Showing papers in "Journal of Thermal Spray Technology in 2013"
TL;DR: In this article, the current status of materials, equipment, processing, and properties aspects for key coatings in the energy industry, especially the developments in large-scale gas turbines, are reviewed.
Abstract: Functional coatings are widely used in energy generation equipment in industries such as renewables, oil and gas, propulsion engines, and gas turbines. Intelligent thermal spray processing is vital in many of these areas for efficient manufacturing. Advanced thermal spray coating applications include thermal management, wear, oxidation, corrosion resistance, sealing systems, vibration and sound absorbance, and component repair. This paper reviews the current status of materials, equipment, processing, and properties’ aspects for key coatings in the energy industry, especially the developments in large-scale gas turbines. In addition to the most recent industrial advances in thermal spray technologies, future technical needs are also highlighted.
231 citations
TL;DR: In this article, the effects of commercially pure titanium particle morphology (spherical, sponge, and irregular) and size distributions (mean particle sizes of 20-49 μm) on the cold spray process and resulting coating properties were investigated.
Abstract: The effects of commercially pure titanium particle morphology (spherical, sponge, and irregular) and size distributions (mean particle sizes of 20-49 μm) on the cold spray process and resulting coating properties were investigated. Numerous powder and coating characterizations were performed including: powder oxygen and nitrogen contents, powder flowability, powder compressibility, coating microhardness, coating porosity, LOM/SEM analyses, and XRD. Compared to spherical powders, the sponge and irregular CP-Ti powders had higher oxygen content, poorer powder flowability, higher compression ratio, lower powder packing factor, and higher average particle impact velocities. XRD results showed no new phases present when comparing the various feedstock powders to corresponding coatings. A higher particle temperature was also obtained with larger particle size for all feedstock powder morphologies processed with the same set of spray parameters. A spherical powder with 29 μm mean particle size was found to have the lowest porosity coating and best cold sprayability. The relationships of several as-cold sprayed coating characteristics to the ratio of particle impact and critical velocities were also discussed.
120 citations
TL;DR: In this paper, the authors describe the difficulties and the development of process related solutions by employing diagnostic tools for thermal barrier coatings (TBCs) for gas turbines by plasma spraying.
Abstract: Growing demands on thermal barrier coatings (TBCs) for gas turbines regarding their temperature and cyclic capabilities, corrosion resistance, and erosion performance have instigated the development of new materials and coating systems. Different pyrochlores, perovskites, doped yttria-stabilized zirconia, and hexaaluminates have been identified as promising candidates. However, processing these novel TBC materials by plasma spraying is often challenging. During the deposition process, stoichiometric changes, formation of undesired secondary phases or non-optimum amorphous contents, as well as detrimental microstructural effects can occur in particular. This article describes these difficulties and the development of process-related solutions by employing diagnostic tools.
111 citations
TL;DR: In this article, the authors used thermoplastic and thermosetting polymer materials as substrates to study the behavior of a high velocity particle with the polymer substrate and found that the particle behaviors were unique with respect to the substrate.
Abstract: Cold spraying is a successful and promising coating technique for many engineering applications due to its high-rate and high-dense coating development abilities. Nevertheless, their practical use in polymer substrate is still in the fledgling phase. There are very few articles about the cold spray coating on polymers; however, the interaction of metallic particle with the polymer substrate is poorly understood, and thus a thick coating has not successfully been developed on the polymer substrate. In order to rationalize as full as possible the entire behavior of the high velocity particle with the polymer substrate, we used thermoplastic and thermosetting polymer materials as substrates. The particle behaviors with the substrate were observed under various gas pressure and temperature, and with various particles feed rate. The result showed that the particle behaviors were unique with respect to the substrate. Also it was clearly understood that the metal particles not experienced any plastic deformation due to the soft nature of the polymer substrates. The particles attached to the thermoplastic substrate either through adhesive bonding and/or mechanical inter locking, whereas only pure localized fracture observed on the thermosetting substrate and thus no particles attached firmly on the substrate.
98 citations
TL;DR: In this paper, the effect of spray parameters on the bonding ratio is presented to reveal the main droplet parameters controlling bonding formation, which reveals that the temperature of the spray particle rather than its velocity dominates the bonding formation.
