Search

Purpose This paper aims to perform the solid particle erosion studies in simulated coal-fired boiler conditions with a view to compare the erosion behavior of two different types of detonation gun (D-Gun) sprayed cermet coating powders, that is, WC-12%Co and Cr3C2-25%NiCr on ASTM A36 steel and bare (uncoated) ASTM A36 steel.Design/methodology/approach Erosion studies were performed using an air jet erosion test rig at impingement angles of 45°, 60° and 90°. During the erosion studies weight loss, erosion rates in terms of volume loss (mm3/g) and measurement of erosion profiles were determined using optical profilometer.Findings Both cermet coatings had successfully protected the ASTM A36 steel from erosion at impingement angles of 45°, 60° and 90°. In the case of bare ASTM A36 steel, the erosion rates were maximal at an impingement angle of 45° and minimal at an impingement angle of 90°, thus depicting the peculiar erosion behavior of ductile materials. WC-12%Co coated specimens exhibited erosion behavior that is closer to the behavior of ductile materials. Cr3C2-25%NiCr coated specimens exhibited the maximum erosion rate at an impingement angle of 90° and minimum at an impingement angle of 45°, hence depicting the typical behavior of brittle materials.Practical implications It is expected that these results will contribute to the improvement of erosion resistance of induced draft fans, by the application of D-Gun sprayed WC-12%Co and Cr3C2-25%NiCr cermet coatings.Originality/value This paper evaluates the solid particle erosion behavior of bare and cermet-coated ASTM A36 steel which will be helpful in choosing the suitable cermet coating for induced draft fan applications. [ABSTRACT FROM AUTHOR]

In this work, the wear resistance and fracture characteristics of (Ti,Al)N-Cu, (Ti,Al)N-Ni, and (Ti,Al)N coatings deposited onto a carbide substrate by the filtered cathodic vacuum arc deposition method were investigated comparatively under various loading and friction conditions. The (Ti,Al)N-Cu and (Ti,Al)N-Ni metal-ceramic coatings showed an equiaxial structure with a ceramic phase grain size of about 15–20 nm. The coatings showed a hardness of about 50 GPa and maintained their fracture toughness (the relative work of plastic deformation was ~65%). The (Ti,Al)N ceramic coating showed a columnar structure having elements with a diameter of about 120 nm. This coating exhibited a hardness of about 27 GPa and was characterized by a significantly lower fracture toughness (the relative work of plastic deformation was ~45%). The tribological properties of these coatings were examined at 20 and 500 °C. It was found that the metal-ceramic coatings showed significantly lower friction coefficient values (~0.56 and 0.61) than the ceramic coatings (~0.68 and 0.70). The fracture pattern of the metal-ceramic coatings was obtained by simulating their abrasive wear during a scratch test. Complete abrasion of the coatings was not observed until 90 N. Under similar tests, the (Ti,Al) N coating showed adhesive destruction by the separation of large fragments from the substrate. Complete coating wear was observed at a load of ~70 N. The erosion of the coatings during hydroabrasive treatment under multicycle impact loading was investigated. It was found that the nanostructured (Ti,Al) N-Cu and (Ti,Al)N-Ni coatings were 1.5 and 2 times less susceptible to wear than the (Ti,Al) N coating, respectively. The wear characteristics of the coatings were analysed on the basis of their structures and physical and mechanical properties, including their H/E and H3/E2 parameters, which denote the resistance of a material to elastic and plastic deformation respectively. [ABSTRACT FROM AUTHOR]

The primary objective of the present study is to investigate the influence of nanocrystalline grain size on the solid particle erosion behavior of nickel. For the above purpose, 450- μm-thick nanocrystalline Ni coatings having the average grain sizes of 21, 42, 70, and 195 nm were obtained using pulsed electrodeposition (PED). All these samples along with bulk annealed Ni samples (43 μm grain size) were subjected to solid particle erosion using SiO particles as an erodent at a constant impact velocity of 45 m/s and two impact angles (30 and 90 deg). Erosion results indicate that bulk Ni and PED Ni coatings of grain sizes 195 and 70 nm exhibit the same erosion rate, while PED Ni coatings of 42 and 21 nm grain size exhibit marginally higher erosion rates with a clear trend of increasing erosion rate with decreasing grain size. It was also observed that the higher erosion rates exhibited by 21- and 42-nm-grain size PED Ni samples were associated with the formation of adiabatic shear bands (ASBs) originating from the eroded surface and propagating into the eroded sample. The experimental observations have been understood on the basis of a transition from a localization model for erosion for coarse-grained Ni (> 70 nm) to an ASB-induced erosion model for grain sizes less than 70 nm. [ABSTRACT FROM AUTHOR]

In this paper, a continuous and uniform Mg-alloy coating was deposited by magnetron sputtering to protect flexible polyimide substrate from atomic oxygen (AO) erosion in the low earth orbit. AO exposure experiments indicated that the erosion yield of the as-deposited Mg-alloy coating was 8.897 × 10 −26 cm 3 atom −1 , about two orders of magnitude lower than that of blank polyimide. During AO exposure, a relatively compact and continuous thin MgO scale formed on the surface of the Mg-alloy coating, resulting in the enhanced AO erosion resistance of the polyimide with Mg-alloy coating. [ABSTRACT FROM AUTHOR]

