DE102019131623A1 - Process for the production of a functional layer by means of cold gas spraying, powder mixture and component - Google Patents

Abstract

A method for producing a functional layer by means of cold gas spraying, comprising the steps: - providing a surface to be coated; - providing a powder mixture for forming a layer on the surface to be coated, the powder mixture having at least two components, with a ratio of the hardness of a first component the hardness of a second component is in a range from 0.1 to 0.4; - adding the powder mixture to a process gas and applying a layer to the surface to be coated using cold gas spraying

Description

The invention is directed to a method for producing a functional layer by means of cold gas spraying, in particular for coating valve seats of cylinder heads of internal combustion engines, on a powder mixture and on a component.

It is known from the prior art to coat components locally in order to provide the component with specific properties in a targeted manner. The DE 101 60 958 A1 discloses, for example, a method for coating a cylinder bore of a crankcase of an internal combustion engine, the cylinder bore being sprayed with a dynamic cold gas spray to coat said cylinder bore with a coating material different from the material of said engine block when driving around. It has been found that in practice it is difficult to actually produce coatings that withstand the desired requirements and are suitable for series applications. For example, the service life is too short or problems arise during the production of the layers, such as cracking.

It is therefore an object of the present invention to provide a method for producing a functional layer by means of cold gas spraying, a powder mixture and a component which eliminate the aforementioned disadvantages and are also suitable for series applications.

This object is achieved by a method according to claim 1, by a powder mixture according to claim 6 and by a component according to claim 13. Further advantages and features emerge from the subclaims as well as the description and the attached figure.

• - Bereitstellen einer zu beschichtenden Oberfläche;
• - Bereitstellen einer Pulvermischung zum Formen einer Schicht auf der zu beschichtenden Oberfläche, wobei die Pulvermischung zumindest zwei Komponenten aufweist, wobei ein Verhältnis der Härte einer ersten Komponente zur Härte einer zweiten Komponente in einem Bereich von 0,1 bis 0,4 liegt;
• - Zumischen der Pulvermischung einem Prozessgas und Auftragen einer Schicht auf die zu beschichtende Oberfläche mittels Kaltgasspritzen.

According to the invention, a method for producing a functional layer by means of cold gas spraying comprises the steps:

• - Provision of a surface to be coated;
• Providing a powder mixture for forming a layer on the surface to be coated, the powder mixture having at least two components, a ratio of the hardness of a first component to the hardness of a second component being in a range from 0.1 to 0.4;
• - Mixing the powder mixture with a process gas and applying a layer to the surface to be coated by means of cold gas spraying.

Cold gas spraying is a coating process in which the coating material, in this case the powder mixture, is applied in powder form to a carrier material or substrate at very high speed. In particular, the low heat input due to the low process temperatures should be mentioned as advantageous. The layer advantageously comprises at least two components or materials. The first component or the first material has a lower hardness or a higher ductility than the second component or the second material, the second component or the second material preferably having a higher wear resistance than the first component or the first material having. The first component of the powder mixture advantageously enables the layer as such to have or provide good adhesion to the surface. In particular, the first component enables the second component to adhere well to the surface. The first component is designed in particular to bind the second component to the surface. This is made possible in particular by their ductility and a sufficient deformability of the first component. It has been found that a ratio of the hardness of the first component to the hardness of the second component is preferably in a range from 0.1 to 0.4, particularly preferably in a range from 0.15 to 0.3. As a result, an optimally adhering layer with excellent wear behavior can be achieved, this being achieved in particular by the second component.

• - Aufbringen der Schicht derart, dass die Pulvermischung weder aufgeschmolzen noch angeschmolzen wird.

The method particularly preferably comprises the step:

• - Application of the layer in such a way that the powder mixture is neither melted nor partially melted.

In particular, the method should be carried out in such a way that the first component is not melted on or on. Instead, there is pure deformation. This ensures, among other things, that the layer does not tear, which provides a very reliable process.

According to a preferred embodiment, the surface to be coated is a valve seat of a cylinder head. The method expediently enables valve seat inserts to be substituted, preferably in particular the inlet valve seat inserts. These are separate components which otherwise have to be inserted into the cylinder head in a laborious manner.

• - Aufbringen der Schicht in genau einer Überfahrt mit einer Vollschubgeschwindigkeit von etwa 8-12 mm pro Sekunde, bei einem Pulvermassenstrom von etwa 26-29 cm³ pro Minute.

According to one embodiment, the layer has a thickness or a thickness in a range of approximately 0.6-2 mm. The following process step has proven to be particularly advantageous:

• - Application of the layer in exactly one pass with a full thrust speed of about 8-12 mm per second, with a powder mass flow of about 26-29 cm ³ per minute.