Abstract: Thermal spray ceramic coatings deposited following the conventional routine exhibit a typical lamellar structure with a limited interface bonding ratio. The bonding between particles in the coating dominates coating properties and performance. In this review paper, the bonding formation at the interface between thin lamellae in the coating is examined. The effect of spray parameters on the bonding ratio is presented to reveal the main droplet parameters controlling bonding formation, which reveals that the temperature of the spray particle rather than its velocity dominates the bonding formation. The limitation to increase significantly the ceramic particle temperature inherent to the thermal spray process leads to the observation of a maximum bonding ratio of about 32%, while through controlling the surface temperature of the coating prior to molten droplet impact, the bonding at the lamellar interface can be significantly increased. Consequently, it is shown that with the proper selection of deposition conditions and control of the deposition temperature, the bonding ratio of ceramic deposits can be altered from a maximum of 32% for a conventional deposit to a maximum of 100%. Such wide adjustability of the lamellar bonding opens new possibilities for using thermal spray coatings in various applications requiring different microstructures and properties. The examination of recent studies shows that the bonding control makes it possible to fabricate porous deposits through surface-molten particles. Such an approach could be applied for the fabrication of porous materials, the deposition of high temperature abradable ceramic coatings, and for forming functional structured surfaces, such as a surface with super-hydrophobicity or a solid oxide fuel cell cathode interface with high specific surface area and high catalytic performance. Furthermore, complete interface bonding leads to crystalline structure control of individual splats through epitaxial grain growth.
95 citations
TL;DR: In this article, a phenomenological model is developed to identify basic growth mechanisms for thin and dense ceramic coatings and columnar-structured strain-tolerant coatings with low thermal conductivity.
Abstract: Plasma spraying at very low pressure (50-200 Pa) is significantly different from atmospheric plasma conditions (APS). By applying powder feedstock, it is possible to fragment the particles into very small clusters or even to evaporate the material. As a consequence, the deposition mechanisms and the resulting coating microstructures could be quite different compared to conventional APS liquid splat deposition. Thin and dense ceramic coatings as well as columnar-structured strain-tolerant coatings with low thermal conductivity can be achieved offering new possibilities for application in energy systems. To exploit the potential of such a gas phase deposition from plasma spray-based processes, the deposition mechanisms and their dependency on process conditions must be better understood. Thus, plasma conditions were investigated by optical emission spectroscopy. Coating experiments were performed, partially at extreme conditions. Based on the observed microstructures, a phenomenological model is developed to identify basic growth mechanisms.
86 citations
TL;DR: Inconel 718 was formed to a 6mm thickness on an 8-cm diameter aluminum alloy tube using Sulzer Amdry 1718 powder and the Plasma Giken PCS-1000 cold spray system as mentioned in this paper.
Abstract: Inconel 718 was cold spray formed to a 6-mm thickness on an 8-cm diameter aluminum alloy tube using Sulzer Amdry 1718 powder and the Plasma Giken PCS-1000 cold spray system. The effects of spray particle velocity and post-spray heat treatment were studied. Post-spray annealing was performed from 950 to 1250 °C for 1-2 h. The resulting microstructures as well as the corresponding mechanical properties were characterized. As-sprayed coatings exhibited very low ductility. The tensile strength and ductility of the heat-treated coatings were improved to varying levels depending on the heat-treatment and spray conditions. For coatings sprayed at higher particle velocity and heat treated at 1250 °C for 1 h, an elongation of 24% was obtained. SEM micrographs showed a higher fraction of interparticle metallurgical bonds due to some sintering effect. Corresponding fracture surfaces also revealed a higher fraction of dimple features, typically associated with ductile fracture, in the annealed coatings. The results demonstrate that cold spray forming of Inconel 718 is feasible, and with appropriate heat treatment, metallurgical bonding can be increased. The ductility of the spray-formed samples was comparable to that of the bulk material.
85 citations
TL;DR: In this article, the microstructure was characterized by SEM and optical microscopy while mechanical properties were measured by microhardness and tensile testing, and it was shown that coatings sprayed with nitrogen gas were relatively porous in comparison to the nearly completely dense coatings obtained with helium gas.
