Carbides are interesting materials for many wear resistant and high temperature applications, however, the production of coatings with these materials represents a significant challenge as they tend to oxidise or decompose into gaseous phases when they are exposed to extreme thermal spray conditions. An innovative method merging suspension and solution precursors was developed to allow the production of carbide composite coatings. Suspensions of carbides and borides were modified with the addition of oxide precursors to obtain composite coatings by high-velocity oxy-fuel (HVOF) thermal spray. The transformation of these oxides precursors and their subsequent melting during spraying contribute to protect the carbides from oxidising conditions, avoid their degradation during the spray process and support the development of dense coatings, as it was demonstrated by dispersive X-ray spectroscopy and X-ray diffraction analysis. The relationships between processing and microstructure were studied in terms of porosity phase distribution and mechanical properties, proving that this novel approach could be applied to obtain coatings of materials that are prone to decompose during thermal spraying.

In this study, a novel self-healing concept is considered in order to increase the lifetime of thermal barrier coatings (TBCs) in modern gas turbines. For that purpose, SiC healing particles were introduced to conventional 8YSZ topcoats by using various plasma spray concepts, i.e., composite or multilayered coatings. All topcoats were sprayed by SG-100 plasma torch on previously deposited NiCrAlY bondcoats produced by conventional atmospheric plasma spraying. Coatings were subjected to thermal conductivity measurements by laser flash method up to 1000°C, isothermal oxidation testing up to 200h at 1100°C and finally thermal cyclic fatigue (TCF) lifetime testing at 1100°C. Microstructural coating evaluation was performed by scanning electronic microscope (SEM), in the as-produced and post high-temperature tested states. This was done to analyze the self-healing phenomena and its influence on the high-temperature performance of the newly developed TBCs.

This study assesses the microstructure and properties of SiC-based coatings deposited using liquid and gas-fueled HVOF spraying techniques and a recently developed SiC-YAG ceramic powder. The coatings are shown to be superior to plasma and high-frequency pulse deposition sprayed SiC in terms of density and microstructure and comparable in terms of adhesion values. SEM and EDX analysis of the coatings shows that hard SiC particles are retained in a YAG binder, forming a composite that exhibits good sliding wear and erosion behaviors. Due to its low density (< 4 g/cm 3 ), the SiC composite may be an alternative to coating materials such as WC-CoCr and Cr 3 C 2 -NiCr in weight-sensitive applications.

In this work, silicon carbide coatings were fabricated by plasma spray-vapor deposition in order to study the effect of plasma gas mixtures on coating microstructure and phase composition. Coatings deposited by Ar-H 2 plasma gas were found to contain a composite phase of SiC and Si. Moreover, the content of Si increased with increasing H 2 content in the gas. The deposition of Si is possibly due to the reaction of C and hydrogen species in the plasma jet, which would explain why pure SiC coatings were obtained when Ar-N 2 gas was used.

Different types of tungsten carbide materials (fused tungsten carbide, nickel clad fused tungsten carbide, macrocrystalline WC and sintered and crushed WC/Co) are used for laser dispersing of construction steel surfaces. Surface roughness analyses and metallographic evaluation of cross sections concerning efficiency of carbide embedding as well as crack formation tendency are carried out. Generally, all types of tested carbides permit production of rough surfaces with metallurgical bonding to the metallic matrix, but only use of nickel clad fused tungsten carbide permits to prevent crack formation. The effectiveness of silicon and silicon carbide for production of durable rough surfaces on aluminium alloys is investigated. Both silicon and silicon carbide qualify for production of rough surfaces by laser dispersing. While silicon carbide particles show higher hardness, use of silicon does not include danger of embrittlement due to formation of aluminium carbide.

SiC coatings were prepared with pack powder in different particle sizes in a vacuum atmosphere by pack cementation technique to protect the C/SiC composites substrate from oxidation. The phase and microstructure of the coatings were investigated by XRD, SEM analyses. The relationship between powder granularity in the pack and microstructure of SiC coatings was studied. Cyclic oxidation test at 1573K in air atmosphere was performed and the effect of powder particle size in the pack on high-temperature oxidation resistance of SiC coatings was discussed in detail. It is observed that with powder granularity in the pack increasing thickness and density of SiC coatings increases, corresponding oxidation resistance of the coating is improved. Possible mechanisms related to oxidation were preliminarily discussed.

