Note: Descriptions are shown in the official language in which they were submitted.
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
. ~
4676
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. ~
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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).
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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
-- 6 --
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
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-- 8 --
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.