Abstract: The cold spray of Ti-6Al-4V coatings deposited on Ti-6Al-4V substrates has been investigated. Coatings were produced using nitrogen and helium as propellant gases and subsequently heat treated with various temperature-time conditions. The microstructure was characterized by SEM and optical microscopy while mechanical properties were measured by microhardness and tensile testing. It is shown that coatings sprayed with nitrogen gas were relatively porous in comparison to the nearly completely dense coatings obtained with helium gas. In the as-sprayed condition, coatings displayed high hardness but low tensile strength. Heat treatments at temperatures of 600 °C and higher resulted in a decrease in hardness due to microstructural changes within the particles including recovery, recrystallization, and/or phase transformation. However, an increase in tensile strength was attributed to improved inter-particle bonding due to an observed change from brittle to ductile features on the fracture surface. The highest strength coating produced was a helium-sprayed coating annealed at 600 °C, which featured a tensile strength ~85% of the minimum required bulk value and coating/substrate microstructures similar to the as-received powder/substrate microstructures.
82 citations
TL;DR: In this article, the phase structure of 8YSZ and 20YSZ coatings was investigated to understand the effects of phase structure on the sintering behavior of thermal barrier coatings.
Abstract: Plasma-sprayed YSZ coatings, serving as the thermal insulating top coating for thermal barrier coatings, involve thermally activated microstructural evolution, which may change the physical and mechanical properties and thereby influence the thermal barrier performance and service lifetime. In this study, 8YSZ and 20YSZ coatings annealed at 1300 °C were comparatively investigated to understand the effects of phase structure on the sintering behavior. Results show that, compared with the 20YSZ coating consisting of mainly thermodynamically stable cubic phase, the as-sprayed 8YSZ coating presented a multiphase structure mainly composed of thermodynamically metastable tetragonal phase, and significant phase transformation occurred during high-temperature exposure. The lamellar bonding had significantly improved because of the healing of intersplat pores. Fracture toughness, microhardness, and elastic modulus increased with sintering duration. The 8YSZ coating exhibiting the thermodynamically metastable tetragonal phase structure experienced a slower sintering kinetics than the 20YSZ coatings consisting mainly of thermodynamically stable cubic phase.
71 citations
TL;DR: In this paper, the corrosion characteristics of cold spray zinc coatings have been investigated for the first time and the influence of heat treatment of zinc coating at a temperature of 150°C on its corrosion behavior has also been addressed.
Abstract: Zinc and its alloy coatings have been used extensively for the cathodic protection of steel. Zinc coating corrodes in preference to the steel substrate due to its negative corrosion potential. Numerous studies have been conducted on the corrosion behavior of zinc and its alloy coatings deposited using several techniques viz., hot dip galvanizing, electrodeposition, metalizing or thermal spray etc. Cold spray is an emerging low temperature variant of thermal spray family which enables deposition of thick, dense, and pure coatings at a rapid rate with an added advantage of on-site coating of steel structures. In the present study, the corrosion characteristics of cold sprayed zinc coatings have been investigated for the first time. In addition, the influence of heat treatment of zinc coating at a temperature of 150 °C on its corrosion behavior has also been addressed.
70 citations
TL;DR: In this article, the authors further developed dysprosia stabilised zirconia coatings for gas turbine applications, and the target for these coatings was a longer lifetime and higher insulating p
Abstract: The aim of this study was the further development of dysprosia stabilised zirconia coatings for gas turbine applications. The target for these coatings was a longer lifetime and higher insulating p ...
TL;DR: In this article, the effect of spraying parameters on the resulting chromium carbide coating microstructure after high temperature operation and high temperature sliding wear properties was analyzed through x-ray diffraction and scanning electron microscopy.
Abstract: Chromium carbide-based thermally sprayed coatings are widely used for high temperature wear applications (typical temperature range from 540 to 900 °C). In these extreme environments at those temperatures, several phenomena will degrade, oxidize, and change the microstructure of the coatings, thereby affecting their wear behavior. Although it can be easily conceived that the Cr3C2-NiCr coating microstructure evolution after high temperature exposure will depend on the as-sprayed microstructure and spraying parameters, very little has been done in this regard. This study intends to develop a better understanding of the effect of spraying parameters on the resulting chromium carbide coating microstructure after high temperature operation and high temperature sliding wear properties. The microstructures of different coatings produced from two morphologies of Cr3C2-NiCr powders and under a window of in-flight particle temperature and velocity values were characterized through x-ray diffraction and scanning electron microscopy. Sliding wear at 800 °C was performed and the wear behavior correlated with the spraying parameters and coating microstructure. Vickers microhardness (300 gf) of the coatings before and after sliding wear was also measured.
