DE102013014068A1 - Sliding contact for high and ultra high vacuum applications - Google Patents

Abstract

The present invention relates to a sliding contact with a base body and a counter body, each having at least one sliding surface over which they are in contact with each other and can slide by relative movement to each other. The contacting sliding surfaces of the main body and the counter body are in the proposed sliding contact of mutually different materials, of which a first material tungsten, rhenium or tantalum and a second material is diamond. The proposed sliding contact has a very low friction with high wear resistance and is particularly suitable for high and ultra-high vacuum applications under extreme environmental conditions.

Description

Technical application

The present invention relates to a sliding contact with a base body and a counter-body, each having at least one sliding surface, over which they are in contact with each other and can slide by relative movement to each other.

Sliding contacts are required in many technical fields when two components in mechanical contact or component components make a relative movement to each other. In general, sliding contacts with very low friction without stick-slip effects and high wear resistance are generally desirable, especially for positioning applications in high and ultra-high vacuum. Vacuum positioning applications are particularly important for the electronics industry, for example for the positioning of wafers, and the aerospace industry. For example, the evolution of powerful satellites is heavily dependent on the availability of maintenance-free materials that can withstand extreme environmental conditions; H. Radiation, large temperature ranges, ultrahigh vacuum, etc. Due to the large number of complex contacts and movements of the mechanical components in spacecraft, the life of many spacecraft is limited by the mechanical properties and the sliding properties of the materials used. Unfavorable friction and wear properties can lead to the failure of the moving components and subsequently to significant damage to the spacecraft. A repair is, for example, almost impossible with satellites after they have left the earth.

Therefore, there is a strong demand for the development of aerospace materials or coatings capable on the one hand of surviving the effects of moisture and vibrations during take-off and, on the other hand, of being able to effectively operate over billions of cycles in harsh environments. So the materials in the aerospace industry are exposed due to the changes with the height of different humidities and a wide temperature range of, for example. -40 to + 300 ° C. In addition, planetary exploration can also fail due to attrition, which can be caused by bombardment with particulate matter (eg, CO ₂ particles).

State of the art

So far, mechanical components with sliding contacts due to the above problems in high and ultra-high vacuum systems or spacecraft were avoided as possible. For high-precision positioning, UHV systems (UHV: ultrahigh vacuum) therefore use largely piezo actuators or mechanical feedthroughs. In some cases, solid lubricants are used. These solid lubricants, such as MoS ₂ , have positive tribological properties, but are too soft to resist abrasion in the long term, and do not work in all environments. Hard material layers are in turn thermally stable, but generally have poor tribological properties, such as in RR Chromik et al., "In situ tribometry of solid lubricant nanocomposite coatings", Wear 2007, 262, pages 1239 to 1252 is described. Therefore, a solid lubricant is unlikely to be stable enough for high and ultra-high vacuum and aerospace applications where a variety of conditions have to be met.

The object of the present invention is to provide a sliding contact with very low friction and high wear resistance, which is also suitable for high and ultra-high vacuum applications under extreme conditions, as they may occur, for example, in aerospace applications.

Presentation of the invention

The object is achieved with the sliding contact according to claim 1. Advantageous embodiments of the sliding contact are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

The proposed sliding contact consists in a known manner of a base body and a counter body, each having at least one sliding surface over which they are in mechanical contact with each other and can slide by relative movement to each other. The basic body and the counterpart body are understood to be the two components or components which slide against one another, regardless of whether only one of the two components is moving and the other is stationary or whether both components are moving. The sliding surfaces in contact of the main body and the counter body consist in the proposed sliding contact of different or mutually different materials. The one sliding surface is formed from tungsten, rhenium or tantalum as the first material, which is in contact with this second sliding surface made of diamond as the second material. In this case, the sliding surfaces are to be understood in each case as the surfaces on or on the base body and counter body, which are in mechanical contact with one another and slide against one another during the relative movement.

During the development of the proposed sliding contact, it was recognized that the tribological systems diamond tungsten, diamond rhenium and diamond tantalum have very low coefficients of friction and wear rates in ultra-high vacuum. From ex situ element depth profiles, which were generated by means of X-ray photoelectron spectroscopy of such sliding surfaces of the base and counter-body, it is evident that no chemical interactions or changes between the partners involved by the rubbing process occur and therefore low coefficients of friction are possible. This sliding contacts are made possible in a vacuum with a positioning accuracy by the proposed material pairings, which is significantly increased compared to other solutions. The proposed sliding contact has very low frictional forces (low stick-slip effects) and very low wear rates of the sliding surfaces. The sliding contact can be used without restriction in vacuum, high vacuum and ultrahigh vacuum and requires no additional lubricants. The materials used for the sliding surfaces also have a very low susceptibility to radiation damage and are resistant to high temperatures.

