Apparatus and method for coating the interior surface of a hollow article - Patents.com

Abstract

The present invention relates to an apparatus for forming a coating on and / or modifying the properties of an internal surface of a hollow article (1), comprising a plasma source (2), the plasma source having an elongated shape and including a cathode (3) and a target (4), the target (4) being a thermionic electron emission source, the target (4) being electrically connected to the cathode (3), the plasma source (2) further comprising a masking (5) partially covering the outer surfaces of the cathode (3) and the target (4), the masking (5) being adapted to prevent the formation of plasma on the area covered by the masking (5) during operation of the apparatus, and a plasma formation area (6) is provided on the target (4), the plasma formation area (6) being not covered by the masking (5). The present invention further relates to the target (4), the assembly of the apparatus, the method and the hollow article (1).

Description

[Technical field]

[0001] The present invention relates to an apparatus for forming a coating on an internal surface of a hollow article and / or for modifying the properties of the internal surface of a hollow article. The present invention further relates to a target for use in such an apparatus, an assembly of such an apparatus with a hollow article, a method, and a hollow article. [Background technology]

[0002] Producing coatings inside cavities and on internal surfaces of workpieces is a very relevant process industrially. Coatings on such internal surfaces may be required, for example, to increase the wear resistance, fatigue resistance, oxidation resistance and / or corrosion resistance of said surfaces. Common applications requiring improved surface properties on internal surfaces are pipes, barrels, housings, valves, shock absorbers, fluid handlers, forming tools, forming equipment, nozzles, tanks and heat exchangers.

[0003] In many cases, such coatings are produced by electrochemical or chemical processes, such as chrome plating. The drawback of these techniques is that they rely on many chemicals that pose significant safety-, health- and environmental risks. In particular, the most common coatings on internal surfaces are coatings based on metallic chromium, which are usually derived from carcinogenic Cr(VI) compounds.

[0004] Due to legal restrictions on these types of chemicals, various alternative techniques are known, including laser beam evaporation, gas spraying, soldering processes, explosive evaporation or plasma techniques based on hollow cathode discharge with gaseous precursors.

[0005] Another method conventionally applied to produce coatings on internal surfaces is chemical vapor deposition (CVD), but this technique requires high process temperatures that are not suitable for many component materials.

[0006] A typical industrially applied method for producing coatings on parts is physical vapor deposition (PVD). Physical vapor deposition processes can be realized with several different techniques, including sputtering, cathodic arc evaporation, thermal evaporation, or electron beam evaporation. A typical setup for realizing a physical vapor deposition process is to place the substrate (e.g., workpiece, e.g., tool or part) on a substrate holder that is later introduced into a vacuum chamber and rotated or moved in front of a coating source (often also called plasma source). Typically, the coating source is integrated into the wall, ceiling or bottom of the vacuum chamber. The main drawback of such industrially applied physical vapor deposition techniques is that they are line-of-sight based processes and therefore cannot deposit coatings inside cavities with significant depth.

[0007] Thus, none of the above mentioned techniques fully meets the industrial requirements in terms of low cost, robustness, process temperature, versatility, coating properties, workpiece dimensions, or they are not suitable due to their health and environmental risks. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention can therefore be seen to overcome at least one of the above-mentioned drawbacks of the prior art. A particular object of the present invention can be seen to be providing an apparatus and / or method suitable for the economical deposition of coating materials on the internal surfaces of hollow articles. Preferably, the deposition process of the present invention should be carried out in a controlled and spatially defined manner. A further object of the present invention can be seen to be providing a new industrially tractable solution for the technology for producing coatings inside cavities and on the internal surfaces of hollow articles. [Means for solving the problem]

[0009] At least one of the above objects can be achieved by the present invention.

[0010] According to the present invention, a plasma source can be provided that can reach the internal cavity and / or deflect a flux of coating material into the cavity of a hollow article, and further, a method can be provided for facilitating the deposition process of material onto the internal surface of a hollow article.

[0011] In the context of the present invention, a hollow article can be any article with an internal surface. Examples of hollow articles are tubes, pipes, hollow shafts, etc. The internal surface of a hollow article may in particular be the surface of an opening extending into the hollow article. Non-limiting examples of internal surfaces are the inner surface of a borehole or the surface extending along the inner diameter of a pipe, tube, hollow shaft, etc.

[0012] The apparatus of the present invention includes a plasma source that may include a cathode and a target. One purpose of the cathode is to deliver the plasma near a targeted area on the interior surface of the hollow article.

[0013] According to the invention, the apparatus may further include a masking that partially covers the outer surfaces of the cathode and the target. One purpose of the masking is to eliminate undesirable parasitic discharges around the cathode and the target. Thus, the masking may be beneficial for the localized formation of plasma, resulting in a well-defined material deposition.

[0014] The plasma source of the device of the invention can be connected to a power supply unit. The power supply unit may in particular be adapted to supply electrical energy to the plasma source. The power supply unit may in particular be adapted to supply direct and pulsed current to the plasma source and / or may comprise a control unit adapted to control the current supplied to the plasma source.

