US3232751A - Nickel-chromium-cobalt alloys - Google Patents

Description

Feb. 1, 1966 Filed Jan s. w. K. SHAW ETAL 3,232,751

NICKEL-CHROMIUM-COBAL'I' ALLOYS 3 Sheets-Sheet 1 K 2.5 a 3.5 4 4.5 s 5.5- e as Ho(%/ INVENTORS Feb. 1, 1966 I s. w. K. SHAW ETAL 3,232,751

NICKEL-CHROMIUM-COBALT ALLOYS Filed Jan. 23, 1963 3 Sheets-Sheet 2 I58 I80 I92 52 INVENTORS awn-r L/AL re? Keg SHAH By fee/mu: Massey Coax A True/v6) Feb. 1, 1966 s. w. K. SHAW ETAL 3,232,751

NICKEL-CHROMIUM-COBALT ALLOYS Filed Jan. 23) 1963 3 Sheets-Sheet 5 INVENTORS Res/mow Massey Coo M 9m ,4 WHEY United States 3,232,751 NICKEL-CHROMIUM-COBALT ALLOYS Stuart W. K. Shaw, Sutton Coldfield, and Reginald M. Cook, Kings Heath, Birmingham, England, assignors to The International Nickel Company, lnc., New York, N.Y., a corporation of Delaware Filed Ian. 23, 1963, Ser. No. 253,426 Claims priority, application Great Britain, Jan. 26, 1962,

7 Claims. (Cl. 75-171) about 1000 C. under loads of at least about 7 long tons per square inch (t.s.i.). Although many attempts were made to provide alloys having the required characteristics, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that by special control and interrelation of alloying constituents of nickel-base alloys, alloys can be provided having the presently required engineering characteristics.

It is an object of the present invention to provide a novel heat-, corrosionand stress-resisting nickel-base I alloy.

Another object of the invention is to provide a novel turbine structure made of a novel heat-, corrosionand stress-resisting alloy.

Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a graph showing the interrelation between the molybdenum content and the total aluminum plus titanium content required in alloys in accordance with the present invention;

FIG. 2 depicts a graph showing the interrelation be tween the chromium and molybdenum contents required in alloys in accordance with the present invention;

FIG. 3 is a graph showing the interrelation between the titanium and aluminum contents required in alloys in accordance with the present invention at one content of molybdenum; and

FIG. 4 is a graph showing the effect of the cobalt content upon the stress-rupture life of alloys in accordance with the invention.

In general the alloys according to the invention contain, in percent by weight, about 0.03% to 0.3% carbon, about 8% to 10.9% chromium, about to 13% cobalt, about 2.5% to 6.2% molybdenum, titanium and aluminum in amount such that the sum of the titanium and aluminum contents is about 6.6% to 11.5% and the ratio of titanium to aluminum is from 0.2:1 to 1.521 by weight, about 0.05% to 0.5% zirconium and about 0.005% to 0.05% boron, the balance, apart from impurities, being nickel. The principal impurities that may be present are iron, silicon and manganese and the total amount of these elements must not exceed 3% and should be as low as possible. Advantageously, the iron content does not exceed 0.5 the silicon content does not exceed 0.3% and the manganese content does not exceed 0.3%.

One group of alloys according to the invention contain titanium and aluminum in such amounts that the sum of the titanium and aluminum contents is about 8.4%

3,232,751 Patented Feb. 1, 1966 to 11.5% and the ratio of titanium to aluminum is from 0.7:1 to 1.5:1 by weight.

The contents of chromium and molybdenum, the total content of titanium and aluminum, and the ratio of ittanium to aluminum at which the longest lives are obtained in stress-rupture tests at 1020 C. .on the cast alloys are interrelated. The interrelation of these elements is shown by FIGURES 1 to 3 of the accompanying drawing.

