EP1682697A2

EP1682697A2 - Coating of substrates

Info

Publication number: EP1682697A2
Application number: EP04798168A
Authority: EP
Inventors: Jörg HELLER; Christoph Strobel
Original assignee: Aluminal Oberflachentechnik GmbH
Current assignee: Aluminal Oberflachentechnik GmbH
Priority date: 2003-11-07
Filing date: 2004-11-05
Publication date: 2006-07-26
Also published as: WO2005045102A3; WO2005045102A2; US20070261965A1

Abstract

The invention relates to a method for producing coated workpieces, comprising the following steps: a) electrodeposition of one or more layers containing at least one metal and/or metal alloy on a substrate and b) thermal treatment of the coated substrate at a temperature of between 300 DEG C and 1000 DEG C, in such a way that at least the surface layer of the substrate and the layer or layers applied in step a) partially and/or completely interdiffuse. The invention also relates to coated workpieces that are produced by said method.

Description

Coating substrates

The present invention relates to a coated workpiece, which has an improved temperature resistance, and the provision of a method for its production.

In plant construction, there is a growing demand for workpieces that have a high temperature resistance. In engines, exhaust systems and in gas turbines, such as. B. an aircraft gas turbine, sometimes very high temperatures in the range of 500 - 1000 ° C occur. Components that are used in such places are exposed to a high mechanical load on the one hand and a high thermal load due to the prevailing high temperatures. In particular, the problem arises that such components are cooled back to ambient temperature when the engine or the turbine is switched off. Subsequently, when the engine or turbine is started again, a very rapid heating occurs. This cycle of cooling and cooling of the components represents a special load and only specially equipped workpieces are able to withstand such a load.

The problem here is that materials such. B. titanium or titanium

Alloys that have a low density in combination with high strength and mechanical strength, only have a certain temperature resistance. For the aforementioned titanium and titanium alloys, the maximum temperature at which the workpiece is not adversely affected is approximately 500 ° C. If the temperature exceeds this value, the workpiece made of titanium or the titanium alloy is oxidized. The workpiece becomes unusable.

This oxidative degradation takes place not only in titanium or titanium alloys, but also in all other workpieces made of z. B. a chrome steel, a chrome-nickel alloy or a nickel-based alloy. Only the temperature at which the oxidation begins to differ is different.

There has been no lack of efforts to improve the temperature resistance of workpieces. One possibility is to deposit a layer on the workpiece. In the case of titanium or titanium alloys, layers of aluminum have proven successful. However, depending on the base workpiece used, there is also the possibility of applying a different specific layer that increases the temperature resistance of the workpiece. Ceramic layers can also be used, which, however, require a very high degree of brittleness and therefore only guarantee a moderate mechanical resilience of the surface at high temperatures.

In the case of titanium, it has proven to be aluminum layers on the

To apply titanium material. The aluminum layer applied to the titanium workpiece is heated to a temperature which enables an intermetallic phase to be obtained from the originally existing aluminum layer with the workpiece made of titanium or a titanium alloy underneath. This alloy layer shows an increased temperature resistance of approx. 650 - 700 ° C. Since the surface layer formed in this way is very hard and brittle, it is not possible to mechanically deform such a workpiece in a subsequent treatment step. The temperature-stable surface layer would immediately be damaged.

[0007] WO 02/058923 proposes to apply an aluminum layer to a titanium sheet by roll cladding. In roll cladding, a thin aluminum foil is applied to a titanium sheet or a titanium foil at a high temperature of approx. 500 ° C. Due to the high processing temperatures, the aluminum layer adheres to the titanium sheet. Subsequently, molded parts can be produced from the titanium sheet treated in this way, which are thermally treated in a subsequent processing step. By this thermal treatment forms a corrosion protection layer, which consists of a titanium / aluminum alloy. By exposing this surface layer to oxygen, it is converted into a titanium-aluminum mixed oxide layer. A disadvantage of the method described in WO 02/058923 is that if the titanium sheet is to be provided with an aluminum layer on both sides, this aluminum layer must also be applied to the titanium sheet on both sides. This requires a very high level of operational expenditure, since either a second station in the roll plating system must be available, with which a second aluminum layer can be applied, or it is necessary for the titanium sheet to pass through the roll plating system twice. Another disadvantage of the described method is that only sheets or foils can be provided with an aluminum layer in order to subsequently produce molded components from these sheets. It is not possible to provide a three-dimensional workpiece with an aluminum layer by roll cladding.

