WO2009080009A1

WO2009080009A1 - Method for producing components with a wear-resistant coating, component produced in this way and use thereof

Info

Publication number: WO2009080009A1
Application number: PCT/DE2008/002121
Authority: WO
Inventors: Mathias Herrmann; Hans-Peter Martin
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2007-12-21
Filing date: 2008-12-15
Publication date: 2009-07-02
Also published as: DE102007063517B3

Abstract

The invention relates to a method for producing components with a wear-resistant coating, to a component produced in this way and the use thereof. The aim of the invention is to provide wear-resistant components that can be cost-effectively and flexibly produced. According to the invention, the surface of a component base body consisting of an SiC ceramic, carbon-fibre reinforced carbon or an SiC ceramic precursor is coated with at least one layer containing an organic binding agent and diamond crystals. The coated component base body is subjected to a thermal treatment in an inert atmosphere or under vacuum conditions to obtain the thermal decomposition of the organic binding agent, thus forming carbon. Simultaneously or subsequently an infiltration using silicon or a silicon alloy is carried out at a temperature that lies above the melting temperature of silicon or the silicon alloy and below 1,650 °C, likewise in an inert atmosphere or under vacuum conditions. During said infiltration the carbon that has been formed and/or a small fraction of the diamond reacts with the silicon to produce ß-SiC and the pores are filled with silicon or the silicon alloy, forming a wear-resistant coating that contains diamond crystals and is bonded to the ß-SiC.

Description

Process for the production of components with a wear protection coating, a component thus produced and its use

The invention relates to a method for producing components with a wear-resistant coating, a component produced in this way, and the use thereof.

Thus, for the production of mechanical seals, which are to be operated without lubricant or with deficient lubrication, SiC ceramics, which are provided with diamond layers whose layer thickness is 5 to 20 microns, used. However, these layers tend to flake off under extreme conditions of use and then result in the functionality of such seals no longer being present. Such diamond layers are deposited by a CVD or PVD method under vacuum conditions. It is also known to use a composite material with diamond crystals and a SiC ceramic, which has been infiltrated with silicon, for the production of cutting tools. This is described in EP 0 010 257 Bl and EP 0 056 596 A1.

According to the technical teaching of EP 0 010 257 B1, such tools should be formed entirely of diamond crystals, SiC and infiltrated silicon. During production, the procedure is to use a mixture of diamond and a carbonaceous material. The surface of the diamond crystals should additionally have been provided with a coating of carbonaceous material. Such a carbonaceous material should decompose at a temperature below 1400 ⁰ C and then be present free non-diamond-like carbon. Subsequently, an infiltration with silicon is to take place, in which pores are closed and SiC is to be formed reactive. The entire volume of a tool thus produced is then filled with diamond, SiC and silicon. The production is quite complex, cost-intensive and the properties of these tools are determined exclusively by the one material.

In the technical solution known from EP 0 056 596 A1, two different dispersions, which are formed with uncoated diamond crystals, pure carbon and paraffin, and a mixture which is mixed with carbon, paraffin and a filler (α- or β-SiC) are used become.

These are to be brought into a mold by pressing. Then, in a heat treatment in vacuum, the complete removal of the paraffin, which is to be evaporated.

In liquid silicon infiltration, β-SiC is formed with the carbon, pores are filled, and a body is sintered, formed of two or three different materials in different regions. In this case, in areas a divergent proportion of diamond or a

Area, which is formed exclusively of α-SiC, as filler, be present.

The cost of production is quite high, which is also caused by the effort for the removal of the paraffin. Homogeneous distribution of the individual materials requires uniform distribution, in particular of pure carbon, and compliance throughout the process.

The once given by the pressing mold can not be changed later, but at least only with great effort. Every single component has to be elaborately manufactured in this form. All contained components must be thermally treated and also sintered.

It is therefore an object of the invention to provide wear-resistant components that can be produced inexpensively and flexibly.

According to the invention, the production of such components can be achieved by a method having the features of claim 1. A component produced in this way is defined by claim 15. An advantageous use is defined in claim 21. Nannt. Advantageous embodiments and further developments of the invention can be achieved with features described in the subordinate claims.

In carrying out the method according to the invention, a component base body is provided with a wear protection coating. This is formed with at least one layer, but preferably more than one layer. The component body is one which is made of a SiC ceramic or a carbon fiber reinforced carbon. However, it is also possible to use a SiC ceramic precursor, for example at least one film which is formed with powdery SiC, for this purpose.

The at least one or more layers for the formation of the wear protection coating can be formed with an organic binder, powdery SiC and diamond crystals. The proportion of diamond crystals should be at least 30% by volume in a formed layer of the coating. The surface of the component body is to be coated with these components, which will still be possible to come back for this purpose.