SiC coating with a thickness of 50–70 µm was prepared on the surface of C/C composites by in-situ reaction method. The SiC coated C/C composites were then tested in a wind tunnel where a temperature gradient from 200 to 1600 °C could be obtained to investigate their erosion behavior. The results of wind tunnel test indicated that the service life of C/C composites was prolonged from 0.5 to 44 h after applying the SiC coating. After the wind tunnel test, three typical oxidation morphologies, including glassy SiO 2 layer, porous SiO 2 layer and clusters of honeycomb-like SiO 2 grains, were found on the SiC coated C/C composites. With the decrease of oxidation temperature, the amount of glassy SiO 2 declined and the thermal stress increased, which induced the cracking followed by the degradation of the SiC coating. [ABSTRACT FROM AUTHOR]

WC–10Co–4Cr coating was deposited by high-velocity oxy-fuel (HVOF) process on cast and solution treated (1220 °C/150 min) 23-8-N nitronic steel substrates. Solution treated substrate has shown higher toughness, ductility and impact energy with a marginal reduction in hardness as compared to cast substrate. This influence the coating deposition efficiency and erosion behaviour. Erosion resistance of coatings was evaluated by air jet erosion tester on two different impact angles (30° and 90°). Phases, microstructure and eroded surface of the coating were characterised by X-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FESEM) respectively. It is observed that coating on solution treated substrate was superior to cast substrate. The reason being that coating has dense and well-bonded structure with low porosity, less decarburization and inter-splat oxidation. Higher erosion resistance of coated solution treated 23-8-N nitronic steel was attributed to combination of high fracture toughness and hardness of coating including optimum mechanical properties of the substrate. FESEM analysis reveals that erosion response of WC–10Co–4Cr coating also dependent on the relative size of the impact crater with respect to the WC grain size. Coating is removed by combined mode of ductile and brittle erosion. [ABSTRACT FROM AUTHOR]

Several experimental techniques are ordinarily used to evaluate the strength properties of metal nitride coatings used for cutting tools and molds. However, for gradient coatings, in which the chemical composition changes gradually in the normal direction of depth relative to the surface, the properties at different depth positions of the gradient layer are difficult to evaluate. In this study, our previously developed micro slurry-jet erosion (MSE) test was applied to swiftly evaluate the strength properties of AlCrSiN gradient coating. The specimens of AlCrSiN gradient coating and also with AlCrSiN single layer coatings of different (Al + Si) concentration were deposited on high speed steel by a cathodic arc method. The AlCrSiN gradient coating had (Al + Si) concentration continuously increasing towards the surface. The MSE tests were conducted by impacting the slurry-jet containing 1.2 μm sized alumina particles perpendicular to the coated surface, and the depth profiles of the eroded surfaces were measured and the erosion rate was obtained. For the AlCrSiN single layer coatings, the erosion depth curves changed linearly, and their erosion rates became remarkably larger with increasing (Al + Si) concentration although the hardness decreased gradually. Moreover, for the AlCrSiN gradient coating, the erosion depth curve was approximated by a cubic B-spline curve because the erosion rate changed gradually in the depth direction. From the characterization by transmission electron microscopy and selected area diffraction, the change of the erosion rate was caused by forming nano-composites and also by segregation of a hexagonal closed-packed phase (hcp). It was found that the MSE method is an easy to apply and useful technique to evaluate the distribution of the properties of hard gradient coatings. [ABSTRACT FROM AUTHOR]

In this work, high velocity oxy-fuel (HVOF) thermal spraying was used to develop 65 wt% NiCrSiB–35 wt% WC–Co coatings on AISI 304 stainless steel substrate. Taguchi method was taken to optimize the spray parameters like oxygen flow rate, fuel flow rate, powder feed rate and standoff distance to obtain better erosion resistance at 90° impact angle. Standoff distance and powder feed rate were identified as the highly contributing parameters on the erosion wear loss. The important sequence of the spray parameter is standoff distance>powder feed rate>fuel flow rate>oxygen flow rate. The combination of 220 lpm of oxygen flow rate, 65 lpm of fuel flow rate, 28 g/min of powder feed rate and 300 mm of standoff distance was identified as the optimum condition for minimum erosion wear loss. The microstructure of the optimized coating was characterized using Scanning Electron Microscope (SEM) equipped with Energy dispersive spectroscopy (EDS), Optical microscope (OM), and X-Ray Diffraction (XRD). The microhardness, porosity and surface roughness of the coating was also measured. Finally, erosion wear testing of the optimized coating was conducted at 30°, 60° and 90° impact angle using hot air jet erosion testing machine. The SEM images of the erodent samples were taken to analyse the erosion mechanism. [ABSTRACT FROM AUTHOR]

In this study we explore the cutting performance of ZrAlN coatings. WC:Co cutting inserts coated by cathodic arc evaporated Zr 1 − x Al x N coatings with x between 0 and 0.83 were tested in a longitudinal turning operation. The progress of wear was studied by optical microscopy and the used inserts were studied by electron microscopy. The cutting performance was correlated to the coating composition and the best performance was found for the coating with highest Al-content consisting of a wurtzite ZrAlN phase which is assigned to its high thermal stability. Material from the work piece was observed to adhere to the inserts during turning and the amount of adhered material and its chemical composition is independent on the Al-content of the coating. [ABSTRACT FROM AUTHOR]