TL;DR: In this paper, the cracks in TBC along the direction of the interface between ceramic coating and bond coat were examined from cross-section of TBC experienced different numbers of thermal cycle, and crack number and the total length of cracks were measured to aim at understanding the failure mechanism.
Abstract: The failure of plasma-sprayed thermal barrier coatings (TBC) usually occurs through spalling of ceramic coating. The crack evolution during thermal cycling of TBC is directly associated with its spalling. In this paper, the cracks in TBC along the direction of the interface between ceramic coating and bond coat were examined from cross-section of TBC experienced different numbers of thermal cycle, and crack number and the total length of cracks were measured to aim at understanding the failure mechanism. TBC consists of cold-sprayed NiCoCrAlTaY bond coat on IN738 superalloy and double layered plasma-sprayed 8YSZ with a columnar grain structured YSZ interlayer of about 20 μm thick and about 230 μm lamellar YSZ. With each isothermal cyclic test, the TBC samples were kept at 1150 °C for 26 min hold and then cooled down to a temperature less than 80 °C in 4 min by air forced cooling. Results showed that cracks propagated primarily within lamellar-structured YSZ over the columnar YSZ along lamellar interface. The measurement from the cross-section revealed that crack number and total crack length apparently increased with the increase of the number of thermal cycle. It was found that cracks with a length less than a typical size of 200 μm accounted for the majority of cracks despite the number of thermal cycle during the test. A crack initiation and propagation model for plasma-sprayed TBC is proposed with a uniform distribution of circular cracks. The propagatable cracks form homogeneously within plasma-sprayed porous YSZ coating at the early stage of thermal cycling and propagate at an identical rate during thermal cycling. Only a few of large cracks are formed before most cracks reach to the critical size for multi-cracks linking-up. The propagation of most cracks to the critical size will leads to the rapid crack bridging and subsequent spalling of top ceramic TBC.
TL;DR: In this article, cold spraying copper lines with 1 μm average diameter through a mask was used to print lines as front electrodes in solar cell applications, yielding high aspect ratio electrodes with minimum shadowing effects and maximum electrode-to-silicon contact area.
Abstract: Copper lines with widths varying from 150 to 1500 μm were deposited onto crystalline silicon wafers and soda-lime glass plates by cold spraying copper particles with 1 μm average diameter through a mask. This direct deposition method yielded high-aspect-ratio electrodes with minimum shadowing effects and maximum electrode-to-silicon contact area. The copper lines had triangular cross sections with aspect ratios (height/width) ranging from 0.1 to 1.1, depending on the number of spray gun passes. Copper particles were densely packed with increasing the width of the masking slit. This study presents the potential use of the cold spray technology in printing lines as front electrodes in solar cell applications.
TL;DR: In this paper, velocities of aluminum, zinc, and copper particles accelerated in an axisymmetric cold spray micronozzle are numerically simulated and experimentally measured.
Abstract: In the current study, velocities of aluminum, zinc, and copper particles accelerated in an axisymmetric cold spray micronozzle are numerically simulated and experimentally measured. It is found that aluminum and zinc particles can be accelerated to velocities close to the critical values in a supersonic nozzle with 1-mm exit diameter, 0.5-mm throat diameter, and 20-mm length when helium is used as the process gas. The diameter of the particle jet delivered by the micronozzle does not exceed 1.3 mm for any of the types of the tested powders.
TL;DR: In this article, several thermal spray coatings with high chromium content were sprayed with high velocity oxy-fuel (HVOF) technique and their mechanical properties and high temperature corrosion resistance were tested and analyzed.
