DE3602104A1 - Slide or friction element with functional part of ceramic material and process for its production - Google Patents

Abstract

An apparatus part subjected to sliding or friction is covered with at least one layer of ceramic material by cathode sputtering, a matrix of ceramic material being formed and a stabiliser substance of the nature of a preferably ceramic-like foreign material being incorporated into this ceramic matrix in extremely fine fragmentation and uniform distribution. Between the substrate consisting of a tough heat-resistant material and the ceramic layer or between successive different ceramic layers there may be formed a thin active brazing alloy layer, it being necessary to choose as the active brazing alloy a material which wets the materials of both layers to be bonded.

Description

The invention relates to sliding or friction elements for use in operation at high temperature, for example one Back temperature above 200 ° C, at which a Functional part made of ceramic with a sliding or friction surface Material with embedded stabilizer substance is provided. Within the scope of the invention, and friction elements on sliding or friction stressable Device parts or machine parts of any kind and To understand design.

In the course of increasing the performance of machines, in particular Internal combustion engines, and the aspirations the cooling devices in order to save weight to simplify, especially cooling devices for that Losing lubricating oil is becoming increasingly common the demand for new sliding and friction elements higher fatigue strength and thermal wear resistance raised.

For some years now this has been the replacement of everyone metallic parts in internal combustion engines ceramic materials worked. Of such ceramic Materials are promised for use in Construction of internal combustion engines has many advantages. they can be used at much higher temperatures are considered metallic materials, so that cooling systems are not required or can be significantly simplified and the efficiency of internal combustion engines clearly can be increased. Other desirable benefits include increased wear resistance, which enables longer service life and the low mass of ceramic material, which leads to weight savings. Also stand out  ceramic materials due to good corrosion resistance and high compressive strength. There are ceramic ones Materials but also outstanding negative properties, especially high brittleness and poor thermal shock resistance. Associated with this is a big one Sensitivity to impacts and sudden temperature changes. This sensitivity is the cause of that common "catastrophic failures", i.e. H. the abrupt breakage of a ceramic component without previous deformation, as is the case for metals.

Attempts have already been made to improve the poor thermal shock resistance in so-called cermets by means of the metallic component (e.g. Cr, Co. Ni, Fe, Mo, W and the like), as well as the toughness and impact resistance. With regard to the improvement of brittleness in MTZ-Motortechnische Zeitschrift 45 (1984) 5, p. 190 u. 191 and proposed from "SAE Technical Paper Series 820429" PSZ Ceramics for Adiabatic Engine Components "" partially stabilized "ceramic materials. Such a partially stabilized ceramic material is, for example, zirconium oxide, the microstructure of which is partially stabilized by small additions of calcium oxide, magnesium oxide and yttrium oxide (PSZ), so that the material should remain more resistant to breakage and toughness even at high temperatures. As an alternative to this, aluminum oxide converted by incorporation of zirconium oxide particles has become known (“Transformation-Toughened Aluminia” -TT Al ₂ O ₃ ).

However, as practice has shown, such "partially stabilized" ceramic materials not with the create the required reproducibility, so that in considerable scatter in material properties in practice occur. Cracking under dynamic stress in the form of macroscopic cracks  do not exclude. The so-called "catastrophic Failure "with such partially stabilized ceramic materials do not exclude. Overall, so far known partially stabilized ceramic materials unsuitable for series production. Another essential one Disadvantage of these materials is the difficult cumbersome manufacturing method, which according to SAE Technical Paper Series 820429 Page 5 ten to twelve steps makes necessary. After all, workpieces are from the known "partially stabilized" ceramic material only known as solid ceramic parts, so that is why already a macroscopic breaking point for destruction of the workpiece and the "catastrophic failure" of the Workpiece can lead.

In contrast, the invention is based on the object the disadvantages of the solid parts made of ceramic to avoid and a metal / ceramic layer material create the despite the great hardness of ceramic layers has good adaptability to the counter element and with high dynamic loads not through training of macro cracks leads to failure. The invention slide or friction element to be created should also be due to the good adhesive strength of its ceramic layer mark on the metallic support and compared to the well-known "partially stabilized" ceramic materials be much easier to manufacture.

This object is achieved by training of the sliding or friction element made of or in the manner of a layered composite material solved, in which the ceramic material of the functional part on a substrate made of tough, heat-resistant Material, for example steel or one on the Stubstrat applied intermediate layer by evaporation or dusting in vacuo as solid to the surface  bonded ceramic layer and in the finest Distribution is interspersed with the stabilizer substance.

