US3617263A

US3617263A - Corrosion-resistant nickel-chromium base alloy

Info

Publication number: US3617263A
Application number: US830848A
Authority: US
Inventors: Paul Isidore Fontaine; Michael John Fleetwood; Harry Lewis
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1968-06-11
Filing date: 1969-06-05
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: FR2010696A1; BE734417A; DE1929301B2; GB1199240A; CH505904A; NL6908846A; AT288041B; NL140292B; SE359572B; DE1929301A1

Abstract

A nickel-chromium base alloy adapted for turbine blade manufacture contains, in addition to nickel and chromium, cobalt and correlated amounts of niobium, titanium and aluminum, as well as carbon and boron. Other elements such as zirconium, rare earth metal and yttrium can be present.

Description

United States Patent Inventors Priority Paul Isidore Fontalne Shirley, Solihull;

Michael John Fleetwood, Berkhamsted; Harry Lewis, Northfield, Birmingham, all of England June 5, 1969 Nov. 2, 197 l The International Nickel Company, Inc. New York, NY.

June 11, 1968 Great Britain CORROSION-RESISTANT NICKEL-CHROMIUM BASE ALLOY 1 1 Claims, No Drawings [52] U.S.Cl 75/17l,

l48/32.5, 148/162 [51] Int. Cl C22c 19/00 [50] Field ofSearch 75/171, 170; 148/32, 325,162

[56] References Cited UNITED STATES PATENTS 3,408,179 10/1968 Lewisetal 75/171 3,466,171 9/1969 Fletcher et a1 75/171 Primary Examiner-Richard 0. Dean Attorney-Maurice L. Pine] ABSTRACT: A nickel-chromium base alloy adapted for turbine blade manufacture contains, in addition to nickel and chromium, cobalt and correlated amounts of niobium, titanium and aluminum, as well as carbon and boron. Other elements such as zirconium, rare earth metal and yttrium can be present.

CORROSION-RESISTANT NlCKEL-CHROMIUM BASE ALLOY As those skilled in the art are aware, over the last score of years research efforts have been continuous and relentless in the quest for new and improved materials capable of delivering improved performance at elevated temperatures. And, prompting this developmental process have been the ever-increasing and stringent demands imposed by commercial operating conditions. This has been true, for example, in respect of components for gas turbine engines, rotor. blades. beingillustrative. In this regard and in respect of aircraft gas turbines, the nickel-chromium base alloys have been extensively used for such applications, alloys containing from to percent chromium together with certain amounts of titanium, aluminum and other constituents having been found generally acceptable.

For combating the more severe corrosive conditions encountered. with land-based turbines, a factor arising from the use of cheaper and less pure fuel than aviation kerosene, alloys having greater corrosion resistance are necessary, and the use of higher chromium contents, inter alia, has been advanced. This aspect has required a compositional balance to minimize loss in stress-rupture and creep characteristics. It might also be added, that even aircraft gas turbines operating in marine environments have to withstand severe corrosion attack as a result of ingestion of salt spray. And similar conditions are encountered in gas turbines used in ships and hovercraft.

To meet the requirements of both aircraft and land-based gas turbines, there are described and claimed in British Pat. No. 959,509 alloys containing 27 to percent chromium, 1.2 to 2.5 percent titanium, 0.5 to 1.1 percent aluminum, the total titanium and aluminum being from 2.0 to 3.2 percent, 0.01 to 0.1 percent carbon, 0.001 to 0.01 percent boron, 0.01 to 0.1 percent zirconium and up to 1 percent silicon, the balance being essentially nickel. Such alloys generally have stress-rupture lives in the range of to 140 hours when tested under a stress of 17 tonf/in. at 750 C. in the wrought condition after solution-heating and aging. As indicated in the subsequently issued British Pat. No. 1,040,797, the stress-rupture life under these test conditions can be increased to 200 to 300 hours by the simultaneous addition to the alloys of 12 to 30 percent cobalt and 1 to 7 percent molybdenum, respectively.

Such attributes notwithstanding, it was subsequently found, however, that embrittlement upon prolonged heating at high temperature ensued. This dilemma, it was determined, was largely brought about by the presence of molybdenum, a constituent used to afford high stress-rupture life at elevated temperature. Therefore, the problem to which the present invention is addressed is overcoming this disadvantage without incurring significant loss in either corrosion resistance or stressrupture characteristics at high temperatures.

