EP0883697A1

EP0883697A1 - Device and method for preparing and/or coating the surfaces of hollow construction elements

Info

Publication number: EP0883697A1
Application number: EP97903375A
Authority: EP
Inventors: Valentin Grossmann; Horst Pillhöfer; Martin Thoma
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1996-02-29
Filing date: 1997-02-26
Publication date: 1998-12-16
Anticipated expiration: 2017-02-26
Also published as: EP0883697B1; WO1997032054A1; CA2246805A1; CA2246805C; DE19607625C1; US6180170B1; ES2145573T3

Abstract

The invention concerns a device and method for preparing and/or coating the surfaces of hollow construction elements which have at least two openings linking their outside and inside surfaces. First, at least two reactant-gas mixtures (I, II), for treatment of the outside and inside surfaces of the construction elements are prepared using gas generators, and the first mixture (I) is passed over the outside surfaces and then over the inside surfaces of the construction elements while the second mixture (II) is passed over the inside surfaces and then over the outside surfaces of the construction elements.

Description

Device and method for preparing and / or coating the surfaces of hollow components

The invention relates to a device and a method for the preparation and / or coating of the surfaces of hollow metal components. which have at least two connecting openings between their outer and inner surfaces.

For the preparation and / or coating of the surfaces of hollow metal components which have at least two connecting openings between their outer and inner surfaces, EP 0349420 describes in particular for hollow blades in turbo engine construction

Method with device known, in which a cleaning gas mixture or a coating gas mixture is generated below a blade in a reaction chamber. The blade hangs in the reaction space from which the outer surfaces can be cleaned or coated and the reaction gas first flows around the outer surfaces in one direction and then through a first opening in the hollow blade into the cavities on the inner ones

Surfaces past and finally out of the cavities through a second opening in the hollow blade into an exhaust pipe for disposal or recycling of the residual gases of the reaction gas.

Such devices and methods have the disadvantage that the concentration of individual

Reaction components which are contained in the reaction gas and which react with the surfaces, on the way through the outer surfaces, the first opening, the inner surfaces until they exit the second opening, sink in such a way that considerable reaction differences between the outer and inner surfaces and in the course of the inner surfaces occur.

The differences between outer and inner surfaces are partially overcome by the measures as described in the patents DE 4035 789 and DE 41 19967. However, it can be seen that the differences in the course of the inner surfaces from the entry into the cavities to the outflow from the cavities with the previous ones Procedures can not be significantly improved. The improved methods and devices also have the disadvantage that they require retort structures that are extremely complex and not very variable and appear unsuitable for mass production.

Another major disadvantage is that the known devices and methods do not allow different gas sources for the treatment of the outer and inner surfaces.

These tasks are solved as far as a procedure is concerned with the following steps:

a) providing at least two reaction gas mixtures (I, II) by reaction gas sources for treating the outer and inner surfaces of the hollow components,

b) passing the first reaction gas mixture (I) over the outer surfaces and then over the inner surfaces of the components,

c) guiding the second reaction gas mixture (II) over the inner surfaces and then over the outer surfaces of the components.

This method has the advantage that, with the same action of the reaction gases on the inner surfaces of the same hollow components, a greater homogenization of the reaction results compared to the previous methods, both for a preparation such as reduction of sulfide or oxide surface contaminations and for a coating of the inner surfaces with protective layers against oxidation, corrosion or sulfidation. If the inner surfaces form channels, as are known in the case of hollow turbine or compressor blades, double the channel length can be cleaned or coated compared to cleaning and coating using conventional methods, since the reaction gases not only move the cavities in one direction, but from two opposite ones Can flow through directions in succession.

In a preferred implementation of the method, the reaction gas mixtures (I. II) are composed of similar components, and the direction of flow of the reaction gases is changed several times over the surfaces of the hollow component by repeating steps b) and c). This interval method has the particular advantage that the projections and other obstacles are present on inner surfaces, and reduced effects, for example between the windward and leeward sides of the obstacles, can be eliminated. Another advantage is that higher flow velocities can be used since the wind and leeward effects are compensated for. This means that the hitherto customary creep speeds when flowing through inner surfaces to avoid the formation of differences between the windward and leeward sides at obstacles which can lead to premature depletion of the reaction components no longer have to be maintained, so that firstly the premature depletion is overcome, and secondly a high uniformity of the preparation and / or the coating is achieved, which is particularly the case with coatings by the

Measurement of the coating thickness is detectable. Finally, this method variant reduces the duration of the method if the same preparation and / or coating results can be achieved as with conventional methods or devices.