Due to the particularly fine distribution achieved according to the invention the stabilizer substance are in the ceramic Material "quasi-induced sliding planes" created that allow it to be dynamic in the ceramic material Load and sudden temperature changes in the micro range Cracks appear, which apparently absorb the deformations, so that it does not lead to the formation of macro cracks and accordingly no longer a "catastrophic failure" is coming.

In experiments carried out in connection with the invention surprisingly it turned out that the Sensitivity of the materials constructed according to the invention against sudden loads and sudden temperature changes and reproducible crack formation under alternating loads are reduced to the extent that workpieces according to the invention (e.g. valve guide bushings of the rocker arms with overhead camshaft) under standard test conditions fully meet the demands placed on them. For examinations with the help of the scanning electron microscope (REM) and the micro probe (MISO) was the extremely fine, other than vapor deposition in a vacuum or sputtering not achievable distribution of Stabilization additives documented.

A particularly advantageous development of the invention is that between the substrate or the intermediate layer and attached a layer of active solder to the ceramic layer becomes. With such active solder, the mechanical Bracketing beyond a real bond "metal / Metal "between metallic substrate and by reduction areas of the evaporated or dusted ceramic layer  produced. Substances are used for such active solder, in particular metal alloys that both Ceramic as well as the metal can wet. For example can be used to connect a ceramic layer made of aluminum oxide with a steel substrate a 28Ni-23Co- Alloy can be used as active solder.

The use of active solder layers also represents an essential one Improvement if the ceramic layer consists of several Layers, for example from layers of different ceramic Materials should be built. You can then between the adjacent layers of ceramic material arrange a layer of active solder to ensure a safe, firm bond between the layers of ceramic material to reach.

The sliding or friction elements according to the invention can be produce in simple processes.

A method is preferred in which cathode sputtering is used, the substrate optionally covered with an intermediate layer being coated with a layer of ceramic materials by sputtering in plasma, for example argon, held under a pressure between 10 ^-4 to 10 ^-1 mbar, and thereby a desired amount of one or more desired stabilizer substances is incorporated into the ceramic material by means of the sputtering during the layer build-up together with the ceramic material in the fine distribution caused by the sputtering.

The pre-formed ceramic material and the pre-formed one Stabilizer substance can already be used as such the target used for sputtering be. However, preference can also be given to so-called  use reactive sputtering. You can do this Starting materials, for example of a metallic type, for the ceramic material and / or the stabilizer substance in insert the target. The transfer of these raw materials in the desired ceramic material or in the desired stabilizer substance can then by during sputtering chemical reactions between the starting materials and / or the plasma supplied Reaction gas can be made.

If there are layers of active solder between the substrate or the Intermediate layer and the ceramic layer and / or between the layers of a multilayer ceramic layer provided such an active solder is preferred apply by sputtering, immediately in the recipient and preferably using the same plasma as for the application of the ceramic layer.

If you want to use evaporation processes, you can initially fail due to the fact that ceramic Do not let materials evaporate. However, in the frame the invention also vaporizing vaporizable Starting materials for the ceramic material and implementation chemical reactions to form the ceramic Made of material and the stabilizer substances will. These chemical reactions are preferred on the surface to be coated.

Embodiments of the invention are as follows explained using the drawing. Show it:  

FIG. 1 shows an inventive claimed on sliding or friction device part in the form of a plain bearing half shell in perspective view;

FIG. 2 shows a partial section AB according to FIG. 1 in an enlarged representation; and

Fig. 3 is a further enlarged section C of FIG. 2.

In the embodiment shown in the drawing, the part of the device that is subject to sliding or friction is a plain bearing half-shell 10 , which is constructed in the manner of a layered composite material 11 . This layered composite material 11 has a substrate 12 in the form of a carrier layer made of temperature-resistant steel. A thin active solder layer 13 is applied to one surface of this substrate 12 . This active solder layer 13 carries a two-layer ceramic layer 14 , specifically a lower ceramic layer 15 applied directly to the active solder layer 13 and an upper ceramic layer 17 supporting the free surface of the ceramic layer 14 . A second active solder layer 16 is attached between the two ceramic layers 15 and 17 .

In the example shown, the lower ceramic layer 15 consists of aluminum oxide Al203 with an incorporated stabilizer substance, as will be explained in detail in connection with FIG. 3. The active solder layer 13 attached between the lower ceramic layer 15 and the substrate 12 consists of 28Ni-23Co alloy, which is suitable for wetting both the steel surface of the substrate 12 and the surface of the aluminum oxide.