[0015] In one embodiment, the geometry and characteristics of the target and the cathode are not particularly limited, as long as the target and the cathode are suitable for forming a plasma. In particular, the target should be adapted to be a source of thermionic electron emission. The cathode and the target may be formed as one integral part manufactured from the same material. Alternatively, the target and the cathode may be separate parts connected in an electrically conductive manner. In the latter case, the materials of the target and the cathode may be different.

[0016] The masking may partially cover the outer surfaces of the cathode and / or the target. In particular, the masking may prevent plasma from forming over areas of the cathode and target that are covered by the masking.

[0017] A particular area of ​​the target may not be covered by the masking, and this area may be referred to as the plasma formation region, and thus the plasma may be formed exclusively in the plasma formation region.

[0018] Thus, the plasma source can include at least a cathode, a target and a masking. In order to be able to be introduced into the hollow article, the plasma source can have an elongated shape. In the context of the present invention, the phrase "elongated shape" can particularly refer to the ratio between the diameter of the plasma source and the length of the plasma source being less than 1:5, for example less than 1:8, or less than 1:10.

[0019] The masking may be made of either a non-conductive or conductive material. If the masking is made of a non-conductive material, the masking device may be freely positioned around the cathode and the target. The masking may, but does not have to, be in direct contact with the outer surfaces of the cathode and the target. If the masking device is made of a conductive material, it must be positioned as far around the cathode as possible without electrical contact between the masking and the outer surfaces of the cathode and the target.

[0020] Generally, the shape of the plasma source can be adapted to the diameter and size of the internal surface to be treated. For insertion into a hollow article, the outer diameter of the plasma source must be smaller than the inner diameter of the hollow article to be treated. If the plasma source is placed in front of the cavity, it can have an opening of a similar size to the cavity.

[0021] The length of the plasma source can be as long as necessary to completely treat the interior surface.

[0022] The cathode is preferably made of a high melting point material. The cathode may comprise one or more materials / elements from the following list: hafnium, molybdenum, niobium, tantalum, tungsten, titanium nitride, zirconium nitride, hafnium nitride, graphite.

[0023] The target may be intended in particular as a source of evaporation material to condense on the inner surface of the hollow article. The material of the target may therefore be adapted to the desired coating properties. When using the target for material deposition or plasma treatment, the target may optionally be placed or extended outside the masking. Plasma formation and material evaporation from the target may be achieved by maintaining a high temperature on the surface of the target, in particular in the plasma formation region.

[0024] In certain aspects, the invention may relate to a target itself or a target for use in a device of the invention. The invention may also relate to the use of a target in a device of the invention.

[0025] Such a target can be adapted to be connected to the cathode of the device of the invention. Such a connection can be achieved, for example, by a positive-locking connection, for example a plug connection or a screw connection. Thus, the target can be provided with a connection adapted to establish a connection with the cathode. In this way, the same device can be equipped with various targets. The target can, for example, have a hollow shape.

[0026] The target may comprise one or more materials / elements from the following list: aluminum, boron, carbon, chromium, cobalt, copper, gold, holmium, iron, lanthanum, lithium, magnesium, manganese, molybdenum, nickel, silicon, silver, tin, titanium, vanadium, ytterbium, yttrium, zinc, zirconium, and alloys thereof.

[0027] The plasma formation region may be formed on the target of the plasma source. In a preferred embodiment, the free end of the target also provides the plasma formation region. For example, in the case of a target having a hollow cylindrical shape, the plasma formation region may include a ring-shaped portion formed from one base of the cylinder. If the target is not covered by masking over its entire length, the plasma formation region may further include a portion of the side of the target.

[0028] The device of the invention may further comprise a gas supply channel. The gas supply channel may in particular be a channel arranged in the interior and / or central part of the plasma source. The plasma source may further comprise a gas outlet for the gas supply channel. The gas outlet may in particular be arranged in the plasma formation region.

[0029] The gas supply may be useful to achieve active cooling of the target, which may be necessary due to the elongated geometry of the plasma source. Gas provided through the gas supply channel may be beneficial to maintain the plasma only at the free end of the target. This may result in an elevated pressure at the free end of the plasma source, which preferentially focuses the plasma discharge in that high pressure region.

[0030] Gas supply channels may also be used to supply reactive gases to the coating site to affect the coating composition and / or the material properties of the coating.

[0031] The apparatus of the present invention may further comprise a vacuum chamber adapted to accommodate the hollow article to be coated and at least a portion of the plasma source.

[0032] Additionally, the apparatus may comprise a temperature control system adapted to control the temperature of the hollow article, thereby achieving a desired temperature for optimal coating properties without overheating or negatively affecting the material of the hollow article.

[0033] The apparatus holds the hollow articles in place during the entire operation (i.e., loading-processing-unloading) and may preferably include fixtures designed to fit individual workpieces to cover areas where coating is not desired.

[0034] The apparatus may further comprise an anode capable of consuming electrons emitted by the plasma source. The anode may be a separate part of the apparatus or the grounded wall or other component of the vacuum chamber. However, the hollow article itself (grounded or connected to a pulsed bias voltage) may also be suitable as the anode.

