CA1152359A - Alloys - Google Patents

Abstract

ABSTRACT

An alloy of copper, aluminium and zinc falling within the area of a ternary diagram defined by the points:
A. 78.3%Cu 9.7%Al 12.0%Zn B. 75.1%Cu 7.5%Al 17.4%Zn C. 67.0%Cu 4.2%Al 28.8%Zn D. 72.6%Cu 7.9%Al 19.5%Zn is especially suitable for use in heat recoverable articles which exhibit outstanding stress stability.

Description

~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 ~SZ35g 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 ~523~ig 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.

l~5Z3S9 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 ~5;~359 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 3~9 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.

1~52~

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 35~

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 , ~ ~;i235~

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 S235~

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.

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 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

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A ternary alloy of copper, aluminium and zinc having a .beta.-brass type structure falling within the area on a ternary diagram defined by the points:
A. 78.3% Cu 9.7% Al 12% Zn B. 75.1% Cu 4.5% Al 17.4% Zn C. 67% Cu 4.2% Al 28.8% Zn D. 72.6% Cu 7.9% Al 19.5% Zn said alloy being in its martensitic state and having an Ms temperature of 0°C or lower and having been deformed from an original configuration to render it heat-recoverable, said alloy exhibiting stress stability of at least 1,000 hours at 125°C when caused to recover by being warmed to a temperature at which the alloys exists in its austenitic state so that a degree of unresolved recovery remains.

2, An alloy in accordance with claim 1 wherein said alloy has an eutectoidal composition, said eutec-toidal composition being a composition wherein no metal of the group consisting of copper, aluminium and zinc is present in said alloy in an amount that differs by more than 1% by weight from the amount of said metal present in a composition corresponding to a eutectoidal com-position defined by the line XY of the ternary diagram of Fig. 1.

3. An alloy in accordance with claim 2, wherein said alloy has an eutectoid composition.

4. A process for making a heat-recoverable article comprising the steps:
(a) selecting a ternary alloy, capable of being rendered heat-recoverable, of copper, aluminium and zinc having a .beta.-brass type structure that exhibits stress stability of at least 1,000 hours at 125°C when caused to recover so that a degree of unresolved recovery remains and which alloy has an Ms tem-perature of 0°C or lower falling within the area on a ternary diagram defined by the points:
A. 78.3% Cu 9.7% Al 12% Zn B. 75.1% Cu 7.5% Al 17.4% Zn C. 67% Cu 4.2% Al 28.8% Zn D. 72.6% Cu 7.9% Al 19.5% Zn (b) fabricating said article from the selected alloy into an original, heat-stable configuration, (c) cooling said article to a second, heat-unstable configuration from which recovery occurs when said article is warmed to a temperature at which the alloy reverts to austenite from said martensitic state.

5. A process according to claim 4, wherein said alloy has an eutectoidal composition, said eutectoidal composition heing a cornposition wherein no metal of the group consisting of copper, aluminium and zinc is present in an amount that differs by more than 1% by weight from the amount of said metal in a composition corresponding to an eutectoid composition defined by the line XY of Fig. 1.

6. A process according to claim 5 wherein said alloy has an eutectoid composition.