DE102004022358B3 - Method for coating substrates with hard materials, useful in producing radiation guides, comprises spraying them with induction plasma - Google Patents

Abstract

Method for coating substrates (40) with hard materials comprises spraying them with an induction plasma (38).

Description

The The invention relates to a hard material coating method in which a hard material layer applied by means of plasma spraying on a support becomes.

In the not previously published German Patent Application No. 10 2004 008452.1 of 13 February 2004 are structural elements which withstand corrosive and / or abrasive hot gas flows, described, which comprise a fibrous ceramic body, where the main body from a C-C molding is formed, which in a region adjacent to an upper side of the body volume area comprising a fiber-ceramic structure reacted with Si to C / C-SiC. At least on a portion of the top of the body is a applied by plasma spraying ceramic hard coating applied. This will ensure that this Structural element corrosive and / or abrasive hot gas flows withstands and at the same time has advantageous dynamic and thermal shock resistant properties.

In the articles "Plasma Spraying of Boron Carbide Using Pressures up to Two Bar" by W. Maller and D. Stover, Proceedings of the 1993 National Thermal Spray Conference, Anaheim, CA, 7-11 June 1983, pages 291 to 295, " Development and test of B ₄ C-covered heat shields for TJ-II "by C. Fuentes et al, Fusion Engineering and design 56 to 57 (2001) 315-319, pages 315-319,"Young's modulus and residual stress of plasma Sprayed boron carbide coatings "by Y. Zeng et al., Journal of the European Ceramic Society 21 (2001) 87-91, pages 87 to 91 and" Study on Plasma Sprayed Boron Carbide Coating "by Y. Zeng et al., Journal of Thermal Spray Technology, pages 129 to 133 plasma-sprayed boron carbide coatings are described.

In the article "Special features on impact and cooling induction plasma-sprayed ceramic particles "by B. Dzur et al., Galvanotechnik 91 (2000) No. 6, pages 1674 to 1679 are investigations of the deformation individual particles on a smooth substrate described.

From the US 4,897,282 a method for producing a coating is known, wherein particles of the coating material are evaporated by plasma heating. An inductively coupled plasma is used for this purpose.

From the article "SiC Coating Synthesis by RF Induction Plasma Spraying from Liquid Silane Precursor" by E. Bouyer et al., Thermal Spray Surface Engineering via Applied Research, Proceedings of the 1 ^St International Thermal Spray Conference, May 8 to 11, 2000 , Montreal, Quebec, Canada, pages 919-928 describe methods for alpha / beta SiC ceramic synthesis and deposition utilizing high frequency induction plasma.

Out the article "Reactive deposition of tungsten and titanium carbides by induction plasma "by X. L. Jiang et al., Journal of Materials Science 30 (1995), pages 2325 to 2329 is the use of induction plasmas for the preparation of dense freestanding Deposits of tungsten carbide and titanium carbide from metallic Powders and methane described.

at However, the plasma spraying of boron carbide layers occur considerably Problems on (see the article by W. Malléner and D. Stöver).

Of the The invention is therefore based on the object described above Process to improve so that can be produced in a simple way defined hard material layers.

These The object is achieved according to the invention in the method mentioned solved that the hard material layer is sprayed by means of an induction plasma.

One Induction plasma can be in comparison with a DC plasma with the same power supply in a larger volume produce. A corresponding plasma jet then points at an induction plasma also a higher one Volume up. This allows particle velocities in one Plasma jet, which is a carrier for Applying a hard coating applied, in comparison greatly reduce to a DC plasma. The abrasive effect of the entrained in a plasma jet Injection molding is thereby greatly reduced. This means that damage of the carrier are greatly reduced by the plasma and particle beam itself and the layer removal by the plasma jet compared to a DC plasma jet is greatly reduced. In the inventive solution, in which uses an induction plasma jet for coating application will get Therefore, a significantly improved Pulveraufschmelzung at considerable reduced abrasive attack of the vehicle.

It Homogeneous layers can be produced that reduce one Variation width, for example, in terms of thickness, porosity and adhesion on the substrate.

