RU2462536C1 - Method to apply coatings - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: method includes installation of a plasmatron into a chamber with lower pressure, arrangement of a substrate for coating application in a chamber, maintenance of dynamic vacuum in the chamber, supply of plasma-forming gas and powder of sprayed material into the plasmatron and spraying of material by supersonic flow of plasma in the chamber to form melted particles of powder and steam phase of the sprayed material. In front of the substrate, onto which a coating is applied, a mask with holes and links between them is installed, flow of steam phase of a sprayed substance is ensured around links, underpressure waves are developed behind the links, where the steam phase condenses to form nanoparticles, which drop onto the substrate and form a coating in the form of narrow strips made only of nanoparticles and arranged around sections of the coating provided oppositely to the mask holes from powder particles. The mask is moved relative to the applied coating, and subsequent layers of the coating are generated on the applied layer to produce a coating with a structure of several applied layers.

EFFECT: improved working characteristics of a coating under multiple thermocyclic loads.

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Description

The invention relates to the field of nanotechnology used for coating, and can find application in the engineering industry, namely in rocket science and aircraft construction.

A known method of coating [1], in which using plasma spraying of powders of micron-sized materials, supersonic plasma flows in chambers with reduced pressure are applied to a substrate. During coating, a dynamic vacuum is maintained in the chamber, i.e. the process takes place in a chamber into which plasma enters from the plasma torch on one side, and on the other hand, the atmosphere of the chamber is constantly evacuated by vacuum pumps.

The disadvantage of this method is that the coatings obtained have a coefficient of thermal expansion (CTE), which is usually 2-3 times different from the CTE of the substrate, which leads to the appearance of cracks in the coating and its destruction when there are multiple thermocyclic loads.

The objective of the invention is to significantly improve the performance of the coating at multiple thermocyclic loads due to conducting longitudinal layer-by-layer nanostructuring with it.

To achieve this technical result in the proposed method of coating, including installing a plasma torch in a chamber with reduced pressure, placing a substrate for coating in the chamber, maintaining a dynamic vacuum in the chamber, supplying a plasma-forming gas and powder of the sprayed material into the plasma torch and spraying the material with a supersonic plasma stream in chamber with the formation of molten powder particles and the vapor phase of the sprayed material, in front of the substrate on which the coating is applied, install with holes and jumpers between them, they only allow the vapor to flow around the jumpers with the vapor phase of the sprayed substance, create rarefaction waves behind the jumpers, in which the vapor phase condensates to form nanoparticles, which fall onto the substrate and form a coating in the form of narrow bands consisting of only nanoparticles and located around the coating areas created opposite the mask openings from powder particles, in addition, the mask is shifted relative to the applied coating and the following coating layers are formed on the already applied SG coating for structures of several coatings.

The figure 1 presents a diagram of the location of the plasma torch, substrate and mask, with which the proposed method can be implemented. A plasmatron [2] is placed in a vacuum chamber, into the plasma-forming gas of which a powder of material is added, which is coated. A plasma jet containing a plasma-forming gas, molten powder particles and material in the vapor phase, into which it partially passed in the plasmatron and supersonic nozzle 1 of the plasma torch, flows into the dynamic vacuum region. In this case, in the underexpanded plasma jet, a hanging shock wave of compaction 2 occurs, inside which a supersonic flow is realized, which coincides with the outflow of the jet into vacuum [3].

In front of the substrate 3, a mask 4 is installed, in which there are openings 5 of arbitrary shape with jumpers 6 between them. On the substrate opposite the holes 5, the usual coating 7, characteristic of plasma-cluster technology, occurs. In this part of the coating on the substrate there are both large particles and small particles of the sprayed substance with the presence of large pores between them. At the same time, in the coating areas opposite to the jumpers 6 (in the so-called “shaded areas” from direct plasma leakage), the Prandtl-Meyer flow is realized — the supersonic flow of vapor through the vapor phase of the material in the mask with the formation of a fan of rarefaction waves 8, which passes from the vapor phase of the sprayed The material condenses nanoparticles, which fall onto the substrate and form narrow bands 9 in the coating, consisting entirely of nanoparticles, with almost no pores between them. In this case, in those parts of the coating that are opposite the holes, the protective properties of the traditional coating are fully preserved, and in narrow bands around these areas, the coating consists of nanoparticles alone, which have increased adhesive strength compared to a conventional coating, but with slightly deteriorated protective properties due to the absence of pores between them.

Thus, in the longitudinal direction, a cellular structure of the coating is formed (see FIG. 1), consisting of regions of ordinary continuous coating 7 and narrow strips 9 bordering these regions consisting of nanoparticles. Such a coating design leads to the fact that in the case of applying multiple thermocyclic loads to the coating, noticeable cracks caused by the difference between the KTP of the coating material and the substrate material do not form at all due to the small size in the absolute value of the areas with a conventional coating, or in the case of a possible crack formation does not go beyond this area, because it is surrounded by a coating strip consisting of nanoparticles having higher strength characteristics, although less protective properties.

Moving the mask in the longitudinal direction relative to the applied coating layer by an amount smaller than the cell size, the next layer of nanostructured coating in the longitudinal direction is applied. Thus, the required number of layers is applied to perform the protective functions of the coating. As a result, a multilayer protective longitudinally nanostructured protective coating is formed on the substrate (see Fig. 2), the effect of which reusable thermocyclic loads will not lead to the destruction of the coating due to the presence in the layers of jumpers made of nanoparticles with increased adhesive strength at the interface between the layers and areas with a normal coating inside each layer.

The proposed technical solution makes it quite simple to obtain a nanostructured coating in the longitudinal direction, which has increased resistance to the effects of reusable thermocyclic loads on it; however, the method of obtaining part of the coating using nanoparticles is environmentally friendly, because the entire process of formation of nanoparticles from the vapor phase of the sprayed material prior to application to the substrate occurs in a closed volume of a vacuum chamber, completely isolated from the staff.

Information sources

1. V.V. Kudinov, G.V. Bobrov. Spray coating. Theory, technology and equipment. - M.: Metallurgy, 1992, p. 144-148.

2. S.G. Rebrov, M.N. Polyansky, R.N. Rizakhanov. Plasmatron for coating. RF patent, application No. 2007147821 from 12.25.2007.

3. B.C. Avduevsky, E.A. Ashratov, A.V. Ivanov, U.G. Pirumov. Gas dynamics of supersonic non-isobaric jets. - M.: Mechanical Engineering, 1989.

Claims (1)

The method of coating, including installing a plasma torch in a chamber with reduced pressure, placing a substrate for coating in a chamber, maintaining a dynamic vacuum in the chamber, supplying a plasma-forming gas and powder of the sprayed material into the plasma torch and spraying the material with a supersonic plasma stream in the chamber to form molten powder particles and vapor phase of the sprayed material, characterized in that in front of the substrate on which the coating is applied, a mask is installed with holes and jumpers between them, o they ensure that only the vapor phase of the sprayed material flows around the jumpers, creates rarefaction waves behind the jumpers, in which the vapor phase condenses to form nanoparticles, which fall on the substrate and form a coating in the form of narrow strips consisting of nanoparticles and located around the coating sections created opposite the mask openings of powder particles, while shifting the mask relative to the applied coating and form the following coating layers on the applied layer to obtain a coating with a structure of several their coats applied.

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