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EP0318724A1 - Process for chemically stripping a high chromic surface coating from a work piece made from a nickel or cobalt based superalloy - Google Patents

Process for chemically stripping a high chromic surface coating from a work piece made from a nickel or cobalt based superalloy Download PDF

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Publication number
EP0318724A1
EP0318724A1 EP88118502A EP88118502A EP0318724A1 EP 0318724 A1 EP0318724 A1 EP 0318724A1 EP 88118502 A EP88118502 A EP 88118502A EP 88118502 A EP88118502 A EP 88118502A EP 0318724 A1 EP0318724 A1 EP 0318724A1
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EP
European Patent Office
Prior art keywords
solution
rest
fecl3
cucl2
following composition
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EP88118502A
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German (de)
French (fr)
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EP0318724B1 (en
Inventor
Vladimir Sova
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BBC Brown Boveri AG Switzerland
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BBC Brown Boveri AG Switzerland
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F1/00—Etching metallic material by chemical means
    • C23F1/44—Compositions for etching metallic material from a metallic material substrate of different composition

Definitions

  • the blade is a critical component, with protective layers against erosion, wear, corrosion and oxidation gaining in importance at high temperatures.
  • the protective layer usually has a shorter lifespan than the core material of the blade, which is why the renewability of the former is becoming increasingly important.
  • the invention relates to the further development of methods for repairing, repairing and renewing components of thermal machines which have been rendered unusable by erosion, wear, corrosion, oxidation or mechanical damage and are provided with protective layers.
  • the old existing protective layer must first be removed, which can basically be done mechanically or chemically.
  • the chemical method generally occupies a leading position in the field of surface change by erosion.
  • it relates to a method for chemically detaching a high-chromium surface protection layer from the base body of a component consisting of a nickel or cobalt-based superalloy.
  • solutions which contain nitrobenzenesulfonic acid and Na compounds for the chemical leaching of so-called "aluminum diffusion layers" on blade materials (cf. EP-A-0 161 387).
  • solutions containing iron sulfate and hydrochloric acid are recommended for removing chromium and aluminum-containing protective coatings based on cobalt, the iron sulfate having an oxidizing effect directly or via hydrolysis as sulfuric acid (cf. DE-B-27 17 435).
  • solutions with HNO3 and HF have been used to remove chromium- and aluminum-containing or aluminum-containing protective layers of nickel or cobalt-based alloys with a chromium content of more than 18% (cf. US-A-3 458 353).
  • the known processes using oxidizing solutions are based on the fact that they only weakly attack the core material of the base body, in the present case a nickel or cobalt-based superalloy, if it contains at least 7% by weight Cr.
  • the base body is always attacked preferentially, while the protective layer to be removed withstands longer. Therefore, the known methods mentioned above are not applicable to the modern material combinations of high-chromium protective layer / moderately chromium-containing superalloy.
  • the invention is based on the object of specifying a method for detaching a surface protection layer based on a Ni or Co alloy with a high Cr content from the base body of a component, which consists of a chromium-containing Ni and / or Co-based alloy.
  • the surface layer should be completely removed without the material of the base body being attacked, removed or damaged or its chemical-physical properties and its behavior with regard to compatibility, in particular impaired or changed, especially when a surface protective layer is subsequently reapplied (renewed).
  • the component is immersed in an aqueous chloride solution which does not give off oxygen and contains iron III and copper II for a period of 10 h to 150 h at a temperature in the range from 50 to 70 ° C. which contains further additives but does not contain any chromium oxide-forming constituents.
  • 1 shows a schematic cross section through the active part of the contents of a vessel for carrying out the method.
  • 1 is the chloride solution for chemical attack
  • 2 the base body (substrate) made of a nickel or cobalt-based superalloy (core material).
  • 3 shows the high-chromium surface protection layer. It can basically be built on a nickel or cobalt base.
  • 4 are pores in the surface protective layer 3, which have been formed by the chemical attack of the chloride solution 1.
  • 5 is an intermediate diffusion layer between the base body 2 and the surface protective layer 3, which is formed by a heat treatment during manufacture or in operation.
  • the surface protection layer 3 When immersed in the solution 1, the surface protection layer 3 shows a negative potential (indicated by the sign - and +) compared to the base body 2, on which the method of the currentless selective removal of the former is based.
  • the mainly present ions H Cooper; Fe3+; Cu2+; Cl ⁇
  • the mechanism of the resolution is shown schematically by symbols and arrows. The less noble chrome comes first moves in solution (Cr3+), while some of the iron and copper sink to the bottom as sludge (Fe o ; Cr o ), the rest remains in solution in the form of low valences (Fe2+; Cu+).
  • FIG. 2 shows a schematic metallographic section through the grain structure of the surface protection layer.
  • 6 are grains of the high-chromium surface protection layer 3 based on nickel or cobalt, which generally contain Al and Si in addition to Cr. At least part of the surface of the grains 6 is coated with a Cr2O3 cover layer, which has a passivating effect.
  • the mainly effective reaction mechanisms are indicated by arrows and symbols.
  • the invention is based on the selective dissolution of metals, characterized by different electrochemical potentials, which are immersed in an aggressive chemical solution. As a rule, the less noble elemental metal displaces the more noble from the solution and thereby goes into solution itself.
  • the general reaction scheme is as follows: Me + Fe3+ ⁇ Me+ + Fe2+ Me+ + Fe3+ ⁇ Me2+ + Fe2+ Me + Cu2+ ⁇ Me+ + Cu+ Me+ + Cu2+ ⁇ Me2+ + Cu+
  • the used scoop was cleaned by first immersing it in a 20% solution of NaOH at 100 ° C. for 24 h. The paddle was then removed from the solution, rinsed and immersed in concentrated HCl at 40 ° C for 24 hours. Finally, the shovel was rinsed and brushed with a steel brush.
  • the scoop was left in this bath for 15 hours, then removed, rinsed and brushed. No damage to the core material due to chemical attack was found.
  • a gas turbine blade provided with a surface protection layer and irregularly worn along the entire length of the airfoil was treated by the currentless method according to Example 1.
  • the airfoil had the same dimensions and the core material (MA 6000) the same composition as in Example 1.
  • the surface layer of 120 ⁇ m thick had been applied to the core material by plasma spraying and had the same composition as in Example 1.
  • the used blade was cleaned according to Example 1 by immersion in NaOH and HCl solution and treatment with a steel brush.
  • the bath had a temperature of 50 ° C. After a reaction time of 14 hours, the scoop was removed from the bath, rinsed, brushed and dried. The surface layer had been completely dissolved without attacking the substrate.
  • the partially corroded blade was cleaned according to Example 1 and then placed in a solution of the following composition: 200 g / l FeCl3 ⁇ 6H2O 1 g / l CuCl2 ⁇ 2H2O 10 ml / l glycerin 30 ml / l concentrated HCl rest H2O
  • the bath had a temperature of 70 ° C.
  • the treated gas turbine blade was removed from the bath after a reaction time of 144 hours, rinsed, brushed and dried. After the surface protective layer had completely dissolved, no attack on the core material could be determined.
  • a gas turbine blade provided with a surface protection layer and irregularly corroded along the entire length of the airfoil was treated in a manner similar to Example 1 using the currentless method.
  • the airfoil had the same dimensions and the core material (IN 738) the same composition as in Example 3.
  • the surface protective layer was on average 150 ⁇ m thick and was previously applied to the core material by plasma spraying. It had the same composition as that of Example 3.
  • the used scoop was cleaned according to Example 1 and then immersed in a solution of the following composition: 300 g / l FeCl3 ⁇ 6H2O 2 g / l CuCl2 ⁇ 2H2O 20 ml / l concentrated HCl rest H2O
  • the bath had a temperature of 60 ° C. After a reaction time of 120 hours, the blade was removed from the solution, rinsed, brushed and dried. When the surface protective layer was completely dissolved, no attack on the core material could be determined.
  • the bath temperature was 60 ° C, the total reaction time 1 h.
  • the core material remained unaffected after the treatment.
  • a corroded gas turbine blade provided with a surface protection view and irregular over the entire length of the airfoil was treated in the same way as in Example 1 by the currentless method.
  • the airfoil had the same dimensions and the core material (IN 738) the same composition as in Example 3.
  • the surface protection view was on average 120 ⁇ m thick and was previously applied to the core material by plasma spraying. It had the same composition as that of Example 3.
  • the used shovel was cleaned according to example 1 and then immersed in a solution of the following composition: 250 g / l FeCl3 ⁇ 6H2O 1 g / l CuCl2 ⁇ 2H2O 100 g / l NaCl 200 g / l citric acid rest H2O
  • the bath had a temperature of 65 ° C. After a reaction time of 100 h, the scoop was removed from the solution, rinsed, brushed and dried. When the surface protection view was completely dissolved, no attack on the core material could be determined.
  • the bath temperature was 60 ° C, the total reaction time 1 h.
  • the core material remained unaffected after the treatment.
  • the invention is not limited to the exemplary embodiments.
  • the electroless chemical detachment of a high-chromium surface protection view from a nickel or cobalt-based superalloy is achieved by immersing the component in question in an aqueous chloride solution containing non-oxygen, iron III and copper II, which also contains other additives however no constituents forming chromium oxide contains, valued for a period of 1 h to 150 h at a temperature of 50 to 70 ° C.
  • the chloride solution advantageously has the composition: 200 - 400 g / l FeCl3 ⁇ 6H2O 0.5 - 5 g / l CuCl2 ⁇ 2H2O 10 - 20 ml / l glycerin 120-200 ml / l concentrated HCl rest H2O

