Note: Descriptions are shown in the official language in which they were submitted.
~lS23~
FIELD OF IHE INVEl~TTION
_ _
This invention relates to metal alloys capable
of being rendered heat recoverable In another
aspect, it re]ates to heat recoverable metal articles.
5BACKGROUND OF THE INVE~ITION
Materials, both organic and metallic, capable of
being rendered heat recoverable are well known. An
article made from such materials can be deformed from
an original, heat-stable configuration to a second,
heat-unstable configuration. The article is said to
be heat recoverable for the reason that, upon the
application of heat, it can be caused to revert from
its heat-unstable configuration to its original, heat-
stable configuration.
15Among metals, for example certain alloys of
titanium and nickel, the ability to be rendered heat -
recoverable is a result of the fact that the metal
undergoes a reversible transformation from an
austenitic state to a martensitic state with changes
in temperature. An article made from such a metal,
for example a hollow sleeve, is easily deformed from
its original configuration to a new configuration when
cooled below the temperature at which the metal is
transformed from the austenitic state to the
~5 martensitic state.
This temperature, or temperature range, is
usually referred to as the Ms temperature. When an
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article thus deformed is warmed to the temperature
at which the metal reverts back to austenite,
referred to as the As temperature or range, the
deformed object will revert to its original configura-
tion. Thus, when the hollow sleeve referred to aboveis cooled to a temperature at which the metal becomes
- martensitic, it can be easily expanded to a larger
diameter, for example, by using a mandrel. If the
expanded sleeve is subsequently allowed to warm to
the temperature at which the metal reverts back to
its austenitic state, the sleeve will revert to its
original dimensions.
Ordinarily, such a sleeve would recover all or
substantially all of the deformation, i.e., it would
revert completely to its original dimensions,
However, it should be noted that under certain circum-
stances the article might be deformed to such an
extent that all of the deformation cannot be recovered
on heating. Alternatively, if something, e.~. an
intervening rigid substrate having a greater external
dimension than the internal pre-deformation dimensions
of the sleeve is interposed within the sleeve, the
sleeve cannot recover to its original dimensions.
Any dimensional change up to the maximum available
which an article can recover absent any intervening
substrate is called the heat recoverable strain
That portion of the heat recoverable strain which an
intervening substrate or other agency precludes
~L~5~359
recovery of, is referred to as unresolved recovery.
Finally, any deformation which exceeds the maximum
available heat recoverable strain is said to effect
non-recoverable strain.
That the titanium nickel alloys referred to
above possess the property of heat recoverability
has been known for many years. More recently for
example in the United States Patent No, 3,733,037
there is disclosed a method for producing a heat
recoverable article in which an alloy comprising
an inter-metallic compound that undergoes a
diffusionless transformation into a banded mar-
tensite upon cooling with or without working is
deformed after appropriate heat treatment. On
reheating the article, it at least partly resumes
its original shape. The alloys indicated as
preferred are copper based alloys which transform
into a martensite of pseudo-cubic symmetry including
the binary copper-zinc and copper-aluminium systems
and the ternary copper-aluminium-zinc, copper-zinc,
tin, copper-zinc-silicon, copper-aluminium-manganese,
copper-aluminium-iron and copper-aluminium-nickel
systems.
In U.S, Patent No. 3,783,037 (Col, 8, Ln. 63 et
seq,) it is noted in respect to the copper-aluminium-
zinc system that "... as there is progressive increase
in the aluminium content and decrease in the zinc
content ..., the maximum ductility that can be pro-
duced in the ternary alloys when deformed at or near
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the Ms decreases " It is noted that as the aluminium
level increàses, the maximum obtainable heat recover-
able strain decreases. ~or example, in alloys of the
compositions (by weight) 72% copper, 22% zinc and
6% aluminium and 75.7% copper, 17% zinc and 7,5%
aluminium, the maximum heat recoverable strain was
~ reported to be 4.8% and 4.0/O respectively.
