High Velocity Air Fuel Research Articles

Influence of KCl and HCl on high temperature corrosion of HVAF-sprayed NiCrAlY and NiCrMo coatings

The oxidation performance of NiCrAlY and NiCrMo coatings thermally sprayed by high velocity air-fuel (HVAF) technique has been investigated in a chloridizing-oxidizing environment, with and without a KCl deposit, at 600 °C for up to 168 h. Both coatings protected the substrate in the absence of KCl due to formation of a dense Cr-rich oxide scale. In the presence of KCl, Cl−/Cl2 diffused through a non-protective and porous NiCr2O4 scale formed on NiCrAlY, leading to formation of volatile CrCl3. On the other hand, Mo in NiCrMo stimulated the formation of a more protective Cr-rich oxide scale which increased the corrosion resistance by reducing Cl−/Cl2 diffusion.

Influence of Bondcoat Spray Process on Lifetime of Suspension Plasma-Sprayed Thermal Barrier Coatings

Development of thermal barrier coatings (TBCs) manufactured by suspension plasma spraying (SPS) is of high commercial interest as SPS has been shown capable of producing highly porous columnar microstructures similar to the conventionally used electron beam–physical vapor deposition. However, lifetime of SPS coatings needs to be improved further to be used in commercial applications. The bondcoat microstructure as well as topcoat–bondcoat interface topography affects the TBC lifetime significantly. The objective of this work was to investigate the influence of different bondcoat deposition processes for SPS topcoats. In this work, a NiCoCrAlY bondcoat deposited by high velocity air fuel (HVAF) was compared to commercial vacuum plasma-sprayed NiCoCrAlY and PtAl diffusion bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. SPS was used to deposit the topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue testing. Isothermal heat treatment was performed to study bondcoat oxidation over time. The effect of bondcoat deposition process and interface topography on lifetime in each case has been discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs.

High corrosion and wear resistance of Al-based amorphous metallic coating synthesized by HVAF spraying

A uniform and dense Al-based amorphous metallic coating was deposited on AA 2024 substrate by high velocity air fuel (HVAF) spraying. The Al86Ni6Y4.5Co2La1.5 alloy with high glass forming ability was adopted to prepare the feedstock powder. The coating exhibited 0.12% porosity and 83.7% volume fraction of amorphous phase. The corrosion and wear resistance of the coating were investigated compared to AA 2024. It was found that the coating presented an enhanced pitting potential and a lower corrosion potential than that of AA 2024, providing a sacrificial anode-based cathodic protection for the substrate under chloride-containing environment. The excellent corrosion resistance stems from the smaller driving force for the adsorption of aggressive anions and lower carrier density in passive film formed on amorphous coating. The wear resistance of Al-based amorphous coating was apparently superior to AA 2024 substrate, which is primarily associated with the formation of an even and protective oxide film.

Tribology of FeVCrC coatings deposited by HVOF and HVAF thermal spray processes

This work studies FeVCrC-based coatings as potential alternatives to conventional Ni- and Co-based alloys for wear protection. Specifically, the microstructure and tribological properties of the coatings are characterized as a function of the particle size distribution of the feedstock powder, of the deposition technique – High Velocity Oxygen-Fuel (HVOF) or High Velocity Air-Fuel (HVAF) spraying – and of specific processing parameters.HVOF-sprayed coatings obtained from fine feedstock powder exhibit numerous oxide inclusions, which provide high hardness (≈ 900 HV0.3) but do not excessively impair fracture toughness, as determined through scratch testing techniques. HVAF-sprayed coatings obtained from the same feedstock powder contain much fewer oxide inclusions, and some of them possess simultaneously high hardness and high toughness. Defects (e.g. speckles) are instead formed in case unsuitable HVAF torch hardware is employed. A coarse feedstock powder always results in unmelted inclusions, which impair the cohesion of the coatings, particularly of the HVAF-sprayed ones.Most coatings anyway exhibit very low sliding wear rates < 3 × 10−6mm3/(Nm); abrasive grooving and surface fatigue-induced pitting are the main wear mechanisms. Oxide inclusions do not affect negatively the response of HVOF coatings, whereas too many unmolten particles increase pitting under severe test conditions. Rubber-wheel abrasion testing produces comparatively more severe grooving.

