DE102010031539A1 - Depositing a layer system with enhanced unlubricated operation properties on a substrate surface, useful for coating gas valve components, comprises e.g. electrodepositing a layer of hard chrome on a substrate surface - Google Patents

Abstract

Depositing a layer system with enhanced unlubricated operation properties on a substrate surface, comprises: electrodepositing a layer of hard chrome on a substrate surface (1) by applying a pulsed deposition current; and applying a diamond like carbon (DLC) layer (4) on the electrodeposited hard chromium layer (3) by physical vapor deposition (PVD) or chemical vapor deposition (CVD). An independent claimS is also included for a layer system comprising a first galvanic hard chromium layer deposited on a substrate surface, and a DLC layer applied on the first hard chromium layer.

Description

The present invention relates to a process for producing a layer system with improved dry-running properties. The layer system according to the invention has at least one electrodeposited hard chromium layer and a DLC layer (diamond like carbon) applied to this layer. The invention further relates to a layer system produced by the process according to the invention and the use of such for coating valve components, in particular gas valve components.

State of the art

Wear-resistant coatings are used in machine, plant and apparatus construction to extend the service life of components subjected to high mechanical loads. For example, chemically nickel or hard chrome layers have long been used as wear protection in these areas with great success. These layers are applied by electroplating on the components, substrates and base materials to be protected.

In order to extend the life of a component, substrate or base material by means of a wear protection layer, on the one hand trying to lower the stress on the lowest possible coefficient of friction of this protective layer and on the other hand can be minimized by a high hardness of the protective layer material removal at a given load become. Among other things, the tasks of a wear protection layer are to reduce abrasion of the base material and thus counteract ongoing, in particular abrasive, deformation of the base material. In addition, a wear protection layer can provide a suitable friction pairing to a counter-body and prevent the penetration of hard particles, for example from a contaminated fuel, into the base material of a component and thus the destruction of, for example, sealing surface.

In contrast to organic coatings, such as bonded coatings, which wear out in the run-in phase between components and enable perfect matching of the surfaces of these components, which are also called wear bodies, a galvanic wear protection layer performs its task over the entire service life of the components. The galvanic wear protection layers have the material properties of or in each case deposited metals. An adaptation of the properties to a specific requirement profile has hitherto only been possible to a limited extent, namely by the choice of the metal used for this layer, as well as by the variation of the layer thickness or the deposition conditions.

In the case of large differences in hardness of the base material to be protected and the wear protection layer, the so-called eggshell effect may occur. In this case, the hard wear protection layer breaks under load into the base material, since there is insufficient basic hardness in the base material in order to support the wear protection layer.

Recent developments for optimizing the properties of wear-resistant coatings provide for so-called multi-layer systems in addition to the classic single-layer application of a wear-resistant coating on a base material. Here, basically two different concepts are pursued. On the one hand, alternately softer and harder layer layers and, on the other hand, a continuous change in hardness can be provided in the wear protection layer structure. The latter are also referred to as graded wear protection layer systems.

A sequence of wear protection layer layers made of different materials can be produced for example by galvanic methods, for example by reacting the substrate or component to be coated in different electrolyte baths. When different materials are used for the individual layers in a protective layer ply sequence, a challenge is to make an adhesive bond. Another method for the construction of multilayer systems is to apply a material for a Verscheißschicht under changing deposition conditions on the base material. Thus, for example, chromium can be deposited on the one hand as a hard chrome while applying a DC voltage as a deposition current, wherein a crack-free chromium layer is deposited on the deposited hard chrome layer while applying a pulse current.

It is also known to produce protective coatings by, for example, physical vapor deposition (PVD) or related processes, such as chemical vapor deposition (CVD). With PVD process it is possible to deposit almost all metals and also carbon in very pure form. However, only thin layers in the range of a few nanometers down to a few micrometers can be economically produced. In addition, these methods are very expensive.

For heavily loaded components wear protection is often realized with hard chromium layers or a diamond-like carbon layer (DLC). Condition is however in most cases that the underground is sufficiently hard and loadable, in order to impress the wear protection layer in the base material and thus to avoid the occurrence of eggshell effect described above. Often therefore suitable hard base materials such as hardened steel, z. 100Cr6.