Erosion is a serious concern for machinery dealing with particle-laden fluids. For protection against erosion, coatings are usually recommended. Laboratory experiments are conducted to evaluate the erosion rates of these coatings. Alternatively, one could consider the use of modeling and simulation to predict the erosion rates. Although several models are available in literature for bulk materials, there is limited work reported in this direction for coatings. In present work, several models from literature were evaluated for their ability to predict the slurry erosion of coatings. A model based upon contact-fracture theory (CFT), proposed in present work, was also evaluated. Another variant of this model considered the effect of splat size. It was observed that none of the existing models evaluated in the present work could predict the erosion rates of the coatings. The proposed CFT model was able to predict the erosion rates with reasonable accuracy, whereas another variant of this model based upon splat size was observed to be inappropriate for predicting erosion rates of coatings. Possible reasons for the observed disparity are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Various components need protection against superimposed corrosion and wear (abrasion, erosion) loading, e.g. in off-shore applications. The goal of the research has been to develop a PVD multilayer coating by systematically altering the layer architecture in order to protect components against corrosive environments and erosive loadings. Our approach regarding the coating architecture has been to apply a diamond-like carbon (DLC) layer on top of a multilayer coating system, to ensure an excellent erosion resistance while providing a good corrosion protection. Our investigation is focused on the influence of the application technology (PVD or PECVD) and the resulting coating properties of the DLC top-layer. The investigated PECVD-top-layer was produced by a mixture of acetylene and hydrogen gas, whereas the PVD-top-layers were deposited from a graphite-target and different mixtures of acetylene and argon gas. The applicated DLC top-layers are characterized by hardness values between 11 and 23GPa and similar adhesion properties. Note that hardness has been determined by nano-indentation and adhesion characterized by scratch testing. Residual stresses of the DLC-top-layers were determined by means of focused ion beam milling and tracking of the resulting relaxation strains by digital image correlation. Residual compressive stresses up to 2GPa have been determined. Under loading in an erosive environment (combination of abrasive and fatigue loading) the abrasive degradation of the investigated coatings has been found to depend mainly on coating hardness. As expected, the hardest DLC top-layer (PECVD) shows least abrasive degradation. However, when tested under cyclic loading, the coating exhibiting the highest hardness values (PECVD) show the most severe fatigue damage of all DLC coatings investigated. [Copyright &y& Elsevier]

Abstract: The lifetime of titanium-alloy aerospace parts can be greatly enhanced by the application of erosion-resistant coatings (ERC). After many hours in service, the coating will inevitably begin to deteriorate. To permit re-coating and repair of the parts, the coating should be removed. We present here a first attempt to strip TiN-based, 20μm-thick, coatings while comparing the suitability of two pulsed lasers: a femtosecond Ti:Sapphire laser emitting at 800nm, and a nanosecond excimer laser centered at 248nm. Following initial comparison of ablation thresholds for each laser, we optimized four critical laser parameters: power, beam diameter, stage speed and step distance. The results indicate that surface roughness can be improved by 35% with the femtosecond laser in comparison with the nanosecond laser, while the higher energy per pulse offered by the latter one accelerates the etch rate by one order of magnitude. Surface composition analysis confirmed full removal of the coating and higher oxidization of the substrate with the excimer laser. Nanoindentation measurements on the polished cross-section of stripped samples show that the ablation process does not influence the hardness of the remaining substrate. To increase selectivity, plume emission spectroscopy has been investigated, in order to control, in real time, the material removal in regions where the coating thickness may vary. [Copyright &y& Elsevier]

Abstract: Tungsten coatings prepared on heat sink materials (Al2O3–Cu) as PFC not only can release amount of impinging thermal power but also can resist erosion under plasma particles bombardment in the ITER reactor. Therefore electro-deposition technique using for obtaining tungsten coating on Al2O3–Cu substrate was a novel technique especially for fusion applications. In this paper, pure tungsten coatings were successfully deposited under various pulsed current densities at 1173K in Na2WO4–WO3 melts. Furthermore pulse current density, duty cycle and period were investigated respectively so as to obtain well defined structures for tungsten coatings. The composition, crystal structure and microstructure of tungsten coatings were characterized by XPS, SEM and XRD techniques. The results indicated that pulsed current density, duty cycle and period have significant influence on tungsten nucleation and electro-crystallization phenomena. [Copyright &y& Elsevier]

Abstract: Four nitride coatings (CrN, ZrN, CrAlN, and TiAlN) were deposited on YT15 cemented carbide by cathode arc-evaporation technique. Microstructural and fundamental properties of these nitride coatings were examined. Erosion wear tests were carried out, the erosion wear of these nitride coatings caused by abrasive particle impact was compared by determining the wear depth and the erosion rates of the coatings. The wear surface features were examined by scanning electron microscopy. Results showed that the coatings with Al (CrAlN and TiAlN) exhibited higher erosion wear resistance over those without Al (CrN and TiN). The H 3/E 2 of the coating seemed to play an important role with respect to its erosion wear in erosion tests. AlTiN and CrAlN coatings being with high H 3/E 2 exhibited lower erosion rates, while CrN coating with low H 3/E 2 showed higher erosion rates under the same test conditions. Analysis of eroded surface of the coatings demonstrated that the TiN and CrN coatings exhibited a typical brittle fracture induced removal process, while AlTiN and CrAlN coatings showed mainly micro cutting and cycle fatigue fracture of material removal mode. [Copyright &y& Elsevier]