[0035] In one embodiment, the anode can be designed to be introduced into the interior of the hollow article. Such auxiliary anodes can be used to accomplish one or more of the following purposes: stabilizing the deposition process; extracting electrons from the deposition process; increasing the energy of the electrons in the process; achieving deposition of non-conductive materials; limiting and / or confining the deposition area; controlling the temperature of the hollow article; introducing additional process gases.

[0036] The process gas supplied to the plasma via the gas supply channel may be selected from one or more of the following list: hydrogen, argon, helium, krypton, neon, xenon, nitrogen, oxygen, ammonia, methane, ethane, ethene, acetylene, hexane, monosilane, metal alkyls, metal alkylamides, metal alkoxides, metal diketonates, metal carbonyls, metal cyclopentadienyls, metal halides.

[0037] The anode may also be arranged around the cathode, for example as a tubular anode, or adjacent to the cathode in any other geometric configuration.

[0038] The cathode and / or the anode may be realized with cooling elements, for example cooling channels.

[0039] In one embodiment, the device may further comprise a plasma deflection unit having at least one magnetic field source. The plasma deflection unit may be used to influence the shape and density distribution of the plasma generated by the plasma source. By modifying the plasma density, the direction and flow of the evaporated target atoms may be influenced in order to direct the deposition of material towards a desired area. Thus, a direct line of sight may not be necessary if the flight trajectory of the atoms can be influenced by the magnetic field. In a particular embodiment, the plasma deflection unit may comprise a recess in which a hollow article can be introduced. In this case, the magnetic field source may be designed in such a way that the plasma generated by the plasma source may be exposed to magnetic fields from different sides.

[0040] The plasma deflection unit can also be useful for increasing control of coating thickness distribution in undercut cavity geometries and irregularly shaped cavities.

[0041] The magnetic field source of the plasma deflection unit may be realized as a permanent magnet or an electromagnetic coil or a combination thereof.

[0042] The optional plasma deflection unit may also be positionable around the hollow article to adjust the ionization in the deposition process, in which case at least one coil or at least one permanent magnet may be positioned near the hollow article.

[0043] Optionally, the device of the invention may comprise at least one additional secondary plasma source, which may have all the features of the plasma source of the invention, but which does not have to be identical to the first plasma source.

[0044] The secondary plasma source may be inserted into the interior of the hollow article. In the case of a hollow article having a tubular shape, the secondary plasma source may be introduced into the interior of the hollow article from the opposite side to the plasma source. Two or more secondary plasma sources may be provided.

[0045] Generally, the apparatus is not only useful for forming a coating on the interior surface of a hollow article, but may alternatively or additionally be useful for modifying the properties of the interior surface of the hollow article. Thus, the plasma generated by the plasma source may also be used for modifying the interior surface of the hollow article. Such modification may include etching (i.e., removing material from the surface) and / or plasma nitridation.

[0046] The invention may also relate to an assembly of a hollow article and a device according to the invention.

[0047] The present invention further relates to a method for forming a coating on an interior surface of a hollow article and / or for modifying the properties of the interior surface of a hollow article.

[0048] In said method, a plasma source, preferably a plasma source according to the invention, may be introduced into the interior of the hollow article. The internal surface of the hollow article may then be treated, in particular coated, by the plasma source.

[0049] The coating may originate from material evaporated from a target in the plasma source and / or from gaseous materials supplied to the plasma and decomposed by the plasma.

[0050] To achieve a high density plasma, it is beneficial to create a thermionic electron emission process. This can be achieved by emitting electrons from a surface maintained at an elevated temperature. Therefore, the unmasked portion of the plasma source, i.e., the plasma formation region, should be maintained at an elevated temperature.

[0051] This is preferably achieved in a series of steps. In a first step, heating of the plasma formation area can be performed. This can be achieved by applying a pulsed or non-pulsed electric field through the cathode. Since most of the plasma source is covered by masking, no plasma is generated around the masked areas, but only in the plasma formation area. By this technique, a targeted heating of the cathode can be achieved.

[0052] Once the appropriate temperature has been achieved, in a second step, thermionic electrons can be emitted and a high density plasma can be maintained, which is typically done at a lower voltage compared to igniting the plasma and / or heating the target.

[0053] In a preferred embodiment, the pressure in the gas supply channels, in particular the pressure at the gas outlet, is higher than the pressure in the vacuum chamber, which allows the formation of a plasma with a confined shape.

[0054] Coating on the interior surface of the hollow article can be achieved by exposing the interior surface to a plasma discharge generated in a plasma formation region, while the plasma source can be located inside the hollow article or in front of the cavity opening of the hollow article. To treat the interior surface of the hollow article over a large length, the plasma source can be moved relative to the hollow article.

[0055] The plasma discharge may be generated locally in a plasma formation region at the free end of the plasma source. The plasma may be sustained by electron emission from the surface of a target of the plasma source.

[0056] The material of the coating may originate from the material of the target, which is evaporated from the target surface while the vapor condenses on the substrate surface. Additionally or alternatively, the material of the coating may also originate from the gas phase by adding reactive gases to the plasma discharge through gas supply channels and condensing or partially condensing reaction and decomposition products on the substrate. A combination of these two processes may also result in the formation of a coating.

