High Velocity Oxygen Fuel Coatings Research Articles

Analysis of microstructure, surface morphology, and scratch resistance of high velocity oxy-fuel coated nickel based hybrid nano-composites

In recent years, high velocity oxygen fuel (HVOF) coating technology has gained significant interest in the field of surface engineering. In this study, we have investigated the microstructure, surface morphology, and scratch resistance of HVOF coated Nickel based novel hybrid nano-composites. The coatings were prepared using a high-velocity oxy-fuel (HVOF). HVOF coatings have the ability to enhance the surface properties of various materials, making them more resistant to wear, corrosion, and erosion. Thermal spraying technique, and the microstructure and surface morphology of the coatings were analyzed using scanning electron microscopy (SEM). The scratch test was performed using a TR-101, DUCOM made Scratch tester to evaluate the scratch resistance of the coatings. The results of the study revealed that the HVOF coated novel hybrid nano-composites exhibited a fine-grained microstructure with a dense and homogeneous surface morphology. The scratch resistance of the coatings was significantly improved due to the addition of nano composites. The load required to cause the first visible scratch on the coated surface was found to be significantly higher than that of the uncoated substrate. The scratch morphology of the coatings was also studied, which revealed that the scratch-induced damage was mainly due to the plastic deformation of the coating material. The results suggest that the HVOF coated novel hybrid nano composites have great potential in improving the surface properties of various engineering materials and can be used in applications where high wear resistance is required. Overall, the study demonstrates that the combination of HVOF coating technology and hybrid nano-composites can result in coatings with improved microstructure, surface morphology, and scratch resistance, which makes them ideal for use in applications wherever wear resistance is critical.

Enhancing Predictive Quality in HVOF Coating Technology: A Comparative Analysis of Machine Learning Techniques

This paper presents a comparative analysis of the performance of machine learning techniques for enhancing predictive quality in thermal spray coating technology, with a focus on the high velocity oxygen fuel (HVOF) process. The study aims for accurately predicting coating properties, which are pivotal in determining coating quality in HVOF applications. By investigating five influential factors, including the fuel-to-oxygen ratio and coating velocity, this research was designed to improve the understanding and control of these properties. Through advanced statistical design of experiments, correlations between these factors and key coating properties are established. Six machine learning models are trained and evaluated to assess their predictive capabilities for coating properties. The obtained results provide valuable insights into the HVOF coating process and highlight the potential of predictive model-based techniques for accurately predicting such properties. Furthermore, this research offers guidance for selecting an effective machine learning technique in the context of thermal spray technology.

Improved tribological and electrochemical behavior of concentrated chromite coatings developed by HVOF and plasma spray techniques

Mineral coatings have the ability to tackle the most common degradation processes (wear and corrosion) in industries at amazing ‘quality to cost’ ratio, as compared to synthetic ceramics. In the current study, concentrated natural chromite with 55 wt.% Chromium oxide (Cr2O3) is deposited on steel substrate through High Velocity Oxygen Fuel (HVOF) and Atmospheric plasma spray (APS) techniques. Effect of deposition processes and Cr2O3 enrichment on microstructure, hardness, tribological and electrochemical behavior of coatings is studied. Tribological tests were performed using pin-on-disc setup, coatings deposited with APS have shown excellent wear resistance behavior as compared to HVOF coating. Owing to the brittle nature of chromite coatings, they were worn by abrasive wear irrespective of the deposition process. Electrochemical behavior of coatings is evaluated by potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. APS and HVOF coatings have exhibited very high protective efficiency of 93 and 88% respectively, against steel substrate. Equivalent electrical circuit (EEC) based on EIS results has also been conceptualized and verified with ZSimpWin analysis software. Established EEC has illustrated capacitive behavior due to the protective oxide nature of coatings. Despite having relatively higher porosities in APS coatings, they display an excellent potential for wear and corrosion resistant applications. Results revealed that hardness, compactness, tribological and corrosion performance of chromite coatings have been substantially improved due to higher Cr2O3 content.

Thermally sprayed multi-principal element Cr40Co40Ni20 coatings – Oxidation upon coatings' build-up and electrochemical corrosion

Thermally sprayed Cr40Co40Ni20 coatings were produced by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF). The phases formed upon coatings' build-up were sensitive to oxidation at high temperatures, leading to the formation of various oxygen-rich compounds such as chromia and spinel. Chromia tended to be formed at the inner layer, in contact with the metal, and the spinel forming the outer layer. HVAF coatings suffered much less oxidation compared to the HVOF coatings. The pronounced Cr-depletion at the metallic and oxygen compounds caused by formation of spinel and oxide upon deposition of coatings created regions susceptible to readily corrode in chloride-rich electrolyte.

