an HVOF coating of SS316 is applied over the Mg AZ80/91 substrate for better corrosion resistance. The experimental findings demonstrate that the application of an SS316 coating on the ECAP-4P AZ80/91 Mg alloy substrate results in a uniform and dense layer with an average thickness of approximately 80 ± 5 µm. The HVOF-based SS316 coating on 4P-ECAP leads to a noteworthy enhancement in microhardness and a reduction in the corrosion rate, especially in a NaCl solution (3.5 wt.%). This improvement holds great promise for producing reliable, long-lasting, and resilient automotive, aerospace, and defense components. The application of an HVOF-based SS316 coating onto the AZ80 Mg alloy, which had not undergone ECAP treatment, led to a substantial enhancement in corrosion resistance. This resulted in a notable decrease in the corrosion current density, reducing it from 0.297 mA/cm2 to 0.10 µA/cm2.

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.

Performance of Yttria and Zirconia reinforced WC-10Co4Cr HVOF Coatings of Slurry Pump

ABSTRACT This research paper focuses on the development of additive-based erosion-resistant high-velocity oxy-fuel (HVOF) WC-10Co4Cr coating for pump steel. In this study, the WC-10Co4Cr cermet powder consists of yttria and zirconia, each with a concentration of 3 wt.%. The HVOF spraying method was utilised to develop the ceramics-added WC-10Co4Cr coatings. The study conducted erosion tests using a pot tester under mining conditions. The microstructure, crystalline phases and microhardness of the as-HVOF coatings were analysed and compared between the pure and ceramics-based WC-10Co4Cr coatings. The results revealed the effect of ceramics addition on surface erosion of WC-10Co4Cr coating. The results indicate that yttrium oxide enhances the performance of WC-10Co4Cr coating in terms of erosion resistance, while zirconium oxide is not suitable for use in WC-10Co4Cr coating in erosion wear environments.

Effect of spraying time on mechanical and tribological performances of HVOF-sprayed WC–Co and WC–Cr3C2Ni coatings on AISI 1095 steel

Purpose This paper aims to compare the wear behavior, surface roughness, friction coefficient and volume loss of high-velocity oxy-fuel (HVOF) sprayed WC–Co and WC–Cr3C2–Ni coatings on AISI 1095 steel with spraying times of 10 and 15 s. Design/methodology/approach In this study, the pin-on-disc testing technique was used to evaluate the wear characteristics at a speed of 0.24 m/s, load of 40 N and test time of 60 min under dry conditions at room temperature. The wear characteristics were examined and analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The surface roughness of a coated surface was measured, and microhardness measurements were performed on the cross-sectioned and polished surfaces of the coating. Findings Spraying time and powder material affected the hardness of HVOF coatings due to differences in the porosity of the coated layers. The average hardness of the WC–Cr3C2–Ni coating with a spaying time of 15 s was approximately 14% higher than that of the WC–Cr3C2–Ni coating with a spraying time of 10 s. Under an applied load of 40 N, the WC–Co coating with a spraying time of 15 s had the lowest variation in the friction coefficient compared with the other coatings. The WC–Co coating with a spraying time of 10 s had the lowest average and variation in volume loss compared to the other coatings. The WC–Cr3C2–Ni coating with a spraying time of 10 s exhibited the highest average volume loss. The wear features changed slightly with the spraying time owing to variations in the hardness and friction coefficient. Originality/value This study investigated tribological performance of WC–Co; WC-Cr3C2-Ni coatings with spraying times of 10 and 15 s using pin-on-disc tribometer by rotating the relatively soft pin (C45 steel) against hard coated substrate (disc).

Influence of Cr3C2/NiCr Coating on Stainless Steel and Optimization of Mechanical Properties by Thermal Sprayed High Velocity Oxy-Fuel Coatings

Influence of Cr3C2/NiCr Coating on Stainless Steel and Optimization of Mechanical Properties by Thermal Sprayed High Velocity Oxy-Fuel Coatings

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.

