EP0187452B1 - Procédé pour la mise en oeuvre d'un alliage à mémoire à base de nickel-titane et pièce obtenue par ce procédé - Google Patents

Procédé pour la mise en oeuvre d'un alliage à mémoire à base de nickel-titane et pièce obtenue par ce procédé Download PDF

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EP0187452B1
EP0187452B1 EP85308080A EP85308080A EP0187452B1 EP 0187452 B1 EP0187452 B1 EP 0187452B1 EP 85308080 A EP85308080 A EP 85308080A EP 85308080 A EP85308080 A EP 85308080A EP 0187452 B1 EP0187452 B1 EP 0187452B1
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Prior art keywords
temperature
alloy
article
hysteresis
driver member
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EP0187452A1 (fr
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John A. Simpson
Tom Duerig
Keith Melton
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Raychem Corp
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Raychem Corp
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Priority claimed from US06/668,771 external-priority patent/US4631094A/en
Priority claimed from US06/783,371 external-priority patent/US4740253A/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/006—Resulting in heat recoverable alloys with a memory effect

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  • This invention relates to a method of treating a nickel/titanium-based shape memory alloy and to a method of making composite coupling which comprises a nickel-titanium based shape memory alloy driver member.
  • the ability to possess shape memory is a result of the fact that the alloy undergoes a reversible transformation from an austenitic state to a martensitic state with a change of temperature. Also, the alloy is considerably stronger in its austenitic state than in its martensitic state. This transformation is sometimes referred to as a thermoelastic martensitic transformation.
  • An article made from such an alloy for example, a hollow sleeve, is easily deformed from its original configuration to a new configuration when cooled below the temperature at which the alloy is transformed from the austenitic state to the martensitic state.
  • the temperature at which this transformation begins is usually referred to as M s and the temperature at which it finishes M f .
  • Shape-memory alloys have found use in recent years in, for example, pipe couplings (such as are described in U.S.P. 4,035,007 and 4,198,081 to Harrison and Jervis), electrical connectors (such as are described in U.S.P. 3,740,839 to Otte and Fischer), switches (such as are described in U.S.P. 4,205,293 to Melton and Mercier), etc.
  • the alloy austenitic at the service temperature which is often but not necessarily near room temperature, since the austenite phase is stronger than the martensite phase.
  • Military Specification MIL-F-85421 requires a product that is functional to about -55°C. If the product comprises a shape memory alloy, then for convenience in shipping the product in the heat-unstable configuration, the product should not recover prior to about 50°C. It is a matter of commercial reality, within and without the military, that the product satisfy these requirements.
  • the alloy be martensitic in the vicinity of room temperature so that the article can be fabricated, stored, and shipped at or near room temperature.
  • the reason for this is that in the case of an article made from the alloy, a coupling, for example, the article would not recover prematurely.
  • US-3,948,688 discloses a process for conditioning a nickel-titanium alloy which comprises applying a load to the alloy and then, while the load is applied, thermally cycling the alloy between a temperature less than AS and a temperature greater than A f .
  • AS a temperature less than AS
  • a f a temperature greater than A f
  • one way to obtain an alloy that is martensitic near room temperature and which is also austenitic over a large range of temperatures including room temperature is to have an alloy which exhibits a sufficiently wide tranformation hysteresis, say, greater than about 125°C. If the hysteresis were sufficiently wide and room temperature could be located near the middle of the hysteresis, then the alloy could be fabricated and conveniently stored while in the martensitic condition. Since the hysteresis is sufficiently wide, the alloy would not transform to austenite until heated substantially above room temperature. This heating would not be applied until the alloy (in the form of a coupling, for example) was installed in its intended environment.
  • the alloy which would then be in the austenitic condition, would remain in the austenitic condition after cooling down since the service temperature (which may be above or below room temperature) would be substantially above the martensite transformation temperature.
  • the service temperature which may be above or below room temperature
  • the commercially viable near equiatomic binary nickel-titanium alloys can have a hysteresis width of about 30°C.
  • the location of the hysteresis for this alloy is also extremely composition sensitive so that while the hysteresis can be shifted from sub-zero temperatures to above-zero temperatures, the width of the hysteresis does not appreciably change.
  • the alloy were martensitic at room temperature, the service temperature must be above room temperature.
  • the alloy would be martensitic below room temperature so that the alloy would require special cold-temperature equipment for fabrication, shipping, and storage.