It has now been discovered that the foregoing objective can be achieved, indeed, stress-rupture strength can also be improved, with substantially or entirely molybdenum-free alloys that contain small amounts of niobium and in which the contents of chromium, titanium, aluminum and niobium are specially interrelated.

It is an object of the invention to provide nickel-base alloys which by virtue of good stress-rupture characteristics resistance to corrosion and improved long term stability at elevated temperature are suitable for use in the production .of such articles as rotor blades for gas turbines.

Other objects and advantages will become apparent from the following description.

Generally speaking, the alloys contemplated in accordance herewith contain (by weight) at least 27 percent chromium for good high-temperature corrosion resistance but not more than about 31 percent in order to avoid risking undue embrittlement. Preferably the chromium content is from 28 percent to 29.5 percenLFrom 10 to 25 percent cobalt strengthens the alloys, and it is to advantage that from 15 to 22 percent cobalt is present. The alloys are further strengthened by the copresence of niobium, titanium and aluminum. in this connection, stressrupture strength falls off markedly at niobium contents less than 0.2 percent and beneficially the niobium content is from 0.3 to 1.5 percent. More than 2 percent niobium leads to embrittlement and loss of impact strength, and also to loss of stress-rupture strength and ductility. (Tantalum may be introduced incidentally with the niobium in an amount up to about one-tenth of the niobium content. For the purposes of the present invention, such amounts of tantalum are to be regarded as part of the niobium content.)

The sum of the titanium and aluminum contents must be from 2.25 to 4.5 percent, for either above or below these limits the stress-rupture strength falls off, and too much titanium and aluminum also renders the alloys susceptible to embrittlement on prolonged heating at high temperatures. Advantageously, the sum of these constituents is from 3 to 4 percent. It is to be also noted that stress-rupture strength also depends on the ratio of titanium to aluminum, and this. must be from 1:1 to 4:1, and is preferably from 1.521 to 2.521. The best combination of strength and elongation in stress-rupture tests is shown by alloys in which this ratio is about 2: l.

The foregoing notwithstanding, even within the narrow ranges of niobium, titanium and aluminum, some of thealloys may embrittle on prolonged heating at elevated temperatures and in order to minimize or avoid this it is necessary to correlate the percentages of chromium, titanium, aluminum and niobium such that the value of the expression (hereinafter referred to as the A Factor) does not exceed 40.

Carbon is also of importance. If it is too low, stress-rupture strength is reduced, while if to the excess the alleys become susceptible to embrittlement. Hence, the carbon content should be from 0,2 to 0.1 percent, and is preferably from 0.04 to 0.08 percent.

Boron and to a lesser extent zirconium both improve the stress-rupture strength of the alloys, and they must contain at least 0.002 but not more than 0.01 percent boron. Zirconium may be present in, amounts up to 0.6 percent but no particular advantage is found in using more than 0.1 percent.

The resistance of the alloys to oxidation and scaling is improved by the presence of rare earth metals, and one or more of these metals may be added, for example, in the form of misch metal. Advantageously, from 0.01 to 0.3 percent of rare earth metal, e.g., from about 0.03 to 0.08 percent, is added. Yttrium too improves oxidation and scaling resistance and also resistance to sulphidation. Accordingly, yttrium may advantageously be added in amounts from 0.2 to 2 percent, for example, from 0,5 to 1 percent.

Of the elements that may be present as impurities, silicon has a deleterious effect on corrosion resistance and should therefore be kept below 1 percent and preferably below 0.5 percent. Other impurities may include manganese in amounts up to 1 percent and iron in amounts up to 2 percent.

A particularly advantageous combination of properties is exhibited by alloys containing from about 0.04 to 0.06 percent carbon, 28 or 28.5 to 29 percent chromium, 19 to 21 percent cobalt, 2.1 or 2.2 to 2.5 percent titanium, 1.1 to 1.3 or 1.4 percent aluminum, 0.5 to 0.8 or 1 percent niobium, from 0.002 to 0.01 percent, e.g., 0.003 to 0.005 percent boron, boron, up to, say, 0.06 or 0.1 percent zirconium, a range of 0.04 to 0.1 percent zirconium being quite satisfactory, up to 0.3 percent rare earth metal, up to 1% yttrium and the balance, apart from impurities, being essentially nickel.