In particular, a high frequency plasma source is used for plasma generation. At a High-frequency plasma source is provided at least one induction coil, in which a plasma is generated inductively, that is by inductive coupling. As mentioned above, induction plasmas can be produced in a larger volume range than DC plasmas (arc plasmas).

Especially a plasma jet is generated by means of an induction plasma. On the Plasma jet can be then apply a hard coating on a carrier. Especially can be melted powder materials for layer production.

As "melting material" is in particular a Hard material a plasma space in which an induction plasma is generated, fed. The plasma space is the space in which the plasma is created. Appropriate Hard material particles are then through the plasma jet as Entrained particle beam and melted and applied to the support, where by solidification the molten particles a hard material layer is produced.

Especially the hard material is supplied in powder form. This can be done a uniform order to achieve layer production.

It has been considered favorable proved when the hard material with a carrier gas the Plasma room supplied becomes. It can be thereby ensuring a homogeneous supply of powder to the plasma space, wherein the powder feed is in particular substantially pulse-free. This in turn makes it possible to produce layers that are homogeneous, that means little for example, vary Thickness, porosity and liability on the carrier.

Especially For example, the hard material is aerosolized in a carrier gas stream supplied to the plasma room. This can be done a uniform homogeneous Ensure hard material supply to the plasma chamber.

It has proved to be advantageous if the hard material is supplied by means of a powder conveyor and in particular a fluidized bed conveyor to the plasma chamber. An example of such a powder conveyor is in the DE 101 34 498 A1 described.

Especially is the powder conveyor designed so that the feed of hard material in the plasma space substantially pulse-free is. This ensures a homogeneous uniform hard material supply in the plasma room. This in turn allows homogeneous layers produce.

Cheap is it, if the promotion of the hard material in a plasma space to the plasma power customized becomes. As a result, good coating results can be achieved. If the plasma power is too low compared to the flow, then let yourself only part of the subsidized material melt. If the plasma power is too high, then energy will not used and under circumstances the coating result is degraded because the plasma jet is too high in energy and thus the hard material completely or partially evaporated.

All It is particularly advantageous if the hard material axially Plasma space is supplied. By an axial Hartstoffmaterialinjektion in the plasma space can be achieve a better powder melting.

Especially the hard material is supplied to the plasma chamber centrally. Also this carries to an improved powder reflow.

All It is particularly advantageous if the hard material substantially coaxially to an axis of the plasma chamber is supplied to the plasma chamber. As a result, the best melting results have been achieved to let.

constructive Cheap it is when relative to the hard material layer application of the carrier is moved to a plasma source and in particular in a plane is moved. This can be done a flat layer produce without the Plasma source itself must be moved.

to Plasma formation is a working gas used. It is cheap, though this working gas includes helium. Helium increased the "toughness" of the plasma that is called the heat and momentum transfer from the plasma to the sprayed material is improved.

It is also cheap when the working gas comprises argon. Argon relaxes ionise easily.

It has also been shown that it Cheap is when the working gas comprises hydrogen. About hydrogen in the working gas let yourself an enthalpy increase at the end of the flight path due to recombination heat. About that out can be with hydrogen to prevent oxidation of the carrier.

Especially is the working gas for plasma formation a mixture to the cheap Properties of various gases such as easy ionizability, improvement the heat transfer and enthalpy increase to use on the flight path.

Conveniently, the largest volume fraction in the mixture is the proportion of that gas which contributes significantly to the plasma formation, the means the gas which is easily ionizable. In particular, it is an argon fraction.

It is then cheap, if the smallest volume fraction in the mixture is a hydrogen component is because hydrogen is hard to ionize.

All it is particularly advantageous if the particle velocity (the Hard material particles) when hitting the carrier smaller than 100 m / s and in particular less than 50 m / s. This is reduces the abrasive effect of the plasma / particle beam. at the method according to the invention, at When an induction plasma is used, particle velocities can also be determined reach significantly less than 100 m / s.

