Note: Descriptions are shown in the official language in which they were submitted.
3!3~62
FIELD OF THE INVENTION
This invention relates to metal alloys capable
of being rendered heat recoverable. In another aspect,
it relates to heat recoverable metal articles.
BACKGROUND OF THE I~VENTION
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.
Among 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 transfermation 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 martensitic state.
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'~
~a3~
This temperature, or temperature range, is usually referred
to as the M temperature. When an 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
confi-guration. Thus, when the hollow sleeve referred to
above is 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 circumstances the article
might be deformed to such an extend that all of the
deformation cannot be recovered on heating. Alternatively,
if something, e.g. an intervening rigid substrate having
a greater external dimension than the internal pre-
deformation dimensions of the sleeve is int~rposed 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 inter-
vening substrate is called the heat recoverable strain.
That portion of the heat recoverable strain which an
intervening substrate or other agency precludes recovery
of, is referred to as unresolved recovery. Finally, any
deformation which exceeds the maximum available heat re-
coverable strain is said to effect non-recoverable strain.
3~6X:
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 ~o. 3,783,037 there is disclosed
a method for producing a heat recoverable article in
which an alloy comprising an inter-metallic compound that
undergoes a diffusionless transormation into a banded
martensite 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 increasein the aluminium content and decrease in the zinc content
..., the maximum ductility that can be produced in the
ternary alloys when deformed at or near the Ms decreases."
It is noted that as the aluminium level increases, the
maximum obtainable heat recoverable strain decreases. For
example, in alloys of the compositions (by weight) 72%
copper, 22% zinc and 6% aluminium and 75.7% copper, 17%
zinc and 7.5% aluminiu, the maximum heat recoverable strain
was reported to be 4.8% and 4.0% 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 av~ d
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3~
; stress relaxation of the article under conditions of
unresolved recovery. Additionally, if one follows the
teaching of the prior art and avoids ternary alloys con-
taining significant 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 650C, to be in the one-phase
beta condition the phase desired for hot workability. At
such high temperatures, 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 subst~ate such that the substrate pre~ents full 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 compositions 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 applic-
ations 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.
Inasmuch as heat recoverable metals find their
greatest utility in applications in applications where
they exert a high degree of compressive or other form of
stress relaxation process described above is a considerable
impedement to the wide spread use of these metals. For
example, parts made from the binary alloys and the specific
34~
ternary alloys described in above mentioned U.S. Patent
3,783,037, when prevented from recover-i~ng completely to
an initial configuration under conditions of about 4.0%
unresolved recovery, exhibit complete stress rèlaxation
at 125C, in less than 1,000 hours (equivalent to relax-
ation within 100 hours at 150C) so that they are essen-
tially useless in many applications.
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 shcrtcomings severely limiting their use.
Accordingly, one object of this invention is to
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 to that a degree of unresolved recovery remains.
Yet another object of this invention is to provide
heat recoverable articles of ~-brass type alloys that will
preferably maintain a stress for greater than 1,000 hours
at 125C or for greater than 100 hours at 150C.
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6~
The present invention provides certain quaternary
alloys of copper, aluminium, zinc and manganese which manifest
good ductility and are easily worked by hot working ~echniques
in addition to exhibiting excellent long term stress stability.
Both good ductility and hot worka~ility are requisite for com-
mercially useful materials. Heat recoverable articles made
from the alloys of thP present invention exhibit long term
stress stability even when recovered under circumstances such
that a level of unresolved recovery remains. In general, the
stress stability of such heat-recoverable articles is such that
when they are caused partially to recover upon keing warmed to
the temperature at which the alloy reverts to its austenitic
state, they exhibit a stress stability of at least 1000 hours
at 125C (or the equivalent of 100 hours at 150C).
The quaternary alloys of the present invention com-
prise by weight 70-82% copper, 6-12%, preferably 6-10%, alumin-
ium, 0.1-24% zinc and 0.1% to 12% manganese.