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • ing And Chemical Polishing (AREA)
  • Chemically Coating (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)

Abstract

Verfahren zum stromlosen chemischen Ablösen einer hochchromhaltigen Oberflächenschutzschicht (3) vom Grundkörper (2) eines aus einer Nickel- oder Kobaltbasis-Superlegierung bestehenden Bauteils durch Eintauchen in eine nicht Sauerstoff abgebende, Eisen III und Kupfer II enthaltende Chlorid-Lösung (1), welche noch weitere Zusätze, jedoch keinerlei Chromoxyd bildende Bestandteile enthält. Temperatur des Bades 50 bis 70 °C. Zeitdauer des Verweilens des Bauteils im Bad 10 bis 150 h. Typische Badzusammensetzung: 200 - 400 g/l, FeCl3 · 6H2O; 0,5 - 5 g/l, CuCl2 · 2H2O; 10 - 20 ml/l, Glyzerin; 120 - 200 ml/l, konzentrierte HCl; Rest, H2OProcess for the electroless chemical detachment of a high-chromium surface protection layer (3) from the base body (2) of a component consisting of a nickel or cobalt-based superalloy by immersion in a chloride solution (1) which does not give off oxygen and contains iron III and copper II, which still further additives, but contains no chromium oxide-forming constituents. Bath temperature 50 to 70 ° C. Duration of the component in the bath 10 to 150 h. Typical bath composition: 200 - 400 g / l, FeCl3 · 6H2O; 0.5 - 5 g / l, CuCl2 · 2H2O; 10-20 ml / l, glycerin; 120-200 ml / l, concentrated HCl; Rest, H2O

Description

Technisches GebietTechnical field

Gasturbinen für höchste Ansprüche. Kritisches Bauteil ist die Schaufel, wobei Schutzschichten gegen Erosion, Verschleiss, Korrosion und Oxydation bei hohen Temperaturen an Bedeutung gewinnen. Die Schutzschicht hat meist eine geringere Lebens­dauer als der Kernwerkstoff der Schaufel, weshalb die Er­neuerbarkeit der ersteren mehr und mehr in den Vordergrund rückt.Gas turbines for the highest demands. The blade is a critical component, with protective layers against erosion, wear, corrosion and oxidation gaining in importance at high temperatures. The protective layer usually has a shorter lifespan than the core material of the blade, which is why the renewability of the former is becoming increasingly important.

