CA1276814C - High-temperature fabricable nickel-iron aluminides - Google Patents

Abstract

HIGH-TEMPERATURE FABRICABLE NICKEL-IRON ALUMINIDES
Abstract of the Disclosure Nickel-iron aluminides are described that are based on Ni3Al, and have significant iron content, to which additions of hafnium, boron, carbon and cerium are made resulting in Ni3Al base alloys that can be fabricated at higher temperatures than similar alloys previously developed. Further addition of molybdenum improves oxidation and cracking resistance. These alloys possess the advantages of ductility, hot fabricability, strength, and oxidation resistance.

Description

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HIGH-TEMPERATURE FABRICABLE NICKEL~IRON ALUMINIDES

This lnventlon relates to high streng~h n~ckel-lron alum1nide alloys that exh~bit des~rable hot duct~t~ty and fabricabil~ty.
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. Ordered 1n~ermetallic alloys based on trl-n~ckel alum~nide (Ni3Al3 have unique propert~es that make them ?ttract~ve for structural appll-cat~ons at elevated temperatures~ They exhib~t the unusual meohan kal behav~or of increas1ng y~eld stress w1th increasing temperature whereas ~n conventional alloys y~eld stress decre~ses wlth temperature. Trl-nkke~ alu~in~de 1s the ~ost lmportant strengthen1ng constltuent of 10 comoercldl n~ckel-base superall~s and ~s respons~ble for thetr hlgh-temperature strength and creep reslstance. The major llm~tation of the use of such nlckel alumlnldes as eng~neerlng materlals has been the~r tendency to exh1b~t brlttle fracture and low duct~l~ty.

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Recently alloys of this type have been improved by the additions of iron ~o increase yield s-trength, boron to increase ductility, and titanium, manganese and niobium for improving cold fabricability (Commonly assigned U. S. Patent No. 4,711,761, Ductile Aluminide Alloys for High Temperature _ plicat1 s, Liu and Koch). Another improvement hàs been made to the base Ni3Al alloy by adding iron and boron for the aforernentioned purposes and, in addition, hafnium and ~irconium for increased strength at higher temperatures (Commonly assigned U. S. Patent ~o. ~,612,165, Ductile Aluminide Alloys for High Temperature Applications, Liu and Steigler).

Although these improved alloys have many beneficial characteristics, they still exhibit some shortcomings which detract from their usefulness. For example, the previous nickel aluminide alloys suffer a decrease in ductility and workability with increasing temperature. Any fabrication of the alloys into structures of desired conf~gurations by rolling or forging must be achieved at temperatures less than 700C. Such alloys would be of greater value if the hot fabricability could be achieved at a higher temperature of up to about 1,200C since industry fabrication experience and capability exist at this temperature.
Other benefits derived from fabrication at higher temperatures include reduction in the fabrication cost and the elimination of the need for high-power fabrication equipment.

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Sunmary of the Invention Therefore, to address the above-mentioned problem it is an object of -this invention to provide a nickel-iron aluminide alloy that is fabricable by hot rolling or forging at -temperatures of about l,200C.
Another object is to provide a high-temperature fabricable nickel-iron aluminide alloy that possesses high yield strength, good ductility and resistance to oxidation at elevated temperatures.
A further object of this invention is to provide a nickel-iron aluminide alloy having the above-mentioned characteristics that can be manufactured at relatively low cost using existing manufacturing techniques.
Additional objects, advantages and novel features of the invention will be set forth in part in the description ~hich follGws, and in part will become apparent to those skilled in the art upon examination of the following or may ; be learned by practice of the present invention. The objects and advantages of the invention may be realized and attained by means of the instr~mentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance wi-th the purpose of the present invention, as embodied and broadly described herein, a nickel-iron aluminide consists essentially of a Ni3Al base, a sufficient concentration of a Group rVb element or mixtures thereof to increase high ; temperature strength, a sufficient concentration of material selected frcm the group consisting of iron and a rare earth element or mixtures thereof to increase hot fabxicability, a sufficient concentration of boron to increase ductility, molybdenum in the amount of 0.0 to 4.0 weight percent and carbon in the amount of 0.00 to 0.06 weight percent.

