,Pape r f o r G a t l i n b u r g Conference September -11-14, 1995

---- -

CouF- "fSOqDB -03 INTERMETALLICS FOR STRUCTURAL APPLICATIONS

Vinod K. Sikka, Seetharama C. Deevi Metals and Ceramics Division Oak Ridge National Laboratory

P.O. Box 2008 Oak Ridge, Tennessee 37831-6083

Abstract

Intermetallics are introduced as possible structural materials. The attributes and useful temperature limits of eight of the most likely candidates have been described. In addition, detailed descriptions are given for chemical compositions, corrosion properties, mechanical properties, melting and processing. and applications of Ni3Al- and Fe3Al-based alloys. Mechanical properties of NigAl-based alloys are comparcd with commercially used HU alloys in the cast condition and Haynes 214 in the wrought condition. The mechanical properties of Fe3Al-based alloys are compared with an oxide-dispersion-suengthened (ODS) Inco alloy MA-956. Comparisons have shown that Ni3Al-based alloys offer thc hcst combination of oxidation and carburization resisiance and are significantly stronger than the commc~ially uscd IfU alloy for many of the furnace-fixture applicauons I lowever. the Fe3Al-based alloys, which offer dic hcsl sulfidauon resistance of the commercially available alloys. are significandy weaker in creep than the ODS MA-956 alloy. Even with the Current strength level, Fe3AI- bawd alloys arc supxior as prous, sintered metal filters for hot-gas cleanup in coal gasification systems. Oxide- dispersion strengthening of the Fe3Al-based alloys is cumntly u n d a way to improve their creep strength.

Intermetallics are materials that are formed by the reaction of two elements in proper ratio into compounds. The compounds have ordered structures which exhibit attractive elevated-temperature properties due to their reduced dislocation mobility and slower dislocation processes. The phase diagrams show the existence of thousands of compounds. However, the practical compounds with the most chance of successful use are limited to only eight compounds. These compounds, their melting points, crystal structures, and fracture modes are shown in Table I. The basic properties of the constituent elements of the compounds are also included. The research activity in intermetallics accelerated in the early 1980s, and since then, several symposiums have been held and proceedings published (1-1 I ) on this subject. Based on literature data (1-11) and extensive experience at the Oak Ridge National Laboratory, Table I1 was prepared to show the significant attributes and maximum use temperatures for the important intermetallics listed in Table I. The remainer of the paper will describe detailed properties of Ni3Al- and FqAl-based intermetallic alloys and compare them with relevant commercial alloys.

Compositions of Ni3AI- and Fefil-Based Alloys

THE 1980s WIVE SEEN EX-IRAORDINARY progress in technology in the areas of electronics, computers, and automation. Because of these advances, chemical and manufactunng processes have become more monitored and controlled. However, there has only been a limited shift in the usc of Improved and advanced materials for many of the chemical and manufacturing processes. There are several reasons for the hck in shift to the improved or advanced mruenals., but the lading cause for not shifting is resrsrance ro change. The purpose of this paper is to describe the advances in the dcvclopmcnt of intermetallics with special emphacu on nickel and imn aluminides.

Since gaining the howledge that boron can ductilize polycrystalline Ni3A1, three Ni3Al-based alloy compositions have been developed for structural applications (see Table 111). The Ni3Al-based alloys compete with the wrought nickel-based alloy, Haynes 214, or a cast-iron-based HU alloy. The compositions of both of these alloys are also included in Table 111 for comparison. The oxidation and carburization resistance of Ni3Al-based alloys is also included in Table 111. The specific contribution of each alloying element for the NigAI-based alloys listed in Table XI1 is described in detail elsewhere (12).

Since the knowledge (13) of environmental effects that occur in the Fe3AI system from the reaction of aluminum in the compound with moisture in air became evident, three +

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FqAl-based compositions with minimum environmental effects have been identified (see Table IV). These alloys

and type 310 stainless steel; therefon% their compositions are also included for comparison in Table IV.