Die Erfindung bezieht sich auf die Weiterentwicklung von Verfahren zur Reparatur, Instandstellung und Erneuerung von durch Erosion, Verschleiss, Korrosion, Oxydation oder mechanische Beschädigung unbrauchbar gewordenen, mit Schutz­schichten versehenen Bauteilen thermischer Maschinen. Dabei muss zunächst die alte bestehende Schutzschicht entfernt werden, was grundsätzlich mechanisch oder chemisch erfolgen kann. Die chemische Methode nimmt ganz allgemein auf dem Gebiet der Oberflächenveränderung durch Abtrag eine führende Stellung ein.The invention relates to the further development of methods for repairing, repairing and renewing components of thermal machines which have been rendered unusable by erosion, wear, corrosion, oxidation or mechanical damage and are provided with protective layers. The old existing protective layer must first be removed, which can basically be done mechanically or chemically. The chemical method generally occupies a leading position in the field of surface change by erosion.

Insbesondere betrifft sie ein Verfahren zum chemischen Ablösen einer hochchromhaltigen Oberflächenschutzschicht vom Grund­körper eines aus einer Nickel- oder Kobaltbasis-Superlegie­rung bestehenden Bauteils.In particular, it relates to a method for chemically detaching a high-chromium surface protection layer from the base body of a component consisting of a nickel or cobalt-based superalloy.

Stand der TechnikState of the art

Die Entfernung von Schutzschichten auf Grundkörpern (Substrat) aus Superlegierungen wird in herkömmlicher Weise unter an­derem nach dem stromlosen chemischen Auflösungsverfahren durch Einwirkung von Lösungen vorgenommen, welche oxydierende Säuren als wesentlichen Bestandteil enthalten. So wird allgemein die Verwendung von HNO₃-haltigen Lösungen zur Auflösung von Nickelaluminide enthaltenden Schutzschichten empfohlen (Vergl. US-A-4 425 185; AU-B-10761/76; US-A-4 339 282; US-A-3607 398; US-A-3 622 391; US-A-3 833 414). Andere oxy­dierende Lösungen enthalten zum Beispiel H₂O₂ und werden zur Ablösung von Nickel eingesetzt (Vergl. US-A-4 554 049). Es ist ferner bekannt, Lösungen, welche Nitrobenzolsulfon­säure und Na-Verbindungen enthalten, zum chemischen Ablaugen von sogenannten "Aluminium-Diffusionsschichten" auf Schaufel­werkstoffen einzusetzen (Vergl. EP-A- 0 161 387). Des wei­teren werden Eisensulfat und Salzsäure enthaltende Lösungen zum Entfernen von Chrom und Aluminium enthaltenden Schutz­überzügen auf Kobaltbasis empfohlen, wobei das Eisensulfat direkt oder über Hydrolyse als Schwefelsäure oxydierend einwirkt (Vergl. DE-B-27 17 435). Ausserdem wurden schon Lösungen mit HNO₃ und HF zur Ablösung chrom- und aluminium-­haltiger oder aluminiumhaltiger Schutzschichten von Nickel- oder Kobaltbasislegierungen mit einem Chromgehalt von mehr als 18 % (Vergl. US-A-3 458 353) verwendet.Protective layers on base bodies (substrates) made of superalloys are removed in a conventional manner, inter alia by the electroless chemical dissolving process, by the action of solutions which contain oxidizing acids as an essential component. Thus, the use of HNO₃-containing solutions for dissolving protective layers containing nickel aluminides is generally recommended (cf. US-A-4 425 185; AU-B-10761/76; US-A-4 339 282; US-A-3607 398 ; US-A-3,622,391; US-A-3,833,414). Other oxidizing solutions contain, for example, H₂O₂ and are used to detach nickel (see US Pat. No. 4,554,049). It is also known to use solutions which contain nitrobenzenesulfonic acid and Na compounds for the chemical leaching of so-called "aluminum diffusion layers" on blade materials (cf. EP-A-0 161 387). Furthermore, solutions containing iron sulfate and hydrochloric acid are recommended for removing chromium and aluminum-containing protective coatings based on cobalt, the iron sulfate having an oxidizing effect directly or via hydrolysis as sulfuric acid (cf. DE-B-27 17 435). In addition, solutions with HNO₃ and HF have been used to remove chromium- and aluminum-containing or aluminum-containing protective layers of nickel or cobalt-based alloys with a chromium content of more than 18% (cf. US-A-3 458 353).

Die bekannten, mit oxydierenden Lösungen arbeitenden Verfahren, stützen sich auf die Erfahrungstatsache, dass sie den Kern­werkstoff des Grundkörpers, im vorliegenden Fall eine Nickel- oder Kobaltbasis-Superlegierung nur schwach angreifen, wenn er wenigsten 7 Gew.-% Cr enthält. Ein Verfahren, bei dem ausser der der Schutzschicht auch noch der Grundkörper ab­getragen wird, ist selbstverständlich in den meisten Fällen für die Praxis unbrauchbar.
Durch den Uebergang zu immer höheren Cr-Gehalten der Schutz­schichten werden jedoch die Verhältnisse der elektrochemi­schen Potentiale des Kernwerkstoffs zu demjenigen der Schutz­schicht gerade umgekehrt: Die Schutzschicht wird in oxydieren­der Lösung gegenüber dem Grundkörper positiv. Das hat zur Folge, dass die Schutzschicht weder elektrolytisch noch stromlos-chemisch entfernt werden kann. Es wird immer der Grundkörper bevorzugt angegriffen, während die zu entfernende Schutzschicht länger standhält. Deshalb sind die oben ge­nannten bekannten Verfahren auf die neuzeitlichen Material­kombinationen hochchromhaltige Schutzschicht / mässig chrom­haltige Superlegierung nicht anwendbar.The known processes using oxidizing solutions are based on the fact that they only weakly attack the core material of the base body, in the present case a nickel or cobalt-based superalloy, if it contains at least 7% by weight Cr. A process in which In addition to the fact that the protective layer is also removed, it is of course unusable in practice in most cases.
The transition to ever higher Cr contents of the protective layers, however, reverses the ratio of the electrochemical potentials of the core material to that of the protective layer: the protective layer becomes positive with respect to the base body in oxidizing solution. The consequence of this is that the protective layer cannot be removed electrolytically or electrolessly. The base body is always attacked preferentially, while the protective layer to be removed withstands longer. Therefore, the known methods mentioned above are not applicable to the modern material combinations of high-chromium protective layer / moderately chromium-containing superalloy.