Another method for surface finishing of titanium workpieces is disclosed in DE 41 12 218. A layer is applied to a titanium substrate, which has the composition MCrAL or MCr, where M is a metal selected from the group consisting of iron, nickel, cobalt and mixtures thereof. These alloys are applied to the titanium substrate by very complex processes, such as. B. plasma spraying, chemical vapor deposition or physical vapor deposition. Above all, it can be seen that these processes result in an only thin metal layer in the case of angled workpieces in hard-to-reach places. It is precisely at these points that the surface layer is particularly thin, which should guarantee the temperature stability of the workpiece. Another disadvantage is that the aforementioned coating processes, such as plasma spraying, chemical vapor deposition or physical vapor deposition, can only be carried out with relatively small workpieces, since the reaction chambers required for this usually only have space for smaller workpieces. In the event that larger workpieces are to be treated, it turns out that these methods are unsuitable. The present invention thus has as its object to overcome the disadvantages of the prior art. The technical object of the present invention is in particular the provision of a coated workpiece, which has superior high-temperature resistance, and the provision of a method for producing the coated workpieces. In particular, geometrically complex and large workpieces are to be provided with a protective layer which is distributed homogeneously on the workpiece. The method used for this should be easier to carry out and less expensive.

The technical object of the present invention is achieved by a method for producing coated workpieces comprising the steps:

a) galvanic deposition of one or more layers containing at least one metal and / or a metal alloy on a substrate and

b) heat treatment of the coated substrate at a temperature between 300 ° C. and 1000 ° C., so that at least the surface layer of the substrate and the layer or layers applied in layer a) partially and / or completely diffuse into one another.

In a preferred embodiment, the substrate of step a) is electrically conductive. It is further preferred that the substrate of step a) is a metallic substrate and / or a metallized substrate. The metallic substrate and / or metallized substrate can contain one or more metals, which are preferably transition metals.

Preferably, the substrate is selected from the group of substrates containing the metals magnesium, zinc, tin, titanium, iron, nickel, chromium, vanadium, tungsten, molybdenum, manganese, cobalt and mixtures thereof and / or alloys thereof. Preferred substrates include substrates. tend titanium, titanium alloys, chrome-nickel steel, chrome-nickel alloys, and / or nickel-based alloys.

The electrodeposition of the layer (s) (step a) can be carried out using any galvanic method known to the person skilled in the art. In particular, the layer which is applied in step a) can be applied from a non-aqueous electrolyte or from an aqueous electrolyte.

[0014] The layer of step a) is preferably selected from aluminum, magnesium, tin and mixtures thereof and / or alloys thereof. The layer preferably contains an aluminum / magnesium alloy and / or an aluminum / tin alloy.

If two or more galvanic layers of step a) are present, the layer (intermediate layer) first applied to the substrate preferably contains metals selected from the group consisting of iron, iron and nickel, tin and nickel, nickel, cobalt, copper, chromium , Molybdenum, vanadium or alloys of the above metals. One or more intermediate layers can be applied to the substrate. The outer layer selected from aluminum, magnesium, tin and mixtures thereof and / or alloys thereof is then applied to the intermediate layer. The outer layer preferably contains an aluminum / magnesium alloy and / or an aluminum / tin alloy

If the layer or the outer layers of a layer structure contains an aluminum / magnesium alloy, it is preferred that the layer 1-80% by weight magnesium, more preferably 2-50% by weight magnesium, more preferably contains 3 to 40% by weight of magnesium and most preferably 4 to 30% by weight of magnesium. If the layer or the outer layers of a layer structure contains an aluminum / tin alloy, it is preferred that the layer 1-80% by weight of tin, more preferably 2-50% by weight of tin, even further preferably contains 3 to 30% by weight of tin and most preferably 4 to 25% by weight of tin.

Each layer applied in step a) preferably has a layer thickness of 0.1 μm - 100 μm. In a further preferred embodiment, the layer thickness is 0.5 μm to 70 μm, more preferably 1 μm - 50 μm, preferably 2 μm - 40 μm, more preferably 3 μm - 30 μm, more preferably 4 μm - 28 μm and most preferred 5 μm - 25 μm.

If the layer or one of the layers of step a) is electrodeposited from an aqueous electrolyte, solutions of the aforementioned metals can be used as possible electrolytes. In particular, the metals can be present as halides, sulfates, sulfonates or fluoroborates. The electrolytes can contain other additives, such as. B. complexing substances.