As the total titanium and aluminum content is increased at the expense of nickel in a series of alloys of otherwise similar composition, the ratio of titanium to aluminum being held constant, the stress-rupture life at 1020 C. increases to a maximum and then again decreases. In a similar series of alloys having a different molybdenum content, the maximum stress-rupture life is found to occur at a ditierent total titanium and aluminum content, the value of which decreases as the molybdenum content increases within the range 2.5% to 6.2%. Furthermore it is found that the maximum value of the stress-rupture life in the series of alloys also depends on the molybdenum content, passing through a maximumat molybdenum contents between 2.5 and 6.2% and falling off sharply when the molybdenum content is below 2.5% or above 6.2%. In the alloys of the invention the titanium and aluminum contents are therefore so related to themolybdenum content that when the ratio of titanium to aluminum is from 0.721 to 1.5:1 the values of the titanium plus aluminum content and the molybdenum content, expressed as percentages by weight, lie within the area ABCDA in FIGURE 1 of the accompanying drawing, and preferably within the area EFGHE. At these ratios of titanium to aluminum, the minimum (Ti-l-Al) content is 8.4% at a molybdenum content of 6.2%, as shown in FIGURE 1. At lower ratios of titanium to aluminum, between 0.7 :1 and 0.2: l, we find that the ratio of titanium to aluminum also enters into the relationship between the (Ti-t-Al) content and the molybdenum content, and the total percentage content of titanium and aluminum must then be from a minimum of (3.7 Ti/Al)-0.43 (Percent Mo)+8.48

to a maximum of (1.6 Ti/Al)0.43 (pfircent Mo)+11.45

The effect of variations in the proportions of titanium and aluminum is clearly shown by FIGURE 3 of the drawings, in which the points represent the compositions of a large number of alloys each of which contained, apart from titanium and aluminum, 0.10% carbon, 10%

chromium, 10% cobalt, 4% molybdenum, 0.1% zir-' conium, and 0.01% boron, the balance, apart from impurities, being nickel. The number beside each point represents the stress-rupture life of the alloy at a stress of 7 long tons/square inch (t.s.i.) at 1020 C. determined on cast test-bars without heat treatment. The outer and inner curves represent the limits of the regions in which the alloys have lives in excess of 10 hours and 60 hours respectively under these conditions. The lines VQ, UR and TS, respectively, represent the Ti:A1 ratios 1.5 :1, 0.7:1 and 02:1, and the line QRSTUVQ encloses Table I Alloy N M0, lltl'ktlli 'li-l- Al, ltilt'v to l lloiuzutlou,

' Pt'l't'tlltrupture. lir. percent.

.3 ll 42 4.2 4 ll) 23'. 0.7 0.5 ltil') 3.0 7 8.5 110 1 2. 1

Alloys Nos. 2 and 3 are in accordance with the invention. while Nos. 1 and 4 are not.

The chromium content of the alloys affects both the composition at which longest lives are obtained at [020 C. and the level of these lives. As the chromium content of the alloys is increased, the molybdenum content at which the longest lives are obtained at 1020 C. decreases, and according to the invention the chromium and molybdenum contents are so related as to lie within the area IJKLI in FIGURE. 2 of the accompanying drawing.

Most. advantageously the chromium content is not less than 9%, and the alloys have contents of chromium and molybdenum represented by points within the area MNOPM in FIGURE 2 of the accompanying drawing.

The effect of varying the chromium content in a series of alloys containing cobalt having optimum contents of titaniunt-t-alt1ttrinum and of molybdenum for each chromium content is shown in Table 11.

Each of the alloys was tested at l020 C. and 7 t.s.i.

Table I1 cc .-r- .c we Alloy (.r, per- 5 Mo, pt-r- 'lH-Al, bite to i litnuunt nu, Nu. cont. cent. percent. rupture, lir. percent,

2 ll 03 I 4.U 10 4 10 232 l at 5 h ll. 5 ltill l 2.. ti

Apart from cobalt, chromium, molybdenum and titanium+aluminum in the amounts stated, all the alloys of Tables I and It contained 0.1% carbon, 0.1% zirconium and 0.01% boron, the balance being nickel and impurities and the titanium to aluminum ratio, except where otherwise stated, being unity.

