DE102006061977A1 - Method and apparatus for thermal spraying - Google Patents

Abstract

The invention relates to a method for coating a substrate by means of a thermal spraying method, in which, after the transfer transition, cooling of the deposited layer and also of the substrate takes place. According to the invention, a defined cooling of the deposited layer and also of the substrate takes place in such a way that on average there is a temperature level of at least 200 K above the ambient temperature in the layer / substrate composite. Advantageously passes between the splash transition and the defined cooling of this deposited layer a period of less than 100 ms, in particular less than 10 ms and in particular between 0.1 and 5 ms after the spray transition. The increased temperature level associated with the defined cooling after the application process allows by this method, on the one hand, the production of thin, gas-tight layers <100 microns and on the other hand thicker layers (> 100 microns) with a high Segmentationsrissdichte.

Description

The The invention relates to a coating method, in particular a thermal spraying method and a device suitable for this purpose.

State of the art

With Help of coating processes become a single or even several adherent layers of shapeless material on the surface of a workpiece applied. This can be a thin layer or a thick Act shift, the distinction is not well defined and oriented on the coating process and application.

The Coating processes themselves differ on the one hand in the Type of coating application in chemical, mechanical, thermal and thermomechanical processes, and on the other hand, the initial state of the material to be applied. Here one differentiates in particular the gaseous Apply, such as over the chemical vapor deposition (also CVD of English chemical vapor deposition) or the physical vapor deposition (also PVD from engl. physical vapor deposition), the liquid application, such as during painting, spraying and thermal spraying including the Flame spraying, the high-speed flame spraying, the wire arc spraying as well as the plasma spraying and also the firm application method like in sintering process.

Under The term thermal spraying is understood to mean different Spraying, which is characterized by the nature of the spray additive (wire or powder), the production or the energy carrier.

When fuels for the On or melting of the spray additive serve in the Usually electronic arc, laser beam, fuel gas-oxygen flame or kerosene-oxygen high-velocity flame, high-kinetic gases and the plasma jet. The density of the coating, the adhesion of the sprayed layer and the adhesion between Coating and base material usually result from the Energy, which coincides with the particle velocity and temperature is coupled.

thermal Spray processes are characterized in that for the coating envisaged material in the form of meltable particles on a substrate meets and trains a shift there. Both to the generation the molten one Particle used thermal energy sources, such as plasmas, arcs or Combustion processes and the thermal energy content of the particles themselves, to lead regularly to one warming of the substrate. This warming has often negative consequences, such as distortion, corrosion or oxidation of the substrate.

For this reason, cooling is typically used in thermal spraying. The cooling used is usually via cooling nozzles, through which the substrate with a cooling medium, such as. B. compressed air is blown. The cooling nozzles are fixedly directed to the substrate or they are arranged next to the burner and move accordingly with this. Out WO 2004005575 For example, a device for internal coating of cavities by thermal spraying with two cooling lances is known, which are arranged on opposite sides of the burner. In part, both cooling methods are used simultaneously. It's over C. Coddet, Surface & Coatings Technology 201 (2006) 1969-1974 Also known cooling methods that are used in conjunction with preheating prior to thermal spraying. These are for temperature management in the layer / substrate interconnections and are designed to maintain the substrate temperature at the ambient (room temperature) level.

Task and solution

task The invention is a coating method available which makes the production of layers with a good bond of allowed individual splash blades without preheating and so on simple way, on the one hand, a deposition of high-density, thin layers but also allows for thicker, segmented layers. It is another object of the invention to provide a device for carrying out this Provide method.

The Tasks are solved by a method of coating with the entirety of the features of the main claim, and by a device for coating according to additional claim. Advantageous embodiments the method according to the invention as well as the device result from the respective draw-dependent subclaims.

Subject of the invention

In the context of the invention, it has been found that the type of cooling of the substrate or of the deposited layers has a decisive influence on the result of the layer formation of the coating. It has been found that cooling the substrate or an already deposited layer before coating proves to be disadvantageous, while the immediate direct cooling after the coating process shows significant advantages.

at In the coating process of the present invention, that a cooling is controlled so that only the targeted areas chilled in which a coating has been applied immediately before. Appropriately, can be So for example, realize that the use of the burner attached cooling nozzles with the Burner movement is tuned.

A first embodiment of the method provides that a burner with a cooling nozzle used is, with the cooling nozzle relative to the direction of movement of the burner relative to the substrate behind located on the burner. When driving over the Substrates, this cooling nozzle is now activated, so the cooling always cool only the just applied spray spot. In In this embodiment, the substrate is run over only in one direction.