SOLID PARTICLE EROSION RESISTANCE OF HVAF-SPRAYED WC-10Co-4Cr COATING ON CA6NM STEEL

In the present investigation, WC-10Co-4Cr coating was deposited by high velocity air-fuel (HVAF) process on CA6NM hydro turbine steel. A detailed microstructural and phase compositional study was carried out on the coating. Mechanical properties of the coating were also evaluated. WC-10Co-4Cr coating showed a homogeneous, well-bonded structure with low porosity, which is mainly attributed to less decarburization of WC. Erosion resistance of the coating was evaluated by air jet erosion tester at three different impingement angles (30[Formula: see text], 60[Formula: see text] and 90[Formula: see text]) for 35 and 70[Formula: see text]m/s impact velocities. The FESEM micrographs were taken, before and after erosion tests, to determine the erosion mechanism. The test results revealed that the coating protects the substrate at 30[Formula: see text], 60[Formula: see text] and 90[Formula: see text] impingement angles. At 70[Formula: see text]m/s impact velocity, uncoated and coated steel showed higher cumulative volume loss than in the case of 35[Formula: see text]m/s impact velocity. It was observed that uncoated steel showed a ductile behavior during erosion and WC-10Co-4Cr coating showed mixed (ductile and brittle) mode of fracture during erosion.

Electrochemical Behavior of Bilayer Thermal-Spray Coatings in Low-Temperature Corrosion Protection

Cr3C2-NiCr coatings are greatly used to protect critical components in corrosive environments and to extend their lifetime and/or improve functional performance. However, the pores formed during spraying restrict the coating’s applicability area for many corrosion protection applications. To overcome this technical challenge, bilayer coatings have been developed, in which an additional layer (the so-called “intermediate layer”) is deposited on the substrate before spraying the Cr3C2-NiCr coating (the so-called “top layer”). The corrosion behavior of the bilayer coating depends on the composition and microstructure of each layer. In the present work, different single-layer coatings (i.e., Cr3C2-NiCr, Fe- and Ni-based coatings) were initially sprayed by a high-velocity air fuel (HVAF) process. Microstructure analysis, as well as electrochemical tests, for example, open-circuit potential (OCP) and polarization tests, were performed. The potential difference (ΔE) had a great influence on galvanic corrosion between the top and intermediate layers, and thus, the coatings were ranked based on the OCP values (from high to low) as follows: NiCoCrAlY &gt; NiCr &gt; Cr3C2-NiCr &gt; NiAl &gt; Fe-based coatings (alloyed with Cr) &gt; pure Ni. The Ni-based coatings were chosen to be further used as intermediate layers with the Cr3C2-NiCr top layer due to their capabilities to show high OCP. The corrosion resistance (Rp) of the bilayer coatings was ranked (from high to low) as follows: NiCoCrAlY/Cr3C2-NiCr &gt; NiCr/Cr3C2-NiCr &gt; NiAl/Cr3C2-NiCr &gt; Ni/Cr3C2-NiCr. It was shown that splat boundaries and interconnected pores are detrimental for corrosion resistance, however, a sufficient reservoir of protective scale-forming elements (such as Cr or/and Al) in the intermediate layer can significantly improve the corrosion resistance.

A pragmatic approach and quantitative assessment of silt erosion characteristics of HVOF and HVAF processed WC-CoCr coatings and 16Cr5Ni steel for hydro turbine applications

In the present study, WC-CoCr hard composite coatings were deposited on the hydro turbine steels using two different thermal spray techniques such as High Velocity Air Fuel (HVAF) and High Velocity Oxy Fuel (HVOF). The slurry erosion tests were performed with three different jet impingement kinetic energies and at five different impact angles. The influence of impact angle on the erosion wear behavior of the coatings was analyzed using CFD simulation technique. Erosion mechanisms were investigated in detail using SEM and laser scanning confocal microscopy. Among all the WC–CoCr coated samples, the HVAF coating sprayed at highest spray velocity has shown superior erosion resistance compared to the HVOF coatings. It could be attributed to the better adhesion, higher density, enhanced hardness and surface compressive residual stresses coupled with lower oxidation of the coated samples. The erosion wear mechanisms were found to be nearly micro-cutting and plowing with layered material removal at a lower impact angle and a low cycle fatigue linked to repeated impact leading to rounding of the edges and brittle cracking of the WC grains at normal impact conditions.

