Note: Descriptions are shown in the official language in which they were submitted.
1~ 117~Z87
Background _ _ he InventiGn
This invention relates to the art of po~der metallurgy
and more particularly to the metho~ of ma~ing a high density
po~ered metal alloy article and to the products of such method.
For many years, powder metallurgists have been attempt-
ing to produce structural powder metal alloys which exhibit a
! high sintered density. To accomplish this, various techniques
I have been developed to reduce the porosity of the powder alloys
I to a minimum to therebv increase the sintered density of the
10 ¦ concerned article to near theoretical.
¦ For example, it has been known in the prior art to
produce high density powdered metal products by the use of
secondary processing techniques such as hot or cold working
and/or hot isostatic pressing. These secondary operations,
however, greatly add to the cost of the finished product and
i are to be avoided, if possible.
Ii In addition, it is knot~n in the art to produce rela-
¦¦ tively lligh density powdered products by sintering them at a
!! temperature which introduces a liquid phase. Much of the
20 ¦¦ recent wor~ in this area has involved introducing a transient
liquid phase. ~lowever, the use o~ a liquid phase has the draw-
¦i back of introducing many reliability ~ro~lems, esyecially with
¦ regard to brittleness. Add~tionally, the control of the exact
sintering temperature becomes very important and in commercial
~ractice is very difficult to main~ain.
Also, it is known in the art to produce relatively
high density powdered products bv forming them entirely out of
a very ine grain powder. This technique, as evidenced by
U.S. Patent 3,744,993, requires extra processing steps to pro-
duce the fine powder and to assure that all the pouder is of
!¦ the proper size. However, this ~echnique is not withou~ signi-
I ficant problems. In this regard, perhaps the most significant
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1177;Z8~
problem associated with the technique of using all fin~ po~Jder
is that the smaller the particle size of the powder, the
greater is its tendency to be pyrophoric. Obviously, it is
desirable to avoid or minimize problems associated with the use
of such pyrophoric materials.
Accordingly, it is the principal object of the present
invention to provide a method of producing a sintered powdered
metal alloy article by powder metallurgy techniques which
article exhibits a higher degree of aensification than is found
in a similar article produced by prior art techniques.
It is another object of the present invention to
provide an improved method of producing high density powder
metal alloys from powders by means of a single pressing and
sintering operation.
lS It is still another object of the present invention
to provide an improved sintered powdered metal article having
a relatively high density.
A further object of the invention is to provide a
powder metallurgy technique for producing a high density
sintered metal while reducing the amount of fine particles
required to produce the same to thereby minimize the problems
typically associated with the handling of pyrophoric materials.
Other objects of the-invention will become apparent
from a reading of the following specification and claims.
Summary of the Invention
In one aspect, the present invention concerns a
process for producing a sintered powdered metal alloy articie
composed of a base metal and an alloying metal which article
is characterized by having a density near theoretical which
method comprises:
(a) providing base metal particles having a median
particle size of greater than ~0 microns;
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1177;~H7
(b) providing alloy ~orr,ling particles ha~in~ a median
partlcle size of 20 microns or less, with the alloy forming
particles being allo~able ~Jith said base metal particles;
(c) mixing the al.loy forming particles ~7ith base
metal particles so as to form a particle mixture capable of
being sintered to near theoretical density which mixture con-
tains a minor amount of alloy forming particles;
~d~ compacting the mixture of allo~ forming particles
and base metal particles into an article of the desired con-
figuration having a ~,reen density sufficient to render the
¦ so-formed article capable of being sintered to near theoretical
density; and
(e) sintering the article at a temperature below that
¦ at which any liquid phase is formed in said article.
In another aspect, the present invention relates to
¦ a sintered powdered metal alloy article having a density
¦l approaching theoretical which is characterized by having physi-
¦¦ cal properties similar to those o~ a wrought metal alloy article
I¦ having the same chemical composition which sintered article is
¦I produced by a process which comprises:
I (a) providing base metal. particles having a median
¦ parti~le size of grea~er than ~0 microns;
(b) providing alloy forming particles having a median
particle size of 20 microns or less, with the allo~J-forming
particles being alloyable with said base metal particles;
(c) mixing the alloy forming particles with base
metal particles so as to form a particle mixture capable of- .
