EP0318724B1 - 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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EP0318724B1
EP0318724B1 EP88118502A EP88118502A EP0318724B1 EP 0318724 B1 EP0318724 B1 EP 0318724B1 EP 88118502 A EP88118502 A EP 88118502A EP 88118502 A EP88118502 A EP 88118502A EP 0318724 B1 EP0318724 B1 EP 0318724B1
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solution
fecl3
cucl2
following composition
nickel
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German (de)
French (fr)
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EP0318724A1 (en
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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.
  • a method of the type mentioned in the preamble of claim 1 is known from FR-A-2 349 663.
  • a coating containing aluminum, chromium and cobalt is removed from a substrate based on a nickel-based alloy by immersion in a solution kept at a temperature between 15 and 75 ° C.
  • This solution contains ferric sulfate and hydrochloric acid.
  • the proportion of iron (III) sulfate should preferably be 8 to 10 percent by weight and the proportion of hydrochloric acid should preferably be 7 to 9 percent by weight. With such high hydrochloric acid concentrations, the risk of the substrate being adversely affected, in particular due to corrosion pitting, cannot be ruled out with certainty.
  • US Pat. No. 4,339,282 describes a process for detaching nickel aluminide coatings from a substrate based on a nickel-based superalloy, in which an aqueous, predominantly nitric acid and to a lesser extent hydrochloric acid, and smaller proportions of iron III Solution containing chloride and copper (II) sulfate is used to remove the coating.
  • this solution does not attack the substrate, which also contains chromium, among other things, it is, however, not suitable for dissolving a surface layer containing high chromium.
  • Such a protective layer has a positive potential in relation to the substrate in a strongly oxidizing solution caused by the nitric acid can then not be removed by chemical or electrolytic means without significantly affecting the substrate.
  • 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 transition to ever higher Cr contents of the protective layers 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 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.
  • 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 being impaired or changed, particularly when a surface protective layer is subsequently reapplied (renewed).
  • 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 represents the high-chromium surface protection layer. It can in principle be constructed on a nickel or cobalt basis.
  • 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 protective layer 3 When immersed in the solution 1, the surface protective layer 3 shows a negative potential (indicated by the sign - and +) compared to the base body 2, which is the basis for the currentless selective removal of the former.
  • the mainly present ions H tripod; Fe3+; Cu2+; Cl ⁇
  • the mechanism of the resolution is shown schematically by symbols and arrows.
  • the less noble chrome is preferred in solution (Cr3+), while part 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 shovel 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 according to 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 scoop 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, containing 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

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

Ein Verfahren der im Oberbegriff von Patentanspruch 1 genannten Art ist aus FR-A- 2 349 663 bekannt. Beim bekannten Verfahren wird ein Aluminium, Chrom und Kobalt enthaltender Überzug von einem Substrat auf der Grundlage einer Nickelbasislegierung durch Eintauchen in eine auf einer Temperatur zwischen 15 und 75°C gehaltenen Lösung entfernt. Diese Lösung enthält Eisen-III-Sulfat und Salzsäure. Um hierbei ein vergleichsweises rasches Auflösen des Überzugs zu ermöglichen und dabei zugleich ein zu starkes Angreifen des Substrates zu vermeiden, sollte der Anteil an Eisen-III-Sulfat vorzugsweise 8 bis 10 Gewichtsprozent und der Anteil an Salzsäure vorzugsweise 7 bis 9 Gewichtsprozent betragen. Bei derart hohen Salzsäurekonzentrationen ist die Gefahr einer Beeinträchtigung des Substrates, insbesondere durch Korrosionslochfrass, nicht mit Sicherheit auszuschliessen.A method of the type mentioned in the preamble of claim 1 is known from FR-A-2 349 663. In the known method, a coating containing aluminum, chromium and cobalt is removed from a substrate based on a nickel-based alloy by immersion in a solution kept at a temperature between 15 and 75 ° C. This solution contains ferric sulfate and hydrochloric acid. In order to enable a comparatively rapid dissolution of the coating and at the same time to avoid excessive attack on the substrate, the proportion of iron (III) sulfate should preferably be 8 to 10 percent by weight and the proportion of hydrochloric acid should preferably be 7 to 9 percent by weight. With such high hydrochloric acid concentrations, the risk of the substrate being adversely affected, in particular due to corrosion pitting, cannot be ruled out with certainty.

