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EP0217126B1 - Galvanic hard chromium layer - Google Patents

Galvanic hard chromium layer Download PDF

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Publication number
EP0217126B1
EP0217126B1 EP86111775A EP86111775A EP0217126B1 EP 0217126 B1 EP0217126 B1 EP 0217126B1 EP 86111775 A EP86111775 A EP 86111775A EP 86111775 A EP86111775 A EP 86111775A EP 0217126 B1 EP0217126 B1 EP 0217126B1
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EP
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Prior art keywords
cracks
chromium layer
layer according
hard chromium
solid particles
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EP86111775A
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German (de)
French (fr)
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EP0217126A1 (en
Inventor
Rudolf Linde
Ulrich Dipl.-Ing. Buran
Hans-Jochem Dr. Neuhäuser
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Goetze GmbH
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Goetze GmbH
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
    • C25D15/02—Combined electrolytic and electrophoretic processes with charged materials

Definitions

  • the invention relates to a galvanic hard chrome layer with a crack network extending through the entire layer thickness and its production method.
  • Electroplated hard chrome layers have above all a high hardness and associated high wear resistance, a strong surface smoothness and associated low coefficient of friction and low adhesive power as well as a good resistance to aggressive chemical, corrosive, erosive and oxidative stress at possibly higher temperatures.
  • the treads of machine parts such as the treads of piston rings or cylinders in internal combustion engines, are coated with hard chrome layers in order to achieve special wear resistance.
  • Pressing tools and molds for the production of plastic molded articles are provided with chrome layers or are used to achieve special smoothness and wear resistance
  • valve parts are especially protected by chrome layers in chemical plants.
  • Hard chrome layers are also not very elastic and brittle. Especially in the case of shock loads and strong vibrations, breaks can occur in the layers, which then lead to the layers flaking off.
  • the present invention is therefore based on the object of providing a hard chrome layer with improved physical and technological properties in which, above all, the disadvantages indicated are eliminated.
  • the aim is to find a galvanic process which can be used as universally as possible and with which layers of this type can be produced simply and cost-effectively.
  • this object is achieved by a hard chrome layer.
  • solid particles are embedded in the cracks.
  • the gap width of the cracks should preferably be over 0.5 ⁇ m, but in particular over 11 ⁇ m, so that solid particles can be deposited at all, and the preferred thickness of the hard chrome layer is between 10 ⁇ m and 1,000 ⁇ m.
  • the invention thus creates a hard chrome layer, in the crack network of which solid particles are embedded, which improve the properties of the hard chrome layer in the desired manner, particularly in the case of a high crack density, in accordance with their properties, such as in the case of a galvanic dispersion layer.
  • the substances used in the production of galvanic dispersion layers are suitable as solid particles, individually or in combination, but they must not dissolve in the microcracking chromic acid baths, their grain size must be below the gap width of the chromium cracks, i.e. preferably between about 0.5 and 15 ⁇ m and the thickness of the chrome layer should be several times larger than the grain size of the particles.
  • Solid particles made primarily of aluminum oxide, boron carbide, boron nitride, chromium carbide, silicon dioxide, titanium carbide, diamond and / or tungsten carbide are suitable as solid particles for improving wear resistance. Such chromium layers containing solids are then particularly suitable for coating the tread of piston rings or cylinder liners in internal combustion engines.
  • the solid lubricant particles used consist of hexagonal boron nitride, graphite and / or polymer particles, especially of polyvinyl chloride and / or polytetrafluoroethylene, and for improvement ductility or reduction in brittleness, ductile metals or metal alloys made of tin, titanium or bronze can be embedded in the cracks. The tendency of chrome to adhesive wear can also be reduced by embedded molybdenum particles.
  • the color of the chrome layers according to the invention can be influenced by organic dyes or colored metal salts embedded in the cracks. It was also found that filling the cracks with solid particles increased the corrosion resistance of the layers.
  • the cracks were preferably filled with polyvinyl chloride particles, and the polyvinyl chloride was then melted into the cracks, so that the cracks were sealed and protected against corrosive attacks.
  • solid particles of one or more types of substance can be used in combination to fill the cracks, so that several physical properties are improved at the same time.
  • the cracks need not be completely filled with the solid particles.
  • cracks in the chrome layer zones directly on the substrate can be filled with a corrosion-preventing substance, while the cracks in the outer chrome layer zones are filled with wear particles or sliding substances or are even particle-free, so that corrosion-protected layers with good wear and sliding properties are created.
  • the outermost zones can additionally be filled with a substance that promotes enema, such as elemental tin or iron oxide.
  • chromium-cracking chromium plating baths such as preferably acidic chromic acid baths, with solid particles dispersed therein are used.
  • the workpiece to be chrome plated is first switched cathodically, so that a micro-cracked chrome layer forms, then the workpiece is switched anodically, so that the micro-cracks widen to the desired gap width and the cracks fill with the solid particles and then again occurs a cathodic circuit so that the solid particles are encapsulated and sealed by closing the cracks.
  • This periodic current reversal can, if necessary, be repeated several times, the person skilled in the art being able to vary the chromium plating parameters in accordance with the application in such a way that the desired crack width, crack density and crack filling are produced with, if necessary, different solid particle fillings.
  • Hard chrome layers are thus created by the invention, the physical and technological properties of which are significantly improved by solid particles embedded in the cracks.
  • the chrome layers can above all, as shown, have improved wear behavior, better sliding properties, better running-in behavior, better fire trace safety, better protection against fractures and flaking and better corrosion behavior individually or in combination.
  • all known chromic acid-insoluble solid particles can be used to fill the cracks.
  • the process according to the invention for producing the chromium layers is relatively simple to carry out and allows the person skilled in the art to produce the desired properties universally by varying the chromium plating parameters and adapted to the application.
  • the invention is illustrated by the exemplary embodiments and the micrographs.
  • the chrome plating takes place for a total of about 5 hours at 55 ° C. with the formation of a chrome layer with a total thickness of 0.2 mm.
  • a test rod (diameter 12 mm) 5 cm long and 5 cm wide is first cathodically chromium-plated at 65 A / dM2 for 30 minutes and then the layer is anodically etched by anodically switching the test rod for 30 sec with a current density of 150 A. / dm 2 .
  • This periodic chrome plating takes place in a total of 10 stages, the chrome plating and etching taking place under the same process parameters.
  • the cracks extending through the chrome layer in the manner of a cobweb can be seen in FIG.
  • the silicon carbide particles embedded in the cracks can be recognized as bright particles.
  • FIG. 2 shows the cross sections of the cracks, which extend approximately at right angles to the surface.
  • the cracks are closed by the periodic reversal of the current during chrome plating by means of chromium layers formed over them, so that the embedded bright silicon dioxide particles are encapsulated in the cracks.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Pistons, Piston Rings, And Cylinders (AREA)