The present invention will be described in more
detail, by way of example only, w;th reference to the accompany-
ing drawings, in which ~Pigures I to I[I being absent);
Figure IV is a graph of the eutectoid line of copper-
aluminium-zinc-manganese quaternary alloys having a Ms of
50C
Figure V is a graph showing the relationship between
the manganese content and the long term stress stability of the
quaternary alloys of this invention,
Figure VI is a graph showing the relationship between
the aluminium content and the long term stress stability of the
quaternary alloys of the present invention.
~.,
Figure VII is a graph $howing the relationship
between the Ms temperature and the long term stress statoili:ty
of the quaternary alloys of the present invention, and
Figure VIII is a graph s-howing the preferred compo-
sitional limits for quaternary alloys of the present inyention
having an Ms temperature of -50 C.
As previously discussed, I have unexpectedly dis-
covered that articles formed from the ~-brass type compositions
known to the prior art suffer the serious disadvantage of
being unstable with respect to the maintenance of stress when
the article has been exposed to modestly elevated temperatures
for extended periods of time under conditions of unresolved
recovery. This phenomenon manifests itsel in actual use
situations uhen an article made from such an alloy is deformed
when in its martensitic state to thereby render it heat recover-
able, and then allowed to recover by warming it to a temperature
at which the alloy reverts to austenite in a manner that pre-
cludes the article from completely recovering to its original
configuration and thereafter exposed to temperatures above
about 80C. That portion of the strain which remains in the
article after this partial recovery is, as already indicated,
referred to as unresolved recovery.
I 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.
Attention is drawn to United States Patents 4,146,392
and 4,144,104 which describe ~-brass type ternary alloys of
copper, aluminium and manganese; and copper, aluminium and
zinc; respectively.
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33a~2
The alloys described and claimed in those patents
are also suitable for making heat-recoverable articles with
good stress stability but there are certain practical con-
sequences which impose limits on their usefulness. Firstly,
in the Cu-Al-Zn ternary system, the composition range of
maximum stability lies on or very near the eutectoid line even
though the stability of the eutectoid composition can be
equalled by moving into the gamma rich region, i.e., by in-
creasing the aluminium content. However, as the alloy compo
sition is moved into the gamma rich region, hot working and
annealing at undesirably high temperatures becomes necessary
to avoid significant precipitation of the gamma phase with
concommitant embrittlement. In the case of Cu-Al-Mn ternary
alloys, there is a level of stability which cannot be improved
upon for any Ms temperature. However, because of the high
aluminium content of the alloys which give the best stakility,
they may not be ductile enough for some uses.
The quaternary alloys of the present invention,
overcome the shortcomings inhérent in the ternary alloys, and
provide alloys in whlch the stability ductility and Ms can be
optimised to meet a desired application. Thus, by virtue of
the degree of freedom offered by the fourth metal, for each
desired Ms temperature there is a nearly infinite number of
eutectoid compositions.
3~ Z
This is shown by way of exemplification in Figure IV where
there is plotted the eutectoid compositions for alloys
having an M of -50C as,,a function of the manganese and
aluminium concentration. The zinc concentration along
this eutectoidal line also varies and may be estimated
from equations (b), (c), or (d) shown infra.
Another unexpected benefit of the use of these
quaternary alloys is that the great majority of the alloys
described herein do not form the or phase until cooled
to temperatures of 550C or even lower. By contrast, many
of the unstable alloys contemplated by the prior art form
the ~ory phase even at temperatures in excess of 650C.