To develop the full stress-rupture properties of the alloys in wrought form they must be subjected to a heat treatment comprising solution heating and subsequent aging. The solution treatment may comprise heating from 1 to 8 hours in the temperature range of 1,050 to 1,200 C., and the alloys may then be aged by heating for 1 to 24 hours in the temperature range of 800 to 950 C. An intermediate aging treatment consisting of heating for l to 16 hours at 800 to l,050 C. may be interposed between the solution treatment and the final aging stages. The alloys may be cooled at any convenient rate after each heat treatment stage, e.g., by air-cooling (generally to As will be seen from results in table II, alloy D, which contained too little titanium and aluminum, had a low stress-rupture life in comparison with alloys 1 and 2 according to the invention. Alloy 5, which contained too much niobium and had room temperature) or by direct transfer from a furnace at one 5 an A Factor greater than 40, had very low impact strength temperature to one at a lower temperature. after prolonged heating at 850 C. In marked contrast, alloy 3,

For the purpose of giving those skilled in the art a better aphaving an A Factor value of less than 40 is in accordance preciation of the invention the following illustrative data are herewith, exhibited both good stress-rupture properties and given. good impact resistance. Alloy F contained too much niobium,

A series of alloys within the invention, alloys 1-3, table I, 10 and although it had good stress-rupture life, its A" Factor were tested in the form of specimens machined from forged was greater than 40 and its impact strength was low. lts stressbar that had been heat treated by solution heating for 4 hours rupture elongation was also rather low. Alloy F is an example at l,l50 C., air-cooling, aging for 16 hours at l,050 C., airof an alloy which is excluded from the invention only because cooling and finally aging for 16 hours at 850 C. and again airthe contents of niobium, titanium, aluminum and chromium cooling. For purposes of comparison, there is included some 15 are not interrelated as required by the invention. of the best alloys (alloys A, B and C) in accordance with the The resistance of alloys according to the invention to corroaforementioned British Pat. No. 1,040,797. The test results resion by the combustion products of impure hydrocarbon fuels ported were obtained using a test temperature of8l5 C. with and by marine salts was assessed (table 111) by tests in which a stress of 12.5 tonf/inF. specimens were exposed to a molten mixture of 25 percent by TABLE I Composition, percent Stress rupture Elon- Life gation,

C Cr Mo Ti Al Nb Zr B (hours) percent Alloy I A (0. 04) (30) (20) (2) (1. 7) (0. 8) NJ}. (0. 05) (0. 003) 179 4. 6

B- 0. (30) (20) (2; (1. 7) (0. 8) N.a. (0. 05) (0. 003) 141 5. 7

C- (28) (20) (4 1. 7 0. 85 NJ}. 0. 05 0. 003 144 20. 2

3 28. l 20. 1 N.a. 2. 50 l. 40 1. 1 0. 06 0. 003 864 5. 6

Nora:

=Balance substantially all nickel. (#)=nominal.

N.a.=not added.

The necessity of correlating the respective percentages of weight of sodium chloride and 75 percent sodium sulfate at chromium, titanium, aluminum and niobium to avoid embrit- 900 C. The corrosion damage was evaluated by comparing tlement is reflected by the results of stress-rupture and impact the weight of each specimen, after removing the corrosion tests as given in table II. All the specimens were machined products by cathodic descaling in molten sodium hydroxide, from forged bar that had been solution treated for 4 hours at 40 with the initial weight before exposure. The more resistant l,l50 C. and air-cooled. Alloys D, l, 2 and E were given the materials are those that show the least loss in weight. The tests double aging treatment used for the tests in table I, while alwere performed in two ways: in test A, samples of each alloy loys 3, F and G were aged in a single stage by heating for 16 were half immersed in the salt mixture while heated in air hours at 850 C. and air-cooled. The tests were then perwhereas in test B samples of each alloy were heated in a vertiformed under the same conditions as those in table I, but the 4 cal open-top furnace into which the salt mixture was continuspecimens used for the impact tests (Charpy V-notch were ously fed as a fine dispersion at a rate of5 g./hour.

TABLE III Weight loss (mg/cm!) Test A Test B after Composition, percent after 300 72 121 C Cr Co Ti Al Nb Zr 13 hours hours hours Alloy:

Balance substantially all nickel.

heated for a further 1,000 hours at 850 C b f testing (A1- 60 The data set forth in table 111 indicate that the corrosion reloys D, E and F, a di ti t f 1 2 d 3, are id the i sistance of alloy 1 according to the invention is comparable to vention.) that of alloy .1, which is a commercially available alloy having TABLE II Composition, percent Stress rupture Elon- A Life gatlon, Impact C Cr Co Nb Ti Al B Zr factor (hours) (percent) strength Balance substantially all nickel.

that of alloy H, which is a commercially available alloy of comparable stress-rupture strength but lower chromium content.