  • room temperature should be located near the middle of the transformation hysteresis.
  • the width of the hysteresis in the binary alloy is so narrow, the range of service temperatures for any particular alloy is necessarily limited. As a practical matter, the alloy would have to be changed to accommodate any change in service temperatures.
  • Nickel/titanium/iron alloys e.g., those in Harrison et al., U.S.P. 3,753,700, while having a wide hysteresis, up to about 70°C, are the typical cryogenic alloys which always undergo the martensite/ austenite transformation at sub-zero temperatures.
  • the colder shape-memory alloys such as the cryogenic alloys have a wider transformation hysteresis than the warmer shape memory alloys.
  • the alloys In the case of the cryogenic alloys, the alloys must be kept very cold, usually in liquid nitrogen, to avoid the transformation from martensite to austenite. This makes the use of shape memory alloys inconvenient, if not uneconomical.
  • the nickel/titanium/copper alloys disclosed in U.S. Patent Application No. 537316 which served to establish a priority date for EP-A-88604 and the nickel/titanium/vanadium alloys disclosed in U.S. Patent Application No. 541844 which served to establish a priority date for EP-A-140621, are not cryogenic but their hysteresis may be extremely narrow (10 ⁇ 20°C) such that their utility is limited for couplings and similar articles.
  • Aging, heat treatment, composition, and cold work can all effectively shift the hysteresis.
  • the hysteresis may be shifted so that the martensite phase can exist at a temperature at which there would normally be austenite.
  • the alloy Upon removal of the stress, the alloy would isothermally (or nearly isothermally) transform from martensite to austenite.
  • the pipe coupling may be a monolithic pipe coupling as described in the earlier-mentioned Harrison and Jervis patents.
  • the pipe coupling may be a composite coupling as described in the earlier-mentioned Clabburn patent and in U.S. Patent Nos. 4,379,575; 4,455,041; and 4,469,357 to Martin.
  • the composite coupling comprises a driver member and a sleeve member.
  • the sleeve may be assembled with the driver just after the expansion of the driver so as to take advantage of the elastic springback of the material.
  • the driver and sleeve members are then stored in a cryogenic fluid until ready for installation.
  • the driver alone may be stored in a cryogenic fluid and then joined with the sleeve at the time of installation. Once joined with the sleeve, the driver is allowed to fully recover.
  • the driver may be expanded and, after springback has occurred, joined with the sleeve while both are immersed in a cryogenic fluid. Since no recovery of the driver has occurred, the sleeve is only loosely joined and would, in fact, become separated from the driver if means were not provided to prevent this separation.
  • the means to prevent this separation is usually provided in the form of a flaring of one end of the sleeve which makes for a slight interference fit between the sleeve and the driver.
  • a keeper is utilized to apply a stress sufficient to temporarily raise the austenite transformation temperature.
  • the shape-memory alloy remains in the martensitic state while the stress is applied. This method is known as constrained storage.
  • this invention provides a method of temporarily expanding the transformation hysteresis, defined by M s , M,, As and A f temperatures, of a nickeltitanium based shape memory alloy, so that the As and A f temperatures are increased temporarily to A s ' and A f ' where the difference between A s ' and M s is greater than the difference between As and M s , the method comprising:
  • the invention provides a method of making a composite coupling which comprises a driver member formed from a nickel-titanium based shape memory alloy that has a transformation hysteresis defined by M s , M f , As and A f temperatures, and a sleeve member positioned in the direction of recovery of the driver member, the method comprising:
  • Figure 1 illustrates the shifting of the transformation hysteresis as would occur if, for example, a stress was applied.
  • the hysteresis has moved upwardly in temperature from position 2 to position 4, shown in dotted lines. While the entire hysteresis has moved upwardly in temperature it can be seen that the width of the hysteresis, indicated generally by 6 has remained approximately constant.
  • M s , M f , A s , and A f have all been translated to higher temperatures and are now denoted as M s ', M f ', A s ', and A,'.
  • M s ', M f ', A s ', and A,' are now denoted as M s ', M f ', A s ', and A,'.
  • Figure 2 now illustrates in general the expansion of the hysteresis. It can be seen that the martensite transformation temperatures remain constant but the austenite transition temperatures have been translated upwardly so that the width of the hysteresis indicated generally by 6 has now been expanded as indicated generally by 8. That is, M s and M, remain constant or nearly constant while As and A f have been translated to higher temperatures and are now denoted as A s ' and A,'.
