Note: Descriptions are shown in the official language in which they were submitted.
6~1)(3~5
Background of the Invention
The present inventlon concerns a method of bonding
together two or more powder metal members or s~ructures. The method
of the invention is accomplished by fabricating one powder metal
member from an iron base composition which contains copper so as to
cause it to expand upon sintering and another powder metal member
from an iron base compositlon which contains nickel so as to cause
it to shrink upon sin~ering. These members are configured such that
they engage each other in an interference fit relationshlp and upon
sintering become metallurgically bonded together~
Powder metallurgy is a technique which is often utilized
to fabricate intrically~shaped articles. Its advantages over con-
ventional metal fabrlcating techniques are well known. However,
difficulty is often experienced when one attempts to permanently
bond two powder metal members or articles together.
In the past, to accomplish the bonding of sintered powder
metal artlcles together such techniques as brazing, molten metal
infiltration and simple mechanical bonding employing interference
fit arrangement have all been utilized with varying degrees of suc-
cessO
However, brazing techniques are undesirable due to the
fact that they require multiple heat treatments and the use of ex
pensive brazing materials.
Likewise, molten metal infiltration techniques suffer from
a plurality of problems. The main problem is that the bond achieved
is usually imperfect and the technique is generally limited to ~oin-
ing or bonding together shapes having a limited degree of com~
plexity. In addition, this technique suffers from the fact that the
process in itself and the material utilized therein are relatively
expensive and, perhaps most i~portantly, that it is difficult to
control the size of the final structure.
The use of an interference Eit arrangement to bond powder
metal articles together has met with some limited success. ~owever,
this technique is deficient in that mechanical ~oints are unreliable
as they have a tendency to separate when sub~ect to vibrations and
0~36~i
can only be used on si~iple configuratlon6.
Accordlngly, it 18 the principal ob~ect of the present
invention to provide a method oE bonding together two or more powder
metal members or article~ regardless of their degree of complexity
so as to produce a resultant structure which i8 metallurgically
bonded together.
Another obJect of the invention i5 to provide a method of
bondlng together t~o or more powder metal members or artlcles 80 as
to obtain an integral bond betwelen the respective membera or
articl~s in an economic and efficient manner under production con-
ditions.
These and other ob~ects of the invention will become
apparent to those skilled in the art from a reading of the followlng
speclfication and claim3.
Summary of the Invention
In one aspect, the present in~ention concerns a method of
bonding together two or more powdered metal member~ compr~sing:
formin~ a first iron base powder metal member havlng the desired
configuration, with the first iron base powder metal member contaln-
ing a sufficlent amount of copper to cause it to expand upon sinter-
lng; formlng a second iron base powder metal member into a con-
figuration such that lt is adapted to engage in an lnterference fit
relationsh~p at least part of the flrst iron base powder metal
member, with the second iron base powder metal member contalning a
sufficient amount of nickel to cause lt to shrlnk upon sinterlng;
bringing the first iron base powder metal member into contact with
the second iron base powder metal member in such a manner that when
the members are sub~ected to a slnterlng treatment the first member
expands against the second member which, in turn, shrinks against
said first member; and heating the members at a sintering tem-
perature which is sufficient to cause the members to become
metallurgically bonded together.
In another a~pect, the present lnvention concerns a
~intered powdered metal article which is obtained by a process which
comprises: forming a first iron base powder metal member having the
3~i
desired c.onfiguration, wlth the first iron base ~powder metal member
containing a sufficlent amount oE copper to cause it to expand upon
sintering, forming a second iron base powder metal member into a
configuration such that it i8 adapted to engage in an interference
fit relationship at least part oE the first iron base powder metal
member, with the second -lron base powder metal member containing a
sufficient amount of nickel to cause it to shrlnk upon sintering;
bringing the flrst iron base po~der metal member lnto contact ~/ith
the second iron base powder metal member in 9uch a manner that when
the members are sub~ected to a sintering treatment the Eirst member
expands against the second member whlch, ln turn, shrinks against
the first member; and heating the members at a sinterlng temperature
whlch ls suffi.cient to cause the members to become metallurglcally
bonded together.
Brief Description of the Drawings
The lnvention may take physl.cal form lrl certaln parts and
arrangement of parts, the preferred embodiments which will be de-
scrlbed in detall in the speclflcation and lllustrated ln the
accompanying drawings whlch form a part hereof and wherein:
FIGURE l is a plan view of a bearing assembly produced
accordlng to the subject invention;
FIGURE 2 is a cross-sectional view talcen along lines 2-2
in FIGURE l; and
FIGURE 3 is a photomlcrograph of the bond area formed be-
tween the first powder metal member and the second powder metal
member.
Deta_led Description of the Preferred Embodlment of the Inventlon
Referring now to the drawlngs whereln the showlngs are for
the purpose of lllustrating the preferred embodiment of the inven-
tion only and not for the purpose of limiting the same, Figures 1
and 2 show a bearing assembly generally designated A which consists
of a first or inner powder member 10 and a second or outer powder
metal member 12.
The inner member lO is somewhat oval in shape and has an
upper surface 14 and a lower surface 16. An aperture 18 is formed
in the inner member 10 and is adapted to receive or support a rotat-
able member (not shown).