An Influence of Oxygen Flow Rate and Spray Distance on the Porosity of HVOF Coating and Its Effects on Corrosion—A Review

Thermal spray coating, exceptionally high-velocity oxyfuel (HVOF), improves the corrosion resistance and wear of metal. Coating parameters play a vital role in the properties of the coating. The quality of coating can be increased by selecting appropriate coating parameters. In the case of HVOF, the oxygen flow rate and spray distance are the most significant parameters that directly influence the porosity and corrosion resistance of the coating. Porosity is essential in thermal barrier coatings for low thermal conductivity, but there is a limit of porosity beyond which it can cause failure. Hence, understanding the effects of these parameters is essential to evaluate and further minimize the porosity in order to improve the corrosion resistance and durability of the thermal barrier coating. This article reviews hot corrosion in thermal barrier coatings, the stages of corrosion, the importance of spray parameters, and the effect of the oxygen flow rate and spray distance on the corrosion resistance of HVOF-sprayed coatings. Afterwards, the coating materials, the substrate, the flow rate of oxygen, the spray distance, and the fuel used during the HVOF spraying process from recent articles are summarized. In summary, this review compares the flow rate of oxygen and the spray distance with the corrosion capacity of the coating under different corrosive environments and materials to optimize these parameters for high-quality coating, which would sustain under high temperatures for future applications.

Improvements in Hot Corrosion Behavior of CO2 Laser-Welded Fe-Based A-286 Alloy in an Aggressive Salt Environment by High-Velocity Oxy-Fuel Coating

Improvements in Hot Corrosion Behavior of CO2 Laser-Welded Fe-Based A-286 Alloy in an Aggressive Salt Environment by High-Velocity Oxy-Fuel Coating

Performance of thermal-sprayed WC-Cr3C2-Ni coatings in slurry erosion for hydrodynamic turbines

ABSTRACT Hydrodynamic turbine and slurry pump components are frequently influenced by severe wear due to the impact of solid particles present in the water. A WC-based coatings deposited by thermal spray techniques is known for the protection against slurry erosion. In the present work, WC-Cr3C2-Ni powder was sprayed on a turbine steel substrate using high-velocity oxy-fuel (HVOF) and atmospheric plasma spray (APS) techniques. Microstructural and phase constitutions of as-sprayed coatings were examined. The effect of speed, slurry concentration and particle size on slurry erosion resistances of both coatings and substrate materials was comparatively studied in a slurry pot erosion tester. The results exhibit that the HVOF coating has better properties in terms of density, micro-hardness and slurry erosion resistance than those of APS coating. The improvement in slurry erosion resistance of bare turbine steel by using APS and HVOF coatings is approximately 37% and 62%, respectively.

Microstructural, Mechanical and Wear Behavior of HVOF and Cold-Sprayed High-Entropy Alloys (HEAs) Coatings

HEAs powders, unlike standard alloys which contain one or two base elements, are new alloys that contain multiple elements in the same quantity. These materials have outstanding physical and mechanical properties and for this reason, are of great interest in the material science community for their application in advanced industrial sectors. In this investigation, cold spray (CS) and high-velocity oxy fuel (HVOF) processes were used to deposit Cantor alloy (FeCoCrNiMn) coatings. Starting feedstock powders were thoroughly characterized in terms of size, shape, phase and elastic modulus. For CS process, the coating deposition efficiency and porosity could be optimized by varying gas pressure, gas temperature and stand-off distance. In the case of HVOF process, stand-off distance influenced the thickness of the coatings. Besides, on the optimized CS and HVOF coatings, corrosion tests in 3.5% NaCl solution, as well as rubber wheel, ball on disk and jet erosion tests were carried out to evaluate their wear behavior. Also, to benchmark the corrosion and wear behavior of optimized coatings, the results were compared to 316L and C-Steel bulks. The tribological study shows that Cantor alloy coatings deposited via CS and HVOF are promising to protect parts and components in a harsh environment.