Alloys Nos. Sand 6 in Table It were not in accordance with the invention, and it will be seen that the stressrupture life attainable falls off quite sharply with increasing chromium contents. Although the stress-rupture lives of the best alloys with less than 8% chromium are still quite good, the resistance of these alloys to oxidation and sulfidation is very poor. Thus the apparent satisfactory life to rupture of the alloy of Table ll containing 5% chromium is offset by the fact that as the chromium is lowered from 10% to 5%, the oxidation resistance and the sulfidation resistance of the alloy sutiers greatly as shown in Table 111.

till

crties. This is shown by the graph forming FIGURE 4 of the drawing, in which the abscissae are the cobalt contents of a series of alloys containing, besides cobalt, 10%

chromium, 4% molybdenum, 5% titanium, 5% aluminum, 0.l% carbon. 0.1% zirconium and 0.01% boron, the balance, apart from impurities, being nickel, and the ordi hates are their stress-rupture lives in hours at 7 t.s.i. and l020 C.

Preferably the cobalt content of the alloys according to the invention is from 9 to l2%, for example, from 9 to 11%.

The carbon content of the alloys is preferably from 0.05% to 0.25%, the zirconium content not more than 0.20% and the boron content not more than 0.025%.

An alloy (alloy A) that is particularly suitable for use in the cast form has the composition:

10% Cr, 10% Co, 4% Mo, 5% Ti, 5% A1, 0.1% C, 0.1% Zr, 0.01% B, balance Ni and impurities.

Cast alloy specimens of this composition have been found to exhibit stress-rupture lives of over 200 hours under a stress of 7 t.s.i. at 1020 C. with elongations at rupture of 5% to 109 and to have an unnotched impact strength (0.45 inch diameter testpiece) at 900 C. of 35 ft.-lbs. and a notched impact strength (standard Charpy testpiece) at 900 C. of 7.2 ft.-lbs.

Another very suitable alloy (alloy B) has the composition:

l0% Cr. i092 Co. 4% M0. 2.5% Ti, 6.5-7% Al, ().l% C, 01% Zr, 0.01% B, balance Ni and impurities.

Cast alloy specimens of this composition have been found to exhibit stress-rupture lives of over 170 hours under a stress of 7 t.s.i. at i020 C. with clongations of about 9%, and lives of about 100 hours at 6 t.s.i. at 1950 C. with clongations oi" about 10%.

The alloys according to the invention may be air melted, but are preferably melted under vacuum. Whether or not they are vacuum melted, the alloys are advantageously subjected to a vacuum rclining treatment comprising holding them in the molten state under high vacuum before casting the melt. We prefer to hold the melt at a temperature of 1400 C. to 1600 C. at not more than 100 microns pressure (most preferably not more than 5 microns) for a period of at least 15 minutes and advantageously for minutes or more. The duration of the treatment depends to some extent on the purity of the ingredients of the melt, a longer time being required when less pure ingredients are employed.

When producing small-casting, for example, turbine blades or stress-rupture testpieces, the alloys are preferably cast under vacuum, but when producing large castings front a melt that has been produced or refined under vacuum it makes little ditterence to the properties obtained whether casting is carried out in vacuum, inert gas or air. All the stress-rupture test results referred to in this specification and in the drawings were obtained on test pieces machined from cast specimens that had been vacuum cast from vacuum melted material that had been vacu' 5. um refined for at least 15 minutes at 1500 C. under a pressure of less than 1 micron.

Articles and parts cast from the alloys may be used in the as-cast condition for high temperature service, for example, as rotor blades in gas turbine engines, and no marked improvement in properties is found on subsequent heat treatment.

The alloys also exhibit useful stress-rupture properties in the wrought form after solution heating and aging. Generally speaking, solution heating may be performed at temperatures in the range 1150 C. to 1250 C. for periods between l and 3 hours. Heating at these temperatures for longer than 3 hours leads to excessive grain growth. Within this temperature range an upper limit is set by the incipient melting point of the alloy, and for alloys having a (TH-Al) content of 10% the preferred solution heating temperature is 1225 C. As the (Ti-t-Al) content of the alloy is increased, the temperature required to take the whole of the primary gamma-phase into solution also increases, and at (Ti+Al) contents above 11.5% it is impossible to obtain complete solution of this phase below the incipient melting point, so that the stress-rupture properties of the alloy after aging fall 01f. The stress-rupture properties after age hardening also fall otf as the (TH-Al) content is decreased below 10%, in a similar manner to the properties of the cast alloys. Aging is preferably etfected by heating in the range 900 C. to 1100 C. for from 1 to 24 hours, the time required de creasing as the temperature is increased and increasing with increasing section size. The temperatures during aging may be varied within the above mentioned range or, if desired, aging may be effected by cooling the alloy By way of example, a specimen of a wrought alloy having the composition:

