CH717335A2 - A method of treating the surface of an object. - Google Patents

Abstract

The invention relates to a method of surface treatment of an object (1) having at least one conductive substrate (2), the method using an electrochemical process involving an electric discharge between an electrode and the conductive substrate (2) at the same time. through a dielectric medium. The method comprises: i) providing the object (1) having the conductive substrate (2), ii) treating said substrate (2) by said electrochemical process, The method is characterized in that, before treating said conductive substrate (2) ) by said electrochemical process, said substrate (2) is prepared in a texturing step to create a pattern of micrometric structures (3) on said substrate (2), said pattern (3) comprising hollows (4) and reliefs ( 5). The invention also relates to a device comprising an object (1) having a conductive substrate (2) at least partially treated by a method according to the invention, for example chosen from timepieces, pieces of jewelry or jewelry, circuits, in particular superconducting circuits.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method of surface treatment of an object. The invention also relates to a device comprising an object having a conductive substrate at least partially treated by a method according to the invention.

STATE OF THE ART

There are several electrochemical processes which make it possible to modify a metal surface of an object. These methods are used in particular for working the surface or part of the surface of a timepiece or a piece of jewelry.

[0003] Among the existing methods, mention may be made of anodization, electroplating or else electroerosion.

[0004] Anodizing is an electrolytic passivation process which is used to increase the natural oxide layer on the surface of a metal substrate.

Electroplating is a process for applying by means of a direct electric current, a metal deposit on the surface of an object, the metal being initially in the form of cations in a solution called electrolyte and containing other ions to conduct electricity.

[0006] Spark erosion is a well-known subtractive machining process which consists in removing material from a conductive substrate by using electric discharges between an electrode and said substrate both immersed in a dielectric medium. Under the action of a high electric voltage (typically between 60 and 400V), a breakdown occurs in the dielectric medium creating an ionized plasma channel between the electrode and the substrate through which an electric arc propagates. At the foot of said electric arc and given the high current, a small surface of the substrate is melted and deteriorated. By successive sparking, a continuous removal of material is obtained.

[0007] Alternatively, the Applicant has previously developed an original method described in document CH705973. This document describes an additive machining process using an electric discharge between an electrode and the conductive substrate through a dielectric medium. The originality of the method described in document CH705973 lies in the use of a composite liquid with various powders in suspension as dielectric medium and of a wire electrode.

The present invention is part of an aim of improving existing electrochemical processes, in particular for known surface treatment processes, in particular which implement an electric discharge between an electrode and a substrate through a dielectric. Even if there are known methods of this type, such as that described in document CH705973, there remain aspects to be improved, in particular as regards the efficiency and the yield which it would be advantageous to optimize.

OBJECT OF THE INVENTION

[0009] An object of the present invention is therefore to solve, improve, or at least minimize the drawbacks of the existing methods described above, in particular the method described in document CH705973.

These objects are at least partially achieved by the present invention.

The present invention relates to a method of surface treatment of an object having at least one conductive substrate, the method comprising an electrochemical process implementing an electric discharge between an electrode and the conductive substrate through a dielectric medium , the method comprising: i) providing the object having the conductive substrate to be treated, ii) treating said substrate by said electrochemical process, the method being characterized in that, before treating said conductive substrate by said electrochemical process, said substrate is prepared in a texturing step to create a pattern of micrometric structures on said substrate, said pattern comprising recesses and reliefs.

The present invention advantageously proposes to prepare the conductive surface of the object to be treated before implementing the electrochemical process. The conductive surface is for example a metal surface. The preparation step makes it possible to texturize or structure the conductive surface to be treated by a suitable surface treatment (by an electrochemical process) to form a pattern of micrometric structures.

The term pattern designates the distribution of micrometric structures on the conductive surface. The pattern comprises a set of structures or micrometric elements (that is to say having a size of the order of a micrometer), for example reliefs (protuberances or points) spaced by recesses.