A Study of Cr3C2-Based HVOF- and HVAF-Sprayed Coatings: Microstructure and Carbide Retention

The research on high-velocity air-fuel (HVAF)-sprayed Cr3C2-based materials has mostly focused on conventional Cr3C2-25NiCr composition. In this paper, two alternative compositions (Cr3C2-50NiCrMoNb and Cr3C2-37WC-18NiCoCrFe) were sprayed with high-velocity oxy-fuel (HVOF) and HVAF spray processes to evaluate the material behavior during spraying and to provide characterization of the microstructures and mechanical properties of the coatings. For comparison, coatings from the Cr3C2-25NiCr composition were sprayed with both processes. Spray diagnostics were carried out to obtain average particle velocity and temperature for each material and process combinations. The measured average in-flight particle data were 1800 °C and 700 m/s for HVOF process, and 1450 °C and 900 m/s for HVAF process. Characterization of the coating microstructures was carried out by scanning electron microscopy and X-ray diffraction. In addition, the carbon content of the feedstock powders and sprayed coatings was measured with carbon analyzer. The results show that carbide rebounding or selective deposition of particles with higher metal matrix content is the dominating reason for carbide loss during HVAF spraying, while carbide dissolution is an additional source for the HVOF spraying. Higher particle velocities and controlled temperature measured for the HVAF process produced dense coatings with improved toughness and more homogenous coating structure.

Sliding wear behaviour of HVOF and HVAF sprayed Cr3C2-based coatings

Thermally sprayed tungsten carbide (WC) and chromium carbide (Cr3C2) based hard metal coatings are commonly applied on component surfaces as corrosion and wear resistant layers. Typically, WC-Co/Ni with optional Cr addition and Cr3C2-25NiCr powders are sprayed with high velocity oxy-fuel (HVOF) or high velocity air-fuel (HVAF) processes. Due to the poor oxidation resistance of the WC particles, Cr3C2-25NiCr composition is typically selected for high temperature environments, up to 800–900°C. In this study, two distinct Cr3C2-based compositions of Cr3C2-50NiCrMoNb and Cr3C2-37WC-18NiCoCr were selected as interesting alternatives to conventional Cr3C2-25NiCr. Sliding wear behavior of the coatings sprayed with HVOF and HVAF processes were tested with a ball-on-disk configuration against an Al2O3 ball at room temperature and at 700°C. It was found that both alternative materials had comparable coefficients of friction with the Cr3C2-25NiCr coatings. The Cr3C2-37WC-18NiCoCr coatings provided improved wear resistance at room temperature conditions, but at 700°C the wear rate was increased to the level of the Cr3C2-50NiCrMoNb coatings. Cr3C2-25NiCr coatings experienced the lowest wear rates at elevated temperatures, which was even lower than at room temperature.

Isothermal oxidation behavior of HVAF-sprayed Ni and NiCr coatings in H2-H2O environment

The formation of a protective chromia scale on stainless steels is known to be suppressed by the presence of water vapor in reducing conditions. Thermal spray coatings present a promising approach to improve the durability of steels by transferring the first line of oxidation attack from the bulk steel to the coating. In the present work, isothermal oxidation behavior of Ni and NiCr coatings deposited by High-Velocity Air Fuel (HVAF) process on 304L stainless steel was investigated at 600°C for 168h. Ar-10%H2-20%H2O was selected as the oxidation environment to study the oxidation behavior of the coatings in a low pO2 environment containing H2 and H2O. BIB/SEM, EDS, and XRD techniques were used to characterize the as-sprayed coatings and to investigate the oxidation mechanisms in the coated samples. Results showed that both Ni and NiCr coatings imparted oxidation protection to the 304L substrate. The chromia-forming 304L steel presented a duplex but non-protective oxide scale comprising of an outer Fe3O4 layer on an inner (Fe, Cr)3O4-spinel oxide. In contrast, the NiCr coating presented superior oxidation behavior due to the formation of a continuous, thin, and slow-growing Cr2O3 scale. The Ni coating, too, protected the substrate owing to limited nucleation and growth of the deleterious NiO scale in the low-oxygen-activity environment.