Description

Die Erfindung betrifft eine galvanische Hartchromschicht mit einem durch die gesamte Schichtdicke sich erstreckenden Rißnetzwerk und ihr Herstellungsverfahren.The invention relates to a galvanic hard chrome layer with a crack network extending through the entire layer thickness and its production method.

Galvanisch abgeschiedene Hartchromschichten besitzen vor allem eine hohe Härte und damit verbunden eine hohe Verschleißfestigkeit, eine starke Oberflächenglätte und damit verbunden einen geringen Reibungskoeffizienten und eine geringe Klebefähigkeit sowie eine gute Widerstandsfähigkeit gegenüber aggresiv-chemischer, korrosiver, erosiver und oxydativer Beanspruchung bei gegebenenfalls höheren Temperaturen. Deshalb werden zur Erzielung einer besonderen Verschleißfestigkeit die Laufflächen von Maschinenteilen, wie beispielsweise in Verbrennungsmaschinen die Laufflächen von Kolbenringen oder Zylindern, mit Hartchromschichten überzogen, es werden zur Erzielung einer besonderen Glätte und Verschleißfestigkeit Preßwerkzeuge und preßformen für die Herstellung von Kunststofformartikeln mit Chromschichten versehen oder es werden zur besseren Haltbarkeit Armaturenteile vor allem in Chemieanlagen durch Chromschichten besonders geschützt.Electroplated hard chrome layers have above all a high hardness and associated high wear resistance, a strong surface smoothness and associated low coefficient of friction and low adhesive power as well as a good resistance to aggressive chemical, corrosive, erosive and oxidative stress at possibly higher temperatures. For this reason, the treads of machine parts, such as the treads of piston rings or cylinders in internal combustion engines, are coated with hard chrome layers in order to achieve special wear resistance.Pressing tools and molds for the production of plastic molded articles are provided with chrome layers or are used to achieve special smoothness and wear resistance For better durability, valve parts are especially protected by chrome layers in chemical plants.

