EP0219536A1

EP0219536A1 - Protection layer.

Info

Publication number: EP0219536A1
Application number: EP86902820A
Authority: EP
Inventors: Heiko Gruner
Original assignee: Plasmainvent AG
Current assignee: Plasmainvent AG
Priority date: 1985-04-17
Filing date: 1986-04-17
Publication date: 1987-04-29
Anticipated expiration: 2006-04-17
Also published as: ATE68019T1; DE3681778D1; JPS62502974A; US4808487A; DE3513882A1; WO1986006106A1; EP0219536B1

Abstract

PCT No. PCT/EP86/00225 Sec. 371 Date Jan. 15, 1987 Sec. 102(e) Date Jan. 15, 1987 PCT Filed Apr. 17, 1986 PCT Pub. No. WO86/06106 PCT Pub. Date Oct. 23, 1986.The protection layer (3,4,5) applied to a support (1) by a vacuum plasma spraying process comprises an adherence layer (3), an intermediate layer (4) and a coating layer (5). In order to enable a universal application of the protection, particularly in the construction of turbines, foundry and nuclear technique, the adherence layer (3) is made of a selected material having a composition and a thermal expansion coefficient close to those of the material of the object to be coated (1). The intermediate layer (4) is comprised of a mixture of the material of the adherence layer (3) and of that of the coating layer (5) and the coating layer is comprised of a thick layer of sprayed material selected in the group of borides, carbides, nitrides and oxides of preferably TiB2 or Al2O3.

Description

PROTECTIVE LAYER

The invention relates to a protective layer applied to a metallic carrier in the plasma spraying process, consisting of at least one metallic adhesive layer and a multilayer top layer, which has different proportions of metallic and ceramic materials in its layers. Protective layers of this type can be applied to very different carrier bodies. This is always associated with the intention of increasing the service life of the carrier body in a specific application and / or opening up new areas of use for the carrier material. With

With the help of the protective layer, workpiece surfaces can be given specific specific properties at certain points. This expands the possible uses of the workpieces and increases their resistance in daily use.

PCT-WO-82/01898 has made known protective layers of the type described at the outset, which include an adhesive layer made of NiCrAlY and a multilayer top layer with different layers of oxide-ceramic materials such as

Zr0 ₂ -Y ₂ ° ^A1 2 ° ₃ ^oα - ^he Ca-SiO. exhibit. The total layer thickness given there on the examples is between 0.8 mm and 2.5 mm, according to the claims there 0.5 to 8 mm or 2 to 7 mm. The adhesive layer thickness there is 0.1 mm, 0.15 mm or 0.2 mm.

Very different techniques are used today for coating workpiece surfaces. Due to the high energy density in the plasma flame, plasma spraying quickly secured a leading role in coating technology. With this coating technique, practically all powdery materials can be coated on a wide variety of different materials under certain conditions technology secured. Practically all powdery materials can be deposited as a layer on a wide variety of carrier materials with this coating technique under certain conditions. Usually, it is hard, resistant, high-temperature-resistant and corrosion-resistant plasma spray layers which significantly extend the service life of high-quality machine components in harsh environmental conditions. However, the industrial application of plasma spraying technology also shows its physical application limits. In many cases the spray coating is not sufficiently dense and its adhesion to the base material is insufficient. With reactive wettable powders, the chemical composition in the spray layer changes too much. Relatively easy can atmospheric oxygen in ^'single diffuse the plasma flame, oxidizing and disturbing.

The vacuum plasma spray technology (VPS technology) was developed from these points of view. Their development, taking into account the special requirements of this new technology, led to significant improvements in coating conditions and layer properties compared to spraying in the atmosphere. Vacuum plasma spraying is a further development and addition to the atmospheric plasma spraying process (APS process). It differs from this principle in that the coating process takes place in a vacuum chamber at negative pressure.