Disclosure of the invention

• – galvanisches Abscheiden einer Hartchromschicht auf einer Substratoberfläche unter Anlegen eines gepulsten Abscheidestroms;
• – aufbringen einer DLC-Schicht auf die galvanisch abgeschiedene Hartchromschicht mittels PVD oder CVD.

The invention provides a method for depositing a layer system with improved dry-running properties on a substrate surface, comprising at least the method steps:

• - Electroplating a hard chromium layer on a substrate surface by applying a pulsed Abscheidestroms;
• - Apply a DLC layer on the electrodeposited hard chrome layer by PVD or CVD.

The inventive combination of hard chrome layer and DLC layer, the favorable properties of the two layers are combined in a layer system. The layer systems thus deposited are characterized by their hardness and their excellent dry running properties.

The hard chrome layers deposited according to the invention in a first method step can be both monolayers and multilayer systems. Especially suitable are multi-layer systems, which consist of a combination of a micro-cracked hard chromium layer and a crack-free chromium layer deposited thereon with the application of a pulse current.

The process according to the invention has the advantage that the substrates to be coated do not have to be subjected to a complex pretreatment, as is normally necessary in the deposition of a DLC layer on a substrate. Thus, it has hitherto been necessary to prepare the substrate surfaces to be provided with a DLC layer in complex and costly grinding steps for the subsequent coating. Such an intensive pretreatment of the substrate surfaces can be avoided by the method according to the invention, whereby the costs per workpiece can be optimized.

The inventive galvanic deposition of a hard chrome layer prior to the application of a DLC layer results in the further advantage that by the galvanic coating process itself any organic radicals such. For example, grease or the like and also fine particles have been removed from the substrate surface, so that in only roughly pre-cleaned substrates after the galvanic coating process, a very clean and dry substrate is provided which is optimally prepared for a subsequent application of a DLC layer. As a result, cleaning distances can be omitted before a DLC coating, resulting in further economic benefits.

In addition, electrodeposited hard chrome layers do not place any special demands on the surface quality of the substrates to be coated. However, they usually trace the surface structure of the substrate, whereby the roughness of the hard chrome coating depends on the nature of the substrate surface. Advantageously, however, a leveling effect can be achieved here by the deposition of a multilayer system, so that after completion of the electrodeposition of a hard chrome layer in the process according to the invention, a substrate surface with optimized surface roughness is obtained, to which a DLC layer is then applied in an outstanding manner can be.

New materials, particularly based on sintered materials or metal injection molding (MIM) metals are often cheaper and, moreover, easier to process than conventional materials such as steel, but often do not provide sufficient wear protection. Due to their morphology, the inhomogeneity in the surfaces, which frequently occurs with such materials, has hitherto not been able to be equipped with suitable wear protection layers, or only with great difficulty. The inventive method, it is possible to equip these new materials with multilayer wear protection layers. This opens up the opportunity to combine the manufacturing advantages of these new materials with the excellent wear characteristics of DLC coatings in large-scale manufacturing.

By the method according to the invention and the layer system according to the invention, by a mechanical stress such. B. impact on the substrate or the substrate surface acting impact energy can be compensated by the hard chrome layer, so that there is only a small deformation of the base material. An eggshell effect caused by such a deformation and the consequent flaking off of an applied DLC layer is thus avoided. As a result, a significantly higher lifetime of the wear layers and thus the Substarte itself is achieved.

In one embodiment of the method according to the invention, the hard chrome layer is deposited with a layer thickness between 0.5 μm and 300 μm, preferably between 1 μm and 200 μm, more preferably between 3 μm and 50 μm. Such a layer thickness is suitable for a mechanical to provide a sufficiently stable substrate for a DLC layer applied to it to avoid spalling of the DLC layer upon exposure to conventional mechanical stresses.

In a further embodiment of the method according to the invention, a deposition current with an average current density between 10 A / dm ² and 100 A / dm ² , preferably between 20 A / dm ² and 80 A / dm ² , more preferably 25 A, is used for electrodeposition of the hard chrome layer / dm ² and 60 A / dm ^{2 are} set.

According to a further embodiment of the method according to the invention, a pulse frequency of the separation current between 0.1 Hz and 1000 Hz, preferably set, for galvanic deposition of the hard chromium layer.

According to the invention, provision can be made for a current pulse sequence with anodic and cathodic current pulses to be set on the substrate and, if appropriate, intervening rest pauses having a pause voltage of zero or more volts, by means of a control device and thus a current which is variable over time.