Bei der galvanischen Chromabscheidung treten in den Chromschichten relativ hohe Zugspannungen auf, die bei Erreichen einer bestimmten Schichtdicke durch Überschreiten der Dehnfähigkeit des nur schwach elastischen Chroms zu Mikrorißbildungen führen, die im geätzten Oberflächenschliffbild in der Form eines spinnwebeartiken Netzwerkes feiner Linien und Sprünge in Erscheinung treten. Solche Mikrorißnetze erleichtern bei ölgeschmierten Verschleißschutzschichten als Ölnuten oder oder Ölnäpfchen die Benetzbarkeit der Chromschichten mit Öl und damit die Ausbildung des für die Schmierung erforderlichen Ölfilms, so daß in diesem Fall während oder nach der Verchromung durch Auswahl geeigneter Verchromungsparameter, durch periodische Stromumkehr, durch thermische Nachbehandlung oder durch Ätzverfahren das Chromrißnetzwerk unter Bildung einer porösen Chromschicht aufgeweitet wird. Vor allem korrosionsschützendere Chromschichten sollen jedoch möglichst frei von Rissen sein und man wählt dann ein Verchromungsverfahren, bei dem die Chromschichten allenfalls ein Mikrorißnetzwerk aufweisen.With electroplated chrome deposition, relatively high tensile stresses occur in the chrome layers, which, when a certain layer thickness is reached by exceeding the elasticity of the chromium, which is only slightly elastic, lead to microcracks, which appear in the etched surface micrograph in the form of a spider-woven network of fine lines and cracks. In the case of oil-lubricated wear protection layers as oil grooves or or oil wells, such micro-crack nets facilitate the wettability of the chrome layers with oil and thus the formation of the oil film required for the lubrication, so that in this case during or after the chrome plating by selection of suitable chrome plating parameters, by periodic current reversal, by thermal aftertreatment or the chrome crack network is expanded by etching to form a porous chrome layer. Above all, however, corrosion-protecting chrome layers should be as free from cracks as possible, and a chrome plating process is then chosen in which the chrome layers have at most a micro-crack network.

Hartchromschichten sind darüberhinaus wenig elastisch und spröde. Vor allem bei Stoßbelastungen und stärkeren Erschütterungen können Brüche in den Schichten entstehen, die dann zum Abplatzen der Schichten führen.Hard chrome layers are also not very elastic and brittle. Especially in the case of shock loads and strong vibrations, breaks can occur in the layers, which then lead to the layers flaking off.

Zur Verbesserung der physikalischen Eigenschaften galvanisch abgeschiedener Metallschichten ist es bekannt, in das Matrixmetall fein dispergierte Feststoffteilchen einzulagern, indem man die Metallabscheidung aus einem galvanischen Bad mit darin fein dispergierten Feststoffteilchen vornimmt. So besitzen Nickeldispersionsschichten mit eingelagerten Hartstoffteilchen aus vor allem Siliziumkarbid ein verbessertes Verschleißverhalten und Nickeldispersionsschichten mit eingelagerten Festschmierstoffteilchen besitzen einen geringeren Reibungskoeffizienten. Während die Herstellung galvanischer Nickeldispersionsschichten relativ unproblematisch ist, können Chromdispersionsschichten nicht so ohne weiteres hergestellt werden und galvanische Chromdispersionsschichten mit entsprechend verbesserten Eigenschaften sind in der Praxis nicht im Einsatz. Offensichtlich wegen der stärkeren Wasserstoffentwicklung am Chrom während der Galvanisierung werden dispergierte Feststoffteilchen am Abscheiden in der Chromschicht verhindert. Deshalb müssen Hartchromschichten mit darin fein dispergierten Feststoffteilchen relativ aufwendig durch bevorzugt Plasmaspritzverfahren hergestellt werden.In order to improve the physical properties of electrodeposited metal layers, it is known to incorporate finely dispersed solid particles into the matrix metal by performing the metal deposition from a galvanic bath with solid particles finely dispersed therein. Nickel dispersion layers with embedded hard material particles, especially silicon carbide, have an improved wear behavior and nickel dispersion layers with embedded solid lubricant particles have a lower coefficient of friction. While the production of galvanic nickel dispersion layers is relatively unproblematic, chromium dispersion layers cannot be easily produced and galvanic chromium dispersion layers with correspondingly improved properties are not used in practice. Obviously due to the increased hydrogen evolution on the chromium during the galvanization, dispersed solid particles are prevented from being deposited in the chromium layer. For this reason, hard chrome layers with finely dispersed solid particles have to be produced relatively expensively by preferably plasma spraying processes.