The known improvements in coating conditions and layer properties of VPS technology can be summarized in 4 groups:

1. Particle speed

The heating of the plasma gas in the arc and its ex- expansion into vacuum accelerate the gas atoms to more than three times the speed of sound. Compared to atmospheric spraying, the jet speed in vacuum is about 2 to 3 times higher. The spray powder particles, which are still injected into the hot zone of the plasma jet within the burner nozzle, are correspondingly faster. Higher powder particle speeds result in denser spray layers and significantly reduce residual porosity and surface roughness.

2. Surface cleaning

With the help of the transmitted arc, the workpiece surface can be cleaned in a sputtering process before coating. Gas contamination, water vapor and oxide layers are dusted off. This leads to a significant improvement in the adhesion of the spray layers, especially on smooth surfaces. In addition to the mechanical interlocking of the spray layer with the material of the carrier, free surface energy of cleaned carriers is saturated by layer atoms. In addition, favorable conditions are created for interdiffusion processes between the carrier material and the layer.

3. Workpiece temperature

Since the coating process runs in a vacuum, all substrates can be heated up to their thermal stability limit before coating. The heating effect of the plasma flame can be increased with the help of the transmitted arc. Targeted temperature changes during or after coating are possible without the risk of oxidation for the substrate and layer. This avoids or reduces internal stresses in the spray layer. 4. Layer cleanliness

The coating process takes place without reactive gas partners. Oxide-free layers are formed which have the same chemical composition as the wettable powder. Reactive powders find no reactant, their melting temperature and heat of fusion are not influenced.

With specific use of the advantages of VPS technology, further applications for plasma spray coatings have been developed. Also in connection with cover layers sprayed in the VPS process, new fields of application were only possible for known carrier materials.

Examples of preferred areas of application of such vacuum plasma spray layers are:

Hot corrosion -:., Oxidation and erosion protection of turbine components,

Electrical insulation and / or insulation,

Chemical resistance and

Radiation protection in nuclear technology.

So far, a protective layer that can only be used in this application has been developed for practically every individual application of plasma spray coatings. The development criteria for this protective layer are essentially the stress, the temperature behavior and its mechanical and / or chemical stability. However, the carrier material and the ambient conditions also influence the choice of the layer material and its thickness, which should again only be as thick as necessary for reasons of economy. > -

The invention has for its object to provide a protective layer of the type described above, which can be used practically universally in all four main areas of application of the plasma spray layers, in particular the carrier simultaneously effective against corrosion, oxidation, erosion, chemical attack and Radiation protects, it is electrically isolated and temporarily protected from overheating by thermal insulation.

According to the invention, this object is achieved by

a) that the protective layer is applied free of cracks and pores in the vacuum plasma spraying process, b) that in the protective layer on the pronounced adhesive layer of defined thickness there is a pronounced intermediate layer of defined thickness and then a pronounced cover layer. Defined thickness follows, c) that the adhesive layer consists of a material whose chemical composition essentially corresponds to that of the material of the carrier and has a thermal expansion coefficient very similar to that of the carrier, d) that the adhesive layer is sprayed as a dense Layer is built up.

The fact that the intermediate layer is sprayed from a. Mixing the materials of the adhesive layer and the cover layer results in a particularly good connection of the tightly sprayed adhesive layer with the tightly sprayed cover layer, their different thermal expansion coefficients being matched to one another. As a result, the adhesive layer and intermediate layer are practically not limited in their layer thickness

The intermediate layer is expediently constructed with a continuously graded transition from the material of the adhesive layer to the material of the cover layer. - <_ -

The intermediate layer is advantageously sprayed on starting with the spray chamber when the adhesive layer is applied and gradually transitioning to the spray chamber pressure when the cover layer is applied.

Appropriately lie

a) the thickness of the adhesive layer in the range from approximately 20 μm to approximately 50 μm, at approximately 100 μm or at approximately 200 μm, b) the thickness of the intermediate layer in the range from approximately 20 μm to approximately 200 μm, preferably in the range from approximately 20 microns microns to about 50 microns, in particular at about 50 or about 200 microns, c) the thickness of the topcoat in the range from about 30 microns to about 100 microns, preferably .in the range of about 50 ^•• microns to about 80 microns, in particular at about 50 μm or about 100 μm.