  • a coupling may be expanded and held in the expanded condition so as temporarily to raise, i.e., temporarily shift, the hysteresis. As long as the stress is applied, the hysteresis will be shifted. If it is desired, for example, to use this coupling in ambient temperature, indicated by T A , the coupling will not transform to austenite as long as temperature T A is below A s '. Upon the removal of the stress, the coupling will isothermally (or nearly isothermally) transform into austenite.
  • the coupling will be at T A when the stress is removed but the hysteresis will have shifted from position 4 back to position 2.
  • the coupling being martensitic before the shift from position 4 to position 2 must necessarily be austenitic after the shift.
  • This method may be used for constrained storage (see, e.g., Clabburn, U.S.P. 4,149,911) wherein a coupling is expanded and then held on a mandrel in the expanded condition until it is ready to be used, at which time it is cooled to below the M s temperature so that it may be released from the mandrel and then installed.
  • the problem with this method is that while the coupling is held (during shipping, for example) in the expanded position which is necessary to shift the hysteresis, the coupling may relax so that a certain, perhaps very substantial, amount of recovery motion will be permanently lost.
  • the method comprises temporarily expanding the transformation hysteresis by elevating the As and A f temperatures to A s ' and A f ', respectively, so that the temperature difference between A s ' and M s is greater than the temperature difference between As and M s .
  • the means for expanding the transformation hysteresis may be removed and then the alloy is stored at a temperature less than A s '.
  • both the M s and M, temperatures will remain essentially constant during the expansion of the hysteresis.
  • either or both of the M s and M f temperatures may permanently change. This change may result from the varying of the slope or even movement of the martensitic part of the transformation hysteresis curve due to the interaction of certain metallurgical conditions.
  • the important point to emphasize here is that there will always be a net increase of the width of the transformation hysteresis according to the method of the invention.
  • the means for expanding the transformation hysteresis comprises overdeforming the alloy by applying a stress sufficient to cause nonrecoverable strain in the alloy.
  • nonrecoverable strain means strain which is not recovered after deformation and subsequent no-load heating to at least the A f ' temperature.
  • the stress will be removed after the alloy is overdeformed.
  • the overdeforming takes place at a temperature which is less than about the maximum temperature at which martensite can be stress-induced. To those skilled in the art this temperature is commonly known as M d . It is preferred however that the overdeforming temperature be above M s .
  • At least partial recovery of the alloy article can occur when the alloy is heated to a temperature greater than about A s '.
  • the heating temperature be greater than A f ' so as to effect full recovery of the alloy.
  • the nickel/titanium-based shape memory alloy may be a binary or it can be at least a ternary. If it is a ternary nickel/titanium-based shape memory alloy the ternary consists essentially of nickel, titanium and at least one other element selected from the group consisting of iron, cobalt, vanadium, aluminum, and niobium. The most preferred ternary, for reasons which will become apparent hereafter, consists essentially of nickel, titanium, and niobium.
  • FIG. 3 schematically illustrates a stress-strain curve for a typical shape memory alloy which was overdeformed. The load was then removed. With overdeformation there is by definition a substantial amount of non-recoverable strain imparted to the alloy. Nonrecoverable strain will occur when the alloy, generally speaking, is strained past its second yield point indicated approximately by reference numerical 10. After removal of the stress, the alloy was heated.
  • curve 12 illustrates the heating afterthe removal of the stress.
  • the alloy was cooled down as illustrated by curve 14. During the cooling down under a small load and M s and M f temperatures were measured. The alloy was then reheated (curve 16) to measure the recovered austenitic transition temperatures As and A f .
  • the effective austenitic and martensitic transformation temperatures may be conveniently determined by the intersection of tangents to the transformation hysteresis curves.
  • tangents 22 on curve 12 locate As' and A f '.
  • the mid-point of the transformation, for example A 50 ' on curve 12 is vertically equidistant from the literal starting and ending points, for example 18 and 20 on curve 12, of the transformation.
  • austenitic and martensitic transformation temperatures refer to the austentic and martensitic transformation temperatures determined by the above noted method of intersecting tangents.
  • the literal starting and ending points of the martensitic and austentic transformations are indicated these temperatures will be referred to as the true martensitic and austenitic transformation temperatures.
  • true A s ' and true A,' are the literal starting and ending points of the austenitic transformation after expansion of the hysteresis.
  • Curves 14 and 16 represent the shape memory alloy transformation hysteresis in the recovered state while curves 12 and 14 represent the shape memory alloy transformation hysteresis in the unrecovered state.
