METHOD OF FORGING A NICKEL BASE SUPERALLOY
A method of forging a nickel base superalloy comprising providing a nickel base superalloy preform (40) with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy. The nickel base superalloy preform (40) is forged to produce a nickel base superalloy forged component (50) with a second predetermined shape. The first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of the forging is less than 1. The nickel base superalloy forged component (50) is given a supersolvus heat treatment to produce a large grain size in the nickel base superalloy forged component (50).
Latest ROLLS-ROYCE PLC Patents:
The present invention relates to a method of forging a nickel base superalloy and in particular to a method of forging a nickel base superalloy turbine disc or a nickel base superalloy compressor disc.
Currently high strength, powder processed nickel base superalloys such as RR1000, Rene 104, Alloy 10, LSHR, IN100, Rene 88DT and Rene 95 etc may be processed to produce one of three different microstructures or combinations thereof. These different microstructures are a) fine grain size microstructure ASTM 10-12 ALA 7, b) midi gain size microstructure ASTM 7.5-9 ALA 4 and c) coarse grain size microstructure ASTM 5-7 ALA 2.
In addition a single component may be processed to produce a range of grain sizes, with different grain sizes at different locations, e.g. a dual microstructure turbine disc.
The grain size achieved in these nickel base superalloys is influenced by three factors. The first factor is alloy chemistry, in particular the levels of boron and carbon. The levels of boron and carbon dictate the levels of borides or carbides present in the nickel base superalloy and these borides or carbides pin grain boundaries and restrict grain growth. The second factor is processing parameters, principally forging temperature, strain rate and final strain. The third factor is heat treatment. Fine grain nickel base superalloys are heat treated below the gamma-prime solvus temperature, a subsolvus heat treatment, the gamma-prime phase acts to pin the grain boundaries. Coarse grain nickel superalloys are heat treated above the gamma-prime solvus temperature, a supersolvus heat treatment. Midi grain nickel base superalloys are forged at a lower than usual temperature and then heat treated above the gamma-prime solvus temperature, supersolvus heat treatment. In any heat treatment that involves going above the gamma-prime solvus temperature it is necessary to have an understanding of both the chemistry of the nickel base superalloy and prior mechanical working history to avoid critical grain growth.
There is a need within the industry for a nickel base superalloy which has a large grain size in excess of coarse grain without changing the chemistry of the nickel base superalloy.
Accordingly the present invention seeks to provide a novel method of forging a nickel base superalloy which has been produced by powder metallurgy, which reduces, preferably overcomes, the above mentioned problem.
Accordingly the present invention provides a method of forging a nickel base superalloy comprising the steps of:
(a) providing a nickel base superalloy preform with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy,
(b) forging the nickel base superalloy preform to produce a nickel base superalloy forged component with a second predetermined shape, wherein the first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of the forging is less than 1,
(c) supersolvus heat treating at least a region of the nickel base superalloy forged component to produce a large grain size in the at least a region of the nickel base superalloy forged component, wherein the large grain size in the nickel base superalloy is 80 to 140 micrometers.
Preferably in step (b) the effective strain at the end of forging is less than or equal to 0.75.
More preferably in step (b) the effective strain at the end of forging is less than or equal to 0.5.
Preferably step (a) comprises providing a stepped cylindrical preform, the cylindrical preform having a first substantially cylindrical portion and a second substantially annular portion arranged coaxially around the first portion, the first cylindrical portion having a first thickness, the second annular portion having a second thickness and the second thickness is less than the first thickness and step (b) comprises forging the stepped cylindrical preform to a substantially disc shaped forged component and after step (c) the second portion having coarser grains than the first portion.
Preferably step (a) comprises providing a substantially cylindrical preform, the cylindrical preform having a third substantially annular portion arranged coaxially around the second annular portion, the third annular portion having a third thickness and the third thickness is less than the second thickness and after step (c) the third portion having coarser grains than the second portion.