The process gas mass flow is advantageously around 100 m ³ / h. The aforementioned process parameters particularly counteract any crack growth. For valve seats in particular, layer thicknesses in a range of approximately 0.9-1.5 mm have proven to be particularly advantageous.

• - Aufteilen der Pulvermischung auf mehrere Teilströme und Zumischen der Teilströme zu dem Prozessgas.

According to one embodiment, the method comprises the step:

• - Dividing the powder mixture into several substreams and admixing the substreams to the process gas.

Several powder feeders are expediently used, for example two. The layer structure can be optimized through this division. The process gas is, for example, nitrogen or helium.

• - Bereitstellen oder Zumischen einer dritten Komponente zum Einstellen einer Porosität der Schicht.

According to one embodiment, the method comprises the step:

• Providing or admixing a third component for setting a porosity of the layer.

According to a preferred embodiment, the powder mixture has a third component, which according to a preferred embodiment is in particular copper, and the third component is designed to reduce friction within the powder mixture. This enables an optimal distribution of the powder mixture when it hits the surface to be coated and a desired porosity to be set.

• - Heizen des Prozessgases auf 700-1000 °C, wobei sich insbesondere etwa 800 °C als vorteilhaft erwiesen haben.

According to one embodiment, the method comprises the step:

• - Heating the process gas to 700-1000 ° C, in particular about 800 ° C have proven to be advantageous.

Preferred pressures for the process gas are in a range of approximately 45-51 bar, in particular approximately 48 bar.

According to a preferred embodiment, the process temperature of the process gas is 800 ° C., the pressure is 48 bar, and a powder delivery rate is 4.5 rpm (rotations per minute), with 3 cm ³ being delivered per rotation. The number of powder feeders is preferably two.

The invention is also directed to a powder mixture for cold gas spraying, comprising at least two components, a ratio of the hardness of a first component to the hardness of a second component in a range of preferably 0.1 to 0.4, particularly preferably between 0.15 and 0.3. The first component expediently has a lower hardness than the second component, the second component expediently having a higher wear resistance than the first component. The first component is preferably more ductile than the second component, and it has been found that the aforementioned hardness ratio of the components is ideal in order to produce a layer that can not only be manufactured reliably, but also for use in the most difficult conditions , such as the combustion chamber of an internal combustion engine, is suitable. It should be mentioned here that the advantages mentioned in connection with the method apply analogously and correspondingly to the powder mixture, and vice versa.

According to a preferred embodiment, the first component is 316L, the second component being MoNiCrO. 316L is an austenitic stainless steel with very good corrosion resistance and an optimal ductility or hardness for the present requirements.

The first component of the powder mixture, in particular the material 316L, expediently has a hardness in a range from 200 to 300 HV 0.025. The second component of the powder mixture, in particular the material MoNiCrO, expediently has a hardness in a range of 1100-1200 HV 0.025.

In this way, layers with a (mixed) hardness in a range from 320 to 380 HV 1 can advantageously be produced. After coating, the first component, in particular 316L, has a hardness in a range from 330 to 390 HV 0.025, the second component, in particular MoNiCrO, a hardness in a range from 1100 to 1200 HV 0.025.

It has been found to be particularly advantageous if a ratio of the first component to the second component, based on their mass, is in a range of 0.8-2.1. The mass ratio is particularly advantageously 1.2-1.3, in particular 1.25. 50 percent by weight of the first component and 40 percent by weight of the second component are preferably used, the remaining 10 percent by weight advantageously being accounted for by a third component, the third component advantageously being designed to set a porosity of the layer.

According to a preferred embodiment, the powder mixture has a third component, which according to a preferred embodiment is in particular copper, and the third component is designed to reduce friction within the powder mixture. This enables an optimal distribution of the powder mixture when it hits the surface to be coated and the setting of a desired porosity.

A porosity of the layer to be produced can expediently be set via the third component. In the present case, this is preferably less than 0.8%, particularly preferably less than 0.5%. The aforementioned values can be obtained, for example, via a gray value distribution of a section.

According to a preferred embodiment, a ratio of a particle size of the first component to a particle size of the second component is in a range from 0.1-3.5. In particular, a ratio between 0.3 and 1.6 has proven to be particularly advantageous.

According to a preferred embodiment, the particle sizes of the first component, in particular of the material 316L, are in a range from 7-50 μm, preferably 15 to 38 μm, the particle sizes of the second component in a range from 15 to 60 μm, preferably 25 to 43 µm, and the particle sizes of the third component, in particular copper, in a range from 7 to 50 µm, in particular 15-38 µm.

The aforementioned particle sizes make a decisive contribution to enabling a reliable process. It has been shown that, for example, particles that are too large break open and particles that are too small reach too high a speed, both of which are problematic for a high-quality layer structure.

The invention is also directed to a component comprising at least one functional layer produced by the method according to the invention.

