US3767479A

US3767479A - Multicomponent eutectics for high temperature applications

Info

Publication number: US3767479A
Application number: US00226297A
Authority: US
Inventors: L Tarshis
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-02-14
Filing date: 1972-02-14
Publication date: 1973-10-23
Anticipated expiration: 1990-10-23

Abstract

Chromium added to form a multicomponent eutectic in Ni-Cb-Al alloys enhances oxidation resistance and hot corrosion resistance at high temperatures. Alloys of the system Ni-Cb-Al-Cr have excellent mechanical properties in addition to their good oxidation and hot corrosion resistance, particularly when cast and unidirectionally solidified.

Description

United States Patent 1 11 1 Tarshis 1451 Oct. 23, 1973 MULTICOMPONENT EUTECTICS FOR HIGH TEMPERATURE APPLICATIONS [75] Inventor: Lemuel A. Tarshis, Latham, N.Y.

[73] Assignees General Electric Company,

Schenectady, NY.

[22] Filed: Feb. 14, 1972 [21] Appl. No.:-226,2 97

Related U.S. Application Data [63] Continuation of Ser. No. 87,907, Nov. 9, 1970,

Primary Examinerl Dewayne Rutledge Attorney-Charles T. Watts [57] ABSTRACT Chromium added to form a multicomponent eutectic in Ni-Cb-Al alloys enhances oxidation resistance and hot corrosion resistance at high temperatures. Alloys of the system Nl-Cb-Al-Cr have excellent mechanical properties in addition to their good oxidation and hot corrosion resistance, particularly when cast and unidirectionally solidified.

16 Claims, 5 Drawing Figures M-m-cb-cr AL 501 can as/770 A DIRECTIONAL L Y 30L lO/F/EO abandoned.

52 U.S. c1. 148/32, 75 134 F, 75/135, 75/171,75/122 51 1111. C1.., C22c 19/00 58 Field of Search 75/135, 171,122, 75/134 R, 134 F; 148/32 [56] References Cited UNITED STATES PATENTS 3,260,505 7/1966 Vel' Snyder 75/111 1/ w 2 e a w k /00- k 01 1 a R 6 TEMP. (F)

0 4&0 e50 /2 aa /6 'oo 2b I r mswz'ao PATENTEUUCTPZS 197s 3, 767,479

In venfi'or': Lemuel A. Wars/71's,

%vv His Attorney.

MULTICOMPONENT EUTECTICS FOR HIGH TEMPERATURE APPLICATIONS This is a continuation of application Ser. No. 87,907, filed Nov. 9, 1970, now abandoned.

FIELD OF THE INVENTION The present invention relates to new and useful alloys, and more particularly to alloys containing eutectic systems for high temperature structural applications in corrosive and oxidizing atmospheres.

BACKGROUND OF THE INVENTION Unidirectional solidification of eutectic alloys is known, for example from US. Pat. No. 3,124,452 of Kraft. Directionally solidified eutectic alloys have distinct advantages over ordinary composites for longterm high temperature structural applications. The near-equilibrium phase transformation is brought about by unidirectional solidification directly from the liquid state, and usually produces structures having long-term metallurgical stability at high temperatures even approaching that of decomposition of the eutectic. The preparation of final shapes by casting directly from the melt has the advantage of eliminating many complex processing steps.

However, heretofore, no eutectic alloy was known which provided an adequate combination of high temperature strength and oxidation resistance for practical application. Furthermore, in uses such as turbine blades, metallic bodies and articles produced from such alloys are exposed to hot corrosive conditions which include sulfurous gases as well as oxygen, and no known eutectic alloy has provided the requisite hotcorrosion resistance, strength, long life and stability under dynamic stress conditions.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a multicomponent eutectic alloy which will have high temperature strength, oxidation and hotcorrosion resistance, long life and metallurgical stability.

Another object of the invention is to provide an alloy comprising a composition of complex intermetallic compounds, each compound containing other elements in solid solution, which alloy will be castable into shaped, directionally solidified articles capable of exhibiting excellent properties and long life under dynamic stress and corrosive conditions at temperatures over 1,300F.

Other objects and advantages of the invention will become apparent from the following description and appended claims.