In a further preferred implementation of the method, at least one of the reaction gas sources provides reaction gases which are used to clean outer and inner surfaces, preferably halogen-containing gases. Among these, chlorine- or fluorine-containing gases, which have a caustic effect on the surfaces to be cleaned, have proven their worth.

The reaction gas sources do not always have to be of the same type. In the case of surface preparations, at least one of the reaction gas sources preferably supplies reaction gases which serve to reduce sulfidic or oxidic deposits on the outer or inner surfaces, preferably hydrogen-containing gases and which in a preferred direction provide the surfaces 4 flow around the components, while a different type of coating source acts in the direction set. Flushing gases for cleaning a system before treated components are removed from the system can flow around the surfaces in the reaction spaces in a preferred direction, for example to drive toxic components in the preferred direction. Furthermore, connecting holes between outer and inner

Component surfaces, as are known in turbine blades as film cooling bores, are kept free of undesired deposits and unwanted contaminants during a cooling phase after a coating process by an inert gas in the direction of the reaction gas mixture II from the inside to the outside via the connecting holes while the components flows through the cooling phase.

The second reaction gas (II) can consequently be a coating reaction gas, such as preferably a chromating or alitizing reaction gas, a reducing gas, such as preferably a hydrogen-containing gas or an inert gas. The inert gas is preferably used in the heating or cooling phase.

In the case of a gas diffusion coating of the outer or inner surfaces, preferably gases containing halide decompose on the metallic outer or inner surfaces of the hollow components into a metallic component which is deposited as a coating on the outer and inner surfaces and a halogen component which can be reused as an activator. The depletion of the metal source and the dilution of the reaction gas is particularly serious at the flow rates of conventional methods and has a negative effect on an equalization of the layer thicknesses, which is overcome by the method according to the invention.

In order to be able to carry out the method according to the invention and to overcome the disadvantages of the previous devices, which due to their complexity are unsuitable for a single blade for mass production, a device is specified with the features of claim 6. This device is suitable for the preparation and / or coating of the surfaces of metallic hollow components which have at least two connecting openings between their outer and inner surfaces. The device has a reaction container with an outer reaction space and a central holding tube. Removable, hollow support arms aligned radially to the holding tube are arranged on the holding tube. These can each hold at least one hollow component and usually carry up to 30 hollow components, a first connection opening of the components being connected to the outer reaction space and a second connection opening being connected to the interior of the holding tube via the hollow support. The reaction gases from the outer reaction space flow first over the outer surfaces of the hollow components and then over the first connection opening to the inner surfaces of the hollow components. They are guided to the interior of the holding tube via the second connection opening in the hollow components and via the support arms. Conversely, the reaction gases from the interior of the holding tube via the support arms through the second connection opening of the component first over the inner surfaces and then through the first connection opening over the outer surfaces of the components in the outer

Flow reaction space.

This device has the advantage that the surfaces of the components can be flowed around in succession or alternately from two opposite directions. The removable support arms can be separated and equipped with hollow components outside the reaction spaces. The hollow components on the support arms can have different structures and are individually adapted to the support arms and gas-tightly connected to the hollow support arms with the second connection opening. Several support arms are then connected to the holding tube via uniform connection openings. These connections can be conical, spherical, flange-like or sleeve-shaped. They are preferably designed as hemispherical, releasable connections.

The support arms are finally attached to a fir tree, the support tube, like a branch, the branch and tree trunk being hollow and the tree trunk being an internal reaction gas source can take up, which is thus advantageously separated from the outer reaction space. so that the surfaces of the hollow components can flow around from opposite directions.

