Nickel-base superalloy

1. A nickel-base superalloy consisting essentially of, by weight:

14.75 to 26.5 percent cobalt;

4.1 to 4.65 percent aluminium;

1.1 to 1.9 percent titanium;

3.85 to 6.3 percent tantalum;

1.2 to 2.55 percent niobium;

up to 0.07 percent boron;

up to 0.06 percent carbon;

up to 14.0 percent chromium;

up to 1.0 percent iron;

0.2 to 1.0 percent manganese;

up to 4.2 percent molybdenum;

0.15 to 0.5 percent silicon;

up to 4.9 percent tungsten;

up to 0.1 percent zirconium;

the balance being nickel and incidental impurities;

wherein the overall concentration in the alloy of aluminium, titanium, tantalum, and niobium is from 13 to 14 atomic percent and the atomic ratio of aluminium to titanium is from 4.625:1 to 6.333:1.

2. The nickel-base superalloy of claim 1 , including, by weight, one or more of the following:

0.01 to 0.07 percent boron;

0.02 to 0.06 percent carbon;

10.0 to 14.0 percent chromium;

0.4 to 1.0 percent iron;

1.9 to 4.2 percent molybdenum;

1.5 to 4.9 percent tungsten;

0.035 to 0.1 percent zirconium.

3. The nickel-base superalloy of claim 1 , including, by weight, one or more of the following:

15.0 to 24.0 percent cobalt;

4 to 5.5 percent tantalum;

1.2 to 2.2 percent niobium;

0.02 to 0.045 percent boron;

0.02 to 0.04 percent carbon;

10.0 to 12.5 percent chromium;

0.2 to 0.6 percent manganese;

2.4 to 3.4 percent molybdenum;

0.15 to 0.35 percent silicon

3.0 to 4.9 percent tungsten;

0.05 to 0.1 percent zirconium.

4. The nickel-base superalloy of claim 1 , consisting essentially of, by weight:

14.75 to 26.5 percent cobalt;

4.1 to 4.65 percent aluminium;

1.1 to 1.9 percent titanium;

3.85 to 6.3 percent tantalum;

1.2 to 2.55 percent niobium;

0.01 to 0.07 percent boron;

0.02 to 0.06 percent carbon;

10.0 to 14.0 percent chromium;

up to 1.0 percent iron;

0.2 to 1.0 percent manganese;

1.9 to 4.2 percent molybdenum;

0.15 to 0.5 percent silicon;

1.5 to 4.9 percent tungsten;

0.035 to 0.1 percent zirconium;

the balance being nickel and incidental impurities.

5. The nickel-base superalloy of claim 4 , containing less than 60 ppm phosphorus and less than 20 ppm sulphur.

6. The nickel-base superalloy of claim 1 , consisting essentially of, by weight:

15.0 to 24.0 percent cobalt;

4.1 to 4.65 percent aluminium;

1.1 to 1.9 percent titanium;

4.0 to 5.5 percent tantalum;

1.2 to 2.2 percent niobium;

0.02 to 0.045 percent boron;

0.02 to 0.04 percent carbon;

10.0 to 12.0 percent chromium;

0.4 to 1.0 percent iron;

0.2 to 0.6 percent manganese;

2.4 to 3.4 percent molybdenum;

0.15 to 0.35 percent silicon;

3.0 to 4.9 percent tungsten;

0.05 to 0.1 percent zirconium;

the balance being nickel and incidental impurities.

7. The nickel-base superalloy of claim 6 , containing less than 40 ppm phosphorus and less than 5 ppm sulphur.

8. The nickel-base superalloy of claim 1 , containing less than 60 ppm phosphorus and less than 20 ppm sulphur.

9. Powder form of the nickel-base superalloy of claim 1 .

10. Powder form of the nickel-base superalloy of claim 2 .

11. Powder form of the nickel-base superalloy of claim 3 .

12. A method of producing a nickel-base superalloy article, comprising:

consolidating a powder according to claim 9 to produce an intermediate;

forging the intermediate under isothermal conditions to produce a forging;

solution heat treating the forging above the gamma prime solvus temperature of the nickel-base superalloy;

quenching the forging;

performing a plurality of post-solution heat treatments on the forging.

13. The method of claim 12 , in which the post-solution heat treatments comprise:

a first aging treatment at a first temperature for a first period of time;

a second aging treatment at a second temperature less than the first temperature for a second period of time.

14. The method of claim 13 , in which the second period of time is longer than the first period of time.

15. The method of claim 13 in which the first temperature is from 820 to 860 degrees Celsius and the first period of time is from 1 to 4 hours.

16. The method of claim 13 , in which the second temperature is from 760 to 810 degrees Celsius and the second period of time is from 1 to 8 hours.