[0057] The distribution of the coating thickness can be controlled by the power input to the plasma process, by the optional magnetic field of the plasma deflection unit, as well as by the movement of the plasma source relative to the hollow article, as well as by the pressure of the gas supplied during treatment.

[0058] Possible coating materials include, but are not limited to, nitrides, oxides, carbides, borides, silicides or metal compounds or elements. Exemplary material systems of particular interest include: metallic chromium, oxidation and / or corrosion resistant and / or wear resistant metals or alloys, CrN, CrCN, AlCrN, AlCrCN, AlN, AlCN, Ti, TiN, TiC, TiCN, TiAlN, TiAlCN, TiSiN, TiSiCN, Si, SiN, SiC, SiCN, SiO, AlSiO, AlO, AlCrO, AlON, AlCrON, CrO, CrON, MCrAlY, or C-based coatings (e.g. diamond-like carbon (DLC), amorphous carbon or ta-C). By changing the target of the plasma source or optionally using additional plasma sources, coatings including layers with different chemistries of the metal sublattice can be achieved. In general, the coating composition can be determined by using one or more plasma sources, different target materials, different process gases, pressures, temperatures and plasma parameters.

[0059] Optionally, a plasma cleaning or plasma etching process of the interior surface of the hollow article may be provided using the plasma generated by said plasma source.

[0060] Optionally, a plasma nitridation step may be performed before or during the coating process by introducing nitrogen gas into the plasma.

[0061] During material deposition, the substrate may be maintained at a floating potential, depending on the characteristics of the plasma and the deposition process itself. To adjust the properties of the deposited coating, a bias voltage may be applied to the substrate, which increases the ion bombardment of the growing coating. The bias voltage may preferably be realized in RF (radio frequency), DC (direct current), pulsed DC, or bipolar pulse mode.

[0062] The operation of the plasma source can be realized in DC or pulse mode, but is preferably realized in a bipolar operation mode, in which the cathode and anode operation are periodically reversed. In this option, it is possible to evaporate a single target, but it is also possible to evaporate material from two or more different targets, thus achieving multi-component coatings that include a mixture of materials from at least two different targets, as well as multi-layer coatings from two or more materials. As in the other described operating processes, optionally, reactive gases can be added to the process.

[0063] The plasma process preferably has a plasma pressure of 10 kW / cm2 with respect to the surface of the plasma formation region. 2 The power density is adjusted to less than 20 W / cm for Ti. 2 may not be sufficient to vaporize the material, but maintaining a continuous plasma discharge with increasing power density results in an increased evaporation rate of the target material.

[0064] The method of the present invention may include the step of heating the hollow article prior to depositing the coating, which may improve the material properties of the coating.

[0065] The method of the invention may comprise a step of cleaning the internal surface of the hollow article before depositing the coating. The cleaning step may in particular be a plasma cleaning step in which a gas, for example an inert gas such as a noble gas, or a reactive gas such as hydrogen, is introduced into the vacuum chamber. The gas may be introduced to a partial pressure between 0.1 and 100 Pa.

[0066] The plasma can then be ignited directly on the hollow article, which acts as a hollow cathode. A bias voltage can be applied to the hollow article to accelerate the generated ions to achieve sufficient kinetic energy of the bombarding species to facilitate material removal.

[0067] Optionally, if a stronger material removal rate is required, the plasma etching process can be further enhanced by adding the plasma source itself as a thermionic electron source.

[0068] The coating may be doped with additional elements to enhance or modify the properties of the coating or the deposition process itself. Thus, the final coating disposed on the interior surface of the hollow article may contain less than 20% by weight of the doping element.

[0069] Doping can be achieved by using at least one of the following: a secondary plasma source with a target containing at least one doping element; an auxiliary anode containing at least one doping element; addition of at least one doping element as a gaseous precursor through a gas supply channel; selective alloying of the target with the doping element.

[0070] The doping elements may be one or more selected from the following list: boron, aluminum, cerium, chromium, gallium, indium, phosphorus, arsenic, antimony, bismuth, lithium, germanium, silicon, xenon, molybdenum, niobium, nitrogen, oxygen, carbon, gold, silver, titanium, tungsten, platinum, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium.

[0071] The present invention can optionally be implemented in a conventional PVD system where the coating on the internal surface is realized by a plasma source according to the present invention, while the coating on the external surface of the workpiece is preferably realized by a conventional PVD coating source. This arbitrary process combination can preferably be realized in a single process, but all combinations are possible that separate the two individual process segments spatially (e.g., by providing a second chamber) and / or temporally (e.g., by providing a second process step).

[0072] The present invention may also relate to a hollow article having a coating on its interior surface, said coating being formed by the apparatus and / or method of the present invention.

[0073] The present invention relates to an apparatus for optionally forming a coating on and / or modifying a property of an interior surface of a hollow article, the apparatus comprising a plasma source having an elongated shape and including a cathode and a target, the target being a thermionic electron emission source, the target being electrically conductively connected to the cathode.

