Note: Descriptions are shown in the official language in which they were submitted.
L2~
RD 15,123
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METHOD FOR IMPARTI~G SIRENGIFl TO INIERMElALLIC_EHAS~S
BACKGROUND OF TFlE INV~NTIQN
By a previous U. S. Patent No. 4,478,791,
issued October 23, 1984, the inventors disclosed and
claimed a set of alloys having a boron additive whic~
made possibie the achievement ot a novel combinatio
of ~rencJ~h and ductility in certain composit:io~ls.
It Ls poin~ed ou~ in the ~rior patellt t~clt
in many systems composed of two or more meta.llic
elements there may appear, under certain combinations
of compositions and treatment conditions, phases other
than the primary solid solutions. Such other phases
are commonly known as intermediate phases~ Many
intermediate phases are referred to by means of
the Greek symbol such as ~ or ~ '. Also they are
referred to ~y formula as for example, Cu3~1, CuZn
and My2Pb. The compositions of the intermediate
phases which have silnple approximate stoichiometric
ratios of the elements may exist over a range of
temperatures as well as of compositions.
Qccasionally as in the case of Mg2Pb,
which occurs in the Mg-Pb system, a true
stoichiometric compound, which compound is completely
ordered, is found to occur. Where each of tlle
elements of the coMpound is a metallic element, the
intermediate compound itself is commonly called an
intermetallic compound.
. .
~L2S~
~D 15,123
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The intermediate phases and intermetallic
compounds often e~hibit properties entirely different
from those of the component metals comprising the
system. They also frequently have complex
crystalographic structures. The lower order of
crystal symmetry and fewer planes or dense atomic
population of these complex crystallographic
structures may be associated with certain differences
in properties, e.g. greater hardness, lower ductility,
lower electrical conductivity of the intermediate
phases as compared to the properties of the ~rirnary
solid solutions.
Although several intermediate intermetallic
coMpounds with otherwi~e desirable properties, e.g.
hardness, strenyth, stability and resistarlce to
oxidation and corrosion at elevated temperatur~s "lav~
be~n identi~i~d, the~1r characte~ristic l~ck OL
ductility has posed formidable barriers to their use
as structural materials. In fact soMe of these
materials are so friable that they have been prepared
as solids in order that they may be broken up into
powdered form for use in powder metallurgical
processes for fabrication of articles.
A recent article appearing in the Japanese
literature disclosed that the addition of trace
alaounts (0.05 to 0.1~ wt.~) of boron to Ni3Al
polycrystalline material was successful in improving
the ductility of the otherwise ~rittle and noll-ductile
intermetallic compound. See in this reyard Journal of
the Japan Institute of Metals, Vo. 43, page 35~
published in 1979 by the authors Aoki and Izumi.
Although the roorn temperature tensile strain to
fracture of the Ni3Al was improved by the boron
additiion to about 35~, as compared to a~out 3% for
; 35 the Ni3Al without boron, the room temperature yield
strength remained at about 30 ksi. The Japanese
.,
RD 15,123
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article did not refer at all however to rapid
solidification of the boron containing composition
which they studied.
By the method of the prior Unled States
Patent 4,47~,791 the addition of 0.01 to 2.5 % boron
demonstrated further improvements where the alloy
preparation included the step of rapid
solidification. In particular as it is brought out in
this prior patent preferred properties are found in
rapidly solidified compositions containiny between 0.5
and 2.0~ boron and an optimum combination of yield
stress and strain to fracture is found in rapidly
solidified compositions containing approximately 1.~%
boron or less.
BRIEF ~TATEI~ T OF ~r~E INVEI~TI~N
It is, accordingly, one o~ject of the
present inv~ntion ~o provide an improve~ alloy ~or
operatiorl at higher temperatures.
Another object is to provide an alloy of
nickel and aluminum capable of operating at elevated
; temperatures for sustained periods of time.
Another object is to provide a nickel
aluminum alloy having an L12 type crystal
structure but having significant ductility and
strength.
Another object is to provide an alloy of
aluminum and nickel in which another element is
substituted for a portion of the aluminum and
which has a unique combination of physical properties.