In accordance with the objects of this invention, an alloy system is provided containing the four elements: nickel, aluminum, columbium and chromium. The eutectics of the invention contain at least two metallic phases of the group: Ni Al, Ni Cb, N iAl, Cb(Ni,

novel eutectic compositions of the invention, when unidirectionally solidified from the melt, exhibit excellent high temperature strength as well as resistance to hotcorrosion and oxidation.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood from the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an electron micrograph (30,000X) of the structure of a directionally solidified alloy of the invention, identified herein as composition A;

FIG. 2 is a light micrograph (2000X) of the structure of another directionally solidified alloy of the invention, identified herein as composition B;

FIG. 3 is a plot of ultimate tensile strength in KSI versus temperature in degrees Fahrenheit, comparing ultimate tensile strength of one of the eutectic alloys of the invention with other known nickel-base super-alloys at elevated temperatures;

FIG. 4 is a plot comparing cyclic high-temperature oxidation behavior of one of the eutectic alloys (composition A) of the invention with a known superalloy; and

FIG. 5 is a plot comparing cyclic high temperature oxidation behavior of another of the alloys (composition B) of the invention with known superalloys in the as-cast condition.

As is apparent from FIGS. 1 and 2, the microstructures of the alloys of the present invention comprise at least a three-phase eutectic alloy of alternate, spaced lamellae or plates, with a third phase contained in one of the spaced lamellar phases. X-ray evidence (not shown) indicates that the lamellar phases are specifically oriented with respect to each other.

For the purposes of discussion, the following designations will refer to the various intermetallic compounds or phases of the compositions:

(B) NiAl (CSS) Chromium solid solution In FIG. 1, there is shown an electron micrograph (30,000X) of one of the eutectic compositions (composition A) according to the invention. Three phases may be seen in the micrograph, and appear to be (by electron micro-probe) chromium solid solution (CSS), epsilon phase (e), and delta phase (8). The composition of the alloy of FIG. 1 is set forth below in Table I.

In FIG. 2, there is shown a light micrograph (2000X) of another alloy (composition B) according to the invention. Three phases are visible in FIG. 2, which appear to be beta phase ([3), lambda phase (A) and chromium solid solution (CS8). The composition of the alloy of FIG. 2 is set forthbelow in Table I.

Table I lists preferred compositions of two of the novel eutectics, identified below as A and B" of the present inventionv TABLE I Composition A Composition B Element Weight Atomic Element Weight Atomic Nickel 58.6 58.6 Nickel 43.4 42.3 Chromium 13.9 15.7 Chromium 26.4 29.] Aluminum 5.4 11.7 Aluminum 6.6 14.1 Columbium 22.1 14.0 Columbium23.6 14.5 Total 100.0 100.0 Total 100.0

The weight percentages (w/o) of each of the respective elements listed in composition A and composition B may vary i 0.3 w/o.

The average chemical composition of observed eutectic morphologies were obtained using electron microprobe and chemical techniques.

EXAMPLE 1 In order to demonstrate the remarkable properties of the alloys of the present invention, samples of each of the compositions of Table I were cast from the melt and directionally solidified in a Bridgman crystallizing apparatus, as described, for example, in the book: Growth of Crystals by J. C. Brice, North Holland Publishing Co., (1965) p. 125. The entire mold assembly rested on a water-cooled copper plate so that unidirectional cooling was obtained.

Unidirectionally solidified bodies of composition A, cast from the melt and directionally solidified in accordance with the foregoing description, were tested for high temperature strength, oxidation resistance and hot corrosion, and compared with the properties exhibited by other known nickel-base superalloys. Table II and FIG. 3 show typical strength comparisons.

TABLE II ULTIMATE TENSILE (PSI) 77W Temp. Composition A" IN-100 Rene 80 75F 225 to 250,000 130,000 135,000 1500F 180,000 120,000 120,000 1600F 132,000 1 10,000 108,000 1700F 95,000 92,000 87,000

FIG. 3 shows a plot of ultimate tensile strength (KS1), at high temperatures, of directionally solidified samples of composition A, contrasted with two known nickel base superalloys, lN-lOO and Rene 80. The arrow at T on the temperature scale of FIG. 3 designates the eutectic temperature of composition A. The data in Table II and the curves of FIG. 3 indicate that the directionally solidified alloy of composition A of the present invention exhibits substantially improved tensile strength properties over known nickel base superalloys at room temperature and also at the technologically important temperature range of 1,500 to 1,700F. The compositions of the known superalloys referred to herein are given in Table V for convenience.