[0074] The plasma source may further comprise a masking partially covering an outer surface of the cathode and the target, the masking adapted to prevent formation of plasma over areas covered by the masking during operation of the apparatus, and a plasma formation area is provided at the target, the plasma formation area being uncovered by the masking.

[0075] The target may be hollow.

[0076] The target may have an essentially tubular shape and the plasma formation region may include a ring-shaped portion, preferably located at the free end of the plasma source.

[0077] The masking may completely cover the outer surfaces of the cathode and target, except for the plasma formation area which is not covered by the masking.

[0078] The plasma source may include a gas delivery channel having a gas outlet disposed in the plasma formation region.

[0079] The gas outlet may be disposed within the plasma formation region.

[0080] The gas supply channel at the gas outlet is 7 mm 2 It may have a cross-sectional area of:

[0081] The masking may be made of an electrically insulating material.

[0082] The masking may be made of a conductive material and the masking may not be connected in electrical continuity to the cathode and the target.

[0083] The plasma source may have a diameter of 0.1 mm to 150 mm, and / or the plasma source may have a length of 80 mm to 5000 mm.

[0084] The target may consist of or include a material selected from one or more of the following groups: a metal, such as metallic chromium, or another oxidation- and / or corrosion-resistant metal; an alloy of at least two different metals; a metal compound, such as a metal nitride, carbide, boride, oxide; or a carbon-based compound, such as graphite.

[0085] The plasma source may be disposed in a vacuum chamber, which may be adapted to accommodate the hollow article.

[0086] The apparatus may further comprise an anode adapted to consume electrons emitted by the plasma source.

[0087] The apparatus may further comprise a plasma deflection unit having at least one magnetic field source for influencing the shape of the plasma generated by the plasma source, the plasma deflection unit being positioned in proximity to the hollow article.

[0088] The plasma deflection unit may be provided with a recess into which the hollow article can be introduced.

[0089] The cathode may be integrally formed with the target, where the cathode and target may be made from the same material.

[0090] The cathode and target may be separate components connected to each other, where the cathode and target may be made from the same material or from different materials.

[0091] The present invention may also relate to a target for use in a device according to the invention and / or a target adapted for use in a device according to the invention.

[0092] The target may be connected in electrical conductivity to the cathode.

[0093] The invention may also relate to an assembly of a device according to the invention and a hollow article, in which the plasma source is inserted inside said hollow article.

[0094] The hollow article may be held by a fixture.

[0095] The present invention also relates to a method for forming a coating on an interior surface of a hollow article and / or for modifying the properties of the interior surface of a hollow article.

[0096] The method may comprise the step of inserting a plasma source of an apparatus according to the invention inside the hollow article.

[0097] The method can include generating a plasma by producing thermionic electron emission from a cathode of a plasma source.

[0098] The method may include evaporating material from a target in a plasma source and / or decomposing a gaseous precursor with the generated plasma.

[0099] The method can include depositing the evaporated and / or decomposed material on an interior surface of the hollow article to form a coating.

[0100] The generation of plasma involves the following steps: (i) igniting a plasma by applying a voltage between 100V and 1000V to the cathode; (ii) sustaining the plasma by applying a discharge voltage between 10V and 500V. a surface of the target (4) may be heated by the plasma, and a voltage in the step of igniting the plasma may be higher than a voltage in the step of maintaining the plasma.

[0101] The step of igniting the plasma may include: (ia) a first ignition phase in which a pulsed high voltage is applied to the cathode, and (ib) a second ignition phase in which a direct current is applied to the cathode.

[0102] The hollow article may be placed in a vacuum chamber of the apparatus, where the pressure in the vacuum chamber may be less than 500 Pa.

[0103] The pressure in the gas supply channels of the plasma source may be higher than the pressure in the vacuum chamber.

[0104] The power density applied to the cathode is 10 kW / cm relative to the size of the plasma formation region. 2 It may be less than.

[0105] A stream of gas may be supplied to the plasma forming region, the gas may be selected from one or more of the following: hydrogen; a noble gas; nitrogen; oxygen; ammonia; an alkane, such as methane; an alkene, such as ethane; an alkyne, such as acetylene; silanes, such as monosilane; a metal compound, such as an organometallic compound or a metal halide.

[0106] The present invention may also relate to a hollow article having a coating on its interior surface, said coating being formed by the apparatus of the present invention and / or the method of the present invention.

[0107] Further features of the invention can be derived from the claims, the drawings and the following detailed description of exemplary embodiments according to the invention.

[0108] The invention will now be described in more detail with reference to exemplary embodiments of aspects of the invention, which are not intended to limit the scope of protection which is defined solely by the features of the independent claims.

[0109] [Brief description of the drawings]

[0110] In the drawings: FIG. 1 shows a schematic cross-sectional view of a plasma source of an apparatus according to a first exemplary embodiment, the plasma source being disposed within a hollow article; FIG. 2 shows a schematic cross-section across plane AA of FIG. 1; FIG. 3 shows a schematic diagram of an apparatus according to a first exemplary embodiment; FIG. 4 shows a schematic cross-sectional view of a plasma source of an apparatus according to a second exemplary embodiment, the plasma source being disposed within a hollow article.