Darstellung der ErfindungPresentation of the invention

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zum Ablösen einer auf einer Ni- oder Co-Legierung mit hohem Cr-Gehalt basierenden Oberflächenschutzschicht vom Grund­körper eines Bauteils anzugeben, der aus einer chromhaltigen Ni- und/oder Co-Basislegierung besteht. Dabei soll die Ober­flächenschicht vollständig entfernt werden, ohne dass der Werkstoff des Grundkörpers angegriffen, abgetragen oder beschädigt oder in seinen chemisch-physikalischen Eigenschaften und in seinem Verhalten bezüglich Verträglichkeit insbeondere beim nachträglichen Wideraufbringen (Erneuern) einer Ober­flächenschutzschicht beeinträchtigt oder verändert wird.The invention is based on the object of specifying a method for detaching a surface protection layer based on a Ni or Co alloy with a high Cr content from the base body of a component, which consists of a chromium-containing Ni and / or Co-based alloy. The surface layer should be completely removed without the material of the base body being attacked, removed or damaged or its chemical-physical properties and its behavior with regard to compatibility, in particular impaired or changed, especially when a surface protective layer is subsequently reapplied (renewed).

Diese Aufgabe wird dadurch gelöst, dass im eingangs erwähnten Verfahren das Bauteil während einer Zeit von 10 h bis 150 h bei einer Temperatur im Bereich von 50 bis 70 °C in eine nicht Sauerstoff abgebende, Eisen III und Kupfer II enthal­tende wässrige Chlorid-Lösung, welche noch weitere Zusätze, jedoch keinerlei Chromoxyd bildende Bestandteile enthält, getaucht wird.This object is achieved in that, in the process mentioned at the outset, the component is immersed in an aqueous chloride solution which does not give off oxygen and contains iron III and copper II for a period of 10 h to 150 h at a temperature in the range from 50 to 70 ° C. which contains further additives but does not contain any chromium oxide-forming constituents.

Weg zur Ausführung der ErfindungWay of carrying out the invention

Die Erfindung wird anhand der nachfolgenden, durch Figuren näher erläuterten Ausführungsbeispiele beschrieben.
Dabei zeigt:

  • Fig. 1 einen schematischen Querschnitt durch den aktiven Teil des Inhalts eines Gefässes zur Durchführung des Verfahrens,
  • Fig. 2 einen schematischen metallographischen Schnitt durch die Kornstruktur der Oberflächenschutzschicht.
The invention is described on the basis of the following exemplary embodiments which are explained in more detail by means of figures.
It shows:
  • 1 shows a schematic cross section through the active part of the contents of a vessel for carrying out the method,
  • Fig. 2 shows a schematic metallographic section through the grain structure of the surface protective layer.

In Fig. 1 ist ein schematischer Querschnitt durch den aktiven Teil des Inhalts eines Gefässes zur Durchführung des Verfah­rens dargestellt. Die unwesentlichen Teile, welche nicht massgebend am prinzipiellen Verfahrensablauf beteiligt sind, wie das Gefäss selbst, Rühreinrichtungen etc. sind der Ueber­sichtlichkeit halber weggelassen worden. 1 ist die Chlorid-­Lösung für den chemischen Angriff, 2 der Grundkörper (Sub­strat) aus einer Nickel- oder Kobaltbasis-Superlegierung (Kernwerkstoff). 3 stellt die hochchromhaltige Oberflächen­schutzschicht dar. Sie kann grundsätzlich auf einer Nickel- oder Kobaltbasis aufgebaut sein. 4 sind Poren in der Ober­flächenschutzschicht 3, welche sich durch den chemischen Angriff der Chlorid-Lösung 1 gebildet haben. 5 ist eine Diffusions-Zwischenschicht zwischen dem Grundkörper 2 und der Oberflächenschutzschicht 3, welche sich durch eine Wärme­behandlung während der Fabrikation oder im Betrieb bildet. Die Oberflächenschutzschicht 3 zeigt beim Eintauchen in die Lösung 1 gegenüber dem Grundkörper 2 ein negatives Po­tential (durch Vorzeichen - und + angedeutet), worauf das Verfahren des stromlosen selektiven Abtragens der ersteren beruht. In der Chlorid-Lösung 1 sind die hauptsächlich vor­handenen Ionen (H⁺; Fe³⁺; Cu²⁺; Cl⁻) angedeutet. Der Mecha­nismus der Auflösung ist schematisch durch Symbole und Pfeile dargestellt. Dabei geht vor allem das unedlere Chrom bevor­ zugt in Lösung (Cr³⁺), während ein Teil des Eisens und des Kupfers als Schlamm zu Boden sinken (Feº; Crº), der übrige in Form niedriger Valenzen (Fe²⁺; Cu⁺) in Lösung bleibt.1 shows a schematic cross section through the active part of the contents of a vessel for carrying out the method. The insignificant parts, which are not significantly involved in the basic process, such as the vessel itself, stirring devices etc., have been omitted for the sake of clarity. 1 is the chloride solution for chemical attack, 2 the base body (substrate) made of a nickel or cobalt-based superalloy (core material). 3 shows the high-chromium surface protection layer. It can basically be built on a nickel or cobalt base. 4 are pores in the surface protective layer 3, which have been formed by the chemical attack of the chloride solution 1. 5 is an intermediate diffusion layer between the base body 2 and the surface protective layer 3, which is formed by a heat treatment during manufacture or in operation. When immersed in the solution 1, the surface protection layer 3 shows a negative potential (indicated by the sign - and +) compared to the base body 2, on which the method of the currentless selective removal of the former is based. The mainly present ions (H hauptsächlich; Fe³⁺; Cu²⁺; Cl⁻) are indicated in the chloride solution 1. The mechanism of the resolution is shown schematically by symbols and arrows. The less noble chrome comes first moves in solution (Cr³⁺), while some of the iron and copper sink to the bottom as sludge (Fe º ; Cr º ), the rest remains in solution in the form of low valences (Fe²⁺; Cu⁺).

