WO2005073433A1

WO2005073433A1 - Method for removing a coating and single-chamber device for carrying out said method

Info

Publication number: WO2005073433A1
Application number: PCT/CH2005/000015
Authority: WO
Inventors: Udo Rauch; Wolfgang Kalss; Christian Wohlrab; Carolina Siebert; Norbert FRÖMEL
Original assignee: Unaxis Balzers Ag
Priority date: 2004-01-29
Filing date: 2005-01-14
Publication date: 2005-08-11
Also published as: EP1725700A1; ES2337268T3; EP1725700B1; KR20060127040A; JP2007519825A; PT1725700E; DE502005008787D1; KR101118383B1; ATE453739T1; PL1725700T3; JP4675908B2

Abstract

The invention relates to a method and a device for removing a hard material layer system from tools or components. In order to improve said removal method, at least one layer containing chromium and aluminium is directly applied to the workpiece, and the coating of the workpiece is removed by means of an alkali solution containing a strong oxidant.

Description

COATING METHOD AND COMPACTION SYSTEM FOR IMPLEMENTING THE COATING PROCESS Technical field

The invention relates to a method for detaching layer systems according to the preamble of claim 1, in particular for the detachment of chromium and aluminum-containing layers.

State of the art

Decoating methods for detaching layer systems which have been applied to metallic materials, for example by means of electroplating, PVD or CVD methods, are known from the prior art. For example, TiN layers can be easily solubilized with an aqueous hydrogen peroxide solution. However, if one wants to replace more complex, for example, terraneous or quaternary layer systems, which are particularly suitable for many applications in the tool and mechanical engineering industry due to their mechanical or chemical properties, one generally has to resort to more complex methods which require the use of A variety of, sometimes expensive and / or environmentally harmful or toxic chemicals that include electrical contacting of the workpieces for electrolysis or the like and often still require a long for industrial manufacturing processes unacceptable treatment time.

JP 3320965 discloses in the examples a method for detaching TiAlN, ZrAlN, HfAlN and Si ₃ N ₄ hardstock layers. Alkaline solutions containing permanganate and dichromate ions in different concentrations are used. However, the indicated layers could only be obtained at relatively high dichromate concentrations, high pH and temperatures above 40 ° C., or in the case of additional application. Use of electrolytic processes are satisfactorily detached. The fastest decoiling times ranged from one to five hours. However, dichromates are known to have a high toxic potential due to the hexavalent chromium and are therefore applicable or disposable only under special precautions. Furthermore, the process causes the formation of small pores in the substrate, whereby a better layer adhesion is to be achieved. However, this is not desirable, for example, for polished substrates.

JP 02-285081 discloses a method for stripping chromium or chromium oxide layers. The process is carried out in an aqueous solution with the addition of an etchant and an aromatic or fluorine-containing surfactant.

The patent application DE 4339502 describes the non-destructive stripping of hard metal substrates coated with u.a. TiAlN layers. The advantages over previous methods are given by the fact that, in addition to the conventional complexing agents and stabilizers, inhibitors for corrosion protection and other auxiliaries are used and the solution is adjusted to a pH, in conjunction with the other reagents triggering of Co prevented from the workpiece. Disadvantages of this solution are the comparatively long stripping time for TiAlN or the like, the relatively high use of chemicals and the associated costs, the relatively complicated (because precisely to be observed) formulations and reaction conditions and the use of fluorine-containing reagents.

In W09964646 a de-coating method is described in which first a thin TiN layer on a workpiece and only then the hard-to-remove TiAlN functional layer is applied. The EntSchichtung then takes place with a hydrogen peroxide solution, which dissolves through the pores in the cover layer, the TiN intermediate layer. However, TiN layers have the disadvantage of a relatively lower temperature resistance compared to TiAlN or AlCrN, for example. For example, in the case of TiN coatings in air, even at temperatures around 600 ° C, a damaging oxidation process takes place, which leads to complete failure of the coating system on prolonged exposure. To solve such high temperature resistant layers after any errors in the manufacturing process or re-coating an expensive tool without damaging the sensitive workpieces, therefore, quite a number of more complex, including electrolytic, stripping as already mentioned in JP 3320965 or in WO 1999-54528 , developed.