[0111] Unless otherwise indicated, the drawings generally show the following features: hollow article 1, plasma source 2, cathode 3, target 4, masking 5, plasma formation region 6, gas supply channel 7, gas outlet 8, vacuum chamber 9, anode 10, plasma deflection unit 11, recess 12, interior 13, connection means 14.

[0112] FIG. 1 shows a schematic cross-sectional view of a plasma source 2 of an apparatus according to a first exemplary embodiment of the invention, the plasma source 2 being arranged within a hollow article 1 .

[0113] The plasma source 2 has an essentially tubular elongated shape and comprises a cathode 3 and a target 4 electrically conductively connected to the cathode 3. The connection between the cathode 3 and the target 4 is achieved by means of connection means 14 designed as a pin, in order to obtain a telescopic connection between these two parts.

[0114] The cathode 3 and the target 4 are covered by a masking 5, which in this embodiment is made of a non-conductive material. The free end of the plasma source 2, in particular the part of the target 4 at the free end of the plasma source 2, is not covered by the masking 5.

[0115] The masking 5 serves the purpose of preventing plasma in the areas covered by said masking 5, but plasma can form in the areas not covered by the masking 5. The latter areas are therefore referred to as plasma formation areas 6.

[0116] In this embodiment, the target 4 is tubular in shape and the masking 5 completely covers the circumferential outer surface of the target 4. The plasma formation region 6 therefore has a ring shape.

[0117] The plasma source 2 of the first embodiment has a gas supply channel 7 arranged in the middle of the cathode 3 and the target 4 , with a gas outlet 8 located at the free end of the plasma source 2 .

[0118] In FIG. 1, a plasma source 2 is disposed inside 13 of a hollow article 1, which in this example is a tube.

[0119] FIG. 2 shows a schematic cross-section across the plane AA of FIG. 1, showing the hollow article 1, the target 4, the masking 5, as well as a cross-section of the interior 13 of the hollow article 1 and the gas supply channels 7.

[0120] The functioning of the device according to the first exemplary embodiment is further explained with respect to Figure 3, which shows a schematic diagram of said device. Apart from the features explained in relation to Figures 1 and 2, said device further comprises a vacuum chamber 9, an anode 10 and a fixture 14.

[0121] A vacuum chamber 9 houses the hollow article 1 as well as the plasma source 2 to allow for controlled pressure regimes to exist during the deposition process. A fixture 14 holds the hollow article 1 in place. An anode 10 is used to capture electrons generated by the plasma source 2. In this embodiment, the anode 10 is grounded.

[0122] The gas supply channel 7 of the device is connected to a gas supply (not shown) adapted to supply the desired gas. Together with the gas supply there is provided a power supply (not shown) which is connected to a power supply unit (not shown). The power supply unit is adapted to supply power to the plasma source.

[0123] In this exemplary embodiment, the target 4 is made of elemental copper having a purity of about 99.95%. The target has an outer diameter of about 6 mm.

[0124] The device of the first embodiment can be used in a method for coating the internal surface of a hollow article 1. In this example, the hollow article 1 is a pipe of about 1 m length with an internal diameter of about 1 cm.

[0125] In an exemplary embodiment of the method, the hollow article 1 is placed on a fixture 14 inside a vacuum chamber 9 .

[0126] The gas pressure inside the vacuum chamber 9 is controlled to be less than 500 Pa.

[0127] A plasma process for the treatment of the internal surface of the hollow article 1 using a plasma source 2 is achieved by thermionic electron arc emission from a target 4, while coating deposition is facilitated by interaction of the emitted electrons with the process gas and by thermionic electron evaporation of the target material.

[0128] When igniting the plasma, argon gas is introduced into the vacuum chamber 9 with a partial pressure of 8 Pa. The plasma is ignited by applying a pulsed voltage of about 450 V to the cathode 3 in a first ignition phase. The frequency of the pulsed voltage used is about 100 kHz with 50% alternation. In a second ignition phase, the power supply is switched to a direct current power supply and the voltage is reduced to about 200 V in order to achieve a discharge current of about 0.44 A. For operation, the plasma is maintained using a discharge voltage of about 120 V and a discharge current of about 0.6 A. The electrons emitted from the target during operation play a double role: first, they ionize the gas or vapor in the interior 13 of the hollow article 1. Secondly, they heat the target 4. Thus, material is evaporated from the surface of the heated target 4, which can then be deposited on the substrate inner surface.

[0129] A plasma source 2 having an outer diameter of about 9 mm is then moved through the interior 13 of the hollow article 1 .

[0130] The material of the target 4 is evaporated by the plasma and deposited on the interior surface of the hollow article 1, thus resulting in a metallic copper coating on the interior surface of the hollow article 1. By controlling the moving speed of the plasma source 2 throughout the interior 13, the desired coating thickness and thickness distribution can be controlled.

[0131] In an alternative example, the method can be carried out as a nitride coating process, when nitrogen is introduced through the gas supply channel 7. In this example, the target 4 of the above example is replaced by another target made of elemental titanium. The gaseous nitrogen reacts with the titanium in the deposition process to form TiN.