Preferably in the first cylindrical portion the effective strain is about 0.9, in the second annular portion the effective strain is about 0.75 and in the third annular portion the effective strain is about 0.5.
Step (c) may comprise a subsolvus heat treatment in a first region of the forged component and a supersolvus heat treatment in a second region of the forged component. The first region may comprise the first portion and the second region may comprise the second portion or the second region comprises the second portion and the third portion.
Step (c) comprise supersolvus heat treating all of the nickel base superalloy forged component to produce a large grain size in all of the nickel base superalloy forged component.
The forged component may comprise a forged component for a turbine disc or a compressor disc.
The present invention will be more fully described by way of example with reference to the accompanying drawings in which:
A turbofan gas turbine engine 10, as shown in
The gas turbine engine turbine disc 24, as shown more clearly in
There is a need within the industry for a nickel base superalloy which has a large grain size in excess of a coarse grain size (ASTM 5-7). The range of grain sizes for these large grain size microstructures in nickel base superalloy is ASTM 5-2 ALA 00. A large uniform grain size such as this is desirable because increasing the grain size increases the resistance to both creep deformation and fatigue crack growth. However, strength and fatigue properties are reduced.
In the prior art a nickel base superalloy turbine disc is produced by isothermal forging a substantially cylindrical preform to a substantially disc shaped forged component using a large amount of plastic deformation. The effective strain at the end of the forging process is greater than 1. Subsequently, the nickel base superalloy forged component is given a supersolvus heat treatment to produce a coarse grain size in the nickel base superalloy forged component limited to the ASTM 5-7 range of conventional coarse grain nickel base superalloys.
In the present invention the nickel base superalloy preform is provided with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy, the nickel base superalloy preform is forged to produce a nickel base superalloy forged component with a second predetermined shape, wherein the first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of the forging process is less than 1. Subsequently, the nickel base superalloy forged component is given a supersolvus heat treatment to produce a large grain size in the nickel base superalloy forged component in the ASTM 5-2 ALA 00, 80 to 140 micrometers, which is greater in size than the conventional coarse grain in nickel base superalloys.
The definition of effective strain is given by the equation {acute over (ε)}=√⅔[(ε1−ε2)2+(ε2−ε3)2+(ε3−ε1)2]1/2, where {acute over (ε)} is the effective strain at the end of forging, ε1, ε2 and ε3 are the principal strains in each of the three principal directions. Thus for an isotropic material, knowledge of the uniaxial tensile test behaviour together with the yield function enables the stress-strain behaviour to be predicted for any stress system. The effective strain equals the square root of two divided by three multiplied by the square root of the squares of the difference in the principal strains.
Considering the strain in the portions 42, 44 and 46 of the stepped cylindrical preform 40 in
It is preferred to use an effective strain Eeff of less than or equal to 0.5 in order to produce a uniform large grain size in the nickel base superalloy. An effective εeff of less than, or equal, to 0.75 but greater than 0.5 would produce a slightly finer grain size than the large grain size in the nickel base superalloy.
In an alternative example a stepped cylindrical preform may be provided, the cylindrical preform has a first substantially cylindrical portion and a second substantially annular portion arranged coaxially around the first portion, the first cylindrical portion has a first thickness, the second annular portion has a second thickness and the second thickness is less than the first thickness. The stepped cylindrical preform is forged to a generally disc shaped forged component and then the nickel base superalloy forged component is given a supersolvus heat treatment and ageing heat treatment and then machined to produce a nickel base superalloy turbine disc or compressor disc. The second portion has coarser grains than the first portion.
By controlling the shape of the nickel superalloy preform and the shape of the nickel alloy forged component the effective strain is kept to a level below 1, such that on subsequent supersolvus heat treatment a large grain size is produced in the nickel base superalloy. It is the final effective strain and not the maximum instantaneous strain rate of the forging process, or forging step, which dictates the grain size in the nickel base superalloy. The supersolvus solution heat treatment may be applied directly after the forging step or a subsolvus heat treatment may be applied after the forging step and a supersolvus heat treatment applied after the subsolvus heat treatment. The forging step may comprise isothermal forging and isothermal application of strain during the isothermal forging step allows the imparted strain levels to be accurately controlled. The present invention may be applied to specific locations of a component. The present invention produces a very creep resistant, fatigue crack growth resistant nickel base superalloy with a high gamma prime volume fraction.