Presentation of the invention

The invention is based on the object to provide a method for delamination of hard coatings available, in which the disadvantages of the prior art are avoided. In particular, this method should be easy and quick to carry out using harmless chemicals feasible. Another object of the invention is to provide a stripping method for layer systems which are also suitable for use at extremely high application or processing temperatures. For example, with TiAlN, oxidative damage only occurs at temperatures of approx. 800 ° C. Especially well the method but AlCrN, Al ₂ 0 ₃ -, (AlCr) ₂ 0 ₃ - _z or (AlCr) _x O _y N layers, in which only at temperatures above 1000 ° C, a failure of the layer or the layer / substrate composite is detectable. These objects are achieved by the features according to the invention in the characterizing part of claim 1.

For this purpose, at least one aluminum- and chromium-containing layer is applied directly on the workpiece to improve the detachment behavior, since it has been found in extensive preliminary tests that such compared to other conventional stripping extremely resistant layers completely surprisingly in an alkaline solution containing a strong oxidizing agent already at about 5 ° C begin to dissolve and at ambient temperatures quickly and completely dissolve or dissolve. This is all the more surprising since ternary titanium aluminum nitride layers are difficult to decoatle, for example with special chelating agents or electrolytic processes (see above), although TiN, unlike the chemically highly resistant CrN, is easily soluble in dilute hydrogen peroxide, for example.

Suitable oxidizing agents are, for example, potassium permanganate, cerium ammonium nitrate, potassium peroxodisulfate or sodium peroxodisulfate.

Such layers may comprise, for example, at least one of the following materials: metallic AlCr, TiAlCr and other AlCr alloys and / or the nitridic, carbidic, carbonitridic, boridic or nitroboridic hard compounds of aluminum chromium or other AlCr alloys.

The layer can be constructed either as a substantially homogeneous single layer or as a multilayer sequence of aluminum and chromium-containing layers. In front- Partially, an Al content of at least 30% atomic percent is chosen in each layer, since otherwise the influence of the highly resistant CrN predominates and makes the detachment process more difficult. At the top, the Al content is advantageously limited to at most 80 atomic percent, since the coating process at the latest here, but usually starting at about 70 atomic percent, deposition of, for example, nitridic AlCr layers, relatively soft hexagonal phases arise due to the lower mechanical load capacity are less suitable for tasks in the field of wear protection.

Such layers can be removed, for example, in a permanganate solution in a broad parameter range. For example, if one wishes to detach layers of hard metals which are sensitive to an alkaline environment, it is sufficient for a high permanganate concentration, such as about 20 to 50 g / l, to have a pH of about 7 in order to detach the layers. Additionally, as is known to those skilled in the art, to speed up the dissolution process, complexing agents such as, for example, potassium sodium tartrate tetrahydrate, sodium gluconate, EDTH, sulfonic acid derivatives of aliphatic or aromatic hydrocarbons, derivatives of a carboxylated aromatic hydrocarbon (eg Phenols), inter alia, and inhibitors, such as mononuclear or polynuclear nitrogen-containing heterocycles (eg morpholine, benzotriazole, ..), amine borates, amine carboxylates, alkyl-aryl-sulfonamides, fatty acid amides, amine- and sodium-neutralized phosphoric acid esters of the solution for protection be added to the sensitive substrate surface. The removal process can be carried out advantageously at temperatures between 5 and 70 ° C.

For stripping of workpieces which are insensitive to alkaline solutions, such as steel substrates and many others Iron-containing alloys, however, recommend a higher pH range, preferably between 9 and 14. In general, a lower permanganate concentration, for example between 10 and 30 g / l, is sufficient, even at room temperature, ie at about 15 to 30 ° C achieving a complete stripping of 2-10 μm thick AlCrN layers within 15-60 minutes. However, an increase in the permanganate concentration above 30 g / l accelerates the rate of decaying once again. It is irrelevant whether the AlCrN layers are applied to the workpiece with a metallic AlCr intermediate layer or grow up without a metallic intermediate layer.