The alloys of the present invention exhibit especially good properties with respect to corrosion and oxidation at high temperatures.

INTERRUPTED OXIDATION TESTS EXAMPLE 2 Cyclic interrupted oxidation tests were conducted in static air at 1,900F for interrupted 25-hour exposures, simultanteously exposing specimens of composition A (directionally solidified) and Rene 80 (fully solution treated). The oxidation, plotted in weight gain per unit area (mg/cm) versus cumulative time of exposure (hours) is indicated in the graph of FIG. 4 and in Table III.

EXAMPLE 3 In an interrupted oxidation test similar to Example 2, specimens of composition B (directionally solidified) were exposed, in static air at 1,900F for 25-hour exposures, simultaneously with as-cast Rene 80 and Rene 100. The results are shown in the graph of FIG. 5 and in Table IV.

Composition A Fully soln. treated Rene 42 mg/cm 51 mg/cm TABLE IV Weight Gain per Unit Area in 500 Hp irs (l900F) I Composition B Rene 80 (as ca s tl Rene 100 752550 75 mg/cm mg/cm 101 mg/em TABLE V COMPOSITIONS OF KNOWN NICKEL-BASE SU- PERALLOYS IN- Rene Rene Udimet Udimet 80 100 500 700 Carbon 0.18 w/o 0.17 w/o 0.18 w/o 0.07 w/o 1O w/o Manganese 0.20 0.50 .20 Silicon 0.20 0.50 .30 Chromium 10.0 14.00 9.50 18.5 18.00 Cobalt 15.0 9.50 15.00 18.5 1800 Aluminum 5.5 3.00 5.50 3.0 2.9 Titanium 4.7 5.00 4.20 3.0 2.9 Molybdenum 3.0 4.00 3.00 4.0 4.0 Iron 0.20 1.00 2.0 Boron .014 0.015 0.015 006 0.01 Zirconium .06 0.03 0.06 Tungsten 4.0 Vanadium 1.0 1.00 Nickel Bal. Bal. Bal. Bal. Bal.

EXAMPLE 4 To test the hot-corrosion properties of a typical alloy of the invention, specimens were exposed at 1,800F in a small gas burner in an atmosphere containing 1 percent sulfur and 476 parts per million of sea salt, and the results were measured in average depth of corrosive attack after 100 hours exposure. Specimens of composition A of the invention are compared in Table VI below with similar tests conducted on superalloys U-50O and U-700. The corrosive attack appearance on the surface of the specimen of the invention after exposure was perfectly uniform, with no evidence of spike" attack, indicating no tendency to form selected regions of corrosive penetration.

TABLE VI HOT CORROSION TEST Test at l800F Small Gas Burner Tests Atmosphere: 1% S, 476 ppm Sea Salt Average Depth of Corrosion Attack After 100 hrs. Ex-

posure Composition A Range: 0.00097" to 0.00116" loys may also be solution heat treated and precipitation hardened, to further enhance their strength.

Although the disclosed alloys described herein con-' tain 3-phases, it will be understood that eutectics of other order (e.g. quaternary etc.) containing more than three intermetallic compounds or phases may also be used, with the disclosed and other additional elements. Accordingly, a fifth element modifier to the Ni-Al-Cb- Cr eutectic system may be added to improve certain properties. For example, one or more of the elements tantalum, titanium, tungsten and molybdenum may be added. Tantalum may be added to replace a portion of the columbium, and titanium may be added to replace a portion of the aluminum. I

While the present invention has been described with reference to particular embodiments and compositions thereof, it will be understood that numerous modifications and alterations can be made by those skilled in the art without actually departing from the scope of the invention or the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A method for preparing an article having properties of high tensile strength at elevated temperatures and good resistance, to oxidation and hot corrosion conditions, which comprises a. providing a casting alloy melt containing the elements nickel, aluminum, columbium and chromium,

b. unidirectionally solidifying from the melt a cast shape from said alloy, the rate of said directional solidification being such as to form a eutectic microstructure consisting of at least three phases seed f m e. .ar ups N s Llil NiAl, Cb(Ni AlI) Cr Cb and chromium solid solution, two of said three phases being specifically oriented with respect to each other and the third of said phases being contained at least partially within one of said two specifically oriented phases.