The micrometric pattern makes it possible to provide the conductive surface to be treated with a controlled roughness. Surprisingly, it has been observed that the preparation of the surface to provide it with a certain roughness makes it possible to improve the efficiency and the yield of the electrochemical process, (in particular when it is a question of electroerosion or of electroerosion. (additive sparking), compared to an unprepared conductive surface, for example a smooth or polished conductive surface.

The texturing or preparation of the surface beforehand of the electrochemical process makes it possible to improve the yield and the efficiency of the electrochemical process, in particular when the electrochemical process is that described in document CH705973.

Texturing or surface preparation makes it possible to give new properties to all types of surfaces, for example to adjust the wettability of a surface, or even optical properties such as reflectivity.

The prepared surface has micrometric structures in the form, for example, of micrometric protuberances or points. These points have a beneficial effect for the efficiency of the electrochemical process.

[0018] For example, in electroerosion, these points act as lightning rods considerably favoring the sparking process. Indeed, there is a local increase in the electric field by geometric effect. The geometric or peak effect, also called peak power, is the name given to the accumulation of electric charges, and therefore the creation of a strong electric field, at the level of the pointed areas of the surface of an electric conductor (a metal object for example). A typical application of this phenomenon is the lightning rod. The additive sparking process is thus significantly improved. The efficiency and the yield of the electrochemical process, in particular the additive sparking, for example that described in the document CH705973, are thus notably improved by an easier and regular breakdown of the dielectric liquid present between the surface and the electrode.

According to one embodiment, the pattern of micrometric structures has a roughness Ra less than or equal to 20 micrometers and greater than or equal to 0.1 micrometers, preferably between 10 micrometers and 1 micrometers, for example between 7 micrometers and 3 micrometers.

The preparation or structuring or texturing of the surface can be carried out by various techniques, for example by laser scanning, by sandblasting, milling, guilloche, electro-erosion.

Laser scanning offers the advantage of great flexibility, the creation of surfaces with evolving or anisotropic roughness, of very great regularity or having periodic or quasi-periodic structures.

Sandblasting is interesting by its lower cost but also by the possibility of treating other types of surfaces (if the laser does not allow, for example for questions of wavelength).

In one embodiment, the pattern of micrometric structures is regular, random, or periodic.

A regular pattern or regular texture provides an isotropic work surface for the design of decorative or artistic structures, such as a painting canvas, or the frame of a sheet of paper (typical example).

A random pattern or texture offers the same advantages as the regular texture, with the addition of a 'biometric' advantage in the event that the design inscribed on this surface should serve as a means of identification (fingerprint).

A periodic pattern or texture can produce interesting aesthetic visual effects, by cumulative effects on the reflection of light. Also, a pattern of periodic structures allows the multiplication of identical metallurgical structures on a macroscopic surface (cascading metal junctions, solar cells, etc.).

According to one embodiment, said electrochemical process is chosen from additive electrochemical processes, for example additive sparking, or else electroplating. The additive sparking allows a targeted and selective treatment on certain regions of the structured surface, while the electroplating makes it possible to treat larger surfaces.

In one embodiment, the electrochemical process comprises: ii) a) Applying a voltage between the electrode and said substrate of the object to initiate at least one discharge, the electrode being separated from the substrate by a predetermined distance (d) or gap occupied by the dielectric medium in which the discharge occurs, said voltage and the discharge time being configured so that said discharge induces a breakdown in the dielectric medium and the formation of a conductive ionized plasma channel, ii ) b) Discharging an electric current from a current source through said conductive ionized plasma channel, said current being set so that a surface of the substrate at the base of the electric arc melts so as to obtain an imprint on said substrate having chemical and / or physical and / or metallurgical properties different from those of the substrate.

This embodiment of the invention uses electrical discharges between a metal electrode, for example a very fine metal tip, a wire, a bar or any other suitable geometric shape and a conductive surface constituting the substrate of an object. The electrode and the substrate are separated by a distance or a gap of a few microns which is entirely filled by a dielectric medium in which the discharge therefore takes place, which is a micro discharge. The discharges are configured to create a breakdown in the dielectric medium forming a conductive ionized plasma channel between the electrode and the substrate and in which an electric current generated by a generator or any other suitable means can pass. Said electric current is for its part configured to melt the substrate at the base of the electric arc on a surface having the shape of a disk without volatilizing the substrate.