Der vorliegenden Erfindung liegt daher die Aufgabe zugrunde, eine Hartchromschicht mit verbesserten physikalischen und technologischen Eigenschaften zu schaffen, in denen vor allem die aufgezeigten Nachteile beseitigt sind. Gleichzeitig soll ein möglichst universell anwendbares galvanisches Verfahren gefunden werden, mit dem sich derartige Schichten einfach und kostensparend herstellen lassen.The present invention is therefore based on the object of providing a hard chrome layer with improved physical and technological properties in which, above all, the disadvantages indicated are eliminated. At the same time, the aim is to find a galvanic process which can be used as universally as possible and with which layers of this type can be produced simply and cost-effectively.

Erfindungsgemäß wird diese Aufgabe durch eine Hartchromschicht gelöst. in deren Risse Feststoffpartikel eingelagert sind. Bevorzugt soll dabei die Spaltbreite der Risse über 0,5 um, insbesondere aber über 1 11m liegen, damit sich überhaupt Feststoffpartikel einlagern können, und die bevorzugte Dicke der Hartchromschicht liegt zwischen 10 pm und 1.000 um. Durch die Erfindung ist somit eine Hartchromschicht geschaffen, in dessen Rißnetzwerk Feststoffteilchen eingelagert sind, die insbesondere bei einer hohen Rißdichte entsprechend ihren Eigenschaften, wie bei einer galvanischen Dispersionsschicht, die Eigenschaften der Hartchromschicht in der gewünschten Weise verbessern.According to the invention, this object is achieved by a hard chrome layer. solid particles are embedded in the cracks. In this case, the gap width of the cracks should preferably be over 0.5 μm, but in particular over 11 μm, so that solid particles can be deposited at all, and the preferred thickness of the hard chrome layer is between 10 μm and 1,000 μm. The invention thus creates a hard chrome layer, in the crack network of which solid particles are embedded, which improve the properties of the hard chrome layer in the desired manner, particularly in the case of a high crack density, in accordance with their properties, such as in the case of a galvanic dispersion layer.

Als Feststoffteilchen kommen dementsprechend die bei der Herstellung von galvanischen Dispersionsschichten verwendeten Substanzen einzeln oder in Kombination in Frage, allerdings dürfen sie sich nicht in den mikrorißbildenden Chromsäurebädern auflösen, ihre Korngröße muß unterhalb der Spaltbreite der Chromrisse, also bevorzugt etwa zwischen 0,5 und 15 um liegen und die Dicke der Chromschicht sollte um ein Mehrfaches größer sein als die Korngröße der Teilchen.Accordingly, the substances used in the production of galvanic dispersion layers are suitable as solid particles, individually or in combination, but they must not dissolve in the microcracking chromic acid baths, their grain size must be below the gap width of the chromium cracks, i.e. preferably between about 0.5 and 15 μm and the thickness of the chrome layer should be several times larger than the grain size of the particles.