The advantage of the present invention is that it enables critical rotating components to be produced with enhanced high temperature properties, in particular creep resistance and fatigue crack growth resistance. This provides an increase in the operating life of the component or enables the component to operate at higher temperatures and may decrease the weight of the component.
The present invention is applicable to all high strength powder processed nickel base superalloys used for gas turbine engine turbine discs, compressor discs, high-pressure compressor cones and turbine cover plates.
Other suitable nickel base superalloys are Rene 95, Rene 88DT, Alloy 10, LSHR, Rene 104 and IN100. Rene 95 consists of 8.12 wt % Co, 12.94 wt % Cr, 3.45 wt % Mo, 3.43 wt % W, 3.42 wt % Al, 2.44 wt % Ti, 3.37 wt % Nb, 0.05 wt % Zr, 0.07 wt % C, 0.012 wt % B and the balance Ni and incidental impurities. Rene 88DT consists of 13.1 wt % Co, 15.8 wt % Cr, 4 wt % Mo, 3.9 wt % W, 2 wt % Al, 3.7 wt % Ti, 0.7 wt % Nb, 0.045 wt % Zr, 0.05 wt % C, 0.016 wt % B and the balance Ni and incidental impurities. Alloy 10 consists of 17.93 wt % Co, 10.46 wt % Cr, 2.52 wt % Mo, 4.74 wt % W, 3.53 wt % Al, 3.79 wt % Ti, 1.61 wt % Ta, 0.97 wt % Nb, 0.07 wt % Zr, 0.027 wt % C, 0.028 wt % B and the balance Ni and incidental impurities. LSHR consists of 20.8 wt % Co, 12.7 wt % Cr, 2.74 wt % Mo, 4.37 wt % W, 3.48 wt % Al, 3.47 wt % Ti, 1.65 wt % Ta, 0.049 wt % Zr, 0.024 wt % C, 0.028 wt % B and the balance Ni and incidental impurities. Rene 104 consists of 20.6 wt % Co, 13.0 wt % Cr, 3.80 wt % Mo, 2.1 wt % W, 3.4 wt % Al, 3.7 wt % Ti, 2.4 wt % Ta, 0.05 wt % Zr, 0.04 wt % C, 0.03 wt % B and the balance Ni and incidental impurities. IN100 consists of 18.5 wt % Co, 12.5 wt % Cr, 3.2 wt % Mo, 5.0 wt % Al, 4.4 wt % Ti, 0.06 wt % Zr, 0.07 wt % C, 0.02 wt % B and the balance Ni and incidental impurities.
In general the subsolvus heat treatment for these nickel base superalloys is at a temperature of 20° C. to 40° C. below the gamma prime solvus temperature for times of 1 to 6 hours and the supersolvus heat treatment for these nickel base superalloys is at a temperature of 20° C. to 50° C. above the gamma prime solvus temperature for times of up to 4 hours. Alternatively the subsolvus heat treatment is 1110° C. to 1150° C. for times of 1 to 6 hours and the supersolvus heat treatment is 1160° C. to 1210° C. for times of up to 4 hours.
Claims
1. A method of forging a nickel base superalloy comprising the steps of:
- (a) providing a nickel base superalloy preform with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy,
- (b) forging the nickel base superalloy preform to produce a nickel base superalloy forged component with a second predetermined shape, wherein the first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of forging is less than 1,
- (c) supersolvus heat treating at least a region of the nickel base superalloy forged component to produce a large grain size in the at least a region of the nickel base superalloy forged component, wherein the large grain size in the nickel base superalloy is 80 to 140 micrometers.