Isothermal oxidation of HVAF-sprayed Ni-based chromia, alumina and mixed-oxide scale forming coatings in ambient air

The power generation industry has been progressively shifting towards higher operating steam temperatures and pressures to increase efficiency and reduce CO2 emissions. However, higher operating temperatures lead to more aggressive oxidation of the boiler components. A promising route to improve the durability of degradation-prone components is through deployment of high-performance coatings. In the present work, four Ni-based coatings - Ni21Cr, Ni5Al, Ni21Cr9Mo, and Ni21Cr7Al1Y - thermally sprayed by the high-velocity air fuel (HVAF) technique on boiler steel (16Mo3) substrates were investigated. The isothermal oxidation behavior of the coatings was studied in ambient air environment at 600°C for different time intervals i.e. 1, 5, 10, 24, 48, 96, and 168h. The oxidation behavior of the as-sprayed and polished coatings was compared. The protective α-Al2O3 was not detected on the exposed alumina-forming NiAl coating. On the other hand, Cr2O3 along with a small amount of NiO were the main oxidation products on the surface of the NiCr and NiCrMo coatings, and were found to be relatively less protective. The mixed-oxide scale forming NiCrAlY coatings showed the best oxidation resistance due to the formation of a thin and slow-growing Al2O3 scale along with Ni(Al,Cr)2O4 and Cr2O3. The polished coatings were found to significantly reduce the oxidation rate in each case as the protective scale-forming elements were more uniformly supplied to the surface oxide scale by removing the surface asperities.

Application of TiC reinforced Fe-based coatings by means of High Velocity Air Fuel Spraying

In the field of hydraulic applications, different development trends can cause problems for coatings currently used as wear and corrosion protection for piston rods. Aqueous hydraulic fluids and rising raw material prices necessitate the search for alternatives to conventional coatings like galvanic hard chrome or High Velocity Oxygen Fuel (HVOF)-sprayed WC/Co coatings.In a previous study, Fe/TiC coatings sprayed by a HVOF-process, were identified to be promising coating systems for wear and corrosion protection in hydraulic systems. In this feasibility study, the novel High Velocity Air Fuel (HVAF)-process, a modification of the HVOF-process, is investigated using the same feedstock material, which means the powder is not optimized for the HVAF-process. The asserted benefits of the HVAF-process are higher particle velocities and lower process temperatures, which can result in a lower porosity and oxidation of the coating. Further benefits of the HVAF process are claimed to be lower process costs and higher deposition rates. In this study, the focus is set on to the applicability of Fe/TiC coatings by HVAF in general. The Fe/TiC HVAF coating could be produced, successfully. The HVAF- and HVOF-coatings, produced with the same powder, were investigated using micro-hardness, porosity, wear and corrosion tests. A similar wear coefficient and micro-hardness for both processes could be achieved. Furthermore the propane/hydrogen proportion of the HVAF process and its influence on the coating thickness and the porosity was investigated.

STEM analysis of WC-Co coatings modified by nano-sized TiC and nano-sized WC addition

Thermally sprayed hardmetal WC-Co-based coatings are widely applied in order to provide good wear resistance to mechanical components working in demanding environment. The WC-Co coatings are obtained by various spraying methods such as High Velocity Oxygen Fuel (HVOF) or High Velocity Air Fuel (HVAF) techniques. Additional improvement of coatings' properties can be achieved by adding very fine carbides to the WC-Co powder feedstock. The usual approach is the agglomeration and sintering of submicron-sized carbides without or with micro-sized carbides (bimodal distribution). In this work, WC-Co powders were modified by blending them with 5wt% nano-sized TiC (<100nm) or 5wt% nano-sized WC (<100nm). The coatings were deposited by High Velocity Air Fuel (HVAF) on a steel substrate. As reference, pure WC-Co coating was also sprayed. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) were employed for the microstructural characterization of the deposited coatings. The formation of solid solution of tungsten in cobalt with the composition Co0.9W0.1 by selected area electronic diffraction, was detected. W dissolution effect was observed to be lower in the case of nano-sized TiC-added coatings. Microstructural investigation by STEM indirectly indicates that nano-sized WC completely dissolved in the cobalt matrix, inducing solid solution of tungsten in cobalt formation in the 5wt% WC-added coating. The formation of new phases containing Ti, except TiC, was not found in the coating. Obtained results suggest that nano-sized TiC may increase the stability of metallic matrix microstructure in a WC-Co-based coating.