It can be provided that the carrier is a fiber composite material. It can be characterized, for example Producing structural elements with low weight. The fiber composite, which basically is highly sensitive to Hot gas corrosion or abrasive particles, can be through just protect the hard coating.

For example contains the fiber composite carbon fibers and / or ceramic Fibers such as SiC fibers or alumina fibers.

Of the carrier may be made of a C / C-SiC fiber ceramic material.

When Hard material materials can be, for example, carbides, borides or nitrides.

One particularly advantageous material is boron carbide. Boron carbide settles with the method according to the invention defined example, apply to a fiber composite material. By the method according to the invention can be produced Borkarbidschichten, which in particular a Thickness smaller than 1 mm. It can be layers with great homogeneity in particular in terms of Thickness, porosity and create adhesion to the carrier. The influence of the carrier by the plasma / particle beam can be minimized. boron carbide itself has the advantage that from about 1100 ° C a higher one Hardness as Diamond at this temperature has and therefore also beneficial in be called Atmospheres used can be. According to the current state of research Boron carbide is one of the hardest known materials at temperatures above 1100 ° C.

Especially is with the method according to the invention a hard material layer for a thruster made. Thrusters are near outlet ends used by engines. With them a missile can be controlled. Thrusters are exposed to corrosive and / or abrasive hot gas flows. By the coating method according to the invention let yourself produce a hard material coating, which provides appropriate protection for the body represents the thruster.

The Hard material coating method according to the invention let yourself for the production of jet thrusters use.

The The following description of preferred embodiments is used in conjunction with the drawing of the closer explanation the invention. Show it:

1 a schematic representation of a system for carrying out the method according to the invention;

2 a micrograph of a boron carbide layer produced by means of the inventive method on a C / C-SiC fiber ceramic and

3 a schematic representation of an embodiment of a flying object with Strahlrudern.

An exemplary embodiment of a plasma spraying system with which the hard material coating method according to the invention can be carried out is disclosed in US Pat 1 shown schematically and there as a whole with 10 designated. This plasma spray system 10 includes a high frequency plasma torch apparatus 12 as a plasma source in which an induction plasma (high-frequency plasma) can be produced. For this purpose, the high frequency plasma torch device 12 one or more induction coils 14 on. This at least one induction coil 14 is in a housing 16 arranged.

The at least one induction coil 14 is coupled to a high frequency generator. Corresponding connections are in 1 by the reference numeral 18 indicated.

By the at least one induction coil 14 is a plasma chamber in a plasma chamber 20 formed in which just an induction plasma (high-frequency plasma) can be generated. This plasma room 20 is through the at least one induction coil 14 limited; the induction coil 14 surrounds the plasma room 20 , The plasma room 20 has a substantially cylindrical shape.

For plasma formation, a working gas in the plasma chamber 20 blown. This is a corresponding feeder 22 intended. This is connected to a working gas source or with a mixing device 24 , by means of which a working gas can be produced as a mixture of different gases. Via supply lines 26 . 28 then the working gas in the plasma chamber 20 blown.

In the embodiment shown, working gas is used as central gas centrally in the plasma chamber 20 coupled. This is done via the supply line 26 , This leads at least approximately axially into the plasma chamber 20 , with a corresponding mouth in the plasma chamber 20 substantially coaxial with an axis 30 the plasma room 20 is arranged. It can be provided that the central gas is given a radial component during injection.

Further, working gas as sheath gas in the plasma chamber 20 blown. The supply line 28 has to a corresponding mouth, which the mouth of the supply line 26 for example, surrounds annular.

For feeding hard material 32 in the plasma room 20 is preferably a powder conveyor 34 intended. This is especially designed as a fluidized bed conveyor, on the hard material largely pulse-free the plasma space 20 can be fed.

An example of a fluidized bed conveyor is in DE 101 34 498 A1 discloses, to which reference is expressly made.

