EP3850120A1

EP3850120A1 - Method for coating a component and coated component

Info

Publication number: EP3850120A1
Application number: EP19778427.5A
Authority: EP
Inventors: Tobias KALFHAUS; Caren Sophia GATZEN; Daniel Emil Mack; Robert Vassen
Original assignee: Forschungszentrum Juelich GmbH
Current assignee: Forschungszentrum Juelich GmbH
Priority date: 2018-09-11
Filing date: 2019-08-19
Publication date: 2021-07-21
Also published as: US20210317558A1; WO2020052917A1; DE102018215389A1

Abstract

The object of the invention is to further develop the coating of a component (4). The object of the invention is achieved by a method for coating a component (6), in which the surface to be coated of the component (8) is roughened by a laser and the roughened surface is coated by cold gas spraying. The invention also relates to a component (8) produced by the method that is coated with a layer (5).

Description

Method for coating a component and coated component

The present invention relates to a method for coating a component. The invention also relates to a component coated according to the method.

It is known from the document DE 10 2015 207 602 A1 to coat a component by cold gas spraying. It is also known from the publication DE 10 2015 207 602 A1 to roughen the surface of the substrate to be coated by sandblasting to improve the adhesion between a substrate consisting of steel and the coating material to be applied.

From document DE 10 2012 217 685 A1 it is known to create inclined structural elements on a surface in order to be able to satisfactorily coat regions of a component that are difficult to access by cold gas spraying.

In cold gas spraying, a surface of a component is coated by depositing a powdery coating material. A heated gas such as nitrogen or helium is accelerated to very high speeds, for example by expansion in a lava nozzle in the direction of the surface to be coated. The speeds are above the speed of sound and are, for example, 500-1000 m / s. The powder coating material is injected into the accelerated gas jet. As a result, the powdery coating material impacts the surface to be coated at such a high speed that the particles of the powder plastically deform upon impact and as a result adhere to the surface to be coated. In contrast to thermal coating processes such as plasma spraying, arc spraying, flame spraying, the particles of the powder are not melted.

The impact of a powder particle on the surface to be coated creates a shear stress that plastically deforms the material of a powder particle. The resulting shear stress leads to adiabatic shear instability, which brings the surface areas of a powder particle to temperatures close to the melting point of the coating material and thus softens it, thereby binding powder particles and component to one another. Good adhesion between a substrate and the coating material is therefore a problem Cold gas spraying requires that sufficient shear instabilities are created by the impact.

The publication "Materials Science & Engineering A 720 (2018) 75-84, W. Sun et al, Deposition characteristics of cold sprayed Inconel 718 particles on Inconel 718 Substrates with dinerent surface conditions" published on February 16, 2018 shows that a Roughness of a surface to be coated significantly influences an adiabatic shear instability on impact. To achieve sufficient adiabatic shear instabilities on impact and thus good adhesion, sufficiently smooth surfaces are required.

A component can be coated with metals, polymers, ceramics, composite materials and nanocristailin powder by cold gas spraying.

The object of the invention is to further develop the coating of a component.

The object of the invention is achieved by a method according to claim 1. A subsidiary claim relates to a component coated according to the method. Advantageous configurations result from the dependent claims.

The object of the invention is achieved by a method for coating a component, in which a surface of the component to be coated is roughened by a laser and the roughened surface is coated with a high-energy thermal spraying method, such as cold gas spraying. Basically, it is roughened like a crater.

The inventors have found that a combination of the two measures “roughening by laser” and “coating by cold gas spraying” lead to particularly stable adhesion between the component and the layer. It has been found that roughening using a laser does not disadvantageously modify the material of the component on its surface physically or chemically in such a way that adhesion between the component and the layer is reduced. Roughening using a laser is therefore advantageous compared to roughening by sandblasting. It has further been found that the physical and chemical properties of the surface are also not adversely changed by cold gas spraying, so that the combination of Both measures a very good adhesion between the component and the coating can be achieved.

In one embodiment of the invention, the surface of the component to be coated is ground and / or polished, that is, smoothed, before it is roughened by means of a laser. With this configuration, ground and / or polished surface areas can advantageously be retained even after processing by a laser in order to favorably influence adiabatic shear instabilities and thereby achieve further improved adhesion properties.

