FI66205C - FOERFARANDE FOER ATT DAEMPA FOERLUSTEN AV REVERSIBITET HOS EN METALLBLANDNING MELLAN AUSTENITISKT OCH MARTENSITISKT TILLSTAOND - Google Patents

Description

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Patent and octagonal literature AinBfc — watejil od> aUMtei patltefd 31-05-64 (3 ^ (33) (31) awtew HM phorttm 18.02.75 USA (US) 550556 (71) Raychem Corporation, 300 Constitution Drive, Menlo Park, California 94025, USA (72) Greville Bertram Brook, High Wycombe, Buckinghamshire, United Kingdom-Storbritannien (GB), Peter Leonard Brooks, Palo Alto, California,

Roger Francis lies, Foster City, California, USA (74) Berggren Oy Ab (54) Method for locking the loss of alloy return between an austenitic and martensitic state - Förfarande för att dämpa förlusten av reversibitet hos en metallblandning mellan Austen iti skt och Martens iti This invention relates to a method for controlling the loss of reversibility between a martensitic and austenitic state in an alloy which can change reversibly between an austenitic and martensitic state.

Alloys are known, for example alloys, which have properties such that they are capable of undergoing a reversible change from the austenitic to the martensitic state, and some of these can be formed into elements which are heat reversible. Such alloys are, for example, those disclosed in U.S. Patents 3,012,882, 3,174,851, 3,351,463, 3,567,523, 3,753,700 and 3,759,552, Belgian Patent 703,649 and English Patents 1,315,652, 1,315,653, 1,346,046 and 1,346,047 ("Fulmer * patents").

Such alloys are also disclosed in NASA's SP "55-Nitinol - the alloy with a memory, etc." (U.S. Government Printing Office, Washington, D.C. 1972), N. Nakanishi et al.,

Scripta Metallurgy 5, 433-440 (Pergamon Press 1971).

2 66205 What all these and other alloys have in common is that they undergo a shear stress change upon cooling from a high temperature (austenitic) state to a low temperature (or martensitic) state. If an element made of such an alloy is deformed while in its martensitic state, it thus remains deformed. If it is heated to return it to the temperature at which it is austenitic, it tends to return to its undeformed form. The transition from one state to another occurs in both directions within a certain temperature range. The temperature at which martensite begins to form on cooling is called M, while the temperature at which this process is completed is called M, both of these temperatures being those obtained with large, e.g. 100 ° C / min, temperature changes in the sample, i. "basic M-M and M". Similarly, the initial and final temperatures for austenitization are denoted by the letters Ag and Af. In general, Mf is a lower temperature than A and M is a lower temperature than A „. M can be equal, lower-SS X s higher or higher than A depending on the alloy alloy and also the thermomechanical history of the alloy The change from one form to another can be monitored by measuring some of the material's numerous physical properties in addition to the deformation recovery described above, for example its electrical resistivity, where an anomaly occurs when changes occur. or stress-temperature curves, the line joining the points M, M „, A, A„ and again the point M forms a loop

called the hysteresis loop. For many substances M and A

S s are at approximately the same temperature.

One particularly useful alloy having heat recovery or shape memory is the intermetallic compound TiNi, U.S. Patent 3,178,851. The temperature at which deformed bodies of alloys return to their original shape depends on the alloy mixture, as in U.S. Patent 1,202,404 and U.S. Pat. shown, for example, the restoration of the original form can be effected at, below or above room temperature.

In certain commercial applications using heat-recoverable alloys, it is desirable for A to be at a higher temperature.