Fig. 2 stellt einen schematischen metallographischen Schnitt durch die Kornstruktur der Oberflächenschutzschicht dar. 6 sind Körner der hochchromhaltigen Oberflächenschutzschicht 3 auf Nickelbasis oder Kobaltbasis, welche ausser Cr in der Regel noch Al und Si enthalten. Wenigstens ein Teil der Oberfläche der Körner 6 ist mit einer Cr₂O₃-Deckschicht überzogen, die passivierend wirkt. Die hauptsächlich wirk­samen Reaktionsmechanismen sind durch Pfeile und Symbole angedeutet.2 shows a schematic metallographic section through the grain structure of the surface protection layer. 6 are grains of the high-chromium surface protection layer 3 based on nickel or cobalt, which generally contain Al and Si in addition to Cr. At least part of the surface of the grains 6 is coated with a Cr₂O₃ cover layer, which has a passivating effect. The mainly effective reaction mechanisms are indicated by arrows and symbols.

Die Erfindung beruht auf der durch verschieden hohe elek­trochemische Potentiale charakterisierten selektiven Auf­lösung von Metallen, die in eine aggressive chemische Lösung getaucht werden. Dabei verdrängt in der Regel das unedlere elementare Metall das edlere aus der Lösung und geht dabei selbst in Lösung. Das allgemeine Reaktionsschema stellt sich dabei wie folgt:

Me + Fe³⁺ → Me⁺ + Fe²⁺
Me⁺ + Fe³⁺ → Me²⁺ + Fe²⁺
Me + Cu²⁺ → Me⁺ + Cu⁺
Me⁺ + Cu²⁺ → Me²⁺ + Cu⁺
The invention is based on the selective dissolution of metals, characterized by different electrochemical potentials, which are immersed in an aggressive chemical solution. As a rule, the less noble elemental metal displaces the more noble from the solution and thereby goes into solution itself. The general reaction scheme is as follows:

Me + Fe³⁺ → Me⁺ + Fe²⁺
Me⁺ + Fe³⁺ → Me²⁺ + Fe²⁺
Me + Cu²⁺ → Me⁺ + Cu⁺
Me⁺ + Cu²⁺ → Me²⁺ + Cu⁺

Ausführungsbeispiel 1:Example 1:

Eine mit einer Oberflächenschutzschicht versehene, an ihrem Schaufelblatt korrodierte und teilweise mechanisch beschädigte Gasturbinenschaufel hatte folgende Abmessungen (Schaufelblatt): Länge = 185 mm Grösste Breite = 93 mm Grösste Dicke = 24 mm Profilhöhe = 30 mm A gas turbine blade provided with a surface protective layer, corroded on its airfoil and partially mechanically damaged, had the following dimensions (airfoil): Length = 185 mm Largest width = 93 mm Greatest thickness = 24 mm Profile height = 30 mm

Der Kernwerkstoff der Gasturbinenschaufel bestand aus einer oxyddispersionsgehärteten Nickelbasis-Superlegierung mit dem Handelsnamen MA 6000 von INCO von folgender Zusammen­setzung: Cr = 15 Gew.-% W = 4,0 Gew.-% Mo = 2,0 Gew.-% Al = 4,5 Gew.-% Ti = 2,5 Gew.-% Ta = 2,0 Gew.-% C = 0,05 Gew.-% B = 0,01 Gew.-% Zr = 0,15 Gew.-% Y₂O₃ = 1,1 Gew.-% Ni = Rest The core material of the gas turbine blade consisted of an oxide dispersion hardened nickel-based superalloy with the trade name MA 6000 from INCO with the following composition: Cr = 15% by weight W = 4.0% by weight Mo = 2.0% by weight Al = 4.5% by weight Ti = 2.5% by weight Ta = 2.0% by weight C = 0.05% by weight B = 0.01% by weight Zr = 0.15% by weight Y₂O₃ = 1.1% by weight Ni = rest

Die Oberflächenschutzschicht von 100 µm Dicke war durch Plasmaspritzen auf den Kernwerkstoff aufgetragen worden und hatte folgende Zusammensetzung: Cr = 20,5 Gew.-% Al = 11,5 Gew.-% Si = 2,5 Gew.-% Ta = 1 Gew.-% Co = 12 Gew.-% Ni = Rest The surface protective layer, 100 µm thick, was applied to the core material by plasma spraying and had the following composition: Cr = 20.5% by weight Al = 11.5% by weight Si = 2.5% by weight Ta = 1% by weight Co = 12% by weight Ni = rest

Die gebrauchte Schaufel wurde gereinigt, indem sie zunächst während 24 h bei 100 °C in eine 20%ige Lösung von NaOH ge­taucht. Dann wurde die Schaufel aus der Lösung herausgenommen, gespült und während 24 h bei 40 °C in konzentrierte HCl getaucht. Zum Schluss wurde die Schaufel gespült und mit einer Stahlbürste gebürstet.The used scoop was cleaned by first immersing it in a 20% solution of NaOH at 100 ° C. for 24 h. The paddle was then removed from the solution, rinsed and immersed in concentrated HCl at 40 ° C for 24 hours. Finally, the shovel was rinsed and brushed with a steel brush.