Als Feststoffteilchen zur Verbesserung der Verschleißfestigkeit kommen dabei Hartstoffteilchen aus vor allem Aluminiumoxid, Borkarbid, Bornitrid, Chromkarbid, Siliziumdioxid, Titankarbid, Diamant und/oder Wolframkarbid in Frage. Solche Festkörper enthaltenden Chromschichten sind dann vor allem zur Laufflächenbeschichtung von Kolbenringen oder Zylinderlaufbüchsen in Verbrennungskraftmaschinen geeignet. Die verwendeten Festschmierstoffteilchen bestehen aus hexagonalem Bornitrid, Graphit und/oder Polymerteilchen aus vor allem Polyvinylchlorid und/ oder Polytetrafluorethylen und zur Verbesserung der Duktilität beziehungsweise Verringerung der Sprödigkeit können in die Risse duktile Metalle oder Metallegierungen aus Zinn, Titan oder Bronze eingelagert sein. Ebenso kann die Neigung von Chrom zu adhäsivem Verschleiß durch eingelagerte Molybdänteilchen verringert werden.Solid particles made primarily of aluminum oxide, boron carbide, boron nitride, chromium carbide, silicon dioxide, titanium carbide, diamond and / or tungsten carbide are suitable as solid particles for improving wear resistance. Such chromium layers containing solids are then particularly suitable for coating the tread of piston rings or cylinder liners in internal combustion engines. The solid lubricant particles used consist of hexagonal boron nitride, graphite and / or polymer particles, especially of polyvinyl chloride and / or polytetrafluoroethylene, and for improvement ductility or reduction in brittleness, ductile metals or metal alloys made of tin, titanium or bronze can be embedded in the cracks. The tendency of chrome to adhesive wear can also be reduced by embedded molybdenum particles.

Gefunden wurde aber auch, daß die Farbe der erfindungsgemäßen Chromschichten mit in den Rissen eingelagerten organischen Farbstoffen oder gefärbten Metallsalzen beeinflußt werden kann. Gefunden wurde ferner, daß durch die Ausfüllung der Risse mit Feststoffteilchen die Korrosionsfestigkeit der Schichten erhöht wurde. Bevorzugt wurden die Risse dazu mit Polyvinylchloridteilchen gefüllt, und das Polyvinylchlorid wurde anschließend in den Rissen aufgeschmolzen, so daß die Risse damit versiegelt und gegenüber korrosiven Angriffen geschützt sind.However, it was also found that the color of the chrome layers according to the invention can be influenced by organic dyes or colored metal salts embedded in the cracks. It was also found that filling the cracks with solid particles increased the corrosion resistance of the layers. For this purpose, the cracks were preferably filled with polyvinyl chloride particles, and the polyvinyl chloride was then melted into the cracks, so that the cracks were sealed and protected against corrosive attacks.

Im Sinne der Erfindung können dabei Feststoffteilchen einer Stoffart oder merherer Stoffarten in Kombination zur Füllung der Risse verwendet sein, so daß gleichzeitig mehrere physikalische Eigenschaften verbessert sind. Ebenso brauchen die Risse nicht vollständig mit den Feststoffteilchen ausgefüllt zu sein. Im Sinne der Erfindung ist es darüberhinaus auch möglich, die Risse in den einzelnen Schichtlagen mit verschiedenen Festschmierstoffarten zu füllen. So können Risse der Chromschichtzonen unmittelbar am Substrat, mit einer korrosionsverhindernden Substanz gefüllt sein, während die Risse der äußeren Chromschichtzonen mit Verschleißpartikeln oder Gleitsubstanzen gefüllt sind beziehungsweise sogar partikelfrei sind, so daß korrosionsgeschützte Schichten mit gleichzeitigen guten Verschleiß-und Gleiteigenschaften entstehen. Ebenso können die äußersten Zonen zusätzlich mit einer den Einlauf fördernden Substanz, wie elementarem Zinn oder Eisenoxid, gefüllt sein.For the purposes of the invention, solid particles of one or more types of substance can be used in combination to fill the cracks, so that several physical properties are improved at the same time. Likewise, the cracks need not be completely filled with the solid particles. In the sense of the invention, it is also possible to fill the cracks in the individual layer layers with different types of solid lubricants. For example, cracks in the chrome layer zones directly on the substrate can be filled with a corrosion-preventing substance, while the cracks in the outer chrome layer zones are filled with wear particles or sliding substances or are even particle-free, so that corrosion-protected layers with good wear and sliding properties are created. Likewise, the outermost zones can additionally be filled with a substance that promotes enema, such as elemental tin or iron oxide.