Alternatively or additionally, by means of a control device, a voltage pulse sequence and thus the voltage can be variably set potentiostatically over time. A galvanostatic pulse progression according to the invention can be exemplified by a suitable pretreatment which improves the adhesive strength of the coating with a waiting time of 0 s to 240 s, activation of the base material over an activation time of 10 to 30 s and again a waiting time of 0 s to 20 s and the actual pulse sequence alternating pulse and reverse pulse, with a pulse length of 1 ms to 10 s and each having a current density of 10 to 100 A / dm ² , wherein analogous parameters can be selected for the reversing pulses exist. Within a chromium layer deposition these parameters can be varied to achieve graded properties.

In one embodiment of the method according to the invention, a ratio of the negative / positive current density between 1: 1 and 1:10, preferably 1: 2 and 1: 5 is set for the electrodeposition of the hard chrome layer. This means that in this embodiment of the method, the reversing pulse has a length between 1/10 to 1/1 of the Abscheidepulses.

Advantageously, an adjustment of the properties of the chromium layer can be achieved according to the invention by controlling only the current and / or voltage process parameters. The individual chromium layer layers can be deposited with desired different properties alone by current and / or voltage control with or without polarity reversal. Here, chromium layers can be selectively deposited with different structures. In this way, for example, first layer layers of crack-free soft chrome with a hardness of ≥ 450 HV to ≥ 700 HV and then chrome layers of increasing hardness of ≥ 700 HV to ≤ 1100 HV can be produced on a substrate made of relatively soft base material.

The DLC layer deposited on the hard chrome layer according to the invention may in a preferred embodiment of the invention have a layer thickness of between 1 μm and 10 μm. Such a layer thickness provides excellent wear protection and shows very good dry running properties. This is especially for the application of the method according to the invention for the coating of z. B. valve components, in particular gas valve components advantageous, as well as lack of friction-reducing agents such. As oils or fats, a functionality of the valve or valve member is guaranteed.

The DLC layer can according to the invention by means of the known from the prior art method for DLC coating, such. As chemical vapor deposition (CVD), physical vapor deposition (PVD plasma deposition) or related processes are applied to the electrodeposited hard chromium layer.

The invention additionally provides a layer system comprising a first hard chromium layer deposited galvanically on a substrate surface and a DLC layer applied to the first hard chrome layer, wherein the hard chrome layer has a layer thickness between 0.5 μm and 300 μm.

The layer system according to the invention exhibits outstanding dry running properties as wear protection layer on different base materials such as steel or also sintered materials as well as a good resistance to mechanical loads. In particular, the layer system according to the invention shows no or only a very small detachment of the applied DLC layer even under normal mechanical loads.

In one embodiment of the layer system, the hard chrome layer may have a hardness of> 700 HV, preferably between ≥ 750 HV and ≦ 1100 HV.

The DLC layer may have a layer thickness between 1 μm and 10 μm in the layer system according to the invention.

The invention will be explained below with reference to embodiments in conjunction with the figures, without being limited thereto. The same components are identified by the same reference numerals.

It shows:

1 a schematic sectional view of a substrate with a chromium protective layer according to the prior art.

2 a schematic sectional view of a substrate with a wear protection layer applied according to the invention.

3 a schematic sectional view of a substrate having a wear protection layer applied according to the invention with a multilayer hard chrome layer.

1 shows a wear protection layer according to the prior art, consisting of a on a substrate surface ( 1 ) deposited hard chrome layer ( 2 ). The electrodeposited hard chrome layer ( 2 ) has good mechanical stability. The dry-running properties of such hard chrome layers ( 2 ) are not optimal, so that the use of such layers in the range of components, which are exposed to a corresponding mechanical stress with simultaneous risk of dry running, so the lack of friction-reducing agents, only very limited possible.