In this example, the upper ceramic layer 17 additionally provided in this example consists of zirconium oxide ZrO ₂ with an incorporated stabilizer substance, while the active solder layer between the two ceramic layers 15 and 17 can consist of an alloy wetting both ceramic materials, for example 28Ni-23Co alloy. Optionally, the substrate 12 can also be a steel layer provided with an electroplated copper layer 18 .

The ceramic layer 14 can also be single-layer, for example as a single-layer aluminum oxide layer with an incorporated stabilizer substance or a single-layer zirconium oxide layer with an incorporated stabilizer substance.

As can be seen more clearly from FIG. 3, the lower ceramic layer 15 is interspersed with the finest particles 21 of zirconium oxide ZrO ₂ in a practically uniform distribution. The amount of zirconium oxide added to the aluminum oxide can be 1 to 5% by mass. The extremely fine distribution of the zirconium oxide in the aluminum oxide was achieved in that the lower ceramic layer 15 was built up by sputtering, the aluminum oxide and the zirconium oxide being applied at the same time in a molecularly fine distribution, so that an aluminum oxide matrix was formed and fine particles formed therein Zirconium oxide were evenly distributed.

In the upper ceramic layer 17 , aluminum oxide particles 22 as stabilizer substance and finest graphite particles 23 (indicated as thicker points) are embedded in a matrix of zirconium oxide ZrO ₂ formed by cathode sputtering in a uniformly finest distribution as active filler improving the sliding properties. Even with the upper ceramic layer 17 , the finest, uniform distribution of both the aluminum oxide and the graphite in the zirconium oxide matrix is carried out by sputtering. The proportion of graphite particles in the upper ceramic layer can be 5 to 10% by mass and the proportion of aluminum oxide can be 1 to 5% by mass of the ceramic layer 17 .

The foreign matter particles 21 and 22, which are finely distributed as stabilizer substance in both ceramic layers 15 and 17, form "quasi-induced sliding planes" in the respective ceramic matrix. Due to this in the ceramic mass finely divided foreign particles occurs under dynamic loading of the ceramic layer 14 and abrupt temperature changes on the ceramic layer 14 to form micro-cracks 24 which are limited by the fine distribution of the foreign particles 21 and 22 respectively. These microcracks 24 are suitable for absorbing deformations on the ceramic layer 14 without the formation of macrocracks and "catastrophic failure".

For the production of a device part, for example a plain bearing half-shell 10 shown in FIGS. 1 to 3, the procedure can be as follows:
The substrate 12 , for example a plate made of sheet steel, in particular temperature-resistant sheet steel, is first brought into the shape desired for the device part, ie the plain bearing half-shell 10 , after it has optionally been galvanically coated with a copper layer. After the first cleaning, this prepared semi-finished product is brought into a recipient equipped for cathode sputtering, in a heat-conducting connection to an electrically conductive and electrically connectable, preferably metallic support, which is equipped with heating devices, for example a chamber that can be flushed with a liquid heat transfer medium, and off according to temperature-resistant material. After the recipient is closed, the recipient is evacuated until a pressure of 10 ^-5 mbar is reached. During the evacuation, the support and the semi-finished product placed on it are heated up, for example up to a temperature in the range from about 300 to 800 ° C. This results in an effective degassing of the semi-finished product.

After degassing, the surface of the semi-finished product to be covered with the ceramic layer is subjected to cleaning and roughening by means of reverse cathode sputtering. In the case of the anomalous glow discharge to be set up for this purpose, the support carrying the substrate or the semifinished product is switched as a cathode and a negative etching voltage of 400 V to 1200 V, preferably 600 V to 750 V, is applied to it. An etching current density between 10 and 40 mA / cm ^{2 of} the surface to be etched is set. During the etching process, suitable plasma, for example argon, is maintained under an etching pressure between 5 · 10 ^-3 mbar and 5 · 10 ^-2 mbar. Due to the combined effect of the heating of the substrate occurring during the etching and the heat transfer medium supplied to the support, the substrate or semi-finished product is set to a temperature between 500 and 800 ° C., preferably at 600 ° C. The duration of the etching process is selected on a case-by-case basis in accordance with the respective material of the substrate and the degree of roughening to be achieved.

After the surface has been cleaned and roughened by reverse sputtering, an active solder layer 13 is then applied to the roughened surface of the substrate by sputtering. For this purpose, the support carrying the substrate is switched as an anode and a sputter voltage between 300 V and 700 V is applied to the target consisting of the desired active solder, for example 28Ni-23Co alloy. The sputter current density to be maintained during this sputtering of the active solder layer 13 should be kept at 10 to 30 W / cm ^{2 of} the surface to be coated. The substrate temperature is to be kept essentially at the value set during the etching. The plasma to be used when applying the active solder layer is oxygen-free, preferably argon, under a pressure of 1 · 10 ^-3 mbar to 5 · 10 ^-2 mbar. The duration of this sputtering is set up in such a way that an active solder layer of approximately 5 μm to 10 μm thickness is built up.