This work deals with ZrB 2 -based coatings prepared by inert plasma spraying and their behavior under high heat flux in moist atmospheres. ZrB 2 coatings with different compositions and microstructures were produced and subjected to high-temperature oxidation testing in order to identify the most oxidation-resistant sample. It is shown that coating microstructure can significantly influence oxidation kinetics and that uniformly dispersed nanoscale additives are particularly effective for slowing oxidation.

In this work, SiC coatings varying in content were prepared on carbon-fiber-reinforced silicon-carbide composite (C/SiC) substrates in order to study the effect of free silicon on oxidation resistance. The coatings were formed in a vacuum atmosphere by means of pack cementation using a powder mixture ranging in content as follows: 20-50 wt% SiC, 20-60 wt% Si, 7-12 wt% graphite, and 6-10 wt% Al 2 O 3 . Coating surface and cross-sectional morphologies were examined using SEM, EDS, and semiquantitative XRD analysis and oxidation resistance was determined by cyclic oxidation testing in air at 1300 °C. The results show that cracks and voids decrease with increasing free silicon content and that coatings with an appropriate amount of free silicon have better oxidation resistance than those with no free silicon at all. However, further increases in silicon content were found to be detrimental to oxidation behavior for a number of reasons that are discussed.

Novel synthesis of thermal spray grade silicon carbide (SiC) feedstock powder is necessary to allow deposition of this material using atmospheric plasma spraying (APS) method. SiC particles with average size of 1.0 µm are treated using co-precipitation techniques to deliver yttrium aluminum garnet (YAG) binder from its solution precursor as a nano-film onto SiC particles surface. The YAG nano-film will protect SiC core from direct interaction with plasma jet thus hindering their decomposition as well as providing matrix phase within the SiC particles vicinities. The modified SiC particles are sintered and crushed and then sieved to separate 25-45 µm and 45-90 µm size powders, which are then plasma sprayed to deposit SiC coatings of about 300 µm in thickness. Both the feedstock and the coatings were analyzed and compared with regards to their phase composition and microstructures.

In this work, Al/SiC composite coatings were deposited on the surface of aluminum alloys through atmospheric plasma spray. The effects of SiC volume in Al/SiC composite powders on the deposition behavior and the properties of the Al/SiC coatings were investigated. It was found that there were decarburization and oxidation during the deposition of pure SiC powders in the plasma flame. With the increase of SiC content, the deposition of the Al/SiC composite powder became more difficult through plasma spray. There were cracks between pure SiC and the bond coat on the Al alloy substrate resulting in poor adhesion between them. The hardness of the composite coating became higher with the increase of SiC contents. The Al/SiC(50:50) deposit with a thickness of 70 µm and a hardness of 369 Hv resulted in a strengthening and protection on the surface of Al alloy.

In the present investigation, Al5056 alloy-based metal matrix composites having SiC particles of different sizes were prepared by cold spraying. The average particle sizes of the used SiC feedstock varied from 66.94 µm to 1.64 µm. The calculated results by the FLUENT software show that the velocity of SiC particle decreases with the increase of the particle size, while the kinetic energy is greatly increased with increasing the particle size. The addition of SiC particles effectively reduces the porosity of the composite coatings. Furthermore, the porosity of the composite coatings increases with the decrease of SiC particle size, while the content of SiC in the coatings decreases with the decrease of SiC size. In addition, two effects of SiC particles determine the coating properties, i.e., the advantageous peening effect and the disadvantageous effect that reduces the effective contact between the coating and substrate.