Thus the quaternary alloys of the instant invention may
advantageously be worked in the ~-phase at much lower
temperatures than those of the prior art with the conse-
quence of greatly improved tool life. Yet another unexpected
benefit of these alloys is that the kinetics of formation
of the ~and ~phase is very significantly retarded when
compared with any known prior art compositions. Thus in
the majority of the quaternary alloys of the instant
invention, air cooling is sufficiently rapid't,o retain
substantially all the material in the~ -phase. A highly
beneficial result of this is that the warpage which results
from rapid quenching (as when using water as the quenchant)
and variations in quenching rate across relatively thick
sections with a noncommitant variation in phase composition
can be avoided. The improvements obtained by the addition
of combinations of either Mn or Zn, with other metals or
pairs of other metals, to mixtures of Cu and Al, are minor
'0 when compared with the benefits accruing from the addition
of Mn and Zn in combination.
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A consideration of Figure IV will show that the
eutectoid composition for an Ms of -50C can be varied
by substituting manganese for zinc (but not on an equal
weight basis). For this reason, the aluminium content
of the alloys can be increased with a corresponding
increase in stability.
I have found that the stress stability of the
quaternary alloys of this invention are influenced by:
1. The position of the composition relative to
the eutectoid,
2. The Ms temperature,
3. The aluminium content of the alloy.
The influence of these factors was found by the
following procedure. Each alloy was quenched with water
at 20C from 650C. A 3" 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 temperature and the constraint was then removed.
When this was done, the amount of springback, i.e.,
movement toward the original configuration, was measured,
The specimen was then replaced in the constraint and held
for a further period of time at either 125C 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. This is the time that
is given in the tables of the Example.
The manner in which each of these factors affect
the stress stability of these alloys can be seen from a
consideration of Figures V-VIII. Referring now to Figure
- 11 - , .
36~6~
V there is shown the effect of varying the composition
relative to the eutectoid for an alloy having an M of
-40 C and a constant aluminium content ( 10% by weight).
The eutectoid composition contains 4.6% by weight of
manganese.
Figure VI illustrates the effect of increasing
aluminium content for alloys all having an Ms of about
-30 C. From Figure VI it can be seen that stress stability
increases with the increase in aluminium content.
Figure VII shows the effect of varying the M
temperature. The alloys used in the study for Figure VII
all had the same aluminium content (10%). However, the
relative proportions of the other elements were adjusted
to obtain the desired Ms. From this Figure it can be seen
that alloys of lower Ms are more stable.
In one aspect of the practice of the present
invention one selects an Ms temperature that is convenient
for the application to which a heat recoverable article
is to be put. Then, from curves like those in Figures V -
VII, the required levels of aluminium, manganese and zinc
required for a desired life time can he estimated. It will
- be appreciated that for a given Ms there is an associated
large family of eutectoid compositions. Thus for any given
Ms, the eutectoid line, as a function of Mn and Al content,
is defined by the limiting ternary compositions of that
Ms, i.e. the compositions where the Mn and Zn content
are respectively 0%. In the case of alloys having an Ms
of -50C, these alloys are Cu (81.05%), Al (11.75%) Mn
(7.2%) and Zn (0%) and Cu (73.3%), Al (7%), Mn (0%) and
Zn (19.2%). Referring now to Figure VIII, there is shown
a graph of the line XY defined by the limiting ternary
compositions described above, Thus, for all compositions
on this line there is a coincidence between the eutectoid
point and an Ms of -50C.
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3~:262
SimiLar lines can be obtained for alloys of M other
than - 50C. The following equation has been derived from
which the line XY for other M temperatures can be
approximated.
S Mn(wt. %) = ~1.78 Al(wt. %) - ~ 90 +M~ ~ 5 =
The following equations have been derived to allow the
estimation of the Ms temperature for a variety of alloys
after having been quenched from 650C into water at 20C.