Comlon Resistance oFNiNI and Fe*I

compete with c ~ ~ e r c i a l alloys Such as Fenalloy, MA-956,

The oxidation and carburization resistance data for Ni3Al-based alloys are compared in Figures 1 and 2. The comparative data for these figures were developed by Intemational Nickel Company. It is dear from Figure 1 that the Ni3Al-based materials that form A1203 as protective oxide on the surface have significantly better oxidation resistance than nonaluminum-containing Alloy 800. The formation of protective Ai203 scale on the surface of Ni3Al- based alloys also makes them highly resistant to carburizing environments (see Figure 2).

Similarly, the binary Fe3AI alloy with 15.9 wt 96 (28 at. %) A1 that forms protective A1203 provides superior sulfidation resistance superior to aluminum-free type 310 stainless steel and FecraJloy with 4.7 wt 96 Al. In fact, the binary Fe3AI. or the FAS alloy with 2.2 wt % (2 at. %) Cr, shows the best sulfidation resistance of the commercially available alloys (14).

Mechanical Properties of Ni-jAl- and Fe pi )-Based Alloys

The oxidation and carburization resistance of Ni3AI- based alloys can be put to an advantage if their strength propcrtics are equal to or superior to the currently used alloys for the same applications. The cast HU alloy (15) is the most commonly uscd material for most furnace applications requinng carburization and oxidation resistance. Figure 4 compares the tensile properties of the cast Ni3Al-based IC-396M and IC-221M alloys with that of the cas! HLJ alloy. I t Is clcar from this figure that the Ni3Al-based alloys are ncariy twice as strong at room temperature and six times as strong at IOOO’C. However, at furnace operating tempcratures, the creep is the primary deformation mechanism. Such data for the two alloys are compared in Figure Sa. which shows that as with tensile. the creep propcnies of Ni3Al-based alloys are also suprior by a factor of 3. The Ilayncs 214 alloy is the wrought alloy having the highest aluminum contcnt in a commercial nickel-bed alloy that compctcs with the Ni3Al-based alloys. The crecp and tentile propcrtics of the wrought N i 3 A l - b ~ d compositions are comparcd with Hayncs 214 in Figures 5b and 6. Figure 6 shows that the cast and p m s s e d NilAl-based alloys are similar in tensile properties to Haynes 214. However, Ihe pwdcr metallurgy IC-221W alloy is significantly stronger. The crcep propcrties of the Ni3Al-hrrscd alloys and llayncs 214 are also comparable. Although the mechanical proptics of wrought Ni3Al-based alloys arc compmhlc to ffaynes 214, the higher aluminum conicnt of Ni3Al-batcd alloys is expclcd to make them significantly superior in their oxidation and cahurization resiwrc.

Tensile and creep properties of wrought Fe3Al-based alloys are cornpad with ODs MA-956 alloy in Figures 7 and 8. The tensile properties of Fe3Al-based alloys are similar to those of the ODs MA-956 alloy. However, the Y203 dispersion m MA-956 significantly enbances its ctee~ properties (16). Tbe oxide dispersion strengthening of Fe3Al-based alloys is currently under way at ORNL to enhance their creep strength so that the advantage of tbe excellent sulfidation resistance can be achieved in the monolithic form.

Melting, Casting, and Processing of NiML and Fefll-Based Alloys

The high-aluminum contents of Ni3Al- and Fc3Al-based alloys had previously kept the commercial manufacturers away from their production (see Tables111 and IV). However, only recently, a process has been developed for their successful melting using conventional equipment. The process is known as Exo-MeltTM (17). and it effectively uses the heats of formation of the compounds from their constituent elements to advantage. The key feature of the

-Exo-MeltTL” process is in the proper loading of the alloying elements into the furnace crucible. A typical loading sequence for the melting of Ni3Al-based IC-221M alloy is shown in Figure 9. The EXo-MelP process off- several advantages over a conventional process where aluminum would be added to the molten nickel or iron (see Table V). The availability of molten metal through the Exo-MeltrY process can be used to produce Ni3A.l- and Fe3Al-based alloys by conventional methods through steps shown in Figure 10. Various components of Ni3Al- and FqAl-based alloys produced through the use of the Exo-MeltN process are shown in Figure 11. Some of these components are currently in test in commercial equipment at different user companies.