If the layer or one of the layers of step a) is electrodeposited from non-aqueous electrolytes, it is possible to use all non-aqueous electrolytes which are known to the person skilled in the art. Possible electrolytes contain compounds of the above-mentioned metals. The metals are preferably in the form of halides which can be complexed with ether, in particular diethyl ether. However, it is also possible for the metals to be present as acetyl acetonates (acac).

Alternatively, it is possible in step a) for a layer if it is a

Layer containing aluminum / magnesium, aluminum or a layer containing aluminum / tin is to use any electrolyte that is known to the person skilled in the art. [0022] In particular, the electrolyte preferably contains organoaluminum compounds of the general formulas (I) and (II):

M [(R ¹ ) ₃ AI- (H-AI (R ² ) ₂ ) _n -R ³ ] (I)

AI (R ⁴ ) ₃ (II)

where n is 0 or 1, M is sodium or potassium and R ¹ , R ² , R ³ , R ^{4 may be the} same or different, wherein R ¹ , R ² , R ³ , R ^{4 is} a C 1 -C ₄ alkyl group are and a halogen-free, aprotic solvent is used as a solvent for the electrolyte.

A mixture of the complexes K [AIEt], Na [AIEt] and AIEt ₃ can be used as the electrolyte. The molar ratio of the complexes to AIEt ₃ is preferably 1: 0.5 to 1: 3 and more preferably 1: 2.

The electrodeposition of the layer can be carried out using a soluble anode containing the metals intended for the deposition. This anode can either contain the metals intended for deposition as a metal alloy, or several soluble anodes of the respective pure metals can be used. If a layer containing an aluminum / magnesium alloy is to be deposited, it is possible to use a soluble aluminum and a likewise soluble magnesium anode or an anode made of an aluminum / magnesium alloy.

Accordingly, it is possible if a layer containing one

Aluminum / tin alloy is to be deposited, a soluble aluminum and a likewise soluble tin anode or an anode made of an aluminum / tin alloy. The electrolytic coating of a non-aqueous electrolyte is preferably carried out at a temperature of 80-105 ° C. A temperature of the electroplating bath of 91-100 ° C. is preferred.

In a preferred embodiment, an electrically conductive layer is applied to the substrate before the layer is applied galvanically in step a). The layer which conducts the electrical current can be applied to the substrate by any method which is known to the person skilled in the art. The layer that conducts the electrical current is preferably applied to the substrate by metallization.

In step b) of the method according to the invention, the temperature and / or the duration of the heat treatment is chosen such that, at least in the boundary region between the substrate and the applied layer of step a), an alloy containing metal of the surface layer of the substrate and metal and / or Metal alloys of the applied layer is formed. The temperature and / or the duration of the heat treatment are to be selected so that they are matched to the properties of the substrate and the specific layer applied.

In principle, it is possible to choose the conditions in such a way that the coated substrate is treated below the melting temperature of the layer applied in step a). In the case of a layer containing aluminum or an aluminum alloy, this temperature is preferably <650 ° C.

The heat treatment generally forms an intermetallic phase on the surface of the coated workpiece, in which the layer applied in step a) is converted either partially or continuously into the intermetallic phase.

Alternatively, it is possible to anneal the coated substrate below / along the liquidus line of the resulting mixture of materials. The liqui duslinie is the melting temperature of the material mixture formed depending on the specific composition. In the event that an aluminum layer is applied to a titanium substrate, the proportion of aluminum in the surface layer is first 100%. A titanium-aluminum alloy with a specific melting point will form during the heat treatment. If the temperature is now selected during the heat treatment so that the melting point of the alloy that is formed is reached or is just below, then this heat treatment is to be understood as heat treatment below / along the liquidus line of the resulting material mixture.

Alternatively, it is possible that the heat treatment of the coated substrate is carried out in such a way that a liquid phase is formed on the surface of the coated substrate. This is achieved by treating at a temperature that is higher than the melting temperature of the resulting surface layer.

[0033] The heat treatment can be carried out under a protective gas atmosphere. It is preferred here that a protective gas is used which does not react with the coated material. The protective gas is preferably a rare gas, e.g. Argon. However, it is not necessary for the heat treatment to take place in a protective gas atmosphere. Alternatively, the heat treatment can also be carried out in air.