¦ being sintered to near theoretica]. density which mixture con-
¦ tains a minor amount of alloy forr.ling particles;
~ (d~ compacting the mix~ure of alloy forming particles
¦! and base metal particles into an article of the desired config-
1l uration having a green density sufficient to render the
'7~ ~ 7
so-forme(l ar~icl~ c~E-ahle of b~in~ sint~r~ to ne~r th~oretical
I detlsity; ancl
I (c) sintering the article at a t~mperature belo~
¦I that at which any li~uid phase is formed in said article.
ll Br_ef Descrip~ion of the Preferred Practice of the Invention
Tlle present invention concerns a novel sintered powder
,¦ metal alloy article and the method of producing the same.
In practice, the article of the invention is produced
from at least two special types of powdered metal particles,
I specifically alloy forming particles and base metal particles,
which particles, in turn, are mixed togetl~er, compacted and
then sintered in a manner such that no liquid phase is formed
during the sintering procedure. In this regard, as used herein
the term "alloy forming particles" includes one or more
ll elemental metal particles whic~l combine to form an alloy,
articles of a pre-alloyed material and mixtures of such par-
ticles. In addition, as used herein the term 'lapproaching"
or "near theoret~cal" densitv is in~e~ded to mean a density
¦I which is higher (greater) than the density of a sirnilar article
1 which is formed by prior art powder metal forming techniques.
, The chemical composition of the ~loy forming particles
Il is not cri~ical, except that i~ ~us~ be chemically compatible
with the base metal par~icles, that is, it must be alloyable
with such particles. In addition, it is thought that the
- 25 relative diffusion rates of the alloy forming particles and the
base metal particles must be of a relatively comparable
magnitude By way of example and not for the purpose of limit-
ing the sco~e of the invention, typical of materials used to
I form such alloy forming particles or mixing with titanium are
ll aluminum-vanadiu~ alloys; alu~inum-vanadium-tin alloys;
and aluminur.-tln-molybdenum-zlrconium alloys, For
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117'7Z87
I ~ixin~ with iron, typical ~aterials are elemental silicon,
,I tungsten, molybdenu~, chromiu~, nickel, and vanadium.
To obtain the maximum benefits of the present inven-
tion it is essential that the median particle size of the alloy
1¦ forming particles be 20 microns or less. This can be accom-
¦ plished via a number of well l~no~m techniques. ~owever, it has
been found that such particles can be readily obtained by
attriting alloy forming particles in a commerciall~ available
l apparatus, such as a Szegvari 1 ~ attri~or; manufactured by
¦ Union Process Inc., Akron, Ohio. In practice, it has been
found desirable to utilize alloy forming particles having a
median particle size ranging from about 0 5 to 20 microns, with
the best results obtained when the particle size range is from
¦ about 2 to about 10 microns.
I The base metal particles used in the practice of the
i present invention can be produced by a myrid of well known
¦ techniques and as such techniques do not orm a part of the
¦ present invention they will not be described herein. However,
¦ it is essential to the practice of the invention that the base
1! metal particles utilized have a ~edian particle size by ~eight
¦ of greater than 40 microns, uith good results being realized
¦ when the median particle size by weight of the base metal
p~rticles ranges froM about 40 to about 177 microns, and
exceptional results being achieved when ~he particle size range
by weight is from abou~ 44 to 105 microns.
Typical base metals are titanium, zirconium, iron
and nickel. While it is preferred that the base metal particles
utilized be chemicall~J pure, as used herein the term "base
I metal" particles i5 intended to include elemental metals and
¦ metal alloys wherein the allo~yin~ element or elements are
present in minor or trace amounts. Generally speaking, the
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i
17 ~ ~ 7
the base metal utilized should be commercially pur~ and contain
in excess of about 99 we ght percent of the selected metal.
The alloy forming ~articles and the base metal par-
ticles can be mixed together in any conventional manner, for
example by simple mechanical blending, with the alloy forming
I particles being present in an amount sufficient to cause
satisfactory densification upon sintering. However, it is
essential that the major component of the alloy forming par-
ticle-base metal particle mixture be base metal particles. In
¦ practice, if the base metal is titanium, it is preferred that
it be present in the resultant mixture in an amount ranging
from about 70 weight percent to about 95 weight percent with
exceptionally good results being achieved when the amount of
base metal ranges from 75 to 92 weight percent. ~hen the base
¦ metal is iron, these ranges are 70 to 98 and 85 to 98, respec-
tively.