The clear teaching of this patent is therefore
that the aluminium content of the alloy should be
reduced as much as possible to achieve maximum heat
recoverable strain. Unfortunately, I have found that,
unknown to the prior art, reducing the aluminium
content has a severe adverse effect on the stability
i.e., ability to avoid stress relaxation of the
15 article under conditions of unresolved recovery
Additionally, if one follows the teaching of the
prior art and avoids ternary alloys containing sig-
nificant quantities of aluminium, limitations are
encountered in hot working. In particular, low
energy input hot working requires avoidance of a
second phase in the structure. Unfortunately, low
aluminium content alloys must be maintained at very
high temperatures, e.g. at least in excess of 650 C
to be in the one-phase beta condition,the phase
25 desired for hot workability. At such high tempera-
tures, tool life is shortened and the avoidance of
coarse grain size in the product is difficult.
If a heat recoverable article is recovered onto
a substrate such that the substrate prevents ~ull
~L~S~359
recovery of the article to its original configuration,
i.e., under conditions of unresolved recovery, then
the residual strain results in a stress in the article.
I have now discovered that all copper alloy com-
positions having the ~-brass structure are more or
less unstable if complete recovery is prevented.
Thus, I find that at moderate temperatures such as
would typically be seen during service, for example,
in hydraulic or electrical applications in aircraft,
the residual stress in incompletely recovered articles
will decay steadily to zero such that after a certain
period of time the recovered object, for example, a
sleeve recovered about a substrate, can be easily
removed from the substrate.
15Inasmuch as heat recoverable metals find their
greatest utility in applications where they exert a ~ -
high degree of compressive or other form of stress
relaxation process described above is a considerable
impediment to the wide spread use of these metals.
For examples, parts made from the binary alloys and
the specific ternary alloys described in above
mentioned U.S. Patent 3,783,037, when prevented from
recovering completely to an initial configuration
under conditions of about 4.0/0 unresolved recovery,
exhibit complete stress relaxation at 125 C, in less
than 1,000 hours ~equivalent to relaxation within
100 hours at 150 C) so that they are essentially
useless in many applications.
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Therefore, although a wide variety of ~-brass
type copper alloy compositions capable of being
rendered heat recoverable are known to the prior
art, those compositions possess serious short-
comings severely limiting their use.
Accordingly, one object of this invention isto provide improved ~-brass type alloys.
Another object of this invention is to provide
heat recoverable articles of ~-brass type alloys
that will exhibit long term stress stability when
recovered under conditions so that a degree of
unresolved recovery remains.
Yet another object of this invention is to
provide heat recoverable articles of ~-brass type ~:
15 alloys that will preferably maintain a stress for ` ~-
greater than 1,000 hours at125C or for greater than
100 hours at 150C.
The present invention provides certain ternary
alloys of copper, aluminium and zinc which manifest
good ductility and are easily worked by hot working
techniques in additi~n to exhibiting excellent long
;term stress stability. Both ~ood ductility and hot
workabilïty are requisite ~for commercially useful
materials. Heat recoverable articles made from the
alloys of the present invention exhibit long term
stress stability even when recovered under circum
stances such that a level of unresolved recovery
remains
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The ternary alloys of the present invention fall
on or near t~e line formed by the copper-aluminium,
beta (alpha + gamma) eutectoid as it crosses the
ternary field. This will be referred to hereinafter
as the eutectoid line.
The copper-aluminium zinc ternary alloys fall
within the area defined in a ternary diagram by the
points:
A. 78.3% Cu 9. 7% Al 12 Zn
10B. 75~1% Cu 7~5% Al 17~4% Zn
C, 67 % Cu 4,2~/o Al 28.8% Zn
D. 72~6% Cu 7.9% Al 19.5% Zn
The present invention will be described in more
detail, by way of example only, with reference to the -
15 accompanying drawings, in which ,
Figure I is a ternary diagram on which is shown .
the area encompassing the copper,aluminium, zinc
ternary alloys of the present invention, wherein
line XY is the eutectoid line,
Figure II is a ternary diagram for alloys of
copper, aluminium and zinc showing the coincidence
of the eutectoid line XY and Ms (copper is not
specifically shown but, of course, copper + aluminium
+ zinc = 100%), the alloys in question being quenched
from 650C into water at 20C.