Products made of basalt are recently gaining sufficient attention due to depletion of raw materials serving as reinforcement for construction, and wear resistant materials. Basalt has sufficient mechanical strength, high hardness, low density and superior corrosion resistance. Basalt and other minerals are used in thick metal coatings to adjust their thermal expansion to that of the steel substrate. High velocity oxygen fuel (HVOF) sprayed coating method allows to prepare solid basalt-steel composite materials since the melting temperatures of basalt and steel are very close and materials obtained by casting or sintering will have low mechanical properties. The aim of the current work is to study the change in tribological response under erosive, abrasive, reciprocal and continuous sliding conditions when basalt is added to the harder matrix. It was found that the addition of 12 vol % of basalt to the FeCrSiB HVOF sprayed coating is generally unfavourable in tribological conditions due to the brittleness of basalt and its flake shape. The worst relative performance was observed in reciprocal sliding conditions and the best one in mild conditions of continuous sliding. Discussion on the mechanisms of materials performance is based on SEM and EDS results. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the performance of coatings that were subjected to solid particle erosion tests was evaluated. These coatings can be used to protect die casting molds. The main interest of this research project was to find possible alternatives to increase the wear resistance of these mechanical components. Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity, which is machined into two hardened tool steel or coated dies. Most die castings are made from non-ferrous metals, such as aluminium, copper, magnesium, lead, zinc, tin based alloys but also they can be protected by specific coatings that have high wear resistance. The erosive wear damage in die casting molds is caused due to the molten metal is blown into the mold by high pressure dry air. Filling the mold cavities during the blown step, molten metal and sand particles impact the internal surface producing erosive wear damage. Coatings such as chromium nitride (CrN) and titanium aluminium nitride (TiAlN) that exhibit low wear damage in these types of applications due to high abrasion and erosion resistance were tested. In addition, uncoated 4140 steel and 6061 aluminium were also tested. An erosion test rig similar to that shown in ASTM G76-95 standard was designed and built to perform the tests. The abrasive particle used was angular silicon carbide (SiC) with a particle size of 420–450μm. Tests were carried out using different impact angles (30°, 45°, 60° and 90°) with a particle velocity of 24±2m/s and an abrasive flow rate of 0.7±0.5g/min. The particle velocity and the abrasive flow rate were low in all of the tests to reduce the interaction between the incident particles and the rebounding particles in the system. The surfaces were examined with a scanning electron microscope (SEM) to characterize the erosive damage. The wear mechanisms identified were pitting and ploughing action at low impact angles (α ≤45°) due to sliding component commonly observed at these incident angles whereas bigger craters, radial cracks and a more roughened surfaces were seen at angles near or at 90°.In addition, it was observed that the damaged area was extended in all of the cases at 30° and 45° reducing considerably at 60° and 90°. The wear scars were characterized by an elliptical shape at 30° and 45°, which is a characteristic feature when the specimens are impacted at low-incident angles (α ≤45°) whereas a roughly circular was seen at 60° and 90°. [Copyright &y& Elsevier]

Abstract: ZrAlN/Cu coating has been deposited onto Ti-6Al-4V substrate by reactive magnetron sputtering in order to improve its erosion resistance. The morphology and microstructure were studied combined with Field Emission Scanning Electron Microscrope(FSEM), X-ray Diffraction(XRD), X-ray Photoelectron Spectroscopy(XPS) and Transmission Electron Microscopy(TEM). Coatings hardness and toughness were measured by nano-indentation method and Vicker indentation method respectively. It has been found that Zr0.79Al0.19Cu0.02N coating possess dense columnar structure with 20∼40nm columnar grains exbibiting (100) preferential orientation. XRD reflection peaks slightly shifts to higher angle, showing some of 19at%Al and 2at%Cu substitutely dissolves into face-centered cubic(FCC) ZrN lattice, XPS proves the existence of AlN and Cu phase in coating. Zr0.79Al0.19Cu0.02N coating demonstrates best erosion resistance at 15°∼90° impingement angle compared with Ti6Al4V substrate, ZrN and Zr0.80Al0.20N coating, attributing to combination of high hardness(40.7GPa) and good toughness. [Copyright &y& Elsevier]

Abstract: The erosive-corrosive effect of aqueous NaCl slurries on metals and metals coated with a multilayer system was analyzed. The erosion-corrosion experiments were performed in a test machine in which the impingement velocity, impact angle, concentration of solids and pH of the solution were controlled. Polarization curves were simultaneously obtained to correlate the electrochemical effects to the erosive wear mechanisms. The slurry used consists of silica particles suspended in a mixture of acid solution and 3.5% NaCl, with a pH value of 5.6. Electrochemical results showed the best corrosion resistance for steel coated with CrN/AlN system deposited with 50 bilayer. Additionally, the surface analysis by SEM micrograph revealed formation of cracks in CrN/AlN multilayers coating and plastic deformation in both steel substrates (AISI D3 steel and 304 stainless steel), especially when the mean impact angle is a critical value of 90°. Measurements of critical and passive current densities showed that the behavior of coated materials differed depending on the substrate that is used. Nonetheless, in a general way, by increasing the impact angle and by changing its incidence from normal to grazing, it led to an improved resistance to erosion-corrosion processes. [Copyright &y& Elsevier]