In a preferred embodiment of the device according to the invention are on the outside

Reaction space between the carrier arms radially arranged to the holding tube outer pellet baskets fastened with a first reaction gas source material. Reactipons gas source materials of this type are known for gas diffusion processes from US Pat. No. 5,071,678 and consist of halogen granules which are gaseous at high temperatures as an activator, metal donor granules and fibers such as granular metal oxides. They are advantageously suspended in the outer reaction chamber in the vicinity of the surfaces to be coated in granule baskets which are positioned between the carrier arms and, in a further preferred embodiment of the invention, are arranged with the carrier arms in several layers one above the other on the holding tube. As a result, up to 1000 hollow components can advantageously be coated in one batch on their outer and inner surfaces.

Such a device can also be expanded as desired and is suitable for mass production.

A second reaction gas source material is preferably arranged in the interior of the holding tube in inner granule baskets. One advantage is that if the source material is the same, the

Surfaces are flowed around from two directions and thus windward and leeward effects on obstacles and sharp edges are largely compensated for at high flow rates. In addition, different reaction source material can preferably also be used, so that, for example, chromium is predominantly deposited on the inner surfaces if the inner granule baskets carry a chromium-containing reaction gas source and a predominantly aluminum-containing coating is carried out on the outer surfaces when the outer granulate baskets in the outer reaction chamber have aluminum-containing donor granules. In order to ensure safe switching of the gas flow directions, the holding tube is preferably located centrally on the bottom of the reaction vessel and the bottom of the reaction vessel has at least one first inlet or outlet opening for the outer reaction space and at least one second inlet or outlet opening for the interior of the holding tube.

The following figures and examples explain preferred embodiments and application examples of the present invention.

1 shows a partial area of a device according to the invention for carrying out the method according to the invention.

2 shows a top view of a layer made of granulate baskets and carrier arms of the device according to the invention

3 shows a hollow blade which is suitable for use in the device according to the invention and in the method according to the invention.

1 shows a partial area of a device according to the invention for carrying out the method according to the invention. For the preparation and / or coating of the surfaces of hollow metal components 100, these are arranged in support arms 1 to 60, so that the hollow components 100 are located between two reaction gas sources 201 to 280 and 290. These reaction gas sources 201 to 280 and 290 provide two reaction gas mixtures (I, II) for treating the outer and inner surfaces of the hollow components 100, a first reaction gas mixture (I) of the first reaction gas source 201 to 280 in an outer reaction space 110 in Direction of arrow A over the outer surfaces and then over the inner

Surfaces of the components 100 is guided and a second reaction gas mixture (II) of the second reaction gas source 290 in a second reaction space 120 in the direction of arrow B is first passed over the inner surfaces and then over the outer surfaces of the components 100. The direction of the reaction gas streams can be staggered in time between the streams. directions A and B can be changed several times in order to compensate for windward and leeward effects on obstacles and sharp edges of the hollow components 100 on the outer and inner surfaces of complex components 100 in the direction A or B.

One of the reaction gas sources can also be connected upstream of the outer or inner reaction space 110 and through reaction openings 111 or 121 in the bottom 131 of the reaction vessel, such as halogen-containing gases, which are preferably used for cleaning the outer and / or inner surfaces, respectively. Hydrogen-containing reducing gases are also supplied from external sources via the supply openings 111 and 121 to the outer and / or inner surfaces for reducing sulfidic or oxidic deposits, with at least one of the two granule basket arrangements as described in positions 01 to 280 or Item 290 show, can be dispensed with.

For a gas diffusion coating of the outer or inner surfaces of the hollow components 100, gases containing halide are generated in the outer or inner reaction space 110 or 120. These reaction gases partially decompose on the metallic outer or inner surfaces of the hollow components 100 into a metallic component, which Coating is deposited on the outer and inner surfaces and a gaseous halogen component which can be reused as an activator after it has condensed on cool surfaces or transported donor metal atoms to the outer or inner surfaces of the hollow components 100 in heated rooms as activator gas. In order to maintain the transport in the opposite directions A and B according to the invention, an inert carrier gas, such as argon, is usually required, which is passed successively in the direction of arrow A or B over the outer or inner surfaces of the hollow components 100 to be coated and carries the reaction gases with them .