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mode than M for the following reason. For example, hydraulic components

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The switches for patents disclosed in English Patents 1,632,441 and 1,327,442 are sold in deformed (i.e., stretched) form. The customer places the stretched coupling on the components (e.g., the ends of the hydraulic pipelines) that are to be joined together and raises the temperature of the coupling. When its temperature reaches the austenitic change range, the switch returns or attempts to return to its original configuration and shrinks onto the components to be connected. Since it is necessary for the switch to remain in its austenitic state during use (e.g. to prevent stress triggering during a martensitic change and because the mechanical properties of the austenite are better), the material M is selected for its

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below the temperature it may reach in use so that during use the material remains in austenitic state at all times. For this reason, after deformation, it must be kept in, for example, liquid nitrogen until it is used. However, if the A temperature, as used herein, means the temperature that marks the onset of a continuous sigmoidal change plotted on the stress-time curve for the entire martensite capable of becoming austenite, the austenitic state could be raised even temporarily, e.g., for one heating period without corresponding M increase, the stretched coupling could be considered higher

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sa and at a more comfortable temperature.

In Finnish Patent Application No. 753757, we have described a method by which the A temperature of certain alloys can be raised for one heating period. In this method, the temperature of the mixture is first lowered from where it occurs in the austenitic state to below its M 1 temperature. The mixture is then heated to the temperature at which it would normally occur in the austenitic state, i. Above the A ^ temperature. However, the change from martensitic to austenite does not occur if the selected heating rate is "slow" as defined in the above patent. Suffice it to say that it depends on the alloy, but can be easily determined by one skilled in the art after reading the subject. patent.

If the mixture is cooled after the slow heating is completed and then reheated at high speed, it will not begin to change from martensite to austenite until approximately the temperature at which the slow heating was terminated is reached. More importantly, if an element was made from this mixture and deformed while in the martensitic state, either before or after the slow heating ends 66205, it would not begin to return to the state it was in the austenitic state until it reached approximately the temperature at which the slow heating was stopped.

This method is called "thermal pretreatment".

Finnish patent application No. 733755 describes another method by which the temperature of alloys A can be raised. Here

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in the method, the mixture is maintained in a deformed configuration at a temperature above its normal A -A „range, sufficient time to maintain some of the deformation when the forcing device is removed. The amount of deformation retained is a function of the temperature at which the mixture is maintained and also a function of the duration of the holding step.

The mixture can be deformed while in the austenitic state. However, this typically requires a large amount of force. Thus, it is advisable to deform the mixture while in a more deformable state, which occurs near, inside or below the M-M 2 range, and then to raise its temperature, while attached, to the desired holding temperature.

By analogy with "thermal pretreatment", this method is referred to as "mechanical pretreatment". When the element thus pretreated is heated at a high speed, part of the retained tension is restored.

As a result of these inventions, it is possible to produce heat-recoverable elements with an elevated A temperature. Often, however, metal alloys that have been converted to a martensitic state tend to lose all or part of their ability to return to austenite when heated through the A -A „region. In other cases,

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do not react favorably to a thermal or mechanical pretreatment procedure to raise the A temperature. It is obvious that it would be very advantageous if a method were available to prevent the loss of these desired properties.

Thus, the present invention also provides a method of controlling the loss of martensite-austenite recoverability in alloys and of making alloys more responsive to methods of providing an elevated A temperature.

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The present invention further provides a method of controlling the loss of reversibility in an alloy between a martensitic and Austenitic state, wherein the method is maintained at a temperature above the M point while in the austenitic state for a time sufficient to reduce the loss at ambient temperature.

An additional result of the method is the improved ability to become a pretreatment. The holding time required to achieve these goals depends on the mixture and the holding temperature. Normally the required holding time decreases as the temperature increases. The process of the invention may be referred to as "aging" and the mixtures thus treated may be referred to as "aged".

The present invention also provides the use of aged alloys. Such alloys are better suited for heat recovery.

The present invention provides a method for controlling the loss of recovery between the martensitic state and the austenitic state in those alloys that are capable of undergoing reversible changes between the martensitic state and the austenitic state with temperature changes. When alloys are subjected to the process of this invention, their pseudoelasticity, i. their ability to change from the austenitic to martensitic state with subsequent deformation when subjected to stress and to return to the Austenitic state and return to its original form is improved.

The above-mentioned loss of reversibility manifests itself in many ways. In some cases, a sample of the alloy cooled below the M ^ point does not fully or partially recover to austenite when allowed to warm through its normal A -A „range. Thus, any deformation provided to the sample while it is in the martensitic state may at least partially fail to recover when the sample is heated under conditions under which recovery would be expected to occur.