Abstract: Repeated impact by solid particles causes erosion and degradation of engineering components. In internal combustion engines, during combustion, hot gases are generated in large quantity which causes erosion of cylinder, combustion chamber, exhaust system, etc. In this work, two types of plasma sprayed coating systems were developed on Al-6061 substrate. For each system, a systematic microstructural study was carried out to understand changes occurred after spraying. Mechanical properties like density, adhesion strength and hardness of coatings were determined. A solid particle erosion test was conducted on coating systems according to ASTM G-76-02 and results were correlated with the microstructural and subsequent mechanical property change. It was observed that volume erosion is more at 45° angle of impact and shows that behavior is in between ductile and brittle. This work also discusses the mechanism involved in erosion wear of plasma sprayed coating systems. [Copyright &y& Elsevier]

Abstract: Present work is an investigation of slurry erosion behavior of WC–CoCr cermet coatings deposited with two different WC grain sizes. HVOF thermal spray process was employed due to its high velocity and low flame temperature characteristics resulting in quality coating. HVOF spraying was assisted with in-flight particle temperature and velocity measurement system to control its heating. Slurry erosion testing was performed using a pot-type slurry erosion tester to evaluate slurry erosion resistance of the coatings. Two parameters were considered for testing viz. erodent particle size and slurry concentration. Surface morphology was examined using SEM images and phase identification was done by XRD. The erosion behavior and mechanism of material removal was studied and discussed based on microstructural examination. It was observed that WC–CoCr cermet coating deposited with fine grain WC exhibits higher slurry erosion resistance under all testing conditions as compared to conventional cermet coating. [Copyright &y& Elsevier]

Abstract: Detonation-gun (D-gun) spray technology is a novel coating deposition process which is capable of achieving very high gas and particle velocities approaching 4–5 times the speed of sound. This process provides the possibility of producing high hardness coatings with strong adherence. In the present study, this technique has been used to deposit Cr3C2–NiCr coating on T22 boiler steel. Investigations on the behaviour of this coating subjected to high-temperature oxidation in air and oxidation–erosion in actual boiler environment at 700±10°C under cyclic conditions have been carried out. The weight change technique was used to establish the kinetics of oxidation. X-ray diffraction (XRD), field emission-scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS) and EDS elemental mapping techniques were used to analyse the oxidation/oxidation–erosion products. The uncoated boiler steel suffered from a catastrophic degradation in the form of intense spalling of the scale in both the environments. The Cr3C2–NiCr coating showed good adherence to the boiler steel during the exposures with no tendency for spallation of its oxide scale. [Copyright &y& Elsevier]

Abstract: (Ti,Cr)N nanolayer coatings were deposited on Ti–6Al–4V, 17-4PH and Inconel 718 substrates using cathodic arc physical vapor deposition for improved erosion and corrosion resistance. Coating corrosion performance was highly dependent on the coating thickness and packing factors and correlated with increased chromium content within the (Ti,Cr)N nanolayer coatings. The change in cathode current predominantly affected coating thickness and the bias affected the packing factor. Erosion tests of the coated and uncoated substrates at both 30° and 90° erodent impingement angles were conducted using angular aluminum oxide media at particle velocities up to 145m/s. Chromium evaporator current and substrate bias were varied to change film stoichiometry and microstructure for erosion performance evaluation. When chromium evaporator current was varied, the increase in chromium content led to an increase in binary CrN phase volume and a decrease in TiN phase volume. The increase in CrN phase volume decreased both hardness and erosion performance at both impingement angles. Lower bias values resulted in better erosion performance. At 30° erodent impingement, all coated samples outperformed the uncoated substrate; whereas, for 90° impingement, only coatings deposited at low bias values (−25V, −50V, and −100V) and high Ti:Cr ratios (>2.4) outperformed the uncoated substrate. The primary coating failure mechanism was microchipping. [Copyright &y& Elsevier]

The effect of such structural features as porosity and grain size on the erosion capacity of electrode materials of the composition 92% WC-8% Co is studied. It is established by calculation and experiment that the high erosion capacity of electrode material is mainly facilitated by its high porosity. A reduction in carbide phase grain size to a size of the order of 100 nm also increases material erosion capacity, but to a markedly lesser extent. Intensification of mass transfer with a reduction in WC grain size and presence of porosity within electrode material gives rise both to a reduction in volumetric heat capacity and thermal conductivity, and also to an increase in its specific electric resistance. All the factors listed above are affected by an increase in local electrode material warming in a spark discharge arc. [ABSTRACT FROM AUTHOR]