In Another embodiment is a burner with at least two Cooling nozzles provided. During the Coating, however, only the cooling nozzle is activated, which is behind in the direction of movement to the burner. this makes possible advantageous overriding of the substrate in at least two directions, e.g. B. in the form of a Meander. In terms of plant technology, this can be achieved by a valve control the cooling nozzles accordingly the burner movement.

On cylindrical samples or complex shaped components, such as turbine blades, that can be Transfer procedure accordingly. Likewise several cooling nozzles attached be, so also a run over possible in several directions is provided that a corresponding control of the cooling nozzles for a defined downstream cooling the just deposited spray spot provides.

Suitable cooling media are both gases, such as CO ₂ , compressed air, nitrogen, helium or water vapor, as well as liquids, such as water in question. Further, a solid such. As CO ₂ snow, also suitable.

The targeted cooling has a decisive influence on the stratification of the Coating. By the exclusive cooling afterwards it is avoided that the already deposited layer, or the substrate, directly cooled before the layer deposition becomes. In addition, the substrate temperature is due to the targeted cooling dosing adjusted so that even after cooling one opposite the Ambient temperature increased temperature is present. In the first injection, this can be advantageous by preheat with the burner without injecting particles. By the opposite increased in the prior art Temperatures of the substrate is now reached that the newly deposited Layers can advantageously deposit with a high density. The subsequent, targeted cooling leads now to that the allowable temperatures of the substrate are not exceeded, on the other hand, one enough high temperature level can be adjusted to a layer deposition to achieve high density. The temperatures of the substrate are advantageously 200 to 800 K above the ambient temperature, ideally between 300 and 600 K over the ambient temperature. This can be done without the high temperature load of the substrate and the associated negative consequences, such as distortion, corrosion or oxidation high density, relatively thin, typically smaller as 100 μm deposit thick layers.

In the case of deposited layers with a layer thickness of more than 100 μm, another advantageous microstructure is additionally achieved. The intensive, targeted cooling immediately after the layer deposition leads to a very rapid cooling and thus to a high level of tensile stress in the layer. This in turn results in a high density of segmentation cracks. If this mechanism is to be activated, precise alignment of the cooling nozzles is required so that the cooling medium strikes the layer immediately after deposition. Typical distances between the spray spot and the maximum of the cooling flow are in the millimeter range. At a burner speed of 1 m / s, this results in times between the deposition and the onset of external cooling in the millisecond range. During this time, the temperature transfer from the separated spray particle (splat) to the substrate has not yet taken place regularly. That is, the temperature of the splat at this time is still significantly above the substrate temperature, and the chosen configuration leads to a significant increase in the tensile stress level in the deposited layer. The cooling time of the splats can be estimated from the lamella thickness, which is typically 5 μm, divided by the root of the thermal diffusivity (depending on the material, typically 10 ^-6 m ² / s), which gives about 5 ms.

The targeted cooling further includes that the diameter of the flow of the cooling gas medium is matched to the spray spot size. Ideally, the cooled area should not be larger than the spray spot. For typical spray spot sizes of a few millimeters, the profile of the cooling flow should accordingly be only a few millimeters in diameter. This can be z. B. by using suitable nozzles with a small diameter and with low divergence of the cooling medium can be achieved after the exit. In addition, it is favorable to place the exit of the cooling medium from the nozzle as close as possible to the area of the spray spot. This can be z. B. by high temperature resistant materials, such as ceramic pipes realize.

Furthermore, it is favorable to make the alignment of the cooling nozzle to the burner axis in such a way that both axes are inclined towards each other and reflected by the layer / substrate composite cooling medium is guided only to a small extent in the hot gas region of the burner. This in turn increases the particle composite. Accordingly, according to 2 , Angle A less than 90 °, preferably between 30 and 60 ° and for values for the angle B, less than 90 °, preferably between 30 and 60 °, are taken.

It It is known that layers with segmentation cracks are common as well Have delamination cracks, d. H. Cracks between the layers of the Connected to an early Failure of the layer lead can. Due to the high substrate temperatures during the layer deposition However, when using the cooling according to the invention is a regular one achieved very good bond between the spray lamellae and thus the tendency to Delaminationsrissen significantly reduced.

The choice of the material of the coating depends inter alia on the application of the coating. A particularly suitable material for an ion-conducting membrane for a solid electrolyte fuel cell may be mentioned with yttrium-stabilized zirconium oxide (YSZ). Likewise, instead of the YSZ, it is also possible to use another material, such as a mixed-conducting oxide (for example, a La _x Sr _1-x Fe _y Co ₁ -y O ₃ perovskite Ba _x or Ba _x Sr ₁ Co _y Fe _{1). y} O ₃ with x, y = 0 to 1, for example in the application of a gas separation membrane or else a proton conductor, such as an SrZr _x Y _1-x O ₃ or BaCe _x Gd _1-x O ₃ perovskite based perovskite with x = 0 to 1, typically 0.3 to 0.7).