[0132] The conditions for igniting and maintaining the plasma depend inter alia on the material of the target 4. The appropriate selection of the conditions is entirely within the general knowledge of the person skilled in the art.

[0133] The coating produced by the method can include at least one layer, with a first layer adhering directly to the interior surface of the hollow article 1. By moving the plasma source 2 along the interior surface additional times, multi-layer coatings having two or more layers can be produced. Between deposition of each individual phase, the target 4 itself, the plasma source 2, the process gas composition or a combination thereof can be optionally replaced to deposit a multi-layer coating having a coating comprising a variety of compositions.

[0134] During operation of the plasma source 2, a grounded anode 10 is used to consume electrons generated by the plasma. The use of the anode 10 is particularly useful for coatings with high electrical resistivity, such as oxides, because this can result in high energy consumption, process instability, or poor coating quality.

[0135] The anode 10 at least partially consumes electrons emitted at the target 4 during the plasma discharge. The use of the anode 10 can provide additional thermal management for the hollow article 1 by reducing electron bombardment on the interior surface of the hollow article 1. Furthermore, the use of the anode 10 allows for the deposition of a non-conductive coating on the interior surface of the hollow article 1. The anode 10 can be realized in a design where it enters the interior 13 of the hollow article 1 from an opening on the opposite side to the plasma source 2.

[0136] Other configurations and / or designs are also possible for the anode 10. For example, if the cavity diameter permits, the anode 10 can enter through the same opening as the plasma source 2, or may be realized as a cylindrical tube around the plasma source 2.

[0137] FIG. 4 shows a schematic cross-sectional view of a plasma source 2 of an apparatus according to a second exemplary embodiment, the plasma source 2 being arranged within the hollow article 1 .

[0138] The plasma source 2 of the apparatus shown in FIG. 4 is similar to that of the first embodiment, except that the masking 5 does not completely cover the complete circumferential surface of the target 4, so that the plasma formation region 6 includes a ring-shaped portion as in the first embodiment, but additionally includes the outer surface of the target 4 that is not covered by the masking 5.

[0139] In further contrast to the first embodiment, the cathode 3 and the target 4 are welded to each other.

[0140] Furthermore, the device according to the second embodiment comprises a plasma deflection unit 11 which is provided with a magnetic field source. The plasma deflection unit 11 comprises a recess 12 into which the hollow article 1 can be introduced.

[0141] This additional magnetic field can be used to influence the shape of the plasma generated by the plasma source 2. In this embodiment, the magnetic field source is an electromagnetic coil. The direction of the magnetic field controls the direction of the plasma deflection, while the magnetic field strength of the field controls the curvature of the trajectories of the deflected electrons and subsequent ions. The magnetic field can further be used to fine-tune the properties and thickness distribution of the growing coating film. Thus, applying an external magnetic field makes it possible to control the coating coverage on the internal surface of a substrate with an irregular geometry.

[0142] Many applications require multi-component composite coatings. In some applications, the desired metal components and their different phases are too similar to achieve evaporation from a target 4 made of a single alloy. In a third exemplary embodiment, not shown in the corresponding drawing, a combination of at least two plasma sources 2 according to the invention is used.

[0143] The plasma sources 2 are equipped with respective targets 4 of different materials, which enter the interior 13 of the hollow article 1 at opposite or the same cavity opening. Each additional plasma source 2 can optionally function as an anode or a cathode. For example, the plasma sources 2 can be used in a bipolar pulse mode. In this mode, during a voltage pulse, a negative voltage is applied to one of the plasma sources and a positive voltage is applied to the other plasma source. This means that the plasma source 2 to which a positive voltage is applied actually acts as an anode 10, while the plasma source 2 to which a negative voltage is applied acts as a cathode 3, and evaporation of the material of the target 4 takes place.

[0144] After the voltage pulse has ended, the applied voltage can be reversed and evaporation from the other plasma source 2 occurs. With long pulse durations, a multi-layer type can be created, while with short pulse durations, evaporation from both plasma sources 2 occurs in a sufficiently close temporal relationship to allow mixing of the materials and subsequent deposition of a multi-component composite coating. This optional setup ensures that the anode 10 is always inside the plasma discharge and therefore can easily extract the emitted electrons from the plasma discharge. This ensures stable plasma conditions for the deposition of a multi-component composite coating.

Claims

1. An apparatus for forming a coating on and / or modifying the properties of an internal surface of a hollow article (1), comprising a plasma source (2), the plasma source having an elongated shape and including a cathode (3) and a target (4), the target (4) being a thermionic electron emission source, the target (4) being connected in electrical conduction to the cathode (3), The plasma source (2) further comprises a masking (5) partially covering the outer surfaces of the cathode (3) and the target (4), the masking (5) being adapted to prevent the formation of plasma on the areas covered by the masking (5) during operation of the device, and a plasma formation area (6) is provided on the target (4), the plasma formation area (6) being not covered by the masking (5).

2. 2. The apparatus of claim 1, wherein the target (4) is hollow.

