US3151981A - Nickel-chromium-cobalt alloy - Google Patents

Description

Oct. 6, 1964 R. A. SMITH ETAL 3,151,981

NICKELCHROMIUMCOBALT ALLOY Filed Feb. 26, 1962 a Q B e a Z C 1N VEN 1 CR5 6 01mm A. SMITH BY day/v f/sswp United States Patent 3,151,981 NICKEL-QHROIVHUM- IOBALT ALLOY Ronald A. Smith, West Hagiey, and John Heslop, Sutton Coidfield, England, assi mors to The International Nickel Company, Inc, New York, N.Y., a corporation of Delaware Fiied Feb. 26, 1962, Ser. No. 175,555 Ciaims priority, application Great Britain Feb. 28, 1961 16 Claims. (Cl. 75-471) This invention relates to heatand creep-resistant alloys and, more particularly, to nickel-chromium-cobalt alloys suitable for use in rotor discs for gas turbines.

The power rotors of gas turbines are subjected to the most severe operating conditions of any part of the turbine and much eifort has been expended to ensure their satisfactory behavior. A common type of rotor consists of a disc mounted on a shaft and carrying a number of blades fastened to its rim by means of the well known fir-tree type of joint. Advances in the field of alloy evelopment during the last two decades have resulted in improved blading materials which have enabled operating temperatures, and hence turbine efliciency, to be greatly increased. The materials used for the disc components have not been correspondingly improved, partly owing to improvements in design, including the development of disc cooling techniques. However, operating conditions are now such that many discs currently in use have no margin of safety to allow for temperature overshooting due to failure of the cooling air supply or other causes. Furthermore, with the marked increase in severity of operating conditions accompanying the transition from subsonic to supersonic flight, a material with properties significantly better than those of the currently used alloys is essential.

The diiferent properties required of a rotor disc material are manifold and complex and, to a large extent, conflicting. Of particular significance is the large variation of temperature occurring radially between the center or hub and the periphery or rim of the disc. This temperature gradient is accompanied by a stress gradient in the opposite sense so that the highest stress occurs in the low temperature region near the hub and vice versa. A rotor disc material must, therefore, have a high creep strength, i.e., a low creep rate at high stresses, up to relatively high temperatures, e.g., 600 C., to ensure freedom from distortion by creep in service, particularly at the rim, and a high proof stress and ultimate tensile strength at more moderate temperatures to ensure that the high hub stresses do not lead to distortion or fracture on loading. Preferably, the disc material should have a high value of Youngs modulus and a low coefiicient of thermal expansion to minimize the overall expansion of the disc. It must have adequate ductility and must not be notch sensitive at temperatures corresponding to that at which the rim, with its fir-tree recesses, operates. Furthermore, the need to produce a relatively complex shape of appreciable size requires that the alloy shall be hot workable.

It has now been discovered that by specially correlating alloy ingredients, including nickel, chromium, cobalt, carbon, columbium (niobium), titanium, etc., an alloy especially suitable for use as gas turbine power rotor discs can be provided.

It is an object of the present invention to provide a novel alloy having an advantageous combination of tensile characteristics, creep characteristics, ductility, thermal expansion characteristics, elastic characteristics, working characteristics, etc.

Another object of the invention is to provide a novel alloy especially suited for use as gas turbine structures, especially power rotor discs.

The invention also contemplates providing gas turbine power rotor discs made of an alloy having an advantageous combination of tensile characteristics, creep characteristics and other characteristics, properties, etc., necessary to provide enhanced qualities of utility in a turbine power rotor.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which the figure is a graph relating the percentage by weight of iron to the percentage by weight of niobium in the present alloys.

According to the invention, the alloy contains, in percent by weight, about 0.03% to 0.09% carbon, about 14% to about 22% chromium, about 10% to 20% cobalt, from 3% to about 8% molybdenum, from 2% to about 3.5% titanium, from 0% to about 0.8% aluminum, the sum of the titanium and aluminum contents being greater than 2.5% (i.e., at least 2.6%), about 2% to about 5.25% niobium (i.e., columbium), from 0% to about 25% iron, the contents of niobium and iron being so correlated that they are within the area ABCDEA in the accompanying drawing, about 0.001% to 0.01% boron and about 0.01% to about 0.1% zirconium, the balance, apart from impurities and residual deoxidants, being nickel. The molybdenum content of the alloy can be up to about 10% (i.e., from 3% to 10%). The usual major impurities in alloys of this kind are silicon and manganese and not more than 1% of each of these may be present, and the total amount of impurities and residual deoxidants should not exceed 2%. The impurity content should be kept as low as is practicable and, in particular, it is advantageous to keep the silicon content below 0.3%.

