Investigation of the morphologies of chelate flame-sprayed metal oxide splats
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The working principle and development status of several thermal spraying technologies was introduced,including plasma spraying,flame spraying,and arc spraying technology.The issues of improving the bonding strength of spray coatings were discussed.The development of nano-coating materials for thermal spray coating in recent years was introduced.
Technology Development
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Abstract Thermal spray is a generic term for a group of coating processes used to apply metallic, ceramic, cermet, and some polymeric coatings for a broad range of applications. This article provides a brief description of commercially important thermal spray processes, namely, powder-fed flame spray, wire- or rod-fed flame spray, electric arc spray, plasma arc spray, vacuum plasma spray, high-velocity oxyfuel spray, detonation gun deposition, and cold spray, and their advantages. It provides details on the microstructural characteristics of thermal spray coatings. The article also presents information on a wide variety of materials that can be thermal sprayed, such as metals, ceramics, intermetallics, composites, cermets, polymers, and functionally gradient materials. Tables are included, which list the thermal spray processes and coating properties of importance for various industrial applications.
Cermet
Spray forming
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The overall aim of this research project was to expand the understanding of the deposition of titanium and the nickel-based superalloy Inconel 718 by spray deposition methods. The spray processes employed were cold spraying and high velocity oxy-fuel (HVOF) thermal spraying.
The first part of the work was undertaken to expand the understanding of the deposition of titanium by cold spraying; the HVOF process is unsuitable for Ti because of the metal's high reactivity. The deposits were produced from commercially pure titanium using cold spray equipment designed in the University. Using helium gas, the effects of different powder particle size ranges, types of substrate, substrate preparation methods, and spray parameter conditions on deposit formation were investigated. Using a simple one-dimensional model of compressible gas flow and particle acceleration, particle velocity distributions were calculated to aid interpretation of experimental data. Results show that titanium can be successfully cold sprayed onto substrates of Ti6AI4V and mild steel, with the critical velocity for deposition of this powder type of approximately 690 m s-1. The level of porosity was generally in the range of 13-23% and the adhesive bond strength was dependent on surface preparation but independent of gas pressure with values ranging from 22 MPa to 10 MPa for ground and grit blasted substrates respectively. This compares with a value of around 80 MPa which is typical for well adhered HVOF sprayed coatings.
The second part of the study was concerned with comparing the deposition of Inconel 718 by cold spraying and HVOF thermal spraying; the latter employed a JP5000 liquid fuel gun. A Tecnar DPV-2000 instrument was used to systematically investigate the effect of changes in spray parameters (spraying stand-off distance, oxygen/fuel ratio, total mass flow rate, combustion pressure), on particle velocity and temperature during HVOF spraying. It was found that generally the particle velocity was more strongly affected by the stand-off distance and combustion pressure of the spraying gun whereas the particle temperature was mostly influenced by the particle size and combustion pressure. The microstructures of coatings sprayed under 4 different well controlled conditions were investigated and changes in the morphology of splats and partially melted particles in the coating were related to the particle temperature and velocity at impact. The HVOF had high bond strength and low oxygen level of typically 0.45 wt% (corresponding to an oxide content of less than 1.6 wt.%). By contrast, in the cold sprayed coatings, the bonding was considerably low (-14 MPa), independently from the process conditions. It was found that the process parameter that mainly affected the properties of the cold sprayed deposits was the gas pressure. More specifically, the microhardness of the coatings increased with the pressure whereas the relative porosity decreased.
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Inconel
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Abstract This paper considers the deposition of a commercial steel powder with a chemical composition that allows the coating to obtain an amorphous structure using thermal spray techniques. The processes used are characterized by high cooling speeds of the particles after the impact upon the substrate. The powders were sprayed with two different processes: cold gas spray (CGS) and high velocity oxyfuel (HVOF). A comparison between the samples obtained reveals that only the CGS coatings are completely amorphous; the HVOF samples exhibit nanocrystalline phases, detected with XRD analysis and SEM micrographs. Furthermore, the CGS coatings are more compact and show lower hardness with a comparable Young’s modulus. A hypothesis is that the formation of the amorphous structure is related to plastic deformation at impact (due to the high energy of the particles), rather than to the temperature; the mechanism could resemble that of a severe plastic deformation process. Additional thermal treatments and mechanical tests are in progress to investigate the toughness and other mechanical properties of the coatings.
Nanocrystalline material
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Suspension
Particle (ecology)
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Cermet
Tungsten Carbide
Spray forming
Cladding (metalworking)
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Abstract Cold spray is a new emerging coating technology in which particles in a solid state are deposited via plastic impact on a substrate at a high velocity and a temperature that is much lower than the melting point of the starting powder. Compared to the conventional thermal spray processes, dense coatings without any degradation can be obtained by cold spray process with high deposition efficiency. CoNiCrAlY coatings are widely used for land-based gas turbines to resist high-temperature oxidation and hot corrosion. Owing to the high cost of the low-pressure plasma spray (LPPS) or some degradation in the hyper-velocity oxy-fuel (HVOF) spray process, cold spray process is a prospective candidate for coating preparation. In the current study, CoNiCrAlY coatings were prepared by cold spray and LPPS processes, and a comparison of the coating’s properties between the LPPS and cold spray process was carried out. The spray conditions of cold spray were optimized by the measurements of deposition efficiency and the observations of microstructure.
Deposition
Degradation
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This chapter contains sections titled: Introduction Flame Spraying (FS) Atmospheric Plasma Spraying (APS) Arc Spraying (AS) Detonation-Gun Spraying (D-GUN) High-Velocity Oxy-Fuel (HVOF) Spraying Vacuum Plasma Spraying (VPS) Controlled-Atmosphere Plasma Spraying (CAPS) Cold-Gas Spraying Method (CGSM) New Developments in Thermal Spray Techniques References
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Abstract From the appearance of high velocity oxygen fuel (HVOF) thermal spray system on 1980s, WC cermet coatings have been used as an anti-wear coating in many industrial manufacturing. Recently, WC cermet spray materials were applied to new thermal spray methods such as warm spray and cold spray under research phase. In HVOF spraying, WC-Co or WC-Ni series powder are used as standard contents. Ni and Co are binder metals for WC because of good wettability and suitable melting point. On the other hand, warm spray and cold spray are lower temperature process than HVOF. It is considered that any other factors of metal material such as hardness, toughness and crystal phase should be investigated in warm spray and cold spray. In this study, WC with Co or Fe alloy powders were sprayed by cold spray and HVOF to investigate the influence of binder metal for spray efficiency and coating property. It is cleared that Ni and Fe were superior to Co in spray efficiency and coating property in cold spray. The detail of above reason was under investigation, however, plastic deformability of binder metal is expected to be an important factor for WC cermet cold spraying.
Cermet
Spray forming
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Abstract From the appearance of high velocity oxygen fuel (HVOF) thermal spray system in the 1980s, WC cermet coatings have been used as anti-wear coatings in many industrial manufacturing applications. Recently, WC cermet spray materials were applied using new thermal spray methods such as warm spray and cold spray, which are still in the research phase. In HVOF spraying, WC-Co and WC-Ni powders are regularly used as coating materials. On the other hand, using cold spray, WC-Fe alloy series can be deposited as dense and thick coatings, better than WC-Co. In this study, WC-Fe alloy powders were sprayed by cold spray to investigate the influence of binder metal on the coating properties and compared with those of HVOF WC-CoCr coatings. It was observed that the lower metal ratio and FeCrNi chemical composition exhibited improved results.
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