The outer member 12 is generally rectangular in cross-
sectional configuration and has opposed sides 20, 22 and 24, 26 and
is provided with a first outwardly extending f]ange 28 and a second
outwardly extending flang~ 30. An aperture 32 is provided in the
outer member 12 which is configured such that it is adapted to re-
ceive in an interference fit relationship i~mer member 10.
In the practice of the lpresent invention9 the first iron
base powder metal member or structure is fashioned to the desired
configuration by conventional powder metal technlques from a mixture
of lron base powder9 copper powder and powdered carbon, with the
copper being present in an amount sufficient to cause the resultant
member to expand upon sintering. In this regard, excellent results
are achieved when the first iron base powder metal member is
fabricated from a composition which contains from about 93 to about
96 weight percent iron, from about 3.0 to about 6.0 weight percent
copper, and from about 0.5 to about 1.0 weight percent carbonO The
technlques utilized to form such an article are well known in the
art and as they do not form a part of the present invention will not
be discussed herein in detailO All that is critical is that the
first iron base powder metal article be fabricated from an iron base
composition which contains sufficient amount of copper to cause it
to expand upon sintering.
The second iron base powder metal member or structure is,
likewise, fabricated by conventional powder metal techniques into a
configuration such that it is adapted to engage in an interference
fit relationship at least part of the first iron base powder metal
member. The second iron base powder metal article is ~abricated
from a mixture of iron base powder, nickel powder and carbon powder,
with the nickel powder being present in an amount sufficient to
cause the resultant member to shrink upon sintering. In this re-
gard, excellent results are achieved when the second iron base
powder metal member is fabricated from a composition which contains
from about 95 to about 9~.5 weight percent iron, from about 2.0 to
about 4.0 weight percent nickel and from about 0.5 to about l.0
weight percene carbon. As the technique utilized to Fo~m the second
iron base powder metal member i9 well known in the art and does not
form a part of the sub~ect lnvention, it will not be discussed here-
in in detail.
In practice, a Eirst iron base powder metal member is
fabricated from a composition of the type described above with a
typical configuration being that shown in the drawings. This powder
metal member is then brought into contact in an interference fit re-
lationship with a second iron base powder metal member, of the com-
posltion described above, in such a manner that the respective
members are mechanically bonded together.
The so-arranged assembly is then subjected to a sintering
treatment in a reducing gas atmosphere at a temperature preferably
in the range of from about ~,000-2,150~F. ~owever, the exact
sintering temperature utilized is not critical except it is required
that it be of sufficient magnitude so as to cause copper to diffuse
into the second or outer member to cause both the first or inner and
second or outer members to become metallurgically bonded together by
the formation of a complex iron-copper-nickel-carbon a]loy at the
interface therebetween. It is thought that this unique metallurgi-
cal bond is caused by the diffusion of copper in~o the outer member.
This diffusion is assisted by ehe presence of carbon, which pre~
ferably is originally added to the mixture of powdered metals as
graphite. Durlng the sintering treatment, the graphite goes into
solution ln both the inner and outer members. The copper diffuses
through the wall of the outer member at a temperature of about
2,050F and alloys with the iron and nickel present creating a
material which has a higher melting point than 2,050F. As the
sintering temperature utilized is lower than 2,050F, this material
freezes resulting in a metallurgically diffused ~oint which has been
found to be stronger than the individual strength of both the inner
and outer materials themselves. Afeer slntering, the actual ~oint
area cannot l~e seen by using no~lal viewing methods. However, the
bond which is formed between the respective members, whlch are
3~
~oined according to the teachlngs of the present invention, is
clearly observable ln Figure 3 which is a photomicrograph having a
magnification of 50 times. In the photomicrograph, the reference
character D shows the structure of the inner member and reference
character E shows the copperlcarbon diffuslon area zone of the outer
member generally identified F.
The bearing assembly shown in Figures 1 and 2 was
fabricated as follows:
The outer member was formed in a suitable mold from a com-
position which contained about 97.5 weight percent iron, 200 weight
percent nickel and 0.5 weight percent carbon. The particle size of
the iron was -~0 mesh (U.S. Sieve). The particle size of the nickel
was in the range of 4-7 microns. The particle si~e of the carbon
was about 2 microns. These materia~s were mixed and poured into a
suitable mold and compacted at a pressure oE about 30 T.S.I.
The inner member was formed from a mixture of about 94.25
weight percent iron, 5.0 weight percent copper and 0.75 weight per-
cent carbon. The mi~ture was poured into a suitable mold and com-
pacted at a pressure of about 30 T.S.I.
The inner member was positioned ln an interference fit re-
lationship in aperture 32 of outer member 12. This structure was
then placed in a furnace and heated in an endothermic atmosph~re to
a temperature of about 29050F for a period of about 0.2 hours.
The resultant structure was then removed from the sin~er-
ing furnace and it was observed that the inner member was metal-
lurgically bonded to the outer member.
From the foregoing, it is obvious that the technique of
the present invention makes it possible to fabricate complicated
powder metal articles from a plurality of parts in an efficient and
economical manner. In production, the technique of the present
invention results in significant energy and cost savings.
While there have been described herein what are at present
considered to be the preferred embodiments of this invention9 it
will be apparent to those skilled in the art that various changes
and modifications may be made therein without departing from the
inverltion, and it i8, there~Eo~e~ intended the appended claim~ to
cover all s~ch changes ancl ~odificatiorls as fall within the spirit
and scope of the invention.