3. 3. Apparatus according to claim 1 or 2, wherein the target (4) has an essentially tubular shape and the plasma formation region (6) comprises a ring-shaped portion, preferably arranged at a free end (10) of the plasma source (2).

4. 3. Apparatus according to claim 1 or 2, wherein the masking (5) completely covers the outer surfaces of the cathode (3) and the target (4), except for the plasma formation area (6) which is not covered by the masking (5).

5. 3. Apparatus according to claim 1 or 2, wherein the plasma source (1) comprises a gas supply channel (7) having a gas outlet (8) arranged in the plasma formation region (6).

6. 6. The apparatus according to claim 5, wherein the gas outlet (8) is arranged within the plasma formation region (6).

7. The gas supply channel (7) at the gas outlet (8) is 7 mm ２ 6. The device of claim 5 having a cross-sectional area of:

8. - said masking (5) is made of an electrically insulating material, or the masking (5) is made of an electrically conductive material and is not connected in electrical continuity to the cathode (3) and to the target (4); 3. Apparatus according to claim 1 or 2.

9. The apparatus according to claim 1 or 2, wherein the plasma source (2) has a diameter between 0.1 mm and 150 mm and / or the plasma source (2) has a length between 80 mm and 5000 mm.

10. The target (4) is selected from the following group: Metals, such as metallic chromium or another oxidation- and / or corrosion-resistant metal; alloys of at least two different metals; metal compounds, such as metal nitrides, carbides, borides, oxides; carbon-based compounds, such as graphite.

3. The device according to claim 1 or 2, which is made of or comprises a material selected from one or more of:

11. 3. Apparatus according to claim 1 or 2, wherein the plasma source (2) is arranged in a vacuum chamber (9), the vacuum chamber (9) being adapted to accommodate the hollow article (1).

12. 3. The apparatus of claim 1 or 2, further comprising an anode (10) adapted to consume electrons emitted by the plasma source (2).

13. 3. The apparatus according to claim 1 or 2, further comprising a plasma deflection unit (11) having at least one magnetic field source for influencing the shape of the plasma generated by the plasma source (2), the plasma deflection unit (11) being capable of being arranged in close proximity to the hollow article (1).

14. 14. Apparatus according to claim 13, wherein the plasma deflection unit (11) comprises a recess (12) into which a hollow article (1) can be introduced.

15. - said cathode (3) is integrally formed with said target (4), said cathode (3) and said target (4) being made of the same material; Alternatively, the cathode (3) and the target (4) are separate components connected to each other, where the cathode (3) and the target (4) are made of the same material or of different materials; 3. Apparatus according to claim 1 or 2.

16. 3. A target for use in an apparatus according to claim 1 or 2, wherein the target (4) may be connected in electrical conduction to the cathode (3).

17. 3. An assembly of a device according to claim 1 or 2 and a hollow article (1), wherein a plasma source (2) is inserted into the interior (13) of said hollow article (1).

18. 18. The assembly according to claim 17, wherein the hollow article (1) is held by a fixture (14).

19. A method for forming a coating on and / or modifying the properties of an internal surface of a hollow article (1), comprising the steps of: - inserting a plasma source (2) of the device according to claim 1 or 2 into the interior (13) of said hollow article (1), - generating a plasma by producing thermionic electron emission from the cathode (3) of the plasma source (2); - evaporating material from the target (4) of the plasma source (2) and / or decomposing gaseous precursors by the plasma generated; - depositing the evaporated and / or decomposed material on the internal surface of said hollow article (1) to form a coating.

20. The step of generating plasma comprises the steps of: - igniting a plasma by applying a voltage between 100V and 1000V to said cathode (3); - maintaining the plasma by applying a discharge voltage between 10V and 500V; 20. The method according to claim 19, wherein the surface of the target (4) is heated by a plasma and the voltage in the step of igniting the plasma is higher than the voltage in the step of maintaining the plasma.

21. The step of igniting a plasma includes: a first ignition phase during which a pulsed high voltage is applied to said cathode (3), and a second ignition phase during which a direct current is applied to said cathode (3); 21. The method of claim 20, comprising:

22. 20. The method according to claim 19, wherein the hollow article (1) is placed in a vacuum chamber (9) of the apparatus, the pressure in the vacuum chamber (9) being less than 500 Pa.

23. 23. The method according to claim 22, wherein the pressure in the gas supply channel (7) of the plasma source (2) is higher than the pressure in the vacuum chamber (9).

24. The power density applied to the cathode (3) is 10 kW / cm with respect to the size of the plasma formation region (6). ２ 20. The method of claim 19, wherein the

25. A stream of gas is supplied to the plasma formation region (6), said gas comprising: hydrogen; noble gases; nitrogen; oxygen; ammonia; alkanes, such as methane; alkenes, such as ethane; alkynes, such as acetylene; silanes, such as monosilane; metal compounds, such as organometallic compounds or metal halides, 20. The method of claim 19, wherein the ion exchange rate is selected from one or more of:

26. 3. A hollow article having a coating on an interior surface, said coating being formed by the apparatus of claim 1 or 2.

27. A hollow article having a coating on an interior surface, the coating being formed by the method of claim 19.

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