Nach der Reinigung wurde die Schaufel in eine 70 °C warme Lösung der nachfolgenden Zusammensetzung getaucht: 300 g/l FeCl₃ · 6H₂O 2,5 g/l CnCl₂ · 2H₂O 15 ml/l Glyzerin 150 ml/l konzentrierte HCl Rest H₂O After cleaning, the scoop was placed in a 70 ° C warm Solution of the following composition immersed: 300 g / l FeCl₃ · 6H₂O 2.5 g / l CnCl₂ · 2H₂O 15 ml / l glycerin 150 ml / l concentrated HCl rest H₂O

Die Schaufel wurde während 15 h in diesem Bad belassen, nachher herausgenommen, gespült und gebürstet. Dabei konnte keine Beeinträchtigung des Kernwerkstoffs durch chemischen Angriff festgestellt werden.The scoop was left in this bath for 15 hours, then removed, rinsed and brushed. No damage to the core material due to chemical attack was found.

Ausführungsbeispiel 2:Example 2:

Eine mit einer Oberflächenschutzschicht versehene, auf der ganzen Länge des Schaufelblattes unregelmässig abgenutzte Gasturbinenschaufel wurde nach dem stromlosen Verfahren gemäss Beispiel 1 behandelt. Das Schaufelblatt hatte die gleichen Abmessungen und der Kernwerkstoff (MA 6000) die gleiche Zusammensetzung wie in Beispiel 1.
Die Oberflächenschicht von 120 µm Dicke war durch Plasma­spritzen auf den Kernwerkstoff aufgetragen worden und hatte die gleiche Zusammensetzung wie in Beispiel 1. Die gebrauchte Schaufel wurde gemäss Beispiel 1 durch Eintauchen in NaOH- und HCl-Lösung und Behandlung mit einer Stahlbürste gereinigt.A gas turbine blade provided with a surface protection layer and irregularly worn along the entire length of the airfoil was treated by the currentless method according to Example 1. The airfoil had the same dimensions and the core material (MA 6000) the same composition as in Example 1.
The surface layer of 120 μm thick had been applied to the core material by plasma spraying and had the same composition as in Example 1. The used blade was cleaned according to Example 1 by immersion in NaOH and HCl solution and treatment with a steel brush.

Nach der Reinigung wurde die Schaufel in ein Bad der nach­folgenden Zusammensetzung getaucht: 500 g/l FeCl₃ · 6H₂O 5 g/l CuCl₂ · 2H₂O 20 ml/l Glyzerin Rest H₂O After cleaning, the shovel was immersed in a bath of the following composition: 500 g / l FeCl₃ · 6H₂O 5 g / l CuCl₂ · 2H₂O 20 ml / l glycerin rest H₂O

Das Bad hatte eine Temperatur von 50 °C. Nach einer Reaktions­zeit von 14 h wurde die Schaufel aus dem Bad herausgenommen, gespült, gebürstet und getrocknet. Die Oberflächenschicht war vollständig aufgelöst worden, ohne dass das Substrat angegriffen worden war.The bath had a temperature of 50 ° C. After a reaction time of 14 hours, the scoop was removed from the bath, rinsed, brushed and dried. The surface layer had been completely dissolved without attacking the substrate.

Ausführungsbeispiel 3:Example 3:

Eine mit einer Oberflächenschutzschicht versehene, an ihrem Schaufelblatt teilweise korrodierte Gasturbinenschaufel hatte folgende Abmessungen (Schaufelblatt): Länge = 170 mm Grösste Breite = 86 mm Grösste Dicke = 22 mm Profilhöhe = 27 mm A gas turbine blade provided with a surface protection layer and partially corroded on its airfoil had the following dimensions (airfoil): Length = 170 mm Largest width = 86 mm Greatest thickness = 22 mm Profile height = 27 mm

Der Kernwerkstoff der Gasturbinenschaufel bestand aus einer Nickelbasis-Guss-Superlegierung mit dem Handelsnamen IN 738 von INCO mit folgender Zusammensetzung: Cr = 16,0 Gew.-% Co = 8,5 Gew.-% Mo = 1,75 Gew.-% W = 2,6 Gew.-% Ta = 1,75 Gew.-% Nb = 0,9 Gew.-% Al = 3,4 Gew.-% Ti = 3,4 Gew.-% Zr = 0,1 Gew.-% B = 0,01 Gew.-% C = 0,11 Gew.-% Ni = Rest The core material of the gas turbine blade consisted of a nickel-based cast superalloy with the trade name IN 738 from INCO with the following composition: Cr = 16.0% by weight Co = 8.5% by weight Mo = 1.75% by weight W = 2.6% by weight Ta = 1.75% by weight Nb = 0.9% by weight Al = 3.4% by weight Ti = 3.4% by weight Zr = 0.1% by weight B = 0.01% by weight C = 0.11% by weight Ni = rest

Die Oberflächenschutzschicht von 120 µm Dicke war durch Plasmaspritzen auf den Kernwerkstoff aufgetragen worden und hatte die nachfolgende Zusammensetzung: Cr = 25 Gew.-% Al = 7 Gew.-% Y = 0,7 Gew.-% C < 0,002 Gew.-% Co = Rest The surface protection layer, 120 µm thick, was applied to the core material by plasma spraying and had the following composition: Cr = 25% by weight Al = 7% by weight Y = 0.7% by weight C < 0.002% by weight Co = rest

Die teilweise korrodierte Schaufel wurde gemäss Beispiel 1 gereinigt und dann in eine Lösung der folgenden Zusammen­setzung gestellt: 200 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 10 ml/l Glyzerin 30 ml/l konzentrierte HCl Rest H₂O The partially corroded blade was cleaned according to Example 1 and then placed in a solution of the following composition: 200 g / l FeCl₃ · 6H₂O 1 g / l CuCl₂ · 2H₂O 10 ml / l glycerin 30 ml / l concentrated HCl rest H₂O

Das Bad hatte eine Temperatur von 70 °C. Die behandelte Gasturbinenschaufel wurde nach 144 h Reaktionszeit aus dem Bad herausgenommen, gespült, gebürstet und getrocknet. Nach vollständiger Auflösung der Oberflächenschutzschicht konnte kein Angriff des Kernwerkstoffs festgestellt werden.The bath had a temperature of 70 ° C. The treated gas turbine blade was removed from the bath after a reaction time of 144 hours, rinsed, brushed and dried. After the surface protective layer had completely dissolved, no attack on the core material could be determined.