It is important that the content of each of the constituents of the alloy should lie within the limits set out above.

Some carbon is necessary to ensure adequate ductility, but the carbon content must be carefully controlled. If it is too low the alloy is unworkable, and at least 0.03%, and preferably at least 0.04%, should be present. As the carbon content increases the proof stress and tensile ductility decrease, and for this reason the carbon content must not exceed 0.09%.

At chromium contents less than 14%, the resistance of the alloy to oxidation and to attack by the products of combustion of turbine fuel falls off. On the other hand, increasing the chromium content tends to reduce the hot workability of the alloy. The chromium content must, therefore, not be greater than 22%. Cobalt has some beneficial effect on creep resistance and also improves hot workability, and may usefully be present in amounts from 10% up to 20%. Molybdenum has a beneficial effect on both tensile and creep ductility and is very desirable in order to avoid notch sensitivity. On the other hand, excessive additions of molybdenum carry the penalties of increased creep rate and decreased machineability and the content should, therefore, not exceed 10% and, advantageously, is not more than 8%. Molybduced. Aluminum has a particularly harmful effect on ductility, and not more than 0.8% may be present. Other things being equal, lower levels of ductility are obtained in the presence of much iron than in its absence, and if the iron content exceeds 10%, the aluminum content preferably does not exceed 0.5% Increasing the titanium content also leads to a decrease in the room temperature impact strength of the alloys, and the titanium content must not exceed 3.5%.

The presence of titanium and niobium together within the ranges set out above leads to a remarkable combination of strength and ductility, while outside these ranges there is a marked fall in one or both of these properties. If the niobium content is too low the creep rate at high temperatures is too high, while excessive amounts of niobium having regard to the iron content of the alloy lead to marked embrittlement of the alloys.

The best combination of properties, characteristics, etc., necessary for practical utilization of the alloy in turbine parts, structures, rotors, etc., operating at temperatures from room temperature up to about 600 C. or higher, are obtained when iron is absent or present only as an impurity advantageously in amounts not exceeding about and the niobium content is at the upper end of the range, that is, when the alloy is represented by a point lying within the area AFGEA in the accompanying drawing. As the iron content is increased, the niobium con tent must be decreased, and it is an important feature of the invention that the contents of these two elements are so related that they are within the area ABCDEA in the accompanying drawing. Replacement of nickel by iron makes the alloys cheaper, but also somewhat reduces their'tensile strength and proof stress at high temperatures. The iron-containing alloys are, however, suitable for use where the operating conditions are not extremely severe.

Niobium available from commercial sources is usually contaminated by tantalum, which element is substantially equivalent to niobiurn in its efiect, and niobium may be partly or wholly replaced by an equal weight of tantalum up to a maximum tantalum content of 3%.

Small additions of boron and zirconium have markedly beneficial effects on tensile ductility at temperatures of 600 C. and above, and both of these elements must be present. However, as the content is increased the melting point of the alloys falls, and if more than 0.01% boron or 0.1% zirconium 'is present, serious deterioration in the hot working properties of the alloys results.

Advantageous compositions of iron free and iron containing alloys are set forth below:

The alloys can be air melted, but advantageously, they are melted and cast under vacuum conditions. If they are melted in air they are advantageously deoxidized by means of magnesium. If too much deoxidant is added the workability of the alloys is seriously reduced and, advantageously, the residual magnesium content does not exceed 0.01%. Air melted alloys are advantageously refined by holding under vacuum in the molten state for some time before casting. The pressure during this treatment should not be more than 0.1 mm. Hg and advantageously is lower, e.g., 5 microns or less. The temperature is suitably 1400" C.-1600 C., and the holding timeshould be at least 5 minutes and, advantageously, is at least 10 minutes. The cast ingots can be processed to rotor disc form by conventional extrusion, forging, or pressing techniques.