Abstract: Heat exchanger surfaces of waste to energy and biomass power plant boilers experience often severe corrosion due to very aggressive components in the used fuels. High velocity oxy-fuel (HVOF) coatings offer excellent protection for boiler tubes against high temperature corrosion due to their high density and good adherence to the substrate material. Several thermal spray coatings with high chromium content were sprayed with HVOF technique. Their mechanical properties and high temperature corrosion resistance were tested and analyzed. The coating materials included NiCr, IN625, Ni-21Cr-10W-9Mo-4Cu, and iron-based partly amorphous alloy SHS9172 (Fe-25Cr-15W-12Nb-6Mo). High temperature corrosion testing was performed in NaCl-KCl-Na2SO4 salt with controlled H2O atmosphere at 575 and 625 °C. The corrosion test results of the coatings were compared to corrosion resistance of tube materials (X20, Alloy 263 and Sanicro 25).
TL;DR: In this article, the manufacturability of pyramidal fin arrays produced using the cold spray process has been explored using masks made of commercially available steel wire mesh and the standoff distances between the substrate, mesh, and nozzle were empirically determined.
Abstract: This work explores the manufacturability of pyramidal fin arrays produced using the cold spray process. Near-net shaped pyramidal fin arrays of various sizes and fin densities were manufactured using masks made of commercially available steel wire mesh. The feedstock powders used to produce the fins are characterized using scanning electron microscopy. Obstruction of the masks was investigated. The standoff distances between the substrate, mesh, and nozzle were empirically determined. Fin array characterization was performed using digital microscopy. The fin arrays’ heat transfer performance was assessed experimentally for a range of Reynolds number relevant to the application sought. The fins produced using the cold spray process outperform traditional straight (rectangular) fins at the same fin density and it is hypothesized that this is due to increased fluid mixing and turbulence.
TL;DR: In this article, the authors present a systematic evaluation of coatings for advanced fossil fuel plants and address fireside corrosion in coal/biomass-derived flue gases using a series of laboratory-based fire-side corrosion exposures.
Abstract: This article presents a systematic evaluation of coatings for advanced fossil fuel plants and addresses fireside corrosion in coal/biomass-derived flue gases. A selection of four candidate coatings: alloy 625, NiCr, FeCrAl and NiCrAlY were deposited onto superheaters/reheaters alloy (T91) using high-velocity oxy-fuel (HVOF) and plasma spraying. A series of laboratory-based fireside corrosion exposures were carried out on these coated samples in furnaces under controlled atmosphere for 1000 h at 650 °C. The tests were carried out using the “deposit-recoat” test method to simulate the environment that was anticipated from air-firing 20 wt.% cereal co-product mixed with a UK coal. The exposures were carried out using a deposit containing Na2SO4, K2SO4, and Fe2O3 to produce alkali-iron tri-sulfates, which had been identified as the principal cause of fireside corrosion on superheaters/reheaters in pulverized coal-fired power plants. The exposed samples were examined in an ESEM with EDX analysis to characterize the damage. Pre- and post-exposure dimensional metrologies were used to quantify the metal damage in terms of metal loss distributions. The thermally sprayed coatings suffered significant corrosion attack from a combination of aggressive combustion gases and deposit mixtures. In this study, all the four plasma-sprayed coatings studied performed better than the HVOF-sprayed coatings because of a lower level of porosity. NiCr was found to be the best performing coating material with a median metal loss of ~87 μm (HVOF sprayed) and ~13 μm (plasma sprayed). In general, the median metal damage for coatings had the following ranking (in the descending order: most to the least damage): NiCrAlY > alloy 625 > FeCrAl > NiCr.
TL;DR: In this paper, a transpiration cooling system for gas turbine applications has been developed with plasma spraying process, and the properties of the porous coating material such as permeability of cooling gas, thermal conductivity, and adhesion strength are examined.
Abstract: A transpiration cooling system for gas turbine applications has significant benefit for reducing the amount of cooling air and increasing cooling efficiency. In this paper, the porous ceramic coating, which can infiltrate cooling gas, is developed with plasma spraying process, and the properties of the porous coating material such as permeability of cooling gas, thermal conductivity, and adhesion strength are examined. The mixture of 8 wt.% yttria-stabilized zirconia and polyester powders was employed as the coating material, in order to deposit the porous ceramic coating onto Ni-based super alloy substrate. It was shown that the porous ceramic coating has superior permeability for cooling gas. The adhesion strength of the porous coating was low only 20% compared with the thermal barrier coating utilized in current gas turbine blades. Simulation test of hot gas flow around the gas turbine blade verified remarkable reduction of the coating surface temperature by the transpiration cooling mechanism. It was concluded that the transpiration cooling system for the gas turbine could be achieved using the porous ceramic coating developed in this study.
