High Velocity Oxy-fuel Process Research Articles

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.

Effect of carbon nanotubes on microhardness and adhesion strength of high-velocity oxy-fuel sprayed NiCr–Cr3C2 coatings

NiCr–Cr3C2 coatings are widely used for high temperature and tribological applications due to their high hardness, oxidation, and wear resistance properties. In the present investigation, an attempt is made to further enhance the hardness and adhesion strength of NiCr–Cr3C2 coatings by reinforcing them with multi-walled carbon nanotubes. The carbon nanotubes (3–7 wt%) with varying weight percentages were mixed with NiCr–Cr3C2 using a planetary ball rolling mill and sprayed on SA213 T12 (T12 alloy steel tube) using a high-velocity oxy-fuel spraying process. The microstructures of mixed powder, coating cross-section, and fractured coating surface were characterized using a scanning electron microscope while X-ray diffraction was used for phase identification in the fractured coating surface. The coated samples were subjected to microhardness and adhesion strength tests according to ASTM E384 and ASTM D4541-09 standards. Out of all coatings, NiCr–Cr3C2/7% carbon nanotube composite coating showed the lowest porosity of 1.17%, highest microhardness, and adhesion strength of 563.8 HV and 55.8 MPa, respectively. A fracture analysis after a pull-off adhesion test revealed adhesion failure for NiCr–Cr3C2 coating and combined adhesion/cohesion failure for NiCr–Cr3C2/7% carbon nanotube composite coating.

EFFECT OF LASER POST-TREATMENT ON MICROSTRUCTURAL AND SLIDING WEAR BEHAVIOR OF HVOF-SPRAYED NiCrC AND NiCrSi COATINGS

In this study, NiCrC and NiCrSi coatings are deposited on the MDN 310 steel using High-Velocity Oxy-Fuel (HVOF) process. Laser Surface Melting (LSM) post-heat treatment is carried out on as-sprayed coatings using Laser Engineered Net Shaping (LENSTM) with a power of 300[Formula: see text]W. The characteristics of both coatings in terms of mechanical and metallurgical properties have been investigated. The thicknesses of the as-sprayed NiCrC and NiCrSi coatings are in the range of 170–200[Formula: see text][Formula: see text]m. Laser-treated NiCrC and NiCrSi coatings exhibit a thickness range of 162–185[Formula: see text][Formula: see text]m, respectively. The microstructure of laser-treated NiCrC-300W coating clearly shows a dendrite-like structure, whereas the laser-treated NiCrSi coating exhibits hard layer and columnar homogeneity. Microhardness of as-sprayed NiCrC coating is [Formula: see text] [Formula: see text] and that of NiCrSi coating is [Formula: see text] HV[Formula: see text]. Microhardness of laser-treated NiCrC coating is [Formula: see text] HV[Formula: see text] and that of NiCrSi coating is [Formula: see text] HV[Formula: see text]. Dry sliding wear tests are conducted at room temperature (RT) and 400∘C with 10-N and 20-N loads. The wear rates at 400∘C temperature of laser-treated NiCrC and NiCrSi coatings produced are slightly below [Formula: see text][Formula: see text]mm3/m and [Formula: see text][Formula: see text]mm3/m, respectively. Laser-treated coatings produced better dry sliding wear behavior compared with as-sprayed coatings owing to dense microstructure. Formation of SiC phase in NiCrSi coating imparts high wear and frictional resistance compared to the NiCrC coating.

A REVIEW ON THE INFLUENCE OF PROCESS PARAMETERS AND HEAT TREATMENT ON THE CORROSION PERFORMANCE OF NI-BASED THERMAL SPRAY COATINGS

Various typical engineering components fail from surface under aggressive conditions like oxidation and hot corrosion. This paper is focused on the responsible failure mechanism of oxidation and hot corrosion. The surface properties like corrosion resistance can be enhanced by introducing a layer of Ni-based materials by using thermal coating techniques. The coatings developed by using processes like high velocity oxy-fuel, plasma spray and cold spray exhibits some surface defects like porosity, surface roughness and un-melted particles. Such defects can be further minimized by using optimization of process parameters and various heat treatment processes. The current study is restricted to the analysis of Ni-based coatings developed using high velocity oxy-fuel, plasma spray and cold spray process. In this paper, the optimization of various process parameters along with heat treatments has been discussed in regard to the tailoring of microstructure and the mechanical properties of the developed coatings.

