GB2036793A

GB2036793A - Nickel or Nickel-Cobalt Base Alloys with Improved Corrosion Resistance

Info

Publication number: GB2036793A
Application number: GB7846979A
Authority: GB
Original assignee: PELLS A
Current assignee: PELLS A
Priority date: 1978-12-02
Filing date: 1978-12-02
Publication date: 1980-07-02
Also published as: GB2036793B

Abstract

The invention enhances the corrosion resistance of Ni or Ni/Co based alloys by the addition of Th, Y, Ce, La or Mg in an amount not exceeding 1.0%, preferably 0.1%. The preferred addition is 0.03% Ce. In one form of the invention is a bulk alloy. In another form, the invention provides a method of enhancing the corrosion resistance of a metal component (particularly but not exclusively an aircraft gas turbine blade) by coating the component with a Ni or Ni/Co based metal powder including the above addition, and heating to fuse the powder into a thin film on the component, The powder is suspended in a liquid carrier for coating.

Description

SPECIFICATION Corrosion Resistant Alloy, and Method of Enhancing Corrosion Resistance Using the Alloy This invention relates to the resistance to corrosion of nickel and nickel/cobalt based alloys, and is of particular but not exclusive relevance to gas turbine blades using such alloys.

It is known to attempt to enhance the corrosion resistance of gas turbine blades, particularly after repair, by providing the blade with a thin coating of alloy. In one known process, the blade is sprayed with a liquid vehicle containing metal powder and is then heated in a furnace under vacuum to drive off the liquid vehicle and to fuse the metal powder into a thin alloy film. The metal powder may for example be brazing powder sold by Dewrance Metals Ltd.

under the name "CM.60" and having the composition Cr 19.0%, Si 10.0%, C 0. 15% max, Ni balance.

It has been found that such layers eventually fail, especially in the environment of an aircraft gas turbine. The thin alloy film tends to spall revealing an area of the under-lying alloy, and corrosion which starts in this area can advance under the remaining thin film causing further spalling. An object of the present invention is to improve the adherence of the film to the underlying component and thus lengthen the life of the component.

In accordance with one aspect of the present invention, defined in claim 6 hereinafter, this is achieved by including in the metal powder coated onto the blade or other article between 0.003% and 1.0%, preferably between 0.003% and 0.1%, of thorium, yttrium, lanthanum, cerium or magnesium. A particularly preferred addition is 0.03% cerium.

From another aspect as defined in claim 1 hereinafter, the invention provides a novel alloy, useful also as a bulk material, by the inclusion in a Ni or Ni/Co based alloy of between 0.003% and 1.0%, preferably between 0.003% and 0.1%, of thorium, yttrium, lanthanum, cerium or magnesium. Again, cerium at 0.03% is particularly preferred.

Examples of the invention will now be described.

A preferred form of the invention relates to aircraft gas turbine blades, for example blades in which cracks have been repaired by brazing or welding followed by grinding to restore the desired profile. In accordance with this example of the invention, such blades are then coated with a liquid carrier containing a metal powder mixture having the composition given in Table I, II or Ill below. The carrier is suitably aqueous with an agent such as cellulose to aid adhesion. The coating is preferably applied by spraying; alternatively brushing or dipping may be used.

The coated blades are then placed under vacuum in a furnace and heated to a temperature (typically 1 1001 2000C) and for a time sufficient to drive off the carrier and cause the metal constituents to fuse into a thin alloy coating bonded to the blades. The blades could alternatively be placed in an atmosphere of pure dry hydrogen or non-reactive gases.

Table I Constituent wt % Ni Balance Cr 19.0 Si 10.0 C 0.15 max Ce 0.03 Table II Constituent wt % Ni Balance Cr 11.5 Si 3.25 B 2.5 Fe 3.4 C 0.6 W 16.0 Co 2.5 Ce 0.03 Table Ill Constituent wt % Ni Balance Cr 19.0 Si 2.5 B 1.5 C 0.5 W 9.0 Co 50.0 Ce 0.03 In another form of the invention, the constituents given in Table I, II or Ill above are alloyed together as a bulk material.

The cerium may be replaced by thorium, yttrium, lanthanum or magnesium. It is believed that a concentration of about 0.03% gives the optimum improvement in adhesion but up to .1.0% is considered to yield a useful result.

Claims

1. In a nickel or nickel/cobalt based alloy, the improvement comprising the inclusion of between 0.003% and 1.0% of thorium, yttrium, lanthanum, cerium or magnesium.

2. The alloy of claim 1, in which the other elements present are one or more of chromium, silicon, boron, iron, carbon and tungsten.

