This paper evaluates the cavitation erosion wear rate and failure modes of WC-10Co-4Cr coatings. These coatings are used in various industrial applications to protect against erosive, abrasive, sliding and cavitation wear in corrosive environments. Cavitation erosion tests were performed using a modified ASTM G-32 cavitation test rig. Thermally sprayed High Velocity Oxy-Fuel (HVOF) WC-Co-Cr coatings were deposited using industrially optimised coating process parameters on carbon steel and stainless-steel substrate coupons. Coatings were tested to simulate the cavitation bubbles occurring in valves, pumps, and ship propellers. Indirect cavitation was used to impact the cavitation bubbles on the test specimen at a fixed offset distance from the vibrator end. Test specimens were immersed in natural seawater. A water circulation cooling system was used to control the temperature of the water. The cumulative mass cavitation erosion and erosion rate results were evaluated. The coating microstructure was analysed using Scanning Electron Microscopy (SEM) and x-ray diffraction. Post-test evaluations included SEM observation in combination with energy dispersive x-ray analysis (EDX) to understand the failure modes. Results are discussed in terms of the factors controlling the cavitation erosion rate.

Iron-based coatings are often considered as replacement of hard chromium and WC-Co, as they pose lower health and environmental impact. In many cases the combination of mechanical and chemical properties of ferrous based alloys may be satisfactory and their relatively low cost make these coatings an interesting candidate for many applications. This study is inspired by opportunities to harden the ferrous base materials by strain hardening, solid solution strengthening, dispersion strengthening, and precipitation hardening. Already commercially available Fe-based coating materials with precipitates of mixed carbides and borides in the metastable austenitic matrix achieve a high hardness. In this study the cavitation erosion and abrasion resistance of various Fe-based coatings produced by HVAF and HVOF processes were investigated. Two experimental precipitation containing materials were prepared, and the sprayed coatings were tested for abrasive and cavitation erosion wear. In addition to precipitations, the importance of proportion of ferrite and retained austenite phases were studied by affecting the microstructure by heat treatments as the ability of different phases to affect hardening and ductility may become crucial in generating desired material properties. The properties of experimental and some commercial Fe-based alloys are compared with WC-Co and Cr 3 C 2 -NiCr coatings by property mapping.

This study investigates the solid particle erosion performance of cold sprayed tungsten carbide-nickel coatings using alumina particles as erodent material. After coating fabrication, specimens were annealed in an electric furnace at a temperature of 600 °C for 1 hour. The coatings were examined in terms of microhardness and microstructure in the as-sprayed (AS) and annealed (AN) conditions. Subsequently, the erosion tests were carried out using a General Full Factorial Design with two control factors and two replicates for each experimental run. The effect of the annealing on the erosion behavior of the coating was investigated at the two levels (AS and AN conditions), along with the impact angle of the erodents at three levels (30°, 60°, 90°). Finally, two regression models that relate the impact angle to the mass loss were separately obtained for the two cold spray coatings.

This work provides a new in-situ measurement method for the analysis of the spray-spot geometry and the thermal properties of the coating. The new approach is based on infrared detection of the thermal radiation from the coating surface combined with a subsequent automated spray-spot characterization. With this method it is possible to describe the geometry, the axis-position of the torch, the powder injection properties, and the temperature distribution in of the spray-spot. Especially for the automated production in high quantity the spray-spot analysis is a useful assistance for the operator because the detector reacts very sensitive on small changes of the process conditions. With regard on important fields of application (e.g., gas turbine production) the sensor is suitable to detect drifting spray system parameters. Also, the progression of wear at the nozzle, injector and electrode can easily be estimated. In recent research the in-situ spray spot analysis is being developed further for the characterization of multipair electrode plasma generators.