¦ In mixing the alloy forming par~icles and base metal
particles it is essential that the weight ratio of particles
¦ be selec~ed in such a manner that the resultant powder is
¦ capable of being formed and then sintered to near theoretical
I density without the formation of any liquid phase. That is,
¦ depending on the specific co~position of the alloy forming
¦ particles, various amounts or ratios of alloy forming particles
to base metal particles can be utilized. This can~be deter-
¦ mined emperically with the criterion being that (a) the alloy
forming particles have a median particle size by weight of
~0 microns or less and (b) that the formed article be compac-
tible to a degree sufficient to yield upon sintering an article
having a density which is near theoretical.
I In forming the article of the invention no special
¦¦ procedures are required, exce~t tha~ the article must be com-
pacted to a degree sufficient to render the resultant article
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1177Z87
¦ capable of being sinterecl to near theoretical ~ensity. Both
Il conventional and isostatic molding techniques have been
¦l employed successfully. In practice, it has been found satis-
~ factory to fonm or compact the green article to a density of
I about 65 to about 90 percent of theoretical with excellent
¦ results being achieved when the green density ranges from
about 80 to about 90 percent of theoretical.
Once the desired articl~ is formed it can be sintered
in a conventional manner. The e.cact sintering temperature
employed will vary somewhat depending on thé composition and
amount of the various components which make up the article,
with the only requirement being that no liquid phase be formed
¦ during the sintering procedure.
¦ Typical physical properties of articles produced
¦ according to the present invention using titanium as the base
¦¦ metal material are: 135 ksi U.T.S., 125 ksi Y.S., 15% elonga-
tion, and 27% RoA~ (the product of Example II).
By way of contrast, the minimum properties specified
for a forged, wrought article, as set forth in ASTM B348,
¦ having a similar chemical composition are as follows 130 ~si
U.T.S., 120 ksi Y.S., 10% elongation, and 25% R.A.
The subject invention will now be described with
¦¦ reference to the follo~ing examples which are set forth for
I the purpose of illustrating the present invention and not for
25 ~ the purpose of limiting the same
Examp'e I
Consistent with prior art practice, a 3.7" by 0.58"
by 0060" sintered 90 titanium-6 aluminum-4 vanadium alloy
article was obtained as follows.
I Approximately 10 weight percent of a nominal 60 Al/
¦ 40 V alloy powder, -~0 mesh, was blended with 90 ~eight percent
-100 mesh Ti. This blend was then cGmpacted at 50 tsi in a
~1~77~87
rigid mold to a green density of about 88-90% of theoretical,
and the so-formed article was then vacuum sintered 4 hours at
2300F I 25 to a final density of about 94.5-96 5% of theore-
tical. This article exhibited the following physical properties:
115 ksi U.T.S., 108 ksi Y.S., 6% elongation, and 9% ~.A.
Example II
Two pounds of 60 Al/40 V were put into a Szegvari S-l
attritor along with about 40 pounds of 1/8" steel balls and
about 1/2 gallon of Freon ~trade mark for a fluorocarbon includ-
ing trichlorotrifluoroethane~. This Al/V alloy was attrited for
30 minutes, removed from the attritor and dried. The resultant
median particle siæe, as determined by Coulter counter, was
about 3.0 microns. This powder was added to -100 mesh Ti, and
processed and sintered as in Example I. The resultant sintered
density was 99.3-99.8% of theoretical.
Example III
The procedure of Example II was repeated, except
attrition time was 7 minutes with resulting median particle
size being approximately 10 microns. The resultant sintered
density was 99.0% of theoretical.
Example IV
The procedure of Example II was repeated, except 8
pounds of powder were attrited to a resultant median particle
size of about 6.5 microns. The resultant sintered density was
99.5% of theoretical.
Example V
The procedure of Example II was repeated, except dis-
tilled H20 was used instead of Freon in the attritor. The
resultant sintered density was 99.5-99.8% of theoretical.
Example VI
The procedure of Example II was repeated, except
sintering was at 2200F + 30F. The resultant sintered
density was 99.3-99.4% of theoretical.
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~177'Z87
Example VII
The procedure of Example II was repeated, except the
compaction pressure was about 30 tsi. The green density was
83-84% of theoretical. The sintered density ~as 99.0-99.1%
of theoretical.
Example VIII
The procedure of Example II was repeated, except
mullite balls were used, with the resultant median particle
size being less than 10 microns. The sintered density was
99.5% of theoretical.
Example IX
The procedure of Example II was repeated, except
-60 +200 mesh Ti was used. The resultant sintered density
was 99.4% of theoretical.
Example X
The procedure of Example I was repeated, except the
powder was compacted at 60,000 psi in a flexible mold in an
isostatic press to form a 3" diameter billet with a green
density of about 86-88% of theoretical. After sintering; the
billet had a density of 88-92% of theoretical.
