Cavitation is a wear process in engineering systems caused by the energy release of collapsing bubbles leading to the failure of critical components such as valves, pumps, and propellers. Thermally sprayed coatings can be applied to improve the wear resistance of these components. This investigation considers a WC-NiCrBSi coating composition under cavitation wear, where the WC phase provides the strength and the NiCrBSi matrix offers corrosion resistance in seawater. Coatings were deposited on AISI 440C stainless steel discs of 32mm diameter and 8mm thickness using industrially optimized parameters for the HVOF JP5000 system. Indirect cavitation tests were conducted using a modified ASTM G32 testing procedure on coated test coupons in as-sprayed and Hot Isostatic Pressed (HIPed) conditions. Two tests were performed for each coating using natural seawater of pH 8.19 at room temperature, and averaged wear values are reported to compare the cavitation rate and cumulative mass loss of the coatings. Coating microstructural phases in the as-sprayed and HIPed conditions were identified using X-ray diffraction. The microstructure of the coating substrate system and post-cavitation test wear scars were investigated using Scanning Electron Microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). This investigation provides an understanding of the corrosive-cavitation wear behavior and failure modes of coatings. The cavitation erosion rate and cumulative mass loss results showed that the as-sprayed WC-NiCrBSi coatings improve the cavitation wear resistance of the substrate.

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.

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.

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 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.

Thermally sprayed ceramic coatings are used in environments requiring good wear- and corrosion resistance among others. However, a typical issue with ceramic coatings is their low impact resistance and tendency to fail catastrophically by cracking. In bulk ceramics, the Al 2 O 3 -ZrO 2 –composition has been of interest for long since already small additions of ZrO 2 into Al 2 O 3 have shown improvements in fracture toughness compared to pure Al 2 O 3 . Efforts are being made to induce this increased resistance to fracturing in thermally sprayed coatings as well, resulting in higher wear resistance due to a more predictable behavior and damage-tolerance. In this work, Al 2 O 3 -ZrO 2 -coatings have been deposited by atmospheric plasma spray (APS) and high-velocity oxy-fuel spray (HVOF) processes. The wear characteristics of the coatings were evaluated with cavitation erosion, delving into the mechanics of the erosion and the resulting microstructural changes in the coatings. Evidence of phase transformation of t-ZrO 2 to m-ZrO 2 was found during the erosion. The HVOF-sprayed coating exhibited greater wear resistance against the cavitating bubbles due to its finer microstructure.

This study assesses the erosion resistance of WC-CoCr coatings produced from multimodal and conventional powders. The feedstocks were sprayed with a high-velocity oxyfuel (HVOF) torch using propane and kerosene as the fuels. Powder morphology and coating structures were analyzed by OM, SEM, and XRD. Coating properties including porosity, hardness, and fracture toughness were measured and erosion resistance was determined by dry sand blasting. The mechanical properties of WC-CoCr coatings deposited using kerosene are shown to be superior to those sprayed with propane. Multimodal WC-CoCr coatings deposited using kerosene had the highest microhardness and fracture toughness, the lowest porosity, and the greatest resistance to solid particle erosion wear.

The mist cooling technique was developed and applied to various thermal spraying guns. For example, aluminum-magnesium coatings prepared using a gas flame thermal spraying gun with mist cooling had superior anticorrosion characteristics. Stellite coating thermally sprayed with mist cooling had higher anti-cavitation-erosion characteristics. Next, we endeavored to develop high velocity oxygen fuel guns with mist gas cooling to improve high-temperature toughness.

Sprayed deposits using conventional wire and powder materials open a wide range of possibilities to solve wear problems in engineering equipment. The option for new different spray technologies and consumables like nanostructured powder materials and nanocomposite cored wires has expanded the engineering possibilities. Cored wire technology allows the use of compositions that cannot be drawn into wire form like carbides in metallic matrix and high-temperature materials, thus intensifying the use of low operating cost welding and spraying processes to demanding wear applications. The objective of this work was to compare the mechanical characteristics and erosive wear performance of coatings obtained by Flame Spray and High Velocity Oxygen Fuel Spray using some selected powder and flexi-cord wire materials. The wear resistance of the coatings was determinate by slurry erosion wear test.

The present study investigates the microstructure and properties of cold spray coatings produced from gas-atomized CuAl10Fe5Ni5 powders. To obtain information relevant to ship rudder cavitation-erosion performance, GL-A shipbuilding steel, equivalent to S235, was chosen as the substrate material. Thick Cu-Al-bronze coatings were deposited on grit-blasted plates using a wide range of parameter sets with different powder treatments, nozzle geometries, gas and substrate temperatures, and particle impact conditions. Coating samples were examined via SEM and XRD analysis, cavitation tests were performed, and bond strengths were measured. Powder and single impact morphologies were also investigated and, along with coating properties and structures, are correlated with spraying conditions. The results indicate that cold sprayed bronze coatings have good potential for ship rudder protection.

This work demonstrates a new single-cathode, multi-anode plasma spray process and compares it with conventional APS and HVOF spraying. Alumina feedstock powders mixed with 13, 40, and 44 wt% titania were deposited under a wide range of spraying conditions following a design of experiments approach. Deposition rate and efficiency were measured and coating characteristics, including microstructure, phase composition, hardness, Young’s modulus, electrical resistivity, and cavitation wear, are compared. The results are presented and the advantages of each process are discussed.