3. The alloy of claim 1 or claim 2, in which the thorium, yttrium, lanthanum, cerium or magnesium does not exceed 0.1%.

4. The alloy of claim 2, in which cerium is present at substantially 0.03%.

5. An alloy having substantially the constitution listed in Table I, Table II or Table Ill hereinbefore.

6. A method of enhancing the corrosion resistance of a metal component, comprising coating the component with a liquid vehicle

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Corrosion Resistant Alloy, and Method of Enhancing Corrosion Resistance Using the Alloy This invention relates to the resistance to corrosion of nickel and nickel/cobalt based alloys, and is of particular but not exclusive relevance to gas turbine blades using such alloys. It is known to attempt to enhance the corrosion resistance of gas turbine blades, particularly after repair, by providing the blade with a thin coating of alloy. In one known process, the blade is sprayed with a liquid vehicle containing metal powder and is then heated in a furnace under vacuum to drive off the liquid vehicle and to fuse the metal powder into a thin alloy film. The metal powder may for example be brazing powder sold by Dewrance Metals Ltd. under the name "CM.60" and having the composition Cr 19.0%, Si 10.0%, C 0. 15% max, Ni balance. It has been found that such layers eventually fail, especially in the environment of an aircraft gas turbine. The thin alloy film tends to spall revealing an area of the under-lying alloy, and corrosion which starts in this area can advance under the remaining thin film causing further spalling. An object of the present invention is to improve the adherence of the film to the underlying component and thus lengthen the life of the component. In accordance with one aspect of the present invention, defined in claim 6 hereinafter, this is achieved by including in the metal powder coated onto the blade or other article between 0.003% and 1.0%, preferably between 0.003% and 0.1%, of thorium, yttrium, lanthanum, cerium or magnesium. A particularly preferred addition is 0.03% cerium. From another aspect as defined in claim 1 hereinafter, the invention provides a novel alloy, useful also as a bulk material, by the inclusion in a Ni or Ni/Co based alloy of between 0.003% and 1.0%, preferably between 0.003% and 0.1%, of thorium, yttrium, lanthanum, cerium or magnesium. Again, cerium at 0.03% is particularly preferred. Examples of the invention will now be described. A preferred form of the invention relates to aircraft gas turbine blades, for example blades in which cracks have been repaired by brazing or welding followed by grinding to restore the desired profile. In accordance with this example of the invention, such blades are then coated with a liquid carrier containing a metal powder mixture having the composition given in Table I, II or Ill below. The carrier is suitably aqueous with an agent such as cellulose to aid adhesion. The coating is preferably applied by spraying; alternatively brushing or dipping may be used. The coated blades are then placed under vacuum in a furnace and heated to a temperature (typically 1 1001 2000C) and for a time sufficient to drive off the carrier and cause the metal constituents to fuse into a thin alloy coating bonded to the blades. The blades could alternatively be placed in an atmosphere of pure dry hydrogen or non-reactive gases. Table I Constituent wt % Ni Balance Cr 19.0 Si 10.0 C 0.15 max Ce 0.03 Table II Constituent wt % Ni Balance Cr 11.5 Si 3.25 B 2.5 Fe 3.4 C 0.6 W 16.0 Co 2.5 Ce 0.03 Table Ill Constituent wt % Ni Balance Cr 19.0 Si 2.5 B 1.5 C 0.5 W 9.0 Co 50.0 Ce 0.03 In another form of the invention, the constituents given in Table I, II or Ill above are alloyed together as a bulk material. The cerium may be replaced by thorium, yttrium, lanthanum or magnesium. It is believed that a concentration of about 0.03% gives the optimum improvement in adhesion but up to .1.0% is considered to yield a useful result. Claims

4. The alloy of claim 2, in which cerium is present at substantially 0.03%.

6. A method of enhancing the corrosion resistance of a metal component, comprising coating the component with a liquid vehicle containing a metal powder mixture, and heating the component to drive off the liquid vehicle and cause the metal constituents to fuse to form a thin alloy layer bonded to the component; and in which the metal powder mixture is a nickel or nickel/cobalt based mixture containing between 0.003% and 1.0% thorium, yttrium, lanthanum, cerium, or magnesium.

7. A method according to claim 6, in which the other constituents of the mixture are one or more of chromium, silicon, boron, carbon, and tungsten.

8. A method according to claim 6 or claim 7, in which the thorium, yttrium, lanthanum, cerium or magnesium does not exceed 0.1%.

9. A method according to claim 8, in which cerium is present in the powder mixture at substantially 0.03%.

1 0. A method according to claim 9, in which the powder mixture has substantially the constitution listed in Table I, Table

II or Table Ill hereinbefore.

1 A method according to any of claims 6 to 10, in which the component is coated by spraying.

12. A method according to any of claims 6 to 11, in which the component is heated in a furnace under vacuum or an atmosphere of pure dry hydrogen.

13. A method according to any of claims 6 to 12, in which the component is a gas turbine blade.

14. A gas turbine blade treated in accordance with claim 13.