The device for the preparation and / or coating of the surfaces of metallic hollow components 100 is only suitable for components which have at least two connecting openings 103, 104 between their outer and inner surfaces. A first connection The opening 103 of the component 100 is connected to the outer reaction chamber 110. A second connection opening 104 is connected via the hollow support arm 1 to 60 to the interior of a holding tube 105, which in this example also serves as an inner reaction space 120. Thus, reaction gas from the first reaction gas source 201 to 280 can flow from the outer reaction space 110 first over the outer surfaces and then over the first

Flow connection opening 103 to the inner surfaces of the components 100 and via the support arms 1 to 60 to the interior of the holding tube 105 in the direction of arrow A. Conversely, reaction gas can flow from the interior of the holding tube 105 via the support arms 1 to 60 through the second connection opening 104 of the component 100 first via the inner surfaces and then through the first connection opening 103 via the outer surfaces of the components 100 into the outer reaction space 110 in Flow in direction of arrow B.

For this purpose, the hollow components 100 are fastened and sealed with their second connecting opening 104 in the hollow support arm 1 to 60. This seal is achieved with a sealing compound 108, such as a sintered compound, with, for example, a lower end 106 of the hollow component

100 protrudes with the second connection opening 104 into the cavity 107 of the support arm 1 to 60 and is kept free of sealing compound 108 in the opening area. The hollow support arms are detachably connected radially outward to the central holding tube 105. The detachable connection 109 consists of a conical, spherical, hemispherical or flange-like seat 112, which has a pawl-like latching device 113, which enables the carrier arms 1 to 60 to be quickly attached to the central hollow tube 105.

2 shows a top view of a sectional plane CC of a layer composed of granule baskets 201 to 220 and support arms 1 to 20 of the device according to the invention. The granule baskets 201 to 280 with a first reaction gas source material are in this example with donor granules and

Activator granules filled and are suspended for a gas diffusion coating between the support arms 1 to 20 and almost completely surround the outer surfaces of the hollow components 100 to be coated. They first supply the outer surfaces of the hollow components 100 with reaction gases. A central pellet basket 290 with a second reaction gas source material in pellet form is arranged in the middle of the holding tube 105. It supplies the internal surfaces of the hollow components 100 with reaction gases for a gas diffusion coating via connecting openings 115 to the cavities 107 of the carrier antennas 1 to 20 and via the second connecting openings 104 shown in FIG. 1 in the hollow components 100. The reaction gases then flow via the first connection opening 103 shown in FIG. 1 to the outer surfaces in the direction of arrow B.

Carrier arms 1 to 60 and granulate baskets 201 to 280 can, as shown in FIG. 1, be connected or fastened in several layers to the holding tube 105 one above the other. In this example, three layers, each with 20 support arms 1 to 60 and 20 granulate baskets 201 to 280, are connected or fastened to the holding tube 105. In this example, each support arm accommodates 4 hollow components, so that 240 hollow components 100 can be cleaned and coated at the same time.

The bottom 131 of the reaction container 130 has, in addition to the inlet openings in the outer reaction chamber 110 and in the inner reaction chamber 120, outlet openings 116 and 122 in the outer and inner reaction chamber 110 and 120, respectively. To switch the flow direction A or B, the openings are connected via supply or discharge lines to corresponding control valves, not shown, via which inert carrier gases or caustic, reducing or deoxidizing reaction gases can be supplied or removed.

3 shows a hollow blade 300 which is suitable for use in the device according to the invention and in the method according to the invention. The hollow vane 300 is used in turbo engines and must be protected against corrosion and oxygen embrittlement by the aggressive gases in the flow channel of the turbo engine. These hollow blades 300 usually have first connecting bores 303 and 304, respectively, on their front edges 301 and / or on their rear edges 302, which connect the outer surfaces 305 to the inner surfaces 306. In addition, these hollow blades 300 have a blade root 317 whose outer surfaces 318 are to be protected from coating. In the blade base area there are second connecting openings 313 and 314, through which cooling air can enter during operation, for example, which can flow out as cooling air film at the front and / or rear edges 301 and 302 through the cooling film bores 303 and 304, respectively. Using these openings, a cleaning and / or coating gas can be used with the aid of the invention

Device and according to the inventive method flow through the surfaces of the blade 300 one after the other in direction A and in direction B when the blade 300 is connected gas-tight to a support arm 1 of the device. In this example, the support arm consists of a hollow profile with attached holding and supporting device 310 for the hollow blade 300, into which the blade root 317 is inserted and then enclosed with a sealing compound 108, which in this example is a sintered compound, so that the openings 313 and 314 of the blade root 317 are connected to the cavity 307 of the support arm 1.