High-temperature erosion and sliding wear of thermal sprayed WC–Cr3C2–Ni coatings

ABSTRACT The present work focuses on high-temperature solid particle erosion and sliding wear behaviours of WC–Cr3C2–Ni coatings deposited by atmospheric plasma spray (APS) and high-velocity oxy-fuel (HVOF) processes. The high-temperature erosion behaviour and the effects of temperature on the sliding wear performance of coated specimens were comparatively studied using an air-jet erosion tester and a ball-on-disc tribometer, respectively. Unidirectional dry sliding wear has been tested up to 800 °C, whereas the erosion tests were up to 650 °C. Interestingly, in a high-temperature sliding, the wear rates of both the coatings decreased after 500 °C due to the development of tribofilm. Furthermore, erosion resistance of both coatings was observed to be more prominent at 650 °C. HVOF coating offers higher erosion resistance than APS coating due to higher hardness, lower splat cohesion, lesser degree of decarburisation, and retained oxide layer. The HVOF-deposited WC–Cr3C2–Ni coating improves the high-temperature sliding wear and solid particle erosion resistance of the base material appreciably.

Micro-deformation Study of Stainless Steel Impacted by Ceramic Particle Using Electron Moiré Method

High-velocity oxy-fuel (HVOF)-sprayed metallic coating can be used to create a surface layer that plays a significant role in enhancing the overall strength, stiffness, and fatigue life of the treated material. The micro-deformation around a single impacted particle is a critical factor that must be considered for the optimization of the HVOF process. In this study, the micro-deformation field of stainless steel impacted by a ceramic particle was characterized at the micro-scale. A grid with a frequency of 1200 lines/mm was fabricated on the surface of stainless steel specimen. The microscopic deformation field formed on the substreate surface, induced by the impact of micro-particles with a diameter of 18 µm, was determined using the electron moire method and numerical simulations. The in-plane plastic strain around the impacted particle was found to be as high as 9.1%, and the value sharply decreased with the increase of the distance to the edge of the impacted particle. The diameter of the plastic area was about 40 µm, which was approximately 2.2 times larger than the particle size. The experimental results were compared with numerical simulation results, and good agreement between the results was found. The electron moire technique can be a useful tool for the measurement of the deformation field induced by an impacted particle in a very local area with a size on the order of microns.

Effect of HVOF spraying parameters on fracture, erosion and thermal properties of Fe alloy-based coating materials

Fe-based coating (Fe50Mo5C15Si10Cr10Ti10) was deposited on 316L stainless steel substrate by high-velocity oxy-fuel spraying coating process. High-velocity oxy-fuel spraying process parameters such as oxygen flow rate and spray distance were varied to investigate their effect on mechanical, wear and thermal properties. The prepared coatings were characterized in terms of mechanical properties such as micro-hardness and fracture toughness, thermal properties and erosion wear properties. X-ray diffraction analysis showed presence of hardened phase Fe2Ti and Fe-Cr. Results of this study indicated that increase in oxygen flow rate from 200 to 250 slpm improved the fracture toughness and micro-hardness by 33% and 6.7%, respectively. On the other hand, increase in spray distance decreased the fracture toughness and micro-hardness by 27.2% and 6.7%, respectively. The wear rate was increased with the increase in oxygen flow rate and decreased with the increase in spray distance. The erosion wear rate was more dependent on fracture toughness as compared to micro-hardness.

