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.

This study investigates the influence of plasma spray conditions on the structural, mechanical, and plasma-erosion properties of yttrium oxide coatings. Powder feed rate, plasma power, and primary particle size appear to have little effect on plasma erosion properties, hardness, surface morphology, and coating structure. However, a Y 2 O 3 coating produced with fine powder retained a smooth erosion surface despite its porosity and relatively low hardness.

Escalating operation and maintenance costs and increasing intervals between outages place a heavy burden upon electric power producing components. To meet this demand, component life cycles must be extended with either material upgrades or utilization of surface protection products. This paper will discuss the experiences of the Tennessee Valley Authority in the application of thermal spray coatings and try to relate some of these experiences to component performance in fossil power plants' steam turbine components. The development of high velocity thermal spray processes has given coatings an advantage over the use of high priced material upgrades. Chromium carbide coatings have proven the most economical of the surface protection products for use in high temperature applications where solid particle erosion occurs. These coatings have received extensive laboratory testing where limited field results are now just becoming available. Various thermal spray coatings will be described. The development of newer coatings and laboratory test data will be discussed. Optical microscopy and wear studies will be included in the discussion. Where appropriate and available, comparisons to standard plasma sprayed coatings and uncoated substrata are made.

Iron ore pellets are sintered and reduced in continuous large industrial oil-fired furnaces. From the furnace, large volumes of hot gas are sucked by powerful fans. Being exposed to gas-borne iron particles and temperatures ranging between 125°C and 328°C fan components are rapidly deteriorated. Extensive part repair or replacement are required for maintaining a profitable operation. The arc spraying technique has been suggested for repair provided it could produce erosion resistant coatings. Commercial wires were arc sprayed using various spray parameters to produce thick coatings. Arc-sprayed coatings and reference specimens were erosion tested at 25°C and 330°C and impact angles of 25° and 90° in a laboratory gas-blast erosion rig. This device was designed to impact materials with coarse (32 -300 μm) iron ore particles at a speed of 100 m/s. The volume loss was accurately measured with a laser profilometer. Few arc sprayed coatings exhibited erosion resistance comparable with structural steel at low impact angles. Erosion of arc sprayed coatings and reference specimens dramatically increases at 330°C for both 25° and 90° impact angles. Erosion-enhanced oxidation was found responsible for the increase in wastage above room temperature. Though arc spraying can be appropriate for on-site repair, the development of erosion resistant coatings is required for intermediate temperatures.

Several recently published studies have shown remarkable improvements in dry abrasion resistance and corrosion resistance of aluminum phosphate sealed oxide coatings when compared to unsealed ones. There are numerous applications in chemical industry where a corrosive environment is accompanied with abrasive or erosive particles. In this study the wet abrasion resistance and slurry erosion resistance of aluminum phosphate-sealed and unsealed oxide coatings were studied and compared to their dry abrasion resistance. In wet abrasion tests kaolin and water mixture was used as the abrasive. In slurry erosion tests several abrasives in water with various pH values was used as the erosive medium. The coatings were characterized for microstructure and their wear mechanisms were analyzed using SEM. The results from wear tests are reported and correlated with coating properties. The influence of coating quality to the relative improvement achieved by sealing is presented and discussed.

The elevated temperature erosion resistance of experimental amorphous thermal spray coatings was determined in a laboratory elevated temperature erosion tester. Test conditions attempted to simulate the erosion conditions found at the combustor waterwall tubes in fossil fuel fired boilers. Erosion tests were conducted on four experimental amorphous thermal spray coatings, using the bed ash retrieved from an operating coal fired boiler. An experimental arcspray process was used to spray coatings. These results were compared with erosion test results of two common structural materials, two commercially available arc-sprayed coatings, and a proprietary HVOF coating. Test results indicated that the Duocor coating had the highest erosion resistance among the four experimental coatings, it showed equal resistance to the HVOF coating (DS-200). Compared to AISI 1018 steel, both Duocor and DS-200 coatings reduced material wastage by 26-fold. Other test results indicated that the XJ-16, 60T and Armacor M coatings had equal erosion resistance reducing material wastage approximately 7-fold, while Armacor CW reduced by 10-fold. Only slightly better than the unprotected 1018 steel, the X-20 coating performed poorly on erosion tests. The high erosion resistance of Duocor and DS-200 coatings was attributed to their high densities and fine splat structures.