With the method according to the invention can also dense, insulating layers are produced, for. More colorful Use of powders comprising alumina, spinel compounds, Steatite, Forsterite, Porcelan, Pyrochlore, Mullite, Magnesium Oxide, Zirconia, zirconia (unstabilized and stabilized) and titanium oxide.

As well is the production of dense ceramic or metallic protective coatings to avoid corrosion and oxidation possible.

When Application methods can In addition to plasma spraying, other thermal spraying methods, such as the high-speed flame, under Use of the stated cooling after the deposition of high-density layers at low thermal Load of the substrate can be used.

The inventive method combines the advantages of an overall increased temperature level of the Substrates with a direct on the Spritzfleckaubbringung following defined cooling to achieve particularly advantageous gas-tight, thinner or also highly segmented thicker layers.

Special description part

following The subject of the invention is based on figures and embodiments explained in more detail, without that the subject of the invention is limited thereby. Show it

1 : Arrangement and activation of the cooling nozzles relative to the burner, with different direction of movement of the burner during the coating process.

2 : Arrangement of burners and cooling medium nozzles.

3 : Microstructures of thermally sprayed layers, left with the targeted, cooling according to the invention in the wake, right with cooling before coating.

4 : Microstructures of layers produced according to the invention, manufactured at robot speeds of 250 mm / s (left) and 125 mm / s (right).

5 : Gas-tight and thin plasma sprayed layer of YSZ, produced by the method according to the invention with a downstream cooling.

6 : Plasma sprayed YSZ coating using compressed air after cooling.

In 1 is a schematic representation of the movement of the burner during thermal spraying with according to the disclosure of the invention specified cooling. In these cases, a burner with two cooling nozzles is used on each side of the burner. at 1a ), the cooling is activated according to the burner movement during the coating process by selectively activating the left or the right cooling nozzle, whichever is located in the burner direction behind the burner. In the case of 1 b) the burner movement is always only in one direction, here from left to right, provided. Therefore, according to the invention always only the left cooling nozzle activated, which is arranged in this case during the coating process in the burner direction behind the burner. Alternatively, this could also be a burner with only one cooling nozzle are used, which is arranged such that it is located during the coating in the burner direction behind the burner.

3 shows the microstructures of thermally sprayed layers, left with the targeted, cooling according to the invention in the wake, right with cooling before coating. It can be seen clearly the strong improvement of the microstructure in the inventive method. In the 3 Deposited deposited layers were prepared with a TRIPLEX II burner using yttria-stabilized zirconia (YSZ) powder. For coating both layers, identical plasma spray conditions were set. When coating in 3a ) a CO ₂ cooling according to the invention was used and 9 transitions performed. The layer in 3b ), on the other hand, was cooled immediately before deposition, as is customary in the prior art. Furthermore, 10 transitions were performed. While the shift in 3a ) has a plurality of segmentation cracks (about 5 per mm) are in the layer of 3b ) to recognize no segmentation cracks. Furthermore, the individual transitions there are clearly recognizable by an increased porosity between the individual layers. This does not occur in the coating according to the invention.

In addition, the application efficiency, ie the layer thickness deposited per coating cycle, is significantly increased, as is the result of the significantly greater layer thickness in FIG 2a is apparent.

1st embodiment

With the aid of a TRIPLEX II burner and using YSZ hollow sphere powder (Metco 204NS), a layer was subsequently deposited on a stainless steel substrate at a robot speed of 250 mm / s with the CO ₂ cooling according to the invention. The spray distance was 100 mm, the process gases used were 50 standard liters per minute (slpm) of Ar and He. The coating temperature was between 700 and 800 ° C, a preheat cycle heated the substrate to about 500 ° C. The layer was deposited by passing four times with the burner. With the hot spray parameters used an extremely dense layer with a high density of segmentation cracks (> 3.5 per mm) could be deposited. Furthermore, this layer shows no delamination cracks, as seen from 4a ) is recognizable.

With reduced burner speed (125 mm / s) became a second Layer on a Bondcoat (NiCOCrAlY) coated superalloy substrate (IN738) deposited according to the invention. These Layer has a reduced segmentation crack density according to the above on, with no delamination cracks as well as the extreme emphasize high density of the layer between segmentation cracks is.

2nd embodiment

In a transition, a thin layer of YSZ using fused and crushed powders when using a CO ₂ was prepared in the wake of cooling by means of atmospheric plasma spraying. The spray distance was in this case 95 mm, the burner power about 61 kW. The temperature of the substrate during coating was about 450 ° C, preheated to about 400 ° C. The layer shows a high density and no segmentation cracks, such as 5 can be seen.