2. A method as claimed in claim 1 wherein in step (b) the effective strain at the end of the forging is less than or equal to 0.75.
3. A method as claimed in claim 1 wherein in step (b) the effective strain at the end of the forging is less than or equal to 0.5.
4. A method as claimed in claim 1 wherein step (a) comprises providing a stepped cylindrical preform, the cylindrical preform having a first substantially cylindrical portion and a second substantially annular portion arranged coaxially around the first portion, the first cylindrical portion having a first thickness, the second annular portion having a second thickness and the second thickness is less than the first thickness and step (b) comprises forging the stepped cylindrical preform to a substantially disc shaped forged component and after step (c) the second portion having coarser grains than the first portion.
5. A method as claimed in claim 4 wherein step (a) comprises providing a substantially cylindrical preform, the cylindrical preform having a third substantially annular portion arranged coaxially around the second annular portion, the third annular portion having a third thickness and the third thickness is less than the second thickness and after step (c) the third portion having coarser grains than the second portion.
6. A method as claimed in claim 5 wherein in the first cylindrical portion the effective strain is about 0.9, in the second annular portion the effective strain is about 0.75 and in the third annular portion the effective strain is about 0.5.
7. A method as claimed in claim 4 wherein step (c) comprises a subsolvus heat treatment in a first region of the forged component and a supersolvus heat treatment in a second region of the forged component.
8. A method as claimed in claim 7 wherein the first region comprises the first portion and the second region comprises the second portion.
9. A method as claimed in claim 5 wherein step (c) comprises a supersolvus heat treatment in a first region of the forged component and a supersolvus heat treatment in a second region of the forged component.
10. A method as claimed in claim 9 wherein the first region comprises the first portion and the second region comprises the second portion and the third portion.
11. A method as claimed in claim 1 wherein step (c) comprises supersolvus heat treating all of the nickel base superalloy forged component to produce a large grain size in all of the nickel base superalloy forged component.
12. A method as claimed in claim 1 wherein the forged component comprises a forged component for a turbine disc or a compressor disc.
13. A method as claims in claim 1 wherein the nickel base superalloy consists of 18.5 wt % cobalt, 15 wt % chromium, 5 wt % molybdenum, 2 wt % tantalum, 3.6 wt % titanium, 3 wt % aluminium, 0.5 wt % hafnium, 0.015 wt % boron, 0.06 wt % zirconium, 0.027 wt % carbon and the balance nickel plus incidental impurities.
14. A method as claimed in claim 1 wherein step (b) comprises forging at a temperature in the range of 1050° C. to 1150° C. and at a strain rate in the range of 0.001 to 0.1 per second.
15. A method as claimed in claim 1 wherein step (c) comprises supersovlus heat treating at 20° C. to 50° C. above the gamma prime solvus temperature for up to 4 hours.
16. A method as claimed in claim 1 wherein step (c) comprises supersolvus heat treating at a temperature of 1110° C. to 1150° C. for up to 4 hours.
17. A method of forging a nickel base superalloy comprising the steps of:
- (a) providing a nickel base superalloy preform with a first predetermined shape, the nickel base superalloy preform having been produced by powder metallurgy.
- (b) forging the nickel base superalloy preform to produce a nickel base superalloy forged component with a second predetermined shape, wherein the first predetermined shape and the second predetermined shape are arranged such that the effective strain at the end of forging is less than 1,
- (c) supersolvus heat treating at least a region of the nickel base superalloy forged component to produce a large grain size in the at least a region of the nickel base superalloy forged component.
18. A nickel base superalloy forged component with a large grain size in at least a region, wherein the large grain size is 80 to 140 micrometers.
Type: Application
Filed: Sep 15, 2010
Publication Date: Apr 21, 2011
Applicant: ROLLS-ROYCE PLC (London)
Inventor: Robert J. MITCHELL (Nottingham)
Application Number: 12/882,405
International Classification: C22F 1/10 (20060101); B22F 3/24 (20060101); C22C 19/05 (20060101); B22F 3/17 (20060101);