2. A method-according to claim 1, said eutectic microstructure containing as phases chromium solid solution and the two intermetallic compounds: Cr Cb and Ni Cb.

3. A method according to claim 2, said Ni Cb phase being contained predominantly within the Cr Cb phase.

4. A method according to claim 1, said eutectic microstructure containing as said three phases the two intermetallic compounds: NiAl and Cb(Ni ,Al and chromium solid solution.

5. A method according to claim 1 wherein said casting alloy melt is a eutectic type alloy.

6. A method according to claim 1 wherein said casting alloy melt is an invariant eutectic type alloy.

7. A method according to claim 1 wherein the eutectic of said alloy is composed approximately of from 58.3 to 58.9 w/o nickel, 13.6 to 14.2 w/o chromium, 5.1 to 5.7 w/o aluminum, and 21.8 to 22.4 w/o columbium.

8. A method according to claim 1 wherein the eutectic of said alloy is composed approximately of from 43.1 to 43.7 w/o nickel, 26.1 to 26.7 w/o chromium, 6.3 to 6.9 w/o aluminum and 23.3 to 23.9 w/o columbium.

9. A method according to claim 1 wherein said casting alloy. melt is unidirectionally solidified from the molten condition'at a rate of less than 5 inches per hour.

10. The product produced by the method of claim 1.

11. The product produced by the method of claim 2.'

12. The product produced by the method of claim 3.

13. The product of claim 7 wherein the chromium of said alloy is contained, at least in part, in the bimetallic compound Cr Cb.

14. The product of claim 7 wherein the chromium is present in the eutectic of the alloy in excess of about 7.0 weight per cent.

15. The product of claim 7 wherein the chromium is present in the eutectic in excess of about 8.0 atomic per cent.

16. A method according to claim 1, said casting alloy melt further including at least one modifier element selected from the group: tantalum,titanium, tungsten and molybdenum.

Claims

2. A method according to claim 1, said eutectic microstructure containing as phases chromium solid solution and the two intermetallic compounds: Cr2Cb and Ni3Cb.
3. A method according to claim 2, said Ni3Cb phase being contained predominantly within the Cr2Cb phase.
4. A method according to claim 1, said eutectic microstructure containing as said three phases the two intermetallic compounds: NiAl and Cb(Ni1 xAlx)2 and chromium solid solution.
5. A method according to claim 1 wherein said casting alloy melt is a eutectic type alloy.
6. A method according to claim 1 wherein said casting alloy melt is an invariant eutectic type alloy.
7. A method according to claim 1 wherein the eutectic of said alloy is composed approximately of from 58.3 to 58.9 w/o nickel, 13.6 to 14.2 w/o chromium, 5.1 to 5.7 w/o aluminum, and 21.8 to 22.4 w/o columbium.
8. A method according to claim 1 wherein the eutectic of said alloy is composed approximately of from 43.1 to 43.7 w/o nickel, 26.1 to 26.7 w/o chromium, 6.3 to 6.9 w/o aluminum and 23.3 to 23.9 w/o columbium.
9. A method according to claim 1 wherein said casting alloy melt is unidirectionally solidified from the molten condition at a rate of less than 5 inches per hour.
10. The product produced by the method of claim 1.
11. The product produced by the method of claim 2.
12. The product produced by the method of claim 3.
13. The product of claim 7 wherein the chromium of said alloy is contained, at least in part, in the bimetallic compound Cr2Cb.
14. The product of claim 7 wherein the chromium is present in the eutectic of the alloy in excess of about 7.0 weight per cent.
15. The product of claim 7 wherein the chromium is present in the eutectic in excess of about 8.0 atomic per cent.
16. A method according to claim 1, said casting alloy melt further including at least one modifier element selected from the group: tantalum, titanium, tungsten and molybdenum.