Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2000-04-18
2004-05-25
Turner, Archene (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S336000, C428S469000, C428S472000, C428S408000, C428S698000
Reexamination Certificate
active
06740393
ABSTRACT:
The present invention relates to a system for the protection against wear, for the protection against corrosion and for improving the sliding properties and the like, having an adhesive layer for the arrangement on a substrate, a transition layer for the arrangement on the adhesive layer and a cover layer of an adamantine carbon as well as to a process and an arrangement for producing such layer systems.
Despite the prominent properties of adamantine carbon layers (DLC layers), such as high hardness and excellent sliding properties, and many years of worldwide research activities, it has not been possible to produce pure DLC layers which, also in the case of larger layer thicknesses (>1 &mgr;m), exhibit a layer adhesion which is sufficient for an industrial use in typical protection applications against wear and have a sufficient conductivity in order to be able to eliminate the high-frequency (HF) processes for their production which have many disadvantages with respect to production techniques.
Typical protection applications against wear include, on the one hand, applications in the machine construction field, such as protection against sliding abrasion, pitting, cold fusing, etc., particularly on components with surfaces which move against one another, such as gears, pump and cup plungers, piston rings, injector needles, complete bearing sets or their individual components and many others, as well as, on the other hand, applications in the field of material processing for the protection of the tools used for the cutting or forming machining as well as in the case of injection molds.
In addition to the versatile application possibilities in the field of protection against wear, the protection against corrosion is explicitly mentioned here as another promising field of application of such DLC layers.
Currently, because of the high internal tension and the resulting problematic adhesion, particularly in the case of highly stressed surfaces, in the protection against wear, pure DLC layers can be deposited only with small layer thicknesses which are insufficient for many applications or must be changed in their properties by the additional inclusion of foreign atoms, such as silicon, various metals and fluorine. However, the resulting reduction of inherent layer tension and the improvement of the adhesion has always been connected with a clear loss of hardness which, particularly in the field of the protection against wear, can often have a negative effect on the service life of the respectively coated object.
In the case of plasma-supported processes customary today for producing DLC layers, because of the high electric resistance of hard DLC layers, processes with an HF bias or HF plasma (in the following HF=high frequency will apply to all frequencies >10 MHz), particularly with the industrial frequency 13.56 MHz, are frequently used in order to avoid disturbing charges during the coating. The known disadvantages of this technique are interferences with electronically sensitive process control units (HF feedback, transmitter effect, . . . ) which are difficult to control; increased expenditures for avoiding HF flashovers; antenna effect of the substrates to be coated; and a resulting relatively large minimal distance between the material to be coated which prevents an optimal utilization of space and surface in the coating chamber. Thus, in the case of HF processes, closest attention has to be paid to that fact that, for example, as a result of an excessive loading density, incorrect substrate/holder spacing, etc., there will be no overlapping of dark spaces, which causes harmful secondary plasmas. On the one hand, such secondary plasmas cause energy sinks and thus additionally stress the plasma generators; on the other hand, such local plasma concentrations frequently cause a thermal overheating of the substrates and an undesirable graphitization of the layer.
On the basis of the exponential dependence of the substrate voltage on the substrate surface calculated during HF processes,
U
S
/U
E
=C
E
/C
S
=(
A
E
/A
S
)
4
wherein U is the voltage; C is the capacity; A is the surface; and S indicates the substrate and E indicates the counterelectrode, as the substrate surface A
S
rises, there is a considerable drop of the substrate voltage U
S
accompanied by a significant rise of the dissipated energy. As a result, depending on the capacity of the used generators, only a certain maximal surface can be coated. Otherwise, either sufficient power cannot be fed into the system or the potential difference (substrate voltage) cannot be adjusted to be sufficiently high in order to achieve the ion plating effect required for well adhering dense layers.
In addition, on the system side in the case of HF-processes, additional equipment-related expenditures are usually required in order to mutually dynamically adapt generator impedances and plasma impedances by means of electric networks, such as a so-called matchbox, during the process.
In the following various processes and layer systems known from the state of the art will briefly be mentioned.
European Patent Document EP 87 836 discloses a DLC layer system with a 0.1-49.1% fraction of metallic constituents which is deposited, for example, by means of cathodic sputtering.
German Patent Document DE 43 43 354 A1 describes a process for producing a multilayer Ti-containing layer system with a hard-material layer consisting of titanium nitrides, titanium carbides and titanium borides as well as a friction-reducing C-containing surface layer, the Ti fraction and N fraction being progressively reduced in the direction of the surface.
The process described in U.S. Pat. No. 5,078,848 uses a pulsed plasma beam for producing DLC layers. However, on the basis of the targeted particle radiation from a source with a small outlet cross-section, such processes are only conditionally suitable for the uniform coating of larger surfaces.
Various CVD processes and SiDLC/DLC mixed layers produced by means of such processes are described in the following documents:
European Patent Document EP-A-651 069 describes a friction-reducing protection system against wear of 2-5000 alternating DLC and SiDLC layers. A process for depositing a-DLC layers with an Si intermediate layer and an adjoining a-SiC:H transition zone for improving the adhesion is described in European Patent Document EP-A-600 533. European Patent Document EP-A-885 983 and EP-A-856 592 also describe various methods for producing such layers. For example, in European Patent Document EP-A-885 983, the plasma is generated by a DC-heated filament and the substrates are acted upon by negative direct voltage or MF between 30-1,000 kHz (in the following MF=medium frequency is the frequency range between 1 and 10,000 kHz).
U.S. Pat. No. 4,728,529 describes a method for depositing DLC while applying an HF plasma, during which the layer formation takes place in a pressure range of between 10
−3
and 1 mbar consisting of an oxygen-free hydrocarbon plasma to which, as required, a noble gas or hydrogen is admixed.
The process described in German Patent Document DE-C-195 13 614 uses a bipolar substrate voltage with a shorter positive pulse duration in a pressure range between 50-1,000 Pa. As a result, layers are deposited in the range of from 10 nm to 10 &mgr;m and of a hardness of between 15-40 GPa.
A CVD process with a substrate voltage which is generated independently of the coating plasma is described in German Patent Document DE-A-198 26 259, in which case, preferably bipolar but also other periodic changed substrate voltages are applied. However, this requires a relatively high-expenditure electric supply unit, because it has to be provided in a twofold construction, for implementing the process.
Correspondingly, it is an object of the present invention to provide relatively thick DLC layer systems with a high hardness and an excellent adhesion which, in addition, still have a sufficiently high conductivity in order to be able to be deposited without HF bia
Eberle Hubert
Grischke Martin
Massler Orlaw
Pedrazzini Mauro
Wohlrab Christian
Balzers Aktiengesellschaft
Crowell & Moring LLP
Turner Archene
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