In other cases, although the mixture may undergo reversible conversion to austenite after being converted to martensite as a result of rapid heating, the mixture may not respond more to thermal than mechanical pretreatment when attempting to raise its Ag temperature because reversibility is lost in the pretreatment process.

6 66205

The invention further provides a method for improving the response of certain alloys to mechanical or thermal pretreatment (i.e., increasing the amount of added heat recovery) by carefully adjusting the aging within certain time and temperature limits, although overall recovery may be reduced. Optimum aging conditions can be found by those skilled in the art by routine experimentation. Suffice it to say that with these mixtures shown in the accompanying examples, too short an aging time or too low a temperature may provide insufficient useful recovery as mentioned above, and too long an aging time or too high a temperature may provide insufficient useful recovery, although overall recovery is improved in the latter. case.

The method of this invention is generally applicable to a large number of alloys that undergo reversible austenite-martensite changes. It is particularly suitable for alloys which are alloys and, more particularly, for alloys which form electron compounds. Preferred electron compounds are those that meet the definition of Hume-Rothery1 for structurally analogous cubic lattice phases (e.g., betamessing) or electron compounds with ratios of about 3 valence electrons per two atoms. See A.S.M. Metals Handbook, Vol. 1, 8th Ed. (1961) page 4.

Suitable alloys include β-phase alloys, for example, those exemplified by copper-zinc and copper-aluminum alloys, which form internally centered cubic lattice-type β-alloys associated with g-brass. These are those alloys of copper and zinc or copper and aluminum in which zinc and aluminum can at least partially replace each other and which themselves can be partially replaced by other alloying elements, for example silicon, tin, manganese or mixtures thereof. The alloy rings covered by this description are described in detail in the above Finnish patents. Recommended alloys are those containing about 6Ο-85 weight? copper together with varying amounts of zinc and / or aluminum and silicon, manganese or mixtures thereof, for example alloys with 0 to about 40% by weight? zinc, 0 - about 5 weight? silicon, 0 - about 14 weight? aluminum and 0 - about 15 weight? manganese and which form internally centered cubic lattice-type structures. Copper three- or four-component alloys can be used. The examples describe in more detail a number of special alloys which fall within these limits. It is to be understood, however, that the method of the present invention may be applied outside the confines of the preferred embodiments. For example, it is within the scope of this invention to apply the method of this invention to alloys based on metals other than copper.

Alloys of this type are obtained in the g-phase by methods well known in the art. Usually, the g-phase is obtained by rapidly cooling the alloy from an elevated temperature at which it occurs substantially as a stable g-phase to a temperature at which it occurs as a metastable g-phase. If the cooling rate is too slow, large amounts of a second phase may form without reversible austenite-martensite transformation. However, an alloy that is at least substantially in the g-phase, e.g., more than 70 in bulk beta phase, can still have substantially the same beneficial properties as a pure g-phase structure.

As discussed above, in the method of the present invention, the metal alloy is maintained at a temperature at which it occurs in the austenitic state for a time sufficient to control at least in part the loss of reversibility between the martensite and the austenite. The most obvious advantage of this method is that it provides mixtures which, when deformed from a thermally stable state to a thermally unstable state, largely recover from the initial stress.

The time required to control the loss of reversibility may vary depending on the mixture and holding temperature. Because these variables affect the response to the aging process, it is possible to define precise limits on the time and temperature required to achieve the best results with each mixture. Nevertheless, the optimum conditions can be easily determined by those skilled in the art.

In the case of g-phase alloys, the aging temperature must be such that no significant conversion of the g-phase to a phase without reversible austenite-martensite changes occurs.

For B-phase copper alloys, such as those described above, containing varying amounts of zinc, aluminum, silicon, manganese, and combinations thereof, and those having an M-point below room temperature, aging at about 50-125 ° C for a period ranging from 5 minutes 3 or 4 8 66205: hour, is usually sufficient. However, aging at higher or lower temperatures for longer or shorter periods may usually be preferred. For other mixtures, time and temperature may vary, but optimal results can be readily determined by comparing the amount of recovery between martensite and austenite in representative samples by measuring, for example, the amount of elongation recovered as a result of rapid heating of the sample.