Slurry-handling equipment and pipelines particularly used in coal processing and mining industries are continuously exposed to the Impact of liquid-borne solid particles, resulting in progressive damage and loss of material. Cost-effective solutions to slurry erosion in aqueous media have been mainly limited to austenitic stainless steels, although coatings have been proposed. This work was aimed at evaluating the slurry erosion resistance of arc-sprayed coatings and determining what improvement IS achieved after laser melting. Multiphase and Type 316 stainless steel arc-sprayed coatings were obtained by arc spraying in air solid and cored wires. The surface of arc-sprayed coatings was melted using a pulsed Nd-YAG laser producing 1.06 µm wavelength radiation. Arc-sprayed and laser-melted coatings were slurry erosion tested at impact angles of 25° and 90° in a laboratory slurry jet erosion device using quartz sand as erodent. The evaluation of wear damage was done with a laser profilometer. Scanning electron microscopy and X-ray diffraction analysis were used to evaluate the microstructural changes which occurred after laser surface melting. Multiphase arc-sprayed coatings were more slurry erosion resistant than Type 316 stainless steel coatings. Improvement in slurry erosion resistance, particularly at the impact angle of 90°, was achieved by laser melting multiphase arc-sprayed coatings. Although deep microstructural changes occurred within coatings upon laser melting, the removal of stringers between sprayed platelets by laser melting was found responsible for the increase in slurry erosion resistance of multiphase laser-melted coatings.

NiCr-Mo composite coating was prepared by plasma spraying of shell-core-structured NiCr-Mo powders. The morphologies of the NiCr-Mo powders and microstructure of the corresponding NiCr-Mo coating were characterized by SEM. Furthermore, the erosion behavior of the NiCr-Mo coating at impact angles of both 30° and 90° was investigated, and was further compared with that of the Ni20Cr coating and the In-738 alloy bulk. Results showed that fully-dense and homogenous NiCr-Mo coating with excellent interface bonding and no pure Mo inclusions was obtained. Furthermore, the erosion test results showed that the erosion rate of the optimized NiCr-Mo coating is lower than that of NiCr coating at both impact angles. Moreover, the NiCr-Mo coating presented excellent erosion resistance which was comparable as that of In-738 alloy bulk, attributing to the fully-dense microstructure and metallurgical interface bonding within coating.

Inter-lamellae bonding within thermal sprayed coatings is one of the most important factors influencing the properties and performance of coatings. It has been revealed that there exists a critical bonding temperature for a molten ceramic splat to form the bonding to the same splat surface. The erosion behaviors of thermal sprayed coatings are significantly influenced by the interface bonding between lamellae. In this study, the erosion behavior of plasma-sprayed TiO 2 , Al 2 O 3 and YSZ coatings deposited at different deposition temperatures was investigated. The cross section of plasma sprayed coatings was characterized by the scanning electron microscope. It was revealed that the coatings deposited at room temperature exhibit a typical lamellar structure with numerous unbonded interfaces, whereas the coatings prepared at the temperature above the critical bonding temperature present a dense structure with well bonded lamellae. The erosion rate significantly decreases with the improvement of interface bonding. In addition, the erosion mechanisms of the conventional coatings and the lamellae well bonded coatings were further discussed. The unbonded interfaces act as precracks accelerating the erosion of plasma-sprayed coatings. Thus, controlling inter-lamellae bonding based on the critical bonding temperature is conducive to the improvement of erosion resistance of plasma-sprayed ceramic coatings.

In this work a number of different WC-12Co powder formulations were applied to coupons of steel using HVOF (high velocity oxy-fuel) and DSC (detonation spray coating) spray techniques. Two different HVOF guns and a super detonation gun (Super D-Gun ) were used to apply the coatings. The coated specimens were heat treated in an inert atmosphere at various temperatures in the range of 540°C -1000°C and subsequently characterized using optical microscopy, a Vicker’s microhardness tester, SEM (Scanning Electron Microscopy) and XRD (X-Ray Diffraction) to identify the phases generated. Additionally, in situ XRD was performed on a subset of these samples to explore the progression of the phase transformations as a function of temperature. Samples were also exposed to sand erosion with 20-30 mesh Ottawa sand at 825 feet per second to quantify performance. The work shows that the heat treatment and the transformation of amorphous metallic phases, WC and W 2 C to the η phase (Co 6 W 6 C) results in higher hardness and lower sand erosion rates.

