CA1244676A - Ductile aluminide alloys for high temperature applications - Google Patents

Abstract

DUCTILE ALUMINIDE ALLOYS FOR

HIGH TEMPERATURE APPLICATIONS

Abstract of the Disclosure Improved Ni3Al alloys are provided by inclusion of boron, hafnium or zirconium, and in some species, iron.

Description

12~676 DUCTILE ~LUMINIDE RLLOYS FOR
HIGH TEMPERRTURE QPPLICATI~NS

This invention relates to heat and corrosion resistant alloys containing nickel, aluminum, boron, hafnium or zirconium, and in some species, iron.
Because of the limited availability and strategic nature of chromium, there has been an increasing interest in the development of strong, heat and corrosion resistant alloys for use as substitutes for the many chromiuM-containing ferrous alloys commonly referred to as stainless steels. Some nickel and iron aluminides have been found to maintain high strength and resist oxidation at elevated temperatures.
~lthough single crystals of Ni3~1 are known to be ductile, polycrystalline forms of the intermetallic compound are extremely brittle and therefore can not be used to form sheetmetal products.
However, it has been reported recently by Aoki and I~umi in Nipoon Kinzoku Gakkaishi. Volume 43, Number 12, that the addition of a small amount of boron can reduce the brittleness of Ni~At. It is also known that the addition of small amounts of manganese, niobium and titanium . ~

ImprDves the fabricability of Ni3AI alloys, and that the acldition o~
about 6.5 to about 16.0 weight percent iron to such alloys increases their yield str-ength while reducing the amount of nickel used therein.
SummarY of the Invention It i5, therefore, the object of this invention to provide an improved high strength alloy for use in hostile environments.
Another object of the invention is to provide an alloy which exhibits high strength at temperatures well above ~00C.
A further object of the invention is tD provide an alloy which is resistant to Dxidation at elevated temperatures, e.g., 1,000C.
The invention takes on two forms, Type I and Type Il, as shown in Tables I and II, respectively. Type I alloy consists of sufficient nickel and aluminum to form Ni3A1, an amount of boron effective tD
promote ductility in the alloy, and 0.3 to 1.5 at.% of an element selected from the class consisting of hafniu.n and zirconium. The total concentration of aluminum and hafnium ~or zirconium) must be less than 24.5 at.'~. in order to be fabricable.
The Type II alloy consists of Ni3AI plus boron for ductility, iron for strength, and hafnium for increased strength at elevated temperature.
Z0 The Type II alloy may be described generally as follows. In an alloy comprising about 19 to 21.5 at.~. aluminum, 0.08 to 0.3 at.~/. boron. ~ to 12 at.'~. iron, the balance being nickel, the irnprovement comprising the addition of 0.3 to l.S at.'~. of an element selecteri frDm the class '~
..1. ~

~4~676 conslst~ng of hafn~um and z~rconlum. ~he total concentratton of alu~lnum and hafntum (or ztrcontum) must not exceed 22 at.X.
Descr~tlon of the Drawtngs F~g. 1 ts a graph showtng yteld strengths as a funct~on of tem-perature for prev10usly known commerc1al alloys and alloys having com-poslttons tn accordance wtth the lnventton.
F~g. 2 ~s a graph showtng wetght gatn due to oxtdatlon, as a func-~ton of tlme, of an alloy havtng a composttton in accorddnce with the tnventton.

Descrtptlon of Preferred Embodt~ents of the Invent10n Alloys ln accordance wtth the inventton can be prepared as descrtbe~ tn the followtng examples.
Aluminide alloys were prepared hav~ng the composttions shown in Table I (whtch compostttons wlll be referred to heretnafter as Type 1 alloys) and Table Il (whtch compostt~ons wtll be referred to heretnafter as Type II alloys).

Table I. Composttton of hafntum-modlfted ntckel alumtntdes (based on Nt3Al) (Type I Alloys) Alloy number - (at-X) (wt.%) . _ IC-15 Nt-24 Al-0.2B Ht-12.7 Al-O.OSB
IC-71 Ni-23.8 Al-0.25 Hf-0.2B Ni-12.4 Al-O.9 Hf-0.05B
25IC-49 Ni-24.0 Al-0.5 Hf-0.2B Nt-12.5 Al-1.7 Hf-0.05B
IC-5U Ni-23.5 Al^0.5 Hf-0.2B Nt-12.2 AL-1.7 Hf-0.05B
IC-72 N1-23.0 Al-1.0 Hf-0.2B Ni-11.~ Al-3.4 Hf-0.05B
IC-76 N~-22.5 Al-1.5 Hf-0.2B Nt-11.4 Al-5.0 Hf-0.05B
IC-77 Nt-22.0 Al-2.0 Hf-0.2B Nt-11.0 Al-6.6 Hf-0.05B
30IC-78 Nt-21.0 Al-3.0 Hf-U.2B Nl-10.2 A1-9.6 Hf-0.05B