In this work, a novel liquid fuel HVOF process fueled with ethanol was used to prepare 75wt%Cr 3 C 2 –25wt%NiCr coatings on AISI304 stainless steel substrate. Taguchi method was employed to optimize the spray parameters (ethanol flow rate, oxygen flow rate, powder feed rate and standoff distance) to achieve better erosion resistance at 90° impact angle. The results indicated that ethanol flow rate and oxygen flow rate were identified as the highly contributing parameters on the erosion wear loss. The important sequence of the spray parameter is ethanol flow rate > oxygen flow rate > standoff distance > powder feed rate. The optimal spray parameter (OSP) for minimum erosion wear loss was obtained under ethanol flow rate of 28slph, oxygen flow rate of 420slpm, powder feed rate of 76.7 g/min and standoff distance of 300mm. The phase composition, microstructure, hardness, porosities, and the erosion wear behaviors of the coatings have been studied in detail. Besides, erosion wear testing of the optimized coating was conducted at 30°, 60° and 90° impact angle using air jet erosion testing machine. The SEM images of the erodent samples were taken to analyze the erosion mechanism.

Manufacturing of steel components is often done at high temperatures (HT) posing a serious challenge to components such as forming tools. Thermal spray coatings provide a cost-effective solution for surface protection under HT, corrosive environments and severe wear conditions. Thermally sprayed coatings based on cubic hard materials such as TiC and TiCN can provide an alternative to widely used Cr3C2-NiCr. While the latter possess a superb oxidation resistance and wear resistance at HT, they are prone to degradation in the presence of Mn, an element commonly alloyed in many modern steel grades such as TWIP (twinning-induced plasticity steel). In this study, a (Ti,Mo)(C,N)-29% Ni hardmetal feedstock powder was prepared by agglomeration and sintering. Coatings were deposited using a high velocity air-fuel (HVAF) spray process. The coating was benchmarked against a standard Cr3C2-NiCr coating obtained with the same spray process. Our work comprises analyses of the feedstock powder along with the resulting coating microstructure after deposition and heat treatment. Further, the HT sliding behavior against TWIP steel using a HT pin-on-disc tribometer at 700°C was investigated. The results showed a clear benefit of the TiCN-based coating, with almost no wear detected, while the Cr3C2-coating showed a significant wear loss. Based on these results, the TiCN-based coating is regarded as potential solution for prospective forming applications of modern high Mn steels, such as TWIP.

In this investigation, NiTi coatings are applied by atmospheric plasma spraying. Surface and interface morphology of the as-deposited material is studied using scanning electron microscopy, the presence of the different phases are revealed by X-ray diffractometry, and microhardness is determined by Vickers hardness testing. The as-deposited coatings are exposed to air-borne particle erosion to investigate their wear properties while varying erodent impact pressure and angle. It was found that the plasma sprayed NiTi splats are well formed with significant amounts of intermetallic and oxide phases at the surface and interface, contributing to dense splat formation and higher hardness.

This study investigates the synergistic effects of cavitation and corrosion on Cr 3 C 2 -25NiCr coatings with different levels of porosity. The coatings are deposited by HVOF spraying and evaluated based on SEM analysis, Vickers microhardness, potentiodynamic polarization measurements, and cavitation erosion tests in various environments under ultrasonic vibration. The results show that higher porosity reduces both cavitation and corrosion resistance, as expected. However, the samples did not show significant alteration of their cavitation properties in NaCl, probably because of the high corrosion resistance of the different phases in the coating. The influence of HVOF fuel-oxygen ratio and total gas flow on coating porosity, as well as phase morphology, is also discussed.

The current study investigates the influence of the grain size fraction D of a FeCrB/WC-Co feedstock material on the coating properties. In previous studies, novel FeCrB/WC-Co wear and corrosion protection coatings applied by means of high velocity air-fuel (HVAF) spraying were developed by the authors. It was observed that coatings, which were produced with a slightly decreased powder grain size fraction and identical chemical composition showed improved coating properties, i.e. reduced crack formation in the coating at high powder feed rates . and lower current densities at high overpotentials. The goal of this study is to investigate the influence of the powder grain size fraction on the coating properties in more detail. Furthermore, the underlying mechanism for the improved coating properties, with regard to their corrosion behaviour, is investigated. Therefore, the FeCrB/WC-Co feedstock material with the grain size fractions of -20 +3 μm and -32 +11 μm and identical chemical composition was applied by means of HVAF-spraying and the coatings were subsequently analysed. Light microscopy was used to investigate the microstructure of the coatings. The wear and corrosion properties were analysed using pin-on-disc (POD) and electrochemical polarization tests respectively. XRD-measurements were used to investigate the phase composition and to develop a hypothesis for the different corrosion behaviours of the investigated coatings. The results show that HVAF-sprayed FeCrB/WC-Co coatings produced with a powder grain size fraction of -20 +3 μm exhibit lower current densities at high overpotentials, compared to the coatings produced with a powder grain size fraction of -32 +11 μm.