  • a second aspect of the invention provides a method of preassembling a composite coupling having at least one heat recoverable driver member and at least one metallic insert.
  • the driver member is made from a nickel/titanium-based shape memory alloy having a transformation hysteresis defined by M s , M f , As and A f temperatures.
  • the method comprises overdeforming the driver member by applying a stress sufficient to cause nonrecoverable strain in the driver member so that the As and A f temperature are temporarily raised to A s ' and A,', respectively.
  • the method further comprises removing the stress; engaging the driver member and insert; and then warming the driver and insert to a temperature less than A s '.
  • the metallic insert may take many forms.
  • the insert may be tubular, tapered or slotted, all of which are disclosed in the above Martin patents.
  • the insert may be single or multipiece.
  • the insert may have an irregular shape such as to be x-shaped, y-shaped or t-shaped.
  • the insert may also have sealing means as also disclosed in the above Martin patents.
  • the sealing means may comprise, for example, teeth or gall-prone materials.
  • driver member may take many forms. It is preferred, however, that the driver member be a tubular driver or a ring driver.
  • a stress is applied sufficient to cause at least one percent of nonrecoverable strain in the driver member.
  • the nonrecoverable strain may be much more than one percent which is usually the case.
  • the overdeformation should take place at a temperature which is less than about the maximum temperature at which martensite can be stress-induced.
  • the temperature is also known as the M d temperature.
  • M d temperature The reason for this is that when the material has been deformed at a temperature greater than M d the amount of strain recoverable upon subsequent heating is drastically and dramatically reduced. Generally, the more the deformation temperature is raised above M d , the greater will be the reduction in recoverable strain. It is most preferred that the overdeforming temperature be between M s and A s .
  • the nickel/titanium-based shape memory alloy has an M s temperature less than about 0°C.
  • the nickel/titanium-based shape memory alloy is stable, does not contain an R phase and has an M s temperature less than about 0°C.
  • the R phase is known as a transitional phase between the austentite and martensite and has a structure different from both. The effect of the R phase is to depress the austenitic and martensitic transformation temperatures. Alloys that are stable (i.e. exhibit temper stability) have an M s that does not change more than about 20°C after annealing and water quenching and subsequent aging between 300 and 500°C.
  • the resulting ingots were hot swaged and hot rolled in air at approximately 850°C to produce a strip of approximately 6.35 x 10- 4 m (0.025-in). thickness. Samples were cut from the strip, descaled and vacuum annealed at 850°C for 30 minutes and furnace cooled.
  • the strip was then elongated. After elongation the stress was removed and the strip was heated unrestrained so as to effect recovery of the shape memory alloy. The recovery was monitored and plotted as a function of temperature. When the transformation was complete, the sample was cooled and then reheated so as to complete the measurement of the martensite and austenite transformation temperatures before recovery and after recovery. The results are tabulated below in Table 1.
  • a s ' minus M s is very useful since M s is directly indicative of the lower functional limit of the alloy and the A s ' is directly indicative of the highest temperature which may be encountered (e.g. during storing and shipping) before the austenite transformation will effectively begin.
  • a s ' minus M s defines the operating range of the alloy when processed according to the invention. This measure should be compared to As minus M s which defines the operating range of the alloy after the temporary expansion of the hysteresis has been recovered. As minus M s is also indicative of the operating range of the alloy if it were never processed according to the invention.
  • comparing A s ' minus M s to As minus M s provides useful indicia of the expansion of the hysteresis as well as the advantages of the invention.
  • a s ' minus M s and As minus M s are about the same at 5% elongation; however, at 16% elongation, the difference becomes substantial. It is useful to note that A s ' after 16% elongation is above normal room temperature so that the alloy may now be handled at room temperature so that the alloy may now be handled at room temperature without the necessity of providing a cold environment.
  • M so , A so . and A 50 ' values are the martensite and austenite transformation temperatures at which the transformation is 50% complete.
  • Table 1 below it can be seen that the the sample was cooled and then reheated so as to complete the measurement of the martensite and austenite transformation temperatures before recovery and after recovery.
  • the difference between M 50 and A so the permanent width of the hysteresis, is about 60°C.
  • the width of the hysteresis may be temporarily enlarged, i.e., A so ' minus M so , from 64°C at 5% elongation (at which there is no nonrecoverable strain) to 91°C at 16% elongation (at which there is substantial nonrecoverable strain).