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Also, addit~ons of molybdenum and carbon are utlllized to respect~vely improve reslstance to oxidat10n and cracking. '[ron ~s present in an amount from 14 to 17.5 weight percent, a suf:Eicient concentration of boron i5 present to enhance ductility, the comblined concentration of 5 the Group IVb elements are present in an amount less than 1 weight percent, and the rare earth elements are added in trace quantities of sufficient concentrations to 1ncrease hot fabricability to temperatures greater than about 700C~ Molybdenum is added to the alloy composltiQn in an amount adequate to reduce oxidation. Carbon is utili~ed in sufficient quantities to repress hot cracking resulting from the addi-tion of molybdenum. The remainder or balance of the alloy is formed of the base Ni 3Al composition.
More specifically~ ln the preferred embodiment the amount of boron sufficient to enhance ductility is from .01 and .03 weight percent.
The preferred Group IVb elemen~ is hafnium although zirconium~ based on limited results, functions similarly. The preferred rare earth elemen~
is cerium and the amount sufficient to increase hot fabricability to a temperature of about 1,2Q0C is in the range o~ about .002 to .007 weight percent with the preferred amount being about .005 weight percent. It is believed that yttrium, thorium~ and lanthanum would function similarly to cerlum.
Also the amount of molybdenum needed to improve oxidat~on resistance 1s up to about 4 weight percent with up to about 0.1 weight percent carbon to suppress cracking dur1ng hot ~abricatlon.

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~ he nickel-~ron a1uminides o~ th~s invention have ~he advantage of possess~ng the comb1ned properties of ducti1ity, hot ~abricability~
h~gh tensile strenyth up ~o about 600C, and oxldat~on resistanceO In addition~ these alumin~des are of low denslty and low cost compared with commercially available nickel-based superalloys.
~ red Embod~ment The alloy ingots of this ~nvention are prepared by arc melting of correct proportions of pure metal chips and Ni-4 we~ght percent B and Ni-4 weight percent ~e master alloys. The master alloys were used for precise control of Be and Ce concentrations in the alloys. The alloy ingots were fabricated by hot rolling at 1,200C with three passes at a 12% reduction per pass. The ductility and the hot f~bricab~lity of these nickel-iron aluminides are sensltive to the iron concentra~ion, the iron to nickel ratio. and addi~ions o~ rare earth elements such as cerium to the alloy compositionr Table I presents a series oF nickel-iron aluminides based on an alloy designated IC-47 having the composition 10.4 weight percent aluminum, 16.1 weight percent ~ron, 0.05 weight pPrcent boron and the balance nickel, This alloy is modified with Hf (or Ir~ and other ~0 alloys additlons as indicated ln the Table I with these modified alloys possessing different ~IC" numbers.

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Tabl e I

Composition,(a) weight percent Hot fabricability(b) IC-47 Ni-10.4 Al-16.1 Fe-0.05 B Numerous surface cracks IC-105 Ni-10.0 Al-15.9 fe-1.7 Hf~OrO2 B Numerous surface and edge cracks IC-124 Ni-1002 Al-16,0 Fe-0.9 Hf-0.02 B Some surface cracks, no edge cracks IC-126 Ni-10.2 Al-16.0 Fe-0.9 Hf-0~02 B-0.005 Ce Two surface cracks, no edge cracks IC-159 Ni-10.2 Al-16.6 Fe-0.9 Hf-0.015 B-0~005 Ce No cracks IC 165 Nio10.2 Al-16.6 Fe~0.4 Zr-0.015 B-00005 No cracks(C) Ce-0.03 C
IC-166 Ni~10.2 Al-16.3 Fe-0.9 Ze-0.015 B-0.~05 Some surface cracks Ce-0.03 C

20(a)All alloys contain 0.25 to 0.5 at.X Hf or Zr.
(b)Hot-rolled at 1,200S with 3 passes, 12X reduction per pass.
(C)No cracks durlng hot rolling at 1~100C but minor surface cracks during hot rolling at 1,200C
Hafnium or zirconium is added to improve the high-temperature strength of the alloy. However7 the addition of hafnium and zirconium to the alloy composition must be limited to less than 1 weight percent (or 0.5 at.%~ since with greater concentrations of hafnium and : zirconium the hot fabricability of the alloy is impaired.
Surprlsingly9 a small amount of ~erium (0.002 to 0.007 weigh~ percent) substantiallly improves ho~ fabricability of nick~ ^iron aluminides.
The atloy designated IC-159 containing .005 welgh~ percen~ cerium and 16.6 we1ght percent iron had the best hot fabr~cability with no ev~dence o~ cracks during hot rolt~ng at 1,200C.