For applications to avoid corrosion or cavitation of the support, the adhesive layer can advantageously have a thickness of approximately 200 μm, the intermediate layer a thickness of up to 5 mm and the cover layer a thickness of up to 500 μm.

The protective layer effect is given by the tightness of the cover layer, which for refractory materials with very high melting temperatures can practically only be achieved by the VPS process at these layer thicknesses. It is thus possible to combine materials with very different physical properties in a stable and temperature-change-resistant manner without the protective layer coming off, cracking and thus losing its protective effect in the different areas of use.

The grain size of the wettable powder is advantageously a maximum of 25 μm, so that it is ensured that both when the adhesive layer is sprayed with the top layer, but especially when the spray the intermediate layer, all wettable powder particles form the spray layer as molten droplets. This and in conjunction with the high mechanical impact energy ensures the tightness of the spray layer. An essential feature of the protective layer structure is the lamellar overlap of the materials of the adhesive layer and the cover layer in the intermediate layer, which is caused by the bursting of the liquid wettable powder particles on impact on the workpiece surface.

In contrast to thermal barrier layers previously produced by plasma spraying, which e.g. consist of stabilized ZrO_ and whose thermal stability is essentially given by microcracks and a porosity of up to 15% by volume, the protective layer produced according to the invention only develops its effect when its density practically corresponds to the solid value.

Due to the advantages of VPS technology mentioned, for the first time all backing materials can also be realized as a spray layer, without chemical changes and practically with identical tightness and temperature behavior, so that the top layer made of refractory material is connected to the backing material in the best possible way via the intermediate layer and adhesive layer can.

The refractory material of the top layer TiB_, whose temperature resistance is 3200 ° C., is advantageous.

Exceeds in: θxidierend. \ _ At_mosphäre: die Oberflächeritem- xa ur..T.1.00 ⁰ .- Cy. ^' .sό is considered. Refractory material of the ^ top layer preferably A1-0-. used.

The material of the carrier and the adhesive layer can advantageously be made of Ti and the material of the intermediate layer can be made of 80% Ti and - 3 -

20% TiB_ exist, the material of the cover layer being TiB_.

Alternatively, the material of the carrier and the adhesive layer can consist of a superalloy such as In 738 and the material of the intermediate layer can consist of 100% In 738 graded transition into 100% TiB or ^A1 2 ° 3.

The material of the carrier can advantageously also consist of a superalloy such as In 738 and the material of the adhesive layer can consist of an alloy of the type MC AlY which is matched to the alloy of the carrier, where M is Fe, Co ^' or NiCo as the main alloy component. Here, the material of the intermediate layer advantageously consists of 100% M-CrAlY graded, transitioning into 100% TiB ₂ or A1 ₂ 0 ₃ .

The material of the intermediate layer can expediently also consist of M-CrAlY and A1 ₂ 0, and the intermediate layer has a ^' tightly sprayed, laminated, crack and pore-free structure, A1 ₂ 0 being used for the material of the cover layer . The protective effect of the M-CrAlY alloy layer is also due to the constant conversion of the AI portion into AI. _J O3 caused. It is essential for the protective layer according to the invention when building up with oxides as refractory portion, especially with A1 ₂ 0 ₃ in M-CrAlY, that no portion of stabilized oxides is required, that no micro-cracks or pores in the

Layer are present and that also here the Al ₂ 0 ₃ ~ particles were liquid when the layer was formed and are embedded in the interlayer in the form of a surface or build up the cover layer.

Finally, the material of the carrier and the adhesive layer can advantageously be made of steel and the material of the intermediate layer can consist of 50% steel and 50% TiB ₂ . - 3 -

The invention is explained below using exemplary embodiments and with reference to the drawing. Show in the drawing

1 shows a section through a protective layer applied to a carrier in the cutout, and

FIG. 2 shows the structure of the intermediate layer in the protective layer according to FIG. 1.