Ausführungsbeispiel 4:Example 4:

Eine mit einer Oberflächenschutzschicht versehene, auf der ganzen Länge des Schaufelblattes unregelmässig korrodierte Gasturbinenschaufel wurde nach dem stromlosen Verfahren ähnlich Beispiel 1 behandelt. Das Schaufelblatt hatte die gleichen Abmessungen und der Kernwerkstoff (IN 738) die gleiche Zusammensetzung wie in Beispiel 3.
Die Oberflächenschutzschicht war durchschnittliche 150 µm dick und war ehemals durch Plasmaspritzen auf den Kernwerk­stoff aufgetragen worden. Sie hatte die gleiche Zusammen­setzung wie diejenige von Beispiel 3.
Die gebrauchte Schaufel wurde gemäss Beispiel 1 gereinigt und daraufhin in eine Lösung der folgenden Zusammensetzung eingetaucht: 300 g/l FeCl₃ · 6H₂O 2 g/l CuCl₂ · 2H₂O 20 ml/l konzentrierte HCl Rest H₂O A gas turbine blade provided with a surface protection layer and irregularly corroded along the entire length of the airfoil was treated in a manner similar to Example 1 using the currentless method. The airfoil had the same dimensions and the core material (IN 738) the same composition as in Example 3.
The surface protective layer was on average 150 µm thick and was previously applied to the core material by plasma spraying. It had the same composition as that of Example 3.
The used scoop was cleaned according to Example 1 and then immersed in a solution of the following composition: 300 g / l FeCl₃ · 6H₂O 2 g / l CuCl₂ · 2H₂O 20 ml / l concentrated HCl rest H₂O

Das Bad hatte eine Temperatur von 60 °C. Die Schaufel wurde nach 120 h Reaktionszeit aus der Lösung herausgenommen, gespült, gebürstet und getrocknet. Bei vollständiger Auflö­sung der Oberflächenschutzschicht konnte keinerlei Angriff des Kernwerkstoffs festgestellt werden.The bath had a temperature of 60 ° C. After a reaction time of 120 hours, the blade was removed from the solution, rinsed, brushed and dried. When the surface protective layer was completely dissolved, no attack on the core material could be determined.

Ausführungsbeispiel 5:Example 5:

Der Versuch gemäss Beispiel 4 wurde wiederholt, wobei jedoch die Lösung zur Entfernung der Oberflächenschutzschicht die nachfolgende Zusammensetzung hatte: 300 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 30 g/l NH₄HF₂ Rest H₂O The experiment according to Example 4 was repeated, but the solution for removing the surface protective layer had the following composition: 300 g / l FeCl₃ · 6H₂O 1 g / l CuCl₂ · 2H₂O 30 g / l NH₄HF₂ rest H₂O

Die Badtemperatur betrug 60 °C, die totale Reaktionszeit 1 h. Nach der Behandlung war der Kernwerkstoff unangegriffen geblieben.The bath temperature was 60 ° C, the total reaction time 1 h. The core material remained unaffected after the treatment.

Ausführungsbeispiel 6:Example 6:

Eine mit einer Oberflächenschutzsicht versehene, auf der ganzen Länge des Schaufelblattes unregelmässige korrodierte Gasturbineneschaufel wurde nach dem stromlosen Verfahren änlich Beispiel 1 behandelt. Das Schaufelblatt hatte die gleichen Abmessungen und der Kernwerkstoff (IN 738) die gleiche Zusammensetzung wie in Beispiel 3.
Die Oberflächenschutzsicht war durchschnittliche 120 µm dick und war ehemals durch Plasmaspritzen auf den Kernwerk­stoff aufgetragen worden. Sie hatte die gleiche Zusammen­setzung wie diejenige von Beispiel 3.
Die gebrauchte Schaufel wurde gemäss Beispiel 1 gereinigt und daraufhin in eine Lösung der folgenden Zusammensetzung eingetaucht: 250 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 100 g/l NaCl 200 g/l Zitronensäure Rest H₂O A corroded gas turbine blade provided with a surface protection view and irregular over the entire length of the airfoil was treated in the same way as in Example 1 by the currentless method. The airfoil had the same dimensions and the core material (IN 738) the same composition as in Example 3.
The surface protection view was on average 120 µm thick and was previously applied to the core material by plasma spraying. It had the same composition as that of Example 3.
The used shovel was cleaned according to example 1 and then immersed in a solution of the following composition: 250 g / l FeCl₃ · 6H₂O 1 g / l CuCl₂ · 2H₂O 100 g / l NaCl 200 g / l citric acid rest H₂O

Das Bad hatte eine Temperatur von 65°C. Die Schaufel wurde nach 100 h Reaktionszeit aus der Lösung herausgenommen, gespült, gebürstet und getrocknet. Bei vollständiger Auflö­sung der Oberflächenschutzsicht konnte keinerlei Angriff des Kernwerkstoffs festgestellt werden.The bath had a temperature of 65 ° C. After a reaction time of 100 h, the scoop was removed from the solution, rinsed, brushed and dried. When the surface protection view was completely dissolved, no attack on the core material could be determined.

Ausführungsbeispiel 7:Embodiment 7:

Der Versuch gemäss Beispiel 6 wurde wiederholt, wobei jedoch die Lösung zur Entfernung der Oberflächenschutzschicht die nachfolgende Zusammensetzung hatte: 300 g/l FeCl₃ · 6H₂O 0,5 g/l CuCl₂ · 2H₂O 50 g/l NaCl 100 g/l Oxalsäure Rest H₂O The experiment according to Example 6 was repeated, but the solution for removing the surface protective layer had the following composition: 300 g / l FeCl₃ · 6H₂O 0.5 g / l CuCl₂ · 2H₂O 50 g / l NaCl 100 g / l Oxalic acid rest H₂O

Die Badtemperatur betrug 60 °C, die totale Reaktionszeit 1 h. Nach der Behandlung war der Kernwerkstoff unangegriffen geblieben.The bath temperature was 60 ° C, the total reaction time 1 h. The core material remained unaffected after the treatment.