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Another serles of nickel-1ron aluminides based on the IC-47 alloy was prepared and further mod~f~ed with th~ additions o~ hafn1um, cer1um, molybdenum and carbon as shown 1n Table XI. Again, the modified alloys are provided with d1fferent "IC" numbers.
Tabl e I I

Composit1On, wetght percent Hot fabricabil ity*

IC-47 Ni-10.4 Al-16.1 Fe-O.OS B Numerous surface cracks IC 109 N1-9.8 At-1308 Fe-1.7 Hf-3.7 Numerous surface and edge Mo-0.025 B cracks IC-117 Ni-10.0 Al-13.3 Fe-O.9 Hf-3.7 Numerous surface cracks, Mo-0.025 B no edge cracks IC-123 Ni-10.0 hl-15.8 Fe 0.9 Hf-3.7 Some surface cracks, no Mo 0.02 B edge cracks IC-152 Ni-10.0 Al-15.8 Fe-O.9 Hf-3~7 No cracks Mo-O.OlS B-0.005 Ce-0.06 C
IC-157 Ni-lOoO Al-15.8 Fe-O~,9 ~f-3,7 Three surface cracks~ no Mo-0.015 B-O.OOS Ce edge cracks IC-158 Ni-10.1 Al-16.4 Fe-0.9 Hf-2.7 One mlnor surface cracks, Mo-0.015 B-0.005 Ce no edge cracks *Hot-rolled at 1,200C with 3 passes, 12~ reduction per pass.
Motybdenum was added to the alloy composition to improve oxidation resistance. With a molybdenum concentration at 3.7 weight percent the hot fabricability of the nickel-iron aluminides was strongly dependent on a small change in alloy composit10n~ With iron conentration less than abou~ 14.5 weight percent, considerable cracking occurred during hot fabricab~ y. A combinat~on of .OOS weight percent cerium and 30 .06 weight percent carbon together with 1ron at 15.8 weight percent ~2~6~

completely suppressed the oraek formation resulting 1n a preferred alloy having the composition as designated by IC 152. The iron content in the alloys is lim~ted to less than 17.5%; otherwise the alloys may lose some of their high-temperature strength, These are examples of two nickel-iron aluminide alloys that can be readily fabricated by hot rolling or forging at 1,200C. By comparison commercially available nickel alu~inides canno~ be hot ~a~ricated by hot rolling or forging at temperatures above 700C.
Upon metallographic examination of the two prepared alloys, a significant amount ~20-30~ by volume) of a second phase, probably B2 (ordered bcc phase similar to FeAl), was detected after water quenching from 1,200C. The volume fraction of the B2 phase decreases with the decrease in annealing temperature, showing less than about 2~ B2 phase after annealing for sixteen hours at 800C~ Comparison of the microstruc~ure of the alloys further indicates that alloying with molybdenum additions reduces the formation of ~he disordered phase in nickel-i ron al uminides.
The tensile properties of the nickel-iron ~luminides set forth in Tables I and II were determined at temperatures to 1,200C on sheet specimens with a gage section of 12.7 mm x 0.8 mm at a crosshead speed of 25 mm/min. in vacuum. The tensile properties of alloys designated IC-152 and IC-159 were compared with tensile properties done on a nickel alum1nide having the composit~on of 11.9 weight percent aluminum, 1.7 weight percent hafnium1 .015 weight percent boron and the balanc~ n~ckel and designated IC-136. These comparisons at various temperatures are shown in Table III.

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Table III

Alloy Number Yield S~ress Tenslle Streng~h Elongation (ksi ) (ksi ) [X) Roo~ Tempera~ure IC~136 52.0 1g5.3 38.1 IC-159 77.4 195.0 40.3 IC-15~ 97.5 222~0 29.0 1~ ~009C
IC-136 9206 1S~8 50.6 IC-159 94.9 14000 47.9 IC-152 112~0 150~0 26~8 850~
IC-136 86.2 111.9 t8.6 IC-159 68~0 72~2 29~8 IC-152 78~1 84~2 26~4 1 ~, O00C
IC-136 46.2 52~2 16.Z
IC~159 26~6 28.6 40.6 IC-152 27.1 33.9 48.1 1 9 ~00C
IC-13S 21.2 22O3 25~0 IC-159 2.5 2.8 152.5 ~5 1~-152 2~2 2~2 199~5 As shown in Table III the yield strengths of the nickel-iron aluminides of the present invention are higher than those of the nickel aluminide (IC-136) at room temperature and 600C. However, these 30 nickel-~ron aluminides show a substan~ial decrease in strength at temperatures above about 600C and actually become weaker ~han thc nlckel aluminide at temperatures above ~50C. ~owever9 and signifi-cantly, the nickel-tron aluminides o~ the present in~ention are much more ductile than the nickel aluminide at 1,000C and 1,200C and both nickel-lron aluminide alloys exhibit superplas~lc behavior with tensile elongations exceeding 15~X at 1~200C~ The high ductility of the ~68~

nickel -iron al uminides is cons~stent with the~r excellent hot fabr~ca-bl l i ~y at 1 > 200C .
The creep propertles of the nickel -iron al uminide IC-159 has been determined at 760C and 138 and 276 MPa~ Lim1ted results set forth ~n 5 T~ble IV below indicate that the creep rupture life of the nickel-iron aluminides is considerably shorter than nickel aluminldes but slightly better than that of Hastelloy X, a trademarked alloy available from Cabott Corporation, Kokomo~ Indiana.
Table IV
}O _ _ __ _ _ _ Ni aluminides N~-Fe aluminide Hastelloy-Xb WaspalloyC
(IC-159~