1 shows a carrier 1 which has been degassed on its surface 2 before the application of a composite protective layer 3, 4, 5 and has been heated to a certain temperature. The surface 2 of the carrier 1 can be specially treated, for example roughened by sandblasting, and sputter-cleaned and coated with absorbed gases, water and thin oxide layers before coating with the aid of the transmitted arc.

An adhesive layer 3 is applied to the surface 2 of the carrier 1 using the VPS method, the chemical composition of which largely corresponds to the material of the carrier 1 and has practically the same thermal expansion coefficient as the carrier 1. The thickness of the adhesive layer 3 is preferably approx. 50 μm, but can also be any greater if e.g. in the event of a repair, a worn surface is to be returned to its original dimension.

An intermediate layer 4 of any thickness is applied to the adhesive layer 3, and a densely sprayed cover layer 5 with a preferred thickness of 50 to 1.00 μm made of a refractory material, for example TiB ₂ , is applied to this intermediate layer 4. Both the intermediate layer 4 and the cover layer 5 are also deposited using the VPS method. The intermediate layer 4 consists of a mixture of the materials of the adhesive layer 3 and the cover layer 5 and is formed, for example, with a graded transition between the latter two layers. The cover layer 5 made of refractory material represents the actual protective layer of the composite protective layer 3, 4, 5, which layer structure corresponds as closely as possible to the solid material, that is to say is as dense as possible, in contrast to previously known layers made of refractory material, that is to say has no residual porosity and no microporosity. and built in macro cracks.

2 shows schematically the structure of the intermediate layer 4, in which the materials of the adhesive layer and the cover layer overlap like lamellae.

Several application examples of the protective layer according to the invention are explained in more detail below.

example 1

A turbine component, which for reasons of weight and mechanical properties consists of a titanium alloy, is exposed to severe erosion loads in practical operation. By means of a protective layer according to the invention, consisting of a Ti adhesive layer 3, an intermediate layer 4, produced by simultaneous powder injection of 80% Ti and 20% TiB ₂ , and a pure TiB ₂ ~ top layer 5, the erosion attack succeeds very strongly to diminish. In this application, the adhesive layer 3 is approximately 20 to -50 μm thick, the intermediate layer 4 advantageously approximately 20 to .50 μm and the cover layer 5 on average 40 μm. The coating is carried out in such a way that the thickness of the TiB ₂ top layer 5 was specifically increased to approximately 50 μm at the gas entry points exposed to the particularly erosive forces, such as the leading edge or the pressure side of a turbine blade. -. 1 -

It is important that the TiB ₂ top layer 5 has a very low erosion rate at a layer hardness above 2300, measured according to the Vickers method, while according to the prior art, rather softer materials have a high erosion stability.

Due to the deposition of the Ti adhesive layer 3 and the intermediate layer 4 made of Ti and TiB_ by the VPS method and the sputter cleaning of the Ti carrier surface 2 carried out prior to coating, there is practically no transition between

Carrier 1 and protective layer 3, 4, 5 can be seen. The layer adhesion can no longer be measured using the known test methods. A measurement carried out in accordance with D N 50160 does not provide any adhesive tensile strength values for the protective layer, since there is a breakout in the adhesive point.

Example 2

^• In a second example, a carrier 1 is to au, s alloy of a super, for example, in 738, to erosion and / or Heißgasoxida- tion to be protected. These grades are made according to the

Coating subjected to a specific heat treatment for

Generation of a material structure which only has the mechanical high-temperature properties. This heat treatment takes place at temperatures where intermetallic

Diffusion can take place. Therefore, it is particularly advantageous to coat this carrier 1 with an adhesive layer 3 of the same material composition, since the depletion and enrichment of the alloy components in the adhesive layer 3 and in the carrier 1 is prevented, which is always associated with changes in the mechanical properties that must be avoided.