The discs require suitable heat treatment in order to develop the critical combination of properties required. The alloys are of the age-hardenable type and require both solution and aging treatments. The former is most important in that for a given alloy it largely decides the relative levels of creep strength and proof strength that can be achieved. Very high solution treatment temperatures give the highest possible creep resistance, while on the other hand lower solution treatment temperatures favor increased proof strength. The solution heating temperature should, of course, not be higher than the solidus temperature of the alloy, but high enough to ensure that all constituents of the alloy are taken into solution. Subject to this, a suitable heat treatment for discs made from the alloys comprises solution treatment for /2-8 hours at 900 C.-1200 0., followed by air cooling or oil quenching and then aging at temperatures in the range 600 C.-850 C.

To eliminate the effects of residual cold work and to ensure reproducible mechanical properties the solution temperature is advantageously at least 1000 C. and a high level of proof strength together with reasonable creep strength is obtained after a heat treatment comprising solution heating for one hour at 1050 C., followed by air cooling and aging for 16-40 hours at 700 C. A further increase in proof stress is achieved by following the solution heating by a double aging treatment comprising heating for 2-4 hours at 750 C.-800 C., air cooling and heating for 16-40 hours at 680 C.-720 C., e.g., 700 C. For iron-free alloys the solution heating temperature is advantageously at least 1100 C.

By way of example, two alloys, Nos. 1 and 3, were made by vacuum melting at a pressure of less than 1 micron Hg and cast under vacuum to ingots which were extruded to bar. The extruded bar was heat treated by solution heating for one hour at 1000 C. followed by air cooling and aging at 700 C. for 16 hours and tensile and creep test pieces were machined from it.

Two further alloys Nos. 1a and 3a, of similar composition to Nos. 1 and 3 respectively, were air-melted and cast into 2 /2 inch diameter ingots which were forged to /2 inch diameter bar. The forging was completed at a temperature of about 800 C. to about 900 C. The forged bar was heat treated by solution heating for 1 hour at 1050 C., followed by air cooling and aging at 700 C. for 16 hours, and tensile and creep test pieces were machined from it.

Two additional alloys, Nos. 2 and 4, were air melted, and No. 4 was also vacuum refined. Both were then cast into 7 inch square ingots that were forged to round cheeses 2 inches thick and 18 inches diameter, the forging being completed at temperatures above about 1050 C. The cheeses were solution heated for three hours at 1050 C. and air cooled. Specimens cut from the centers of the cheeses were aged by heating for 16 hours at 700 C. (except where otherwise indicated), air cooled and machined to form tensile and creep test pieces. The compositions of the six alloys are given in Table I below and the results of tensile and creep tests in Table II. The tensile tests are performed with a Hounsfield tensometer:

TABLE I IComposition, percent by weight] Alloy Number Element 0. 06 0. 04 0. 08 0. 09 0. 07 0. 06 18. 7 19. 2 20. 4 13.9 15.8 15. 9 14. 25 14. 3 14. 4 13. 5 14. 5 13. 8 3. 95 4. O 3. 75 4. l 4. 9 4. 5 2. 65 2. 48 2. 62 3. l 3. 55 2. 76 0. 73 0. 53 0. 52 0. 1 0. 32 0. 27 4. 5 5.10 4. 75 2. 4 2. 2 2. 36 0. 2 0. 2 0. 2 20. 3 19. 6 19. 7 0.005 0.004 0. 004 0.005 0. 002 0.003 Zirconiunn 0.09 0. 06 0. 06 0. 03 0.03 0.02 Manganese 0. 05 0. 05 0. 05 0. 05 0. 05 0.07 -'lic0n 0. 2 0. 3 0. l3 0. 2 0. 3 0. l3 Nickel Bal. Bal. Bal. Bal. Bal. Bal.

TABLE II Alloy No. Creep Properties 45 t.s.i./575 O No strain 0.05% strain No strain 0.05% strain in 338 in 197 in 230 in 275 hrs. hrs) hrs. hrs.

43 t.s.i./600 C- No strain in 150 hrs.

32 t.s.i./650 O 0.04%

strain in 170 hrs.

40 t.s.i./050 C Fracture 0.2% strain 02% strain in 750 in 1400 in 250 hrs., hrs. hrs., fracfracture in ture in 1063 hrs., 1556 hrs., elongation elongation 3.1%. 5.9%.

32 t.s.i./700 0.- Fracture in 95 hrs., elongation 21% Alloy N o. Tensile Properties 0.1% PS (t.s.i.) 70 59 53 UTS (t.s.i.) 98 86 79 0 EClongation, percent 21 25 0.1% PS (t.s.i.) 57 66 53 50 54 48 UTS (t.s.i.) 85 91 76 64 76 65 Elongation, percent 16 15 15 14 19 17 1 Aged for 24 hours at 650 0.