Applications

The applications of Ni3Al-based alloys take advantage of their oxidation and carburization resistanm and high- temperature strength. Based on the data presented in this papcr and initial reports of indusuial tests. NigAl-based alloys can provide significant improvements for applications where the HU alloy is currently being used. ?bus, the use of NigAl-based alloys is presently being pursued for numerous furnace fixture applications.

The applications of Fe3Al-based alloys need to take advantage of their oxidation and sulfidation resistance. The currcnt applications of FegAI-based alloys are in porous, gas- m e a filters for coal gasification and as coatings and weld overlays for oxidation- and sulfidation-bearing environments.

Summary and Conclusions

Intermetallic compounds as suuctural materials are inutwluccd with emphasis on Ni3AI- and Fe3Al-based alloys. The compositions, corrosion properties. mechanical

i properties, processing procedures, and applications are descr i i The following conclusions are possible from this presentation:

1. Ni3Al-based alloys 8 f e highly resistant in oxidizing and carburizing environments.

2. Ni3Al-bad alloys have sjgnifkantly higher tenSile and creep properties than the commonly used commercial cast Hu alloy.

3. The powder metallurgy can produce a wrought Ni3Al- based alloy with much higher strength than a Commercial, high-saengtb alloy such as Haws 214.

4. The FegAl-based alloys have significantly better sulfidation resistance than commercial alloys.

5. The Fe3Al-based alloys are comparable in tensile strength but significantly weaker in creep than the ODs

6. The development of the Exo-MeltrY process for melting aluminides has made many Cast applications of Ni3N- based alloys possible.

7. The water-atomized powder of the Fe3Al-based alloys has made their porous filter application possible.

MA-956 alloy.

Acknowledgments

Dr. S. C. Deevi is on sabbatical at ORNL under the Philip Moms Fellowship Program. The authors thank C. R. Howell for data plotting, C. A. Blue and R. W. Swindeman for paper review. K. Spnce for editing. and M. L. Atchley for prepring the manuscript.

Rewarch was sponsored by Ihe U.S. Deparunent of Energy. Assistant Secretary for Energy Efficiency and Rcncwahlc Energy, Office of Industrial Technologies, Advmccd Industrial Materials Program. and the Office of Fossil Energy. Advanced Research and Technology Dcvclopmcnt Materials Program DOE/FE AA 10 10 0, Work Breakdown Suucture Element ORNL-Z(H)] under contract DE-ACOS-MORZ1400 with Martin Marieua Energy Systems. lnc.

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References

Koch. C. C.. C. T. Liu. and N. S. Stoloff, eds., "High Temperature Ordered Intermetallic Alloys." in Rocccdmgs of Matcrials Research Society Symposium (Mater. Res. Soc. Symp. Proc., 39, Pittsburgh. PA, 1985) StololT, N. S.. C. C. Koch. C. T. Liu. and 0. Izumi e& 'lligb Tempmure Ordered Intermetallic Alloys 11.' in &dings of Materials Research Society Symposium (Maur. Res. Soc. Symp. Proc., 81, Pittsburgh. PA. 1987) Liu. C. T.. A. I. Taub. N. S. Stoloff, and C. C. Koch. cds.. 'liigh Tcmpcrature Ordered Intermetallic Alloys 111.' in Rocccdings of Materials Research Society Symposium (Mater. Res. Soc. Symp. Proc.. 133. Rusburgh. PA 1989) Johnson, L. A.. D. P. Pop. and J. 0. Sdegtcr. eds., 'iiigb Temprature Ordered Intemeullic Alloys tV.' in Proceedings of Materials Research Society

5

8

9

10

11

12

13

14

15

16

17

Symposium (Mater. Res. Sac. Roc., 213, Pittsburgh, PA, 1991) Baker, I, R h l i a . J. D. Whittenberger, and M. H. Yoo, cd., "High Temperature Ordered Intermetallic Alloys V," in Proceedings of Mattrials Research Society Symposium (Mater. Res. Soc. Symp. Roc., 288, Pittsburgh, PA 1993) Wbang, S. H, C. T. Liu, D. P. POP. and J. 0. Stiegler, eds, "High Temperaaae Alumhides and Intermetallics," in Proceedings of TMS/ASM Symposium, TMS-AIME Wanendale. PA, 1990 Wbang,S.H., C.T.Liu, D . P . F b p . and J. 0. Stiegler, eds., "High-Tempemare Aluminidc Intermetallics," Mater. Sci. Eng., A152A153 (1992) humi 0.. ed.. "IntermetaIIic Compounds - Structm