This study examines the high-temperature erosion characteristics of carbide cermet coatings produced by HVOF spraying. The coating materials tested include three Cr 3 C 2 cermets, WC, and WC-Cr 3 C 2 . A low carbon steel and an arc-sprayed iron-base coating are also tested for reference. A nozzle-type elevated-temperature erosion tester is used to spray bed ashes collected from several coal-fired boilers. Coating samples are analyzed and compared based on composition, surface morphology, erosion wastage, and hardness relative to that of the bed-ash particles. From the comparisons, a number of conclusions are drawn. Paper includes a German-language abstract.

In order to characterize the performance of nanostructured coatings during wear, nanostructured and conventional titania (TiO 2 ) coatings were sprayed via three different thermal spray processes: APS, VPS and HVOF. Three distinct types of wear resistance were evaluated: dry-abrasion and slurry-erosion at 30° and 90°. The ranking of the wear performance of the different coatings varied for the three wear tests, except for the HVOF-sprayed nanostructured titania. The HVOF-sprayed nanostructured coating exhibited the highest wear resistance in all three types of wear. The different angles of erosion (30° and 90°) did not cause a change in the wear performance (ranking) of the HVOF-sprayed nanostructured coating, as was observed for the other coatings tested. The superior mechanical performance of the HVOF-sprayed nanostructured titania can be explained by observing the microstructure of the coating via high magnification SEM. These observations show that the nanostructured zones in the coating microstructure act as crack arresters, thereby increasing the coating toughness. The wear scars for the different coatings were also analyzed via SEM and used to help understand the wear performance of the different materials.

Several novel cored wires for producing Fe 3 Al intermetallic coating, Fe 3 Al/WC intermetallic coating, FeCrAl/WC intermetallic coating and FeCrNi/WC intermetallic coating by arc spraying were developed. The erosion wastage at high temperature of coatings was researched with different impingement angles and temperatures. The results indicated that impingement angle and temperature greatly affected FeCrAl/WC coating and Fe 3 Al/WC coating in erosion wastage. At the same time, the FeCrAl/WC coating had little effects on different temperature while impingement angle was 90° and different impingement angle while temperature was 650°C. As compared with water wall tube material (G20 steel) of power station boiler, the erosion resistance at high temperature of Fe 3 Al coating, Fe 3 Al/WC coating and FeCrAl/WC coating was higher. The erosion resistance rate of Fe 3 Al coating was 1.4~2.91 times of that of G20 steel when temperature was 650°C and particle was polygonal silica. At the same time, the erosion resistance rates of Fe 3 Al/WC coating and FeCrAl/WC coating was 1.4~3.06 and 1.94~2.89 times respectively. The results indicated that erosive condition of high temperature flue gas and fly ash mixture in boiler tube of pulverized coal fired power station could be solved with Fe 3 Al coating, Fe 3 Al/WC coating and FeCrAl/WC coating.

This work investigates the particle erosion properties of wear protection layers at high temperatures. The materials tested include tungsten and carbide cermets, nickel alloys, and chromium steel applied by different thermal spraying methods. Among key findings: HVOF-sprayed Cr 3 C 2 -NiCr cermet coatings showed the least amount of wear after particle erosion testing. It was confirmed that erosion resistance depends on elastic-plastic conditions between the particles and coating surface, not layer hardness. The impact of solid particles does not cause abrasion in elastic friction areas and only rarely causes abrasion in regions where plastic plowing occurs. Paper includes a German-language abstract.

Developing effective heating systems to prevent ice accretion on the surface of wind turbine blades and aircraft wings is of great significance for extreme cold environments. However, due to high velocity impingement of water droplets and solid particles on the surface of these components, an appreciable degree of surface material degradation may occur. In this study, nickel-chromium-aluminum-yttrium (NiCrAlY) was chosen as a metal matrix material for a coating-based heating system. Pure ceramic powders, namely, alumina and titania, and a cermet powder, tungsten carbide-cobalt (WC-12Co), were mechanically admixed with NiCrAlY powder and deposited to fabricate reinforced metal matrix composite (MMC) coatings. The powders were deposited on cylindrical low carbon steel bars by using flame spraying. The specimens were placed in a wind tunnel to conduct a comparative investigation of their erosive wear resistance under water droplet impact. A cold spraying unit was used for solid particle impact erosion tests. The erosive wear rates were quantified by measuring mass loss. The experimentally obtained results showed noticeably lower wear rate in NiCrAlY-WC-12Co and NiCrAlY-titania coatings compared to the other coatings. The results suggest that certain MMC coatings could be effectively employed to decrease the erosion rate of coating-based heating elements.