Since manganese dioxide is precipitated from the permanganate solution during the detachment process, it may be necessary to remove MnO ₂ residues from the workpiece surface after the detachment process. This is especially true if the detachment process is carried out without the assistance of one or more ultrasound transmitters. For this purpose, a cleaning in aqueous solution is advantageously carried out, to which a weak acid or a buffer solution in the acidic to slightly alkaline range has been added. In this case, a pH between 2 and 9, preferably between 3 and 7 should be set. This can, as known to those skilled, for example, by the addition of phosphoric acid, of carboxylic or hydroxycarboxylic acids, in particular by the addition of formic, acetic, oxalic or lactic, malic, tartaric and / or their salts are caused.

The advantages achieved by the invention are also to be seen in the fact that in general complex layer systems, such as those required today for high-performance cutting materials or the use of tools and components at high temperatures, are easily and quickly replaced can, if applied to the directly deposited on the workpiece AlCr-containing layer one or more outer layers of at least one hard compound. Examples of such layer systems are hard material compounds of the IV, V, and VI subgroups of the PSE (ie Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) or aluminum and / or silicon and one or more nonmetals such as C. , N, B, 0 exist. In this case, the AlCr-containing layer is attacked by the pores of the cover layer and thus also the overlying cover layer is detached.

For the production of such layer systems, both PVD and CVD methods or hybrid methods which combine both coating techniques are suitable. Since PVD processes always produce a certain number of pores, these methods are generally applicable and preferable. For CVD layers, the respective cover layer must be selected according to the criteria of microporosity or so that the stripping solution can reach the AlCr-containing layer. This is for example given in Al ₂ 0 ₃ layers, since they usually have a fine crack pattern due to the cooling process.

As substrates ceramic and metallic workpieces, as well as hard metals, but preferably steels and ferrous materials can be stripped.

In the following the invention will be explained in more detail by means of individual embodiments or comparative examples.

Coating of workpieces, coating systems

For the production of the AlCrN layers, on various workpieces, in particular on test drills, in an industrial Balzers type RCS coating system, as described for example in EP1186681 in Fig. 3-6, Description page 12, line 26 to page 14, line 9, Cr layers deposited with different aluminum content. Depending on the diameter, the cleaned workpieces were mounted on two or, for diameters of less than 50 mm, on triply rotating substrate carriers and four powder metallurgy-made targets made of different AlCr alloys were installed in the cathodic arc sources attached to the walls of the coating system.

Subsequently, the workpieces were first brought to a temperature of about 450 ° C. by radiation heaters likewise mounted in the system, and the surface was subjected to an etching cleaning by applying a bias voltage of -100 to -200 V under Ar atmosphere at a pressure of 0.2 Pa subjected by Ar ions.

Subsequently, at a nitrogen pressure of 1 to 3 Pa and a substrate voltage of -50 V, by operating four AlCr sources with a power of 3kW for 120 minutes, an AlCrN layer was deposited. In principle, the process pressure in each of these steps can be set in a range of 0.5 to about 8 Pa, either a pure nitrogen atmosphere or a mixture of nitrogen and a noble gas, such as argon for nitridic layers, or a mixture of nitrogen and a carbonaceous gas, which is mixed with a noble gas if necessary, can be used for carbonitridische layers. Accordingly, for the deposition of oxygen or boron-containing layers, oxygen or a boron-containing gas can be admixed as known. Target composition, crystal structure of the layer, layer composition, layer thickness, layer hardness, wear resistance and adhesion as well as substrate bias and process pressure are listed in Table 1.

For layers in a transition region with an Al content of between 60% and 75%, not only the preferential orientation but also the basic structure of the crystal lattice can be adjusted via the process parameters. For example, in Experiment B, a hexagonal structure is produced at a low pressure of 1 Pa and a substrate voltage of -50 V, while in Experiment A, a cubic face-centered structure is generated in a pressure range of 3 Pa and a substrate voltage of -50V.

Table 1

Furthermore, for comparative purposes, peeling tests were carried out with the following commercially available coatings from Balzers: Balinit A (TiN), Balinite C (WC / C with Cr / CrC adhesive layer), Balinit Futura Nano (TiAlN with a TiAl adhesion layer), Balinit D (CrN), Balinit DLC (DLC with Cr / CrC adhesive layer).