The interior of the hollow blade is structured in narrow channels, so that the reaction gases are deflected several times, and windward and leeward effects are reduced only by minimal flow rates. Only by switching the flow direction according to the invention from the arrow direction A to the arrow direction B and vice versa, the windward and leeward effects at the sharp deflection points are compensated. Depletion of the reaction gas sources on reaction components is reduced and enrichment on

Reaction components, in particular in the interior of the hollow blade, are brought about by the method according to the invention, so that more uniform cleaning effects and more uniform coating results than with conventional devices and methods are made possible.

example 1

A high pressure turbine blade made of a nickel-based alloy of the composition (Rene SO)

Co 9.0-10% by weight

Cr 13.7 - 14.3% by weight

Ti 4.8 - 5.2% by weight

AI 2.8 - 3.2% by weight

W 3.7 ■ ■ 4.3% by weight M Moo 3 3,. 77 - ■ - 44,. 33% by weight

Fe max. 0.35% by weight

Hf max. 0.1% by weight

C 0.15 - 0.19% by weight

Rest Ni, with a complex inner geometry, which has 6 to 8 cooling air holes (see FIG. 3), is coated on the outer and inner surfaces according to the inventive method and the inventive device with an aluminum diffusion layer.

For this purpose, the base area of the turbine blade 300 is first provided with an Al ₂ O ₃ layer by immersion in a slip suspension which essentially consists of Al ₂ O ₃ powder and an aqueous solution. After the Al ₂ O ₃ slip has dried, four blades 300 each are placed on holding and supporting devices 310, which are located on the carrier arms 1 to 60 of the device according to the invention. Each support arm 1 to 60 is then filled with a powder filling 308 made of nickel-based powder and Al ₂ O ₃ powder. This powder fill 308 seals the blade root area in cooperation with the slip casting layer 108 on the outer surfaces 318 of the blade root 317 in the holding and supporting device 310 by sintering together to form a sintered mass during late heating and protects the outer surfaces 318 of the Blade foot 317 before coating. The carrier arms 1 to 60 w prepared in this way outside the reaction container 130 are then hung in the central holding tube 105. The conical or hemispherical connecting pins of the carrier arches are additionally brushed with A UO ₃ slip in order to seal minor gaps.

In this example, more than 30 porters in more than 5 layers or levels are hung on a holding tube 105. Pellet baskets made of perforated sheet are suspended between the support arms in every position. These contain aluminum donor granules of an Al / Cr alloy and a granulate of aluminum fluoride as activator donors as reaction gas sources. In this example, 600 g of aluminum donor granules and 10 g of activator granules are used per scoop. A part of this granulate is filled as a second reaction gas source 290 into a granulate basket in the interior of the holding tube.

After hanging the carrier arms and the granulate baskets on the holding tube, a fir tree load carrier is completed. The fir tree charging carrier is positioned on the base of a retort hood furnace, the holding tube 105 forming the central trunk of the fir tree charging carrier, the central trunk has a feed line 121 and a lead 122 through the retort base. In this example, the outer traction chamber has two supply lines 111 and two discharge lines 116. A retort hood 140 and a hood furnace (not shown) are placed over the fir tree charging carrier and the retort is flushed with argon.

When heated, a flow rate of 40001 / h Ar is flushed through the opening 122 in the direction opposite the arrow A through the fir tree trunk through the hollow components into the first reaction chamber 110, the retort chamber. When a holding temperature of 1050 ° C. is reached, the

Flow changed over and a carrier gas amount of 401 / h H _{2 was} pumped from the retort space in the direction of arrow A into the fir tree trunk. After a holding time of 4 h, the gas flow is fed into the system in the opposite direction B via the opening 121, so that an H ₂ gas flow of 401 / h for two additional hours is now in through the reaction gas source 290 Direction B flows. For cooling, the opening 122 is finally fed with Ar as the inert gas against the flow direction A.

The result is an extremely uniform coating of the outer and inner surfaces 305, 306 of the turbine blades with an aluminum content of the protective layer of over 30

% By weight.

