Ni-Cr-Co alloy for advanced gas turbine engines

Abstract

A wrought age-hardenable nickel-chromium-cobalt based alloy suitable for use in high temperature gas turbine transition ducts possessing a combination of three specific key properties, namely resistance to strain age cracking, good thermal stability, and good creep-rupture strength contains in weight percent 17 to 22 chromium, 8 to 15 cobalt, 4.0 to 9.5 molybdenum, up to 7 tungsten, 1.28 to 1.65 aluminum, 1.50 to 2.30 titanium, up to 0.80 niobium, 0.01 to 0.2 carbon, up to 0.01 boron, and up to 3 iron, with a balance of nickel and impurities. Certain alloying elements must be present in amounts according to two equations here disclosed.

Description

FIELD OF THE INVENTION [0001] This invention relates to wroughtable high strength alloys for use at elevated temperatures. In particular, it is related to alloys which possess sufficient creep strength, thermal stability, and resistance to strain age cracking to allow for fabrication and service in gas turbine transition ducts and other gas turbine components. BACKGROUND OF THE INVENTION [0002] To meet the demand for increased operating efficiency, gas turbine engine designers would like to employ higher and higher operating temperatures. However, the ability to increase operating temperatures is often limited by material properties. One application with such a limitation is gas turbine transition ducts. Transition ducts are often welded components made of sheet or thin plate material and thus need to be weldable as well as wroughtable. Often gamma-prime strengthened alloys are used in transition ducts due to their high-strength at elevated temperatures. However, current commerciall...

AI Technical Summary

Benefits of technology

[0008] The principal objective of this invention is to provide new wrought age-hardenable nickel-chromium-cobalt based alloys which are suitable for use in high temperature gas turbine transition ducts and other gas turbine components possessing a combination of three specific key properties, namely resistance to strain age cracking, good thermal stability, and good creep-rupture strength.

Problems solved by technology

However, the ability to increase operating temperatures is often limited by material properties.

However, current commercially available wrought gamma-prime strengthened alloys either do not have the strength or stability to be used at the very high temperatures demanded by advanced gas turbine design concepts, or can present difficulties during fabrication.

In particular, one such fabrication difficulty is the susceptibility of many wrought gamma-prime strengthened alloys to strain age cracking.

Strain age cracking is a problem which limits the weldability of many gamma-prime strengthened alloys.

The formation of the strengthening gamma-prime phase in conjunction with the low ductility many of these alloys possess at intermediate temperatures, as well as the mechanical restraint typically imposed by the welding operation will often lead to cracking.

The problem of strain age cracking can limit alloys to be used up to only a certain thickness since greater material thickness leads to greater mechanical restraint.

Many high-temperature alloys can form brittle intermetallic or carbide phases during thermal exposure.

It has excellent creep strength, but is limited by poor thermal stability and resistance to strain age cracking.

The M-252 alloy has good creep strength and resistance to strain age cracking, but like R-41 alloy is limited by poor thermal stability.

However, this alloy has marginal creep strength above 1500° F., marginal thermal stability, and has fairly poor resistance to strain age cracking.

This alloy has excellent thermal stability and resistance to strain age cracking, but has very poor creep strength at temperatures greater than 1500° F. The PK-33 alloy (U.S. Pat. No. 3,248,213) was developed by the International Nickel Company and introduced in 1961.

This alloy has good thermal stability and creep strength, but is limited by a poor resistance to strain age cracking.

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