Example XI
The procedure of Example X was repeated, except Al/V
powder prepared as in Example II was used. The resultant
sintered density of the 3" billet was 99. 8% of theoretical.
Example XII
A mixture of -325 mesh 50 Al/50 V alloy, -325 mesh Sn,
and -100 mesh Ti was formed to give a 86 Ti-6 Al-6 V-2 Sn alloy
powder. This mixture was processed as in Example I with the
resultant sintered density being about 96.6% of theoretical.
The physical properties of this article were: 131 ksi U.T.S.,
113 ksi Y.S., 6% elongation, and 10% R.A.
:~177~87
EX~PLE XIII
An alloy of 42 Al-42 V-16 Sn was attrited as des-
cribed in Example II. Subse~uently, this attrited mixture
was mixed with -100 mesh Ti and processed as described in
Example I to produce a composition 86 Ti - 6 Al - 6 V - 2 Sn
alloy. The resultant sintered density was approximately 99.0/O
of theoretical. The physical properties of this article were:
152 ksi U.T.S., 13~ ksi Y.S., 9% elongation and 16.7% R.A.
Illustrating the present invention with respect to
iron base sintered articles produced according to the present
invention are the following Examples XIV through XXII.
EXAMPLE XIV
Elemental silicon powder having a medium particle
size by weight of about 60 microns was blended with atomized
iron (-80 mesh Ancor* steel lOOOB, a standard steel powder com-
prising 99.2% Fe, 0.105% C, 0 018% S, 0.01% Pb and 0.22% Mn)
so as to obtain a resultant mixture of about 3 weight percent
silicon, with the remainder being iron. This mixture was
formed into the desired configuration and compacted at 50 tsi.
The so-formed had a green density o~ 6.6 g/cc. It was then
sintered for 2 hours at 2175F (in hydrogen). The resultant
sintered density was 6.94 g/cc, which is about 90.7% of
theoretical.
EXAMPLE XV
The procedure of Example XIVWas repeated, except the
silicon was attrited to a median particle size of 4 microns.
The green density of the article was 6.69 g/cc. The resultant
sintered density was 7.4 g/cc, which is 96.7% of theoretical.
EXAMPLE XVI
The procedure of Example XV was repeated, except
sufficient silicon was added to produce a mixture containing
5% silicon. The green density of the article was 6.29 g/cc.
The resultant sintered density was 7.17 g/cc, which is 95.0/O
of theoretical.
* trade mark
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1177~7
F.XAMPLF XVII
A ferrosilicon alloy (approximately 50% Fe-50~ Si) was
attrited about 30 minutes in Freon to a median particle size,
by weight, of about 2 microns. This material ~as then added to
iron ~Or the type described in Example XVI) in an amount suffl-
cient to produce a mixture containing 2% silicon, balance iron.
It was compacted to a gIeen density of 7 . o6 g/cc and then sintered
for 30 minutes at 2050F in hydrogen. The resultant sintered
density was 7 . 3 g/cc, which is 94.5% of theoretical.
EXAMPLE XVIII
Elemental molybdenum having a median particle size of
9 microns was mixed with iron (of the type described in
Example XIV) to produce three Fe-Mo blends containing, respec-
tively, 1, 5 and 10% Mo. After compacting to a green density
f 7 25g/cc 7.32 g/cc and 7.38 g/cc, respectively, and sintering for
4 hours at 2300F in hydrogen, the Fe-1% Mo articles exhibited
a density of 7.28 g/cc, the Fe-5% Mo article a density of 7.72 g~cc,
and the Fe-10% Mo article a density of 7.78 gJcc. These sintered
densities are about 92.3, 96.8 and 96.3% of theoretical,respectively.
EXHIBIT XIX
The procedure of Example XVIII was repeated, except
chromium having a median particle size of 5.6 microns was added
to iron to produce articles containing Fe-5% Cr, Fe-10% Cr, and
and Fe-15% Cr. The Fe-5Cr article had a green density of about 7.14
g/cc and a sintered density of about 7.15 gfcc. The Fe-10 Cr article
had a green density of 6.93 g/cc and a sintered density Or 7.38 g/cc.
The Fe-15% Cr article had a green density Or 6.75 g/cc and a sin-
tered density of 7.30 g/cc. These sintered densities are 91.3,
94.7 and 94.4% of theoretical, respectively.