In US-A- 4 339 282 ist ein Verfahren zum Ablösen von Nickelaluminid-Überzügen von einem Substrat auf der Grundlage einer Nickelbasis-Superlegierung beschrieben, bei dem eine wässrige, vorwiegend Salpetersäure und in geringerem Masse Salzsäure, sowie kleinere Anteile an Eisen-III-Chlorid und Kupfer-II-Sulfat enthaltende Lösung zum Entfernen des Überzuges verwendet wird. Diese Lösung greift zwar nicht das unter anderem auch Chrom enthaltende Substrat an, ist jedoch nicht geeignet, eine hochchromhaltige Oberflächenschicht aufzulösen. Eine solche Schutzschicht weist nämlich in einer durch die Salpetersäure hervorgerufenen, stark oxidierenden Lösung gegenüber dem Substrat ein positives Potential auf und kann dann auf chemischem oder elektrolytischem Wege ohne erhebliche Beeinträchtigung des Substrates nicht entfernt werden.US Pat. No. 4,339,282 describes a process for detaching nickel aluminide coatings from a substrate based on a nickel-based superalloy, in which an aqueous, predominantly nitric acid and to a lesser extent hydrochloric acid, and smaller proportions of iron III Solution containing chloride and copper (II) sulfate is used to remove the coating. Although this solution does not attack the substrate, which also contains chromium, among other things, it is, however, not suitable for dissolving a surface layer containing high chromium. Such a protective layer has a positive potential in relation to the substrate in a strongly oxidizing solution caused by the nitric acid can then not be removed by chemical or electrolytic means without significantly affecting the substrate.

Aus US-A- 3 562 040 ist ein Verfahren bekannt, mit dem eine Nickel und Chrom enthaltende Schicht mittels einer wässrigen Lösung sehr rasch geätzt werden kann. Diese Lösung enthält neben dem Wasser Phosphorsäure, Eisen-III-Chlorid und ein Benetzungsmittel. Das bekannte Verfahren wird lediglich bei der Herstellung von integrierten Schaltkreisen, nicht aber beim Entfernen einer Oberflächenschutzschicht vom Grundkörper eines aus einer Nickel- oder Kobaltbasis-Superlegierung bestehenden Bauteils verwendet.From US-A-3 562 040 a method is known with which a layer containing nickel and chromium can be etched very quickly by means of an aqueous solution. In addition to the water, this solution contains phosphoric acid, ferric chloride and a wetting agent. The known method is used only in the production of integrated circuits, but not in the removal of a surface protective layer from the base body of a component consisting of a nickel or cobalt-based superalloy.

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 aluminiumhaltiger 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 removal of the protective layer from the base body, 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. As a result, 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, wie sie in Patentanspruch 1 angegeben ist, 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 insbesondere 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 being impaired or changed, particularly when a surface protective layer is subsequently reapplied (renewed).

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:
Fig. 1
2 shows a schematic cross section through the active part of the contents of a vessel for carrying out the method,
Fig. 2
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 bevorzugt 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 left out 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 represents the high-chromium surface protection layer. It can in principle be constructed on a nickel or cobalt basis. 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 protective layer 3 shows a negative potential (indicated by the sign - and +) compared to the base body 2, which is the basis for the currentless selective removal of the former. 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 is preferred in solution (Cr³⁺), while part 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 protection layer, corroded on its airfoil and partially mechanically damaged, had the following dimensions (airfoil): length = 185 mm Greatest 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 Mon = 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 shovel 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 according to 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 Greatest 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 Mon = 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 scoop 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, containing 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. Process for chemically stripping a surfaceprotection layer (3) with a high chromium content from the main body (2) of a component composed of a nickel-based of the cobalt-based superalloy [sic] in which the component is immersed for 1 h to 150 h at a temperature in the range from 50 to 70°C in an aqueous solution which does not release oxygen, which solution contains an iron(III) compound and at least one further component which does not form any chromium oxide whatsoever, characterised in that the solution contains iron(III) chloride and copper(II) chloride, and in that the component which does not form any chromium oxide whatsoever preferably contains hydrochloric acid, glycerol, NH₄HF₂, citric acid and/or oxalic acid.
  2. Process according to Claim 1, characterised 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 Glycerol 120 - 200 ml/l Concentrated HCl Remainder H₂O
  3. Process according to Claim 1, characterised in that the solution (1) has the following composition: 500 g/l FeCl₃ · 6H₂O 5 g/l CuCl₂ · 2H₂O 20 ml/l Glycerol Remainder H₂O
  4. Process according to Claim 1, characterised in that the solution (1) has the following composition: 200 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 10 ml/l Glycerol 30 ml/l Concentrated HCl Remainder H₂O
  5. Process according to Claim 1, characterised in that the solution (1) has the following composition: 300 g/l FeCl₃ · 6H₂O 2 g/l CuCl₂ · 2H₂O 20 ml/l Concentrated HCl Remainder H₂O
  6. Process according to Claim 1, characterised in that the solution (1) has the following composition: 300 g/l FeCl₃ · 6H₂O 1 g/l CuCl₂ · 2H₂O 30 g/l NH₄HF₂ Remainder H₂O
  7. Process according to Claim 1, characterised 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 Remainder H₂O
  8. Process according to Claim 1, characterised 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 Remainder 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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CH4675/87 1987-12-01
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EP0318724A1 (en) 1989-06-07
CH674851A5 (en) 1990-07-31
US4944807A (en) 1990-07-31
JPH01195290A (en) 1989-08-07
DE3879634D1 (en) 1993-04-29

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