Comparison of FeMnCrSi Cavitation Resistance Coatings Deposited by Twin-Wire Electric Arc and High-Velocity Oxy-Fuel Processes

The hydraulic runners and many other components are exposed to cavitation phenomena and the erosion occurs, and normally are repaired by arc welding processes. However, the heat input from the welding causes microstructural changes in the components materials. Considering the martensitic stainless steel CA6NM, the welding thermal cycle reduces its fracture toughness and consequently the structural integrity of the equipment. Thermally sprayed coatings are an alternative to repair low eroded areas of these components, since the thermal sraying processes do not change the substrate microstructure and/or mechanical properties as the welding process. Different FeMnCrSi alloys deposited by Twin-Wire Electric Arc (TWEA) or High-Velocity Oxy-Fuel (HVOF) are on development and their cavitation resistance, comparable to the substrate CA6NM, are the object of the study in this research. This work presents the comparison of the deposition characteristics and properties of different FeMnCrSi alloys chemical compositions coatings obtained by TWEA and HVOF processes, evaluating the particles in-flight, morphology, hardness, adherence, and cavitation resistance of the coatings.

Characterization and Corrosion Behavior Evaluation of Nanostructured TiO2 and Al2O3-13 wt.%TiO2 Coatings on Aluminum Alloy Prepared via High-Velocity Oxy-Fuel Spray

In this study, nanostructured titania (TiO2; n-TO) and nanostructured alumina-titania (Al2O3-13 wt.%TiO2; n-ATO) coatings were successfully deposited on the 6061 aluminum alloy by applying the high-velocity oxy-fuel process. The n-TO coating showed limited pores or microcracks accompanied by both partially and fully melted areas within splats. The n-TO coating exhibited about 25% higher microhardness compared with the n-ATO coating. The agglomerated non-molten nanostructured TiO2 particles that are randomly dispersed and embedded within the n-TO coating microstructure act as arresters of cracks through either branching or blunting crack tips, resulting in about 17% higher bonding strength, as compared to the n-ATO coating with a looser microstructure. The n-TO coating demonstrated superior hardness, higher wear resistance, and smoother wear scar than the n-ATO and uncoated Al substrate. The electrochemical test indicated that the n-ATO coating had about a 50% higher corrosion rate than the n-TO coating because of its looser structure. The immersion test revealed that the n-ATO coating had been severely attacked by blistering and deep cracks corrosions, whereas limited attacks could be distinguished using the n-TO coating in the substrate interface. Based on the results, the n-TO coating can effectively protect the Al alloy substrate against 3.5 wt.% NaCl solution.

Influences of Mechanical, Corrosion, erosion and tribological performance of cold sprayed Coatings A review

Surface modification is done through various surface modification methods like atmospheric plasma spray (APS), flame spraying, chemical vapour deposition, physical vapour deposition, electroplating process and most widely used technique is High Velocity Oxy Fuel (HVOF). In that technique, powder in the hopper is melted by burning fossil fuel in the combustion chamber. This will develop coatings with high residual stress, crack propagation, oxidation of materials, and phase transition, it can affect mechanical, tribological, erosion and corrosion behavior of coating. Although during the burning of fossil fuels such as (LPG, acetylene and kerosene) with oxygen in the combustion chamber a large amount of energy is consumed, and also many harmful gases (like carbon monoxide (CO), carbon dioxide (CO2) is formed, which is very hazardous to the environment. To come out from this issue an eco-friendly technology cold spray coating process (CS) is the greater replacement for HVOF process. CS coating is formed using solid state impingement of feed stock powder to the substrate with supersonic velocity generated by de Laval nozzle. Cold spray coatings possess the improvement of tribological, mechanical, erosion and corrosion properties in contrast to HVOF. A study has been made to analyze the findings of mechanical, tribological, erosion and electrochemical characteristics of cold spray coating. The cold spray process assists to bring harmony between the environment and industries.