The material commonly used in low-pressure high-rating super critical/ultra super critical steam turbines as well as guide and moving blades of high speed aero compressors is Ti6Al4V alloy. These blades are severely affected owing to erosion which leads to drop in efficiency and increase in maintenance cost. This article deals with SHS 7170 coating on Ti6Al4V alloy using twin wire arc spraying (TWAS), enhancing its bonding by providing a thin bond coat and then treating with high-power diode laser (HPDL). Significant improvement in erosion resistance of this multilayer coating has been achieved because of the formation of fine-grained micro structure due to rapid heating and cooling rates associated with the laser surface treatment. After laser surface treatment, the fracture toughness of this multilayer has improved manifold. The water droplet and particulate erosion test results along with the damage mechanism are reported and discussed in this article. [ABSTRACT FROM AUTHOR]

The influence of ion-plasma coatings made from high-hardness metal compounds on the erosion and corrosion resistance and mechanical properties of the alloy (substrate) + coating system is studied. The influence of the thickness, composition, and design of coatings based on metal nitrides and carbides on the relative gas-abrasive wear resistance of alloy+coating compositions in a gas-abrasive flux of quartz sand is discussed. It is shown that the zirconium nitride coating provides the best protection for compressor blades made of titanium alloys, without any decrease in fatigue resistance of the alloys, and chromium carbide coating is the most appropriate protection for steel compressor blades. [ABSTRACT FROM AUTHOR]

Abstract: Erosion-enhanced corrosion constitutes an essential threat to the integrity of the oilsand slurry hydrotransport system. In this work, a Ni–Co–SiC nano-coating technology was developed by electrolytic deposition on the carbon steel surface to address this problem. Results demonstrate that the coating develops a compact structure, improving significantly the mechanical properties, including hardness and wear resistance, and the resistance to erosion-enhanced corrosion. The incorporation of SiC nano-particles in the coating, rather than the coating thickness, plays an essential role in the improvement of the coating properties and performance. Furthermore, the electrodepositing parameters, including concentration of SiC in the bath electrolyte, cathodic current density, current pattern and temperature, affect remarkably the content of SiC particles in the coating, and thus the coating performance. An optimal condition was proposed to fabricate the nano-coating for this purpose. [ABSTRACT FROM AUTHOR]

Abstract: Nanoscale CrN/NbN multilayer PVD coatings have exhibited resistance to erosion–corrosion. However growth defects (under dense structures and droplets) in the coating produced by some deposition technologies reduce the ability to offer combined erosion–corrosion resistance. In this work a novel High Power Impulse Magnetron Sputtering (HIPIMS) technique has been utilised to pretreat substrates and deposit dense nanoscale CrN/NbN PVD coatings (HIPIMS–HIPIMS technique). This new technique, rich with metal ion plasma, deposits very dense structures and offers virtually defect free coatings (free of droplets as observed in cathodic arc technique and under-dense structures observed in standard dc sputtering). Plasma diagnostic studies revealed a high metal ion-to-gas ion ratio (Cr:Ar) of 3:1 for HIPIMS pretreatment conditions with the detection of 14% Cr2+ and 1% Cr3+ ions and J s of 155mAcm−2. For deposition conditions the metal ion-to-gas ratio was approximately 1:4 which is significantly higher compared to DC at 1:30. Characterisation results revealed a high adhesion of L C 80N, high hardness of 34GPa and Young''s modulus of 381GPa. Low friction coefficient (0.46) and dry sliding wear coefficient, K C (1.22×10−15 m3Nm−1) were recorded. The effect of deposition technique (droplet defect and intergranular void free coatings) on erosion–corrosion resistance of CrN/NbN coatings has been evaluated by subjecting the coatings to a slurry impingement (Na2CO3 +NaHCO3 buffer solution with Al2O3 particles of size 500–700µm) at 90° impact angle with a velocity of 4ms−1. Experiments have been carried at −1000mV, +300mV and +700mV representing 3 different corrosion conditions. [Copyright &y& Elsevier]

Abstract: Tungsten carbide-based thick coatings are used as wear resistant claddings or surface overlays in industrial applications to counter erosive and/or abrasive wear problems. Three-body abrasive wear behaviour of infiltration brazed tungsten carbide (WC) claddings was investigated using a ball-cratering method, a version with a free ball, with slurry containing 150–300μm silica sand particles. Three WC claddings tested had different volume fractions and size distribution of carbides that resulted in their different bulk hardness and the matrix was a Ni–Cr based alloy. It was found that the wear rates of all WC claddings were almost constant with testing time or distance travelled by a rotating ball. The wear rates were independent of the slurry delivery rate and did not increase with increasing rotating ball roughness. The wear rates were affected by the material characteristics of WC claddings such as the volume fraction of carbides, directly related to bulk hardness, and carbide size distribution. SEM examination found that three-body rolling wear was a dominating wear mechanism. The softer matrix was worn out preferentially, leaving behind protruding and weakly-supported carbides. Small solid carbides were then dislodged and larger cemented WC/Co carbides were gradually worn out by a combination of microcracking and attrition. The abrasive characteristics of WC claddings in the ball-cratering tests were then compared to the characteristics of nominally identical materials in the standard ASTM G65 and G76 tests, as reported in the literature, and similarities and differences found are reported. Also, the in-field wear mechanisms found in the WC cladding were compared to the mechanisms observed in the ball-cratering tests. [Copyright &y& Elsevier]