Die Erfindung ist nicht auf die Ausführungsbeisiele beschränkt Das stromlose chemische Ablösen einer hochchromhaltigen Oberflächenchutzsicht von einer Nickel- oder Kobaltbasis-­Superlegierung wird durch Eintauchen des betreffenden Bauteils in eine nicht Sauerstoff aggebende, Eisen III und Kupfer II enthaltende wässrige Chlorid-Lösung, welche noch weitere Zusätze jedoch keinerlei Chromoxyd bildende Bestandteile enthält, während einer Zeit von 1 h bis 150 h bei einer Temperatur von 50 bis 70 °C bewerktelligt. Vorteilhafter­weise hat die Chlorid-Lösung die Zusammensetzung: 200 - 400 g/l FeCl₃ · 6H₂O 0,5 - 5 g/l CuCl₂ · 2H₂O 10 - 20 ml/l Glyzerin 120 - 200 ml/l konzentrierte HCl Rest H₂O The invention is not limited to the exemplary embodiments. The electroless chemical detachment of a high-chromium surface protection view from a nickel or cobalt-based superalloy is achieved by immersing the component in question in an aqueous chloride solution containing non-oxygen, iron III and copper II, which also contains other additives however no constituents forming chromium oxide contains, valued for a period of 1 h to 150 h at a temperature of 50 to 70 ° C. The chloride solution advantageously has the composition: 200 - 400 g / l FeCl₃ · 6H₂O 0.5 - 5 g / l CuCl₂ · 2H₂O 10 - 20 ml / l glycerin 120-200 ml / l concentrated HCl rest H₂O

Claims (8)

1. Verfahren zum chemischen Ablösen einer hochchromhaltigen Oberflächenschutzschicht (3) vom Grundkörper (2) eines aus einer Nickel- oder Kobaltbasis-Superlegierung be­stehenden Bauteils, dadurch gekennzeichnet, dass das Bauteil während einer Zeit von 1 h bis 150 h bei einer Temperatur im Bereich von 50 bis 70 °C in eine nicht Sauerstoff abgebende, Eisen III und Kupfer II enthaltende wässrige Chlorid-Lösung (1), welche noch weitere Zusätze jedoch keinerlei Chromoxyd bildende Bestandteile enthält, getaucht wird.1. A process for the chemical detachment of a high-chromium surface protection layer (3) from the base body (2) of a component consisting of a nickel or cobalt-based superalloy, characterized in that the component is at a temperature in the range from 1 h to 150 h 50 to 70 ° C in a non-oxygen-releasing, iron III and copper II containing aqueous chloride solution (1), which contains other additives but no chromium oxide-forming components. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung (1) die nachfolgende Zusammensetzung hat: 200 - 400 g/l FeCl₃ · 6H₂O 0,5 - 5 g/l CuCl₂ · 2H₂O 10 - 20 ml/l Glyzerin 120 - 200 ml/l konzentrierte HCl Rest H₂O
2. The method according to claim 1, characterized in that the solution (1) has the following composition: 200 - 400 g / l FeCl₃ · 6H₂O 0.5 - 5 g / l CuCl₂ · 2H₂O 10 - 20 ml / l glycerin 120-200 ml / l concentrated HCl rest H₂O
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung (1) die nachfolgende Zusammensetzung hat: 500 g/l FeCl₃ · 6H₂O 5 g/l CuCl₂ · 2H₂O 20 ml/l Glyzerin Rest H₂O
3. The method according to claim 1, characterized in that the solution (1) has the following composition: 500 g / l FeCl₃ · 6H₂O 5 g / l CuCl₂ · 2H₂O 20 ml / l glycerin rest H₂O
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung (1) die nachfolgende Zusammensetzung hat: 200 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 10 ml/l Glyzerin 30 ml/l konzentrierte HCl Rest H₂O
4. The method according to claim 1, characterized in that the solution (1) has the following composition: 200 g / l FeCl₃ · 6H₂O 1 g / l CuCl₂ · 2H₂O 10 ml / l glycerin 30 ml / l concentrated HCl rest H₂O
5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung (1) die nachfolgende Zusammensetzung hat: 300 g/l FeCl₃ · 6H₂O 2 g/l CuCl₂ · 2H₂O 20 ml/l konzentrierte HCl Rest H₂O
5. The method according to claim 1, characterized in that the solution (1) has the following composition: 300 g / l FeCl₃ · 6H₂O 2 g / l CuCl₂ · 2H₂O 20 ml / l concentrated HCl rest H₂O
6. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung (1) die nachfolgende Zusammensetzung hat: 300 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 30 g/l NH₄HF₂ Rest H₂O
6. The method according to claim 1, characterized in that the solution (1) has the following composition: 300 g / l FeCl₃ · 6H₂O 1 g / l CuCl₂ · 2H₂O 30 g / l NH₄HF₂ rest H₂O
7. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung (1) die nachfolgende Zusammensetzung hat: 250 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 100 g/l NaCl 200 g/l Zitronensäure Rest H₂O
7. The method according to claim 1, characterized in that the solution (1) has the following composition: 250 g / l FeCl₃ · 6H₂O 1 g / l CuCl₂ · 2H₂O 100 g / l NaCl 200 g / l citric acid rest H₂O
8. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Lösung (1) die nachfolgende Zusammensetzung hat: 300 g/l FeCl₃ · 6H₂O 0,5 g/l CuCl₂ · 2H₂O 50 g/l NaCl 100 g/l Oxalsäure Rest H₂O
8. The method according to claim 1, characterized in that the solution (1) has the following composition: 300 g / l FeCl₃ · 6H₂O 0.5 g / l CuCl₂ · 2H₂O 50 g / l NaCl 100 g / l Oxalic acid rest H₂O
EP88118502A 1987-12-01 1988-11-07 Process for chemically stripping a high chromic surface coating from a work piece made from a nickel or cobalt based superalloy Expired - Lifetime EP0318724B1 (en)

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