About the powder conveyor 34 can be hard material 32 as an aerosol in a carrier stream of a carrier gas to the plasma chamber 20 respectively. This is a corresponding supply line 36 intended. This supply line 36 flows centrally into the plasma chamber 20 that is, a mouth opening into the plasma space 20 is centrally located and is in particular coaxial with the axis 30 of the plasma room 20 , This mouth is arranged so that the hard material 32 axially, that is parallel or coaxial with the axis 30 in the plasma room 20 is insertable. As a carrier gas, for example, argon is used, which can be ionized easily.

In the high frequency plasma torch apparatus 12 becomes a plasma / particle beam 38 generated over the hard material 32 on a carrier 40 melts to produce a hard coating. Such an injection process takes place in a reactor 42 in which the carrier 40 is positioned. The plasma / particle beam 38 exits the high frequency plasma torch device within the reactor 42 out. For shaping the plasma / particle beam 38 at the exit, a corresponding nozzle may be attached to the high frequency plasma torch apparatus 12 be arranged.

The carrier 40 is preferably positioned on a movable carrier holder. This is for example designed as a carriage, which is one or more coordinate directions movable. (In the embodiment according to 1 this mobility is indicated by the X direction and Z direction. It can also be provided a mobility in the Y direction.) It can also be provided a pivoting or rotation.

In a workroom 44 of the reactor 32 are defined pressure conditions adjustable. In particular, negative pressure conditions can be set. These are to the reactor 42 one or more pumps 46 coupled, in particular a defined pressure in the reactor 42 to be able to adjust. Preferably, corresponding filters are also provided to remove particles from the pump or pumps 46 to be able to hold.

The hard material coating process according to the invention functions as follows:
In the plasma room 20 An induction plasma (high-frequency plasma) is generated. For this purpose, the at least one induction coil 14 acted upon by the high-frequency generator with a high-frequency alternating field. The plasma is produced in the working gas by inductive energy coupling.

It has proved to be advantageous if the working gas is a mixture of a gas which is easily ionizable, such as argon and a gas which ensures a good heat transfer, such as helium. Furthermore, it is favorable if hydrogen is mixed in, since an increase in enthalpy in the flight path is achieved via hydrogen. About hydrogen can be further an oxidation of the carrier 40 prevent.

It has proved to be favorable when the largest proportion in the mixture is the argon content and the smallest proportion in the mixture is the hydrogen content. For example, about 90 liters of argon 20 Liters of helium and 2 liters of hydrogen mixed.

Into this induction plasma becomes the hard material 32 introduced centrally as a powder.

The (subsonic) plasma / particle beam 38 gets on the carrier 40 directed, in which case the hard material is melted, so as to produce a hard material coating. By movement of the vehicle 40 in the reactor 42 in the X and Y directions, a flat layer can be produced. By pivoting or rotation of the carrier 40 It is also possible to coat edges and front sides.

The mobility in the Z direction allows the distance between the high-frequency plasma torch device 12 and the carrier 40 Adjustab len.

It has proven to be beneficial if the plasma spraying is carried out under atmospheric pressure. For example, the pressure is in the reactor 42 between about 300 mbar and 1 bar. At too low pressures an induction plasma is no longer stable and at atmospheric pressures, the conditions are energetically unfavorable.

In a concrete embodiment has a plasma chamber 48 in which the plasma room 20 is formed, an inner diameter of 50 mm. The frequency of the application current was 500 kHz. The plasma power was between 15 and 40 kW and in particular between 22 and 25 kW.

The delivery rate of the hard material 32 in the plasma room 20 was adapted to the plasma power, so that essentially all of the plasma space 20 supplied hard material 32 could also be melted for coating production. A typical feed rate was 0.2 g / min.

A distance A in the direction Z between a front end of the high frequency plasma torch apparatus 12 and the carrier 40 was between 80 mm and 280 mm.

When Hard materials are, for example, carbides, borides or nitrides. An advantageous material is boron carbide. through Boron carbide can produce very hard coatings that are corrosion resistant are and have a high abrasive strength. Such a coating has a very high hardness at about 1100 ° C on, so that coated accordingly Structural elements even at correspondingly high temperatures a high Have corrosion resistance and abrasion resistance.