The temperature of the heat treatment of step b) is preferably between 400 ° C and 1000 ° C, more preferably between 450 ° C and 900 ° C and most preferably between 500 ° C and 800 ° C.

The duration of the heat treatment of step b) can be between one second and 10 hours. Preferably it is between 1 minute and 5 hours and most preferably between 2 minutes and 3 hours. Alternatively, it is possible that the heat treatment of step b) is then carried out when the workpiece is installed at its destination. So it is possible that, for. B. a motor element or turbine element is heated during its first use in such a way that the diffusion of the surface layer of the substrate with the applied layer takes place.

In a preferred embodiment, after the layer has been applied in step a) and before the heat treatment of step b) takes place, the layer can be subjected to a further treatment. All treatment methods that are known to the person skilled in the art can be used here. In particular, the treatment can be an anodic oxidation, which is preferably the anodizing of the layer. Such a treatment is appropriate if a layer containing aluminum was applied in step a).

The coated workpiece used in the method of the present invention is preferably a rack product, a bulk product, an endless product or a molded part. The coated workpiece is preferably a wire, a sheet metal, a screw, a nut, a concrete anchor, a machine component, an engine, an engine part or a turbine blade.

[0038] Those made by the process of the present invention

Workpieces have excellent long-term resistance to thermal stress. With repeated heating and cooling cycles, they show that, due to the temperature load, there is no corrosion of the workpiece over a long period of time. In particular, the coated workpieces show improved resistance to oxidation or other corrosive high-temperature influences at which the uncoated workpiece, that is to say the substrate, is already beginning to corrode.

In the case of an uncoated substrate containing titanium or a titanium alloy, permanent damage by oxidation takes place at 650 ° C. In contrast, a coated titanium substrate according to the present invention, when z. B. with aluminum or an aluminum um / magnesium alloy was coated, a temperature stability in the range of 750 - 1000 ° C.

[0040] The coated substrates of the present invention are significantly more temperature-resistant than those of the prior art. An explanation for this could be without, however, being bound to a theory that a highly pure layer is obtained by the galvanic application, while in the coating processes of the prior art, such as, for. B. chemical vacuum deposition, physical vacuum deposition, or plasma spraying, impurities are present in the applied layer, which have an adverse effect on the temperature stability. Since high-purity layers are obtained by the galvanic process, germs that are caused by contamination are not present in the layer. High-purity diffusion layers are thus formed which, owing to the high purity, have improved stability and, above all, improved temperature stability.

Another disadvantage is that the aforementioned method of

State of the art for applying a layer with geometrically complex substrates can only be used very poorly. In particular at corners and edges, the layer thickness is less than on more accessible areas. As a result, no homogeneous layer forms on the substrate, which inevitably causes deteriorated corrosion resistance at those points where the layer thickness is less. By galvanic deposition of the layer on the substrate a homogeneous and sufficiently thick layer itself is hard to reach places, such ^as', for example, corners and edges, is applied. The result of this is that the diffusion layer obtained by heat treatment also has a sufficient layer thickness at these locations which are difficult to access geometrically and thus has adequate and improved corrosion stability. In particular, the workpieces obtained by the present invention differ from the workpieces of the prior art. Furthermore, as already explained, they also form at these critical points due to the fact that pure layers are applied, after the heat treatment high-purity diffusion layers.

Another advantage of the method of the present invention is that it is less expensive compared to the methods of the prior art. The galvanic application of a layer is less expensive than e.g. B. plasma spraying. Another advantage is that both by plasma spraying such. B. by chemical vacuum deposition or physical vacuum deposition, the substrate is subjected to greater thermal stress. This leads to thermal distortion of the workpiece, in particular in the case of geometrically complex substrates. If the method of the present invention is used, the thermal stress on the workpiece in step a) is significantly lower. This makes it possible to produce coated workpieces with lower manufacturing tolerances, which has significant advantages in subsequent operation as e.g. Turbine blade causes. Furthermore, lower manufacturing tolerances result in an increased level of safety for coated workpieces subject to high thermal loads. The workpieces produced by the method of the present invention, such as. B. ensure turbine blades, when installed in a gas turbine, higher safety reserves compared to the turbine blades of the prior art.

The present invention is illustrated by the following examples without, however, being restricted to these.

