Aluminium oxide forming nickel based alloy

Abstract

Nickel based alloy intended for use at high temperatures wherein it comprises in percent by weight (wt-%)C 0.05-0.2Si max 1.5Mn max 0.5Cr 15-20Al 4-6Fe 15-25Co max 10N 0.03-0.15O max 0.5one or more elements selected from the group consisting of Ta, Zr, Hf, Ti and Nb 0.25-2.2one or more elements selected from the group consisting of REM max 0.5balance Ni and normally occurring impurities.

Description

[0001]The present invention relates to a nickel based alloy intended for use at high temperatures, such as above 900° C. Specifically, the present invention relates to a dispersion strengthened nickel based alloy alloyed with aluminium which enables formation of a stable aluminium oxide on the surface whereby the alloy has a good oxidation resistance. Moreover, the present invention relates to a powder of the nickel based alloy and to the use of the nickel based alloy.BACKGROUND ART[0002]Nickel based alloys alloyed with aluminium are used in a variety of high temperature applications, such as in heat treatment furnaces, since they form a stable and protective aluminium oxide on the surface. The aluminium oxide often is has a very good adhesion and does not tend to spall or fall off the surface. Moreover, the aluminium oxide has a low growth rate even at high temperatures. This type of alloys therefore often has a very good oxidation resistance.[0003]Aluminium oxide forming nickel ba...

AI Technical Summary

Benefits of technology

[0009]The object of the present invention is to accomplish an alloy with excellent oxidation resistance at high temperatures, specifically from about 900° C. to at least about 1250° C., and which still has a good hot workability and good creep strength.

[0011]It has been found that by adding relatively high contents of Fe to an aluminium oxide forming nickel based alloy it is possible to reduce the stability of the intermetallic phase γ′, which in turn makes the alloy easier to manufacture and work. A reduced stability of γ′ renders a slower formation of such precipitations for a given cooling rate, which facilitates hot working of the alloy. This also leads to a reduced risk of reduced activity of Al, which in turn ensures that a stable and oxidation resistant aluminium oxide can be formed on the surface of the alloy.

[0013]The nickel based alloy according to the invention is dispersion strengthened. This is achieved by the addition of one or more elements selected from the group consisting of Ta, Zr, Hf, Ti and Nb. These elements form dispersion strengthening particles with C and / or N and optionally added O. The dispersion contributes to the mechanical strength and gives the alloy excellent creep strength even at high temperatures without impairing the hot-workability of the alloy.

[0015]A powder produced of the nickel based alloy will comprise dispersion strengthened particles as described above, which will render a product produced is of the powder excellent mechanical properties, especially at high temperatures. Furthermore, a powder of the nickel based alloy enables, in addition to manufacturing of traditional forms such as tube, rod, wire, plate and strip, also manufacturing of solid components with complex geometry. Moreover, compound materials wherein the nickel based alloy is incorporated can easily be manufactured if desired, for example in order to produce a final product with a first load-bearing component and with a second corrosion resistant component.

Problems solved by technology

Moreover, the aluminium oxide has a low growth rate even at high temperatures.

Aluminium oxide forming nickel based alloys are known to be difficult to manufacture, especially to hot-work.

This intermetallic phase makes the alloy hard and brittle and consequently difficult to work.

The precipitation of γ′ also reduces the activity of aluminium in the alloy and thereby makes formation of the protective aluminium oxide on the surface more difficult.

However, this type of alloys often has low mechanical strength at high temperatures.

Another problem with this type of alloys is that their ductility at room temperature often is very low which makes welding more difficult.

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