The preferred protective layer structure in this application is adhesive layer 3 in 738 about 100 μm thick, graded over transition from 100% In 738 to 100% TiB ₂ in the intermediate layer 4 to a layer thickness of approximately 200 μm, and top layer 5 TiB-, approximately 50 μm thick ..: with targeted reinforcements to 80 μm ^' at the critical points.

If the oxidation attack outweighs the erosion attack, see above

I.

^• 'can for the adhesive layer 3 advantageously the Trä¬ gerwerkstoff adapted ^{Legierungswerkstof'} f type M-CrAlY! are used, with M Fe, Co, Ni and NiCo being used as the main component. Exceeds the. surface temperature 1100 ° C, so the same layer takes place! best with the refractory material Al ₂ 0 ₃ . In both I cases, the "preferred spray powder granulation is limited to a maximum of 25 μm in order to produce a uniform gradation transition with as homogeneous a material distribution as possible and to spray the top layer 5 tightly ...

Example 3

In application example 3, a carrier 1 made of steel is to be used as an aluminum die casting tool and is to be protected against the attack of liquid Al. In this case, spray powder of this type of steel is used for the adhesive layer 3, the thickness of the adhesive layer 3 preferably being up to 200 μm. In contrast, the thickness of the intermediate layer 4 made of a 50:50 mixture of steel spray powder and TiB _{2 is} relatively small at 50 μm. Since the temperature for liquid aluminum is around 700 ° C, the TiB ₂ ~ top layer 5 is 100 μm thick. Since die casting tools have a perfect fit, the total layer application on the workpiece must be taken into account before coating.

In the case of the repair spraying of a die-casting tool already used, in which certain areas are removed to such an extent that its use means that a no longer erable undersize, the original geometry can be restored by spraying on the adhesive layer material, and then the intermediate layer and cover layer can be applied.

Example 4

In the nuclear field, a protective layer is sought for the first wall boundary of the fusion plasma, which protects the carrier material against ion bombardment and electrical flashovers with a high current density, but is temperature-resistant in an inert gas atmosphere, has a low sputtering rate under particle bombardment and the demand for one if possible low atomic number fulfilled. In this application too, TiB _{2 has} proven itself for the top layer 5, the temperature resistance of which in the ^'. Vacuum at. 3,200 ° C. S.αh ^' utz.schichtaufbau depends on the chosen. Straps, material. And are otherwise assembled according to the invention.

Example 5

Components of hydropower plants are particularly exposed to erosive forces, which are further reinforced by the cavitation effect. In the design of the design, a substantial material reserve is usually included in order to achieve a certain service life despite severe erosion. In addition to reducing the erosion rate on the surface of the component, a protective layer in this application should also be able to be applied correspondingly thickly. The protective layer according to the invention also develops an ideal protective effect here.

After spraying a Haf ^'layer 3 is about 200 microns thick, followed by a for example up to 5 mm-thick intermediate layer 4 material as a mixture with about 20 to 60 weight percent refractory, very fine and uniformly in the matrix of the Adhesive layer material is distributed before in this case an up to 500 μm thick cover layer 5 made of refractory material is sprayed on very densely.

All of the examples listed are very expensive components, the lifespan extension of which is very important for cost reasons. An essential feature of the invention is the ability to repair these components after the protective layer has been used up. Since a material corresponding to the carrier material was applied as the adhesive layer 3, residues of the protective layer 3, 4, 5 can be removed, for example by sandblasting, as far as the adhesive layer material, in order then to be sprayed on again.

At the points where the protective layer 3, 4, 5 and additional material of the carrier, for example, was eroded during the operational use of the component, adhesive layer material can first be sprayed on until the original configuration of the component is reached again in order to finally apply the protective layer 3, 4, 5 again with the tried and tested layer structure.