Ceramic tiles are widely used as ballistic armor due to their ability to absorb high specific impact energy. However, ceramic materials often exhibit very low ductility and have a tendency to exhibit multiple fractures in spider-web patterns around the point of impact. One method used to introduce ductility is to encapsulate the tile in a metal jacket, or to provide a strongly adhered metallic backing plate. Aluminum and titanium metals are of primary interest to decrease the overall weight of the armor material system. The low temperature Kinetic Metallization (KM) process allows direct deposition of the metals onto the ceramic tiles. This is not possible with thermal spray processes due to the extreme mismatch in thermal expansion and adverse metallic-ceramic chemical reactions at high temperatures. Kinetic Metallization has been used to deposit aluminum and titanium coatings onto silicon carbide (SiC) and proprietary ceramic matrix composite (CMC) tiles. Ballistic testing of coated tiles has shown decreased fracturing of the armor material, leading to improved performance for subsequent impacts.

Microstructure and mechanical properties of 7075 Al alloy matrix and SiC reinforced composite coatings deposited on a T6 6061 Al alloy by cold spray are investigated. Feedstocks are prepared as mixtures of 7075 Al alloy and SiC powders with SiC content varying between 0 to 40 vol. %. Microstructural characterization is carried out by optical and scanning electron microscopic examinations and X-ray diffraction (XRD) analysis. The coatings mechanical behavior is evaluated using hardness measurements and wear tests. Wear tests are conducted under dry conditions using a ball-on disc tester under atmospheric conditions. The presence of SiC improves the coatings hardness and wear resistance when compared to pure 7075 Al coatings. The coating hardness increases with increasing SiC content; however SiC content higher than 10 vol.% does not lead to further increase in wear resistance. In this respect, the optimum composition of the coating is determined to be 92 vol. % 7075 Al + 8 vol. % SiC.

Thermal spraying of pure SiC is difficult due to decomposition issues at elevated temperatures. However, the development of suspension plasma spray opens a new path to investigate the deposition of this material since the liquid carrier can hinder this phenomenon. The present work investigates a new route for producing SiC submicron structured coating by suspension plasma spraying (SPS). Classical SiC manufacturing routes using suspension (i.e: spray drying, tape casting) are studied regarding their feasibility to be used on suspension plasma spraying. Aqueous-based suspensions containing 10 wt.% SiC powder (0.60 µm) along with sintering additives are dispersed and stabilized. Both suspensions are sprayed on martensitic stainless steel substrate (AISI 440C) to achieve finely structured and dense coatings. Digital image analysis, X-ray diffraction and scanning electron microscopy are utilized to characterize the coating microstructures. Their dependency on suspension characteristics and spray operation parameters are discussed with respect to the final coating performance.

Coatings containing up to 65 volume % of silicon carbide were deposited by plasma spray. Potential applications can be found in the protection of CMC (Ceramic Matrix Composite) against wear and high temperature oxidation. It is well known that SiC can not be deposited by thermal spray because it decomposes before melting. To face this problem, a mixture of SiC and ZrB 2 was deposited, since those two compounds form an eutectic phase, at a temperature lower to the one of SiC decomposition. Coatings microstructure was characterised by XRD, SEM, and EDS, confirming the presence of SiC in the deposited layer and the formation of the eutectic phase during spraying. Samples of the coatings were exposed in air at high temperature, in the range between 1373 and 1873 K. The oxide scale was investigated by means of SEM and EDS. It was constituted by a SiO 2 layer, which includes islands of ZrO 2 . Test results showed the good potentiality of the material investigated to be used as a protection against the high temperature oxidation.

In this paper, a commercial AZ91D magnesium alloy powder and its mixture with 30 vol.% SiC powder were used to deposit coatings by cold spraying. Two types of converging-diverging nozzles with different cross-sectional shapes were employed. The velocity and temperature of in-flight particles under different operating conditions were simulated using the FLUENT software. The simulated results show that the particle velocity through the rectangular cross-section nozzle is the same with that through the circular one. However, the coating observation shows that the AZ91D coating and its composite could only be deposited using the rectangular cross-section nozzle. The increase of gas temperature has little effect on the coating microstructure, porosity and microhardness. Furthermore, the observation of the composite coating produced under the gas temperature of 600°C shows that the SiC content in the composite is about 23 vol.%. The microhardness of the composite is improved to about 140 HV 0.3 due to the enhancement of SiC particles, compared to that of about 100 HV 0.3 for the AZ91D coating.

