Method Of Manufacturing Strip From Metal Powder

Abstract

A method is provided for forming metal strip from metal powders by spraying the powder as molten metal onto a cooled moving metal foil and thereafter consolidating the foil and sprayed metal by applying pressure.

Description

This invention relates to methods of manufacturing strip from metal powder and particularly to a method of making superalloy strip from powder, although the method will apply to other alloys as well.

Normally the metals known as superalloys, i.e., alloys of iron, nickel or cobalt which will maintain usable mechanical properties at elevated temperatures, are cast into ingots which are then either forged or bloomed into slabs, cut and conditioned, rolled into either bands or plates, conditioned and then finally rolled into strip and cut. There are several heat treatments necessary throughout the process and a final heat treatment dependent on the customers requirements. All of this costs time and money. Perhaps more important is the fact that this large amount of hot working tends to deplete boron from superalloys through oxidation. Boron is essential to stress rupture life at elevated temperature.

Sheet and strip of nickel, aluminum and iron have been rolled directly from metal powder by feeding the powder through a mill with its rolls in a horizontal plane. When rolling strip in this fashion it is necessary that the green strength of the strip be sufficient to allow subsequent processing. This means that the powder must have a special configuration conducive to providing high green strength. Superalloy powder having high purity is generally made by a dry process which results in spherical powder having poor cold compactability lacking the special configuration necessary to provide green strength.

I have invented a method of making metal strip from metal powder which makes it possible to form strip from powder without regard to its shape. In my method I feed the metal powder through a plasma gun or similar metallizing gun onto a substrate of aluminum, copper or iron strip or foil, the foil being in intimate contact with a cooling element at the time the hot metal particles are sprayed onto the substrate. The metal spraying operation is carried out in an inert atmosphere such as in an inert gas purged chamber. Preferably the sprayed foil is cold rolled to a predetermined reduction and then resprayed if greater thickness is desired. The amount of spray applied and the amount of cold rolling are dependent upon the particular alloy and the desired thickness. Each subsequent spraying or metallizing after rolling will stress relieve the strip. Since all heat treatment is carried out in an inert atmosphere oxidation is eliminated. The substrate may be removed from the finished strip by preferential etching using for example hydroxide for aluminum foil and nitric acid for copper or iron.

In the foregoing general description of my invention I have set out certain objects, purposes and advantages of my invention. Other objects, purposes and advantages will be apparent from a consideration of the following description and the accompanying drawings in which:

FIG. 1 is a schematic section through an apparatus for carrying out the practice of this invention, and

FIG. 2 is a section through a strip made from metal powder according to my invention.

Referring to the drawings I have illustrated a sheet of foil 10 being delivered from coil 11 through a chevron seal 12 into the interior of chamber 13 where it passes over a water cooled roll 14. The foil 10 is sprayed with molten superalloy 15 from a plasma gun 16 supplied with powdered superalloy from a hopper 17. The molten superalloy 15 solidifies on the foil 10 to form a layer of superalloy which is passed between pressure rolls 18 to cold roll the newly formed superalloy strip 15.

If a greater thickness of strip 15 is desired than can be applied with one pass in front of plasma gun 16, then the coating operation is simply repeated as many times as is necessary. The spraying of molten superalloy onto the strip 15 will stress relieve the previously formed layer 15 without danger of oxidation.

If the substrate 10 is to be removed the composite strip is passed through an appropriate etch solution to dissolve it away from the superalloy strip 15 after cold rolling.

In the foregoing specification I have set out certain preferred practices and embodiments of my invention, however, it will be understood that this invention may be otherwise embodied.

Claims

I claim:

1. A method of forming strip from metal powders comprising the steps of

a. converting a metal powder to a molten metal spray,

b. applying the molten metal spray in an inert atmosphere to a moving metal foil in a substantially uniform layer to form a major component of the combined thickness,

c. cooling the metal foil and molten spray applied thereto to solidify said molten spray while in said inert atmosphere, and

d. consolidating said foil and sprayed metal by applying pressure thereto.

2. A method as claimed in claim 1 wherein the foil is cooled simultaneously with the application of the molten spray thereto.

3. A method as claimed in claim 1 wherein the foil is coated with metal spray while changing direction of the foil.

4. A method as claimed in claim 1 wherein the metal foil is a member selected from the group aluminum, nickel, copper and iron.

5. A method as claimed in claim 1 wherein the metal is consolidated by pressure rolling.

6. A method claimed in claim 1 wherein the metal powder is passed through a plasma gun to form a molten spray of metal.

7. A method as claimed in claim 1 wherein the foil is removed by etching after consolidation of the metal.

8. A method as claimed in claim 1 wherein the foil is passed over a water cooled roll in an inert atmosphere and the molten metal sprayed onto the foil while the foil is on the water cooled roll.