The alloys can be air melted, but to ensure the best creep properties they are preferably melted and cast under vacuum. They can be readily processed by conventional means such as extrusion, forging, or rolling. Although primarily intended for use in the wrought form as gas turbine blades, the subject alloys are suitable for use in other applications where a combination of good stress-rupture strength and resistance to corrosion is required, particularly for articles ad parts that are subjected in use to stress at high temperatures while exposed to the combustion products of impure hydrocarbon fuels or to salt or both. They may also be used to make cast articles and parts, which may be used with or without heat treatment.

As will be appreciated by those skilled in the art, the term balance or balance essentially" usedin referring to the nickel content does not exclude the presence of small amounts of other elements, commonly present as incidental elements, e.g., deoxidizing and cleansing constituents, and impurities ordinarily associated therewith in small amounts which do no adversely affect the basic characteristics of the alloys.

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

We claim:

1. An alloy consisting of about 27 to about 31 percent chromium, about to 25 percent cobalt, from 0.2 to 2 percent niobium, about 2.25 to about 4.5 percent total of titanium and aluminum with the provisos that (a) the ratio of titanium to aluminum is from about 1:1 to about 4:1 and (b) the much lower stress-rupture strength and greatly superior to V value of the A Factor as determined by the relationship 5(%Nb)+4(%Ti+Al)+c/(%Cr) does not exceed about 40, about 0.02 to 0.1 percent carbon, about 0.002 to 0.01 percent boron, up to 0.6 percent zirconium, up to about 0.3 percent of rare earth metal, up to 2 percent yttrium and the balance essentially nickel.

2. An alloy in accordance with claim 1 containing 15 to 22 percent cobalt.

3. An alloy in accordance with claim 1 containing 0.3 to 1.5 percent niobium.

4. An alloy in accordance with claim 1 containing about 3 to 4 percent total of titanium plus aluminum.

5. An alloy in accordance with claim 1 in which the ratio of titanium to aluminum is from 1.5 :l to 2.5: l.

6. An alloy in accordance with claim 1 containing about 0.04 to 0.8 percent carbon.

7. An alloy in accordance with claim 1 containing about 0.01 to 0.3 percent rare earth metal.

8. An alloy in accordance with claim 1 containing 0.03 to 0.8 percent rare earth metal.

9. An alloy in accordance with claim 1 containing about 0.2 to 2 percent yttrium.

10. An alloy in accordance with claim 1 containing about 0.5 to 1 percent yttrium.

11. An alloy in accordance with claim 1 containing about 28 to about 29 percent chromium, about 19 to about 21 percent cobalt, about 0.5 to about 1 percent niobium, about 2.1 to about 2.5 percent titanium, about 1.1 to about 1.4 percent aluminum, about 0.04 to about 0.06 percent carbon, about 0.002 to about 0.01 percent boron, about 0.04 to about 0.1 percent zirconium, up to about 0.3 percent rare earth metal, up to about 1 percent yttrium, and the balance essentially nickel.

Claims

2. An alloy in accordance with claim 1 containing 15 to 22 percent cobalt.
3. An alloy in accordance with claim 1 containing 0.3 to 1.5 percent niobium.
4. An alloy in accordance with claim 1 containing about 3 to 4 percent total of titanium plus aluminum.
5. An alloy in accordance with claim 1 in which the ratio of titanium to aluminum is from 1.5:1 to 2.5:1.
6. An alloy in accordance with claim 1 containing about 0.04 to 0.8 percent carbon.
7. An alloy in accordance with claim 1 containing about 0.01 to 0.3 percent rare earth metal.
8. An alloy in accordance with claim 1 containing 0.03 to 0.8 percent rare earth metal.
9. An alloy in accordance with claim 1 containing about 0.2 to 2 percent yttrium.
10. An alloy in accordance with claim 1 containing about 0.5 to 1 percent yttrium.
11. An alloy in accordance with claim 1 containing about 28 to about 29 percent chromium, about 19 to about 21 percent cobalt, about 0.5 to about 1 percent niobium, about 2.1 to about 2.5 percent titanium, about 1.1 to about 1.4 percent aluminum, about 0.04 to about 0.06 percent carbon, about 0.002 to about 0.01 percent boron, about 0.04 to about 0.1 percent zirconium, up to about 0.3 percent rare earth metal, up to about 1 percent yttrium, and the balance essentially nickel.