Improvement in hot corrosion resistance of dissimilar alloy 825 and AISI 321 CO2-laser weldment by HVOF coating in aggressive salt environment at 900°C

This study investigated the hot corrosion performance of a dissimilar weldment of Ni-based superalloy and stainless steel joined by CO2-laser welding and improved by high-velocity oxy-fuel (HVOF) coating in a Na2SO4-60wt%V2O5 environment at 900°C. A dissimilar butt joint of AISI 321 and alloy 825 was fabricated by CO2-laser welding with low heat input after obtaining the optimum welding parameters by bead-on-plate trials. The metallurgical and mechanical properties of the laser weldment were evaluated. The tensile test results indicated the occurrence of fracture in the base metal AISI 321 side. The HVOF process was employed to coat Ni-20wt%Cr on the weldment. To evaluate the surface morphology of the corrosion products formed on the uncoated and Ni-20wt%Cr-coated weldments, scanning electron microscopy (SEM) analysis was performed. Energy-dispersive spectroscopy (EDS) was used to determine the different elements present on the surface scales. The existence of oxide phases on the weldments was determined by X-ray diffraction (XRD). The cross sections of the weldments were characterized by SEM with EDS line mapping analysis. The results indicated that the Ni-20wt%Cr-coated weldment exhibited superior hot corrosion resistance due to the development of Cr2O3 and NiCr2O4 protective oxide scales.

Plasma sprayed alumina-yttria composite ceramic coating for electrical insulation applications

A composite ceramic coating consisting of 50:50 weight fraction of alumina (Al2O3)-yttria (Y2O3) blend was deposited as an electrically insulating topcoat on Oxygen-Free Electronic Copper (OFEC) substrates with a cermet interlayer of 30 wt% NiAl-70 wt% Al2O3 blend, both deposited by Atmospheric Plasma Spray (APS) process, and with a NiCrAlY bond coat deposited by High-Velocity Oxy-Fuel (HVOF) process for application in Direct Current (DC) conduction pump of the sodium-cooled fast reactor. The cermet interlayer in between topcoat and bond coat is beneficial for a reduction in the thermal expansion mismatch stresses and further contribute to the improvement in the thermal fatigue life of the multilayer coating system. The coated samples were subjected to a thermal fatigue cycle between 600 °C and 200 °C, simulating sodium-cooled fast reactor temperature patterns in regular operation and transient conditions. The multilayer composite ceramic coating with cermet interlayer successfully endured up to 1000 thermal cycles with no cracking, spallation, or delamination of the topcoat. Surface cross-sectional micrographs before and after the thermal cycle revealed neither significant changes in the splat and lamellae morphology nor distribution of phases, except for the densification effects. X-ray Diffraction (XRD) analysis revealed neither phase change nor the formation of any new phase upon thermal cycling. The adhesion test as per ASTM-C633 revealed that the bonding strength of the coatings lower by ~20% after thermal cycling. The insulation resistance of thermal cycled samples showed a two order reduction in the magnitude, compared to that of the as-coated samples.

High temperature solid particle erosion behaviour of SS 316L and thermal sprayed WC-Cr3C2–Ni coatings

The boiler tubes, steam and gas turbines are commonly affected by severe high-temperature erosion wear due to impingement of solid particles entrained in the stream of fluid. The investigation focuses on the applicability of thermal sprayed WC based coatings for turbines and boiler tubes by improving the erosion resistance of the base material. The present work includes high-temperature solid particle erosion behaviour of WC-Cr3C2–Ni coatings deposited by atmospheric plasma spray (APS) and high-velocity oxy-fuel (HVOF) processes. The effects of temperature and impact angle on erosion performance of uncoated and coated specimens were comparatively studied using air-jet erosion tester (ASTM G76). The eroded surface morphology was analysed using a scanning electron microscope (SEM). Uncoated steel exhibit ductile mechanisms; however, both coated specimens follow the mixed mode of material removal under the same operating conditions. Erosion resistance of APS and HVOF coatings is approximately two and three times higher than uncoated specimens at higher temperatures under 30° and 90° impact angles. The HVOF coating offers higher erosion resistance than APS coating due to lower porosity, greater splat adhesion, a lower degree of decarburisation and higher inter-splat sintering at elevated temperatures.