The cold gas dynamic spray process offers a unique advantage to form composite coatings by applying powder mixtures. The powder mixture constituents are supposed to interact with each other during impact. In this study, Al and Cu-based powder mixtures are used with the aim to define specific features of the coating formation. Composite coatings with different Al 2 O 3 , SiC, and Ti content are sprayed. Impact behavior of various powder mixtures is analyzed based on scanning electron microscopy images. The Al 2 O 3 and SiC phases of the initial powder are found to be fractured on impact and preserved in the coatings. Another advantage of the kinetic spray process is the ability to mix materials which would normally react with each other and form a composite coating. Some experimental data of such reactions are discussed. Within the composite coating, each constituent changes the initial properties of the sprayed powder material: for example, the soft matrix is strengthened, and hard particles are fractured. The fracture and deformation behavior of the particles and their reactions induced by the impact are determined by micromechanical tests and EDX analysis. Morphology, physical and mechanical properties of the sprayed coatings are discussed.

The quality of thermally sprayed coatings depends on a lot of parameters (spraying power, feedstock injection, morphology of the parts, kinetics and environment). But among them, adherence between the coating and the substrate appears as the fundamental point. To favor a good interaction and also a good adherence between the coating and the substrate, it is often necessary to clean and prepare the substrate surface. Conventionally, solvents and sand-blasting are applied to remove the contaminants and increase the surface roughness for a mechanical anchorage. But according to the substrate nature (ceramic) or the substrate morphology, it can be prejudicial to apply a mechanical treatment due to a peeling of the surface or a decrease of the global properties. By this way some other treatments have to be investigated in order to obtain an appropriate preparation. From all of them (water jet, ice blasting, heating treatment, etc.), laser ablation can be an interesting technology to prepare the substrate surface. The aim of this work was to study the modifications induced by 10 ns single or cumulative pulses of a Q-switched Nd:YAG near-infrared laser and its influence on the interface adhesion. The case of an alumina coating sprayed on a Ceramic Matrix Composite (CMC) has been studied. In these conditions, the laser treatment seems favorable from the adherence point of view according to the mechanical effect (induced by a cone-like structure) and the chemical effect

Mullite and mullite/ZrO 2 bi-layer systems are being considered as environment barrier coatings (EBCs) for protection of Si-based (Si 3 N 4 , SiC) substrates against water vapor corrosion for application in forthcoming turbine engines. An approach to reduce the thermal expansion mismatch between mullite and ZrO 2 layers in those coatings would be to tailor intermediate mullite/Y-ZrO 2 composite layers. The feasibility of these composite layers is studied in a comparative manner by plasma spraying both single mullite and bi-layer coatings of mullite and of mullite/ Y-ZrO 2 (75/25 vol %.) over Hexoloy SiC substrates. All feedstock materials are equally prepared using spray drying methods as the mix powders are not commercially available. Singular spraying conditions are used to assure enhanced crystallization of the mullite phase. Coatings are aged for 100 h at 1300 °C in a controlled water vapor environment. The effect of water corrosion on the exposed coatings is comparatively investigated, determining changes in crystalline phase by X-ray diffraction (XRD), the crystallization of amorphous phases is highlighted by the use of differential thermal analysis (DTA) tools and the microstructure of the polished coatings is analyzed by scanning electron microscopy (SEM).

Aluminum-based composite coatings reinforced with different volume fractions of SiC particles were deposited on aluminum substrates by means of pulsed gas dynamic spraying using a mechanically mixed composite feedstock powder. Microstructural features of the coatings are examined and their hardness is reported. The results show that the high fraction of SiC particles in the feedstock powder are retained in the coatings and that increasing SiC content in the aluminum matrix significantly improves coating hardness. The highest hardness value was obtained for a coating with 28 vol% SiC. Beyond that, coating hardness decreased, which is attributed to increasing porosity and decreasing cohesion between deposited aluminum-based particles.