TL;DR: In this article, cold spraying was applied to deposit Ti2AlC on different substrate materials and the results showed that the coating microstructures showed rather low porosity of about <2%, but several cracks between spray layers.
Abstract: Cold spraying was applied to deposit Ti2AlC on different substrate materials. The study of single impacts by scanning electron microscopy indicates that bonding of the first layer is mainly attributed to the deformation and shear instabilities occurring at substrate sites. Nevertheless, as compared to the feedstock particles, the splats appear flattened by the impact. This deformation seems to be attributed not only to local, internal shear but also to internal fracture. By applying up to five passes under optimized spray parameters, Ti2AlC-coatings with thicknesses of about 110-155 μm were achieved. XRD analysis of the coating proved that the crystallographic structure of the feedstock was retained during cold spraying. The coating microstructures show rather low porosity of about <2%, but several cracks between spray layers. Successful build-up of more than one layer can probably be attributed to local deformation of the highly anisotropic Ti2AlC-phase.
TL;DR: In this article, the use of FeBSiNb amorphous coatings synthesized by arc spraying to improve elevated-temperature erosion resistance for boiler applications was discussed.
Abstract: Erosive high-temperature wear in boilers is one of the main causes of downtime and one of the principal engineering problems in these installations. This article discusses the use of FeBSiNb amorphous coatings synthesized by arc spraying to improve elevated-temperature erosion resistance for boiler applications. The influence of test temperature, velocity, and impact angle on material wastage was revealed using air solid particle erosion rig. The experimental results showed that moderate degradation of the coating was predominant at lower impact velocity and impact angles, while severe damage arose for higher velocities and impact angles. The erosion behavior of the coating was sensitive to test temperature. The erosion rates of the coating decreased as a function of environment temperature. The relationship between microstructure and erosion resistance of the coating was also analyzed in details. The FeBSiNb coating had excellent elevated-temperature erosion resistance at temperatures at least up to 600 °C during service.
TL;DR: In this paper, a thermal barrier coating system with different bond coats was fabricated on polymer matrix composites via the air plasma spray process, which consisted of a soft zinc layer as a bond coat, and YSZ as a top coat exhibited the best thermal shock resistance.
Abstract: Thermal barrier coating systems with different bond coats were fabricated on polymer matrix composites via the air plasma spray process. During a thermal shock test at 400 °C, Zn and Al interlayers were helpful in improving the thermal shock resistance of coatings due to the low melting point. The coating system consisted of a soft zinc layer as a bond coat, and YSZ as a top coat exhibited the best thermal shock resistance, attributed to the lower residual stress and lower thermal stress in the Zn interlayer. The failure mechanism of the coating system was mainly ascribable to the residual stress derived from the deposition process, thermal stress, and further damage of the substrate.
TL;DR: In this article, a model for the thermal conductivity of a thermally sprayed coating taking account of the effect of intrasplat cracks besides intersplat thermal contact resistance is proposed for further understanding of the thermal conduction behavior of thermally spraying coatings.
Abstract: Thermal spraying is one of the most important approaches for depositing thermally insulating ceramic top coatings for advanced gas turbines due to the low thermal conductivity of the coating resulting from its lamellar structure. The thermal conductivity of the coating has been explained based on the concept of thermal contact resistance and correlated to microstructural aspects such as splat bonding ratio, splat thickness, and the size of the bonded areas. However, the effect of intrasplat cracks on the thermal conductivity was usually neglected, despite the fact that intrasplat cracking is an intrinsic characteristic of thermally sprayed ceramic coatings. In this study, a model for the thermal conductivity of a thermally sprayed coating taking account of the effect of intrasplat cracks besides intersplat thermal contact resistance is proposed for further understanding of the thermal conduction behavior of thermally sprayed coatings. The effect of the intersplat bonding ratio on the thermal conductivity of the coating is examined by using the model. Results show that intrasplat cracks significantly decrease the thermal conductivity by cutting off some heat flux paths within individual splats. This leads to a deviation from the typical ideal thermal contact resistance model which presents cylindrical symmetry. Based on the modified model proposed in this study, the contribution of intrasplat cracks to the thermal resistivity can be estimated to be 42–57 % for a typical thermally sprayed ceramic coating. The results provide an additional approach to tailor the thermal conductivity of thermally sprayed coatings by controlling the coating microstructure.