Nb and Mo Influencing the High-Temperature Wear Behavior of HVOF-Sprayed High-Entropy Alloy Coatings

To qualify high-entropy alloys (HEAs) as resource-saving and high-temperature wear-resistant coating materials, high-velocity oxygen fuel (HVOF) coatings produced from the inert gas-atomized powder of Al0.3CrFeCoNi, Al0.3CrFeCoNiNb0.5 and Al0.3CrFeCoNiMo0.75 were investigated in reciprocating wear tests at temperatures at 25, 500, 700 and 900 °C. In addition to the high-temperature wear tests, the microstructure and chemical composition of the three HEAs were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). In particular, HVOF coatings are characterized by high hardness (Vickers hardness HV0.1) and low porosity, which were also determined. After high-temperature wear tests, the wear depth was measured using laser scanning microscopy (LSM). It was found that adding Nb and Mo to Al0.3CrFeCoNi significantly reduces the wear depth with increasing temperature. The wear mechanisms change from abrasive wear and delamination (25 °C and 500 °C) to a combination of (abrasion), delamination, adhesion and oxidative wear. Thereby, oxidative wear will be the primary mechanism at 900 °C for all the HVOF coatings investigated. The most important finding is that the adhesion of the oxide layer formed is improved by adding Nb and Mo, resulting in significantly reduced wear depth at 900 °C.

High-velocity air fuel coatings for steel for erosion-resistant applications

High-velocity air fuel (HVAF) coating processes have advantages over conventional high-velocity oxygen fuel (HVOF) processes, resulting in coatings with superior properties. The present review first provides a concise overview of HVAF coatings, highlighting their advantages over HVOF coatings. Then, the fundamentals of solid particle, slurry, and cavitation erosion are briefly introduced. Finally, the performance of HVAF coatings for erosion-resistant applications is discussed in detail. The emerging research consistently reports HVAF-coatings having higher erosion resistance than HVOF-coatings, which is attributed to their elevated hardness and density and improved microstructural features that inhibit the surface damages caused by erosion. The dominant wear mechanisms are mainly functions of particle impact angle. For instance, the removal of the binder phase at high impact angles causes the accumulation of plastic strain on hard particles (e.g., WC particles) in the matrix, forming micro-cracks between the hard particles and the matrix, eventually decreasing the erosion resistance of HVAF coatings. The binder phase of HVAF-coatings significantly affects erosion resistance, primarily due to their inherent mechanical properties and bearing capacity of hard particles. Optimizing spraying parameters to tailor the microstructural characteristics of these coatings appears to be the key to enhancing their erosion resistance. The relationship between microstructural features and erosion mechanisms needs to be clarified to process coatings with tailored microstructural features for erosion-resistant applications.

Microstructural Properties and Wear Resistance of Fe-Cr-Co-Ni-Mo-Based High Entropy Alloy Coatings Deposited with Different Coating Techniques

Materials can be subjected to severe wear and corrosion due to high temperature, high pressure and mechanical loads when used in components for the production of geothermal power. In an effort to increase the lifetime of these components and thus decrease cost due to maintenance High-Entropy Alloy Coatings (HEACs) were developed with different coating techniques for anti-wear properties. The microstructure, mechanical and tribological properties of CoCrFeNiMox (at% x = 20, 27) HEACs deposited by three different technologies—high-velocity oxygen fuel (HVOF), laser cladding (LC) and electro-spark deposition (ESD)—are presented in this study. The relationship between surface morphology and microstructural properties of the as-deposited coatings and their friction and wear behavior is assessed to evaluate their candidacy as coatings for the geothermal environment. The wear rates were lower for the HVOF coatings compared to LC and ESD-produced coatings. Similarly, a higher hardness (445 ± 51 HV) was observed for the HVOF HEACs. The mixed FCC, BCC structure and the extent of σ + µ nano precipitates are considered responsible for the increased hardness and improved tribological performance of the HEACs. The findings from the study are valuable for the development of wear-resistant HEAC for geothermal energy industry applications where high wear is encountered.