PS =Proof stress.

UTS=U1timate tensile stress.

(t.s.i.) =long tons (2240 pounds) per square inch.

Elongations on gauge length 4X 4550i specimen.

The properties of further samples of alloys Nos. 2 and 4 cut from near the rims of the cheeses were similar to those given in Table II, except that the tensile elongations were somewhat greater.

It will be observed that the proof stress and ultimate tensile stress of the alloys were higher in the form of forged bar than in the form of extruded bar or forged rotor disc cheeses. This i due to the greater amount of Working performed at a fairly low temperature on the forged bar. The extruded bar and forged cheeses were Worked at much higher temperatures and the material thus had much less residual cold Work. In order to form relatively large structures such as turbine rotor discs by forging, high working temperatures, e.g., greater than about 1050 C. are necessary, and it is an important characteristic of the alloys that they exhibit high proof strength and ultimate tensile stres even after such treatment.

The following tables show the effects upon the tensile properties determined by the Hounsfield tensometer at 600 C. or" varying the contents of titanium, aluminum and niobium in some iron free and iron containing alloys. Impact strengths, Where given, were determined at 20 C. The compositions given are all nominal. All the specimens were either solution heated at 1000 C. for 1 hour, air cooled, and aged at 700 C. for 16 hours (heat treatment A) or solution heated at 1050 C. for 1 hour, air cooled, and aged at 700 C. for 16 hours (heat treatment B).

TABLE III Efiect of Varying Titanium Content (a) BASE COMPOSITION OF ALLOY [Carbon 0.05%, chromium 20%, cobalt 14%, molybdenum 5%, aluminum 0.4%, niobium 5%, iron 0%. boron 0.003%,

zirconium 0.03%, nickel balance. Specimens machined from forged bar (heat treatment B) Alloy No. Titanium, 0.1% P.S. U.I.S. Elongation,

percent (t.s.i.) (t.s.i.) percent (b) BASE COMPOSITION OF ALLOY [Carbon 0.05%, chromium 15%, cobalt 14%, molybdenum 5%, aluminum 0.3%, niobium 2%, iron 20%, boron 0.003%, zirconium 0.03%, nickel balance. Specimens machined from extruded bar] Heat Elon- Notched Alloy treat- Ti, 0.1% P.S. U.I.S. gation, impact N o. ment percent (t .s.i.) (t.s.i.) percent stfrtenlgth,

All the alloys in Table III, except Nos. 5, 11 and 12, are in accordance With the invention. In Nos. 5, 11 and 12, the total titanium and aluminum content is less than 2.5% and a marked drop in tensile strength and/or ductility (as indicated by percent elongation) is observed. The values of the notched impact strength (Izod test) given in the last column show how this property is impaired as the titanium content increases.

TABLE IV Effect of Varying Aluminum Content BASE COMPOSITION OF ALLOY [Carbon 0.05%, chromium 20%, cobalt 14%, molybdenum Analyzed values.

The fall in ductility of alloy No. 18 (outside the present invention), in which the aluminum content is too high, compared with alloys Nos. 17 and 1 (according to the invention) is very marked.

. 7 TABLE v Effect of Varying Niobium Content (a) BASE COMPOSITION OF ALLOY [Carbon 0.05%, chromium 20%, cobalt 14%, molybdenum titanium 2.5%, aluminum 0.7%, iron boron 0.003%, zirconium 0.03%, nickel balance. Specimens machined from extruded bar (heat treatment B)] (b) BASE COMPOSITION OF ALLOY [Carbon 0.05%, chromium 15%, cobalt 14%, molybdenum titanium 3.0%, aluminum 0.3%, iron 20%, boron 0.003%, zirconium 0.03%, nickel balance. Specimens machined from extruded bar (heat treatment B)] The decrcase'in tensile ductility and in impact strength shows how the alloys are embrittled when the niobium content is too high. Alloys Nos. 1 and 22 through 24 are in accordance with the invention, Nos. 19, 20, 21 and .25 are not.

As an illustration of the low creep strength (higher creep rate) exhibited by alloys in which the niobium content is too low having regard to the iron content, the following creep properties were found for an alloy having the analyzed composition: C 0.06%, Cr 21.5%, C0 13.5%, Ti 2.05%, A1 0.25%, Mo 4.12%, B 0.006%, Zr 0.05%, Nb 2.42%, Fe 0.2%, Si 0.3%, Mn 0.05%, Ni balance, after a heat-treatment comprising solution heating for 1 hour at 980 C. followed by air cooling and aging for 24 hours at 750 C.

