Mechanisms of coating formation with flame spraying

Gavrilenko, T. P.; Nikolaev, Yu. A.; Prokhorov, E. S.; Ul’yanitskii, V. Yu.

doi:10.1007/bf00742417

Cited by 9 publications

(4 citation statements)

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“…Consequently, for the metallic glass coatings to be formed, cooling rates higher than 10 5 K s −1 should be provided for the detonation splats. The cooling rate of the splats can be estimated using the characteristic cooling time defined as t = h 2 a , where h is the thickness of the splat (can be taken equal to 15 µm for particles 45 µm in diameter) and a is the thermal diffusivity of the material, a = k ρc p (k is the thermal conductivity, ρ is the density; c p is the heat capacity) [26]. For calculations, k = 10 W m −1 K −1 and c p = 1 kJ kg −1 K −1 were used.…”

Section: Resultsmentioning

confidence: 99%

Formation of Metallic Glass Coatings by Detonation Spraying of a Fe66Cr10Nb5B19 Powder

Kuchumova

Batraev

Ulianitsky

et al. 2019

Metals

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The present work was aimed to demonstrate the possibility of forming Fe66Cr10Nb5B19 metallic glass coatings by detonation spraying and analyze the coating formation process. A partially amorphous Fe66Cr10Nb5B19 powder with particles ranging from 45 µm to 74 µm in diameter was used to deposit coatings on stainless steel substrates. The deposition process was studied for different explosive charges (fractions of the barrel volume filled with an explosive mixture (C2H2 + 1.1O2)). As the explosive charge was increased from 35% to 55%, the content of the crystalline phase in the coatings, as determined from the X-ray diffraction patterns, decreased. Coatings formed at explosive charges of 55–70% contained as little as 1 wt.% of the crystalline phase. In these coatings, nanocrystals in a metallic glass matrix were only rarely found; their presence was confined to some inter-splat boundaries. The particle velocities and temperatures at the exit of the barrel were calculated using a previously developed model. The particle temperatures increased as the explosive charge was increased from 35% to 70%; the particle velocities passed through maxima. The coatings acquire an amorphous structure as the molten particles rapidly solidify on the substrate; cooling rates of the splats were estimated. The Fe66Cr10Nb5B19 metallic glass coatings obtained at explosive changes of 55–60% showed low porosity (0.5–2.5%), high hardness (715–1025 HV), and high bonding strength to the substrate (150 MPa).

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Section: Resultsmentioning

confidence: 99%

Formation of Metallic Glass Coatings by Detonation Spraying of a Fe66Cr10Nb5B19 Powder

Kuchumova

Batraev

Ulianitsky

et al. 2019

Metals

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“…A comprehensive concept of the formation of detonation coatings was outlined in Ref. [31]. For the formation of a strong bond between the coating and the substrate, inter-diffusion within a depth of several inter-atomic distances should take place.…”

Section: Mechanisms Of Coating Formation By Detonation Sprayingmentioning

confidence: 99%

“…The surface roughness plays an important role in the processes of heat transfer from a sprayed particle to the substrate. The roughness vertices contacting the particle are heated more than the valleys [3,31]. Another mechanism of the coating formation-a dynamic mechanism-may become valid, when rapid energy dissipation in the boundary layer occurs or the diffusion coefficients of the sprayed materials increase significantly due to rapid deformation of the solid particles.…”

Section: Mechanisms Of Coating Formation By Detonation Sprayingmentioning

confidence: 99%

Computer-Controlled Detonation Spraying: Flexible Control of the Coating Chemistry and Microstructure

Ulianitsky

Dudina

Штерцер

et al. 2019

Metals

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This article is a focused review aimed to describe the potential of the computer-controlled detonation spraying (CCDS) for producing and designing coatings with variable chemical and phase compositions and microstructure and promising properties. The development of the detonation spraying method is briefly analyzed from a historical perspective and the capabilities of the state-of-the art facilities are presented. A key advantage of the CCDS is the possibility of using precisely measured quantities of the explosive gaseous mixtures for each shot of the detonation gun and different oxygen to fuel ratios, which can create spraying environments of different chemical properties—from severely oxidizing to highly reducing. The significance of careful adjustment of the spraying parameters is shown using material systems that are chemically sensitive to the composition of the spraying environment and temperature. Research performed by the authors on CCDS of different materials—metals, ceramics, intermetallics and metal-ceramic composites is reviewed. Novel applications of detonation spraying using the CCDS technology are described.

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“…The boundary conditions on the open end of the barrel, which were previously based on empirical data, are posed exactly. In addition, the model predicts the final result of spraying: strength of adhesion (cohesion) between the coating and the substrate [4].…”

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confidence: 99%

Limits of gaseous detonation spraying

Gavrilenko

Nikolaev

2006

Combust Explos Shock Waves

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The maximum possible values of adhesion and cohesion are calculated for a number of powder materials, substrate materials, sizes of installation barrels, and compositions of explosive gas mixtures. These data give a clear idea about the areas of applicability of gaseous detonation spraying.The process of gaseous detonation spraying implies that an explosive mixture is injected through a gas mixer into a tube (barrel) closed on one end, a portion of the powder is fed into the barrel, and then detonation is initiated near the closed end of the barrel. The flow of detonation products expanding from the barrel accelerates and heats the powder particles. Leaving the barrel, the powder particles hit a target (substrate) and form a coating. The general concept of the current status of this technology can be found in the review [1].The main advantage of gaseous detonation spraying is the possibility of obtaining coatings from a wide range of powder materials (metals, alloys, carbides, oxides, and composites), the absence of porosity (less that 1%) in coatings, and significantly higher adhesion and cohesion as compared with coatings obtained by other methods. Owing to the pulse character of spraying, there are no problems with cooling of the barrel and with cooling, warping, or thermal damages of treated parts.In all gas-thermal methods of spraying, coating formation is determined by diffusion processes where the main role belongs to particle velocity and temperature, which energetically complement each other. A detonation coating is formed by elementary acts of interaction of high-velocity melted or partly melted particles with a cold surface of the substrate.The pressure behind the detonation-wave front reaches tens of atmospheres, and the temperature can be as high as several thousand degrees, which allows accelerating powder particles up to several hundred meters per seconds and heating the particles up to the melting point and above.A melted or partly melted particle moving with a velocity greater than 100 m/sec spreads over the substrate surface and forms a cumulative jet, which cleans the substrate surface and ensures good contact (at a molecular level) between the particle and the substrate. A certain part of the substrate surface experiences microscopic plastic deformation upon the impact. Adhesion and cohesion depend on the relative area of the contact surface where interdiffusion occurs to a depth of several interatomic distances during particle cooling on the substrate surface.Ledges of the substrate-surface roughness are under privileged conditions, because they are surrounded by the hot particles to a greater extent and, therefore, are heated to a higher temperature.Particles that are not melted at all do not usually form a coating. Particle overheating has also an adverse effect. Completely melted particles can splash at the impact onto the substrate or spread widely over the substrate surface, which is hazardous from the viewpoint of crack formation in the coating. Being accelerated, melted particles can b...

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Mechanisms of coating formation with flame spraying

Cited by 9 publications

References 0 publications

Formation of Metallic Glass Coatings by Detonation Spraying of a Fe66Cr10Nb5B19 Powder

Formation of Metallic Glass Coatings by Detonation Spraying of a Fe66Cr10Nb5B19 Powder

Computer-Controlled Detonation Spraying: Flexible Control of the Coating Chemistry and Microstructure

Limits of gaseous detonation spraying

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