0.10% C, 10% Cr, 10% Co, 3.5% Mo, 5% Ti, 5% Al,

0.1% Zr, 0.01% B, balance Ni had a life to rupture of 58 hours under a stress of 7 t.s.i. at 1020 C. after a heat treatment comprising solution heating for 1.5 hours at 1250 C. followed by aging at 1000 C. for 6 hours. Similar properties are obtained if the aging step comprises furnace cooling from the solution heating temperature, e.g., down to 1150 C. or 1100 C.

Despite their low chromium content the alloys of the invention have remarkably good resistance to oxidation at high temperatures. Nevertheless, for use at temperatures above 1000 C. under conditions such as are encountered in gas turbine engines involving both oxidation and sulfur attack, articles and parts made from the alloys are preferably provided with a protective coating, for example, of aluminum.

Although the present invention has been described in conjunction with preferred embodiments, it is to be undersood that modifications and variations 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 under high stress at elevated temperatures and characterized by a high stress-rupture life, said alloy consisting essentially of, in weight percent, about 0.03% to about 0.3% carbon, about 8% to 10.9% chromium, about 5% to about 13% cobalt, about 2.5% to about 6.2% molybdenum, about 8.4% to about 11.5% total titanium plus aluminum with the ratio of said titanium to said aluminum being about 0.2 to l to about 1.5

to 1, about 0.05% to about 0.5% zirconium, about 0.005% to about 0.05% boron, the balance apart from impurities being nickel, the elements titanium, aluminum and molybdenum in said alloy being interrelated such 0.2 to l to 0.7 to 1 the said ratio is correlated with the percentage of molybdenum such that the percentage of total titanium plus aluminum is from a minimum of (3.7 Ti/Al) 0.43 X (P rcent Mo) +8.48

to a maximum of (1.6 Ti/Al)--0.43 X(P rcent Mo) +1 1.45

said alloybeing further characterized such that the percentages of molybednum and chromium are correlated so as to represent a point lying within the area IJKLI in FIGURE 2 of the accompanying drawing.

2. An alloy as in claim 1 wherein the chromium content is from 9% to 10.9%, the correlation of the total titanium plus aluminum percentage and the molybdenum percentage is represented by a point lying within the area EFGHE in FIGURE 1 of the accompanying drawing and thecorrelation of the chromium and molybdenum percentages is represented by a point lying within the area MNOPM in FIGURE 2 of the accompanying drawing.

3. An alloy as set forth in claim 2 wherein the cobalt content is about 9% to about 12%, the carbon content is about 0.05% to about 0.25 the zirconium content does not exceed 0.20% and the boron content does not exceed 0.025%.

4. A gas turbine structure made of an alloy as in I peratures and characterized by a high stress-rupture life,

said alloy consisting essentially of, in weight percent, about 0.05% to about 0.25% carbon, about 8% to 10.9% chromium, about 5% to about 13% cobalt, about 2.5% to about 6.2% molybdenum, about 8.4% toabout 11.5% total titanium plus aluminum with the ratio of said titanium to said aluminum being about 0.2 to 1 to about 1.5 to l, and with the total sum of titanium plus aluminum representing a point falling within the area QRSTUVQ of FIGURE 3 of the accompanying drawing, about 0.05% to about 0.2% zirconium, about 0.005% to about 0.25% boron, the balance apart from impurities being nickel, the elements titanium, aluminum and molybdenum in said alloy being interrelated such that at a ratio of titanium to aluminum of from about 0.7 to l to about 1.5 to 1 the correlation of the percentage of total titanium plus aluminum and the percentage of molybdenum is represented by a point lying within the area ABCDA in FIG- URE l of the accompanying drawing and at a ratio of titanium to aluminum of from about 0.2 to 1 to 0.7 to 1 the said ratio is correlated with the percentage of mo-v lybdenum such that the percentage of total titanium plus aluminum is from a minimum of centages of molybdenum and chromium are correlated so as to represent a point lying within the area IJKLI in FIGURE 2 of the accompanying drawing.