Solid-particle erosion of metals and alloys at elevated temperatures is one of the main reasons of the damage of components used in the energy production and utilization industries. Application of protective coating systems can be an attractive and economically reasonable solution for preventing the failure and increasing the durability of the components working in severe conditions of high-temperature corrosion and erosion. However, thermal spraying of intermetallic materials that have excellent high-temperature corrosion resistance is limited because of their low ductility. Present work reports the results of the investigation of abrasion wear resistance at elevated temperatures of combined coatings, which include the intermetallic layer. Such iron aluminide layers have been formed as a result of diffusion during the heat post-treatment of arc-prayed metallic coatings combining Fe- and Al-based layers. Post-treatment of arc-sprayed coatings was carried out by means of infrared radiation and induction heating. It was shown that the abrasion resistance of the developed coating tested at elevated temperatures (T > 500 °C) is considerably higher than that of low-alloyed steel and some nickel-based alloys and depends on the test load condition. The high performance of intermetallic-based graded coatings at elevated temperatures makes them interesting for applications as a low-cost erosion-corrosion-resistant material.

Cavitation erosion frequently occurs in hydraulic components such as turbines, valves, pumps, and ship propellers. Arc thermal spray processing has the possibility to be used for maintenance recovering of hydraulic blade runners. Fe-Cr-Mn-Si is a cavitation-resistant class of steel with a high concentration of oxidation elements—which can be important for arc thermally sprayed coatings—and a strain-induced phase transformation. The influence of chemical composition on oxide formation, microstructure, and cavitation resistance of Fe- Mn-Cr-Si thermally sprayed coatings was studied, and its field performance in a Francis type runner was evaluated. Microstructures and properties were investigated by XPS, XRD, optical microscopy, and ultrasonic cavitation testing. The best cavitation resistance was obtained in Fe-Mn-Cr-Si alloy with a nickel addition; this composition has lower oxide and splash droplets content and exhibits better splat wetting than Fe-Mn-Cr-Si without nickel. Strain-induced phase transformation occurred in arc thermally sprayed coatings during cavitation tests. Better performances for Fe-Mn-Cr-Si alloys, without nickel, were obtained in alloys with higher strain induced martensite contents after cavitation tests. In field tests, after 2000 operation hours, it was verified that the recovered areas presented only a small number of eroded areas, and cavitation erosion was reduced compared with uncoated areas.

This work demonstrates the capabilities of oxide dispersion strengthened MCrAlY coatings and the process used to produce the feedstock powders. Mechanically alloyed powder mixtures were prepared in a high-energy ball mill using commercial NiCoCrAlY and YPSZ powders combined in different amounts. A high-velocity oxyfuel torch was used to deposit the powders on Inconel substrates that were then heat treated for 6 h at 1050 °C. Samples were also produced from unaltered NiCoCrAlY powder to serve as a reference. In high-temperature erosion tests, the strengthened coatings had a mass loss of 47 mg/cm 2 after 30 sec compared to 38 mg/cm 2 for the unstrengthened sample. High-temperature corrosion tests showed that the strengthened coatings were not dense enough to protect the substrate from oxidation. The hard phases inhibited sintering and diffusion effects during heat treatment. As a result, dislocations, defects, and voids could not move and were used by oxygen for diffusion. In further investigations, the strengthened coatings will be treated at a higher temperature to achieve a better sintering effect.

Iron aluminides have been lately proposed as promising materials for wear applications. Many authors have focused their investigations on the friction behaviour of FeAl coatings emphasizing the role of this intermetallic as a new matrix to embed ceramic particles and replace for high temperature the extensively studied WC-Co cermet system. However, few works deal with the evaluation of the different tribological properties and their relationship with the coating microstructure. Thus, in the present study, the near stoichometric Fe40Al was successfully sprayed by means of HVOF using different spraying parameters and the tribological behaviour was assessed through solid particle erosion, abrasive and dry sliding tests. The wear mechanisms that took place in the produced coatings are discussed with regard to the obtained results. The friction coefficient versus sliding distance was obtained. In addition, isothermally treated samples in air were tested showing both lower friction coefficient and lower wear rate.

High velocity oxy-fuel (HVOF) sprayed cermet coatings are required in various industrial fields due to their excellent properties, such as combination of wear resistance, corrosion resistance, high hardness, high bonding strength and stability under high temperature. In order to utilize them in the fields, optimization of composition and structure of the coatings are essentially important meaning that both spray powders and spray conditions are key process parameters. In this paper, developed spray powders of cermet materials are introduced for the specific applications, where 1. cavitation erosion, 2. mechanical impact, 3. corrosion by molten alloy and 4. general abrasive wear are major factors that damage the coatings. In order to solve these factors, HVOF coatings of 1. WC/Co/Cr with large WC particle, 2. WC/Cr 3 C 2 /Ni with addition of metal or alloy, 3. MoB/CoCr composed of double boride and 4. WC particle size in WC based cermet, are proposed and these merits are described.

The cavitation erosion result mass loss. Welding is the most common technique used to recover the geometrical profile of the blades. However it is known that tensile residual stress can develop. The search for manufacture process that could reduce or eliminate the residual stress level will contribute for a longer life service. The target in this study to evaluate the potential of ASP thermal spray to recover surfaces. The influence of processing parameters on the cavitation resistance and mechanisms was evaluated for three alloys, AWS309LT1, AWS410NiMo and a Co stainless steel known as Cavitec. Coatings were analyzed by optical and electronic microscopy, microhardness and cavitation tests regarding the effect of air pressure. The results showed that lamellae morphology, oxide volume fraction and cavitation resistance were modified by the ASP parameters. The increase in the pressure modified the oxide fraction from 26 to 37% in AWSI309LT1, 23 to 31% for AWS410NiMo and 16 to 23% for Cavitec. Mass loss varied from 3.5 to 4.8 mg/h for AWSI309LT1, 6.65 to 18.19 mg/h for AWS410NiMo, and 3.4 to 4.0 mg/h for Cavitec; the best performance occurred with Cavitec and was associated with higher pressure of deposition and minor oxide volume fraction.