A comparative study on wear and corrosion behaviour of HVOF- and HVAF-sprayed WC–10Co–4Cr coatings

In this work, WC–10Co–4Cr coatings were separately deposited on 300M steel by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) spraying processes. Microstructure, porosity, micro-hardness, bonding strength, wear and corrosion resistance of the coatings after different processing were investigated and compared. The result shows that dense and homogeneous microstructure existed in both two WC–10Co–4Cr coatings. Owing to lower temperature flames and higher particle velocity in the HVAF process, the HVAF-sprayed WC–10Co–4Cr coating exhibited less decarburisation, lower porosity (0.74%), higher micro-hardness (1162 HV0.3) and bonding strength (74.68 MPa) than HVOF-sprayed WC–10Co–4Cr coating. In addition, wear and corrosion resistance of these two coatings were evaluated by sliding wear test and electrochemical corrosion test. The HVAF-sprayed WC–10Co–4Cr coating also exhibited excellent wear resistance and superior corrosion property than HVOF-sprayed WC–10Co–4Cr coating.

Chlorine-induced high temperature corrosion of Inconel 625 sprayed coatings deposited with different thermal spray techniques

Ni-based coatings of the type Inconel 625 sprayed with high-kinetic spray processes are applied as protective coatings in many industrial fields where high corrosion resistance is required. High-velocity oxygen-fuel (HVOF) and arc spray are common thermal spray methods used in the industry of power generation. Conversely, high-velocity air-fuel (HVAF) and cold spray are nowadays technologies of rising interest because of their possibilities to create highly dense and low oxidised metallic coatings. This study aims to assess the effect of the different high-kinetic spray systems on chlorine-induced high temperature corrosion protection of Inconel 625 coatings. The coatings were exposed for 168h to the test condition of 550°C under KCl salt deposits in 12% humidity air atmosphere. All the coatings provided effective protection to the substrate with the HVOF and arc sprayed coatings being the most resistant. The coatings were subjected to chlorine induced active oxidation and showed the typical layered structure of the external oxide deposit with chlorine detected at the coating/oxide interfaces. Signs of internal degradation were observed and were attributed to the penetration of chlorine through particle and splat boundaries. Chlorine was detected in some cases up to a depth of 200μm from the surface.

Microstructural characteristics and corrosion behavior of HVAF- and HVOF-sprayed Fe-based coatings

Fe-based coatings have been shown to be viable alternatives to the more expensive and less environmentally friendly Co- and Ni-based coatings. In the present work, the microstructural characteristics and corrosion behavior of Fe-based coatings deposited by high-velocity air fuel (HVAF) and high-velocity oxy fuel (HVOF) processes were comparatively investigated. Different sets of powder composition and particle size were used to decrease the porosity and increase the corrosion resistance of the coatings. The corrosion behavior of the coatings was studied using electrochemical techniques, including open-circuit potential (OCP) and polarization tests in 3.5wt% NaCl at 25°C. Techniques such as scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffractometry (XRD) were used to characterize the as-sprayed and corroded coatings. The results revealed that the HVAF coatings had lower porosity and oxide content than the HVOF coatings. The polarization tests confirmed that the HVAF coatings sprayed with finer particle size (−36+20μm) have higher polarization resistance (Rp) than the coatings produced by powders (−53+20μm). Based on SEM analysis, it was observed that corrosion initiated and grew through the surface defects of the coating and propagated through inter-lamellar boundaries.

A Comparative Study on Ni-Based Coatings Prepared by HVAF, HVOF, and APS Methods for Corrosion Protection Applications

Selection of the thermal spray process is the most important step toward a proper coating solution for a given application as important coating characteristics such as adhesion and microstructure are highly dependent on it. In the present work, a process-microstructure-properties-performance correlation study was performed in order to figure out the main characteristics and corrosion performance of the coatings produced by different thermal spray techniques such as high-velocity air fuel (HVAF), high-velocity oxy fuel (HVOF), and atmospheric plasma spraying (APS). Previously optimized HVOF and APS process parameters were used to deposit Ni, NiCr, and NiAl coatings and compare with HVAF-sprayed coatings with randomly selected process parameters. As the HVAF process presented the best coating characteristics and corrosion behavior, few process parameters such as feed rate and standoff distance (SoD) were investigated to systematically optimize the HVAF coatings in terms of low porosity and high corrosion resistance. The Ni and NiAl coatings with lower porosity and better corrosion behavior were obtained at an average SoD of 300 mm and feed rate of 150 g/min. The NiCr coating sprayed at a SoD of 250 mm and feed rate of 75 g/min showed the highest corrosion resistance among all investigated samples.