A common method to combat abrasive wear and prolong the life of a component is to hardface the exposed region by overlay welding. State of the art coatings for these applications consist of a nickel-based ductile matrix with hard tungsten carbide particles embedded in it. An alternative with low environmental impact in combination with high performance to cost ratio is to use iron-based alloys. Critical in affecting the abrasive and impact wear resistance of these alloys is the coating quality e.g. porosity, cracks, dilution from the substrate combined with chemistry, size and volume fraction of the hard phase particles formed during solidification. Selection of the process parameters is critical for producing sound clads with expected properties. This paper focuses on the properties of PTA welded and laser cladded M2, M4 and A11 high speed steel coatings. Clad quality, hardness, abrasive wear resistance and microstructure are presented and interpreted with support of thermodynamic simulations.

A known family of rare-earth oxide (REO) ceramics have recently been found to exhibit intrinsic hydrophobicity, even after exposure to high temperatures and abrasive wear. In this study, thin CeO 2 coatings were developed for hydrophobic applications using suspension high velocity oxy-fuel (SHVOF) thermal spray. It is an efficient method to produce large superhydrophobic surfaces with a unique hierarchically textured structure on a variety of substrates. The use of suspension also enables the process of fine-grained powders to form nanostructured coatings with significant improvement of mechanical and chemical properties for numerous applications. An aqueous suspension with a solid concentration of 30 wt.% sub-micron CeO 2 particles (<200 nm) was used as suspension feedstock. The as-sprayed CeO 2 coating on a stainless steel significantly improved the substrate’s surface hydrophobicity from a low contact angle of 57° to nearly 150°. The surface chemistry of SHVOF thermal sprayed CeO 2 coatings was also investigated by X-ray photoelectron spectroscopy (XPS). It was confirmed that the near-super-hydrophobicity was mainly attributed to its unique hierarchically structured surface.

Thermally sprayed Cr 2 O 3 coatings have been shown to provide excellent protection against wear in many engineering applications. These coatings are traditionally applied using air plasma spray technology; however, suspension high velocity oxy fuel thermal spraying (SHVOF) is a promising method to improve coating properties as this technique enables powder feedstocks too small to be processed by mechanical feeders to be sprayed, allowing the production of coatings with improved density and mechanical properties. Furthermore, the addition of graphene nanoplatelets (GNPs) to the liquid feedstock has been shown to improve the mechanical properties of SHVOF sprayed ceramic coatings. In this study, an aqueous based nanometric Cr 2 O 3 suspension and a Cr 2 O 3 suspension with 1 wt.% GNP, prepared via a proprietary process, were sprayed by a SHVOF thermal spray onto 304 stainless steel substrates. The microstructure of Cr 2 O 3 and Cr 2 O 3 + GNP coatings was analyzed using SEM and XRD alongside microhardness, fracture toughness and porosity investigations. Dry sliding wear performance was investigated using a ball on flat tribometer against an alpha alumina ball at loads of 16, 30 and 47 N. The GNP containing coating exhibited improved mechanical properties, however its response to sliding wear was very similar to the non-GNP coating.