Ni-based coating protection of 316L stainless steel at dry, elevated temperature and wet sliding condition

The NiCrSiB coatings are used extensively for wear and oxidation resistance in numerous applications like hot forming industries, power generation plants, petroleum refining, and nuclear power plants. In this paper, NiCrSiB powder deposited by APS (atmospheric plasma spray) and HVOF (high velocity oxy-fuel) process on stainless steel 316L substrate was investigated for the friction and wear at RT (room temperature), 700 °C, at the lubricating condition with clean and contaminated oil with nano alumina particles. The sliding wear tests were carried out on standard tribometer against silicon nitride (1580 HV0.3) counter material following ASTM G99 standard. The coatings characterization was performed using porosity analysis, nano-indentation, 3D non-contact analysis, EDX (energy-dispersive X-ray), SEM (scanning electron microscope) and LRS (Laser Raman Spectrum). The wear, friction and the wear mechanisms were investigated for both coatings at tested conditions. Although the coating wear was substantially affected by the temperature, the specific wear rate of the APS and HVOF coatings lies in the range 10-4 to 10-5 mm3/N.m and hence serviceable up to 700 °C. The coating's wear mechanisms at elevated temperature were a combination of adhesive and tribo-oxidative wear. At the dry, wet, and high-temperature condition, the HVOF coating retains higher wear resistance than APS coating, due to the high dense structure, low porosity, low inflight oxidation and high nano hardness. The nano alumina particles in the contaminated oil reduces the COF significantly for HVOF coating whereas, negligible change in COF has been observed for APS coating.

Development of CNT mixed HVOF coating for water tube boiler material to improve the degradations

In most of the thermal power plants, one of the vital components is boiler tube. In thermal power plants the down fall in profits due to hot corrosion, oxidation and erosion. In order to improve properties of the above said, the researchers working on the wide area of combating hot corrosion, erosion and oxidation of boiler tubes by using thermal spray coatings (HVOF) with the combination of carbon nanotubes (CNTs). The corrosion occurs, when the material exposed to open atmosphere it will get corroded. The oxidation occurs due to the material is exposed to high temperatures. Erosion occurs due the presence of unburnt particles striking at high velocity. There by the application of HVOF (High-Velocity Oxy-Fuel) coating playing a vital role in approaching using HVOF parameters such as speed, high temperature, oxygen with fuel flow and fuel ratio, powder flow rate. In the present studies the resistance improvement of corrosion, oxidation and erosion of the boiler tube material SA213 T11. The advantages of HVOF coatings with CNTs percentages like CNT 3%, 5%, 7%. are due to its low porosity, high dense coatings, more adhesive in nature and bond strength also more. The kinetics of hot corrosion, oxidation and erosion will be analysed by measuring weight gain after every cycle under thermogravimetric studies (1 h heating and 20 min cooling). The results will be achieved by using visual examination, and advanced microscopy like XRD and SEM/EDS analysis.

Investigating load-dependent wear behavior and degradation mechanisms in Cr3C2–NiCr coatings deposited by HVAF and HVOF

Wear resistant coatings that comply with non-toxic environment goals are highly desirable. Cr3C2–NiCr is a promising alternative to the toxic, ‘Co’- containing WC–Co coatings to mitigate wear. The purpose of this study was to examine the suitability of Cr3C2–NiCr coatings for automotive brake disc application by systematically investigating their dry sliding wear behavior at different test conditions. Therefore, High Velocity Air Fuel (HVAF) and High Velocity Oxy Fuel (HVOF) were employed to deposit Cr3C2–NiCr coatings. The powder feedstock and as-deposited Cr3C2–NiCr coatings were characterized for their microstructure and phase composition using SEM and XRD. Mechanical properties (hardness, fracture toughness), porosity and surface topography of the as-deposited coatings were evaluated. The coatings were subjected to sliding wear tests at different normal loads (5 N, 10 N and 15 N) using alumina ball as the counter surface. Coefficient of friction (CoF) evolution of HVAF and HVOF deposited coatings, along with their wear performance, was obtained for different normal load conditions. The wear performance ranking of HVAF and HVOF processed coatings was influenced by the test conditions, with HVAF coatings demonstrating better wear resistance than HVOF coatings at harsh test conditions and the HVOF coatings performing better under mild wear test conditions. Detailed post-wear analysis of worn coatings, the alumina ball counter-body and the resulting debris was performed to reveal the degradation mechanisms at different test conditions. Findings from this work provide new insights into the desirable microstructural features to mitigate wear, which can be further exploited to deposit wear-resistant coatings.