Japan Institute of Metals Tokyo, 1991 Liu, C. T., R. W. Cahn, and G. Sautboff, eds., ordered Intermetallics - Physical Metallurgy and Mechanical Behavior, NATO AS1 Series E, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1992 Kim, Y. W. and R. R. Boyer, eds.. "Microstructurekoperties Relationships in Titanium Aluminides and Alloys," TMS-AIME W m d a l e , PA, 1991 Darolia, R., J. J. Lewandowski. C. T. Liu, P. L. Martin, D. B. Miracle, and M. V. Nathal. eds., "Structural Intermetallics," The Minerals. Metals & Materials Society, Warrendale. PA, 1993 Sikka, V. K., Intermetallics for Structural Applications, chapter to be published in Corrosion and Oxidation of Intermetallic Alloys, eds. P. D. De& and C. Y. Ho, CINDAShrdue University, West Lafayeut, IN, 1995 Liu, C. T., E. H. Lee. and C. G. McKamey, Sa. Metall. 23,875 (1 989) DeVan. J. H. p. 107 in "Oxidation of High-Temperature Intermetallics," ed. T. Grobstein and J. Doycbale, TMS. Warrendale, PA, 1989 "Cast Heat-Resistant Alloys," Report No. 11%. Ibe International Nickel Company, lnc, New York, NY, 1974 Tassen, C. S.. J. J. Fischer. G, D. Smith, and M. J. Shaw, Conf. on Heat Resisrant Materials. p. 105, ASM International, Materials Park, OH, 1991 Sikka. V. K., S. C. Deevi, and J. D. Vought, "Exo- MeltN, A Commercially Viable Rocess for Melting Aluminides" LO be published in June issue of Advanced Materials & Processes, ASM International, Materials park. OH, 1995

and Mechanical Properties," in Fbxeedm - gs of ms-&

.

Table L Basic properties of elements and selected intermetallics being developed for structural applications

Elementlcompound Crystal structure Density cs/an2) Melting point CC) Fiaclun 4 ~~

Ni Ti AI Fe Mo Si Ni3 Al Ni3Si R3Al TiAl Ti3AI FeAl NiAl MoSi2

fcc hcp fcc bCC bcc fcc Ll2, fcc Ll2, fcc DO31bCC Ll& tern Doig , hexag. BZ bcc BZ bcc C116. tetra.

8.89 4.50 271 7.86

10.20 233 750 7.30 6.72 3.91 4.20 5.56 5.86 6.24’

1454 1704 660

1535 2610 1414 1400 1140 1540 1460 1600 1300 1640 2020

Ductile Ductile Ductile Ductile DuCtilC Brittle IGb I@ TGC TGC TGC IGb + TGC IGb + TGC IGb + Tff

*At room temperature. htergranular cleavage. liansgranular cleavage.

Table 11. Attributes and upper use temperature limit for selected intermetallic compounds

Intcnnctallic compound

Auribures Maximum use temperature CC)

Strength limit Corrosion limit

Oxidation, carburization. and nividation resistance; high- tempcrature suengtb Oxidation and reducing environment resistance; good resistance in sea wavr and sulphuric acid; good resistance in ammonia reactor up to 900% Oxidation and sulfidation resistance

Low density is the real advantage. Good specific-strenglh pmpenies and wear resistance Low density; good specific strength

Oxidation, sulfidation. molten salt. and carburization mislance High melting p i n c bigb rhennal conductivity; oxidation, carburization. and nitridation resismoc 11igb melting poinc exccllenl resistance D oxidation; exhibits metallic conductivity

lo00

800

600

lo00

760

800 1200

1 loo

1150

lo00

1 loo 900

450 1200 1400

1600

’ . ’ I’

-. Table III. Compositions of Ni3Al-based alloys and commercially available competing alloys

~~

Weight perctnt Element

IC-5W IC-218- IC-396Mc IC-221Md Haynes 214e Huf Alloy 8ooL

0.4 21.0 -

Al cr Mo zr B C Fe TI Ni Si Y

8.7 8.1

0.2 0.02

- - - -

83.1

7.98 7.72 3.02 0.85 0.005 - - -

80.42 -

8.0 7.7 1.43 1.7 0.008 - - -

81.1

45 16.0

11.3 - - 0.6 0.02 - - I

88.08 I

- 18.0 -

I

0.03 3.0

7635 0.1 0.02

- - 0.55

42.45

39.0 -

- 0.05

455 0.4

325

"Cold workable.