The proposed tribosystem of the sliding contact can be made either of solid material or as a layer. A combination of layer on one side and solid material on the opposite side is also possible. Thus, in one embodiment of the proposed sliding contact, at least one of the sliding surfaces may be formed by the surface or a surface region of the main body or of the counter body, wherein the main body or counter body then consists entirely of the first or the second material.

In another embodiment, at least one of the sliding surfaces is formed by a coating of the surface or a surface region of the main body or of the counter body, wherein the coating then consists of the first or second material, but the main body or counter body may be formed of a different material.

In both embodiments, the respective other body can then also be formed completely from the respective other material or be coated with this material.

In the proposed method, the base body and the counterpart body can each have only one sliding surface or even a plurality of sliding surfaces. In this case, locally several smaller sliding surfaces on one body can hit a larger sliding surface of the other body. Also, a plurality of sliding surfaces of one body may correspond to a plurality of sliding surfaces of the other body.

Thus, in a further embodiment of the proposed sliding contact, the sliding surfaces of a body may be formed by diamond particles spaced apart, which then either hit a larger continuous sliding surface on the other body or correspondingly smaller sliding surfaces on the other body corresponding to the diamond particles.

The first and / or the second material are preferably in polycrystalline form in sliding contact. Thus, the sliding surfaces in this embodiment, for example, be formed of polycrystalline tungsten and polycrystalline diamond.

The proposed sliding contact can be used in many technical applications, for example in the electronics industry, in chip manufacture, in the production of MEMS or NEMS components or in the aerospace industry. Thus, sliding contact with the proposed tribology system allows increasing the durability of NEMS / MEMS, chips and aerospace components, such as flywheels, gyroscopes, solar cells, antenna drives, sensor-pointing mechanisms, gears, pumps, scanners, sensors, actuators or locks and locks. Due to the high hardness of the materials involved, it is possible to cover a wide range of pressures, for example. From about 100 to 1010 Pa, and sliding speeds, for example. From about 0 to 20 m / s, which are usually in such Components occur.

Brief description of the drawings

The proposed sliding contact will be described in more detail below with reference to embodiments in conjunction with the drawings. Hereby show:

1 a measurement of the friction coefficient of the tribosystem diamond tungsten in UHV;

2 an MD simulation of diamond versus tungsten;

3 a first example of the proposed sliding contact in a schematic representation;

4 a second example of the proposed sliding contact in a schematic representation; and

5 a third example of the proposed sliding contact in a schematic representation.

Ways to carry out the invention

The following embodiments use the tribosystem tungsten diamond for the sliding contacts, the particularly advantageous Low friction and high wear resistance characteristics in extreme environmental conditions.

1 shows a measurement of the friction coefficient of diamond versus tungsten in UHV compared to the friction coefficient at 50% RH (RH: relative humidity) as a function of the number of sliding cycles. From the 1 It can be seen that the coefficient of friction in the UHV of about 0.04 is clearly lower than the friction at 50% RH of about 0.14. After annealing the UHV chamber for more than 24 hours and the associated reduction of the partial pressure of H ₂ O, the coefficient of friction drops to about 0.006.

These low coefficients of friction can be attributed to the fact that no chemical interactions or changes due to the rubbing process occur between diamond and tungsten. The cause at the molecular level for these minor changes can be described by MD simulations (MD: molecular dynamics) of diamond versus tungsten, which were performed using realistic WHC potentials. The 2 shows the simulated state at the beginning of the sliding process (partial image a) after 100 ps (partial image b) and after 7.4 ns (partial image c). The upper atoms represent the tungsten in a tungsten layer 3 , the lower atoms the carbon in the diamond layer 4 The simulation shows that after the tungsten layer has smeared in 3 a low-friction Tibokontakt without further significant change in material takes place.

3 shows a first example of the proposed sliding contact in a schematic representation, in which the two the basic and the counter body performing substrates 1 . 2 each coated on its surface with tungsten and diamond. In the example of 3 is the upper substrate 1 with a tungsten layer 3 , the lower substrate 2 with a diamond layer 4 coated. The diamond layer 4 can be formed from microcrystalline diamond (MCD) and / or nanocrystalline diamond (NCD).