As previously discussed we have unexpectedly
discovered that articles formed from the ~-brass
type compositions known to the prior art suffer the
serious disadvantage of being unstable with respect
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to the maintenance of stress when the article has
been exposed to modestly elevated temperature for
extended periods of time under conditions of
unresolved recovery. This phenomenon manifests
itself in actual use situations when an article
made from such an alloy is deformed when in its
martensitic state to thereby render it heat
recoverable, and then allowed to recover by warrning
it to a temperature at which the alloy reverts to
austenite in a manner that precludes the article
from completely recovering to its original con-
figuration and thereafter exposed to ternperatures
above about 80C. That portion of the strain which
remains in the article after this partial recovery
15 is, as already indicated, referred to as unresolved ~.
recovery.
We have discovered that articles made from
~-brass type compositions known to the prior art are
unstable with respect to maintaining adequate stress
levels, i.e., the stress gradually decays to zero
the rate of decay increasing with temperature.
Also we have discovered that for copper,
aluminiurn and zinc ternary alloys, the tendency
towards stress instability is composition dependent
and that the most sta~le alloys are those with a com-
position lying on or near the eutectoid line.
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In particular, it is only those alloys falling
within the compositional ranges disclosed and claimed
herein that do not undergo substantially complete
stress relaxation over a period of 1,000 hours or
less at 125C (or the equivalent 100 hours at 150C).
The novel ternary alloys which are the subject of the
instant invention all have a composition falling or
or near the eutectoid line, as defined herein above.
Referring to Figure I, there is shown a ternary
diagram for alloys of copper,aluminium and zinc on which
XY is the eutectoid line for alloys of those elements.
For these alloys also there is only one composition
on the eutectoid line, the line of maximum stress ~-
stability, for any given Ms temperature. For example,
the alloy having an Ms of ~50 C contains about 7%
aluminium.
By adjusting the relative amounts of the
individual components, other alloys of the same Ms
temperature can be obtained. Usually, however,
significant variance from the eutectoid will cause
some diminution in desirable properties. For
example with reference to Figure I it is seen that
increasing the aluminium content to l~/o and adjusting
the amounts of copper and zinc to achieve an Ms of
-50 C also results in moving the alloy to the gamma
side of the eutectoid. Relatively little stability
is lost in either instance as increasing aluminium
content offsets the effect on stability of moving
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away from the eutectoid line. However, use of such
alloys requires great care if precipitation of the
gamma phase is to be avoided during fabricating and
heat treatment. Also, the temperature to which the
alloy must be raised during working to prevent gamma
precipitation may lead to undesirable grain growth
which adversely affects ductility.
By contrast, if the aluminium level is lowered
so that the alloy falls on the alpha side of the
eutectoid, working is easier. However, the stress
stability of the alloy is reduced because of the
cumulative effect of 1) moving away from the
eutectoid and 2) decreasing the aluminium level.
Thus, the desirable effect o increasing the alpha
content in the alloy to allow easier working for
those applications in which articles must be made
by cold working must be weighed against the loss
of stress stability.
Ternary alloys of copper, aluminium and zinc
are not novel in general Furthermore, it is
known (e.g., U S. Patent 3,783,037) that certain
ternary alloys of copper, aluminium and zinc can
be rendered heat recoverable. However, all the
alloys specifically reported by the prior art fall
outside the composition range of the instantly
claimed alloys and hence suffer from fundamental
shortcomings ~including stability, as heretofore
discussed) which precludes their use under many
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circumstances A consideration of the boundary
lines of the claimed compositional areas indicates
why the instantly claimed alloys are uniquely
superior. These boundary parameters are, of course,
unknown to the prior art. Additionally, the
location of the eutectoid line and its significance
to alloy stability are completely unknown to the
prior art.
The claimed copper, aluminium and zinc ternary
io alloys are defined by the area encompassed by the
lines AB, BC, CD, DA on Figure I. Compositions to
the left of line DA must be heated to temperatures
in excess of 650C to preclude formation of the
~-phase of the alloy. Again presence of the
~-phase results in an alloy of such limited
ductility as to effectively preclude its being
cold formed into useful articles. Conversely,
heating above 650C is undesirable because it
fosters excessive grain growth, again affording
poor ductility. Finally, I have found that for
this system, alloys of a composition to the right
of line BC of Figure I cannot meet the 1,000 hours
at 125C stability requirements.