The alloys CuAl9Ni5Fe4Mn and CuMn13Al8Fe3Ni2 were arc-sprayed with a spiral-shaped pattern in this work, using both pressurized air and a mixture of nitrogen and hydrogen. Process temperatures were recorded by thermographic imaging and residual stresses were measured by modified hole-drilling method. Moreover, analyses of the cavitation erosion behavior and other properties were carried out. It was found that a change in the spray pattern can strongly reduce residual stresses and material loss by cavitation erosion.

Especially for industrial applications like pumps, mining or off shore industries, where high demands on the abrasive properties of the materials are required, thermal sprayed Fe-based coatings become increasingly important. Novel FeCrMnBC alloys, which have economic and ecological advantages compared to Ni-based or Co-based coatings, are in the focus of this work. In order to produce adequate coatings with a three-cathode plasma torch, different powder fractions (-45+20 μm, -25+10 μm) and varying chemical composition of FeCrMnBC coatings have been investigated and compared with respect to corrosion, abrasion, and erosion properties. In case of wear reduction, selected coatings were additionally subsequent plasma nitrided to study the effect of this treatment on coating morphology and microstructure. The corrosion and tribological behavior were investigated by means of current/density potential curve measurements and ball-on-disc experiments in view of wear morphologies. Erosion-corrosion behavior has been investigated in a pump test rig with 10 wt.-% solid content of corundum in artificial sea water. In general, samples with small powder fractions exhibit accelerated corrosion and decreased erosion behavior, based on their microstructural characteristics. Plasma nitrided coatings show a decrease in corrosion and erosion resistance, which is presumably due to partial formation of chromium carbide in the coatings. Based on the results, the advantages and disadvantages of FeCrMnBC coatings for the application as wear and corrosion protection of complex pump parts are discussed with respect to varied parameters.

A Vickers indentation method has been applied to determine the interfacial fracture toughness of modern multilayer thermal barrier coatings. The delamination behavior of four types of coating systems will be discussed and compared with results based on modified four-point bending (4PB) tests. The investigated multi-layer coating system consists of a CoNiCrAlY-bond coat applied via low-pressure plasma spray (LPPS) on a nickel-based superalloy and an atmospheric-plasma sprayed (APS) top layer of type gadolinium zirconate (GZO) and yttria-stabilized zirconia (YSZ). A conventional YSZ mono-layer system is used for reference. The effects of GZO and YSZ microstructure were investigated using top coats with low and high porosities for both (multi- and single-layer) coating systems. Isothermal oxidation tests at 1100 °C up to 500 hours were performed to study the interaction between thermal aging and fracture behavior. Investigations of microstructure and sintering behavior show a significant influence of the annealing conditions on fracture toughness. It has been observed, that with increasing annealing time, the stiffness and thus the crack driving force of the GZO layer is increased due to sintering effects and healing of submicron defects. The lower stiffness and higher defect density of GZO seem to be the main reason for the reduced fracture toughness of the YSZ / GZO interface compared to the YSZ / CoNiCrAlY interface. As a result, the delamination of the top coat is observed to shift from the top coat / bond coat interface into the top coat double-layer.

Due to good performance in abrasive and sliding wear and enhanced oxidation behavior, coatings based on Co-Cr-W alloys are widely used in industrial applications, where the material is exposed to high temperature. Within the scope of this study, a Co-based alloy similar to commercial Stellite 6, which additionally contains 20.6 wt.% of vanadium, was deposited by Twin Wire Arc Spraying (TWAS). Multi-criteria optimization using statistical design of experiments (DoE) have been carried out in order to produce adequate coatings. The produced coatings have been analyzed with respect to their tribological behavior at elevated temperatures. Dry sliding experiments were performed in the temperature range between 25°C and 750°C. Oxide phases were identified in the investigated temperature range by X-ray diffraction (XRD) using synchrotron radiation. The V-doped Stellite-based coating possesses a reduced coefficient of friction (COF) of about 0.37 at elevated temperatures (above 650°C), which was significant lower when compared to conventional Stellite 6 coating that serves as reference. In contrast, both produced coatings feature a similar COF under room temperature. X-ray diffraction reveals the formation of cobalt vanadate and vanadium oxides above 650°C. The formation of vanadium oxides exhibits the ability of self-lubricating behavior, thus leading to enhanced tribological properties.