760C9 138 MPa >2,~00 300 200 760C, ~76 MPa 300 to >800a ~ 12 1,000 aThe range depends on the HF content 7n the alloys.
bCommercially fabricable Ni-base alloy with composition Ni-21.8 Cr-2.5 Co-9.0 Mo0.6 W^18~5 Fe, weight percent CConYnercial Ni-base alloy with limited fabricab~lity Ni-19.5 Cr-13.5 Co~4.3 Mo-3.0 Ti-1.4 Al-2~0 Fe-.0096 B-0.07 Zr-0.07 C, weight percen~
Coupons of nickel-iron aluminides were recrystalliYed in a furnace for one hour at 1,050C and then exposed ~o air to determine oxidation resistance. The coupons were periodically ~every one to three days) removed from the furnace for visual examinat~ons and weight measure ments~ The coupons exhibited consis~ent we~ght gain during cyclic 30 oxidation at 800C and 1,000C. The oxidation rates oP nickel-iron 8~91 aluminides containlng molybdenum were comparable at 800C and 1,000C
whereas oxidation rates o~ the nickel-iron aluminides containing no molybdenum were lower at 1,000C than at 800C. This lower rate suggests that aluminum atoms dlffuse rapi ~ y from the interior to the surface at 1,000C to an aluminum oxide ~llm on the surface which protects the base metal from further oxidation. The nickel-iron aluminides showed oxidation reslstance that was comparable to nickel atuminides at 1,000C.
I~ will be seen that the nickel-iron aluminides of the present invention possess the combined bene~i~s of ductility, hot fabricabi-lity, strength, and oxidation resistance. In addition, they have the advantage of low density and low cost when compared with commercial nickel=base superalloys. The density of the aluminides is lower than that of Ni-base superalloy by 10-15X. A critical factor that distinguishes this inventlon oven previous work ~s an increase in iron concentration accompanied by the presence of hafnium and boron. The addition of small amounts of other elemen~s sueh as cerium, molybdenum and carbon result in an alloy with grea~ly improved fabricability properties at h7gh temperatures.
The ~oregoing description of pre~erred embodiments of the inven-tion has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously many modifications and variations are possible in light of the above ~eaching. The embodiments were chosen and described in order to best explain the principles o~ the lZ76~4 - 1~
invention and its practical application to thereby enable others skilled in the art to best utilize ~he inven~ion lrl various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the s~ope of the invention be defined by the claims appended hereto.

Claims (10)

1. A nickel-iron aluminide consisting essentially of:
a Ni3Al base;
a sufficient concentration of a Group IVb element or mixtures thereof to increase high temperature strength;
a sufficient concentration of material selected from the group consisting of iron and a rare earth element or mixtures thereof to increase hot fabricability;
a sufficient concentration of boron to increase ductility;
molybdenum in the amount of 0.0 to 4.0 weight percent;
and carbon in the amount of 0.00 to 0.06 weight percent.

2. The nickel-iron aluminide of claim 1 wherein said concentration of iron is in the range of 14.5 to 17.5 weight percent.

3. The nickel-iron aluminide of claim 2 having a sufficient amount of molybdenum to effect a reduction in oxidation of said nickel-iron aluminide and a sufficient amount of carbon to reduce cracking due to the addition of molybdenum.

4. The nickel-iron aluminide of claim 2 wherein said Group IVb element is selected from the group consisting of hafnium, zirconium and mixtures thereof and present in the amount of less than 1 weight percent.

5. The nickel-iron aluminide of claim 2 wherein said rare earth element is cerium present in the amount of from no more than 0.01 weight percent.

6. The nickel-iron aluminide of claim 2 wherein boron is present in an amount from .01 to 0.05 weight percent.

7. The nickel-iron aluminide of claim 2 having the composition of 10.2 weight percent aluminum, 16.6 weight percent iron, 0.9 weight percent hafnium, 0.015 weight percent boron, .005 weight percent cerium and the balance nickel.

8. The nickel-iron aluminide of claim 3 wherein said molybdenum is present in an amount of not more than 4 weight percent and said carbon is present in not more than 0.01 weight percent.

9. The nickel-iron aluminide of claim 3 having the composition

10.0 weight percent aluminum, 15.8 weight percent iron, 0.9 weight percent hafnium, 3.7 weight percent molybdenum, 0.015 weight percent boron, .005 weight percent cerium, .06 weight percent carbon and the balance nickel.