A short review on the performance of high velocity oxy-fuel coatings in boiler steel applications

A major part of the electric power is generated in coal operated thermal power plants which is operated by low rank fuel. During the operation of boilers with the high temperature combustion of low ranked fuel, few salt films are produced due to the presence of ash and abrasive minerals. This action produces the serious corrosion on the surface of boiler plates which is recognised as hot corrosion. A surface engineering method is used to encounter such problem in order to avoid repair and damage or economic loss such as high velocity oxy-fuel [HVOF] sprayed coatings. Various surface coating methods are being adopted for this purpose. Moreover, post heat treatment processes are also added in terms to retain the long period of surface coating.

The study of Cr3C2-25NiCr and 35WC-Co/65NiCrBSi-based HVOF coatings for high-temperature erosion resistance application

ABSTRACT This work concerns a technique to produce thermal sprayed coatings using HVOF (high-velocity oxy-fuel) method as it is a widely used application in high-temperature erosion and corrosion environment. Two types of hard coatings Cr3C2-25NiCr and 35WC-Co/65NiCrBSi were sprayed on an SS-347 steel substrate. The erosion tests were done using high-temperature jet erosion set up to study the effect of velocity, temperature and impact angles on the coatings produced. The surface morphology of the samples was characterized using 3D laser confocal microscopy, light microscopy, scanning electron microscopy with EDAX and X-ray diffraction. Microhardness, porosity level and roughness parameters were evaluated to infer a probable mechanism of material removal. The Cr3C2-25NiCr coating exhibited ∼3.3 times higher erosion resistance than 35WC-Co/65NiCrBSi coating at 90° and 30° impact angles. SEM and 3D laser confocal images on the eroded surface of the coatings reveal the combination of ductile and brittle fracture of coating.

Electrochemical studies of heat‐treated NiCrMoFeCoAl and NiCrMoFeCoAl‐30%Cr3C2 HVOF coatings on T22 boiler steel

AbstractHerein, we present the corrosion behavior of NiCrMoFeCoAl and NiCrMoFeCoAl‐30%Cr3C2 high‐velocity oxy fuel (HVOF) coatings on the ASTM‐SAE213‐T22 boiler tube steel alloy. The samples exposed to molten salt (Na2SO4–60%V2O5) environment at 700℃ under thermocyclic conditions were investigated in conjunction with electrochemical techniques. The surface structures and morphologies of heat‐treated samples suggest the extent of corrosion is least for the NiCrMoFeCoAl‐30%Cr3C2‐coated steel. Room‐temperature electrochemical analysis of heat‐treated samples demonstrate the good stability with NiCrMoFeCoAl‐30%Cr3C2 layers on T22 steel at solid/liquid interface under neutral pH conditions. The potentiodynamic and impedance analyses reveal that the higher charge transfer resistance was observed for NiCrMoFeCoAl‐30%Cr3C2‐coated steel, followed by NiCrMoFeCoAl‐coated steel and bare T22 steel. The chromium carbide containing the HVOF coating exhibit a highly dense layer and the metal chromites/chromates on the post‐heat‐treated coatings provide poor access for the electrolyte to base alloy and subsequently improve corrosion stability.

Fatigue Behaviour of High Velocity Oxy-Fuel Coatings on Medium Carbon Steel

Fatigue Behaviour of High Velocity Oxy-Fuel Coatings on Medium Carbon Steel