TL;DR: In this paper, the phase composition, microstructure, and anti-ablation property of the ZrB2-based coating were investigated and the linear ablation rate was 0.17μm/s after ablation for 60 seconds in oxyacetylene torch.
Abstract: In order to improve the ablation resistance of C/C composites, ZrB2-based coating was prepared by supersonic atmosphere plasma spraying for SiC-coated C/C composites. The phase composition, microstructure, and anti-ablation property of the coating were investigated. Results show that the supersonic atmosphere plasma spraying is an effective method to prepare a dense ZrB2-based coating. The coating largely improves the ablation resistance of C/C composites. The linear ablation rate is 0.17 μm/s after ablation for 60 s in oxyacetylene torch. In ablation center, the ablation performance is determined by complicated mechanical denudation and chemical erosion. The formation of ZrO2 during ablation can partly prevent the diffusion of oxygen, which contributes to the good ablation resistance of ZrB2-based coating. In transition zone, the generation of SiO2 prevents inner coating from ablation and the chemical erosion becomes the leading mechanism.
TL;DR: In this article, the effects of substrate temperature on bond strength and coating properties are investigated for cold-gas-sprayed coatings of copper and aluminum on Al2O3.
Abstract: This study focuses on cold-gas-sprayed deposition of metallic coatings onto ceramic substrates for application in power electronics. In order to achieve the required surface activation for bonding, the substrate is heated during spraying. The effects of substrate temperature on bond strength and coating properties are investigated for cold-gas-sprayed coatings of copper and aluminum on Al2O3. It is found that the adhesion strengths of the cold-gas-sprayed coatings and that of the single-impacting particles increase with the increasing temperature and roughness of the substrate. Coatings sprayed on heated substrates show relatively low compressive stresses and low hardness, while their electrical conductivity reaches high values of over 90% IACS. Overall, a higher substrate temperature is found to improve the coating properties significantly.
TL;DR: In this paper, a wide variety of metallic materials (Cu, Ag, Zn, Nb, Ta, Ti, and 316L stainless steels) in the powder form have been deposited on a mild steel substrate using the cold spray technique.
Abstract: It is well established that cold spray coatings exhibit substantially lower elastic modulus as compared to bulk material of the same composition. It has also been observed that the heat treatment of the cold spray coatings results in a significant increase in the elastic modulus of the coating. To check whether the presence of inter-splat cracks is responsible for the above behavior, a wide variety of metallic materials (Cu, Ag, Zn, Nb, Ta, Ti, and 316L stainless steels) in the powder form have been deposited on a mild steel substrate using the cold spray technique. These coatings in both as-coated and heat-treated conditions have been characterized for their porosity, extent of inter-splat boundary cracking, hardness, and elastic modulus. Results indicate that the elastic modulus of the coatings are substantially lower than the bulk value and also that the heat treatment of the coatings consistently increase their elastic modulus values. It has been shown that the reduction in elastic modulus of cold spray coatings can be related to the extent of inter-splat boundary cracking. Further, it has been shown that the standard models relating elastic modulus to the crack density are capable of explaining the observed modulus in the case of cold spray coatings in the as-coated and heat-treated conditions.
TL;DR: In this article, the corrosion behavior of Ni alloy coatings deposited by high velocity oxyfuel spraying, and representative boiler substrate alloys in simulated high temperature biomass combustion conditions was reported.
