Note: Descriptions are shown in the official language in which they were submitted.
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D.P.C.(Me) ~838/6859
COPPER-NICKEL-TIN-COBALT SPI~ODAL ALLOY
_
This is a divisional application of Serial No. 487,379
filed July 24, 19~5.
Background of the Invention
The present invention relates to copper-base spinodal
alloys and, in particular, copper-base spinodal alloys also
containing nickel and tin.
Ternary copper-nickel-tin spinodal alloys are known in
the metallurgical arts. As one example, U.S. Patent 4,373,970
discloses spinodal alloys containing from about 5 to 35 welght
percent nickel, from about 7 to 13 weight percent tin, and the
balance copper. The alloys disclosed by this prior art patent
exhibit in the age hardened spinodally decomposed state a highly
desirable combination of mechanical and electrical properties,
i.e. good strength and good electrical conductivity, and thus have
valuable utility as a material of construction for articles of
manufactu~e such as electrical connectors and relay elements. One
particular ternary spinodal alloy composi-tion falling within the
scope of the disclosure of U.S. Patent 4,373,970 contains about 15
weight percent nickel and about 8 weight percent tin and is sold
commercially under the trade name of Pfinodal ~trademark of Pfizer
Inc., New York, N~). This alloy composition combines a sufficient
strength for many commercial applications with a good ductility
and an excellent electrical conductivity. When greater strength
properties than those afforded by the Cu-15Ni-8Sn alloy composi-
tion are required for certain other applications, this can be
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realized hy raising the nickel and tin levels within the ranges
for -those elements disclosed in U.S. Patent 4,373,970. However,
thls increased strength tends to be achieved at the expense of the
valuable ductility, formability and electrical conductivity
properties of the age hardened spinodally decomposed alloy.
Other copper base spinodal alloys containing nickel and
tin are disc]osed in U.S. Patents 3,937,638; 4,012,240; 4,090,890;
4,130,~21; 4,1~2,918, 4,260,432 and 4,406,712, and U.S. Reissue
Patent 31,180 (a reissue of U.S. Patent 4,052,20~).
Quaternary copper-nickel~tin-cobalt alloys are disclosed
in U.~. Patents 3,940,290 and 3,953,249. These al]oys contain
only 1.5% to 3.3~ -tin and thus do not appear to be spinoda]
alloys. Furthermore, these prior art patents -teach that the
cobalt level in -the alloy should not exceed 3% in order to mini-
mize impairment of ductility and hot workability.
Japanese Published Patent Application No. 5942/81
(published January 22, 1981) discloses a series o~ cast copper-
base quaternary spinodal alloys containing 9 wt. % nickel and 6
wt. % tin, including, inter alia, alloys containing 0.5, 0.8 and
2.0 wt~ % cobalt, respectively, as the quaternary element.
It has now been discovered that the replacement of a
portion of the weight percentage of nickel in a copper-nickel-tin
spinodal alloy with an approximately equal weight percentage of
cobalt gives rise to improved ductility, formability (~
bendability) and electrical conductivity in the age hardened
spinodally decomposed state without substantial diminishment of
strength properties in that state.
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Thus, the parent application is directed to a copper
base spinodal alloy consisting essentially of from about 5 to
about 30 percent by weight nickel, from ahout 4 to about 13 per-
cent by weight tin, from about 3.5 to about 7 percent by weight
cobalt and the balance copper, with the sum of the nickel an~
cobalt contents being no more than 35 percent by weight of the
alloy.
Of particular interest is an alloy of the inven-tion
wherein the tin content is from about 8.5 percent by weight to
about 13 percent by weight and the sum of the nickel and cobalt
contents is at least 20 percent by weight. This alloy affords
high strength properties while maintaining satisfactory ductility,
formability and electrical conductivity properties for a wide
variety oE applications.
This divisional application is directed to a novel
copper base spinodal alloy prepared by powder metallurgy consist-
ing essentially of from about 5 to about 30 percent by weigh-t
nickel, from about 4 to about 13 percent by weigh-t tin, from about
0.5 to about 3.5 percent by weight cobalt and the balance copp~r.
This alloy af-fords an excellent combination of strength, ductili-
ty, formability ~e.g. bendability) and electrical conductivity
properties and has an unaged microstructure characterized by an
equiaxed grain structure of substantially all alpha, face-
centered-cubic phase with a substantially uniEorm dispersed
concentration of tin and a substantial absence of tin segrega-
tion.
This divisional application is further directed to a
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powder metallurgical process for preparing the novel alloy of the
invention.
As used herein the term "spinodal a:LI.oy" refers to an
alloy whose chemical composition is such that it is capable of
undergoing spinodal decomposition. An alloy that has already
undergone spinodal decomposition is referred to as an "age
hardened spinodally decomposed alloy", a "spinodal hardened
alloy", or the like. Thus, the term "spinodal alloy" refers to
alloy chemistry rather than alloy physical state and a "spinodal
alloy" may or may not be at any particular time in an "age
hardened spinodally decomposed" state.
The spinodal alloy of the present invention consists
essentially of copper, nickel, tin and cobalt. The alloy may
optionally contain small amounts of additional elements as
desired, ~ iron, maynesium, manganese, molyb~enum, niobium,
tantalum, vanadium, aluminum, chromium, silicon, zinc and zirco-
nium, as long as the basic and novel characteristics of the alloy
are not materially affected in an adverse manner thereby.