Example 2

In this example, a combined pre-cleaning of the inner surfaces of a turbine blade with subsequent coating of the outer and inner surfaces of a turbine blade made of a material similar to that in Example 1 is carried out.

Internal cleaning of this type may be necessary because with the usual pre-cleaning only the outer surfaces are safe from mold residues and reaction products between

Blade material and mold material can be exempted. Reactions of the inner surfaces with the core material when casting a blade can leave partial residues on the inner surfaces which hinder or completely prevent diffusion coating, so that weak points in the hot gas oxidation and corrosion protection layer can occur in the interior of the hollow blades 300.

In this example, a turbine blade made of a nickel-based alloy of the composition (Rene 142)

Co 11.45 - 12.05% by weight

Cr 6.6 - 7.0 wt%

Ti max. - 0.02% by weight

AI 5.94 - 6.3% by weight

W 4.7 - 5.1% by weight Mo 1.3 - 1.7% by weight

Fe max. 0.2% by weight

Hf 1.3-1.7% by weight

C 0.1-0.14% by weight

Re 2.6 - 3.0% by weight

Balance Ni, cleaned and coated.

For this purpose, the casting material is cleaned and coated at the same process temperature so that the cleaned inner surfaces do not become coated with oxide again.

The turbine blades are connected to the central holding tube, five each per support arm, and a batch of 300 rotor blades is distributed over three layers. The cake and heating hood are placed over the fir tree charge and an argon protective atmosphere is created by pumping and rinsing. The argon flow is 20001 / h at

Do the washing up.

Thereafter, the retort at 750 ^C to 1040 C ° C is heated under argon. In the opposite direction A flows through the opening 122, an H ₂ flow of 40001 / h first along the inner surfaces of the hollow vane and then over the outer surface

Hollow bucket.

After a holding temperature of 1040 ° C. has been reached, a mixture of HF and H _{2 is} introduced into the tunnel tree for a period of 2 hours via the opening 122. The reaction gas mixture consists of HF at 0.51 / h per blade and H ₂ together with 5 1 / h per scoop. In the outer reaction space circulates at the same time with 401 / h per

Scoop of hydrogen, which is introduced through opening 111 and discharged through opening 116. A pressure ratio is maintained so that the process pressure in the first reaction space or in the retort space is 5 to 30 hPa below the process pressure in the holding tube or distribution master. The reaction atmospheres of the inner and outer reaction spaces are derived together with the opening 121 closed via the opening 116 in the first reaction space.

After a 2-hour hold time has elapsed, the HF supply is switched off and a further 0.25 hour is flushed with H ₂ (5 l / h per scoop). The gas flow is then reversed. A coating gas mixture of A1F, A1F ₃ and H ₂ (at 20 l / h per blade) is now passed for coating in direction A first over the outer and then over the inner surfaces of the hollow blades. After a holding time of 4 h at 1040 ° C., coating is carried out in the opposite direction B for two more hours. In this case, the reaction gas is first passed over the inner surfaces and then passed over the outer surfaces via the inner reaction gas source through the support arms via the second connection openings in the hollow blades. When the batch cools down, the batch is flushed with Ar against the direction of flow A, the argon being opened via the opening 122 when the opening 121 is closed, first over the inner surfaces of the hollow blades and then over the outer surfaces of the

Hollow blades flow.

The result is a defect-free inner coating with high uniformity of the inner layer thickness.

Example 3

In example 3, a hollow blade is coated on the outside and inside, which has an extreme length of over 500 mm for the inner cooling channels.

The previously available methods and devices with unidirectional reaction gas guidance result in particularly serious reductions in the inner layer thickness from the entry of the reaction gases into the cavities or cooling channels of hollow blades to the exit from the cavities or to the end of the cooling channels. Decreases from 0.5 to 1 μm each Centimeter channel length are quite common. With a coating thickness of 50 μm in the area of the first connection opening 103 to the interior of a hollow blade, the coating thickness approaches zero at the end of a channel with a length of 500 cm. In comparison to this, the new device and the method according to the invention can be used to coat longer cooling channels as well as to make the layer thicknesses more uniform.