Structural elements, which corrosive and / or abrasive hot gas flows withstand and a fibrous ceramic body include, wherein the main body formed from a C-C molded body which is in an adjacent to an upper side of the body Volume range one with Si to C-C-SiC reacted fiber-ceramic structure and in at least a portion of the top of the basic body a ceramic hard material layer produced by plasma spraying is applied in the non-prepublished German patent application No. 10 2004 008452.1 of the same Applicant (Filing date 13 February 2004). This application is expressly referred to taken.

A layer produced by the method according to the invention is a microsection in FIG 2 shown. It can be seen on the lower side of the carrier 50 which consists of a C / C-SiC fiber ceramic, that is a fiber ceramic material in which carbon fibers are embedded. On this carrier 50 is a boron carbide layer 52 applied by the method according to the invention. This boron carbide layer 52 protects the underlying wearer 50 regarding corrosion and abrasion. The grain size of the (boron carbide) powder in the feed was between 8 μm and 32 μm.

In the 2 noticeable black areas are not pores in the boron carbide layer 52 but on the ground surface remaining drops of a preparation.

According to the invention, a hard material layer is sprayed by means of an induction plasma, that is to say by means of a high-frequency plasma. In a high-frequency plasma torch can the plasma chamber 20 form with the same power input with a much larger volume than a DC plasma torch (arc plasma torch) with the same power supply. This in turn has the plasma jet 38 , which is generated via the induction plasma, a larger volume. This allows for better powder reflow. In particular, this means considerably smaller particle velocities of hard material particles in the plasma jet 38 reached. It is possible to achieve speeds of less than 50 m / s. For example, particle velocities can be achieved that are less than 10% of the corresponding particle velocities in a plasma arc of an arc plasma. Because of the larger volume of the plasma space 20 or the plasma jet 38 the density in the plasma is reduced and thereby lower natural oscillations are present, just a lower particle velocity can be achieved. Due to the lower particle velocity, however, the abrasive effect of the plasma jet is again 38 significantly reduced with hard particles, so that the layer structure on the support 40 is greatly improved.

Furthermore, by the axial injection of the hard material 32 in the plasma room 20 the powder reflow greatly improved.

By using a substantially pulse-free powder conveyor 34 is a homogenization of the supply of the hard material 32 in the plasma room 20 ensured. This in turn can ensure that homogeneous layers on the support 40 be deposited. The corresponding injection process avoids strong variations in thickness, porosity and carrier adhesion.

By the use of an induction plasma, the in the literature (article by W. Mal Léner and D. Stöver) and could (see 2 ) Boron carbide coatings as an example of hard coatings on a substrate 40 such as a C / C-SiC fiber ceramic. For example, a coating having a thickness of 0.2 mm of an edge and an edge of a thruster was produced.

In 3 are based on an embodiment of an engine 54 thruster 56a . 56b shown. Such thruster 56a . 56b can be prepared, for example, from a C / C-SiC fiber ceramic, which at one edge 58 and on flanks 60a . 60b coated with a hard material layer.

At the engine 54 is in a housing 62 arranged a propellant with a solid fuel. The propellant 64 can with a central channel 66 be provided.

At a usually rear end 68 of the housing 62 closes a tail cone 70 in which a nozzle 72 is arranged. In operation, this nozzle 72 from a hot gas flow 74 interspersed when burning the propellant 64 formed. The hot gas flow occurs in the region of the end 68 out of the case 62 out. The hot gas flow 74 enters a propellant end 76 the nozzle 72 on and off an exit end 78 into the environment, with the nozzle 72 between the propellant end 76 and the exit end 78 a narrowing 80 having.

The thrusters 56a . 56b are near the exit end 78 the nozzle 72 intended. They serve to the hot gas flow 74 immediately before exiting through the exit end 78 to influence, so that a flying object, which with the engine 54 is provided to direct.

For example, the tail cone comprises 70 additional additional, air-stabilizing air control surfaces 82 , These are also referred to as fins.