Grinding can be done with a grinding machine and polishing can be done with a polishing machine. For the polishing, a polishing paste or a suspension with polishing grains contained therein can be used. In one embodiment of the invention, the surface of the component to be coated is exposed at predetermined locations by means of a laser in such a way that crater-like depressions occur at the exposed locations and other areas of the surface to be coated also after the production of crater-shaped depressions in the previous state, that is to say in particular in one ground and / or polished and thus smoothed. In this way, the ratio between crater-shaped depressions and areas not roughened by laser can be optimized in order to achieve particularly good adhesive properties.

In one embodiment of the invention, the surface of the component to be coated is pulse-exposed several times by laser in such a way that crater-shaped depressions are formed at the exposed locations, in particular to achieve crater depths of at least 1 Cpm or 20 pm, preferably to at least crater depths 30 pm to further improve the adhesion properties. It has been found that excessively great depths deteriorate adhesion properties again. Therefore, the depth of a crater-shaped depression is preferably limited to 60 pm, particularly preferably to 50 pm.

So that a crater-shaped depression can contribute particularly well to stable adhesion, the diameter of the crater-shaped depression at the upper edge corresponds approximately to the depth of the crater-shaped depression. So shows a crater-shaped depression upper edge, for example, has a diameter of approx. 40 pm, then a depth of approx. 40 miti is preferred. The depth should preferably not deviate from the diameter by more than 20%. So if the diameter is 40 pm, the depth should be at least 32 pm and not more than 48 pm in order to further improve the adhesion properties. In one embodiment, the crater-shaped depressions have a diameter of 30 pm to 50 pm and a depth of 30 pm to 50 pm.

Time intervals are preferably provided between the individual light pulses in such a way that material melted by laser light can only solidify again before the predetermined point is exposed again. Crater-shaped depressions can thus be further optimized. The adhesion between the component and the coating can be further improved in this way.

Preferably, each predetermined location is exposed to the light of the laser at least 3 times, preferably at least 5 times, and / or not more than 25 times, preferably not more than 15 times, in order to produce crater-shaped depressions in an optimized manner, and thus particularly good adhesion properties.

In one embodiment of the invention, the crater-shaped depressions have circular diameters. This configuration ensures that areas of the surface to be coated remain between crater-shaped depressions that have not been exposed by the laser and have therefore not been roughened.

In one embodiment of the invention, the upper edge of the crater-shaped depressions protrudes in a bead-like manner towards regions of the surface to be coated which have not been exposed by the light of the laser. The upper edge protrudes in particular by at least 5 pm, preferably by at least 10 pm and / or by no more than 20 pm from regions of the surface to be coated which have not been exposed to the light of the laser.

In one embodiment of the invention, the component is in a gas atmosphere made of noble gas, preferably argon, or nitrogen during its processing. In one configuration, the component is then in a room through which, for example, an inert gas or nitrogen is passed, or else the is gastight and has previously been introduced into the noble gas or nitrogen. Alternatively or in addition, a protective gas jacket is produced which surrounds the laser beam during the exposure. A protective gas jacket can be created using nozzles which are arranged around the light of the laser in such a way that the light beam of the laser impinging on the component is enveloped by the gas which emerges from the nozzles. The adhesion between the component and the coating can be further improved in this way.

In one embodiment of the invention, the coating material matches the material of the surface to be coated. If the material of a component has been damaged by external influences, such damage can be repaired particularly stably and reliably by a coating according to the invention with the same material.

In one embodiment of the invention, beads of crater-shaped depressions adjoin one another and / or overlap or overlap. The diameter of each crater-shaped depression then corresponds approximately to the distance between two center points of two adjacent crater-shaped depressions.

In one embodiment of the invention, the predetermined locations and thus the crater-shaped depressions are arranged according to a repeating pattern and thus according to plan. This can be a checkerboard pattern, for example. In the case of a checkerboard pattern, the predetermined locations and thus the crater-shaped depressions are arranged one behind the other and next to each other along a straight line. In this embodiment, the craters are not arranged randomly.

In one embodiment of the invention, the gas is heated to temperatures of 500 ° C. to 1200 ° C. during cold gas spraying, in order to improve adhesion properties. The component to be coated is preferably not additionally heated. In this way, thermally induced physical and / or chemical changes to the surface to be coated are advantageously avoided. Nitrogen can be used as the gas.