~ther objects and advantayes of the present
invention will be in part apparent and in part pointed
out in the description which follows:
In one of its broader aspects, objects of
the inventiorl can be achieved by providing a rapldly
solidified alloy composition having an L12 crystal
g
RD 15,123
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structure and haviny a composition as follows:
(Nio 75X0 ~5Alo.20)YBloo--y
where 98 ~ y G 99. g and X is a substituent metal
selected from the group consisting of vanadium and
silicon.
BXI~F DESCRIPTION ~F TH~ FIGUR~S
The present invention and the description
which follows will be made clearer by reference to the
accornpanying fiyures in which:
FIGURE 1 is a plot of the values of the
stress of the inventive alloys plotted against the
strain in percent for the base ~i3Al alloy as well
as alloys containing substituents for the nickel and
aluminum constituents.
Surprisinyly it has IIOW been found that
further property improvements are possible in the
alloy system of the gamma prime N13Al intermediate
phase where not only boron is present in the
composition as ternary element but in addition a metal
selected from a group of metals is present as a
quaternary ingredien~ of such compositions as a
substituent metal.
~y a substituent metal is meant a meta
whicll takes the place of and in this way is
substituted or another and different rnetal, where tl~e
other metal is part of a combination of metals forrning
an essential constituent of an alloy system.
For example, in the case of the intermediate
phase system Ni3Al, the constituent metals are
nickel and aluminum. The metals are present in the
stoichiometric atomic ratio of 3 nickel atoms for each
aluminum atom in this system. It had been discovered
that a desirable crystal form and accompanying
~` ~a.2~
R~ 15,123
superior physcial properties can be achieved by
forming a single crystal of Ni3Al. ~owever
polycrystalline Ni3Al is quite brittle and shatters
under stess such as is applied in efforts to form the
material into useful objects vr to use such an article.
It was discovered that the inclusion of
boron in the rapidly cooled and solidified system can
impart desirable ductility to the rapidly solidified
alloy as taught in United States Patent No. 4,478,791
referred to above.
Now it has been discovered that certain
metals can be beneficially substltuted in part for the
constituent aluminum and hence these substituted
metals are designated and known herein as su~stituent
lS metals i.e. as an aluminum substituent in the Ni3Al
strUc~ure. ~oreoVer it has ~een discovered ttlat
valllable and berle~icial proper~ie~ are iln~rted to tlle
rapidly solidified compositiolls which have the
stoichiometric proportions but which have a
substituent metal as a quaternary ingredient of sUcn
rapidly solidified alloy systems.
The alloy compositions of the present
invention must contain a first or primary ingredient
or component and a second ingredient or component
different from the first. The compositions rnust also
contain boron as a tertiary ingredient as tauyht
herein and as taught in United States Patent
Number 4,~78,791 referred to above, and must further
contain a ~luarternary componenk or ingredient as a
substituent for aluMinum as taught in the subject
specification.
The first constituent or ingredient is
preferably nickel.
Further, the first constituent and tile
second constituent must be present in substantially
stoichiometric atornic ratios. ~n example is the
~255~
R~ 1~,123
-- 6
nickel aluminide in which three atoms are present as
the primary component constituent for each aluminum
constituent which is present.
The composition which i5 formed must have a
preselected intermetallic phase havlng a crystal
structure of the L12 type and must have been formed
by cool ng the melt at a cooling rate of at least
about 103C per second to form a solid body the
principal phase of which lS the L12 type crystal
lU structure in either its ordered or disordered state.
The melt composition from which the structure is
formed must have the first constituent and second
constituent present in the melt in an atolnic ratio of
approximately 3:1.
lS As point~d out ill ~he prior United Sta~es
Pat~nt Wo. ~,~7~,791 re~rr~d ~o al)ov~, colnpo~3:itl0lls
having this colnbina~iotl of inyredierlts and WlliCI~ are
subjected to the rapid solidification techni~ue have
surprisingly high values for both the strain to
fracture after yield and for the 0.2% offset yield
stress. Eor boron levels ~etween 1 and 2% the values
of the strain to fracture generally declines so that a
preferred range for the boron tertiary additive is
between 0.5 and 1.5~.