Surprisingly and unexpectedly, by using lower currents and shorter discharge times than those usually used for spark erosion, a greater variety of imprints can be obtained. In addition, with these parameters, the conditions of the discharge are better controlled even in practice.

This configuration also makes it possible to modify the metallurgical structure of the substrate in order to change its physical or chemical properties. For example, by virtue of the method according to the invention, it is possible to harden a steel substrate very locally and thus make it more resistant at a very precise location.

This embodiment of the invention can also be compared to a "writing" method since a high frequency discharge rate associated with a displacement of the electrode relative to the substrate allows the development of alloys continuously, just like their implantation on a surface of the object according to a predefined path.

In one embodiment, the dielectric medium consists of a liquid, a gel or a dielectric paste.

According to one embodiment the electrode is made of refractory metal having a high melting point and / or thermionic emission properties.

According to one embodiment, the voltage is between 1 and 400V.

In one embodiment, the intensity of the current discharged into the ionized plasma channel is between 100mA and 1000A.

According to one embodiment, the gap is between 0.1 and 400 microns.

In one embodiment, the discharge lasts between 0.1 and 800 microseconds.

In one embodiment, a reagent is supplied to the area of the discharge so that elements of the reagent are trapped and melted in the ionized plasma channel and are implanted in the substrate in the molten surface at the base of the electric arc.

In this embodiment, a reagent is brought into the zone of the discharge in order to be melted in the ionized plasma channel formed following the breakdown and to be mixed there with the molten substrate to create an imprint on the substrate which is in fact a new compound or a new alloy formed of elements of the reagent and elements of the substrate. This reagent can be a mixture of ultrafine powders mixed with the dielectric medium, the constituent elements of the dielectric medium or of the electrode or can be brought into the zone of the discharge in the form of a thin layer deposited on the substrate before the discharge.

The ionized plasma channel produced following the breakdown due to the discharge in the dielectric medium locally reaches temperatures and pressures unachievable by means of conventional metallurgy. As a result, this configuration allows the development of new compounds, as well as the synthesis of new variants of metallurgical phases unknown to date, synthesis of the substrate and of the reagent brought into the zone of the electric discharge. This configuration also makes it possible to modify the metallurgical structure of the substrate in order to change its physical or chemical properties. The cylindrical ionized plasma channel created by the discharge and encapsulated by the surrounding dielectric medium constitutes a microscopic autoclave.

[0042] According to one embodiment, the reagent comprises elements constituting the dielectric medium.

In one embodiment, the reagent comprises at least one element initially forming part of the electrode, the parameters of the discharge being chosen to cause progressive and constant wear of said electrode on each discharge.

According to one embodiment, the reagent comprises a thin layer of a conductive material deposited on the substrate before the implementation of the method.

In one embodiment, the reagent comprises particles in the form of powders having a determined particle size, the roughness of the pattern of micrometric structures being adjusted as a function of said particle size of the powder.

According to one embodiment, the reagent comprises particles in the form of powders whose diameter is less than the predetermined distance or gap and mixed with the dielectric medium.

When the electrochemical process implements an electric discharge between an electrode and the conductive substrate through a dielectric medium (for example electroerosion or additive sparking), the presence of the micrometric structures creates a local amplification of the electric field when sparking. This amplification indirectly makes it possible to widen the sparking distance (space between the electrode and the surface) and therefore to increase the volume of powder melted and deposited by spark.

Generally, the sparking process is advantageously carried out by placing a drop of liquid on the surface to be treated. A rough surface condition effectively anchors the edges of the drop. The risk of spreading or dispersing the liquid outside the area to be treated is avoided or greatly reduced. This fluidic anchor provides effective resistance to elastic shock waves caused by sparks inside the liquid, the pressure of which tends to burst the drop.