It should be noted that the aging does not have to be performed at one temperature, but can be varied one or more times or continuously over the aging time.

The following examples illustrate the invention:

Example 1

A series of experiments were performed comparing the reactions of different mixtures in the Cu-Zn-Si and Cu-Zn-Al systems to the aging process of this invention and their effect on thermal pretreatment. Alloy samples were cast from melts with different ratios of copper, zinc, and either silicon or aluminum. The ingots were hot rolled into strips and cut into test pieces, measuring approximately 37 mm x 3 mm x 0.75 mm. All specimens were heated until they reached a high temperature full-beta phase and then cooled in water. Half of the samples were aged at 100 ° C for 10 minutes, the other half was not aged. All samples were deformed by bending at -79 ° C to achieve 6% outer fiber elongation. After deformation, the samples were detached and measured to determine how much elongation was maintained. The specimens from the aged and unaged groups were then heated according to one of the following three methods: (1) rapidly warmed by immersion in a liquid at 40 ° C, cooled to room temperature and measured to determine how much elongation had recovered, then heated rapidly by immersion at 200 ° C and returned to room temperature to determine how much more elongation recovery occurred: (2) slowly warmed at 0.25 ° C / min from -79 ° C to + 40 ° C, cooled to room temperature, measured to determine how much elongation recovered, then rapidly heated by immersion in a liquid at 200 ° C, cooled to room temperature and measured to determine how much more recovery occurred: or (3) handled as in (2) except that the slow heating rate was 9 l ° C / 24 min Instead of 0.25 ° C / min. 66205 The "merit number" for the reactivity of each test mixture to adjust the recovery temperature range is obtained by expressing as a percentage the recovery that occurs at 40 ° C with slowly heated specimens minus the recovery at more than 40 ° C with rapidly heated specimens divided by 5% (which is ideal recovery after elastic rebound associated with the release of bending stress) i.e.

recovery 40 ° C recovery above 40 ° C slowly on the side of rapidly heated test specimens. η, with pieces of steam

Earnings number = 100 x —---- 5

Mixtures found to be particularly suitable for use in this invention will now be described in more detail with reference to the accompanying drawings, in which:

Figures 1a and Ib show the effect of aging on alloys containing copper, zinc and silicon which have been thermally pretreated.

Figures 2a, 2b and 2c show the effect of aging on alloys containing copper, aluminum and zinc which have been thermally pretreated.

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In Figures 1a and Ib, the CV is plotted in the coordinate system as a function of composition in topographic form. The longer axes of the constant earnings zones are usually parallel to the same curves of change in temperature. Mixtures with lower transition temperatures are at the top left of the image, while those with higher transition temperatures are at the bottom right of the image. The clearly distinguishable optimum is shown in Figure 1 in the range 1.8-2.7 Si, 66.2-67.5 Cu, the rest Zn (29.8-32.0%). A comparison of Figures 1a and Ib shows that aging for 10 minutes at 100 ° C extends the optimum from the same general center range. Arbitrary selection of 40 ° C as the end point for slow heating clearly renders ineligible alloys with a normal range of change above or partially above 40 ° C at the bottom right of the figure, but it should be noted that low earnings do not indicate unsuitability for these alloys. in the present invention, but only that a temperature other than + 66 ° C must be selected as the pretreatment temperature. Similarly, for alloys in the upper left of the figure, a low earnings on the curve does not necessarily mean that they do not respond to the process of this invention. In these cases, a low number simply means that the selected slow heating rate was not such as to prevent recovery before reaching 40 ° C. The choice of 40 ° C causes the zone of the same earnings to approach the high transition temperature side (lower right). The alloys in the lower right are in fact reactive to the slow heating process, as shown by the CuZnAl results below.