.~

A

:~.24~;7 - 4 ~

Table II. Composition of hafnium-modified n1ckel aluminides alloyed ~ith iron and other metallic elements (Type II Alloys) -5 Alloy number (at.X) (wt.X) IC-63 Ni-20 Al-10 Fe-0.5 Hf-0.5 N1-10.2 Al-10.6 Fe-1.7 Mn-0.2B ,Hf-0.5 Mn-0.05B

IC-68 Ni-20 Al-9.1 Fe-0.5 Hf-0.5 Ni-10.1 Al-9.5 Fe-1.7 Ta-0.5 Mn-O.lB Hf-1.7 Ta-0.5 Mn-0.025B

IC-69 N~-20 Al-9.1 Fe-0.5 Hf-0.5 Ni-10.2 Al-9.6 Fe-1.7 Nb-O.S Mn-O.lB Hf-0.9 Nb-0.5 Mn-0.025 IC-101 Ni-19.5 Al-9.0 Fe-1.0 Ni-9.8 Al-9.4 Fe-3.3 Hf-0.1B Hf-0.92B

Control samples of boron-doped Ni3Al alloys were prepared for com-parison to the subject improved alloys. The alloys were prepared by arc melting and drop casting pure alum1nu~, iron (when deslred), hafnium, and a master alloy of nickel-4 wt.X B, in proportions which provided the alloy compositions listed in the tables.
The alloy ingots, thus prepared, were homogenized at 1,000C and fabr k ated by repeated cold rolling with intermediate anneals at 1,050C. All the Type I ~lloys were successfully cold rolled 1nto 0.76 mm-thlck sheet except the 3.0 at.X Hf alloy (IC-78) wh1ch cracked during early stages of fabr1cdtion. Table III shows the effect of alloy stoichio~etry on fabrication of n'ckel alumin'des modified with 0.5 at.X ~f (1.7 wt.X Hf).

~2'~676 Table III. Composit~on and Fa~r~cabll~ty of Hafn1um-Modlfied Nickel Alumln'des (based on N~3Al) Contaln~ng U.5 at.X Hf , (1.7 wt.X Hf) ComDos~tion Alloy ~umber (at.X) (wt.X) Fabricat1On IC-48 Ni-24.5 Al-0.5 N~-12.8 Al-1.7 Ingot cracked Hf-0.2 B Hf~0.05 B dur1ng fa~r1cation IC-49 Nt-24.0 Al-0.5 N~-12.5 Al-1.7 Sheet fabricated Hf-0.2 B Hf-0.05 B w~th diff1culty IC-50 Ni-23.5 Al-0.5 Ni-12.2 Al-1.7 Sheet fabrlcated Hf-0.2 B Hf-0.05 The results ~n Table III ~ndicate that the sheet fabrk atlon becomes increas1ngly'd1ff~cult as the total Al and Hf content 1ncreases, and that the alum1n1de w~th a total of 25 at.X Al and Hf can not be successfully fabr1cated by cold rolling. Thus, the total con-centratlon of Al and Hf 1n the Type I alumin1de alloys should be lessthan 24.5 at.X.
The tenslle propert1es of the hafntum-mod~f1ed alum~nide alloys were determined as a function of test temperature ~n vacuum. Table IV
shows the effect of hafn~um add~tlons on tenslle propert~es of the Type I atum~n1de alloys tested at 850C.

~i?,'~67 Table IV. Effect of hafnlum additions on tenslle properties of boron-doped N13Al tested at 850C
.. . . . . . _ Hf concentration Yield Strength Tenslle Strength E1Ongation ~ .
(at.Z~ MPa (ks~) MPa (ks~

0 498 ~72.3) 660.1 (95.8) 7.1 0.25 54~ (79.5) 692.5 (100.5) 3.1 0.50 640.1 (92.9) 866.1 (125.7~ 14.1 1.0 744.1 (10~.0) 926.0 (134.4) 5.5 1.5 922.6 (133.9) 1~85.9 (157.6) 9~6