Because the hot gas flow 74 in the solid propellant 64 not only hot gases but also corrosive and / or abrasive particles due to the burning off of the solid, the thrusters must 56a . 56b resistant to corrosion and resistant to abrasive particles. This is inventively by the coating by means of the hard material 32 such as boron carbide reached.

Also the hot gas flow 74 leading inner wall 84 the nozzle 72 can be provided with a corresponding hard coating.

It will be on the above mentioned not pre-published German Patent Application No. 10 2004 008452.

thruster 56a . 56b , which were coated by means of the method according to the invention with boron carbide, show compared to uncoated Strahlrudern significantly increased life. Only by the use of an induction plasma satisfactory and good coating results were achieved.

Claims (29)

Hard material coating method in which a hard material layer is applied by means of plasma spraying onto a carrier, characterized in that the hard material layer is sprayed by means of an induction plasma. Hard material coating method according to claim 1, characterized in that a High-frequency plasma source is used for plasma generation. Hard material coating method according to claim 1 or 2, characterized in that a plasma / particle beam is generated by means of an induction plasma. Hard material coating method according to one of the preceding Claims, characterized in that hard material a plasma space in which an induction plasma is generated, is supplied. Hard material coating method according to claim 4, characterized in that the Hard material is supplied in powder form. Hard material coating method according to claim 4 or 5, characterized in that the hard material with a carrier gas supplied to the plasma room becomes. Hard material coating method according to claim 6, characterized in that the Hard material as an aerosol in a carrier gas stream the plasma space supplied becomes. Hard material coating method according to one of claims 5 to 7, characterized in that the Hard material is supplied by means of a powder conveyor to the plasma chamber. Hard material coating method according to claim 8, characterized in that the powder Feeder is designed so that the feed of hard material in the plasma space substantially pulse-free is. Hard material coating method according to claim 8 or 9, characterized in that a powder conveyor Fluidized bed conveyor is used. Hard material coating method according to one of the preceding Claims, characterized in that the output of the hard material in the plasma space is adapted to the plasma power. Hard material coating method according to one of the preceding Claims, characterized in that the Hard material is fed axially to a plasma chamber. Hard material coating method according to one of the preceding Claims, characterized in that the Hard material is supplied to the plasma chamber centrally. Hard material coating method according to claim 13, characterized in that the Hard material substantially coaxial with an axis of the plasma space supplied to the plasma room becomes. Hard material coating method according to one of the preceding Claims, characterized in that the Hard material layer deposition of the supports relative to a plasma source is moved. Hard material coating method according to one of the preceding Claims, characterized in that a Working gas for plasma formation comprises helium. Hard material coating method according to one of the preceding Claims, characterized in that a Working gas for plasma formation comprises argon. Hard material coating method according to one of the preceding Claims, characterized in that a Working gas for plasma formation comprises hydrogen. Hard material coating method according to one of the preceding Claims, characterized in that the Working gas for plasma formation is a mixture. Hard material coating method according to claim 19, characterized in that the largest volume fraction in the mixture is an argon content. Hard material coating method according to claim 19 or 20, characterized in that the smallest volume fraction in the mixture is a hydrogen content. Hard material coating method according to one of the preceding Claims, characterized in that the Particle velocity when hitting the carrier smaller than 100 m / s. Hard material coating method according to one of the preceding Claims, characterized in that the carrier is a fiber composite material. Hard material coating method according to claim 23, characterized in that the Fiber composite carbon fibers and / or ceramic fibers includes. Hard material coating method according to claim 23 or 24, characterized in that the carrier of a C / C-SiC fiber ceramic is made. Hard material coating method according to one of the preceding Claims, characterized in that as Hard material carbides, borides or nitrides are used. Hard material coating method according to one of the preceding Claims, characterized in that boron carbide is used as hard material. Hard material coating method according to one of the preceding Claims, in which a hard material coating is produced for a structural element, which serves the hot gas guide and / or hot gas atmosphere is. Use of the hard material coating method according to one of the preceding claims for the production of jet thrusters.