CCastable alloy for static applications (some mimporosity). dCasrable alloy for dynamic applications (minimum mimporosity). Wrought alloy.

bHot and cold workable.

cast alloy.

Table W. Chemical compositions of selected Fe3Al-based aluminides and commercial alloys

Alloys (weight percent) Elcmcnt

FA-129 Fecralloy M A-956 Type 310 FAS FAL

AI cr B zr Nb C Si Y y203 Ti Ni Fe

1s.9 220 0.0 1 - -

15.9 5.5 0.01 0.15 -

15.9 5.5

4.7 16.0 - - - 0.02

0.3 - -

4 5 20.0 -

- 25.0 - - - 0.15 0.50 - - -

20.0 a

- 1 .o 0.05 - - -

05 05

a - -

a

Table V. Key advantages of the Exo-Meltm process versus a conventional process

ExeMeltry process conventional process

Time to melt

Power

Safety

Cost

A very practical method. my to load the furnace with all elements. Tbe exotherm generates the maximum heat, which is sharedwiththesolid, and, thus, the heat is used for increasing the soIid temperature. No temperature overshoot occurs, and melting takes place in a much sborter time.

One-half of conventional unit time

One-half to two-thii of conventional power requirement (2.92 kwb)

Avoids any potential safety issues

Effective use of exotherm and chemistry control results in saving nearly one-half the cost of the conventional method.

One-half the cost of the conventional method

Composition conuol Effective use of the exolherm prevents overheating. and, thus, chemistry is reproducible every time.

Excellent

No excessive heating. Much less oxidation than conventional method.

Oxide inclusion formation

Bath temperature control Real control

Crucible life Uniform wcar

Nom1 wear

Vacuum melting

commercial

Possible with qroducible resulls

Many commarid vendors can easily use the process.

Bath tempemure is overshot from the ex* thermic reaction when aluminum is added to molten nickel alloy. Temperam i n d o v e r s b o o t oxidizes alloying elements, affects crucible life. and deIays the overall process because the melt has to set and cool.

Unit time

Unit power (55 kwb)

Temperature overshooting causes erosion of ceramic crucible and can cause unexpected attack on induction coils by seeping through eroded area

Melting cost is high because the exotheam is not used effectively. The oxidation of alloying elements can q u i r e either adding more of them or a large rejeuion rare resulting from poor repeatability.

Unit cost

Addition of aluminum to molten nickel causes the bath temperature to increase by 500 to 7WC. Such a lemperature rise oxidizes the important elements such as boron, zirconium, chromium. and aluminum. Bath chemistry is missed, and oxide inclusions are mixed in with the alloy. Poor

overheating of bath causes excessive inclusion formation.

No control

The temperature overshoot by 500 to 700% above the melting point of nickel causes excessive erosion of the crucible. Excessive wear

Difficult to add aluminum

Because of p o r results, commercial mellers are not interested.

,

50 1-c

N

\ 6 0 m E 0' -50 0) t

V 1 -100

r 3 -150 I

-200

F " " f " " l " " l " " ~ ' " ' ~ " " ~ t - - 7 -

IC-221

0 100 200 300 Exposure Time (Days)

Fig. 1 - Comparison of oxidation resistance ofNi3Al-baSed alloys with Alloy 800 in air with 5% water vapor at 11oo'C. [Data were developed at The International Nickel Company, New York, NY (151.1

50

- 30 0 CI) E

u ; 20

: 10 n

I

0 0 10 20 30 40

Exposure Time (Days) a

20

c 5 9

0 0 10 20 30 40

Exposure Time (Days) b

Fig. 2 - Cornpison of carburization resistance of Ni3Al-based alloys wilh Alloy 800: a) oxidizing carburizing environment and b) reducing carburizing environmcnL mu were developed at Ibe International Nickel Company, New YO& NY (19.1

' ' .' . .' .-

.