Abstract: The objective of the present study was to evaluate the tribological performance of 200μm thick TiMo(CN)–28Co and TiMo(CN)–36NiCo coatings obtained using the detonation spray coating system. Towards the above purpose, the detonation spray coating conditions were optimized to obtain the best coating properties (low porosity, high wear resistance) by varying two of the important coating process variables, i.e., oxygen to fuel ratio and gas volume. In both the coatings it was observed that the best tribological performance and also the lowest porosity were obtained at intermediate OF ratios. However, the coatings with the highest hardness did not exhibit the best tribological performance. A comparison of the tribological performance of the optimized TiMo(CN) type coatings with that of optimized WC–Co coatings revealed that the abrasion resistance of TiMo(CN) type coatings is comparable to that of WC–Co coatings. However, the erosion and sliding wear resistance of TiMo(CN) type coatings were considerably lower than that of WC–Co coatings. [Copyright &y& Elsevier]

In the present investigation plasma spray intermetallic coating of nickel-aluminide was deposited on mild steel substrates. The response of plasma sprayed nickel-aluminide coatings to the impingement of solid particles has been presented in this study. Nickel pre-mixed with alumina powder is deposited on mild steel substances by atmospheric plasma spraying at various operating power level. The coatings are subjected to erosion wear test. Dry silica sand of average particle size 400 mm is used as the erodent. The erosion rate is calculated on the basis of coating mass loss. The erosion studies are made at different velocities and impingement angles. It is observed that, the erosion wear is strongly influenced by the angle of impact. The test is conducted at room temperature, i.e., at 27°C and 60% RH. Coatings deposited at different power levels are found to exhibit different wear rates under similar test conditions. Microstructure of the coating is analyzed with SEM. [ABSTRACT FROM AUTHOR]

Abstract: Soldering and erosion of casting moulds and their components are one of the most prominent and persistent problems occurring in the die-casting industry. In this study, MoB- and Co-based cermets and alloy, respectively, were deposited on bond coated hard substrates (SKD61) using kinetic spray coating technique. Coating of hard powder materials on hard substrate using kinetic spray technique has also been considered a difficult phenomenon. Microstructural and mechanical characterization of the coatings was carried out by SEM, XRD, micro-hardness, bond strength and wear resistance tests. The results showed that Co-based alloy displayed the highest deposition efficiency along with microstructural properties. However, MoB/NiCr demonstrated the highest mechanical properties. The coatings were tested for soldering resistance by immersion of coated SKD61 cylinders in molten aluminium alloy (ADC-12) bath. MoB/NiCr displayed superior soldering resistance among the coatings. Among the candidate coatings, MoB/NiCr is considered as the one with the highest durability in a die-casting operation. [Copyright &y& Elsevier]

Abstract: Organic coatings are the most commonly used system for protection from corrosion of a metallic product. The required properties of paints include protection from corrosion phenomena, resistance to abrasion and good aesthetic aspect. This is particularly important for the automotive and transport industry, building trade, domestic products, and packaging. The aim of this work is to investigate the effect of wet abrasion and erosion on the protective and aesthetic properties of an organic coating system. Falling abrasive test and Taber test were chosen to produce the mechanical damage, using different abrasive slurries in order to evaluate the influence of the viscosity of the liquid mean and the hardness and shape of the abrasive agents. The level of aesthetic damage was evaluated through gloss measurements; 20° was the most sensitive angle to gloss changes; with this geometry, samples with different damage level could be compared. The correlation between the changes of gloss and the damage was investigated using optical microscopy and environmental scanning electron microscopy. The level of loss of protective properties was evaluated through electrochemical impedance spectroscopy measurements. [Copyright &y& Elsevier]

Abstract: Several different experimental techniques are normally used to evaluate tribological properties of thin hard coatings. However, most of the tests cannot assess properties of coating, substrate and interface independently. In this study, the potential of a Micro-Slurry-jet Erosion (MSE) test to swiftly evaluate the intrinsic wear properties of thin single layered and multilayered coatings is demonstrated. A slurry containing 1.2μm alumina particles was impacted at high velocity perpendicular to CVD TiC/TiN (TiN on top of TiC) and TiC coatings deposited on cemented carbide. In addition, nano-indentation and XRD, GDOES, AFM analyses were done for the original and worn surfaces. For the TiC/TiN coating, the wear depth of the TiN layer increased linearly until the TiC layer was reached. There after the wear occurred at a lower rate but tended to increase towards the TiC/substrate interlayer. The single layered TiC coating showed the same wear behaviour as the TiC layer of the TiC/TiN coating. The wear rate was constant within the individual TiN and TiC layers, but changed near the interfaces. The micro-topographies of the worn surfaces observed by AFM correlated to the difference in the wear rate of the individual layers and the change in wear rate at the interface to the substrate. The TiC layer proved to have about two times higher wear resistance than the TiN layer. Consequently, the MSE test can distinguish between small differences in the properties of the coatings and of the interlayer zones, and can be used as a screening test when evaluating multilayered as well as single layered coatings. [Copyright &y& Elsevier]