1177~87
Example XX
The procedure of Example XIX was repeated, except
-100 mesh electrolytic chromium was used. The Fe-lOCr article
had a green density o~ 6.98 g/cc and a sintered density of
7.1 g/cc. The Fe-15% Cr had a green density of 6.90 g/cc and
a sintered density of 6.96 g/cc. These sintered densities are
91.1 and 89.7% of theoretical, respectively.
Example XXI
Inco 287 (material designation for a standard nickel
powder of International ~ickel) nickel powder (5-10 micron
particle size) was blended with iron powder (of the type
described in Example XIV) to produce a mixture containing 10%
~i. This mixture was compacted to a green density of 7.21 g/cc
and then sintered at 2300F for 4 hours in vacuum. The
sintered density was 7.49 g/cc. This density is 94% of
theoretical.
- Example XXII
The procedure of Example XXI was repeated, except
-200 +325 mesh nickel was used. The green density was 7.21
g/cc. There was essentially no change in density after sinter-
ing. This sintered density is 90.5% of theoretical.
The following Examples concern the use of zirconium
and nickel as base metals.
Example XXIII
A 60 Al/40 V alloy material was attrited for 30
minutes in Freon to a median particle size of 3 microns. This
material was then blended with -100 mesh zirconium to produce
a mixture containing, by weight, 90/0 zirconium, 6% aluminum
and 4% vanadium which mixture, in turn, was formed into the
desired shape and sintered at 2200F for 4 hours under vacuum
conditions (better than 1 micron). The green density was
4.58 g/cc with the sintered density being 5.90 g~cc, which is
98.8% of theoretical density.
1177~7
EX~PLF X~IV
A nickel-alumlnum (approximately 67% Ni - 33% Al) mater~al
was attrited to a median particle size of 3.0 microns. Thls ~Jas
added to -80 ~325 mesh nickel powder to produce a mixture containing
95.5 Ni-4.5 Al. The green article formed therefrom had a density
of 6.4 g/cc. After sintering at 2300F for 4 hours under vacuum
conditions, the resultant article had a density of about 7.1 g/cc.
EXAMPLE XXV
.
The procedure of Example XXIV was repeated, except
sufficient aluminum was added to produce a mixture which con-
tained 92.5~ Ni and 7.5% Al. The green density was 5.5 g/cc,
the sintered density was 6.5 g/cc.
The benefits of the present invention are apparent from
the foregoing illustrative Examples. For example, it is to be
noted that a conventionally produced powdered metal 90 T~- 6 Al- 4 V
alloy had a density of 94.5-96.5~ of theoretical (Example I)
whereas an essentially identical 90 Ti - 6 Al - 4 V alloy produced
by the technique of the present invention had a density of 99.3-99.8%
of theoretical (Example II). This dirference in percent of theoreti-
cal density is exceptionally significant because the article having
a density of 99.3-99.8% of theoretical exhibits chemical and physical
properties similar to a wrought alloy of the same composition whereas
the article having a density which was 94.5-g6.5% of theoretical
does not.
It should be noted that the particle sizes set forth
herein were determined by use of a Coulter counter and that the
particle size given is the median particle size by weight deter-
mined by the use of this apparatus.
Titanium base articles produced according to the
present invention are characterized by the fact that they
can contain relatively high amounts Or oxygen (up to about 0.30-
0.35 weight pe~cent) and still exhibit excellent ductility (an
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1 1177287
elongation of about 12~13 percent). Ihis is in contradistinc-
tion to cast or wrought articles of a si~ilar chemical composi-
¦ tion (having an oxygen content ranging from about C.30 to about
0.35 percent) which exhibit limited ductility (an elon~ation o~
1 about 5-6 percent) That is, titanium base articles produced
¦ according to the present invention get strength from the
presence of relatively high amounts of oxygen, but this does
not destroy their ductility. Such articles are obviously
superior to those produced by ~rior art techniques.
In the practice of the invention, it is preferred to
adjust the process para~eters such that the resultant sintered
density of the concerned powdered metal article is greater
¦ than about 97% of theoretical when the base metal particles are
¦ titanium and greater tllan about 93~o of theoretical when such
15 ¦¦ base metal particles are iron.
~ Jhile there have been described what are at present
considered to be the preferred embodiments of this invention,
! it will be obvious to those skilled in the art that various
¦ changes and ~odifications may be made therein without depart-
¦ ing from the invention, and it is~ therefore, aimed in the
appended claims to cover all such changes and modifications as
fall with~n the true spirit snd scope of the invention.