The prepared surface (in other words textured) has hollows and reliefs which form microcavities, interstices or cells. These microcavities are suitable for physical containment of the powders contained in the reagent, before and during the spark treatment. Thus, the lateral mobility on the surface of the powders is greatly reduced, which makes it possible to optimize the sparking.

The surface of the object is therefore naturally enriched with powders trapped in the cells of the microstructures. The sparking makes it possible to integrate them into the surface by local melting. When the powder is trapped in the cells, this leads to a more dense and compact surface treatment, there is more reagent (powder for example) which is incorporated in the conductive surface. Furthermore, the uniformity of the deposit is improved by the isotropic distribution of the reagents on the surface to be treated.

Advantageously, the forced confinement of the powders or reagent (for example a pigment) thanks to the texture or roughness of the surface allows better definition of the deposit. For example, when the reagent is a pigment to "write" on the surface, a better definition of the writing is observed. The forced confinement of the powder in the cells of the textured surface allows better definition of the edges of the structures deposited or written by the process. On a smooth surface, fragments of powder can be sent laterally by the pressure of the sparks, creating irregularities on the edges of the path of the wire electrode which is not the case in the process according to the invention.

According to one embodiment, the reagent further comprising an additive chosen from glycerin, paraffin, or another mineral oil. The presence of an additive with a high density (greater than the density of water), for example a viscous additive, fatty substances, makes it possible to improve the anchoring of the powder in the pattern.

In one embodiment, the reagent comprises particles in the form of powders whose diameter is less than the predetermined distance or gap and mixed with the dielectric medium.

According to one embodiment, the invention further comprises a sedimentation step so that the powder settles in the engraved pattern. This procedure proves to be advantageous in the case of coarse powders (for example 350 mesh and more) or high density powders (for example tungsten powders) or of mixture of powders. The typical settling time for each reagent (also called composite liquid) can be established by prior observation in a clear test tube. These sedimentation times can vary between 10 seconds and 48 hours.

The sedimentation step takes place after texturing and before the electrochemical process. It is also possible to place an additive in the cells of the textured surface before the application of the dielectric liquid, for example by diffusion, spray or spreading.

The additive can consist of a pigment. Thus, the prior texturing of the surface makes it possible to graft, by additive sparking, either elements coming from the dielectric liquid via the plasma of the spark, elements coming from a preliminary sedimentation of powders present in the dielectric liquid, or else additives placed in the cells before immersion in the dielectric liquid.

The invention also relates to a device comprising an object having a conductive substrate at least partially treated by a method according to the invention, said device being for example chosen from a timepiece, a piece of jewelry or jewelry, a support comprising an electrical circuit, in particular a superconducting circuit.

The invention may include an embodiment in isolation or a combination of embodiments.

The embodiments described for the method according to the present invention also apply to the device according to the invention, mutatis mutandis and vice versa.

BRIEF DESCRIPTION OF THE FIGURES

[0060] Other advantages, aims and particular characteristics of the invention will emerge from the non-limiting description which follows of at least one particular embodiment of the device and of the method which are the subject of the present invention, with reference to the appended figures , wherein Figures 1 to 4 show a first embodiment of the invention;

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present description is given without limitation, each characteristic of an embodiment being able to be combined with any other characteristic of any other embodiment in an advantageous manner. We can now note that the figures are not to scale.

Figures 1 to 4 show the method according to the invention according to a first embodiment.

In the illustrated embodiment, the treatment method of the invention uses additive sparking as an electrochemical process, this process being described in document CH705973.

In this embodiment, the object to be treated is a plate 1 made of 316L steel. This plate 1 can for example serve as an identification plate or aesthetic ornament as shown in Figure 4.

The wafer 1 comprises a conductive substrate 2 on its surface.

Before treating the conductive substrate 2, the substrate 2 is textured (in other words etched) by laser engraving in the illustrated embodiment. The purpose of texturing is to machine the conductive substrate 2 by material subtraction to create a pattern 3 of micrometric structures on the surface (or at least part of the surface) of the substrate 2.