Zur Herstellung der erfindungsgemäßen Chromschichten werden an und für sich bekannte mikrorißbildende Verchromungsbäder, wie bevorzugt saure Chromsäurebäder, mit darin dispergierten Feststoffteilchen verwendet. Während des Verchromens wird dann das zu verchromende Werkstück zunächst kathodisch geschaltet, so daß sich eine mikrorissige Chromschicht bildet, danach wird das Werkstück anodisch geschaltet, so daß sich die Mikrorisse auf die gewünschte Spaltbreite aufweiten und die Risse sich mit den Feststoffpartikein füllen und anschließend erfolgt wiederum eine kathodische Schaltung, so daß die Feststoffteilchen durch Schließung der Risse eingekapselt und eingeschlossen werden. Diese periodische Stromumkehr kann gegebenenfalls mehrfach wiederholt werden, wobei der Fachmann die Verchromungsparameter entsprechend dem Anwendungsfall so variieren kann, daß die gewünschte Rißbreite, Rißdichte und Rißfüllung mit gegebenenfalls unterschiedlichen Feststoffpartikelfüllungen entstehen.In order to produce the chromium layers according to the invention, well-known chromium-cracking chromium plating baths, such as preferably acidic chromic acid baths, with solid particles dispersed therein are used. During the chrome plating, the workpiece to be chrome plated is first switched cathodically, so that a micro-cracked chrome layer forms, then the workpiece is switched anodically, so that the micro-cracks widen to the desired gap width and the cracks fill with the solid particles and then again occurs a cathodic circuit so that the solid particles are encapsulated and sealed by closing the cracks. This periodic current reversal can, if necessary, be repeated several times, the person skilled in the art being able to vary the chromium plating parameters in accordance with the application in such a way that the desired crack width, crack density and crack filling are produced with, if necessary, different solid particle fillings.

Durch die Erfindung sind somit Hartchromschichten geschaffen, deren physikalische und technologische Eigenschaften durch in die Risse eingelagerte Feststoffpartikel wesentlich verbessert sind. Die Chromschichten können dabei vor allem, wie aufgezeigt, ein verbessertes Verschleißverhalten, bessere Gleiteigenschaften, besseres Einlaufverhalten, bessere Brandspursicherheit, bessere Sicherheit vor Brüchen und Abplatzen und ein besseres Korrosionsverhalten einzeln oder in Kombination besitzen. Im Sinne der Erfindung können alle bekannten chromsäureunlöslichen Feststoffpartikel zur Füllung der Risse verwendet werden.Hard chrome layers are thus created by the invention, the physical and technological properties of which are significantly improved by solid particles embedded in the cracks. The chrome layers can above all, as shown, have improved wear behavior, better sliding properties, better running-in behavior, better fire trace safety, better protection against fractures and flaking and better corrosion behavior individually or in combination. For the purposes of the invention, all known chromic acid-insoluble solid particles can be used to fill the cracks.

Das erfindungsgemäße Verfahren zur Herstellung der Chromschichten ist relativ einfach durchzuführen und erlaubt es dem Fachmann, universell durch Variation der Verchromungsparameter die gewünschten und auf den Anwendungsfall abgestimmten Eigenschaften zu erzeugen.The process according to the invention for producing the chromium layers is relatively simple to carry out and allows the person skilled in the art to produce the desired properties universally by varying the chromium plating parameters and adapted to the application.

Die Erfindung wird durch die Ausführungsbeispiele und die Schliffbilder näher erläutert.The invention is illustrated by the exemplary embodiments and the micrographs.

Ausgegangen wird von einem mikrorißbildenden Verchromungselektrolyten mit

  • 250 g/I Chromsäure und
  • 2,5 g/I Schwefelsäure,
The starting point is a micro-cracking chromium plating electrolyte
  • 250 g / l chromic acid and
  • 2.5 g / l sulfuric acid,

in dem durch Rühren 50 g/I Feststoffteilchen mit einer Korngröße zwischen 0,5 und 5 pm dispergiert und während des Verchromens in Schwebe gehalten wird.in which 50 g / l of solid particles with a particle size between 0.5 and 5 pm are dispersed by stirring and kept in suspension during the chrome plating.

Das Verchromen erfolgt insgesamt während ca. 5 Stunden bei 55°C unter Bildung einer Chromschicht von insgesamt 0,2 mm Dicke.The chrome plating takes place for a total of about 5 hours at 55 ° C. with the formation of a chrome layer with a total thickness of 0.2 mm.