A topographic representation of the CV results of the CuZnAl system can be found in Figure 2. Again, the zones of the constant CV are parallel to the curves with the same change in temperature. The effect of aging is to spread the learners from the top left of the image to the bottom right.

Five alloy mixtures with normal A at or above 40 ° C

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side, was used to test the mobility of the recovery area at higher temperatures. Again, the same general test procedure was used, but the slow heating was continued to + 100 ° C instead of being stopped at + ^ 0 ° C. The results of the aged samples are shown in Figure 2c; the new optimum is parallel to the optimum in Figure 2b, but shifted, as expected, toward mixtures with higher transition temperatures. Although the recovery region is mobile with the CuZnAl alloy, the mobility appears to be more limited than with the CuZnSi alloys.

Since the unaged CuZnAl samples lost their memory properties as a result of slow heating to 100 ° C, but the aged samples did not lose, it is apparent that the aging treatment has been successful in maintaining the reversibility of the change over a higher temperature range.

It should be noted that the aging times and conditions selected for Figures Ib and 2b result in certain blends with optimum properties and that other aging times and conditions result in different blends with the same or broadly similar optimum properties. Aged alloys of lines 40, 60 and 80 bounded areas in Figure 1b and the area bounded by line 20 in Figure 2b are particularly suitable for the process of this invention.

66205 11

Example 2

Several test pieces of an alloy of 64.5% copper, 34.5% zinc, 1.0% silicon by weight were cooled in water at 20 ° C after 5 minutes at 860 ° C and then aged at 50 ° C. always for periods of 1 week. After cooling below the Mf point, the specimens were reheated at a rate of 10-20 ° C / min. A slight change in martensite to the β-phase (measured as changes in resistivity) occurred for 5 minutes during heating of the aged specimen. Some change occurred in the specimen aged 45 minutes, the specimens aged 90 minutes or more completely changed. Other specimens of the same alloy were subjected to the same heat treatment and, after aging, were deformed to 8% tension at 5050 ° C and reheated. The amount of heat recovery was approximately proportional to the amount of martensite that had changed in the resistivity experiments on undeformed specimens. Therefore, the use of the perosess of the present invention with an aging of at least 45 minutes made it possible to provide heat recoverable properties to this alloy.

After aging the specimen for 5 minutes at 20 ° C before cooling to -50 ° C, the heat recovery elongation was 2.30%.

After 45 minutes at + 50 ° C before cooling to 5050 ° C, the heat recovery was 6.20%. This increased slowly after longer aging times, to 6.50 5S after 3 hours and to 7.0% after a week.

Example 3

Several samples of the alloy having a weight composition of 66.50% copper, 31.75% zinc and 1.75% silicon were cooled in water at 20 ° C after 5 minutes at 860 ° C. They were then aged at 50 ° C for various times up to 1 week and deformed at 8% -50 ° C. After four minutes at 20 ° C (minimally aged sample), the heat recovery was 0.1%. After 45 minutes at 50 ° C, this was $ 0.1 and after 90 minutes it had risen to only $ 0.55. Three hours raised the heat recovery elongation to 0.70 S?, 1 day to $ 1.0, and 2 days to 3.9. An increase in silicon content can be seen as necessitating an extension of the aging time to achieve an improved recovery.

Example 4

Sixteen samples with 80.8 w / w Cu, 10.5 inverse ·% Al, 12 66205 8.7 wt ί? Μη, was converted to the β form at 800 ° C or 900 ° C in 3 or 6 minutes and then cooled in water at room temperature. Half of the samples were aged for 10 minutes at 100 ° C, the others were not aged. All samples were deformed by bending at -79 ° C to provide 6 * outer fiber elongation, after which the stress was released. Half of the samples were heated to 100 ° C at 0.25 ° C / min, cooled to room temperature and then rapidly heated to 200 ° C. The other half was rapidly heated to 100 ° C, cooled to room temperature and then rapidly heated to 200 ° C. The rapid heating rate was greater than 100 ° C / min. Analysis of the elongation recovered during rapid heating to 200 ° C against the adjusted variables showed that thermal pretreatment significantly increased the rate of recovery above 100 ° C.