Recent studies have demonstrated that WC-12Co and WC- 10Co-4Cr coatings were the best performing HVOF coatings against erosion. This paper looks at the influences of the HVOF process parameters for WC-12Co and WC-10Co-4Cr materials on the erosion resistance of the coatings. The effect of powder morphology, matrix chemistry and HVOF process parameters with respect to both silica slurry erosion and alumina dry erosion has been studied. All coatings were produced using the HVOF JP-5000 system with kerosene-oxygen flame. The spraying parameters were analyzed in term of sprayed particle velocity and temperature as measured with the DFV2000 optical diagnostic system. Simultaneously with in-flight particle measurements, the substrate-coating temperature was monitored by infrared pyrometry during coating deposition. The resulting coating microstructure was evaluated in terms of microhardness, porosity type and extent of wear damage after dry and slurry erosion. The material volume loss under various erosion conditions was related to the coating properties and microstructure. According to the experimental results, the following conclusions are drawn: 1) the kerosene flow rate affects the inflight particle state (velocity and temperature) and the coating porosity. 2) Cobalt-chrome matrix cermet performs better in slurry erosion while denser and harder cobalt matrix cermet performs better in dry erosion. 3) The use of kerosene-rich flame with lower oxygen stoichiometry reduces the carbide degradation and optimizes the wear performance of WC-12Co coatings in both dry and slurry erosion.

Thermally sprayed coatings with Co-based alloy were evaluated for cavitation erosion resistance in order to use as erosion proof coatings. Co-based alloy coatings have been applied by Low Pressure Plasma Spray (LPS) and High Velocity Oxygen Fuel Flame Spray (HVOF) on the AISI 403 stainless steel substrates and half number of each coated specimen were post-heated at 1073K for 1 hour. The mass loss was measured for evaluation in this study. The following results have been obtained in the cavitation test; i) Both of LPS coatings (the post-heated and the as sprayed) have more excellent cavitation erosion resistance than HVOF coatings, ii) With regard to LPS coatings, the post-heated coating has the same weight loss as the as-sprayed coatings. iii)The post heat treatment to HVOF is remarkably effective to improve the cavitation erosion resistance.

Two cored wires L1 and L2, have been developed to produce arc-spraying coatings for treating high temperature erosion wear of four tubes in the power station, grit erosion experiments under various conditions such as temperature, incident angle, grit weight and shocking velocity have been taken, results show that coating L1 prepared by the new cored wire is more erosion resistance than the comparative materials 20g steel, coating L2 has different behavior varies with the distinct state, from the basis of surface structure and erosion performance, it is also concluded that coating L1 and L2 show mainly plastic erosion wear behavior during the grit erosion process.

The use of polymer matrix composites [PMC's] in the gas flow path of advanced turbine engines offers significant benefits for aircraft engine performance, but their useful lifetime is limited by their poor erosion resistance. HVOF and flame sprayed polymer/cermet functionally graded coatings based on a polyimide matrix filled with varying volume fractions of WC-Co are being investigated to improve the erosion and oxidation resistance of polymer matrix composites. A study of the coating's effectiveness as erosion barriers was accomplished through a statistical analysis of the results of solid particle erosion testing of coated and uncoated PMC samples using a design of experiments [DoE] approach. Three coating systems and a control were evaluated in a randomized test matrix. The coatings were tested at room temperature and 250 °C, using an alumina erodent impacting the coatings at a speed of 100 m/s at angles of 20° and 90°. Erosion volume loss at 250 °C was approximately twice than at room temperature, but the maximum erosion volume loss did not exceed 0.30 mm 3 at the elevated temperature. In general, as the angle of incidence of the eroding material increased from 20 degrees to 90 degrees the volume loss increased.

The present investigation compares blast erosion characteristics of coatings that are prepared with abrasion resistant surface treatment materials and various consolidation processes. Furthermore, it elucidates operating mechanisms in blast erosion of various sprayed coatings. The investigation presents the blast erosion test conditions and assessment of test results and discusses the effects of coating materials on abrasion loss and impingement angle on abrasion loss. It includes illustrations on SEM observation and cross-sectional observation of damaged areas. In addition, information on blast erosion resistant characteristics of materials tested and wear mechanism in blast erosion is also provided.