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.

Presently one of the most important tendencies is the use of tungsten (W) monoblock material for the first wall and other plasma facing components (PFCs) in tokamak. The use of low Z materials such as B 4 C for protection of PFCs is a conventional method to decrease heavy impurity influx into tokamak plasma. This study involves the fabrication and characterization of inductively coupled plasma (ICP) thermal sprayed B 4 C coating on tungsten monoblock. Thickness of the coating was about 120μm. Surface morphology of the coating is presented with scanning electron microscope and metallographic microscope analyses. X-ray diffraction analysis and X-ray photoelectron spectroscopy showed that the main phase and chemical composition of the coatings were preserved when compared with that of the initial B 4 C powder. Adhesion test result revealed that the adhesion/cohesion strength of the coating was above 13.1 MPa. This work is innovative not only for the ICP thermal sprayed method for the B 4 C coating fabrication but for the plasma sprayed B 4 C on tungsten substrate.

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.

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 the oil industry, logging systems involving geological sensors are designed to operate under increasing severe service conditions of deep and horizontal boreholes. Under these conditions, metal matrix composites (MMCs) with ceramic reinforcement are applied on components to achieve wear and corrosion resistant systems. The ‘cold spray’ could be described as a cold and inert process to form coating layers through severe plastic deformation of a ductile metal. Ceramic/metal MMC coating could be achieved by co-deposition of a ceramic with a ductile material. In this work, it was it was investigated the use of MMC B 4 C-Ni coating from both mechanically milled blends or B 4 CNi CVD coated batches. Powder blends involving Ni powder with fine or coarse B 4 C powders were prepared by mechanical milling. Three CVD coated B 4 C-Ni powder batches were synthesized with 30, 40 and 50 Ni wt% respectively. Cold spray coatings were achieved with 1 pass and 5 passes to investigate the building-up mechanisms and interfaces with AISI316L. Powders and cold sprayed coatings microstructures were observed by optical and scanning electron microscopies and further quantitative image analysis were carried out to determine the content of B 4 C embedded in the Ni matrix of B 4 C-Ni cold spray coatings. The highest B 4 C vol.%, up to 45%, could be reached in the case of B 4 C-Ni coated powder. Micro-hardness values of such MMC coatings were also determined through Vickers micro-indentation. The beneficial role of the Ni surrounding layer on coating formation is discussed in relation to the unique features of the microstructures obtained by cold spray of B 4 C-Ni coated powders.

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 superior mechanical properties of Boron Carbide make it very attractive for use as a wear resistant coating in tribological applications. Boron carbide is the hardest non-oxide ceramic produced in large quantities. It offers a high erosion and abrasion resistance, high chemical and outstanding heat resistance. B4C can be formed on a suitable substrate by thermal spray process as an alternative to high wear carbide coatings. The objective of this work was to investigate and to characterize the mechanical properties of a boron carbide based coating applied by HVOF spraying using a non commercial powder for corrosion and abrasion applications. The produced coatings were evaluated by metallographic procedure, microhardness, porosity and roughness measurements as well as adhesion and wear tests. The results are promising and signal good applications for such coatings.

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).

The PAS method was used to produce W-ZrC and W-HfC composite powder, and the LVPS process technologies were used to create W composite coating layers. In addition, the mechanical properties, high-temperature resistance, and ablation characteristics of the W composite coatings were compared and analyzed for different types of carbides. For comparison and analysis, Vickers hardness, porosity, and adhesive strength were measured, and plasma torch tests were conducted. The use of the LVPS technologies led to successful production of W composite coatings (W-HfC; W-ZrC), approximately 1,000 μm or above in thickness. ZrC particles were observed in the layers of W-ZrC coating. The porosity was 3.59 % in W-HfC and 7.74 % in W-ZrC, indicating the W-HfC coating had a better pore quality than W-ZrC. Vickers hardness was approximately 120Hv higher in W-ZrC than in W-HfC due to the presence of ZrC particles in the W-ZrC coating. Adhesive strength was found to be nearly identical in both coatings. Results of the evaluation of high thermal resistance characteristics of the W composite coating materials showed that W-ZrC coating performed better in resisting high thermal conditions than W-HfC coating, due to the strengthening effects of ZrC particles in the layers and the generation of ZrO 2 phase with high levels of stability in high temperatures.

Three types of cobalt-based cermet coatings were prepared by high velocity oxy-fuel (HVOF) spraying using cobalt- clad TiC-50Co, SiC-50 Co and WC-18Co powders. The microstructure of three coatings was characterized using a scanning electron microscope (SEM). The adhesive strength of the coatings was tested according ASTM C633-79 standard. The hardness of three coatings was measured using a HV-5 Vickers hardness tester. The abrasive wear performance of the coatings was examined by a dry-sand rubber wheel tester according to ASTM G65-61 standard. The results show that the density, thermo physical properties and volume fractions of the solid carbide phases in the spray particle have a significant influence on the adhesive strength of the coatings. The hardness of WC-18Co coating is higher than that of TiC-50Co and SiC-50 coatings and is much lower than WC-17Co coating deposited with sintered-crushed powders. Moreover, the abrasive wear volume loss of the WC-18Co coating is about 60 times higher than that of the WC-12Co coating sprayed by sintered-crushed powder, and greatly lower than that of TiC-50Co and SiC-50 coatings. The wear mechanisms of three coatings are discussed.

Thermal spray coatings from several different coating families have been metallographically prepared using traditional and modern metallographic techniques. The different recipes used were intended to demonstrate the effect of abrasive on coating appearance. Traditional metallographic recipes, which rely heavily on the use of silicon carbide (SiC) abrasive papers, were found to produce a notably different appearance than those prepared using modern recipes. Modern recipes, which incorporate extended diamond grinding and polishing steps, were found to produce what appears to be a more representative coating structure. Other variables, including mounting media and use of vacuum impregnation, were also found to influence coating appearance.

The combination of excellent mechanical, thermal and chemical properties of silicon carbide (SiC) and titanium carbide (TiC) has made these materials very attractive both for structural ceramics applications and for thermal sprayed coatings. To suppress oxidation and to avoid the formation of silicides during spraying of SiC-based composites, feedstock spray powders have been developed containing 32 wt.-% of an alumina-yttrium ceramic binder matrix. The spray powders are prepared by spray-drying and sintering (a&s). Also, TiC-based composite spray powders showing the same matrix material and content have been developed and produced. Thermal spray processing of the described powders by atmospheric plasma spraying (APS) using an F6 APS torch and high velocity oxygen fuel spraying (HVOF) with the Top Gun G acetylene torch is carried out. Both the produced coatings and feedstock powder are characterized by optical microscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray analyses (EDXS).

Thermo-abrasive blasting is a technique, which combines conventional abrasive blasting and HVAF processes to prepare surfaces prior coating. Thermo-abrasive blasting has a number of advantages over conventional abrasive blasting as the result of a higher nozzle pressure and heat, which helps to remove impurities from the surface. However, practice showed that the short life of blasting nozzles due to thermal stresses and excessive wear is the biggest drawback of this method. Therefore, the correct nozzle geometry and suitable materials are critical for an efficient operation of thermo-abrasive blasting systems. In this study, computational fluid dynamics and finite element analyses were used to obtain the temperature distribution and to evaluate thermal stresses in nozzle materials. The materials investigated include tungsten carbide-cobalt (WC-6wt.% Co), hot pressed dense silicon carbide (SiC) and SiALON (Si 3 N 4 -Al 2 O 3 -AlN). The analysis and experiments showed that WC-CO nozzles produce the best overall results of thermal shock resistance and wear in thermo-abrasive blasting.