2.0 788.9 (114.5) 788.9 ~114.5) <U.l -- .
15 Both tens~le and yield strengths ~ncrease with hafnlum content and peak at about 1.5 at.X Hf. At hafnium contents less than about 0.3 at.X
Hf, the effect becomes ~nsignificant wh~le at Hf contents abovP 1.5 at.X
Hf, the benef klal effect drops off and the alloy can not be fabricated at 3 at.X Hf. Note that the alumintde conta:n~ng 1.5 at.X Hf has a y1eld strength of 923 MPa (134 ksi~ and an ultimate tenslle strength of 1086 MPa (158 ksi), propert~es whlch are h~gher than those of commer-c~al superalloys including cast alloys.
The y~eld strength of boron doped N 3Al and hafnium-modified, boron doped Ni3Al (1.5 at.X Hf) ~s plotted as a functlon of temperature ln Fig~ 1 (specimen IC-76). For compar~son, the strength of commercial solid-solutlon alloys, such as Hastelloy X and type 316 stainless steel, is also 1ncluded ln the plot. Unl~ke the conventional solid-solution alloys, the yleld strength of the boron doped Ni3Al increases as the temperature rises and reaches a maximum a~ about 60UC. Prev~ously, macroalloy1ng of Ni3Al showed that alloy elements only lncreased the _ 7 ~Z~4676 strength level but d1d not ra1se the peak temperature for the maximum strength. ~he un1que feaSure of alloy1ng w1th selected amounts of hafnlum is that the peak temperature 1s extended from about 600C to around ~50C. Th1s ls a breakthrough ln the development of alloys for hlgh temperature use.
Speclm2ns of the Type II hdfn1um-mod1fted aluminlde, alloyed wlth 9 to IO at.X Fe, were fabr k ated lnto 0.8 ~m thlck sheets by repeated cold rolllng as descrl~ed ln the Example. Tenslle properties of the IC-S3 alloy are plotted ln Flg. I along with results obta1ned for IO several other alloys. It can be seen ln Fig. I that IC-63 has the best yleld strength at temperatures below 650C, whlle IC-75 exhi~1ts the h1ghest y1eld strength above 650C. Type II alloys contaln1ng lncreased quant1tles of hafnlum have even better strength at elevated temperature.
To demonstrate the oxldatlon resistance of the subject alloys, speclmens IC-49 and IC-50 were studled by furnaclng at I,000C ln a1r.
The samples were removed from the furnace after each 25 to 75 h expo-sure. Flg. 2 ls d plot of welght galn due to oxidation of speclmen IC-50 as a functlon of exposure t1me at I,000C. Examlnat10n of the hafn1um-mod1f1ed alumlnlde showed no dpparent spalllng. The total welght gain of 0.6 mg/cm2 after 571 h exposure ls much lower than that exh1blted by sta1nless steels and commercial superalloys.
Other elements from group IVA of the periodlc table have also been alloyed wlth boron doped H13Al lntermetall1c alloys. Z1rcon1um showed some improvement ln the hlgh temperature propert1es of alum1nldes but ~2~4676 was not as effectlve as hafnium. T1t mium ~ddit~ons d~d no~ appear to 1mprove ehe mechan~cal propert1es. T3ble V shows the tensile proper-ties of boron doped nlckel alumin1des containiny 0.5 at.X of Hf, Zr or T1.
5 Tabte V. Tenslle properties of boron doped n~ckel aluminides ~lloyed w~th 0,5 at.t Hf, Zr, or Ti (tests at 850C) Yield strengthTens~le strength Elongatlon Alloy addition(ksl) (ksl) (X) 0 72.3 95.8 7.1 Hf Y2,9 125.7 14.1 Zr 83.6 83.6 0.2 T~ 65.6 72.6 1.0 Creep properties of Hf-, Zr-, and T~-modif~ed aluminides ~long with selected commercial sol~d-solution alloys are shown in Table VI.
Table VI. Creep propert~es of Hf-. Zr:, and Ti-modified aluminides and commercial solld-solution alloys 20 tAll materials were tested at 760C and 20,000 psi (138 MPa)]
-Alloy compositiona Steady state creep Rupture l~fe (at.t) Rate (10-6/h) (h) 25Ni3Al 91.0 352 Ni3A1 ~ 0.25 Hf 31.0 599~
~Al + 0.5 Hf 3.3 580b Ni3A1 ~ 0.5 Zr 8.1 507b -;, t j .~

9 :~2~ 676 Table VI (cont. ) Creep propertles of Hf-, Zr-, and Ti-~od~f1ed alumin1des ~nd commerclal solid-solution alloys [All mater~als were tested at 760~C and 2U,000 p5i l138 MPa)~
_ Alloy compos~tlonaSteady state creepRupture 11fe (~t.X~: Rate (10-6~h~ (h) .
Ni3Al + 1.0 Hf 4.3 596b Ni3Al + 1.0 T1 17.1 >503b N13A1 ~ 1.5 Hf 3.7 >~480b Ni3A1 ~ 2.0 Hf 0.5 480 Type 316 sta~nless steel 8540.0 65 Hastelloy X 1320. 0 252 aAll alum1nides were doped w~th 0.2 at.X B.
bTests discontinued without rupture.
The data ~n TableVI show that alloying with Hf-and Zr greatly lowers the steady state creep rate and extends the rupture llfe of Ni3Al alloys.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An alloy consisting essentially of sufficient nickel and aluminum to form Ni3A1, an amount of boron sufficient to promote ductility in the alloy and 0.3 to 1.5 atomic percent of an element selected from the group consisting of hafnium and zirconium.

2. The alloy of claim 1 further including b to 12 atomic percent iron.

3. The alloy of claim 2 comprising about 19 to about 21.5 atomic percent aluminum and about 0.02 to about 0.3 atomic percent boron.

4. The alloy of claim I wherein the total concentration of aluminum and the element selected from said group is less than 24.5 atomic percent.

5. The alloy of claim 2 wherein the total concentration of aluminum and the element selected from said group is 22 atomic percent or less.