An important parameter that affects the protection from wear and tear, is the geometric structure of the abrasive causing the destruction. The equivalent diameter of the particles of the primary influence on protection from wear and tear must be greater than the width of the particle of the crushed abrasive. Here also belongs the requirement for the distribution of the particles inside the matrix was more uniform and dense. The use of solid materials gives this possibility only in the certain circumstances, therefore, it is necessary to use pseudoalloys. Pseudoalloys can be obtained by means of thermomechanical processing of the conventional layers deposited by means of spraying. The particles of the solid material charged with kinetic energy are applied to the heated layers, and they penetrate into inside. Under the influence of the heat energy inside the layers suitable for this, the additional reaction between the substrate and the layer takes place, thus improving the adhesion of the layers. The appropriate regulations were developed, and the reproducible stratification appeared caused by spraying, that is pseudoalloys. A positive consequence of the inclusion of the particles of a solid ceramic material into the spayed layer is the emergence of the current when compressed. The result of the research of the parameters are the optimal performance indexes, optimization criterion served as an indicator of the intensity of the wear. Manufactured pseudoalloys underwent checking in terms of spray wear. The study of spray wear was carried out at the temperatures up to 750 ° C and speed load amounted to 37.5 m/s. The silica sand fractions + 150-212 µm was used as an abrasive. As the covering material the alloys based on aluminum were used. In the places of transition to the substrate the multiphase alloys of the system Fe-Al are formed. It is advisable to use layers with a high iron content to prevent the loose and destruction.

In automotive industry, thermal spray process is used to reduce engine weight by replacing cast iron liners inserted in cylinder bores. Especially, twin wire arc spray is one of widely used thermal spray processes with inexpensive cost and high deposition rate. In this study, two kinds of wire materials, low carbon steel (0.07 wt.%C) and high carbon steel (0.80 wt.%C) were deposited by twin wire arc spray process using two kinds of process gas (i.e., compressed air and nitrogen) in order to elucidate effects of carbon contents of ferrous coating and process gas type on the hardness and wear resistance of coating. In case of hardness, low carbon steel coatings had higher hardness when air was used as process gas whereas high carbon steel coatings had higher hardness when nitrogen was used, which was caused by the counter effects of carbon loss and oxide formation. The results of sliding wear test in lubricated condition indicated that coatings with higher hardness have better wear resistance and oxides improve wear resistance by playing a role as solid lubricant. The main wear mechanism was splat delamination induced by inter-splat crack, and traces of other wear behaviours such as splat tip fracture and abrasive wear were also observed.

Iron-based hardfacing alloys are widely used to counteract abrasive and impact wear of industrial components soil in, sand and mineral processing applications. These alloys show a high performance to cost ratio as well as a low environmental impact. The wear resistance of the components hardfaced with these alloys depends on achieved coating microstructure i.e. on the alloys chemical composition, the coating method and process parameters selected. The present work focuses on iron based hardfacing alloys with varying amount of chromium, vanadium, tungsten, molybdenum, boron and carbon deposited by plasma transferred arc (PTA) overlay welding. Weldability, hardness, abrasive and impact wear of the overlays are presented and interpreted through their microstructure. The performance of the iron based overlays is compared with that of nickel-based metal matrix composite coatings with tungsten carbide (MMC) commonly used for hardfacing of parts subjected to severe abrasive wear. The hardness of the iron based overlays investigated ranges between 60 and 65 HRC while abrasive wear is typically below 20 mm 3 (ASTM G65, procedure A). Microstructure consists of different primary precipitated carbides or borides, a martensitic matrix and eutectic structures.

Boiler tube failure is the number one source of forced outages in all coal-fired and biomass-fired power generation plants. It is estimated that plants lose approximately 6% of their power generation annually, due to boiler tube leaks. The major causes for premature tube failure are excessive fireside boiler tube erosion and corrosion caused by impact, abrasive wear, oxidation and molten corrosion of low eutectic alloys.