Abstract: This paper reports the corrosion behavior of Ni alloy coatings deposited by high velocity oxyfuel spraying, and representative boiler substrate alloys in simulated high temperature biomass combustion conditions. Four commercially available oxidation resistant Ni alloy coating materials were selected: NiCrBSiFe, alloy 718, alloy 625, and alloy C-276. These were sprayed onto P91 substrates using a JP5000 spray system. The corrosion performance of the coatings varied when tested at ~525, 625, and 725 °C in K2SO4-KCl mixture and gaseous HCl-H2O-O2 containing environments. Alloy 625, NiCrBSiFe, and alloy 718 coatings performed better than alloy C-276 coating at 725 °C, which had very little corrosion resistance resulting in degradation similar to uncoated P91. Alloy 625 coatings provided good protection from corrosion at 725 °C, with the performance being comparable to wrought alloy 625, with significantly less attack of the substrate than uncoated P91. Alloy 625 performs best of these coating materials, with an overall ranking at 725 °C as follows: alloy 625 > NiCrBSiFe > alloy 718 ≫ alloy C-276. Although alloy C-276 coatings performed poorly in the corrosion test environment at 725 °C, at lower temperatures (i.e., below the eutectic temperature of the salt mixture) it outperformed the other coating types studied.
TL;DR: In this paper, Ni-Al2O3 coatings have been deposited using a Kinetic®3000 cold-spray system starting from Ni and Al 2O3 powders blend; five blends have been prepared setting the alumina content in the feedstock to 10, 25, 50, 75, and 90 w.%.
Abstract: Cermets coatings are extensively used in energy applications both because of their high wear resistance as required, for example, in components like gas turbine sealants, and because of their specific functionality as required in solar absorbers. So far, high-temperature thermal spraying and physical vapor deposition have traditionally been used to deposit this kind of coatings. In this study, Ni-Al2O3 coatings have been deposited using a Kinetic®3000 cold-spray system starting from Ni and Al2O3 powders blend; five blends have been prepared setting the alumina content in the feedstock to 10, 25, 50, 75, and 90 wt.%. The embedded alumina ranges between a few percent weight up to 16 and 31 wt.%, while the microhardness shows a deep increase from 175 Vickers in the case of pure Ni coatings up to 338 Vickers. The spray and coating growth mechanism have been discussed, with special attention to the fragmentation of the ceramic particles during the impact. Finally, the coating behavior at high temperature was analyzed by oxidation tests performed in air at 520 °C emphasizing a good oxidation resistance that could represent a very promising basis for application in power generation systems.
TL;DR: In this article, the influence of high strength adhesive infiltration on the microstructure and erosion performance of plasma-sprayed Al2O3 coatings was investigated to understand the improving mechanism of adhesion and cohesion through heterogeneous modification of nonbonded interfaces.
Abstract: The mechanical properties and related performance of thermally sprayed ceramic coatings are degraded by their relatively low adhesion and cohesion resulting from the limited bonding at substrate/splat interface and splat/splat interface. In this study, the influence of high strength adhesive infiltration on the microstructure and erosion performance of plasma-sprayed Al2O3 coatings was investigated to understand the improving mechanism of adhesion and cohesion through heterogeneous modification of nonbonded interfaces. Element distribution maps proved that the adhesive can be infiltrated from the coating surface to the coating/substrate interface through the inter-connected open pores including in-plane nonbonded area and microcracks in splats. Both adhesion and cohesion can be significantly improved by the heterogeneous modification of nonbonded lamellar interfaces of both splat/splat and splat/substrate through adhesive infiltration. The adhesive strength of the coating was increased from several MPa to ~50 MPa after adhesive infiltration. The erosion resistance at a large particle jet angle was improved by a factor of 3 due to the significant improvement of the lamellar cohesion, although the erosion resistance at a small particle jet angle was not significantly influenced.
TL;DR: In this article, the tribological properties of composite coating/graphite pairs were evaluated at high load conditions and the average friction coefficients, wear rates, and worn surface temperatures were measured.
Abstract: Al2O3, Cr2O3, and Al2O3-Cr2O3 composite coatings were produced by plasma spraying Their tribological properties were evaluated at high load conditions The average friction coefficients, wear rates, and worn surface temperatures of the coating/graphite pairs were measured Compared with the single coating/graphite pairs, the friction coefficients of composite coating/graphite pairs are more stable The corresponding wear rates and worn surface temperatures are lower, which may be conducive to the formation of more effective and stable graphite transfer film on the surface of the coating subjected to abrasion Especially, 10wt%Al2O3-90wt%Cr2O3 (AC90) composite coating shows better anti-wear performance, which may be attributed to its higher thermal conduction