The etching or texturing is carried out using a laser of the nanopulses type on a surface of the substrate 2 of approximately 1 cm2. The etching is preferably carried out only on the area of the substrate to be treated by the additive sparking process, but it is also possible to etch beyond the area to be treated. This way of proceeding is particularly advantageous if it is desired to offer a substantial visual contrast between the textured part and the zones treated solely by sparking (or another electrochemical process). This contrast is of great interest in aesthetic applications and in general in those requiring good readability.

The nanopulsed laser has a power of between 1W and 100W.

Texturing makes it possible to obtain a substrate having a rough surface as shown in Figure 1b from a substrate having a smooth surface shown in Figure 1a.

The texturing step depends on the micrometric structures of the pattern 3 to be etched. The roughness can be adjusted according to the desired effect, either a robust encrustation of the alloys to be deposited, or better optical contrast. Texturing can be used to create a writing medium with a certain look or design. It is possible to choose the frame and the color of the medium on which to write with the method according to the invention. This choice determines the texturing method to apply.

In the example illustrated in Figure 1b, the texturing lasts about 5 minutes.

The pattern 3 of micrometric structures shown in Figure 1b is random and has hollows 4 and reliefs 5 (or bumps).

After the texturing step, a reagent is deposited on the textured area (or at least part of the area). The reagent is in liquid form and comprises a powder suspended in solution. In the example illustrated in FIG. 2b, the reagent is in the form of a drop 6. The presence of the pattern of micrometric structures 4 makes it possible to anchor the drop on the surface of the substrate 2 to be treated, we speak of fluidic anchoring. . Anchoring is not possible when the surface of the substrate 2 is smooth as shown in Figure 2a while the reliefs 4 and the recesses 5 block the lateral mobility of the drop 6 of reagent as shown in Figure 2b. Thus, the presence of the pattern 3 offers an effective resistance vis-à-vis the elastic shock waves caused by the sparks inside the liquid during the sparking process, the pressure of which tends to burst the drop.

In the embodiment shown in Figures 1 to 4, the method according to the invention comprises a sedimentation step before the spark process.

As illustrated in Figures 3a and b, the surface of the textured or etched substrate 2 has microcavities or interstices suitable for physical confinement of the powders contained in the liquid of the reagent, before (shown in Figure 3a) and after the additive spark treatment (shown in Figure 3b). The lateral mobility of the powders in suspension is greatly reduced thanks to the micrometric pattern 3.

The surface of the substrate 2 is therefore naturally enriched in powders trapped in the cells of the microstructure 3. The subsequent sparking process integrates them into the surface by local melting. This leads to a more dense and compact surface treatment in terms of supply of material from the liquid reagent. Also, the uniformity of the deposit is improved by the isotropic distribution of the reagents on the surface to be treated.

Another advantageous advantage of the present invention is a better definition of the edges of the substrate 2, in other words a better definition of the limits or borders of the reagent deposited thanks to the forced confinement of the powders. This is particularly advantageous when the reagent is a pigment.

After sedimentation, the substrate 2 is treated by sparking (according to a process described in document CH705973) to incorporate the powders into the surface of the conductive substrate as shown in FIG. 4.

For the sparking process, one begins by placing on the surface to be treated an adequate amount of composite dielectric (for example a drop of reagent 6). Next, a metal electrode (for example a tungsten wire with a diameter of 0.1 mm) is approached to said surface. Then an electrical voltage is applied between the electrode and the surface, and a gradual physical rapprochement is triggered between these two elements.

When the space separating the end of the electrode from the surface is small enough, there will be electrical breakdown of the composite liquid and therefore the appearance of an electrically conductive plasma filament. A current generator then injects an electric current of a certain amplitude and of a certain duration. The injected power will melt the powder present in the liquid as well as the anchoring point of the plasma on the surface. This is how the molten metal on the surface will mix with the molten material coming from the plasma. This mixture will form as a solid deposit by cooling after extinction of the plasma by stopping the current.

