US2981620A - Cobalt-nickel base alloy - Google Patents

Description

Aprll 25, 1961 J. T. BROWN El'AL COBALT-NICKEL BASE ALLOY 4 Sheets-Sheet 1 Filed Aug. 24, 1959 O O l W 2 O g 2 F O .w .w w @P o l 5 M e r 7 m 2 m e I e 4 r w mp m w .o m l a I e r a p 09 e m 8 .O.m H e 3% T S A m 6 r. O H o 8 w R 4 2 /H 2 IUW/ T /17 H O O O O O 0 O 5 0 5 0 w w 5 O 6 2 8 4 O 6 3 3 2 2 O 0 0 3 3 2 2 2 l O O 39GB: ,EmEmboma @04 0 '[I-Maximum Shear Stress lOOOpsi WITNESSES INVENTORS Alexander W. Cochordl, Charles P. Mueller, Leonard L. France 8 Jack T. Brown BY M M 5/ A TORNEY A ril 25, 1961 Filed Aug. 24, 1959 Log Decrement J. T. BROWN ETAL 2,981,620

COBALT-NICKEL BASE ALLOY 4'Sheets-Sheet 2 Low Initial Stress Solid Lines-I200 "F Dashed L|nes--Room Temperature ML-7O .Ol f

WV-IOOS /r O 2 4 6 8 l0 l2 l4 l6 Maximum Shear Stress IOOOpsI Heat l4l6 2 .O3- Room Temgerafure Q E G.) 8 (D a .02--

2 0 'C-Maximum Shear Stress lOOOpsi April 25, 1961 J. T. BROWN HAL 2,981,620

COBALT-NICKEL BASE ALLOY Filed Aug. 24, 1959 4 Sheets-Sheet 3 High Initial Stress Solid Lines-I200 F Dashed Lines-Room Temperature E .02 i O O 8 I6 24 32 4O 48 Maximum Shear Stress IOOOpsi Heat of Tiianium and Aluminum Hardened Alloy I200 "F H0O F IOOO F 25- o 1' I350 F 0:

l 3 l5-- 2 I400 F E IO- D O :1: I500 F O a z c c l 2 3 4 5 6789|O 2O 3O 4O 5O Ageing Time (Hours l) Fig.7

April 25, 1961 .1. T. BROWN ETAL COBALT-NICKEL BASE ALLOY 4 Sheets-Sheet 4 Filed Aug. 24, 1959 WV-IOOB Ageing Time (Hours-l) um wmwcubuz Fig. 8

I00 l o oo Hours To Rupture I200 "F S n e m e p s d e h C .Y o 3 N 0 O V S n w e m C 8 p S h .1 0 o m S 987 6 5 4 3 r 2,981,620 Patented Apr. 25, 1961 COBALT-NICKEL BASE ALLOY Filed Aug. 24, 1959, Ser. No. 835,510

9 Claims. c1. 75-170 This invention relates to a cobalt-nickel base alloy particularly suitable for use at temperatures in the range from 1200 F. to 1500" F., and members prepared therefrom.

At the present time, one of the great difficulties confronting the designers of turbines for operation at steam temperatures of 1200 F. and upward has been the unavailability of any alloy that has adequate strength, oxidation resistance, self-damping properties, stress rupture properties, and notch ductility at these temperatures. Certain cobalt-nickel base alloys have been proposed heretofore for this high temperature application. Thus, in U.S. Patent 2,829,048, issued April 1, 1958, to A. W. Cocharclt, one of the inventors of the present invention, and entitled High DampingAlloy and Members Prepared Therefrom, a cobalt-nickel base alloy having a critical proportion ,of titanium and aluminum therein, and exhibiting excellent damping properties, is disclosed. This alloy is proposed for use in turbine buckets and in other environments where extreme conditions of vibration exist. The cobalt-nickel base alloys with the titanium and aluminum addition acting as precipitation hardeners, under some conditions and in certain proportions, have a tendency to overage relatively rapidly at temperatures somewhat in excess of 1300 F. Since overaging and consequent loss of hardness is associated with lower stress rupture properties, it is apparent that some alloys of this type may prove inadequate if they are subjected for an extended period of time to temperatures above 1300" F. 1 t

In determining the relative'damping characteristics of the alloys of this invention, the vibration testsdescribed in the following publication were employed: Fiipph Pertz Damping Machine, Metals-and Alloys, New Products Section, February 1931, page 28. The "logarithmic decrement -as employed herein, and as generally defined, was determined for the alloys at various vibratory surface shear strain values.