After the coating, a thermal treatment in an inert atmosphere (eg argon) or in compliance with vacuum conditions at a temperature below 1550 ⁰ C, preferably below 1400 ⁰ C is performed. At temperatures above 250 ^° C., decomposition of the organic binder into gaseous components, which can be removed, takes place, and into free carbon, which is then distributed homogeneously in the layer. Simultaneously or subsequently to this thermal treatment, infiltration with silicon or a silicon alloy whose silicon content is to be high is carried out. In this case, the silicon or the silicon alloy must be molten and proceed again in an inert atmosphere or under vacuum conditions. In order to avoid a conversion of the diamond crystals into graphite, the maximum temperature of 1650 ⁰ C should also be considered. In this process step, additional β-SiC is formed with the previously released carbon and silicon, and with silicon and / or one of the alloy constituents which may be present, any remaining pores in the one or more layers are optionally filled. The diamond crystals can thus be bonded with β-SiC, so that a solid permanent secure bond with the surface of the component body can be achieved without additional measures and process steps. Chipping can be avoided.

This can be further improved by further layers forming the wear protection coating. In this case, the layers should be formed so that the proportion of granular diamond crystals contained therein, starting from the coated surface of the component body increases from layer to layer.

Before infiltration, a porosity of at least 20%, preferably at least 25%, and more preferably at least 30% of the layer (s) should have been maintained.

If a wear protection coating with two layers is formed, the layer applied directly to the surface of the component main body, as an intermediate layer with 10 to 40 vol.% diamond crystals and 60 to 90 vol.% .beta.-SiC and an outer cover layer formed thereon with 30 to 70 vol.% of diamond crystals and 30 to 70 vol. SiC be formed.

Optionally, a silicide or a silicide-forming element (e.g., Mo) may also be employed in the layer (s) at levels of from 0 to 10% by volume. As a result, for example, the temperature required for the infiltration can be lowered and an increased temperature resistance can be achieved. On the other hand, silicon-forming elements, such as Fe, Co or Ni, should be avoided since they are conducive to the conversion of diamant to graphite.

In addition to silicon, Ti, W, Zr, Hf or V can also be used as further elements, which reduce the temperature required for infiltration and can also form hard carbides.

The wear protection coating should be formed with a layer thickness of 0.1 to 3 mm. As a component body, one of RSiC, LPSSiC, SSiC and / or SiSiC, which is formed predominantly of inexpensive α-SiC, are used. The proportion of α-SiC should be at least 70% by volume.

The coating can be formed by injection molding, dipping pressing, hot casting or electrophoretic deposition.

In particular, when diving a component body of porous SiC, in which preferably further free carbon is included, should be used. The coating can be achieved with a suspension are in addition to the organic binder, diamond crystals and possibly also powdery SiC and a liquid are contained, in which the still contained binder of the component body, as far as it has not been pyrolyzed before, can not be solved. The suspension can be absorbed by acting capillary forces and a layer can be formed. The thermal treatment described above can then be carried out subsequently.

Suitable organic binders for diamond and to form the coating phenolic resins or starch have been found.

In a particularly advantageous form, a wear protection coating can also be formed with films on component main bodies. In this case, one or more films can be laminated on top of one another under the exertion of compressive force and when heated to the respective surface of a component main body and then the infiltration thermal treatment already described above can be carried out. The films contain organic binder and diamond crystals as components, which is also possible with different proportions in individual films. Optionally, Sic may also be present, preferably as β-SiC.

In a further alternative, however, it is also possible to work with films containing SiC. These form a SiC ceramic precursor, which should preferably be formed from α-SiC, which can then be obtained by sintering the SiC particles during in-situ thermal treatment of the component base body. In this / these film (s) no diamond crystals are then included. These and the wear protection Coating film (s) may then be laminated together and then subjected to the thermal treatment. In this case, a plastic deformation can be made in advance, with which the shape of the finished component to be manufactured can be specified.

The films may be cut, stamped or drilled prior to lamination to obtain the desired shape of a green body.

The diamond crystals used in the invention should have an average particle size in the range 2 to 50 microns.

In the invention, a component body or a SiC ceramic precursor should be used, in the free carbon or even by conversion of an organic binder-free carbon is contained in a proportion of 3 to 15 vol .-%, when the

Component body is infiltrated together with the / the layer (s).

However, a component base body can also be densely sintered SiC, which is readily wettable when infiltrated by silicon.

In the invention, it is also possible to use or produce component main bodies which are fiber-reinforced. It can be used in accordance with the known from the prior art for such materials manufacturing process.