Attempts to delaminate

example 1

An aqueous solution with 100 g / l NaOH (pH 14.4) and 20 g / 1 KMn0 and 10 g / l NaCl stripped at room temperature in about 15 to 35 min various steel drills and tools coated with AlCrN as under test designation A to D above.

Example 2 Solution with 200 g / 1 NaOH (pH 14.7) and 5 g / 1 KMnO ₄ stripped in 2.5 hours AlCrN-coated steel drills, layer thickness 3 μm, deposition parameters according to experiment D.

Example 3 In a solution of 200 g / l NaOH and 5 g / l of KMnO 4, AlCrN coated steel drills were stripped off at 60 ° C. in 35 to 50 minutes, layer thickness 3.5 μm, deposition parameters according to test A, B, C.

Example 4

In a solution of 20 g / 1 NaOH (pH 13.7) and 15 g / 1 KMn04 and 20 g / 1 sodium bicarbonate and 20 g / 1 sodium carbonate, an AlCrN coated steel drill was stripped in 40 to 55 minutes, layer thickness 3 microns, deposition parameters according to experiment A, B, C.

Example 5

AlCr / AlCrN-coated HSS drills (6 mm), layer thickness AlCr 0.25, AlCrN 3.71 μm, were coated with an aqueous solution of 20 g / l NaOH and 20 g / l of KMnO 4 (pH 13.47) at a temperature of 20 ° C. completely stripped in 30 minutes.

Example 6

For Example 6, two AlCr (70/30 and 50/50) and four TiAl (70/30 and 50/50) targets, respectively, were incorporated into a coating machine as described above. Subsequently, with the two AlCr targets under, as described under A or C, parameters, using argon instead of nitrogen, an approx. 0.3 μm thick AlCr layer deposited on different workpieces. Finally, a known Balinit Futura Nano layer (TiAlN) with a layer thickness of 4 to 5 μm was applied as cover layer. These layer systems could also be removed with a solution according to Example 1 at room temperature within 30 to 60 minutes.

Example 7

In an equipped with targets as in Example 6 plant was first about 1 micron thick AlCrN layer without metallic intermediate layer under the parameters described under A and C, and finally as a final layer again a Balinit Futura nano-layer (TiAlN) with a Layer thickness of 5 microns applied. Peeling time with a solution according to Example 1, at room temperature 50 to 65 minutes.

Example 8

Here, the temperature dependence of the stripping was examined with a stripping solution with 2% KMn0 ₄ and 2% NaOH (pH 13.46). HSS drills were stripped at room temperature and at 5 ° C. It was found that the delamination at low temperatures, as expected, slower, but still significantly faster than most known Entschichtungsverfahren runs. For details see table 2 below.

Table 2

Comparative examples

Example 9

A DLC layer (Balinit DLC) with a layer thickness of 2 .mu.m applied with a 0.3 .mu.m thick Cr intermediate layer was removed from a steel drill in about 3 hours in a permanganate solution as described in Example 1.

Example 10

In a solution of 200 g / 1 cerium ammonium nitrate and 32.5 g / 1 acetic acid coated with 3 microns AlCrN drills made of different steels were stripped in 2 hours. Depending on the type of steel, however, some of the corrosive attack on the surface could be detected.

Example 11

In a solution according to example 5 it was attempted to remove the following layers of 6 mm HSS drills at 20 ° C.: balinite A (TiN), layer thickness 5.1 μm; Balinit C (Cr / CrC / WC / C), layer thickness 1.4 μm WC / C, 0.5 μm Cr / CrC adhesive layer; Balinit Futura Nano (TiAlN with a thin TiAl adhesion layer), total layer thickness 4.4 μm; Balinit D (Cr / CrN), layer thickness Cr 0.5, CrN 3.2 μm. Unlike the AlCrN layer of Example 5, none of the layers could be stripped fast enough to meet the needs of industrial manufacturing. So even after 8 hours, none of the drills could detect an exposure of the base material. With Balinit A coated drills, even after 10.5 hours no layer removal could be determined, with Balinit Futura Nano after 10.5 hours only a layer removal of one tenth of a μm was measured and with Balinit C coated drills the open area and phase were completely decoated after 10.5 hours, whereas only about 50% of the layer had been detached in the chip flute. Only the relatively thin Balinit C layers could be completely removed after approx. 9 hours.