The object of this invention is to provide an overagingresistant, high strength cobalt-nickel base alloy having a predetermined amount of beryllium therein as a precipitation hardener, in association with zirconium and molybdenum.

Another object of the invention is to provide mem bers, such as turbine buckets, prepared from a high temperature, corrosion-resistantcobalt-nickel base alloy containing predetermined amounts of beryllium, molybdenum, zirconium, and chromium therein, which retains a predetermined hardness. attemperatures over 1300" F. Other objects of theinvention will, in part, be obvious, and will, in part, appear hereinafter.

For a better. understanding ofthe nature and objects of the invention, reference should be. had to the follow ing detailed description and drawings, in which:

Figure 1 is a graph plotting hardness of two alloys against aging temperature in degrees Fahrenheit Figs. 2 and 3 are graphs plotting damping in terms 'of the logarithmic decrementagainst maximum shear stress for alloys of this invention at room temperature and at 1200 F.; i

. Fig. 4 is a graph plotting damping in terms of the logarithmic decrement against maximum shear stress for two alloys of this invention at room temperature and at 1200 F. with low initial stresses;

Fig. 5 is a graph similar to Fig. 4 except that high initial stress was employed; 1

Fig. 6 is a graph plotting hardness against aging time in hours at various temperatures for an alloy of the present invention;

Fig. 7 is a graph similar to Fig. 6 for a titanium-aluminum hardened alloy; and I 'Fig. 8 is a graph plotting stress in pounds per square inch against hours to rupture for smooth and notched bars of an alloy of this invention.

This invention is directed to cobalt-nickel base alloys which, after appropriate heat treatment and aging, exhibit, in the temperature range from 1200' F. to 1500 F., useful damping characteristics, good corrosion resistance, notch-ductility, and a high resistance to overaging. More particularly, the alloy of the present invention comprises essentially, by weight, from 20% to 24% nickel, from 30% to 1.50%. beryllium, up to 2% zirconium, up to 4.0% molybdenum, the total of zirconium and molybdenum lying in the range from 1% to 6.0%, up to 2.5% chromium, and the balance cobalt, in an amount of at least 65%, with impurities and minor additives including iron, silicon, manganese, and carbon not exceeding a total of.2.5

A desirable more restricted range of composition for the alloy comprises from 21.5 to 23.5% nickel, from 0.45% to 0.70% beryllium, from 0.75% to 1.5% zirconium, from 0.8 to 1.2% molybdenum, and the balance being cobalt except for incidental impurities and minor additives in an amount not exceeding 1.5%.

The high temperature properties of the alloy of this invention are obtained by precipitation hardening formed and shaped members of the alloys by applying suitable aging heat treatment. The beryllium, in an amount ranging from .30% to 1.50%, is the primary constituent which is involved in producing the desired hardness through precipitation phenomenon.

Molybdenum may be present in the alloy in amounts up to 4.0% as a solid solution hardener. The preferred amount of molybdenum in the alloys of this invention is approximately 1%, and may range from .8% to 1.2%. In order to assure stress-rupture ductility in the alloy, up to 2% zirconium may be present. As little as 0.02% zirconium has given good results in the alloys. The preferred range of the zirconium addition is from .75% to 1.5

It has been found desirable to add both molybdenum and zirconium to the alloy to obtain maximum properties. The optimum amount of beryllium, whenthe alloy contains about 1% each of molybdenum and zirconium, has been established as the range from .45% to 0.7%,

As much-as 2.5% chromium may be added to the alloy toimpart an improved corrosion resistance. A preferred amount of chromium, in those cases in which it is added to the alloy, is approximately 1%, and may range from .8% to 1.2%.