A study on processing and hot corrosion behaviour of HVOF sprayed Inconel718-nano Al2O3 coatings

In the present work, processing and hot corrosion behaviour of Inconel718-nano-Al2O3 based composite coatings with varying nano-Al2O3 contents (10, 20 and 30 wt. %) was studied. The nano-Al2O3 powders were synthesised by using manual granulation technique. The composite coatings were deposited on grey cast iron (GCI) substrate by using a high-velocity oxy-fuel process (HVOF). Hot corrosion behaviour of bare and coated specimens was determined at 900 °C in a high-temperature furnace for 50 h. The weight change data was used to establish the oxidation kinetics of bare and coated specimens. The coating with the highest proportion of nano-Al2O3 content exhibited the maximum hardness and corrosion resistance. The nano-sized alumina particles enhanced the hardness of the coatings by posing a higher constraint to the plastic deformation during the indentation. The presence of nano-Al2O3 and various protective oxides (Cr2O3, NiCr2O4, and TiO2) resulted in the improved corrosion resistance of coatings in comparison to the GCI substrate.

Study on the Microstructure, Mechanical Properties, and Erosive Wear Behavior of HVOF Sprayed Al2O3-15 wt.%TiO2 Coating with NiAl Interlayer on Al-Si Cast Alloy.

Alumina oxide coatings are widely used in many industrial applications to improve corrosion protection, wear and erosion resistances, and thermal insulation of metallic surfaces. The paper presents study of the microstructure, mechanical, and wear properties of HVOF (high velocity oxy-fuel process) sprayed of Al2O3-15 wt.% TiO2 coating with the NiAl interlayer on the surface of Al-Si alloy castings. The microstructure of Al2O3-15 wt.% TiO2/NiAl coating was characterized by light microscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS). The analysis of the microstructure showed the formation of coating with low porosity, compact structure, good adhesion to the substrate with typical lamellar structure composed of a solid phase consisting of compounds included in the coating material and their phase variations. For analysis of the adhesion of coatings to the substrate, the scratch test was applied. An assessment of the erosive wear resistance of coatings was also carried out, confirming the significant impact of the interlayer as well as the microstructure and phase composition of the oxide coating on the wear resistance of the tested coating system. Moreover, the results were discussed in relation to the bending strength test, including cracks and delamination in the system of the Al2O3-15 wt.% TiO2/NiAl/Al-Si alloy as microhardness and erosion resistance of the coating. It was found that the introduction of the NiAl metallic interlayer significantly increased resistance to cracking and wear behavior in the studied system.

Nickel alloy C-263 protection by WC[sbnd]Cr3C2[sbnd]Ni coatings against high-temperature wear in nuclear applications

Over the years, substantial improvement in the thermal efficiency resulted in higher operating temperatures for Generation IV nuclear reactors. Therefore, reliable material demanded by designers that could sustain at elevated temperatures environment in nuclear applications. The high-temperature friction and wear behaviour of Ni-based alloy C-263 has been comparatively investigated with WCCr3C2Ni coatings. The commercially available WCCr3C2Ni powder deposited by atmospheric plasma spray (APS) and high-velocity oxy-fuel (HVOF) processes. The high-temperature tribometer used for unidirectional sliding tests at 400 °C, 600 °C and 750 °C. The alloy shows higher specific wear rates compared to both coatings at every temperature interval. Development of tribo-film is responsible for the specific wear rates of both the coatings declined after 600 °C. Consequently, the superior wear resistance than Ni-alloy up to 750 °C recommends WCCr3C2Ni coatings for high-temperature gas-cooled nuclear reactors.