For alloys containing 6-10% Al and up to 4% Mn:
Ms ( C) = 2469-68 Zn (wt. %) -172 Al (wt. %) -89 Mn (wt %) (b)
For alloys containing 6-10% Al and 4-10% Mn:
M (C) = 1844-52 Zn(wt. %)-133 Al(wt. %)-56 Mn(wt. %) (c)
For alloys containing in excess of 10% Al:
Ms( C) = 1787-57 Zn(wt. %)-120 Al(wt. %)-60 Mn(wt. %) (d)
As previously indicated, the compositions of maximum
stability for any given aluminium content lie at or near
the eutectoid. In some instance it may be desired to operate
on the gamma or alpha side of the eutectoid. In the case
of the former, relatively limited deviation is permissable
as on the gamma side precipitation of the gamma phase is
difficult to avoid and the compositions containing this
phase have a significant tendency to be less ductile.
Generally good stability and suitable ductility can be
achieved on the gamma rich side up to a 3% deviation in
the content from that of the eutectoid. However, it is
p~referred to stay within about a 1% deviation in the Mn
content.
Moving to the alpha rich side does not lead to a
substantial reduction in ductility but does tend to cause
a reduction in stability. The maximum level of manganese
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addition is controlled by the line EF. The limiting composition
of the two alloys F and E which are respectively a ternary
Cu-Al-Zn alloy and a ternary Cu-Al-Mn alloy are 73% Cu, 6.6% Al,
20.4% Zn and 80.6% Cu, 9.1% Al, and 10.3% Mn. Compositions
with manganese levels in excess of that specified by the line
EF will either have a stability of less than 1,000 hours at
125C or would require heating in excess of 650C to remove
thè ~-phase. However, it is preferred to stay within about 3%
by weight of the eutectoid on the alpha side for best results.
The lines demarcating these bounds for alloys of Ms = -50C are
shown in Figure VIII where line GH and AB, respectively show the
3% and 1% variance in manganese content on the gamma rich side
of the eutectoid. By contrast, DC demarks the 3% variance in
the manganese content and EF is the limiting level for high
manganese content on the alpha side as explained above. Thus
the highly preferred alloys of Ms = -50C are found within the
area bounded by the points ABYCDF.
For alloys of an Ms other than -50C, similar variance
from the eutectoid also leads to alloys having an acceptable
and even a highly desirable balance between stability and
ductility. Graphs like that of Figure VIII for alloys of an
Ms of other than -50C can be derived from equation (a) above
for the eutectoid compositions. Line AB can be calculated from
the following equation:
Mn = ( 1.78 Al - [ 858 + Ms~ (e)
59 445-~1s
Line CD can be calculated from the equation:
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~L~3~
Mn =(~.7a ~
59 45 -
Line GH can be calculated from the equation:
Mn =~7a AL - [ 994 + M~ ~ )
59 5 ~ Ms
- 14a -
- ~ .
EXA~PLE I
The following are examples of alloys according to
the present invention having a long term stress stability at
125C for at least 1000 hours or at least 100 hours at 150C.
Each alloy was quenched into water at 20C from 650C. A 3"
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 temperature and the constraint was then
removed. When this was done, the amount of springback, i.e.
movement toward the original configuration was measured. The
specimen was then replaced in the constraint and held for a
further period of time at either 125C 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.
3(;1162
Copper-Aluminium-Manqanese-Zinc QuaternarY Alloys
Sample Alloy Composition MLifetime
Cu Al Zn Mn at 125 C
1 79.1510 8.25 2.6 -3914,000 hours
2 79.310 7.3 3.4 -4218,000 hours
3 79.310 6.4 4.3 -4120,000 hours
4 79.410 5.5 5.1 -4120,000 hours
79.610 4.4 6.0 -3819,000 hours
6 79.610 3.5 6.9 -3613,000 hours
7 79.710 1.7 8.6 -438,500 hours
8 80.310 0 9.7 -355,000 hours
9 74.1 7 18 0.9 -351,400 hours
78.1 9 9.5 3.4 -354,700 hours
11 79.810 5.9 4.3 -3010,000 hours
12 78.710 7 4.3 -7850,000 hours
16 -
11~3~2
All the alloys of the instant invention, pGssessing 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.
~ he good hot 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.