In the preparation of the alloys of this invention, both vacuum melting and air melting techniques have been used with satisfactory results. The molten alloy may be cast directly into members of desired shape by precision casting or shell molding techniques. For most applications, however, it is desirable to cast an ingot of the alloy, which is then subjected to suitable forging or rolling treatment to refine the grain structure and to produce homogeneous forgings or bar stock. The ingot may be heated to a temperature in the range from 1800 F. to 22.00 F. and hot rolled or forged to shape with suitable reheating if necessary.

Thecastings orbar members are solution heat treated ordinarily at temperatures in the range of 1800 F. to 1900 F. for a period of about an hour. Thereafter, the solution heat-treated member is aged at a temperature of from about 1200 F. to 1500" F. for a period of at least three hours to precipitation harden the alloy. In some cases, a two stage aging treatment is employed in which the alloy member is held at a relatively high temperature for an initial period, then cooled to a lower temperature, and held at that temperature for a somewhat longer period, and then cooled to ambient temperature. The superior resistance to overaging of beryllium hardened heats as compared to the over-aging characteristics of certain titanium-aluminum hardened heats is demonstrated in Fig. 1. Here a beryllium hardened alloy VM' 154, is compared with a titanium-aluminum hardened heat, VM 187. The compositions of these alloys are given immediately below in Table I.

TABLE I VM 154, percent VM 187, percent It will be noted that a pair of curves appears in Fig. 1 for each alloy. One curve in each case represents the hardness of samples of the alloy held for 8 hours at the indicated elevated temperatures, and the other curve represents the hardness of samples of the alloy held for 20 hours, in the case of VM 154, and 24 hours in the case of VM 187, at the indicated elevated temperatures. It will be noted that the beryllium hardened heat VM 154, retains notable hardness at temperatures as high as 1600 F., while the titanium-aluminum hardened heat VM 187, in both cases, suffers a decrease in hardness to an extent such that the benefits of precipitation hardening are completely lost at 1400 F.

The following examples of alloys having damping properties to a useful degree and exhibiting good resistance to overaging in the temperature range 1200 F. to 1500" F, illustrate the practice of the invention:

Example I An alloy identified as No. 1414 was air melted in a ingots of this alloy were. cast and forged to shape from a temperatureof about 2100 F. The wrought members were then solution treated for one hour at 1900 F., oil quenched, and then aged for three hours at 1300 F.

An alloy of the following composition, identificd'as No. 1416, was prepared by air melting:

The molten alloy was cast into an ingot, forged and heat treated in accordance with the procedure set forth in Example I.

The following alloy identified as S25, was prepared by c m ltin Example III Percent Co (73.0) Ni 23.0 Be .51 Zr 1122 Mo (1.0) S .007

The weight percent given in parenthesis is nominal ascharged weight. Ingotsof the alloy were cast and forged to shape from 1900 F. The alloy was then solution heat treated at a temperature of 2000 F. for one hour and then aged at 1200 F. for 16 hours. The hardness of the aged alloy was 314 DPH.

Example IV An alloy of the following composition identified as ML 71, was prepared by air induction melting:

Percent Co 74.6 Ni 20.2 Be .70 Zr 1.27 Mo g 1.06 Cr 1.09 Mn .50 Si .15

The alloy was cast into members and solution heat treated at 1925" F. for one hour, water quenched, then aged 10 hours at 1500 F. and '20 hours at 1200 F. Thealloy had a hardness inthe range 345-355 DPH.

Example V V The following alloy, identified as WV 1003, was prepared by vacuum induction melting:

Percent Co 72.86 Ni 22.7 Be .51 Zr 1.68 Mo .95 Fe 1.30

The alloy was cast into members and solution heat treated at 1925 F. for one hour and then was water quenched. The alloy samples were first aged at 1200 F. for 16 hours and th n i sea d. Th a dne of e ed in alloys made in accordance with this invention. should be understood that the analysis of the several at 1200 F.

TABLE II Applied Rupture Rupture Alloy. Stress Time Strain (p.s.i.) (hrs.)