2 shows a layer system ( 3 . 4 ), which was deposited by a method according to the invention. On the surface ( 1 ) of a substrate, such as a valve member made of steel or a sintered material, according to a standard for the electrodeposition of a hard chromium layer pretreatment, such. B. a degreasing step, a chromium layer ( 3 ) deposited while applying a pulsed deposition current. The pulse length can be varied depending on the substrate or the desired layer properties in the manner known in the art. Thus, for example, a pulse frequency of 20 Hz can be set for deposition at an average current density of 30 A / dm ² . The thus deposited layer shows a mean layer thickness of 50 microns and a hardness of> 900 HV. On the resulting hard chrome layer ( 3 ), a DLC layer is applied by CVD after an optional rinse and dry step. The substrates to be coated are removed from the rack, which was used for electrodeposition and transferred to a suitable for CVD deposition goods carrier. This is preferably done automatically, for example by means of suitable industrial robots. The with the hard chrome layer ( 3 ) coated substrates are then transferred with the product carrier in a corresponding CVD system in which a DLC layer ( 4 ) is applied with a mean layer thickness of 3 microns. The layer system ( 3 . 4 ) shows a high resistance to abrasive wear and a good notch impact resistance. In addition, the layer system ( 3 . 4 ) good dry-running properties.

3 shows a layer system which has been deposited by a method according to the invention. On the surface ( 1 ) of a substrate, such as a valve member made of steel or a sintered material, according to a standard for the electrodeposition of a hard chromium layer pretreatment, such. B. a degreasing step, a first chromium layer ( 5 ) deposited. The chrome layer ( 5 ) is deposited while applying a direct current with an average current density of 20 A / dm ² up to a layer thickness of 30 microns. The chromium layer thus obtained shows a hardness of 500 HV. Without conversion of the substrate into another electrolyte, a hard chrome layer is then applied to the thus deposited chromium layer while applying a pulsed deposition current ( 3 ) deposited. The pulse length can be varied depending on the substrate or the desired Hartchromeigenschaften in the manner known in the art. Thus, for example, a pulse frequency of 60 Hz at an average current density of 70 A / dm ² can be set for deposition. The thus deposited layer ( 3 ) shows a mean layer thickness of 70 microns and a hardness of> 900 HV. On the resulting hard chrome layer ( 3 ), a DLC layer is applied by CVD after an optional rinse and dry step. The substrates to be coated are removed from the rack, which was used for electrodeposition and transferred to a suitable for CVD deposition goods carrier. This is preferably done automatically, for example by means of suitable industrial robots. The with the hard chrome layer ( 3 ) coated substrates are then transferred with the product carrier in a corresponding CVD system in which a DLC layer ( 4 ) is applied with an average layer thickness of 3 μm. The layer system ( 3 . 4 ) shows a high resistance to abrasive wear and a good notch impact resistance. In addition, the layer system ( 3 . 4 ) good dry-running properties.

Claims (10)

Method for depositing a layer system with improved dry-running properties on a substrate surface, at least comprising the method steps: - galvanic deposition of a hard chrome layer ( 3 . 5 ) on a substrate surface ( 1 ) while applying a pulsed deposition current; Applying a DLC layer ( 4 ) on the electrodeposited hard chrome layer by means of PVD or CVD. Process according to claim 1, wherein the hard chrome layer ( 3 . 5 ) is deposited with a layer thickness between 0.5 microns and 300 microns. Method according to one of the preceding claims, wherein for the electrodeposition of the hard chromium layer ( 3 . 5 ) A deposition current with a mean current density of 10 A / dm ² and 100 A / dm ² is adjusted. Method according to one of the preceding claims, wherein for the electrodeposition of the hard chromium layer ( 3 ) A pulse frequency of Abscheidestroms between 0.1 Hz and 1000 Hz is set. Method according to one of the preceding claims, wherein for the electrodeposition of the hard chromium layer ( 3 ) a ratio of the negative / positive current density between 1: 1 and 1:10, preferably 1: 2 and 1: 5 is set. Method according to one of the preceding claims, wherein the layer system is deposited on a metal surface. Layer system comprising a first electrodeposited on a substrate surface ( 1 ) deposited hard chrome layer ( 3 . 5 ) and one on the first hard chrome layer ( 3 . 5 ) applied DLC layer ( 4 ), wherein the hard chrome layer ( 3 . 5 ) has a layer thickness between 0.5 microns and 300 microns. Layer system according to claim 7, wherein the hard chrome layer ( 3 ) has a hardness> 700 HV, preferably between ≥ 750 HV and ≤ 1100 HV. Layer system according to claim 4, wherein the DLC layer ( 4 ) has a layer thickness between 1 .mu.m and 10 .mu.m. Use of a layer system according to one of claims 7 to 9 for coating valve components, in particular gas valve components.

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