Both types of alloys were quenched from 650C
into water at 20 C. In Figure I, lines AB and CD
are the 0 C and-200 C Ms lines, respectively. An
alloy with an Ms of less than 'a -200C has limited
use since it is impractical to store deformed
~ILSZ359
components at lower temperatures. As is known,
heat recoverable metallic articles, e.g., couplings,
are stored in the deformed conditions e.g., in
liquid nitrogen and recovered on warming or being
warmed through their Ms Conversely, we have found
that for both these alloy systems an Ms in excess
of 0C is imcompatible with a stability of at least
1,000 hours at 125C which is equivalent to 100
hours at 150C. Stability of at least 1,000 hours
at 125C is a requirement of electrical connectors
under U.S. Government Spec. MIL-C-23353A Paragraph
4.7.14. It is thus apparent that only those ternary
alloys falling within the composition range defined
by the perimeter ABCD of Figure I possess the unique
15 combination of heat recoverability, a useful recovery -;
temperature (Ms), worthw.lile ductility, and adequate ~ -
stability.
As can be seen from Figure I, we have found that
the eutectoid line runs through the claimed areas.
Alloys of a composition falling on or almost on this
line are of particularly good stability. As used in
the instant specification and the appended claims,
the term "eutectoid composition" connotes an alloy
whose composition falls either precisely on the
eutectoid line or wherein none of the three metal
components of the alloy is present in an amount
which differs by more than 1.0 wt~% from the
percentage of that metal present in the composition
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corresponding precisely to the eutectoid. It should,
of course, be noted that in all instances only
ternary compositions ~alling within the above defined
area ABCD are contemplated by the instant invention
5 and that in some instances compositions wherein there
is less than l.~/o variation of one or more of the
metals from the precise eutectoid composition will
fall outside such area. Inasmuch as the boundary
lines of the claimed area represent other critical
parameters, such compositions, even though eutectoid,
have other shortcomings and are not within the scope
of the present invention.
The ~ollowing Example illustrates the invention.
EXAMPLE 1
lS The following are examples of alloys according
to the present invention having a long term stress
stability at 125 C for at least 1,000 hours or at
least 100 hours at 150 C. Each alloy was- quenched
into water at 20 C from 650 C A 311 long sample
was cooled to below the Ms temperature for the alloy
and deformed 4.25% by being bent into a U-shape about
a rod. The sample was heated to either 125C or
150C while being held in the deformed shape.
Periodically the specimen was cooled to room tem-
perature and the strai~ was then removed. When thiswas done, the amount of springback, i.e., movement
towards the original configuration, was measured.
The specimen was then replaced in the constra~t and
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held for a further period of time at either 125 C
or 150C, When upon removal of the constraint no
springback was observed, the time that it took to
reach that condition was taken as the stability
limit.
Copper-Aluminium-Zinc-Ternary Alloys
. .. . _ _
Sample Alloy Composition Ms Lifetime
Cu Al Zn at 150C
. .
1 75.5 7.5 17 +27C 15 hours
2 72 6 22 -60C 65 hours
. 3 71 6 23 -127C 210 hours
4 70 6 24 -196C 270 hours ~.
74 7 19 -28C 120 hours ,~ ~:
6 74 8 18 +86C ;15 hours I:
69 5 26 156C 250 hours
As is apparent, Examples 1, 2 and 6 are directed
towards compositions outside the scope of this
invention.
All the alloys of the instant invention,
possessing as they do outstanding combinations of
properties as hereinbefore described, are useful in
many and diverse applications. Thus, they may be
used to provide hydraulic couplings and electronic
connectors as described in United States Patent
No, 3,740,839,
~3L5Z3~9
The good workability of these alloys renders
them particularly appropriate for use in extruded
products Thus they may be readily fabricated into
wire, rod and various complex profiles They may be
readily stamped, swaged and formed by techniques well
known to those skilled in the art.
Attention is drawn to United States Patents
4,146,392 and 4,166,739 which describes beta brass
type ternary alloys of copper, aluminium and
manganese, and quaternary alloys of copper,
aluminium, zinc and manganese
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