Zum Verchromen wird ein Teststab (Durchmesser 12 mm) von 5 cm Länge und 5 cm Breite zunächst 30 Minuten bei 65 A/dM2 kathodisch verchromt und anschließend erfolgt das anodische Ätzen der Schicht durch anodische Schaltung des Teststabes für 30 sec mit einer Stromdichte von 150 A/dm2. Dieses periodische Verchromen erfolgt in insgesamt 10 Stufen, wobei das Verchromen und Ätzen unter den gleichen Verfahrensparametern erfolgt.For chrome plating, a test rod (diameter 12 mm) 5 cm long and 5 cm wide is first cathodically chromium-plated at 65 A / dM2 for 30 minutes and then the layer is anodically etched by anodically switching the test rod for 30 sec with a current density of 150 A. / dm 2 . This periodic chrome plating takes place in a total of 10 stages, the chrome plating and etching taking place under the same process parameters.

In Testversuchen wurden zur Herstellung von

  • a) Verschleißschichten Siliziumkarbidteilchen verwendet.
  • b) Gleitschichten mit verbessertem Einlaufverhalten wurden mit hexagonalen Bornitridpartikein hergestellt.
  • c) Zur Herstellung von Schichten mit verbessertem Korrosionsverhalten wurden Polyvinylchloridteilchen eingesetzt, wobei das Polymer in der fertigen Schicht über 10 Minuten bei 80°C zum Aufschmelzen erhitzt wurde.
  • d) Zur Herstellung von gelben Schichten wurden Bleichromatpartikel verwendet.
In test trials, the production of
  • a) Wear layers of silicon carbide particles used.
  • b) Sliding layers with improved run-in behavior were produced with hexagonal boron nitride particles.
  • c) Polyvinyl chloride particles were used to produce layers with improved corrosion behavior, the polymer in the finished layer being heated at 80 ° C. for 10 minutes to melt.
  • d) lead chromate particles were used to produce yellow layers.

In den hergestellten Teststäbchen wurden entsprechend verbesserte technologische und physikalische Eigenschaften festgestellt.Improved technological and physical properties were found in the test strips produced.

Die drei Schliffbilder zeigen rasterelektronenmikroskopische Aufnahmen der erfindungsgemäßen Hartchromschichten nach dem Ausführungsbeispiel.

  • Figur 1 ist dabei ein Oberflächenschliffbild in tausendfacher Vergrößerung,
  • Figur 2 ein Querschliffbild in tausendfacher Vergrößerung,
  • Figur 3 ein Schrägschliffbild in viertausendfacher Vergrößerung.
The three micrographs show scanning electron micrographs of the hard chrome layers according to the invention according to the exemplary embodiment.
  • FIG. 1 is a surface micrograph in a magnification of a thousand times,
  • FIG. 2 shows a cross section in a magnification of a thousand times,
  • Figure 3 is an oblique section image in four thousand times magnification.

In Figur 1 sind die spinnwebenartig durch die Chromschicht sich erstreckenden Risse zu erkennen. Als helle Teilchen sind die in den Rissen eingelagerten Siliziumkarbidteilchen zu erkennen.The cracks extending through the chrome layer in the manner of a cobweb can be seen in FIG. The silicon carbide particles embedded in the cracks can be recognized as bright particles.

Das Querschliffbild der Figur 2 zeigt die Querschnitte der Risse, die sich etwa rechtwinklig zur Oberfläche erstrecken. Die Risse sind durch die periodische Stromumkehr während des Verchromens durch darüber gebildete Chromschichten verschlossen, so daß die eingelagerten hellen Siliziumdioxidteilchen in den Rissen eingekapselt sind.The cross section of FIG. 2 shows the cross sections of the cracks, which extend approximately at right angles to the surface. The cracks are closed by the periodic reversal of the current during chrome plating by means of chromium layers formed over them, so that the embedded bright silicon dioxide particles are encapsulated in the cracks.

Im Schrägschliffbild der Figur 3 ist bei viertausendfacher Vergrößerung zu erkennen, wie die Siliziumkarbidpartikel in den Rissen durch nachträglich abgeschiedenes Chrom teilweise umhüllt und verankert sind.In the oblique section of FIG. 3, at a magnification of four thousand times, it can be seen how the silicon carbide particles in the cracks are partially covered and anchored by subsequently deposited chromium.