For this particular alloy, statistical analysis showed that aging had no effect. Average effects: elongation above 100 ° C *.

Quickly heated 0.39 *

Pretreated 1.89%

The experiment was repeated with a polymer containing 80.9% by weight. Cu, 10.5 wt.% * Al, 9.01 wt.% ?? Mn. Analysis of the elongation recovered during rapid heating to 200 ° C against the adjusted variables showed significance for aging without aging and against non-pretreatment.

, Average effects: above 100 ° C restored elongation at break ??

Indispensable 1.00. Quickly heated 0.15. Obsolete 0.36. Preprocessed 1.21.

Example 5 Samples of an alloy containing 79.2% w / w Cu, 10.0 wt * Al and 10.8 wt * Mn were converted to beta at 550 ° C for 5 minutes and cooled to 20 ° C. water. The alloy M was o ....... s -20 C as a result of this treatment. The samples were aged for either 5 minutes or 1 hour at 50 ° C and then cooled to -30 ° C or cooled to -30 ° C immediately after water cooling without aging. All samples were deformed to 9% tensile at -30 ° C and the stress was removed.

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Half of the samples were immediately heated at a very high rate by immersion in liquids at 20, 40, 100 and 200 ° C. The increased amount of elongation elongated as a result of each immersion was recorded.

The remaining samples were initially heated slowly at 6 ° C / min to 40 ° C, then cooled to -30 ° C and heated rapidly as in the first set of samples. The results are shown in the table below.

Table I

Result Elongation Aging- Aging time Heating- Recovery% recovery temperature (° C) speed at 40 ° C nen 40 ° C (,% elongation) above (% elongation) 1. 3s8 Undated Only fast 1.4 2.1 6 ° C / min to 40 ° C, 0 recooling 2. 3.3 Timeless and fast heating 0.3 1.2 3. 3.2 50 ° C 5 min Fast only 3.1 0 6 ° C / min To 40 ° C, 0.3 recooling 4. 3.7 50 ° C 5 min and rapid heating 0.3 2.8 5. 3.6 50 ° C 1 h Rapid only 3.35 0 6 ° C / min to 40 ° C 2.5 recooling 6. 3.4 50 ° C 1 h and rapid heating 0.3 0.1 *

To first consider those samples that were rapidly heated immediately after deformation, recovery was complete by 40 ° C in samples aged 5 min and 1 h, but most recovery occurred above 40 ° C in the unaged sample. In the samples initially heated from 6 ° C / min to 40 ° C, no recovery occurred by 40 ° C in this first heating cycle in the unaged samples and in the samples aged for 5 min at 50 ° C. However, after recooling and again rapid heating, most of the recovery occurred above 40 ° C. The sample aged for 1 h at 50 ° C showed almost complete recovery in the initial 6 ° C / min heating period to 40 ° C.

66205 14 These findings show that obsolescence can lower the A point,

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for in unaged samples, significant recovery occurred above 40 ° C without pretreatment (compare results 1, 3, and 5). However, the amount of heat recovery elongation obtained when the sample is thermally pretreated improves with aging (compare results 2 and 4). Aging also affects the slow heating rate required for thermal pretreatment. For a sample aged only 5 min at 50 ° C, 6 ° C / min had a "slow" heating rate because there was little recovery before 40 ° C. (See result 4). However, in the case of a sample aged for 1 hour at 50 ° C, a heating rate of 6 ° C / min was qualified as a high heating rate because most of the heat recovery elongation was recovered during the pretreatment attempt. The combined effect of these results is to show that a particular alloy may have an optimal aging treatment, but still only one that is readily determined by those skilled in the art prior to thermal pretreatment.

Example 6

An alloy containing 64 weight # copper, 35 weight # zinc and 1 weight # silicon was investigated. The M 1 temperature of this alloy was -40 ° C.