65,000 87 8.4 1414 60, 000 110 7. 65,000 473 5.0 an a it 1415- 50,000 99 8.0 45,000 167 8.1 55,000 31 13.5 S25 45, 000 103 26. 0 40,000 169 17 ML 71 50,000 37.7 19.5 70,000 68. 9 18. 9 60, 000 125; 0 l6. 9 WV 1003 55,000 294.4 14.9 45,000 '517 26 35, 000 3215 21. 2

From the above tab1e,-it will be observed that the alloys of this invention have substantial service life at a temperature of 1200 F. while under stresses ranging from 35,000 p.s.i. to 70,000 p.s.i., and at the same time, the ductility of these alloys remains at a level sufficient for practical application. The damping capabilities of alloys Nos. 1414 and 1416 areset forth in Figs. 2 and 3, respectively, while the same property ofalloys ML 70 and WV 1003 at low initial stress, is set forth in Fig. 4. The damping capability of WV 1003, at high initial stress, is set forth in Fig. 5.

It will be noted from the above graphs that while the damping capacities of the alloys of this invention are generally lower than some alloys known to the art, nevertheless, a damping capability of useful proportions is present in these alloys.

Referring now to Figs. 6 and 7, a comparison may be made between the beryllium hardened heat, WV 1003, and a titanium-aluminum hardened heat with respect to their resistance to overaging at elevated temperatures. The beryllium hardened heat WV 1003 is clearly harder and more stable than the titanium-aluminum hardened heat. The stability of the beryllium hardened heat is particularly striking above 1300 F. when compared to the titanium-aluminum hardened heat in the same temperature range.

In Fig. 8, the performance of notched and smooth stress-rupture specimens of alloy WV 1003 at 1200 F. are compared. Here, it will be noted, that this alloy is notch ductile, for the notched specimens generally have longer rupture times at a given stress than the unnotched minor quantities of aluminum, iron, copper, carbon, sulfur, magnesium, manganese, lead, silicon, andhafniurn, as well as nitrogen, oxygen, and hydrogen may be present It compositions are accurate to about /z% of thetotal weight. i

, 6 In thebroadest sense, the present invention relates to a cobalt-nickel base alloy having critical amounts of zir conium, beryllium, and m'olybdenum therein. In order to study the properties of the basic cobalt-nickel alloy, and the efiectof zirconium, beryllium, and molybdenumwhen individually added to the basic alloy, four alloys were prepared having the compositions set forth in Table III.

TABLE III Other c0 N1 Zr Be Me N 's Mg Ingots of each alloy were hot rolled andsolutionheat treated at1900 F. for one hour.

VM 97, which is essentially a binary cobaltnickel alloy with nohardeners or significant additives, exhibited a hardness after solution heat treatment at 1900 F. for one hour of 170 DPH. The alloy was not age hardenable. In the stress-rupture test, the test bar of this alloy ruptured after less than one-half'hour at a stress of 26,000 p.s.i. at 1200 F.

VM 99, a beryllium-containing alloy, received a solution heat treatment identical to alloy VM 97 and, after this heat treatment, the alloy had a hardness of 200 DPH. The alloy was aged for 8 hours at a temperature of 1200 F. This last treatment resulted in a hardness of 320 DPH. In the stress-rupture test, VM 99 ruptured after 100 hours at 26,000 p.s.i. at a test temperature of 1200 F. 7

Alloy VM 104, a molybdenum-containing alloy, proved to be unworkable, cracking at rolling temperatures of 2000 F. and 2300 F. In view of this early failure of this alloy, further treatment or testing was not practicable.

Alloy VM 109, a zirconium-containing alloy, was solution heat treated as VM 97 and VM 99. This alloy attained a hardness of 220 DPH after the solution heat treatment. An aging treatment was attempted at 1200 F., however, the alloy proved not susceptible to age hardening. This alloy had no significant damping properties.