Example 12

A TiN / TiAlN coated hob with a total layer thickness of about 6 microns (TiAl about 0.3 microns), and test specimens with different layer thicknesses were in an alkaline 30% H ₂ 0 solution, pH 14.2, at 30 ° C with the addition a potassium sodium tartrate, a fluorosurfactant and other reagents treated analogously to Example 2 of DE 4339502. Only after 24 hours had the substrate surface been exposed on specimens with a layer thickness of 2.2 μm. However, even with thicker layers, a significant reduction in the layer thickness could be measured. Complete stripping of the hob was only achieved after 48 hours. Due to the known high reactivity of such a solution additional Sieherneitsmassnahmen, such as a Sehne11spurlung, rapid cooling or the like to take. Cleaning baths for removal of brown residue

In order to remove any adhering traces of brownish clay, the stripped tools with adhering brownstone residues were immersed for 10 minutes at a temperature of 20 ° C. in an aqueous solution.

Particularly well, as shown in Table 3 below, are weakly acidic solutions, with a pH between 3.5 and 7, since in this area a good solution of the residues can be done without the workpiece surface of the

Attacking steel. In the case of particularly sensitive hard metals, the addition of an inhibitor is recommended in all cases in order to prevent corrosive damage by the cleaning solution.

Experiment M was carried out with ultrasound support. Deconnex 29 AC is a lactic acid-based industrial cleaner that also contains inhibitors (especially benzotriazole) to protect the metal surface, avoiding surface damage from the more acidic environment. Such cleaned workpieces can be readily charged after the usual rinsing and drying steps for recoating in a PVD or CVD coating plant. If required, an additional microblasting process may be provided to compensate for any differences in surface finish, such as may arise from the use of tools after the first or previous coating.

A similar behavior results when the temperature of the cleaning solution is increased to 50 ° and the treatment time is shortened to 2 minutes. However, here too K and L are already finding a slight attack on the steel substrate.

Table 3

Cleaning solutions such as in Experiments H, K and M of the above table are preferable to hitherto conventional hydrogen peroxide-based solutions for the removal of manganese dioxide, since they do not require additional safety measures as mentioned under Example 12. For the sake of completeness, however, mention should be made here of a hydrogen peroxide-based formulation: H ₂ O ₂ 35%, pH 3 to 8, cleaning time at room temperature about 5 min. Such a method can also be carried out particularly advantageously in single-chamber systems, which are otherwise used, for example, for cleaning purposes, since in this case no highly aggressive or difficult-to-control chemicals have to be used, and thus neither expensive special materials for the execution of the chamber and accessories nor special precautions such as rapid rinsing , Quick cooling, pressure collecting vessels or the like are necessary. Such a single-chamber system can be operated at significantly lower costs than conventional stripping systems. It can be both different

Pre- and / or Nachbehandlungs-, in particular cleaning steps and the actual stripping are performed in the chamber with which all pre- or post-treatment steps can be omitted in any additional cleaning equipment. Compared to conventional systems, which usually work with Mehrbek- ken systems and automatic converter, this results in the advantage of a smaller footprint.

Based on FIG. 1 and the table summarizing the process steps, an exemplary sequence of a typical method according to the invention in a single-chamber system is shown below.

FIG. 1 schematically shows a dishwasher 22 to which various media containers 12, 13, 14 are connected. After loading a holder, such as a charging grid 3 with a coated workpiece 29 and closing the spray chamber 1, various process steps can be carried out. Table 4

i

>

Chamber volume: approx. 125 1

In the present example, a pre-cleaning followed by a fine cleaning is carried out according to Table 4 first. In this case, initially from a first container 12 via a first feed pump 15 and a first line 18, a first aqueous cleaning solution is supplied, which contains 3% of a first industrial cleaner and 2% of a second industrial cleaner. At the same time, a circulating pump 5 is switched on, which distributes the cleaning solution via a circulation line 4 and spray rotors 2 uniformly on the workpieces 29. Subsequently, the temperature of the cleaning solution is heated to 55 ° C for three minutes and the spraying process continues. At the end of the pre-cleaning, the first cleaning solution is pumped back into container 12 via a multi-way valve 30 and a first return line 9. In the following fine cleaning a similar procedure is selected, with deionized water via feed 21 and a third industrial cleaner via a first metering lance 23, circulated through the spray circuit 2, 4, 5 and tempered and then via drain pump 7, the multi-way valve 30 and drain 8, which leads in a Sammelbehäl not shown here, it is derived.