Electrochemical Corrosion Behavior of Heat-Treated HVOF Coatings on ASTM SA213-T22 Steel

Herein the electrochemical corrosion behavior of pre- and post-heat-treated composite coatings of NiCrMoFeCoAl-30%SiO2 and NiCrMoFeCoAl-30%Cr2O3 on ASTM SA213-T22 boiler tube steel by a high-velocity oxygen fuel (HVOF) spraying technique are reported. The samples were subjected to hot molten salt (Na2SO4–60%V2O5) corrosion environment in a tubular furnace at 700°C under thermocyclic conditions. The microscopic, structural, and electrochemical investigations of post-heat-treated specimens reveal NiCrMoFeCoAl-30%Cr2O3 composite HVOF coating exhibits a superior corrosion resistance compared to NiCrMoFeCoAl-30%SiO2 composite coating and bare ASTM SA213-T22 steel boiler tube steel in neutral electrolyte. The room-temperature potentiodynamic and impedance investigations of heat-treated samples suggest high interfacial charge transfer resistance for HVOF coatings over a wide anodic potential window. This could be ascribed to the protective nature of the chromium-oxide-containing coatings on high-temperature treatment. AC impedance analysis reveals NiCrMoFeCoAl-30%Cr2O3 coating exhibits very high resistive behavior with very high charge transfer resistance, in the order of 106 Ω higher than the NiCrMoFeCoAl-30%SiO2 coating and uncoated ASTM SA213-T22 steel boiler tube steel. Furthermore, the high-temperature-induced formation of metal chromates/chromites along with the presence of Cr2O3 provides good resistance toward corrosion.

Wear performance analysis and characterization of HVOF deposited Ni–20Cr2O3, Ni–30Al2O3, and Al2O3–13TiO2 coatings

The present study was aimed to analyze a slurry erosion failure of SS316L steel coated with high-velocity oxygen-fuel coatings using Ni–20Cr2O3, Ni–30Al2O3, and Al2O3–13TiO2. Slurry erosion experiments were performed using a pot erosion tester for the time duration of 90–180 min at different velocities. The sand particles were used as an erodent to study the erosion wear phenomenon. The concentration of the two-phase slurry was kept in the range of 30–60 wt%. It was seen from the results that speed of rotation, concentration (wt%), and time duration play a vital role in the erosion wear rate of the coated and uncoated AISI 316L. Except for the impingement angle, an increase in the value of all parameters increases the deterioration of parent material with and without coatings. The deterioration rate of the parent material was improved by using coatings. Erosion performance of the AISI 316L was improved by an average of 43.06%, 23.55%, and 13.73% respectively with the deposition of Ni–20Cr2O3, Ni–30Al2O3, and Al2O3–13TiO2 HVOF coatings while all the parameters were varied from lowest to the highest value. Microscopically, the microcutting, smear regions, debonding, lip formation, fracturing, and cracks wear mechanisms occur in Ni–20Cr2O3 HVOF coating. The Ni–30Al2O3 HVOF coating underwent debonding, crater, microcutting, fracturing, ploughing, and lip formation. The major wear mechanisms in Al2O3–13TiO2 coatings are identified as smear, crater, pitting, microcutting, debonding, fracturing, cracks, ploughing, and lip formation.

High-temperature tribological property of Fe-based amorphous alloy coating

Two kinds of Fe-based amorphous alloy coatings were fabricated by high velocity oxygen fuel (HVOF) spraying and cold spraying (CS). Microstructure, amorphous content, hardness, and high-temperature (below the glass transition temperature) tribological performance were investigated. Results show that the Fe-based amorphous coatings prepared by CS have a high hardness and a low wear rate at room temperature. At 673 K, the oxide layer grew, broke, and peel off periodically, resulting in a high wear rate. Moreover, the high-temperature wear mechanism was fatigue, adhesive, and oxidative wear. Meanwhile, the different crystallization and oxidation behavior of CS and HVOF coatings resulting in the different wear rates at 673 K.

Comparative study on dry sliding wear and oxidation performance of HVOF and laser re-melted Al0.2CrFeNi(Co,Cu) alloys

Al0.2CrFeNiCo and Al0.2CrFeNiCu high entropy alloys were deposited with high velocity oxygen fuel (HVOF) on 316L substrate. Later, a laser re-melting (LR) process was applied to enhancing the coating microstructure. LR process effects on dry sliding wear and oxidation behaviors were investigated. The mixture of powders with free elements led to the formation of inner oxides in HVOF coatings. The oxide and porosity were eliminated using LR. After LR, FCC was the dominant phase in both alloys, while BCC, sigma and Cr2O3 phases were observed in Al0.2CrFeNiCo alloy. The hardnesses of the Al0.2CrFeNiCo and Al0.2CrFeNiCu coatings after HVOF were HV 591 and HV 361, respectively. After LR, the hardnesses decreased to HV 259 and HV 270, respectively. Although HVOF coatings were most affected by increased load, they showed the highest wear resistance compared to other samples. The lowest wear resistance could be seen in the substrate. After the oxidation tests, HVOF coating layer was completely oxidized and also, the coating layer was delaminated from the substrate after 50 h oxidation due to its porous structure. LR coatings exhibited better oxidation performance. Al0.2CrFeNiCo was dominantly composed of Cr2O3, exhibiting a slower-growing tendency at the end of the oxidation tests, while Al0.2CrFeNiCu was composed of spinel phases.

