CA1103062A - Alloys - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Alloys containing copper, aluminium, zinc and manganese having the property of not exhibiting complete stress relaxation at 125°C in less than 1000 hours, heat recoverable articles made therefrom, and processes for their manufacture. The articles may be, for example, hydraulic couplings.

Description

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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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 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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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 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.

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.

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.

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 .

3g~ii2 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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Mn =(~.7a ~

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 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.

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An alloy having a .beta.-brass type structure capable of being rendered heat recoverable and capable of being cooled from a temperature at which it exists in an austenitic state to a temperature at which it exists in a martensitic state, said alloy being a quaternary alloy comprising 70-82% by weight copper, 6-12% by weight aluminum, 0.1-12% by weight manganese and 0.1-24% by weight zinc.

2. A quaternary alloy as claimed in claim 1 wherein the manganese content is not greater than 10.3% by weight.

3. A quaternary alloy as claimed in claim 1, the components of which are present in an amount that corresponds substantially to that for a eutectoid composition of copper, aluminum, mangan-ese and zinc.

4. A quaternary alloy as claimed in claim 3, wherein the manganese content of the alloy deviates from the manganese con-tent of the eutectoid composition by not more than about 3% by weight on the gamma rich side of the eutectoid.

5. A quaternary alloy as claimed in claim 4, wherein the manganese content of the alloy deviates from that of the eutect-oid composition by not more than 1% by weight on the gamma rich side of the eutectoid.

6. A quaternary alloy as claimed in claim 3, wherein the manganese content of the alloy deviates from the manganese con-tent of the eutectoid composition by not more than about 3% by weight on the alpha rich side of the eutectoid.

7. A quaternary alloy as claimed in claim 6, wherein the manganese content of the alloy deviates from that of the eutect-oid composition by not more than 1% by weight on the alpha rich side of the eutectoid.

8. A quaternary alloy as claimed in claim 1, 2 or 3, which when deformed from an original configuration while in its martensitic state and caused partially to recover towards said original configuration upon being warmed to a temperature at which the alloy reverts to its austenitic state, exhibits stress stability of at least 1,000 hours at 125°C.

9. A heat recoverable article made from an alloy as claimed in claim 1, 2 or 3.

10. A process for making a heat recoverable article that exhibits stress stability of at least 1,000 hours at 125°C when allowed to recover so that a degree of unresolved recovery re-mains which comprises the steps of:
(a) fabricating said article from a quaternary alloy as defined in claim 1 into an original, heat-stable configur-ation;
(b) cooling said article to a temperature at which the alloy exists in its martensitic state; and (c) deforming 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.

11. A process as claimed in claim 10, wherein said alloy has a substantially eutectoidal composition.