The lower ceramic layer 15 is now applied to the active solder layer 13 thus formed by reactive sputtering. For this purpose, a target made of aluminum with the addition of zirconium in the amount desired for the stabilizer substance is used. To the plasma used in this stage for maintaining the glow discharge and the sputtering, for example argon, oxygen is continuously added in a for the complete oxidation of the sputtered aluminum to Al ₂ O ₃ and the sputtered zirconium to ZrO2. The sputter voltage is set to 500 V to 800 V, for example 600 V, while maintaining a sputter current density of 20 to 40 W / cm ^{2 of} the surface to be coated. The substrate temperature is kept at the set value between 500 ° C and 800 ° C, preferably at 600 ° C. The pressure in the sputtering plasma is kept between 1 · 10 ^-3 mbar and 5 · 10 ^-2 mbar.

The duration of this sputtering is kept according to the desired thickness of the lower ceramic layer 15 . If the lower ceramic layer 15 is built up in the desired thickness, the recipient is evacuated again to a pressure of 10 ^-5 mbar and then with oxygen-free plasma to a pressure between 1 · 10 ^-3 mbar and 5 · 10 ^-2 mbar set. Under this new plasma, the second active solder layer 16 is sputtered under practically the same sputtering conditions as when the first active solder layer 13 was built up . After this second active solder layer 16 has been built up , the upper ceramic layer 17 is applied by cathode sputtering, specifically in a plasma which contains less oxygen than the plasma for the application of the lower ceramic layer 15 . In addition to zirconium and aluminum, the target used for this process step also contains zirconium oxide and aluminum oxide and graphite, only part of the zirconium oxide used to form the ceramic matrix being formed by reactive sputtering and the rest of the zirconium oxide by direct sputtering from the target. Likewise, the aluminum oxide embedded as a stabilizer substance is partly formed by reactive sputtering and partly drawn directly from the target. During this process step, the substrate or the substrate 12, 18 already coated with the two active solder layers 13 and 16 and the lower ceramic layer 15 is kept at a temperature of approximately 500 to 600 ° C. The substrate temperature should be kept as constant as possible within the individual coating steps.

The chronological order of the treatment steps explained above can be divided into chambers accordingly and various and equipped with locks Recipients provided with facilities are executed one after the other while the substrate or the prepared Semi-finished products from chamber to chamber by the recipient is passed through. There can also be entrance gates at the recipient for introducing the prepared semi-finished product and exit locks for removing the treated device site be provided.

• LIST OF REFERENCE NUMERALS 10 plain bearing half shells
  11 layered composite
  12 substrate
  13 active solder layer
  14 ceramic layer
  15 lower ceramic layer
  16 active solder layer
  17 upper ceramic layer
  18 copper layer
  21 stabilizer substance particles
  22 stabilizer substance particles
  23 graphite particles
  24 micro cracks

Claims (20)