Study of the stress-rupture properties of the alloys of Table III and of the alloys of this invention indicates that properties which are not available in the binary alloy, and which are not imparted to the binary by any one additive, may be secured by adding to the principal constitutents the specified alloying additives in critical proportion in accordance with this invention. Particular attention is directed to the fact that the present alloy containing beryllium, molybdenum and'zirconium when tested at 1200 F. will withstand loads of over 50,000

p.s.i. for a substantial length of time, and inmost cases, for at least 100 hours.

It will be understood that the above specification and drawings are exemplary and not limiting.

We claim as our invention:

1. An alloy having good stability and resistance to overaging under stress at temperatures of 1200 F. and higher, comprising, by weight, from 21.5% to 23.5% nickel, from .45 to .70% beryllium, from .75 a to 1.5% zirconium, from 0.8% to 1.2% molybdenum, and the balance being cobalt except for impurities and minor additives in a total amountnot exceeding 1.5%.

2. An alloy having good tensile and stress rupture properties inthe temperature range of from 1200 F. to 1500 F. and exhibiting damping capacity to a useful degree in that temperature range, comprising, by weight,

from 20% to 24% nickelyfrorn 30% to 1.5% beryl- .lium, up to 2% zirconium, up to 4%; molybdenum, the

7 from 1% to 6%, and the balance being cobalt except for impurities and secondary additives including iron, silicon, manganese, and carbon in a total amount not exceeding 2.5%.

3. The alloy of claim 2 in which at least 1% zirconium is present.

4. The alloy ofclaim 3 in which from 0.8% to 1.2% molybdenum is present.

5. A high temperature alloy having good resistance to overaging under stress at temperatures in the range from l200 F. to 1500 F., comprising, by weight, from 20% to 24% nickel, from .30% to 1.5 beryllium, up to 2% zirconium, up to 4% molybdenum, the total of zirconium and molybdenum amounting to at least 1% but no more than 6%, up to 2.5% chromium, and the balance cobalt, with impurities and minor additives totaling no more than 2.5%.

6. The alloy of claim 5 in which from 0.8% to 1.2% chromium is present. I

7. A precipitation hardened wrought member suitable for use as a turbine blade at temperatures in the range from 1200 F. to 1500 F., comprising an alloy composed of, by weight, from 20% to 24% nickel, from 30% to 1.5% beryllium, up to 2.5% chromium, up to 2% zirconium, up to 4% molybdenum, the total of zirconium and molybdenum lying in the range from 1% to g} 6%, and the balance being cobalt, with impurities and minor additives totaling no more than 2.5%.

8. An alloy when in the precipitation hardened state having good stability and resistance to overaging under stress at temperatures of 1200 F. and higher, having good tensile and stress rupture properties in the temperature range of from 1200 F. to 1500 F., and exhibiting damping capacity to a useful degree in that temperature range, comprising, by weight, from 21.5% to 23.5% nickel, from .45% to .70% beryllium, from 0.02% up to 2% zirconium, from 0.8% to 1.2% molybdenum, and the balance being cobalt except for impurities and minor additives in a total amount not exceeding 1.5

9. An alloy having good stability and resistance to overaging under stress at temperatures of 1200 F. and higher when in the precipitation hardened condition, com prising, by weight, about23% nickel, about 0.50% beryllium, about 1.7% zirconium, about 1% molybdenum, and the balance essentially cobalt except for impurities and minor additives in a total amount not exceeding 1.5%.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 5. A HIGH TEMPERATURE ALLOY HAVING GOOD RESISTANCE TO OVERAGING UNBDER STRESS AT TEMPERATURES IN THE RANGE FROM 1200* F TO 1500* F., COMPRISING, BY WEIGHT, FROM 20% TO 25% NICKEL, FROM .30% TO 1.5% BERYLLIUM, UP TO 2% ZIRCONIUM, UP TO 4% MOLYBDENUM, THE TOTAL OF ZIRCONIUM AND MOLYBDENUM AMOUNTING TO AT LEAST 1% BUT NO MORE THAN 6%, UP TO 2.5% CHROMIUM, AND THE BALANCE COBALT, WITH IMPURITIES AND MINOR ADDITIVES TOTALLING NO MORE THAN 2.5%.

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