Because of the good wear and sliding properties, a component provided with a wear protection coating can be advantageous for mechanical seals be used.

In the production of components according to the invention, at least almost a dimensional change, which usually occurs during sintering, can be avoided. The infiltration does not cause any additional deformation or dimensional change. The wear protection coating can be obtained with a defined layer thickness and consistency.

The wear protection coating can be formed only on surface areas of a component that require the respective functionality.

The invention will be explained in more detail by way of example in the following.

example 1

It is powdery SiC having an average granule size in the range 200 to 300 microns for a production of a SiSiC typical composition of 60 wt% α-SiC (d ₅ o = 60 microns), 30 mass% α-SiC (d ₅ o = 2 microns) and an effective proportion of carbon of 5 mass% and with the proportion of organic binder of 10 mass% plates are produced in a size of 60 * 60 * 10 mm by pressing. These plates are subjected to a heat treatment in an argon atmosphere to produce the carbon residues from the organic binder. The plate is formed of SiC and the residual carbon of the organic binder. A component base body obtained in this way has a pore volume which has 40% of the volume of the component main body. Powdery SiC with an average particle size d ₅₀ = 20 μm and diamond crystals with an average particle size d ₅₀ = 15 μm (grain size between 10 and 20 μm) and organic binder additives are used to produce ceramic films with a thickness of 100 μm by means of film casting. In this case, films are produced with divergent proportions of SiC and diamond crystals. One film is formed with 40% by mass of SiC and 40% by mass of diamond crystals and a second film with 80% by mass of diamond crystals, the remainder being organic binders. In this example, the organic bond used was a mixture with 43% by volume polyvinyl butyral, 27% by volume triethylene glycol (commercially available from Sigma-Aldrich, Steinheim, DE under the designation PVB and TEG) and 8VoI. -% Menhaden fish oil (also available as MFO from Sigma -Aldrich, Steinheim, DE under MFO), the vol .-% data are based on the solid.

The films were cut to a format 60 * 60 mm and placed on the component body made of SiC and laminated with a pressing tool at a temperature of about 100 ⁰ C. It had a pressure below 3 MPa. By lamination, the films were bonded to the organic binder. The film with the higher diamond content was on the second film and arranged on a surface of the component body.

The thus prepared semi-finished product was placed on annular wicks of porous SiC. Silicon was used in these wicks in advance. Silicon was present with a mass that is a mass of 50% of the semifinished product. Wicks and semi-finished products were then placed in a graphite crucible and placed in an oven. ner heat treatment up to a temperature of 850 ° C at a heating rate of 2 K / min subjected. It was carried out at a pressure of 10 ^{~ 2} mbar and in an argon atmosphere. The organic binder was pyrolyzed. Thereafter, the temperature was increased to 1550 ⁰ C, while maintaining a heating rate of 10 K / min. After a holding time of 30 minutes, a cooling and the component could be removed from the oven.

During this heat treatment, the silicon was melted (melting temperature Si 1410 ⁰ C). With formed melt an infiltration was achieved by capillary force action. Carbon residues of the SiC body part and carbon residues of the molten silicon films reacted to SiC. SiC particles or SiC particles and diamond crystals are joined by reaction with secondary SiC particles. The free pore volume was filled with elemental silicon. The result was a ceramic composite, which is formed predominantly from known SiC material SiSiC (silicon-infiltrated silicon). On one surface is the anti-wear coating with SiC and diamond with a lower diamond transition layer between the outside

Layer with a higher diamond content formed on the surface of the component body.

The component produced in this way is characterized by the fact that its essential volume properties correspond to those of SiSiC. In particular, through the upper layer of the wear protection coating outstanding hardness and improved wear protection can be achieved, which correspond to that of polycrystalline SiC-bonded diamond materials. The anti-wear coating thus formed tion is firmly connected to ^' the component body.

Example 2

The film produced according to Example 1 is laminated to a sintered SSiC component body. And subjected to just such a heat treatment. After the infiltration, the temperature was carried out at 1500 ⁰ C and over a period of 45 min annealing. In this case, the remaining silicon in the layer almost completely changed to SiC, so that the residual silicon content was less than 1%.

The component produced in this way is also distinguished by the volume properties achievable equivalent to SiC and a hardness of the wear protection coating ≥ 35 GPa, as well as an increased wear resistance comparable to that of polycrystalline SiC-bonded diamond material. The wear protection coating is permanently and very well bonded to the component body.