Corrosion and mechanical performance of HVOF WC-based coatings with alloyed nickel binder for use in marine hydraulic applications

Hydraulic components used in the maritime environment suffer damage due to the effects of corrosion and marine biofouling accumulation. The application of engineered coatings can overcome these problems. This study investigated the corrosion and mechanical performance of novel high velocity oxygen fuel (HVOF) sprayed ceramic-metal composite coatings; i.e., WC-18 wt% Hastelloy C and WC-10 wt% Ni-5 wt% Cr, designed for the protection of marine hydraulic components. A conventional atmospheric plasma sprayed (APS) ceramic coating (i.e., Al2O3-40 wt% TiO2) and uncoated Monel K500 substrate were tested for benchmarking purposes. The corrosion performance of the samples was assessed using a combination of laboratory-based tests (i.e., electrochemical polarization, neutral salt spray, hot water immersion) and field exposure tests by immersion in seawater. The mechanical properties of the samples were assessed via a drop-weight impact test and the tensile adhesion test. The results showed that the HVOF coatings exhibited better corrosion resistance and mechanical performance compared to the baseline APS ceramic coating and uncoated Monel K500 substrate.

Wear behaviors of HVOF-sprayed NiSiCrFeB, WC-Co/NiSiCrFeB and WC-Co coatings evaluated using a pin-on-disc tester with C45 steel pins

This research aimed to study the mechanical properties and wear behaviors of high velocity oxygen fuel (HVOF) sprayed NiSiCrFeB, WC-Co/NiSiCrFeB and WC-Co coatings on AISI 1095 steel for some interesting applications, in which coatings would be subjected to cumulative wear due to repeated contact against relatively soft sliding steel parts. According to hardness and roughness measurements, the NiSiCrFeB coating displayed the lowest average hardness of 670 H V while the WC-Co coating exhibited the highest hardness of 1,350 H V when the surface roughness value tended to be inversely related to the hardness value of these coatings. The wear performances of HVOF coatings were evaluated using a pin-on-disc method with C45 steel counter pins having a moderate hardness of 745 H V. From the wear test results, the mean friction coefficients of WC-Co/NiSiCrFeB and WC-Co coatings tested for 60 min were similarly lower than that of NiSiCrFeB coating. The mean wear rates of NiSiCrFeB coatings were relatively high compared with the other two coatings while the wear rates of WC-Co/NiSiCrFeB and WC-Co coatings were not significantly different. Therefore, WC-Co/NiSiCrFeB and WC-Co coatings were more appropriate for moderately hard counter work materials such as medium to high carbon steels than NiSiCrFeB coating. Related wear mechanisms were analyzed and discussed.

Effect of Coating Thickness on Fatigue Behavior of AISI 1045 Steel with HVOF Thermal Spray and Hard Chrome Electroplating

The effects of coating thickness on the fatigue lives of AISI 1045 steel shaft-bending specimens with WC-10%Co-4%Cr high-velocity oxygen fuel (HVOF) coatings and hard chrome electroplated coatings under cyclic loading conditions are investigated. Residual stress distributions of the HVOF-coated layer and the hard chrome-plated layer were measured. During cyclic fatigue testing, cracks are initiated near the interface between the HVOF coating and the steel substrate and propagate through the substrate to cause final fracture based on experimental results. For the specimens with hard chrome-plated coatings, the fatigue crack is initiated near the top of the coating, propagates through the coating, and then grows in the thickness direction of the steel substrate to cause final fracture. As the coating thickness of the HVOF-coated specimens increases, the fatigue strength of the specimens increases, which can be attributed to the fact that the magnitude of the compressive residual stress near the interface between the substrates and the HVOF coatings is higher when the coating thickness gets higher. As for the hard chrome-plated specimens, the fatigue strength is deteriorated when the coating thickness is increased. The microcrack density in the hard chrome coatings increases with the coating thickness and, therefore, may result in the decreased fatigue strength.