In this example, the first reaction gas source is equipped with granules of an aluminum donor alloy and the second reaction source with a donor alloy and the granules of a halogen activator. During the heating phase, the device is heated to 1040 ° C. under a low argon flow in the direction of arrow A until the entire activator is present in gaseous form in the second reaction space. Only then is the flow rate controlled for half an hour so that the reaction gases flow in direction B. During this period, sufficient activator gas reaches the first reaction chamber via the inner surfaces of the components in order to form a reaction gas in reaction with the donor metal granules, which after 30 minutes now flows in the opposite direction to A, first over the outer surfaces and then the inner ones Surface coated This change of flow direction takes place every 30 minutes for the next 5 hours. Finally, the activator gas is displaced into the second reaction space under argon at a flow rate of 401 / h per scoop, where it precipitates. This has the advantage that there is no toxic stray in the outer reaction space, which is heavily frequented by installations and removals

Halogen or halide compounds or gases are present. Rather, they concentrate on the inner second reaction space.

With this process variant, the uniformity of the coating thickness could be increased again.

Example 4

Next, problematic superalloys are on which aluminum is difficult or impossible to apply using conventional gas diffusion coating. These alloys include cobah-based alloys and nickel-based alloys with a high proportion of tungsten.

To solve the coating problems, a high content of aluminum halides in the reaction gas called aluminum activity is required. The depletion of aluminum halides in the reaction gas and thus the abnalime of aluminum activity is, however, considerable in conventional processes by depositing aluminum on the surfaces of the hollow components. With the method according to the invention, this depletion is reduced, so that high aluminum activity can be maintained, and problematic superalloys to which aluminum can be applied only with difficulty or not at all by means of conventional gas diffusion coatings can also be satisfactorily coated from the inside.

As an example, turbine guide vanes with the following alloy composition (X 40)

Ni 9.5 - 11.5% by weight

Cr 24.5 - 26.5% by weight

AI max. 0.35% by weight

W 7.0 - 8.0 wt.% Fe max. 2.0% by weight

C 0.45 - 0.55% by weight

Rest co

and turbine blades with the following composition (Mar-M237 LC)

Co 9.0 - 11.0% by weight Cr 6 - 8.0% by weight

Ti 0.9 - 1.2% by weight AI 5.4 - 5.7% by weight

W 3.8 - 10.2% by weight

Mo 0.6-0.8% by weight

Hf 1.0 - 1.6% by weight

C 0.05 - 0.14% by weight

Ta 2.9 - 3.1% by weight

Rest Ni

coated with high AI activity.

For this purpose, 100 hollow blades are arranged in 5 layers in the first reaction space, and 1500 g per bucket of donor metal granules and 20 g activator granules per blade are weighed. A retort hood 140 of 1.3 m ^{3 in} volume is placed over the batch. The retort base 131 has a gas supply line and two exhaust gas lines. The holding tube has a cylindrical container with a capacity of 0.25 m ³ in the lower area above the retort bottom in the heated area.

Before heating, the batch is flushed in the direction B with 10 times the volume of the retort hood with argon. The device is then heated under an argon flow of 10001 / h. At 900 ° C, the hydrogen flow is changed to 20001 / h until a holding temperature of 1080 ° C is reached. Then the flow is reduced and switched to pressure control. For this variant of the method, pressure sensors are arranged in the first and second reaction spaces as measuring transducers. A pressure difference is alternately built up between the pressure sensors with a hydrogen flow rate of up to about 10001 / h

After changing the sign of the pressure difference between the two reaction spaces 110 and 120 several times, the batch is removed in the direction B after 6 hours with argon purge. cools.

The result is a very uniform layer thickness between the outer and inner surfaces of the hollow blades.

Example 5

In this example, a turbine blade for a stationary gas turbine made of the same material as in Example 1 is to be coated essentially with chromium on the inner surfaces and essentially with aluminum on the outer surfaces.

For the operating temperatures of a stationary gas turbine, the blades are equipped with film cooling holes on the trailing edges. The blades also have three inner cooling channels. It has proven to be expedient to coat the inner channels with a different material than the outer surfaces of these hollow blades. For this reason, the inner channels must be coated with chrome and the outer surfaces with aluminum.

In order to achieve such a coating with conventional unidirectional methods, a great deal of effort must be expended with regard to protective temporary covering layers.

With the method according to the invention and the new device, these blades can be coated much more cost-effectively.