Claims (17)

1. Electroplated hard chromium layer with a network of cracks extending through the whole thickness of the layer, characterized in that solid particles are embedded in the cracks.
2. Hard chromium layer according to claim 1, characterized in that the thickness of the hard chromium layer lies between 0,01 and 1,0 mm.
3. Hard chromium layer according to one of claims 1 and 2, characterized in that the width of the cracks is greater than 0,001 mm.
4. Hard chromium layer according to one of claims 1 to 3, characterized in that the grain size of the embedded solid particles lies between 0,0005 and 0,015 mm.
5. Hard chromium layer according to at least one of claims 1 to 4, characterized in that hard material particles are embedded in the cracks as solid particles, in order to enhance the resistance to wear.
6. Hard chromium layer according to claim 5, characterized in that the hard material particles consist of tungsten carbide, chromium carbide, aluminium oxide, silicon carbide, silicon nitride, boron carbide and/or diamond.
7. Hard chromium layer according to at least one of claims 1 to 4, characterized in that solid lubricant particles are embedded in the cracks as solid particles, in order to enhance the sliding characteristics.
8. Hard chromium layer according to claim 7, characterized in that the solid lubricant particles consists of graphite, hexagonal boron nitride and/or polytetrafluoroethylene.
9. Hard chromium layer according to at least one of claims 1 to 4, characterized in that ductile metals and/or metal alloys are embedded in the cracks as solid particles, in order to enhance the ductility.
10. Hard chromium layer according to claim 9, characterized in that the ductile metals and/or metal alloys consist of titanium, tin and/or bronze.
11. Hard chromium layer according to at least one of claims 1 to 4, characterized in that thermoplastic polymers are embedded in the cracks as solid particles, in order to enhance the resistance to corrosion, and in that the thermoplastics are fused after the embedding in the cracks.
12. Hard chromium layer according to at least of claims 1 to 4, characterized in that the organic and/or inorganic dyestuffs are embedded in the cracks as solid particles.
13. Hard chromium layer according to at least one of claims 1 to 4, characterized in that there are embedded in the cracks as solid particles mixtures of at least two components of hard material particles, solid lubricant particles, metals, metal alloys, organic thermoplastics and/or organic and inorganic dyestuffs.
14. Hard chromium layer according to at least one of claims 1 to 13, characterized in that the chromium layer consists of a plurality of chromium layers, in the cracks of which different solids or solid mixtures are embedded.
15. Hard chromium layer according to at least one of claims 1 to 14, characterized in that the cracks of the individual chromium layer sites are filled with solid particles to different degrees.
16. Method of making the hard chromium layers according to at least one of claims 1 to 15, characterized in that the chromium plating takes place in a chromium plating electrolyte known per se which forms micro-cracks, in which the solid particles are dispersed, and in that the workpiece is alternately switched cathodically and anodically by one or multiple periodic reversals of current, so that the chromium layer forms on the workpiece during the cathodic connection and the micro-cracks widen and fill with the solid particles during the anodic connection, whereby the cracks are closed and the solid particles are encapsulated in the cracks during the following cathodic connection.
17. Method according to claim 16, characterized in that the time of the cathodic connection is several times greater than the time of the anodic connection.
EP86111775A 1985-09-03 1986-08-26 Galvanic hard chromium layer Expired - Lifetime EP0217126B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3531410 1985-09-03
DE19853531410 DE3531410A1 (en) 1985-09-03 1985-09-03 GALVANIC HARD CHROME LAYER

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EP0217126A1 EP0217126A1 (en) 1987-04-08
EP0217126B1 true EP0217126B1 (en) 1990-07-04

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US (1) US4846940A (en)
EP (1) EP0217126B1 (en)
JP (1) JP2602499B2 (en)
BR (1) BR8604205A (en)
DE (2) DE3531410A1 (en)
ES (1) ES2001645A6 (en)
HK (1) HK115395A (en)

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DE19752720C2 (en) * 1997-11-28 2000-07-06 Federal Mogul Burscheid Gmbh Process for producing an oil scraper ring
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US6875330B2 (en) 2001-05-03 2005-04-05 Duralloy Ag Process for coating workpieces with bearing metal
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Also Published As

Publication number Publication date
HK115395A (en) 1995-07-21
DE3672431D1 (en) 1990-08-09
BR8604205A (en) 1987-04-28
EP0217126A1 (en) 1987-04-08
ES2001645A6 (en) 1988-06-01
JPS6256600A (en) 1987-03-12
DE3531410C2 (en) 1989-03-23
DE3531410A1 (en) 1987-03-05
US4846940A (en) 1989-07-11
JP2602499B2 (en) 1997-04-23

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