Test conditions Time to 0.2% total Life to Elongastrain fracture tion Stress Temp. (hours) (hours) (percent) (t.s.i.) C.)

The results in TableVI demonstrate the need for some carbon in the alloys to make them forgeable and the way in which the proof stress and ultimate tensile stress fall as the carbon content increases.

TABLE VI Base Composition of Alloy [Chromium 20%, cobalt 14%, molybdenum 6%, titanium l Unlorgeable.

It is to be noted that the present invention provides alloys which for a given iron content exhibit in the age- I 8 hardened condition after solution treatment, an optimum combination of engineering characteristics when the given iron content is correlated to the columbium content in accordance with the accompanying drawing. More particularly it provides such alloys which exhibit, after a heat-treatment suitable for forged gas turbine rotor discs, the high proof and tensile stress values together with high resistance to deformation by creep under high stresses at elevated temperatures, as evidenced by a low creep rate,

0 that are desirable for such parts. Design requirements for turbine structures, in particular, gas turbine rotor discs, often dictate the use of alloys having high proof stress, high ductility and moderate temperature capability under creep conditions. In these circumstances, alloys containing 10% or more of iron together with correlated amounts of columbium within the range of 2% to about 4%, can economically be employed. When design requirements indicate the use of alloys having increased temperature capability under creep conditions together with a high combined level of other engineering characteristics such as low and high temperature proof stress, ductility, tenacity, elasticity, expansivity, etc., alloys con-' taining less than 10% iron, for example, less than 5% iron, together with correlated amounts of columbium within the range of about 3% to about 5.25% can advantageously be employed. Thus, a particular advantage of the present invention lies in the fact that a range of alloys is provided having an optimum combination of engineering characteristics for any particular design of structures subjected in use to conditions similar to those under which gas turbine power rotor discs are employed.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variation may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An alloy for use in turbine structures at temperatures up to about 600 C. and higher consisting essentially in percent by Weight of about 14% to about 22% chromium, about 10% to about 20% cobalt, about 3% to about 10% molybdenum, greater than 2.5% total aluminum and titanium, said aluminum being up to about 0.8% and said titanium being at least 2% to about 3.5%, about 0.03% to 0.09% carbon, about 0.001 to about 0.01% boron, about 0.01% to about 0.1% zirconium, about.2% to about 5.25 niobium correlated with up to about 25% iron with the balance being essentially nickel, said alloy after solution treatment and age hardening exhibiting an optimum combination of high and low tem-' perature tensile characteristics, creep characteristics, ductility characteristics and elastic characteristics for any particular iron content within said range of up to about 25 iron by virtue of the iron content being correlated to the niobium content so that the percentage of iron and the percentage of niobium are together representable by a point lying within the area ABCDEA in the accompanying drawing.

2. An alloy as in claim 1 which contains less than 0.01% magnesium and less than about 0.3% silicon.

3. An alloy as in claim 1 which contains less than about 0.5% aluminum when the iron content exceeds about 10%.

4. An alloy as in claim 1 which is double aged after solution treatment.

5. An alloy for use in turbine structures at temperatures up to about 600 C. and higher consisting essentially in percent by weight of about 14% to about 22% chromium, about 10% to about 20% cobalt, about 3% to about 10% molybdenum, greater than 2.5% total aluminum and titanium, said aluminum being up to about 0.8% and said titanium being at least 2% to about 3.5

about 0.03% to 0.09% carbon, about 0.001% to about 0.01% boron, about 0.01% to about 0.1% zirconium, up to about 25% iron, at least one metal selected from the group consisting of tantalum in an amount up to 3% and nobium in an amount up to 5.25% with the total content of tantalum plus niobium being about 2% to about 5.25% and the balance essentially nickel, said tantalum plus niobium being correlated with the iron content such that the correlation is represented by a point lying within the area ABCDEA in the accompanying drawing, whereby said alloy after solution treatment and age hardening exhibits an optimum combination of high and low temperature tensile characteristics, creep characteristics, ductility characteristics and elastic characteristics at any particular iron content Within the said range of up to about 25% iron.

6. An alloy as set forth in claim 5 wherein the molybdenum is at least partially replaced by an equal atomic percentage of tungsten up to a maximum tungsten content of percent by weight.