Example 3

Diamond crystals having an average particle size of 15 μm were dispersed in acetone in a stirrer under the influence of ultrasound and admixed with 15% by weight of phenolic resin. The mixture was dried in a rotary evaporator and then sieved with a sieve (mesh size <60 μm.) A prefabricated SiSiC (infiltrated) plate was placed in a die and the dried granules (diamond + phenolic resin) added to the die The component was then removed from the pressing tool and then subjected to a heat treatment as follows. heated from 1 K / min to 120 ⁰ C and held this temperature for 6 h to achieve a cure. Thereafter, pyrolysis was carried out for further heating at a heating rate of 2 K / min up to 600 ⁰ C in an argon atmosphere. The further process steps correspond to the thermal treatment, as used in Examples 1 and 2. It was infiltrated at 1550 ⁰ C and then held for the reaction of the residual silicon, a temperature of 1500 ⁰ C over a period of 1 h.

Claims

claims

1. A method for producing components with a wear protection coating, wherein a component base body made of a SiC ceramic, carbon fiber reinforced carbon or a SiC ceramic precursor having at least one layer, which is formed with an organic binder and diamond crystals, on the surface is coated;

subjecting the thus-coated component base to thermal treatment in an inert atmosphere or under vacuum conditions, thereby achieving thermal decomposition of the organic binder to form carbon;

simultaneously or subsequently, infiltration with silicon or a silicon alloy, at a temperature above the melting temperature of silicon or the silicon alloy and below 1650 ° C., is likewise carried out in an inert atmosphere or under the observation of vacuum conditions the carbon formed and / or a small proportion of diamond reacts with silicon to form β-SiC and pores are filled with silicon or the silicon alloy, so that a wear-resistant layer containing diamond crystals is formed which is bonded to the β-SiC.

2. The method according to claim 1, characterized in that on the surface of the component main body before the infiltration fran- te (n) layer (s) having a porosity of at least 20% is / are formed.

3. The method according to claim 1 or 2, characterized in that a plurality of layers are formed on the surface of the component main body, and thereby the proportion of diamond crystal is increased starting from the Bauteilgrundköperoberfläche.

4. The method according to any one of the preceding claims, characterized in that the coating is applied by dipping, injection molding, lamination of film, pressing, electrophoretic deposition or hot casting.

5. The method according to any one of the preceding claims, characterized in that on the surface of a component body prior to the thermal treatment at least one layer containing diamond crystals is formed.

6. The method according to any one of the preceding claims, characterized in that several

Layers are formed with divergent proportions of diamond crystals.

7. The method according to any one of the preceding claims, characterized in that as SiC ceramic precursor at least one SiC-containing diamond crystal-free film is used, which is laminated together with at least one diamond crystal film and then subjected to the thermal treatment.

8. The method according to any one of the preceding claims, characterized in that in a layer next to organic binder and diamond at least one silicide, silicide-forming or carbide-forming element is contained.

9. The method according to any one of the preceding claims, characterized in that a component body of porous SiC, in which free carbon is contained, is used.

10. The method according to claim 9, characterized in that the component base body of porous SiC is immersed in an organic binder and diamond crystals containing suspension.

11. The method according to claim 9 or 10, characterized in that a suspension in which additionally powdery SiC is contained is used.

12. The method according to any one of the preceding claims, characterized in that a component body made of R-SiC, LPSSiC, SSiC or SiSiC is used; wherein the component main body is formed predominantly of α-SiC.

13. The method according to any one of the preceding claims, characterized in that a phenolic resin or a starch is used as the organic binder.

14. The method according to any one of the preceding claims, characterized in that a component body or a SiC ceramic precursor is contained in the free carbon in a proportion of 3 to 15% by mass is used.

15. Component with wear protection coating produced by a method according to one of the preceding hergehen claims, characterized in that on a surface of a component body of SiC or carbon fiber reinforced carbon at least one layer having at least 30% by mass of diamond crystals, at least 30% by mass of β-SiC and 0 to 10% by mass of silicum, a Silicide and / or a carbide is formed with a layer thickness in the range 0.1 to 3 mm.

16. Component according to claim 15, characterized in that the layer with 30 to 70 mass% of diamond crystals and 70 to 30 mass% ß-SiC is formed.

17. Component according to claim 15 or 16, character- ized in that at least two layers the

Form wear protection coating, wherein the proportion of diamond crystals contained in the layers in the layers, starting from the surface of the component main body increases.

18. Component according to claim 17, characterized in that a proportion of diamond crystals between 10 to 40 vol .-% and a proportion of ß-SiC between 60 and 90 vol .-% is maintained in an intermediate layer formed on the surface of the component body.

19. Component according to one of claims 15 to 18, characterized in that the component base body of R-SiC, LPSSiC, SSiC and / or SiSiC is formed.

20. Component according to claim 19, characterized in that the component base body is formed from fiber-reinforced SiC.

21. Use of a component produced by a method according to one of claims 1 to 14 for mechanical seals.