For the pre-cleaning, an industrial cleaner based on amine was used as the first cleaner, whereas the second cleaner consists of a mixture of phosphate, silicate and acetate. The third industrial cleaner used for the fine cleaning consists of potassium hydroxide with an acetate additive.

To carry out the actual stripping step, a 2% strength solution of potassium permanganate and sodium hydroxide solution is added from a second container 13 via a second pump 16 and second inlet 19. With this solution, depending on the layer thickness, the parts are treated for 10 to 40 minutes by switching on the spray circuit 2, 4, 5, and the solution is subsequently returned to the tank 13 via return pump 6 and second return line 10. After an intermediate rinsing with di-water, a process step for removal of possible brown residue, followed by a third container 14 via a third feed pump 17 and third line 20, a 5% aqueous citric acid solution, which advantageously also a corrosion protection, for example, amine-based Morpholine containing is added. After circulating spray and exposure to the citric acid solution, it is returned to tank 14 via drain pump 7, multi-way valve 30 and third return line 11. After rinsing with di-water, deionized water is added, circulated and discharged via feed 21 and sodium hydroxide solution via a second metering lance 24 to carry out an alkaline cleaning. Such intermediate rinses can also be provided between other process steps to eliminate any interfering impurities from a previous process step. Furthermore, it is also advantageous for this reason to keep the discharges from the spray chamber to the pumps 5, 6 and 7 as short as possible.

In order to reliably protect the workpieces 29 from corrosion during the final drying process and any intermediate storage, di-water is added via feed 21 and an amine-based anticorrosion agent via a third metering lance 25 and the mixture is heated to between 25 and 55 ° C heated, treated the workpieces 29 by circulating spray and then the corrosion protection solution via drain pump 7, the multi-way valve 30 and 8 outlet derived.

Finally, the workpieces 29 are dried via a hot air drying or circulation 26, 27, which is only shown schematically here. Preferably, the individual process steps are coordinated in a known manner via a process control. The parts thus treated are completely stripped and can generally be introduced directly into a vacuum treatment plant for re-stratification without further pretreatment. If required, further surface treatment steps, such as corundum or silicon carbide microjets, glass bead blasting or the like, may be performed before or after coating.

Such a method is particularly suitable for substantially cylindrical workpieces, such as rolling, shank, Kugelkopfräser or other shank tools. For the treatment of small parts, for example, a plurality of superposed Chargiergitter or one or more rotary drums can be provided.

In order to monitor the effectiveness / contamination of the individual chemicals, corresponding sensors can be used, for example, in the containers 12 to 14, the corresponding inlets (18 to 20) and return lines (9 to 10) or. be placed in the spray room 1, for example, when exceeding a certain metal ion concentration or too low activity of the cleaning / Entschichtungsreagens cause an alarm function or an automatic change of one or more treatment solutions.

Corresponding single-chamber systems can in principle also be used for other decoating methods, insofar either, similar to the method for decoating AlCr-containing layers, only well controllable chemical processes are carried out or corresponding for example as mentioned above protective devices and / or highly corrosion-resistant materials for individual parts or the entire single-chamber system can be used. LIST OF REFERENCE NUMBERS

1 spray room

2 spray rotors

3 Charging grid 4 Circulation line

5 circulation pump

6 return pump

7 exhaust pump

8 Procedure 9 First return

10 second return

11 third return

12 first container

13 second container 14 third container

15 first feed pump

16 second feed pump

17 third feed pump

18 first inlet 19 second inlet

20 third inlet

21 inlet

22 dishwasher

23 first metering lance 24 second metering lance

25 third metering lance 26 hot air inlet

27 hot air outlet

28 Heating coil 29 Workpiece

30 multi-way valve

Claims

PATENT APPLICATIONS

1. A method for detaching a layer system from a workpiece, characterized in that directly on the workpiece to improve the detachment behavior at least one chromium and aluminum-containing layer is applied, and the workpiece with an alkaline solution containing a strong oxidizing agent, is stripped.