The spinodal decomposition of the alloy is an age
hardening operation carried out for at least about 15 seconds at a
temperature of from about 500F to about 1000F. In any parti-
cular case the upper limit of this temperature range is primarily
established by the chemical composition of the alloy while the
lower limlt of the range is primarily established by the nature
and extent of working of the alloy performed immediately prior to
the age hardening. Spinodal decomposition is characterized by the
formation of a two-phase al.loy m.icrostructure i.n which the second
phase is Einely dispersed throughout the first phase. Optimum
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micros-tructures are ohtained when the alloy i9 annealed and
rapidly cooled before it is age hardened.
The spinodal alloy of the present inventlon may be
prepared by a variety of known techniques involving, for example,
sintering a body of compacted alloy powder (powder metal]urgy)
Because the use of casting processes tends to result in the
presence of substantial tin segregation at grain boundaries in the
spinodally decomposed product, the use of powder metallurgical
techniques is preferred.
A part;cularly preferred powder metallurgical process
for preparing an alloy of the present invention is the one set I
forth tfor -the Cu-Ni-Sn ternary system) in U.S. Patent 4,373,970.
Reference is made to that patent for a detailed description of
this process, including guidelines for the proper selection of
various operational parameters. It should be pointed out that
this process may be readily adapted to prepare an alloy of the
present invention in a wide variety of three-dimensional forms and
not only in the form of a strip.
According to the process of U.S. Patent 4,373,970, as
adapted to prepare the quaternary alloy of the present invention,
an alloy powder containing appropriate proportions of copper,
nickel, tin and cobalt is compacted, preferably to at least about
twice its original uncompac-ted densi-ty, to form a green body
having structural integrity and sufficient porosity to be penetra-
ted by a reducing atmosphere, and preferably, a compacted density
of from about 70 to 95 percent of the theoretical density. The
green body is sintered in the reducing atmosphere, preferably for
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at least one minute at a temperature of from about 1~00F to about
1900F, more preferably from about 1600F t.o about 1700F. The
sintered body is then cooled at a rate, typically at least about
200F per minute until the age hardening temperature range of the
alloy has been traversed, such -that age hardening and embrittle-
ment are prevented. As used herein, the term "alloy powder"
inc]udes both blended elemental powders and prealloyed powders, as
well as mixtures thereof.
Although the sintered body can be subjected directly to
age hardening spinodal decomposition, it is preferred to first
subject the alloy body to working (with cold working preferred to
hot working) and annealing. Thus, prior to age hardening, the
sintered body may be bene~icially cold worked to approach the
theoretical density and then annealed, preferably for at least
about 15 seconds at a temperature of from about 1500F to about
1700F,and rapidly quenched after annealing at a rate, typically
at least about 100F per second, sufficient to retain substantial-
ly all alpha phase. If desired, the sintered alloy body may be
cold worked in stages with intermediate anneal and rapid cooling
between said stages. Also, the alloy body may be cold worked
after the final anneal/cooling and immediately before age harden-
ing in such a manner as to achieve a cross-sectional area reduc-
tion of at least about 5 percent, more preferably at least about
15 percent.
The dura-tion of the age hardening spinodal decomposition
operation should be carefully selected and controlled. The age
hardening process proceeds in sequence through three time periods,
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i.e., the underaged time range, the peak strength aging time range
and, finally, the overaged time range. The duration oE these
three phases will of course vary as the age hardening tempera-ture
is varied, but the same general pattern prevaîls. The strength
properties of the age hardenecl spinodally decomposed alloy are
highest in the peak strength aging range and lower in the under-
aged and overaged ranges, while the ductility of the alloy tends
to vary in the opposite manner (i.e. lowest in the peak strength
aging range). On the other hand, the electrical conductivity of
the alloy tends to continuously increase with the time o-f age
hardening. The optimum age hardening time will depend upon the
combination of electrical and mechanical properties sought for the
alloy being prepared, but will usually be within the pealc strength
aging range and often, especially when a high electrical ccnauc-
tivity is of particular importance, within the la~ter half of that
range.
For purposes of definition, the peak strength aging time
for a particular alloy at a particular age hardening temperature
is that precise time of age hardening at which the yield stress of
the spinodal hardened alloy is at its maximum value. The follow-
ing examples are not to be construed as limiting the invention.
EXAMP1ES 1 TO 6
Elemental powders were blended in the proportions
indicated in Table I for the six examples and then compacted into
3 in. by 0.5 in. by 0.125 in. rectangular bars at about 85 percent
of theoretical density. Each bar was sintered in a dissociated
ammonia atmosphere for about 60 minutes at 1625F and then about
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30 minutes at 1750F, cooled rapidly while still under the reduc-
ing atmosphere to prevent age hardening and embrittlement, cold
rolled in at least four steps (with intermittent homogenization or
anneal in the reducing atmosphere) to a 0.01 i.nch thickness, solu-
tion annealed for 5 minutes at 1650F in the reducing atmosphere
and quenched rapidly in oil. Each bar was then age hardened in
the ambient atmosphere at the time/tempera-ture conditions set
forth in Table I, with the age hardening time in each example
corresponding approximately to the peak strength aging time at the
indicated age hardening temperature, and
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then cooled to ambient temperature. The yield stresS,
ultimate tensile ~t~ess~ percent elongation at break~and
electrical conductivlty of the re~ulting ~ix spinodally
decomposed 3amples were measured and are al~o set forth
S in Table I.
The data of Table I clear1y reveal that the
replacement of a minor portiQn of nickel in a copper-
nick~l-tin age hardened spinodally decomposcd alloy with
an egual weight of cobalt provides a means of sub-
stantially increasing thc ductility and electricalconductivity of ~he alloy without substantially altering
the strength properties of the alloy.
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