Examples

1. Coating the substrate

A sheet of size 5 x 25 x 1 mm made of titanium is provided with a layer of aluminum with a layer thickness of 12 μm by galvanic deposition from a non-aqueous electrolyte. 2. Heat treatment of the sheet

The titanium sheet provided with a layer of aluminum is heated in an oven to the temperature shown in Table 1. The temperature is maintained for the period specified in Table 1. The coated titanium sheet is then removed from the furnace and it cools down in an air atmosphere. During the alloying process, the furnace is either exposed to ambient air or the protective gas argon.

Table 1

3. Determination of the corrosion resistance against elevated temperature.

The coated titanium sheets with the numbers A, B and C are heated in an oven to the temperature shown in Table 2. After the holding time given in Table 1, the material sample is taken out of the furnace, cooled and the corrosion of the coated titanium sheet is assessed visually. This shows that the applied layer has excellent corrosion resistance, even at very high temperatures, such as. B. 900 ° C. A non- coated titanium sheet would be permanently damaged by oxidation at a temperature above approx. 650 ° C. Even with a holding time of 384 hours at 700 ° C, there is no noticeable corrosion of the coated titanium sheet.

Table 2

In summary, it can be stated that a titanium sheet which is produced according to the method of the present invention has an improved corrosion resistance. The workpieces coated in this way are significantly more corrosion-resistant than those of the prior art. In particular, the corrosion resistance is significantly improved at elevated temperatures.

Claims

claims

1. A method for producing coated workpieces comprising the steps:

, a) galvanic deposition of one or more layers containing at least one metal and / or a metal alloy on a substrate, and b) heat treatment of the coated substrate at a temperature between 300 ° C and 1000 ° C, so that at least the surface layer of the substrate and the In step a), the layer / layers applied diffuse partially and / or completely into one another.

2. The method according to claim 1, characterized in that the substrate of step a) is electrically conductive.

3. The method according to claim 1 or 2, characterized in that the substrate of step a) is a metallic substrate and / or metallized substrate.

4. The method according to claim 3, characterized in that the metallic substrate and / or metallized substrate contains one or more metals, which are preferably transition metals.

5. The method according to claim 3 or 4, characterized in that the substrate is selected from the group of substrates containing the metals magnesium, zinc, tin, titanium, iron, nickel, chromium, vanadium, tungsten, molybdenum, manganese, cobalt and mixtures thereof and / or alloys thereof.

6. The method according to at least one of claims 1 to 5, characterized in that the layer of step a) is applied from a non-aqueous electrolyte or from an aqueous electrolyte.

7. The method according to claim 6, characterized in that the layer of 5 step a) is selected from aluminum, magnesium, tin, nickel and mixtures thereof and / or alloys thereof.

8. The method according to claim 6 or 7, characterized in that the metal alloy contains an aluminum / magnesium alloy and / or an aluminum / tin alloy.

ιo

9. The method according to one or more of claims 1 to 8, characterized in that the temperature and / or the duration of the heat treatment of step b) is selected such that an alloy, at least in the boundary region between the substrate and the applied layer of step a), containing metal of the surface layer of the substrate, and metal and / or metal alloy

15 of the applied layer is formed

10. The method according to one or more of claims 1 to 9, characterized in that the temperature of the heat treatment of step b) between 400 ° C and 1000 ° C, preferably between 450 ° C and 900 ° C and most preferably between 500 ° C and 800 ° C.

11. The method according to one or more of claims 1 to 10, characterized in that the duration of the heat treatment of step b) is between 1 second and 10 hours, preferably between 1 minute and 5 hours and most preferably between 2 minutes and 3 hours lies.

12. The method according to one or more of claims 1 to 11, characterized 5 indicates that after the layer has been applied in step a) and before the heat treatment of step b) takes place, the layer is subjected to a further treatment.

13. The method according to claim 12, characterized in that the treatment is an anodic oxidation, which is preferably the anodizing of the layer.

14. The method according to at least one of claims 1 to 13, characterized in that the coated workpiece is a rack, bulk goods, an endless product or a molded part, wherein the coated workpiece is preferably a wire, a sheet, a screw, a nut, a Concrete anchorage, a machine component, an engine, an engine part or a turbine blade.

15. Coated workpiece, obtainable according to one or more of claims 1 to 14.

16. Coated workpiece according to claim 15, characterized in that the coated workpiece is a rack, bulk goods, an endless product or a molded part, wherein the coated workpiece is preferably a wire, a sheet, a screw, a nut, a concrete anchor , a machine component, an engine, an engine part or a turbine blade.