Bond Strength, Hardness, and Microstructure Analysis of Stellite Coating Applied on 410 Steel Surface Using Flame Spray, Plasma Spray, and High-Velocity Oxyfuel Spray Process

Three thermal spray methods often used in industry are flame spray, plasma spray, and high-velocity oxyfuel (HVOF) spray. This research is intended to compare the properties of those methods in depositing Stellite coating on 410 martensitic stainless steel. The results showed that both plasma spray and HVOF coating show an even deposition, which could not be achieved by a flame spray method. Those three coatings meet manufacture minimum bond strength requirements. The highest bond strength and hardness were provided by the HVOF process with a value of 33.1 MPa and 719 HV, respectively. According to bond strength and standard hardness deviation, the HVOF process gives the most homogeneous coating. Substrate hardness just below the coating interface after flame spray, plasma spray, and HVOF process are raised by 236%, 56%, and 65% each from the specification. HVOF coating has the best cross section compared to others. Smallest porosity percentage, porosity size, and average interface unbonding is got by the HVOF process, with a value of 0.2%, 7.2 um, and 31%, respectively. Coating microstructure after etching shows phases related to heat input during application. The dendritic structure is observed on flame spray and plasma spray coating after etching but not on HVOF coating. Oxides and carbides of both cobalt and chrome are formed in the coating.

Microstructural investigation of bonding and melting-induced rebound of HVOF sprayed Ni particles on an aluminum substrate

In this study, nickel powder was sprayed on a polished aluminum substrate using the high-velocity oxy-fuel spraying process. Detailed microstructural characterization was conducted to analyse the mechanims of splat formation, with particular attention to the changes occurring at the splat-substrate interface and the subsequent bonding behaviour due to the impact of high thermal and kinetic energy particles with a soft, low melting point substrate. Characterization was performed using scanning electron microscopy, focused ion beam microscopy, transmission electron microscopy, together with the scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that a large number of particles had rebounded upon impact, which was correlated with the degree of substrate melting and the associated time for re-solidification. The remnant splats that adhered to the substrate surface were found to exhibit both mechanical and metallurgical bonding with the substrate. The experimental results were supported by transient finite element based thermal simulation.

Scratch Resistance of High Velocity Oxy-Fuel Sprayed WC-20% Co Coatings Reinforced with Carbon Nanotubes

Tungsten Carbide-20 weight % Cobalt (WC-20 wt% Co) coatings were extensively used material to achieve a combination of extreme hardness and excellent strength. Hence, an effort has been made to improve the toughening properties of WC-Co coatings through reinforcement of Carbon Nano-Tubes (CNTs) using High-Velocity Oxy-Fuel (HVOF) spraying process. In this work, 2 wt%, 4 wt%, and 6 wt% of CNTs were blended by the ball milling process with WC-Co powders. These composed powders were deposited by HVOF process on to the plain mild steel substrates. The scratch test analysis on as-sprayed coatings showed that due to the addition of CNTs on WC-Co coatings, the resistance to penetrate the coating surface increased. Also, by varying the percentage of CNTs in the coating system, the pores were reduced. This phenomenon is attributed to the toughening mechanism by forming a CNT bridge which avoids the formation of internal cracks.

Tribological behaviour of thermal sprayed high velocity oxy-fuel coatings on tungsten carbide – A review

Thermal spray coating is a surface modification technique that improves the properties of the metal surface. The basic principle of this technique is the combination of melting and acceleration. Thermal spray coatings are also classified as plasma spray, High-Velocity Oxy-Fuel, wire arc, detonation, and so on. Among the types of thermal spraying, the high-velocity Oxy-fuel process is a widely used technique in various applications. Chromium and tungsten carbide are used in down-hole drilling tools and gas turbine engines because of high resistance to wear, erosion, cavitation, high hardness, and toughness. In this review article, wear characteristics, corrosion analysis, hardness, surface roughness, and microstructure of thermal sprayed High-Velocity Oxy-Fuel - Tungsten Carbide coatings have been addressed.