Depending on the substrate material, these coatings can be prepared by various PVD or CVD deposition techniques. The thickness of the layers can be varied in a limited manner with the corresponding system and can be, for example, in the range from 10 nm to 40 μm. In the example of 3 put the tungsten layer 3 and the diamond layer 4 in each case the sliding surfaces of the base body and the counter body which come into contact with one another, which are in the sliding direction indicated by the arrow 6 glide together. These as well as the following figures each represent a section of the base and counter body. Base and counter body can be coated only locally or on their entire, directed to the other body surface.

4 shows another example in which the two substrates representing the base and the counter body 1 . 2 To form the sliding surfaces are coated with tungsten and diamond. In this example, the upper substrate is 1 at the corresponding surface area completely with a tungsten layer 3 coated to a suitable thickness, while the counter surface, ie the surface of the lower substrate 2 only partially with particles 5 made of diamond is coated. The size of the diamond particles 5 may be, for example, between ~ 2 nm and 40 microns. The lower substrate 2 thus has a plurality of sliding surfaces on the surface, passing through the respective diamond particles 5 be formed. By the spaced arrangement of diamond particles 5 instead of a closed diamond layer, the cost of diamond coating can be minimized. Furthermore, this lubrication strategy also simplifies development. So may for the application of the diamond particles 5 a nanocomposite material of, for example, silicon carbide and diamond may be used which is deposited on the surface of the substrate 2 is applied. The matrix material of this nanocomposite layer is then etched away (eg with phosphoric acid H ₃ PO ₄ ) to the diamond particles 5 to expose on the surface. This can also be done using other suitable etchants in conjunction with suitable nanocomposite materials. Especially the development and lifetime of nano- and microsystems (NEMS / MEMS) can benefit especially from this approach. By using etching techniques to expose the diamond particles 5 Friction and wear rates can be minimized while avoiding complicated deposition processes or deposition of liquid lubricants.

Also in the example of 4 is the sliding direction again 6 indicated, along the base and counter body can slide together. The sliding direction is in each case predetermined by corresponding guides of the base and counter body, which are not shown in the figures.

5 finally shows a coating strategy for components in fretting applications. For this particular application are both components, ie the lower component 7 as well as the upper component 8th , which in turn represent the base and counter-body, coated in a targeted manner at the points that are to be in contact. In the present example, as well as the 3 and 4 shows a cross section through the proposed sliding contact is the lower component 7 each with diamond particles 5 for the production of sliding surfaces and the upper component 8th with local tungsten layers or tungsten plates 3 coated, each containing the diamond particles 5 the lower component 7 stand opposite. The fretting direction 9 is also indicated in this example with the arrow.

LIST OF REFERENCE NUMBERS

1

upper substrate

2

lower substrate

3

tungsten layer

4

diamond layer

5

diamond particles

6

sliding

7

lower component

8th

upper component

9

Fretting direction

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited non-patent literature

• RR Chromik et al., "In situ tribometry of solid lubricant nanocomposite coatings", Wear 2007, 262, pages 1239 to 1252 [0004]

Claims (6)

Sliding contact with a main body and a counter body ( 1 . 2 ), each having at least one sliding surface ( 3 . 4 ), over which they are in contact with each other and can slide by relative movement to each other, wherein the sliding surfaces in contact ( 3 . 4 ) of the main body and of the counterbody ( 1 . 2 ) are formed from mutually different materials, of which a first material is tungsten or rhenium or tantalum and a second material is diamond. Sliding contact according to claim 1, characterized in that at least one of the sliding surfaces ( 3 . 4 ) through a surface or a surface region of the main body or counter body ( 1 . 2 ), wherein the main body or counterbody ( 1 . 2 ) consists entirely of the first or second material. Sliding contact according to claim 1 or 2, characterized in that at least one of the sliding surfaces ( 3 . 4 ) by a coating of a surface or a surface region of the main body or counter body ( 1 . 2 ), wherein the coating consists of the first or second material. Sliding contact according to claim 3, characterized in that the sliding surfaces ( 3 . 4 ) of the main body or counterbody ( 1 . 2 ), which consist of the second material, by spaced-apart diamond particles ( 5 ) are formed on a surface region of the main body or counter body ( 1 . 2 ) are applied. Sliding contact according to one of claims 1 to 4, characterized in that the first and / or the second material in polycrystalline form in the sliding surfaces ( 1 . 2 ) is present or present. Use of the sliding contact according to one of claims 1 to 5 in high or ultra-high vacuum applications.

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