In one embodiment of the invention, the laser beam strikes the surface of the component at a right angle so as to produce crater-shaped depressions. It is but it is also possible to provide an angle deviating from 90 ° in order to suitably roughen the surface of the component by means of laser light.

The invention is explained in more detail below with the aid of examples and figures.

Show it:

Figure 1: sectional views of a surface created according to the invention;

FIG. 2: top view of the surface of a component to be coated;

Figure 3: cross section of a component coated according to the invention.

A large number of tests were carried out in which substrates consisting of the alloy 1N738 were used as components and these were coated with a powdered alloy IN738 by cold gas spraying.

Substrates consisting of the 1N738 alloy, i.e. components, were first ground and then polished with a 1 pm diamond suspension, i.e. with diamond grains with an average diameter of 1 mhti, on a soft cloth. After cleaning with ethanol in an ultrasonic bath, a first part of the substrates was brought into a laser processing system, which is commercially available under the name "Laser Marking Trumpf 5020". This comprises an Nd-YAg laser with a wavelength of the laser light of 1064 nm. The focus of the laser was set to 100 pm below the substrate surface to be coated. Argon was used as the atmosphere during the exposure by the laser in order to avoid disadvantageous oxidations. In pulsed mode, the surface of the substrate to be coated was removed at a frequency of 35 kHz and a pulse length of 120 ns at full power, which corresponds to a peak power of 15 kW. In this way, crater-shaped depressions with a diameter of 40 μm were produced on the surface to be coated. Craters were made one behind the other and side by side, i.e. in a checkerboard fashion, at a distance of 40 pm. Every single place where a crater was to be created was exposed a total of 12 times by the light of the laser. However, a single spot was not immediately exposed the next time after exposure immediately afterwards. Instead, each location was first exposed for the first time and then in the same order a second time, etc., until all locations were exposed twelve times in this way. Every single position could cool down after exposure and solidify again before exposure again. Undesired oxidation of the surface could thus be avoided better.

A second part of the substrates was not further processed for comparison tests. The surface to be coated thus remained in the state smoothed by grinding and polishing.

For comparison tests, the surfaces to be coated of substrates made of the alloy IN738 were also roughened by sandblasting. These surfaces to be coated were also previously sanded and polished.

FIG. 1 shows two sectional representations of the surface to be coated according to the invention, according to the aforementioned first part of the substrates, which were determined with a laser microscope. On the one hand, a sectional view of exposed areas in the xz direction and on the other hand in the yz direction is shown. The two sectional representations make it clear that a crater-shaped depression with a diameter of approximately 0.4 pm was created at an exposed location. The depth was almost 0.4 pm.

The centers of the essentially circular, crater-shaped depressions were regularly arranged on the polished surface of the component at a distance of 40 pm in accordance with a checkerboard pattern.

FIG. 2 shows an image of the laser microscope on the surface of a component to be coated, that is to say a substrate. This photograph shows a top view of the distribution of the crater-shaped depressions 1, which was created by repeated exposure, in accordance with a chessboard pattern. There are unexposed, polished areas 2 between obliquely opposed round crater-shaped depressions 1. The edges of the craters have a solidification pattern 3 on the edges due to the individual exposure that protrude up to approx. 15 pm above the unexposed, polished areas, i.e. in the z direction. The bead-like solidification patterns 3 form upper edges of the crater-shaped depressions 1. Upper edges 3 of the craters overlap or at least adjoin one another. The depth of the crater-shaped depressions 1 is approximately 20 pm in relation to the polished base area. In total, a depth of about 35 pm was created. With the help of a laser profilometer, roughness of surfaces of the substrates processed according to the invention and roughness of surfaces to be coated of the other substrates were determined for comparison purposes. For substrates processed according to the invention, that is to say components, with a surface according to FIGS. 1 and 2, an average roughness R _a (pm) = 7.15 and a maximum roughness depth R ™ _c (miti) = 48.85 were determined. For components with a surface roughened by sandblasting, an average roughness R _a (pm) = 2.31 and a maximum roughness depth R _max (pm) = 19.12 were determined. For components with a polished surface, an average roughness R _a (pm) = 0.02 and a maximum roughness depth R _max (pm) = 0.44 were determined.