The sparking process is repeated continuously to trace a predetermined path on the surface. This path is achieved by controlling the movement of the wire electrode, for example by using a digital control.

FIG. 4 represents the wafer 1 made of 316L steel after texturing and application of the sparking process.

The wafer 1 comprises a peripheral zone 7 which is not textured and not treated by the sparking process, in other words this peripheral part has a polished surface made of original metal.

The non-textured peripheral zone 7 surrounds a central laser textured zone 8.

A circular zone 9 located in this textured central zone 8 has been treated by the additive sparking process as described above (described in document CH705973) to deposit an alloy on certain portions and create a particular design or drawing .

Below this circular area, there is a writing area 10 where a text "mutatis mutandis" has been written on a part of the textured central part 8 using the additive sparking process (described in the document CH705973).

REFERENCE NUMBER

1 Plate 2 Conductive substrate 3 Patterns of micrometric structures 4 Hollow 5 Reliefs 6 Reagent 7 Non-textured peripheral zone 8 Textured central zone 9 Circular zone 10 Writing zone

Claims (11)

1. Method of surface treatment of an object (1) having at least one conductive substrate (2), the method comprising an electrochemical process implementing an electric discharge between an electrode and the conductive substrate (2) through a dielectric medium, the method comprising: - i) provide the object (1) having the conductive substrate (2), - ii) treating said substrate (2) by said electrochemical process, the method being characterized in that, before treating said conductive substrate (2) by said electrochemical process, said substrate (2) is prepared in a texturing step to create a pattern of micrometric structures (3) on said substrate (2) , said pattern (3) comprising hollows (4) and reliefs (5). 2. Method according to claim 1, wherein the pattern of micrometric structures (3) has a roughness Ra less than or equal to 20 micrometers and greater than or equal to 0.1 micrometers, preferably between 10 micrometers and 1 micrometers, for example between 7 micrometers. and 3 micrometers. 3. Method according to one of claims 1 and 2, wherein the pattern of micrometric structures (3) is regular, random, or periodic. 4. Method according to one of claims 1 to 3, wherein the texturing is chosen from laser scanning, sandblasting, milling, guilloche, electroerosion. 5. Method according to one of claims 1 to 4, wherein said electrochemical process is chosen from additive electrochemical processes, for example additive sparking or electroplating. 6. Method according to one of claims 1 to 5, wherein the electrochemical process comprises the following steps: - ii) a) Apply a voltage between the electrode and said substrate (2) of the object (1) to initiate at least one discharge, the electrode being separated from the substrate (2) by a predetermined distance (d) or gap occupied by the dielectric medium in which the discharge occurs, said voltage and the discharge time being configured so that said discharge induces a breakdown in the dielectric medium and the formation of a conductive ionized plasma channel; - ii) b) Discharging an electric current coming from a current source through said conductive ionized plasma channel, said current being set so that a surface of the substrate at the base of the electric arc melts so as to obtain an imprint on said substrate (2) exhibiting chemical and / or physical and / or metallurgical properties different from those of the substrate (2). 7. A method according to claim 6, wherein a reagent (6) is supplied to the area of the discharge so that elements of the reagent (6) are trapped and melted in the ionized plasma channel and are implanted in the substrate ( 2) in the molten surface at the base of the electric arc. 8. Method according to claim 7, in which the reagent comprises particles in the form of powders having a determined particle size, the roughness of the pattern of micrometric structures (3) being adjusted as a function of said particle size of the powder. 9. The method of claim 7 or 8, wherein the reagent (6) comprises particles in the form of powders whose diameter is less than the predetermined distance or gap and mixed with the dielectric medium. 10. Method according to one of claims 6 to 9, wherein the method further comprises a sedimentation step so that the powder sediments in the pattern of micrometric structures (3) engraved. 11. Device comprising an object (1) having a conductive substrate (2) at least partially treated by a method according to one of claims 1 to 10, said device being for example chosen from among a timepiece, a piece of jewelry. or jewelry, a circuit including a superconducting circuit.