2. The method according to claim 1, characterized in that the oxidizing agent is potassium permangant, Cerammoniumnitra, potassium peroxydisulfate, sodium peroxydisulfate or a mixture thereof.

3. The method according to claim 1, characterized in that the layer system is applied by PVD or CVD method.

4. The method according to claim 1, wherein the at least one layer comprises at least one of the following materials: metallic AlCr, TiAlCr and other AlCr alloys and / or the nitridic, carbidic, carbonitridic, boridic or nitridoboridic hard material compounds of the Aluminum chrome or other AlCr alloys.

5. The method according to claim 4, characterized in that the at least one layer consists of a sequence of layers, each comprising at least one of said materials.

6. The method according to claim 1, characterized in that the proportion of chromium in the metal content of the layer is between 20 and 70%.

7. The method according to claim 1, characterized in that the proportion of aluminum in the metal content of the layer is between 30 and 80%.

8. The method according to any one of claims 1, 4 and 5, characterized in that in the Schichtεystem on the layer one or more outer layers of at least one hard compound are applied, wherein the hard compound comprises at least one metal and at least one non-metal, the metal at least one of the elements of the IV, V, and VI subgroup of the periodic table of the elements (in particular Ti, Zr, Hf; V, Nb, Ta; Cr, Mo, W), aluminum or Si and the nonmetal C, N, B or 0 is.

9. The method according to claim 1, characterized in that the pH of the alkaline solution between 7 and 15, preferably greater than 9 and a permanganate concentration of 1 to 50 g / 1 is set.

10. The method according to claim 1, characterized in that the stripping temperature of the permanganate solution is maintained between 0 and 30 ° C, but preferably at room temperature.

11. The method according to claim 1, characterized in that after the detachment of the layer system, a cleaning in aqueous solution is carried out to solve any brownstone residues from the surface of the workpiece.

12. learn according to claim 11, characterized in that the pH of the aqueous solution is adjusted between 2 and 9, preferably between 3.5 and 7.

13. The method according to claim 12, characterized in that the solution contains phosphoric acid, a carboxylic acid or a hydroxycarboxylic acid.

14. The method according to claim 11, characterized in that the alkaline and / or the aqueous solution additionally contain an inhibitor for protecting the surface of the workpieces from corrosion.

15. The method according to any one of the preceding claims, characterized in that the workpiece is coated in a single-chamber system, wherein at least one further treatment step is carried out in the single-chamber system.

16. A method for detaching a layer system of a workpiece, characterized in that directly on the workpiece to improve the Ablöseverhal ens at least one chromium and aluminum-containing layer is applied, and the workpiece with an alkaline solution containing a strong oxidizing agent in one Single-chamber system is stripped, wherein at least one further treatment step is carried out in the single-chamber system.

17. The method according to claim 15 or 16, characterized in that the further treatment step comprises at least one cleaning process or at least one rinsing process or a combination of at least one cleaning and rinsing process.

18. The method according to claim 17, characterized in that the cleaning process comprises at least one pre- or fine cleaning.

19. The method according to claim 17 or 18, characterized in that the rinsing process comprises at least one alkaline rinsing or at least rinsing with corrosion protection.

20. The method according to any one of claims 15 to 19, characterized in that the further treatment step comprises a concluding drying of the workpieces.

21. Single-chamber system for carrying out a stripping process according to one of claims 15 to 20.

22. Einkammeranlage according to claim 21, characterized in that the Einkammeranlage (22) a spray chamber (1) with spray circuit (2, 4, 5), at least one support (3) for holding at least one workpiece (29) and at least one, preferably however, at least two media containers (12, 13, 14) connected to the spray chamber (1) via a media circuit (6, 7, 9 to 11 and 15 to 20).

23 single-chamber system according to claim 21 or 22, characterized in that spray circuit (2, 4, 5), medium cycle (6, 7, 9 to 11 and 15 to 20) and any other devices (21, 23 to 28) are process controlled.