By the prior teaching it was found tllat the
optimum boron addition was at about 1 atomic percent
and permitted a yield strength value at room
temperature of about 100 ksi to be actlieved for t~le
rapidly solidified product. The fracture strain of
such a product was about lU% at room temperature.
Surprisingly, it has now been found that the
unusual strength properties which are obtained througll
the use of the rapid solidificaton in combination with
the boron additive may be increase~ to heretofore
unprecedented levels with the addition of a selected
quaternary component or ingxedient as a su~stituent to
RD 15,123
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the priinary al~minum component.
The quaternary ingredient which may ~e
beneficially included in a composition for rapid
solidification as a substituent to make unprecedented
improvements in the properties include the elements
vanadium and silicon.
Further it nas been found, observed and
determined that where an e~uiaxed structure is formed
with the quaternary composition by rapid
solidification, the properties are substantially
better on the average than in those cases where the
non-e~uiaxed structure is formed. The equiaxed
structure is ~elieved to result from
recrystallization. It is known that recrystalli~atio
lS can readily occur in a single-phase Inaterial.
The addition o~: the vanadiuln or ~i Lic~n cl~
~uaternary ingredient and as a substituent for
aluminum at about a 5 atomic percent level apparently
does not form borides or other phases under the
influence of the rapid solidification processing.
; Regarding the improved properties achieved
in the measurements made followiny the preparation of
the alloys, the testing of alloys as descri~ed herein
has yielded some surprising results. ~ne set of the
properties and particularly the stress properties are
indicated in the attached Figure 1 in whicil the stress
in ksi is plotted against the strain in percent.
It is evident from Figure 1 that the alloy
containing Ni3Al with 1~ boron }las the lowest stress
values and that the two other samples which were
tested had significantly and unexpectedly higher
values. The sample with the 5 atomic percent silion
had the highest values found and these were of the
order of 185 ksi.
3S In the practice of this invention, an
intermetallic phase having an L12 type crystal
~5~
R~ 15,123
structure is first selected. The selection criteria
will depend upon the end use environment which, in
turn, determines the attributes, such as strength,
ductility, hardness, corrosion resistance an~ fatigue
strength, required of the material selected.
An intermetallic phase typical of those of
enyineeriny interest and one having particularly
desirable attributes is nickel aluminide ~Ni3Al)
which is found in the nickel-aluminum binary system
and as the yamma prime phase in gamma/gamma prime
nickel-base superalloys. ~ickel aluminide has hiyh
hardness and is stable and resistant to oxidation and
corrosion at elevated temperatures which makes it
attractive as a potential structural material~
A:lthough si~lgle crystals of Ni3~1 exhibit good
~uctility in certain ~ry~tal:lographlc oriel~tatiorl~,
the polycr~stallirle ~orm, i.e., t~e form of ~rimary
significance froM an engineeriny standpoint, has
low ductility and fails in a brittle manner
intergranularly.
Nickel aluminide, whicil has a ordered face
centered cubic (FCC) crystal structure of the CU3Al
type (L12 in the Stukturbericht desiynation which is
the designation used herein and in the appende~
claims) witll a lattice paramter aO = 3.589 at 75 %
Ni and melts in the range of from about 1385
to 1395C, is formed from alumirlum and nickel which
have rnelting points of 660 and 1453C, respectively.
Although frequently referred to as Ni3Al, nickel
3U aluminide is an intermetallic phase and not a
compound as it exists over a range of compositions
as à function of temperature, e.g., about 7~.5
to 77 ~ Ni (85.1 to 87.8 wt. %) at 600C.
The selected intermetallic phase is provided
as a melt w~lose composition corresponds to that of the
preselected intermetallic phase. The melt composition
s~
RD 15,123
_ g _
will consist essentially of the atoms of the two
components of the interMetallic phase in an atomic
ratio of approximately 3:1 and is modi]Eied with boron
in an amount of from about 0.01 to 2.5 %.