20 .................................................................. ............_

10 ++ 1

1000 - (0 n. 3 ?SO

Fig. 3 - Comparison of sulfidation response of Fe3Al-based alloy with type 310 stainless steel and Fecralloy [J. H. Devan, 1989 (14)).

0 200 400 600 800 1000 1200 0

Temperature ('C)

a

750 - - m

---C Hayner-214 IC-so

+ IC-2 1 8LZr

. . . . . . . o 250 U

3 0 200 400 600 800 1000 1200 Temperature ('C)

-9- IC-396 ................................

30

0 1 I Temperature ('C)

0 200 400 600 800 1000 1200

C

b

Fig. 4 - Cornpison of (ensile propetties of cast NiJAl-bzscd alloys with cast f fU alloy: a) 0.2% yield suengrh. b) ultima& ensile strength, and c) total elongation

. 1000

1

n (0 _...... ..................... n I Y

100 u) u) 0) L-

3; ....................... ........................ i

, . , , ,Y!, . . , -....... _.-._..._ .............................. i

10 ~ ' " ' ' " ' " ' ' "

30 35 40 45 50 55 60 P=(T+460)*(20+logt )*1 0-3

c c

i

a 1000

n 100

I Y

c

c ........ .... VI VI

s" l o g v) r

....................................... . . . . . . - ...................................... \, ................................... &................:..I.......... .. + IC-2 18

........... ..... .................... _." ...... -m- Haynes 214

c - L ......................................................................... - c .......................................................................

.............................................. : ...................... -f

1 I I . I

35 40 45 50 55 P=( T+4 60)+( 2 O+ log t,) 7 0-3

b

Fig. 5 - Cornpison of crceprupture strength of Ni3Al-based alloys with comrncrchlly used materials: a) cast alloys with IIU and b) wrought alloys with IIaynes 214.

1560

1250

CI a

Y = 1000

!! 750 x = s o 0 W

r 250

0 S

- * o! 0 0

0 200 400 600 800 lo00 1200 Temperature ('C)

a

1500 I

1250

1000

750

500

250

0 0 200 400 600 800 1000 1200

Temperature ('C) b

150

100

. . . .

. -. .................... 50

0 0 200 400 600 800 1000 1200

Temperature ('C) C

Fig. 6 - Comparison of ensile propenies of wrought Ni3Al- based alloys with Haynes 214: a) 02% yield strength, b) ultimate tensile strength. and c) total elongation.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or respnsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, r a m - manufacturer, or otherwise does not necessarily constitute or imply its endorsement, mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

0 200 400 600 800 1000 1200 Temperature ('C)

a 200

n x 150 v

O

0 Y) C 0 t

-

- 5

1200

1000

800

600

400

200

0 0 200 400 600 800 1000 1200

Temperature ('C) b

0 200 400 600 800 1000 1200 Temperature ('C)

C

Fig. 7 - Comparison of tensile properties of wrought Fe3Al-based alloys wilh MA-956 alloy: a) 0.2% yield sUength, b) ultimate tensile suength. and c) total elongation.

1000

too

10

.....~....._.._ ^.._._.....I... - ............

25 30 35 40 45 50 55 60 P=(T+460)*(20+logt )*1 0-3

r Fig. 8 - Cornpison of crapruptun strength of wrought Fe3Al-based alloys with MA-956 alloy.

Thermocouple Leads

I Zirconia Crucible -

Thermocou 1.5 in.

-spacing 1, 2, & 3 in. deer,

-4 A

EXo-MeIP Product I I 1

I I I

I I I I

Casting

Ingots J I Sand Investment Centrifugal

working t- Sheet, plate,

Consolidation

Hot extrusion PresdSinterlHIP ,&, +EiWi,&i I Fig. 10 - Schematic showing the use of Exo-MelP liquid as the starting point for processing Ni3AI- and Fe3Al-based alloys.

Fig. 11 - Cast compncnts of Ni3N- and Fe3Al-based alloys.