7. An alloy as defined in claim 6 wherein the iron content is a maximum of about 10% and the niobium content is about 3 to about 5.25

8. A gas turbine power rotor disc made of the alloy of claim 6.

9. An alloy for use in turbine structures at temperatures up to about 600 C. and higher, consisting essentially in percent by weight of about 18% to about 22% chromium, about 13% to about 15% cobalt, about 4% to about 6.5 molybdenum, about 2.25% to about 2.75% titanium, about 0.3% to about 0.8% aluminum, about 0.04% to 0.09% carbon, about 0.001% to about 0.01% boron, about 0.01% to about 0.1% Zirconium, about 4.5% to about 5% niobium, up to about 1% iron with the balance being essentially nickel.

10. A gas turbine power rotor disc made of the alloy of claim 9.

11. An alloy for use in turbine structures at temperatures up to about 600 C. and higher consisting essentially in percent by weight of about 14% to about 16% chromium, about 13% to about 15% cobalt, about 4% to about 6.5% molybdenum, about 2.75% to about 3.25% titanium, up to about 0.35% aluminum, about 0.04% to 10 0.09% carbon, about 0.001% to about 0.01% boron, about 0.01% to about 0.1% zirconium, about 2% to about 2.5% niobium, about 18% to about 22% iron and the balance being essentially nickel.

12. A gas turbine power rotor disc made of the alloy of claim 11.

13. An alloy for use in turbine structures at tempera tures up to about 600 C. and higher consisting essentially in percent by weight of about 14% to about 22% chromium, about 10% to about 20% cobalt, about 3% to about 10% molybdenum, gerater than 2.5 total aluminum and titanium, said aluminum being up to about 0.8% and said titanium being at least 2% to about 3.5 about 0.03% to 0.09% carbon, about 0.001% to about 0.01% boron, about 0.01% to about 0.1% zirconium, about 3.5% to about 5.25% niobium correlated with up to about 5% iron with the balance being essentially nickel, said alloy after solution treatment and age hardening exhibiting an optimum combination of high and low temperature tensile characteristics, creep characteristics, ductility characteristics and elastic characteristics for any particular iron content within said range of up to about 5% iron by virtue of the iron content being correlated to the niobium content so that the percentage of iron and the percentage of niobium are together representable by a point lying within the area AFGEA in the accompanying drawing.

14. A gas turbine power rotor disc made of the alloy of claim 13.

15. An alloy as in claim 13 which contains less than 0.01% magnesium and less than about 0.3% silicon.

16. An alloy as in claim 13 which is double aged after solution treatment.

References Cited in the file of this patent UNITED STATES PATENTS 2,920,956 Nisbet et al. Jan. 12, 1960 2,981,621 Thielemann Apr. 25, 1961 2,994,605 Gill et al. Aug. 1, 1961 FOREIGN PATENTS 710,413 Great Britain Mar. 12, 1962

Claims (1)

1. AN ALLOY FOR USE IN TURBINE STRUCTURES AT TEMPERATURES UP TO ABOUT 600*C. AND HIGHER CONSISTING ESSENTIALLY IN PERCENT BY WEIGHT OF ABOUT 14% TO ABOUT 22% CHROMIUM, ABOUT 10% TO ABOUT 20% COBALT, ABOUT 3% TO ABOUT 10% MOLYBDENUM, GREATER THAN 2.5% TOTAL ALUMINUM AND TITANIUM, SAID ALUMINUM BEING UP TO ABOUT 0.8% AND SAID TITANIUM BEING AT LEAST 2% TO ABOUT 3.5%, ABOUT 0.03% TO 0.09% CARBON, ABOUT 0.01 TO ABOUT 0.01% BORON, ABOUT 0.01% TO ABOUT 0.1% ZIRCONIUM, ABOUT 2% TO ABOUT 5.25% NIOBIUM CORRELATED WITH UP TO ABOUT 25% IRON WITH THE BALANCE BEING ESSENTIALLY NICKEL, SAID ALLOY AFTER SOLUTION TREATMENT AND AGE HARDENING EXHIBITING AN OPTIMUM COMBINATION OF HIGH AND LOW TEMPERATURE TENSILE CHARACTERISTICS, CREEP CHARACTERISTICS, DUCTILITY CHARACTERISTICS AND ELASTIC CHARACTERISTICS FOR ANY

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