Alternative metallic matrices for WC-based HVOF coatings

Thermal spray coatings based on WC-CoCr are widely employed to protect industrial components against wear and corrosion. Although they provide good technical performances, it is necessary to replace Co-based hardmetal compositions to protect human health as well as for economic reasons. Alternative hardmetal formulations with little or no Cobalt were deposited by High Velocity Oxygen-Fuel (HVOF) spraying using agglomerated and sintered feedstock powders. They consist of WC as hard phase, but metallic matrices include iron- and nickel-based alloys (WC-NiMoCrFeCo, WC-FeNiCrMoCu, WC-FeCrAl). The characterization is focused on microstructure, mechanical and tribological properties (sliding and abrasive wear behaviour) and corrosion resistance in 3.5% NaCl. Very low porosity, limited carbides' dissolution in the matrix, deposition efficiency ≥50%, and hardness values (≈1200 HV) comparable to conventional WC-CoCr mean that the studied coatings are viable for industrial applications. Both WC-NiMoCrFeCo and WC-FeNiCrMoCu coatings show intrinsically high sliding wear resistance (specific wear rates between 10−8 and 10−7 mm3/(N∙m) in a ball-on-disc test against Al2O3 counterpart), but they are less resistant to high-stress abrasion by coarse particles (wear rates ≈10−3 mm3/(N∙m)). Their performances are anyway comparable to those of reference WC-CoCr samples. Additionally, WC-NiMoCrFeCo coatings show even better corrosion resistance in a 3.5% NaCl aqueous solution (ICorr ~ 10−6 A/cm2). WC-FeCrAl coatings exhibit slightly poorer performances than the other samples: the formation of Al-based oxide inclusions during spraying cause higher wear losses, whilst the FeCrAl matrix has limited corrosion resistance.

Alleviation of thermal corrosion caused by molten ash on heat-exchange tubes in MSW incinerators: Effects of Ni-, Co-, Fe-based HVOF coatings

Thermal corrosion on heat-exchange tubes had an adverse effect on the economical and safe operation of municipal solid waste (MSW) incinerators. In order to alleviate the corrosion caused by molten ash, high velocity oxygen fuel (HVOF) thermal spraying technology was considered for its ability of enhancing corrosion resistance. In this study, 10 typical Ni-, Co-, Fe-based coatings were employed to find the relationship between material composition and high temperature corrosion resistance. The MSW incineration ash adhesion tests at 873 K were performed to specially simulate the corrosion caused by molten ash on tubes. Besides, mass gain measurements under the exposure of Na/K chlorides and sulfates were also performed to assess the failure of tubes. From experimental results, the strong positive correlation between MSW incineration ash adhesion force and mass gain rate proved the feasibility of using the former as an in-furnace corrosion indicator. Fe-based coatings with Fe accounting for up to 80 wt.%, rather than common coatings with Fe content of ca.50 wt.%, had better performance against thermal corrosion. For Ni/Co-based coatings, the optimal content of ternary components, including body metal (Ni/Co), eutectic metal (Cr) and the other strengthening elements (Mo+W+Si+B, et al.), seemed to be 60–20–20 wt.%. The mutual allocation of three kinds of elements, rather than the content of one specific element, affected its MSW incineration ash adhesion tendency. The microstructure characterization indicated the prevented permeation of corrosive species containing Na, K, S, Cl by the presence of strengthening elements such as Mo. Further comparison of NiCr and NiCrMo coatings explored the effect of Mo reinforcing the coating microstructure free from cracking, besides the widely known effect of forming protective oxidation film. This investigation provided insight for the corrosion resistance in MSW incinerators of harsh operating conditions.

Structural behavior and mechanical properties of high-entropy coatings synthesized by HVOF