Claims

- 1 . - Patent claims:

1. In the plasma spraying process, a protective layer (3, 4, 5) applied to a metallic carrier (1), consisting of at least one metallic adhesive layer (3) and a multilayer top layer, which in its layers has different proportions of metallic and ceramic materials featured,

a) that the protective layer (3, 4, 5) is applied free of cracks and pores in the vacuum plasma spraying process, b) that in the protective layer (3, 4, 5) on the pronounced adhesive layer (3) of a defined thickness a defined thickness Embossed intermediate layer (4) of defined thickness and this is followed by a pronounced cover layer (5) of defined thickness, c) that the adhesive layer (3) consists of a material whose chemical composition essentially corresponds to that of the material of the carrier (1) and one thermal expansion coefficient very similar to that of the carrier (1), d) that the adhesive layer (3) is constructed as a tightly sprayed layer ₇ e) that the intermediate layer (4) as a tightly sprayed, by mixing the materials of the adhesive layer (3) and the cover layer ( 5) a clearly laminated layer is built up, and f) that the cover layer (5) consists of a tightly sprayed refractory material from the group of borides, carbides, nitrides and oxides.

Protective layer according to claim 1, characterized in that the intermediate layer (4) with a continuously graded transition from the material of the adhesive layer (3) to the material of the cover layer (5).

Protective layer according to claim 1 or 2, characterized in that the intermediate layer (4) is sprayed on starting with the spray chamber pressure when applying the adhesive layer (3) and gradually progressing to the spray chamber pressure when applying the cover layer.

4. Protective layer according to claim 1, 2 or 3, thereby g e k e n n z e i c h n e t,

a) that the thickness of the adhesive layer (3) is in the range of approximately 20 μm to approximately 50 μm, approximately 100 μm or approximately 200 μm, b) that the thickness of the intermediate layer - (4) is in the range of approximately 20 μm to approximately 200 μm, preferably in the range from approximately 20 μm to approximately 50 μm, in particular approximately 50 μm or approximately 200 μm, and c) that the thickness of the cover layer (5) is in the range from approximately 30 μm to approximately 100 μm, preferably in the range from approximately 50 μm to approximately 80 μm, in particular approximately 50 μm or approximately 100 μm.

5. Protective layer according to claim 1, 2 or 3, characterized in that the adhesive layer (3) has a thickness of about 200 microns, the intermediate layer (4) a thickness up to 5 mm and the cover layer (5) a thickness has up to 500 μm.

6. Protective layer according to one of claims 1 to 5, characterized in that the grain of the wettable powder is at most 25 microns.

7. Protective layer according to one of claims 1 to 6, characterized in that the refractory material of the cover layer (5) iB ₂ or A1.-0-, is.

8. Protective layer according to one of claims 1 to 7, characterized in that the material of the carrier (1) and the adhesive layer (3) made of Ti and the material of the intermediate layer (4) consists of 80% Ti and 20% TiB ₂ .

9. Protective layer according to one of claims 1 to 7, characterized in that the material of the carrier (1) and the adhesive layer (3) consists of a superalloy such as In 738 and the material of the intermediate layer (4) consists of .100% In 738 graded in 100% TiB ₂ or. Al ₂ 0.

10. Protective layer according to one of claims 1 to 7, characterized in that the material of the carrier (1) made of a super alloy such as In 738 and the material of the adhesive layer made of an alloy of the type M- of the carrier (1) matched CrAlY exists, where M is the main alloy component Fe, Co or NiCo.

11. Protective layer according to claim 10, characterized in that the material of the intermediate layer (4) consists of 100% M-CrAlY graded transition into 100% TiB ₂ .

12. Protective layer according to one of claims 1 to 7 or 10, characterized in that the material of the intermediate layer (4) consists of M-CrAlY and Al ₂ 0, be¬ and the intermediate layer (4) a tightly sprayed, laminated, cracked - And has pore-free structure.

13. Protective layer according to one of claims 1 to 6, characterized in that the material of the carrier (1) and the adhesive layer (3) made of steel and the material of the intermediate layer (4) consists of 50% steel and 50% TiB ₂ .