HVOF and HVAF Coatings of Agglomerated Tungsten Carbide-Cobalt Powders for Water Droplet Erosion Application

Water droplet erosion (WDE) is a phenomenon caused by impingement of water droplets of several hundred microns to a few millimeters diameter at velocities of hundreds of meters per second on the edges and surfaces of the parts used in such services. The solution to this problem is sought especially for the moving compressor blades in gas turbines and those operating at the low-pressure end of steam turbines. Thermal-sprayed tungsten carbide-based coatings have been the focus of many studies and are industrially accepted for a multitude of wear and erosion resistance applications. In the present work, the microstructure, phase analysis and mechanical properties (micro-hardness and fracture toughness) of WC-Co coatings are studied in relation with their influence on the WDE resistance of such coatings. The coatings are deposited by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) processes. The agglomerated tungsten carbide-cobalt powders were in either sintered or non-sintered conditions. The WDE tests were performed using 0.4 mm water droplets at 300 m/s impact velocity. The study shows promising results for this cermet as WDE-resistant coating when the coating can reach its optimum quality using the right thermal spray process and parameters.

Microstructural and electrochemical characterization of Ni-based bi-layer coatings produced by the HVAF process

Bi-layer coating systems comprising a Cr3C2-NiCr coating with different underlying coatings of Ni, NiCr, NiCoCrAlY, and CoNiCrAlY were deposited on 304L stainless steel substrates using the high-velocity air fuel (HVAF) process. The corrosion behavior of the coating systems was studied using electrochemical and immersion tests in 3.5 wt% NaCl at 25 °C. The higher open-circuit potential (OCP) value of the NiCoCrAlY coating (− 120 mV/SCE) compared to the value of the Cr3C2-NiCr coating (− 230 mV/SCE) revealed that the underlying NiCoCrAlY coating was sacrificially protected by Cr3C2-NiCr coating. The polarization resistance (Rp) of the bi-layer coatings with the different underlying coatings of Ni, NiCr, NiCoCrAlY and CoNiCrAlY was approximately 77, 189, 487, and 74 kΩ·cm2 respectively, while the value was 101 kΩ·cm2 for the single-layer Cr3C2-NiCr coating and 30 kΩ·cm2 for the 304L substrate, which confirmed a higher corrosion protection of the NiCoCrAlY coating. The electrochemical impedance spectroscopy (EIS) results showed that the corrosion resistance of the 304L substrate was significantly improved by adding an intermediate layer of NiCoCrAlY to the Cr3C2-NiCr coating. Results of the immersion tests confirmed that the underlying coatings in the different bi-layer coating systems acted as protective barriers. Moreover, the NiCoCrAlY coating showed the best corrosion protection among the investigated underlying coatings.

Effect of Spray Particle Velocity on Cavitation Erosion Resistance Characteristics of HVOF and HVAF Processed 86WC-10Co4Cr Hydro Turbine Coatings

The hydro plants utilizing silt-laden water for power generation suffer from severe metal wastage due to particle-induced erosion and cavitation. High-velocity oxy-fuel process (HVOF)-based coatings is widely applied to improve the erosion life. The process parameters such as particle velocity, size, powder feed rate, temperature, affect their mechanical properties. The high-velocity air fuel (HVAF) technology, with higher particle velocities and lower spray temperatures, gives dense and substantially nonoxidized coating. In the present study, the cavitation resistance of 86WC-10Co4Cr-type HVOF coating processed at 680 m/s spray particle velocity was compared with HVAF coatings made at 895, 960, and 1010 m/s. The properties such as porosity, hardness, indentation toughness, and cavitation resistance were investigated. The surface damage morphology has been analyzed in SEM. The cohesion between different layers has been examined qualitatively through scratch depth measurements across the cross section. The HVAF coatings have shown a lower porosity, higher hardness, and superior cavitation resistance. Delamination, extensive cracking of the matrix interface, and detachment of the WC grains were observed in HVOF coating. The rate of metal loss is low in HVAF coatings implying that process parameters play a vital role in achieving improved cavitation resistance.