Generally, the components wi:Ll be two
different elements, but, while still maintaining the
approximate atomic ratio of 3:1, one or more elements
may, in some cases, be partially substituted for one
or both of the two elements which form the
1~ intermetallic phase.
Although the melt should ideally consist
only of the atoms of the intermetallic phase and atom~
of boron, it is recognized that occasionally and
inevitably other atorns of one or more lncid~nt~l
ilnpurity atolns may be preserlt in the melt.
The melt i~ nexk rapidly cooled ~t a rate Oe
at ~ast a~o~lt 103C/sec ~o Eorm a solid ~ody, t~le
principal phase of which is of the LL2 type crystal
structure in either its ordered or diordered state.
Thus, although the rapidly solidified solid body will
principally have the sa~ne crystal structure as the
pre4elected interrnetallic phase, i.e., the L12 type,
the present of other phases, e.g., borides, is
possible. Since the cooling rates are high, it is
also possible that the crysta;L structure of the
rapidly solidified solid will be disordered, i.e., the
atoms wiLl be located at random sites on the crystal
lattice instead of at specific periodic positions on
the crystal lattice as is the case with ordered solid
3~ solutions.
There are several methods by wllich the
re~uisite large cooliny rates may be obtained, e.y,
splat cooling. A preferred laboratory method for
o~taining the re~uisite coolirly rates is the
chill-block melt spinniny process.
~riefly and typically, in the chill-block
~z~
RD 15,123
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melt spinning process molten metal is delivered froln a
crucible through a nozzle, usually under the pressure
of an inert yas, to form a free-standing stream of
li~uid metal or a column of liquid metal in contact
with the nozzle. r~he stream of li~uid metal is then
impinyed onto or otherwise placed in conact Wit~l a
rapidly moving surface of a chill-block, i.e~, a
cooling substrate, made of a material such as copper.
The material to be melted can be delivered
to the crucible as separate solids of the elements
required and melted therein by means such as an
induction coil placed around the crucible or a "master
alloy~ can first be made, comminuted, and the
comminuted particles placed .itl the crucible. When the
lS li~uid mel~ con~cts the cold c~Lll-block, it cools
rapidl~, froln a~out lU3C/sec to lO7C/sec, alld
solidifies in ~he form o~ a continuous lenyth of a
thin ribbon w~lose width is considerably lar~er than
its thickness. A more detailed teaching oE the
chill-block melt spinning process rnay be found, for
example, in U.S. Patellts 2,825,108 - R. B. Pond -
issued March 4, 1958; 4,221,257 M. ~. Narasi]n~lan -
issued September 9, 1980 and 4,282,921 - ~. Lieberlna
- issued Auyust 11, 1981.
Thé following examples are provided hy way
of illustration and not by limitation to further teach
the novel method of the invention and illustrate its
many advantageous attributes.
EXAMPLE 1
A heat of a composition correspondin~ to
about 3 atomic parts nickel to 1 atomic part aluminum
and 1 atomic percent boron was prepared, comminuted,
and about 60 grarns of the pieces were delivered into
an alumina crucible of a chill-block melt spinlli}ly
apparatus. The composition had the formula:
9Z9
~1~ 15,123
( Ni 75Al . 25 ) 99Bl
The crucible terminated in a flat-bottomed
exit section having a slot 0.25 (6~35 mm) inches by 25
mils (0.635mm) therethrough. A chill block, in the
form of a wheel having faces 10 inches (25.4 cm) in
diaMeter with (rim) thickness of 1.5 inches (3.8 cm),
made of H-12 tool steel, was oriented vertically so
that the rim surface could be used as the casting
(chill) surface when the wheel was rotated about a
horizontal axis passing through the centers of and
perpendicular to the wheel faces. The crucible was
placed in a vertically up orientation and brought to
within about 1.2 to 1.6 mils (30-40~) of the castiny
surface with ttle 0.25 inch length dimension of the
~310t ~rien~ed ~rp~en~icular ~o t~l~ dire~ction o~
rotation of the wheel.
r~he wheel was rotated at 1200 rpm. 'rhe rnelt
was heated to between about 135U to 1450C. The melt
was ejected as a rectangular stream onto the rotating
chill surface under the pressure of argon at about 1.5
psi to produce a long ribbon which measured from
about 40-70~ in thickness by about 0.25 inches in
width.