Three substrates each made of the IN738 alloy were coated in the commercially available “GGT-Oerlikon Metco Kinetics 8000” system with a water-cooled D-24 De-Laval nozzle with IN738 powder with an average diameter of 7.89 pm, the first three Substrates treated according to the invention had surfaces to be coated, the second three substrates had surfaces treated by sandblasting and surfaces to be coated and the third three substrates had polished surfaces to be coated. A pressure of 40 bar nitrogen, a gas temperature of 950 ° C. and a coating distance of 60 mm were chosen as coating parameters. The layer thicknesses thus produced were approximately 400 pm.

These coated substrates were bonded between two cylinders for adhesive peel tests, so that the substrate was bonded to one of the cylinders and the coating produced to the other cylinder. In the case of the substrates with the polished surfaces to be coated and with the sandblasted surfaces to be coated, the coating detached from the substrate. In the case of the surfaces to be coated treated according to the invention, a cylinder always detached from the coated substrate. It was thus found that in the case of the surfaces to be coated treated according to the invention, significantly better adhesion between the coating and the substrate was achieved.

FIG. 3 shows a cross section of a component 4 coated according to the invention with a layer 5 on the substrate 6 after the adhesion removal tests have been carried out in the region of a crater-shaped depression 1. FIG. 3 illustrates that the Crater-shaped depressions 1 were completely filled by the cold gas spraying and the adhesive detachment tests carried out could not change anything. No cracks have formed. The invention is not restricted to the exemplary embodiment. For example, it is also possible, alternatively or additionally, to prepare the surface of a component in a different way compared to grinding and polishing, for example by sandblasting or shot peening, in order to subsequently roughen it using a laser. Good adhesion properties can also be achieved in this way, especially in comparison to a surface preparation which only comprises sandblasting, in order to then coat. In order to achieve good adhesion properties, another thermal coating method can be provided instead of cold gas spraying, in which the coating material is brought to a high speed so as to coat. For example, HVAF (High Velocity Air-Fuel) can be used instead of cold gas syringes to achieve good results. However, the alternatives mentioned relating to sandblasting, shot peening or HVAF are less preferable. The object of the invention can also be achieved by a method for coating a component, in which a surface of the component to be coated is roughened by a laser and the roughened surface is coated with high kinetic energy such as cold gas spraying or HVFA by a thermal spraying method.

In comparison to literature values, the maximum achievable layer thickness could be tripled by the invention.

Claims

Expectations

1. A method for coating a component (6), characterized in that a surface of the component (6) to be coated is roughened in a crater shape by a laser and the roughened surface is coated with high kinetic energy by a thermal spraying method.

2. The method according to the preceding claim, characterized in that the surface to be coated is ground and / or polished before roughening.

3. The method according to any one of the preceding claims, characterized in that the surface of the component (6) to be coated is repeatedly pulsed at predetermined locations by means of a laser so that crater-shaped depressions (1) are formed at the predetermined locations.

4. The method according to the preceding claim, characterized in that there are time intervals between the individual light pulses such that material melted by the light of the laser can solidify again before the predetermined location is exposed again by the light of the laser.

5. The method according to any one of the two preceding claims, characterized in that each predetermined location is exposed at least 3 times and / or not more than 25 times by the light of the laser.

6. The method according to any one of the preceding claims, characterized in that crater-shaped depressions (1) with a depth of at least 10 pm and / or with a depth of not more than 60 pm are produced by roughening by means of laser.

7. The method according to any one of the preceding claims, characterized in that by roughening by means of laser crater-shaped depressions (1) are generated, in which the diameter of the crater-shaped depression at the upper edge (3) corresponds approximately to the depth of the crater-shaped depression (1) .

8. The method according to any one of the preceding claims, characterized in that the crater-shaped depressions at the upper edge have a diameter of 30 μm to 50 μm and a depth of 30 μm to 50 μm.

9. The method according to any one of the preceding claims, characterized in that the component (6) is during the roughening and / or during the coating in a gas atmosphere made of noble gas, preferably argon, or nitrogen.

10. A method for coating a component {6) according to one of the preceding

Claims in which the roughened surface is coated by cold gas spraying or HVFA.

1 1. Coated component (4) producible by a method according to one of the preceding claims, characterized in that a coated

Surface crater-shaped depressions (1) with circular diameters and with a depth of at least 20 pm and / or with a depth of not more than 60 pm.

12. Coated component (4) according to the preceding claim, characterized in that the upper edge (3) of each crater-shaped recess (1) protrudes in a bead-like manner from adjacent polished regions (2) of the coated surface, in particular by at least 10 pm.