  • the M so , A so , and A so ' values are also useful because they are the most easily determined as will become apparent hereafter.
  • the width of the hysteresis and the operating range have been enlarged as a result of the 16% elongation of the alloy.
  • the import of this is that after elongation of the alloy, the alloy no longer has to be stored in liquid nitrogen to prevent it from transforming into austenite. Since A s ' has been raised to -88°C other forms of cold storage may now be used to store and ship the nickel/titanium/iron alloy prior to its final use. It is believed that this will result in greater utility of the alloy.
  • the hysteresis width (A 50 ⁇ M 50 ) in the fully recovered state is about 55°C with As being -56°C.
  • the austenite temperature in this range it is still necessary forthe alloy to be cold stored in order to prevent transformation of the martensite into the austenite.
  • the ring is now enlarged about 5%, the A s temperature has been temporarily raised to -14°C which would still require cold storage.
  • the As has been temporarily increased to 27°C.
  • the alloy may be stored and shipped at room temperature. No cold storage provisions are required.
  • the temperature of deformation be above M s .
  • the importance of this limitation is illustrated in the next sample which was deformed at -70°C (compared to an M s of -90°C). It can be seen that A s ', and A 50 ' ⁇ M 50 and A s ' ⁇ M s have all been increased more than any of the previous samples.
  • the nickel/titanium/niobium ternary alloys are preferred alloys due to their ready susceptibility to expansion of the transformation hysteresis as illustrated above.
  • those that are stable have an M s greater than 0°C and do not have an R phase are the most preferred.
  • the R phase is a transitional phase between austenite and martensite. Since the R phase is not present, there is substantial uniformity in the martensite and austenite transformation temperatures from sample to sample. Alloys that are stable (i.e., exhibit temper stability) have an M s that does not change more than about 20°C after annealing and water quenching and subsequent aging between 300 and 500°C.
  • compositions of: 46 atomic percent nickel, 49 atomic percent titanium, and 5 atomic percent vanadium; 49 atomic percent nickel, 49 atomic percent titanium, and 2 atomic percent cobalt; and 50 atomic percent nickel, 48.5 atomic percent titanium, and 1.5 atomic percent aluminum.
  • Each of the compositions was melted and 6.35 x 10- 4 m (0.025-in.) thick strips prepared in the same way as that previously stated with respect to the binary.
  • the stress was removed and the strip was heated unrestrained so as to effect recovery which was monitored and plotted as a function of temperature.
  • the sample was cooled and then reheated so as to complete the measurement of the martensite and austenite transformation temperatures before recovery and after recovery.
  • the martensite and austenite transformation temperatures were measured with a load of 1.38 x 107 Pa (20 ksi) and then extrapolated to 0 Pa. The results are tabulated below in Tables 4, 5, and 6.
  • the large discrepancy between the martensite and austenite transformation temperatures at 5 and 16%, respectively, is believed due to the interference of the R-phase.
  • the presence of the R phase 28 is most noticeable on the austenite leg of the transformation hysteresis for the alloy deformed 5%.
  • the R phase is a transitional phase between the austenite and martensite and has a structure different than either.
  • the effect of the R phase is to depress the austenite and martensite transformation temperatures.
  • Figure 6 illustrates the transformation hysteresis curve for the same alloy, but after recovering from 16% deformation.
  • the R phase is noticeably absent.
  • the austenite and martensite transformation temperatures in Figure 6 are also noticeably higher.
  • Example 6 the sample deformed 16%, and thus having substantial nonrecoverable strain, shows. a marked expansion of the transformation hysteresis (as in the previous two examples) whereas the sample deformed at 5% shows essentially no expansion of the transformation hysteresis.
  • a cylindrical driver member was made from an alloy having the composition of 47 atomic percent nickel, 44 atomic percent titanium and 9 atomic percent niobium.
  • the nickel/titanium/niobium alloys in general, are the most preferred alloys. These alloys are disclosed in U.S. Patent Application No. 668777 which served to establish a priority date for EP-A-185452.
  • the driver was melted and processed as noted in our patent application above except that a coupling was machined instead of a ring.
  • the driver was machined to have an inside diameter of 2.15 x 10- 2 m (.847 inches), an outside diameter of 3.34 x 10- 2 m (1.313 inches) and a length of 5.39 x 10- 2 m (2.12 inches).
  • a cylindrical insert was then made to be eventually joined with the driver so as to form a composite coupling.