This paper discusses the technology, structure and functional–mechanical properties of surface layers made of high-entropy materials with a high-temperature shape memory effect, nickel (Ni)–cobalt (Co)–titanium (Ti)–zirconium (Zr)–hafnium (Hf), nickel–copper (Cu)–titanium–zirconium–hafnium and titanium–nickel–zirconium–hafnium–cobalt–copper. The developed technology and equipment for the formation of high-entropy coatings on the surface of steel products included mechanical activation of powders, high-velocity oxygen fuel (HVOF) spraying in a protective atmosphere and subsequent thermal and thermomechanical treatment. This allowed carrying out this process in a single technological cycle. The authors have developed statistical models of the formation process of highly entropic HVOF coatings in a protective atmosphere according to the criteria of adhesive strength and porosity with optimization of parameters. Based on complex X-ray diffraction and electron microscopy studies, the authors determined the structural parameters of high-entropy alloy coatings obtained by HVOF, followed by thermal and thermomechanical treatment. It was shown that all three alloys, nickel–cobalt–titanium–zirconium–hafnium, nickel–copper–titanium–zirconium–hafnium and titanium–nickel–zirconium–hafnium–cobalt–copper, which make up the surface compositions, are in an austenitic–martensitic state with a grain size of 32–120 nm. The authors performed calorimetric studies of the functional properties of the coatings. The studies showed the manifestation of austenitic–martensitic transformations. The authors also carried out tests for ‘friction wear’ and mechanical multicycle fatigue of the obtained high-entropy compositions on a steel surface.

Evaluation of Residual Stresses and Their Influence on Cavitation Erosion Resistance of High Kinetic HVOF and HVAF-Sprayed WC-CoCr Coatings

Thermal spray processes have been developing toward lower particle temperature and higher velocity. Latest generation high-velocity oxygen-fuel (HVOF) and high-velocity air-fuel (HVAF) can produce very dense coating structures due to the higher kinetic energy typical for these thermal spray processes. Thermally sprayed coatings usually contain residual stresses, which are formed by a superposition of thermal mismatch, quenching and, in case of high kinetic energy technologies, peening stresses. These stresses may have a significant role on the mechanical response and fatigue behavior of the coating. Understanding these effects is mandatory for damage tolerant coating design and wear performance. For instance, wear-resistant WC-CoCr coatings having high compressive stresses show improved cavitation erosion performance. In this study, comparison of residual stresses in coatings sprayed by various thermal spray systems HVOF (Thermico CJS and Oerlikon Metco DJ Hybrid) and HVAF (Kermetico AcuKote) was made. Residual stresses were determined through thickness by utilizing Tsui and Clyne analytical model. The real temperature and deposition stress data were collected in the coating process by in situ technique. That data were used for the model to represent realistic residual stress state of the coating. The cavitation erosion and abrasion wear resistance of the coatings were tested, and relationships between residual stresses and wear resistance were discussed.

ANN and RSM models approach for optimization of HVOF coating

High-Velocity Oxygen Fuel (HVOF) coating process is employed in many industries, not only for extending the life of the material, but also to improve or restore the dimensions/surface properties of the component, by spraying molten or semi-molten powder materials over the surface of the component. Porosity and Hardness are the significant properties required to assess the quality of coatings. In this research, response surface methodology (RSM) and artificial neural network (ANN) are used for optimizing the powder composition to obtain the desired response. Based on the mixture design, twenty-five HVOF coatings were performed and the data were used for training and testing the ANN. The composition of five powders, Chromium Carbide (Cr3C2), Nickel (Ni), Chromium (Cr), Boron (B) and Silicon (Si) were varied and performed HVOF coating to obtain minimum porosity and maximum hardness to serve in high temperature oxidation environment. Optical Microscope, X-ray diffraction, Scanning electron microscope, and Vickers hardness tester were used to carry out the cross-section analysis on the coated samples. Optimized powder composition was identified to achieve a dense coating. Response value obtained by RSM and ANN models indicate that the values obtained by “ANN Model” exhibit a better prediction over “RSM Model”.

Wear Resistance of Boron-Modified Supermartensitic Stainless Steel Coatings Produced by High-Velocity Oxygen Fuel Process

The wear resistance of boron-modified supermartensitic stainless steel coatings produced by high-velocity oxygen fuel (HVOF) was investigated through pin-on-disk measurements. It was shown that addition of boron leads to the formation of an interconnected and rigid boride network delimiting the grain boundaries of the martensitic matrix. A very refined structure was formed as result of the high cooling rates imposed to the molten alloy during the HVOF process. The specific wear rates of the HVOF coatings were about tenfold lower than the boron-free supermartensitic stainless steel, lying in the order of 10−5 mm3/N m. The refined boride skeleton along the HVOF coating was found to be effective to reduce the materials’ removal from the exposed softer martensitic matrix. While the supermartensitic stainless steel master alloy and the mild steel substrate displayed severe adhesive wear, the HVOF coatings exhibited mild delamination wear at low sliding velocities (10 and 20 cm/s) and abrasive wear at the highest tested velocity (40 cm/s). The studied boron-modified supermartensitic HVOF coatings are an interesting approach to protect the surface of inexpensive steel substrates against wear.