Abstract: Composites of Cr3C2–NiCr provide superior oxidation resistance to WC–Co composites, which has seen them applied extensively to components subjected to combined high temperature erosion and oxidation. This work characterises the variation in oxidation mechanism of thermally sprayed Cr3C2–NiCr composites at 700°C and 850°C as a function of heat treatment. Carbide dissolution during spraying increased the Ni alloy Cr concentration, minimising the formation of Ni oxides during oxidation. Compressive growth stresses resulted in ballooning of the oxide over the carbide grains. Carbide nucleation with heat treatment reduced the Ni alloy Cr concentration. The oxidation mechanism of the composite coating changed from being Cr based to that observed for NiCr alloys. [Copyright &y& Elsevier]

Abstract: In Part 1 of this two part series the variation in erosion mechanisms as a function of as-sprayed coating microstructure was presented. The oxidation resistance of Cr3C2–NiCr coatings means that they are used in high temperature applications where WC–Co based systems are no longer suitable. High temperature exposure has been shown to generate microstructural development in these coatings, leading to variations in coating hardness. In this work the effect of such coating development on the high velocity erosion response is investigated. The HVAF and HVOF coatings of Part 1 were heat treated for up to 30 days at 900 °C to generate a range of coating microstructures up to steady state. Erosion was performed under the same conditions as in Part 1. Heat treatment increased the ductility of the NiCr phase, enabling ductile erosion deformation to occur. Intersplat sintering reduced the significance of splat based erosion mechanisms and forced mass loss to become dictated by the phase microstructure. Such developments improved the quantified erosion resistance of both coating systems relative to the as-sprayed conditions. The coating microhardness was shown to be a poor indicator of erosion response across the range of coating microstructures investigated. [Copyright &y& Elsevier]

Abstract: The influence of structure on erosion performance of thermally sprayed Cr3C2–NiCr coatings under industrial turbine conditions has been investigated. Thermal spraying of these materials results in substantial variation in composition and microstructure due to exposure of the coating powders to the high temperature accelerating gas. Coatings were characterised using Back Scatter Electron imaging in conjunction with X-ray diffraction which showed carbide dissolution into the matrix of varying extent depending on deposition technique. Heat treatment at 900 °C caused carbide precipitation and matrix refinement. Erosion testing of as-sprayed and heat treated coatings was conducted at ambient and elevated temperature. Single impacts were characterised using Scanning Electron Microscopy in order to determine the erosion mechanism. At ambient temperature the single impacts caused a brittle response with both carbide grains and matrix being cleaved by the erodent particle. Brittle cracks surrounded each impact and intersected with splat boundaries leading to a significant contribution to erosion rate from splat structure. Following heat treatment the erosion response of the coatings was more ductile with mounds of plastically deformed material surrounding each impact, this significantly reduced erosion rate. [Copyright &y& Elsevier]

Abstract: Erosion from and deposition on JET divertor tiles used during the 2007–2009 campaign and on inner wall guard limiter (IWGL) tiles used during 2005–2009 are studied. The tungsten coating on the divertor tiles was mostly intact with the largest erosion ∼30% in a small local area. Locally high erosion areas were observed on the load bearing divertor tile 5 and on the horizontal surface of the divertor tile 8. The IWGL tiles show a complicated distribution of erosion and deposition areas. The total amount of carbon deposited on the all IWGL tiles during the campaign 2005–2009 is estimated to be 65g. The density of carbon deposits is estimated to be 0.67–0.83g/cm3. [Copyright &y& Elsevier]

As was already observed experimentally, the erosion of tungsten (W) coated graphite (C) tiles in ASDEX-Upgrade (AUG) exhibits regular erosion patterns on the micrometre rough surfaces whose origin is not fully understood: surfaces inclined towards the magnetic field direction show strong net W erosion while surfaces facing away from the magnetic field are shadowed from erosion and may even exhibit net W deposition. This paper presents a model which explains the observed erosion/deposition pattern. It is based on the calculation of ion trajectories dropping through the plasma sheath region to the rough surface with combined magnetic and electrical fields. The surface topography used in the calculations is taken from atomic force microscope measurement of real AUG tiles. The calculated erosion patterns are directly compared with secondary electron microscopy images of the erosion zones from the same location. The erosion on surfaces inclined towards the magnetic field is due to ions from the bulk plasma which enter the sheath gyrating along the magnetic field lines, while the deposition of W on surfaces facing away from the magnetic field is due to promptly re-deposited W that is ionized still within the magnetic pre-sheath. [ABSTRACT FROM AUTHOR]

Abstract: The erosion of W coatings with the different content of C was investigated in Ar and Ar+H2 plasmas. The enhanced erosion was registered in Ar+H2 plasma for coatings containing 40at.% of C and more, which might be owing to chemical erosion of carbon. The erosion kinetics was analyzed together with the studies of coatings microstructure, phase composition and Vicker hardness properties. The C distribution profiles in W were investigated in dependence on the redeposition rate of sputtered C and simultaneous 0.3keV Ar+ ion irradiation. It is shown that C penetration depth depends on the coverage of W by C during ion irradiation. Deep C penetration was registered when W was partially covered by redeposited carbon. The computer simulation was used to extrapolate obtained results to experimental investigations performed by Ueda Y, Fukumoto M, Sawamura I, Sakizono D, Shimada T, Nishikawa M. [Fusion Eng Des 2006;81:233–9]. It is revealed that the ballistic relocation of implanted C atoms is the dominant process which explains the deep penetration of C and formation of WC compound in the near-surface region of W. [Copyright &y& Elsevier]