3rd embodiment

By means of the atmospheric plasma spraying method, a YSZ layer was deposited. As cooling, compressed air was subsequently used in this case. Alternatively, in addition to the CO ₂ already mentioned, cooling media such as He, Ar, water vapor or other liquids can also be used.

The obtained YSZ layer has a high density of segmentation cracks (about 3 per mm) but without the deleterious delamination cracks (see 6 ). The substrate temperature during the coating was below 500 ° C, resulting in only a small thermal and corrosive load.

4th embodiment

Here, a thermal spraying method was used in which instead of a flowable powder, a suspension z. B. from partially stabilized zirconium oxide was used and the cooling was carried out according to the invention in the wake. Here, the high segmentation crack densities achievable via suspension plasma spraying could be further increased. In a deposition of very thin layers below 100 microns, regularly high density layers can be achieved in which gas tightness below 0.1 mbar l / s / cm ² , preferably below 10 ^-3 mbar l / s / cm ² can be achieved.

Claims (24)

A method of coating a substrate by means of a thermal spraying method, in which after the injection transfer, a cooling of the deposited layer and also of the substrate he follows, characterized in that a defined cooling of the deposited layer and also of the substrate takes place in such a way that on average there is a temperature level of at least 200 K above the ambient temperature in the layer / substrate composite. The method of claim 1, wherein the cooling is so takes place that a temperature level between 300 and 600 ° C above the ambient temperature in the layer / substrate composite is present. Method according to claim 1 or 2, wherein between the spray transition and the defined cooling this deposited layer has a time of less than 100 ms, especially in less than 10 ms and in particular between 0.1 and 5 ms after the spray transition passes. Method according to one of claims 1 to 3, wherein before Coat the substrate with a downstream plasma torch cooling but preheated without powder injection. The method of claim 4, wherein prior to coating the substrate with a plasma torch with downstream cooling but without powder injection to at least 200 K above ambient temperature is preheated. Method according to one of claims 1 to 5, wherein the range the cooling not bigger than the area of the spray spot is set, in particular in the the area of cooling corresponds to the spray spot. Method according to one of claims 1 to 6, wherein the outlet of the cooling medium immediately next to the spray spot. Method according to one of claims 1 to 7, wherein the cooling medium is a gas, such as. As CO ₂ , compressed air, nitrogen, helium, water vapor or a liquid such as water or a solid such. As CO ₂ snow, is used. Method according to one of claims 1 to 8, wherein the relative speed between substrate and burner above 100 mm / s, preferably between 250 and 1000 mm / s. Method according to one of claims 1 to 9, wherein a coating yttria-stabilized zirconia (YSZ) or other oxidic Materials, in particular from a perovskite, an aluminate, a Spinel or a pyrochlore is produced. Method according to one of claims 1 to 10, wherein an atmospheric Spray method (APS) is used as a thermal spraying method. Method according to one of Claims 1 to 10, in which a high-speed flame spraying (HVOF) is used as a thermal spraying method. Method according to one of claims 1 to 12, wherein the coating in the form of a gas-tight layer with a total layer thickness of less than 100 μm will be produced. The method of claim 13, wherein the coating in the form of a gas-tight layer with a total layer thickness of less than 100 μm by crossing once will be produced. Method according to one of the preceding claims 1 to 14, in which the coating in the form of an ion-conducting membrane for one Solid electrolyte fuel cell comprising YSZ. Method according to one of the preceding claims 1 to 14, wherein the coating comprises in the form of a gas separation membrane a mixed conducting oxide or a proton conductor is produced. Method according to one of the preceding claims 1 to 14, wherein the coating in the form of an insulating layer comprising an alumina, a spinel compound, a steatite, a fosterite, a porcelan, a pyrochlore, a mullite, a magnesia, a zircon, an unstabilized or stabilized zirconia or titanium oxide is produced. Method according to one of the preceding claims 1 to 14, wherein the coating in the form of a corrosion protection layer will be produced. Method according to one of claims 1 to 12, wherein a segmented coating is produced with a layer thickness of more than 100 microns. Method according to the preceding claim 13, wherein a segmented coating is produced by driving over once. Apparatus for carrying out the method according to one the claims 1 to 19 with a burner and at least one means for cooling, wherein the Orientation of this means is positioned such that the exit a cooling medium from the coolant directed to a previously deposited spray spot. Apparatus according to claim 21, comprising at least two coolants at the side of the burner, the orientation of these means being such are positioned that selectively exit a cooling medium a coolant depending on the relative movement of the burner to the substrate on a previously deposited spray spot is directed. Apparatus according to claim 21 or 22, optionally controllable coolants. Device according to one of claims 21 to 23 with high temperature resistant Cooling nozzles as Mühlmittel.