The specimens were converted to beta for 5 minutes at 860 ° C, cooled in water at 20 ° C and then aged for various times in the metastable beta phase, which was performed at 50 ° C in this series of experiments. After placing the specimens in a tensile loading device (approximately 5 minutes to settle at room temperature), they were cooled to -65 ° C and deformed to 8 ° tensile. After deformation, a forcing device was placed on the draw jaw so that shrinkage could not occur, but the specimens were free to undergo spontaneous expansion, if any. The forced test piece was placed in water at 40 ° C with a very high heating rate and kept at this temperature for various times before recooling below the M 2 point. The specimens were released from the forcing device during cooling, expanding slightly compared to the original series after deformation. The forcing device was removed from the apparatus so that the specimens, now in their "pretreated" state, could recover freely when reheated at a "high" rate in an oven set at 600 ° C.

Temperatures and heat recovery elongations were measured as a function of two main variables, namely the aging time at 50 ° C and the forced holding time at 40 ° C.

The results of the "mechanical pretreatment" are shown in Table II. At each aging time at 50 ° C, some specimens have also been rapidly heated directly after deformation at -65 ° C to compare the effect of "mechanical pretreatment" to A temperature.

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Table II clearly shows the trend that the second A temperature, the one obtained by mechanical pretreatment, increased as the holding time at 4 ° C increased and in many cases exceeded 4 ° C. On the other hand, the total heat-recovering elongation (i.e., 1. A -A 2) decreased with increasing retention time at 40 ° C, and this loss of reversibility occurred mainly in the part of the heat-recovering elongation between 2. Ag-A 2. Extending the aging time at 50 ° C in the metastable β-phase greatly improved the overall heat recovery elongations, but had only a minor effect on lowering the second A temperature.

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Table II

Aging- Pretreatment Elongation A -1 state ° C Recovery Total return time hold time% ® Ag-1 state change at 4QPC * 'above, elongation% elongation%

No pretreatment 7.05 -50 - - 6.50 5 min ho- 10 seconds 6.90 -45 -4 5.65 6.80 neenothermal- 30 "7.10 -37 31 4.15 5.65 in mode 1 min 6.90 -40 19 4.80 5.90 5 min 7.65 -37 59 2.90 3.95 10 min 6.95 -17 23 2.80 3.55 1 h 7.10 -45 19 3, 10 4.00

No pretreatment 7.25 -33 - - 6.95 45 min 10 seconds 6.75 "49 -9 5.30 6.55 at 50 ° C 30" 6.35 "52 4 4.40 5.85 1 min 7.10 -43 23 4.45 5.70 5 min 7.35 -40 20 5.60 7.00 10 min 7.20 -51 19 3.65 5.15 1 h 7.55 -44 54 2, 65 4.20

No pretreatment 7.00 -32 - - 6.75 3 hours 10 seconds 7.25 -4l -4 5.75 7.00 at 50 ° C 30 seconds 7.20 -32 15 4.15 5.65 1 min 7.05 -30 19 5.65 6.85 5 min 6.85 -47 13 4.80 6.20 10 min 7.20 -32 29 5.65 6.65 1 h 7.30 -37 38 4, 15 5.25 5 h 7.15 -44 44 5.60 6.75 16 h 7.50 -39 80 3.75 5.25 66205 16

Table II (continued)

Aging Pretreatment Elongation A -1 state ° C Recovery Total time holding time% ^ „A -1 state elongation at 1.0 C above, elongation * elongation%

No pre-treatment 7.20 -27 - - 6.70 24 hours 10 seconds 7.06 -37 -4 5.85 6.55 at 50 ° C 30 seconds 7.25 -42 -5 5.80 7.25 1 min 7.45 -43 0 5.70 6.95 5 min 7.50 -35 24 5.75 6.70 10 min 7.50 -42 35 5.85 7.25 1 h 7.80 -34 29 4 .70 5.80 5 h 7.40 -34 35 5.05 5.95 16 h 7.15 -47 69 2.90 4.70

No pre-treatment 7.10 -33 - - 6.80 1 week 10 min 7.00 -28 33 5.60 6.45 at 50 ° C 1 h 7.25 "37 47 5.20 6.20 5 h 7 , 45 -37 40 5.15 6.70 16 h 7.55 -40 33 5.60 6.70