For example, 160 turbine blades in 4 layers are connected to 20 support arms, each support arm holding two blades. In the second inner reaction space, 10 kg of chrome tablets are arranged in perforated metal baskets and 5 g of NH ₄ C1 per blade are positioned in the lower area of the holding tube. Another 3 g of NH ₄ C1 is arranged in the bottom area of the first reaction chamber. The aluminum donor granulate with a fluorine compound as activator for the outer coating is placed at 400 g per scoop in the granulate baskets between the carrier arms. The batch is flushed with argon and heated to a first holding temperature of 1080 ° C. without any flow. At 1080 ° C, an argon flow in direction B over the inner surface of the blade of 160 1 / h is set, which coats the inner surfaces with chrome. At the same time, an argon flow of 40001 / h, which protects the outer surfaces from a chromium coating, circulates in the first reaction space via the inlet 11 and the outlet 116.

The amount and the location of the NH ₄ Cl activator for the alitation are dimensioned or selected such that the NH ₄ Cl activator is completely evaporated in the 4 hours given the temperature distribution and the temperature gradient present. After 4 hours, the argon flow is switched to alitizing the outer surfaces. At a temperature of 1040 ° C and an argon flow of 4001 / h in direction A, the outer surfaces are alitated in the following 4 hours.

After cooling the batch under argon flow in the direction B to room temperature, a measured average inner coating thickness of 25 μm results, which essentially consists of chromium and an aluminum layer on the outer surfaces with an average thickness of 45 μm.

Claims

claims

1. Process for the preparation and / or coating of the surfaces of metallic

Hollow components with the process steps

a) provision of at least two reaction gas mixtures (I, II) by reaction gas sources for treating the outer and inner surfaces of the hollow components,

2. The method according to Anspmch 1, characterized in that the Reaction Gas Mixtures (I, II) are composed of similar components and the flow direction of the reaction gases over the surfaces of the hollow component by repeating the

Steps b) and c) are changed several times.

3. The method according to Anspmch 1, characterized in that at least one of the reaction gas sources provides reaction gases which serve to clean outer and inner surfaces, preferably halogen-containing gases.

4. The method according to any one of claims 1 to 3, characterized in that at least one of the reaction gas sources provides reaction gases which serve to reduce sulfidic or oxidic deposits on the outer or inner surfaces, preferential wise gases containing hydrogen.

5. The method according to any one of claims 1 to 4, characterized in that the reaction gas sources supply reaction gases which serve the gas diffusion coating of the outer or inner surfaces, preferably halide-containing gases which are on the metallic outer or inner surfaces of the hollow components in a metallic Component which is deposited as a coating on the outer and inner surfaces and decomposes a halogen component which is reused as an activator.

6. Device for the preparation and / or coating of the surfaces of hollow metal components which have at least two connecting openings between their outer and inner surfaces, characterized in that the device has a reaction vessel with an outer reaction space and a central holder tube, on the removable radial hollow support arms aligned to the holding tube are arranged, each of which accommodates at least one hollow component, a first connection opening of the component being connected to the outer reaction space and a second connection opening being connected via the hollow support arm to the interior of the holding tube, so that reaction gas from the outer Reaction space can flow first over the outer surfaces and then over the first connection opening to the inner surfaces of the components and via the support arms to the interior of the holding tube and vice versa, reaction gas from the interior of the holding tubes s can flow via the support arms through the second connection opening of the component over the inner surfaces and then through the first connection opening over the outer surfaces of the components into the outer reaction space.

7. Apparatus according to Anspmch 6, characterized in that in the outer reaction space between the support arms radially arranged to the holding tube outer granule baskets are fastened with a first reaction gas source material.

S. Device according to claim 6 or 7, characterized in that in the outer reaction space support arms and granulate baskets are connected or fastened in several layers one above the other on the holding tube.

9. Device according to one of claims 6 to 8, characterized gekennzeiclinet that inner granule baskets are arranged with a second reaction gas source material in the interior of the holding tube.

10. Device according to one of claims 6 to 9, characterized in that the Hal¬ terohr is centrally on the bottom of the reaction container, the at least one first inlet or outlet opening for the outer reaction space and at least a second inlet or outlet opening for has the interior of the holding tube.