1) sliding or friction element for use in operation at high temperature, for example a back temperature above 200 ° C, in which a functional part carrying the sliding or friction surface is provided made of ceramic material with embedded stabilizer substance, characterized by the formation of the sliding or friction elements made of or in the form of layered composite material ( 11 ), in which the ceramic material of the functional part is deposited on a substrate ( 12 ) made of tough, heat-resistant material, for example steel, or on an intermediate layer ( 18 ) on the substrate ( 12 ) Dusting in a vacuum is formed as a ceramic layer ( 14 ) firmly bonded to the surface and is interspersed with the stabilizer substance in the finest distribution. 2) sliding or friction element according to claim 1, characterized in that the ceramic layer ( 14 ) from one of the groups of metal oxides, such as aluminum oxide, zirconium oxide, metal titanates, such as aluminum titanate, silicon nitrides or carbides or mixtures of such ceramic compounds and formed with the respective ceramic Connections corresponding stabilizer substances is added. 3) sliding or friction element according to claim 2, characterized in that the ceramic material is a formed by reactive sputtering Al ₂ O ₃ and the stabilizer substance formed by reactive sputtering ZrO ₂ and / or Y ₂ O ₃ and / or MgO. 4) sliding or friction element according to one of claims 1 to 3, characterized in that the ceramic layer ( 14 ) via a layer ( 13 ) of active solder to the substrate ( 12 ) or the intermediate layer ( 18 ) is bound. 5) sliding or friction element according to claim 4, characterized in that the substrate ( 12 ) is a steel layer, the material of the ceramic layer ( 14 ) Al ₂ O ₃ and the active solder is a 28Ni-23Co alloy. 6) sliding or friction element according to one of claims 1 to 5, characterized in that the ceramic layer ( 14 ) from two or more layers ( 15, 17 ) is constructed of different ceramic materials. 7) sliding or friction element according to claim 6, characterized in that between adjacent layers ( 15, 17 ) of the ceramic layer ( 14 ) a thin active solder layer ( 16 ) is attached. 8) sliding or friction element according to one of claims 1 to 7, characterized in that in the ceramic layer ( 14 ) the sliding or friction properties improving substances such as MoS ₂ , graphite, BN, PTFE in generated when dusting or vapor deposition of the ceramic layer finest distribution are stored. 9) Method for producing sliding or friction elements according to one of claims 1 to 8, characterized in that the substrate, which may be covered with an intermediate layer, by sputtering in a plasma, for example argon, held under a pressure between 10 ^-4 to 10 ^-1 mbar , coated with a layer of ceramic material and a desired amount of one or more desired stabilizer substances is deposited in the ceramic material by means of the cathode sputtering during the layer build-up and together with the ceramic material in the fine distribution caused by the cathode sputtering. 10) Method according to claim 9, characterized in that the ceramic material by chemical reaction of one or more atomized starting materials together and / or reaction gas added with the plasma during cathode sputtering. 11) Method according to claim 9 or 10, characterized in that that the stabilizer substance or stabilizer substances by chemical reaction of one or more Starting materials with each other and / or with the plasma added reaction gas during sputtering is or will be formed. 12) Method according to one of claims 9 to 11, characterized characterized in that the ceramic material and the  Stabilizer substance or stabilizer substances or their starting materials in the desired for the ceramic layer Quantity ratio in one for sputtering used target are combined. 13) Method according to one of claims 9 to 12, characterized characterized in that with the ceramic layer surface to be covered after cleaning and possibly Roughen by cathode sputtering about 1 to 5 µm thick layer of active solder is applied and that then the ceramic layer by sputtering is built up on the surface of this active solder layer. 14) Method according to one of claims 9 to 13, characterized characterized in that the to be covered with the ceramic layer Surface of the substrate or the intermediate layer in the one intended for sputtering Plasma before applying the ceramic layer or the Active solder layer cleaned by reverse sputtering and is roughened. 15) Method according to one of claims 9 to 14, characterized characterized in that to be embedded in the ceramic layer, fillers which improve the sliding or rubbing properties into the ceramic material and the stabilizer substance or stabilizer substances or the Starting materials for both target contained in one the addition quantity desired in the ceramic layer appropriate amount are stored. 16) Method of making sliding or friction elements according to one of claims 1 to 8, characterized in that in vacuum on that with an intermediate layer if necessary coated substrate evaporated a ceramic layer is by the vaporizable raw materials of the ceramic material and the stabilizer substance  or stabilizer substances evaporated in vacuo, in the vaporized state with simultaneous precipitation on the surface to be coated chemical reactions with each other and / or with in Vacuum introduced reaction gas or gases in the ceramic material and the stabilizer substance or stabilizer substances transferred and in the finest mutual distribution to the ceramic layer being constructed. 17) Method according to claim 16, characterized in that over at least one part receiving the substrate of the evacuated room leading to the substrate electric field is maintained and that electrical charge carriers for accelerated movement of the vaporized substances on the substrate in the Vacuum vaporized substances are introduced, preferably in itself to the direction of the electric lines of force transverse direction. 18) Method according to claim 17, characterized in that electrically charged particles, preferably ions, such substances introduced into the substances evaporated in a vacuum be covered with the vaporized substances Formation of the desired ceramic material and / or the desired stabilizer substance or stabilizer substances react chemically. 19) Method according to one of claims 16 to 18, characterized characterized in that between the surface of the substrate or the intermediate layer and the ceramic layer and if necessary between the layers of a multi-layer structure Layers of active solder to be provided through the ceramic layer Evaporation or ion plating in a vacuum immediately before the start or between the stages of building  the ceramic layer are formed. 20) Method according to one of claims 16 to 19, characterized characterized in that the starting materials to be evaporated for the formation of the ceramic material and / or the desired stabilizer substance or stabilizer substances from different sources in short succession be evaporated by means of electron bombardment.