The ribbons were tested for bend ductility
and a value of 1.0 was found. This value or bend
ductility designates that the ribbon can be bent fully
to 130C without fracture.
EXAMPLE 2
rrhe procedure of Example 1 was repeated
using the same equipment to prepare a master heat of
the boron doped nominal ~i3Al composition but one
which was modified to the following composition:
RD 15,123
- 12 -
(Nio ~5Alo 20Tio.05)99B:L
Ribbons were cast from the heat as descri~ed
in Example 1.
The ribbons were tested for bend ductility
and a value of 0.04 was found for the ribbon thus
prepared. This value of bend ductility was calculated
by dividing the ribbon thickness by the bend radius at
which the ribbon fractures.
EXAMPLES 3 THRO~G~ 12
Ten additiorlal master heats
alloys 96, 101, 111 through 117 and 125 were prepared
having the compositions as set forth in Table I
below. These heats were prepared in the manller
described witll reference to tlle ~irst descri~ed a~c~ve
and were t~ted ~or ~end ~uctility in the ~alne rnann~r
as that prepared a~ove. 'rhe values for ~end ductility
which were obtained are listed in Table I.
It was also found that there is a
correlation between the full bend ductility ~bend
ductility = 1.0) of the samples which were prepared
and the formation of an e~uiaxed configuration in the
crystallographic structure which was formed. The
Table indicates also those samples for which an
e~uiaxed format was found and also those for which the
non-e~uiaxed forïnat was found.
" ~,.,~s5~
R~ 15,123
- 13 -
TABLE I
Crystallo-
Alloy Composition Bend graphic
Example Number Formula _ Ductility Structure
2 92 ( 0.75 0.20 0.05 99 1
3 96 [~io.75 0.25)0.98 0.02 99 1 N
4 :Lll (l~io 75AlO.20Tao.o5)99 1 N
112 (NiU 75~1o.2oN~o.uo5)99 1 0.02
6 113 (L~io.75Alo.2ovo.o5)99Bl 1.0 E
~7 114 (1~iu.75~lo.2o~i~.os)
8 115 (Nio.6sFeo.l~lo.25)99Bl
9 116 (Nio 65Mno.loA10.25)99 1
117 (l~io 70Cro-osAlo 25)99 1 0.06 N
11 125 [(Nio 75Al0.2s)Reo.o3]99Bl 0.1
12 lO:L (Nio 70coo.o5Alo 25)99 1 l.U E
: N designates non-e~uiaxed; E designates e~uiaxed.
E~D 15,123
-- 14 --
Returning to a consideration of the data
plotted in Figure 1, it is evident that t~le stress in
ksi of the rapidly solidified boron doped nickel
aluminide base alloy containing the silicon as a
partial substituent for aluminum is substantially
higher than that of the similar alloy without the
substituent for the aluminum.
The stress in ksi for the vana~ium modified
aluminide is shown by the lower plot and this
composition has a stress of 135 ksi at yield.
The stress at yield for the uppermost plot is
some 37~ higher at 185 ksi and this is a significant
and unexpected advance in the ability of those ~killed
in this art to increase the tensile properties of tlle
:L5 rapidly solidi~ied~ boron doped nickel aluminide base
~llo~.
It is furthe~r evident froln rl'abLe I that
~xample 6 which involved the incorporation of the
vanadiurn in the rapidly solidified boron doped
tri-nickel alulninide as a substituent for aluminuln
also resulted in a composition having a bend ductility
test value of 1Ø Further this compositioll was found
to be equiaxed.
Based on comparison with other materials of
Table I which are incorporated as substituents Eor
aluminum it is evident that the silicon and vanadium
provide uni~ue and advantageous improvements in the
boron doped tri-nickel aluminide of the prior United
States Patent Number 4,478,791.