According to a preferred embodiment, the component is a metallic component, in particular a cast component, for example made of aluminum or an aluminum alloy. Preferred casting methods are permanent mold casting, pressure casting or low-pressure casting, although this list is not to be understood as being exhaustive.

According to a preferred embodiment, the component is a cylinder head of an internal combustion engine. The functional layers are advantageously the valve seats, in particular the inlet valve seats. The insertion of valve seat inserts can expediently be dispensed with. The functional layer can advantageously be applied directly to the (cast) component. Depending on the quality of the (cast) component, pre-processing, for example mechanical, can be useful in order to increase the adhesion of the layer, whereby methods such as grinding, irradiation with an abrasive medium for roughening or laser treatment, etc. can be expedient.

According to a preferred embodiment, the layer has a hardness in a range from 320 to 380 HV 1. The shape or characteristics of the layer are not subject to any restrictions. In the case of a valve seat, the layer is circular. The application takes place accordingly by following a circular path. Alternatively, however, any flat designs are possible, which z. B. be traversed line by line with the spray lance. At this point it should be mentioned that it has proven to be advantageous to choose a distance of approx. 50 mm when coating.

Further advantages and features emerge from the following description of an embodiment of the method with reference to the attached figure.

• 1: eine schematische Ansicht einer Vorrichtung zum Kaltgasspritzen zur Veranschaulichung des Verfahrens.

It shows:

• 1 : a schematic view of a device for cold gas spraying to illustrate the method.

1 shows a schematic view of a device for cold gas spraying, this comprising a pressure chamber in which a heating device 42 is arranged. This pressure chamber 40 becomes a process gas 20th fed. According to a preferred embodiment, the process gas is heated to about 800 ° C. and brought to a pressure of about 48 bar. The powder mixture is then mixed in. In a preferred embodiment, the powder mixture is divided into two substreams 30th . The admixing takes place via corresponding powder feeders, which are not shown here. A working beam 60 , comprising the process gas 20th which the partial flows 30th are mixed, leaves the device via a lance 44 , the process gas 20th , enriched with the powder mixture, is accelerated to supersonic speed. A typical diameter of the coating lance or an outlet opening is, for example, about 6-6.5 mm. As a result, arises on a surface 10 a layer 12th . A distance a is preferably about 50 mm.

List of reference symbols

10

surface

12th

layer

20th

Process gas

30th

Partial flow

40

Pressure chamber

42

Heating device

44

lance

60

Working beam

a

distance

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 10160958 A1 [0002]

Claims (15)

A method for producing a functional layer (12) by means of cold gas spraying, comprising the steps: - Provision of a surface to be coated (10); - Providing a powder mixture for forming a layer (12) on the surface (10) to be coated, the powder mixture having at least two components, the ratio of the hardness of a first component to the hardness of a second component in a range from 0.1 to 0 , 4 is; - Adding the powder mixture to a process gas (20) and applying the layer (12) to the surface (10) to be coated by means of cold gas spraying. Procedure according to Claim 1 , wherein the surface to be coated (10) is a valve seat of a cylinder head. Procedure according to Claim 1 or 2 , the layer (12) having a thickness in a range from about 0.6 to 2 mm, comprising the step: - applying the layer (12) in exactly one pass at a feed rate of about 8 to 12 mm / s at a powder mass flow of about 26 to 29 cm ³ / min. Method according to one of the preceding claims, comprising the step: - Dividing the powder mixture into several substreams (20) and admixing the substreams with the process gas (20). Method according to one of the preceding claims, comprising the step: - Providing or admixing a third component for setting a porosity of the layer (12). Powder mixture for cold gas spraying, comprising at least two components, wherein a ratio of the hardness of a first component to the hardness of a second component is in a range from 0.1 to 0.4. Powder mixture after Claim 6 , wherein the first component has a hardness in a range from 200 to 300 HV 0.025. Powder mixture after Claim 6 or 7th , wherein the second component has a hardness in a range from 1100 to 1200 0.025 HV. Powder mixture according to one of the Claims 6 - 8th , wherein the first component is 316L and the second component is MoNiCrO. Powder mixture according to one of the Claims 6 - 9 , wherein a ratio of the first component to the second component based on their mass is in a range from 0.8 to 2.1. Powder mixture according to one of the Claims 6 - 10 wherein the powder mixture has a third component, and wherein the third component is configured to reduce friction within the powder mixture. Powder mixture according to one of the Claim 6 - 11 wherein a ratio of a particle size of the first component to a particle size of the second component is in a range from 0.1 to 3.5. Component comprising at least one functional layer (12) produced by a method according to one of the Claims 1 to 5 . Component after Claim 13 , wherein the component is a metallic cast component. Component according to one of the Claims 12 - 14th wherein the layer (12) has a hardness in a range from 320 to 380 HV 1.

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