6. An alloy for use under high stress at elevated temperatures and characterized by a high stress-rupture life of over 200 hours at a temperature of 1020 C. under a cobalt, about 4% molybdenum, about 5% titanium, about 5% aluminum, about 0.1% zirconium, about 0.01% b0- ron and the balance essentially nickel. 7. An alloy for use under high stress at elevated temperatures and characterized by a stress-rupture life of over 170 hours under a stress of 7 long tons per square inch at a temperature of 1020 C. in the cast condition, said alloy consisting essentially of, in weight percent, about 0.1% carbon, about 10% chromium, about 10% cobalt, about 4% molybdenum, about 2.5% titanium, about 6.5% to 7% aluminum, about 0.1% zirconium, about 0.01% boron and the balance essentially nickel.

References Cited by the Examiner DAVID L.

U N IT ED STATES PATENTS 9/1960 Brown 75--171 3/1961 Bieber 75-171 10/1963 Gittus 75--171 11/1963 Gittus et a1 7517l FOREIGN PATENTS 12/1959 Australia.

5/ 1959 Great Britain. 9/ 1955 Great Britain.

RECK, Primary Examiner.

15 WlNST ON A. DOUGLAS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,232,751 February 1, 1966 Stuart W. K. Shaw et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 4, for "it-" read ticolumn 4, line 39, for "1950 C." read 1050 C. line 55, for "casting" read castings column 5, line 19, for gamma-phase" read gamma phase column 6, line 49, for "0.25%" read 0 025% Signed and sealed this 7th day of February 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. AN ALLOY FOR USE UNDER HIGH STRESS AT ELEVATED TEMPERATURES AND CHARACTERIZED BY A HIGH STRESS-RUPTURE LIFE, SAID ALLOY CONSISTING ESSENTIALLY OF, IN WEIGHT PERCENT, ABOUT 0.03% TO ABOUT 0.3% CARBON, ABOUT 8% TO 10.9% CHROMIUM, ABOUT 5% TO ABOUT 13% COBALT, ABOUT 2.5% TO ABOUT 6.2% MOLYBDENUM, ABOUT 8.4% TO ABOUT 11.5% TOTAL TITANIUM PLUS ALUMINUM WITH THE RATIO OF SAID TITANIUM TO SAID ALUMINUM BEING ABOUT 0.2 TO 1 ABOUT 1.5 TO 1, ABOUT 0.05% TO ABOUTR 0.5% ZIRCONIUM, ABOUT 0.005% TO ABOUT 0.05% BORON, THE BALANCE APART FROM IMPURITIES BEING NICKEL, THE ELEMENTS TITANIUM, ALUMINUM AND MOLYBDENUM INSAID ALLOY BEING INTERRELATED SUCH THAT AT A RATIO OF TITANIUM TO ALUMINUM OF FROM ABOUT 0.7 TO 1 TO ABOUT 1.5 TO 1 THE CORRELATION OF THE PERCENTAGE OF TOTAL TITANIUM PLUS ALUMINUM AND THE PERCENTAGE OF MOLYBDENUM IS REPRESENTED BY A POINT LYING WITHIN THE AREA ABCDA IN FIGURE 1 OF THE ACCOMPANYING DRAWING AND AT A RATIO OF TITANIUM TO ALUMINUM OF FROM ABOUT 0.2 TO 1 TO 0.7 TO 1 THE SAID RATIO IS CORRELATED WITH THE PERCENTAGE OF MOLYBDENUM SUCH THAT THE PERCENTAGE OF TOTAL TITANIUM PLUS ALUMINUM IS FROM A MINIMUN OF

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