  • the insert was machined from 316 stainless steel so as to have an inside diameter of 2.16 x 10- 2 m (.850 inches), an outside diameter of 2.46 x 10- 2 m (.970 inches) and a length of 5.39 x 10- 2 m (2.12 inches). It is not necessary to the invention that the insert be made from stainless steel. It is only necessary that the insert be made from a material that is sufficiently soft such that it may be crushed by the driver upon full recovery thereof.
  • the M s temperature was -90°C
  • the As temperature was -56°C
  • the M d temperature was -10°C.
  • such an alloy expanded about 16% at -50°C would be expected to have a true A s ' of -52°C and an A s ' of +52°C.
  • the driver was near the literal starting temperature of the austenitic transformation of the temporarily expanded transformation hysteresis.
  • the driver was removed from the cold fluid and placed on a work bench.
  • the insert was then slipped into the driver. Thereafter, the driver and insert were allowed to warm to room temperature, which it is noted is substantially belowA,'. It was found that the driver and insert were snugly engaged and could only be moved relative to each other with great difficulty. It should be noted that while the driver and insert became snugly engaged, there was no crushing of the insert.
  • the driver prepared as described above, would be expected to have about 8% recoverable strain. About 1% of that recoverable strain was utilized in the preassembling of the driver and insert. Thus, about 7% recoverable strain remains for the actual coupling of the substrates.
  • the composite coupling is now preassembled and ready for storage or use.
  • compositions of 50.7 atomic percent nickel and 49.3 atomic percent titanium Commercially pure titanium and carbonyl nickel were weighed in proportions so as to give a composition of 50.7 atomic percent nickel and 49.3 atomic percent titanium. Additionally, commercially pure titanium, carbonyl nickel and amounts of vanadium, cobalt, aluminum and iron were weighed in proportions so as to give compositions of: 46 atomic percent nickel, 49 atomic percent titanium and 5 atomic percent vanadium; 49 atomic percent nickel, 49 atomic percent titanium and 2 atomic percent cobalt; 50 atomic percent nickel, 48.5 atomic percent titanium and 1.5 atomic percent aluminum; and 47 atomic percent nickel, 50 atomic percent titanium and 3 percent iron.
  • the resulting iron-containing ingots were hot swaged at approximately 850°C. Round, tensile bars (6.35 x 10- 3 m 1 ⁇ 4 ") in diameter were then machined from the hot swaged ingot, vacuum annealed at 850°C for 30 minutes, and then furnace cooled. The tensile bars were then elongated. After elongation, the stress was removed and the bars were heated unrestrained so as to effect recovery of the shape memory alloy. The recovery was monitored and plotted as a function of temperature. When the transformation was complete, the sample was cooled and then reheated so as to complete the measurement of the martensitic and austenitic transformation temperatures before recovery and after recovery. The results are tabulated in Table 8.
  • the remaining ingots were hot swaged and hot rolled in air at approximately 850°C to produce a strip of approximately 6.35 x 10- 4 m (0.025-in.) thickness.
  • Samples were cut from the strip, descaled and vacuum annealed at 850°C for 30 minutes and furnace cooled. The stip was then elongated. After elongation, the stress was removed and the strip was heated unrestrained so as to effect recovery which was monitored and plotted as a function of temperature. When the transformation was complete, the sample was cooled and then reheated so as to complete the measurement of the martensitic and austenitic transformation temperatures before recovery and after recovery.

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Claims (11)

1. Procédé d'élargissement temporaire de l'hystérésis de transformation, définie par les températures Ms, Mf, As et Af, d'un alliage à mémoire de forme à base de nickel et titane, de manière que les températures As et Af soient élevées temporairement à des valeurs As' et Af' pour lesquelles la différence entre As' et Ms est supérieure à la différence entre As et Ms, procédé consistant:
(a) à déformer l'article qui est réalisé en l'alliage par application à l'article d'une charge suffisante pour créer une déformation d'au moins 1% dont la reprise ne serait pas possible si, après la déformation, l'article était chauffé sous charge nulle au moins jusqu'à la température Af', la charge de déformation étant appliquée à l'article de manière qu'à tous instants, cependant que la déformation survient sur l'article, la température de ce dernier soit inférieure:
(i) à la température à laquelle l'alliage commence à passer de la phase martensitique à la phase austénitique et,
(ii) à la température maximale à laquelle l'alliage peut être transformé de la phase austénitique à la phase martensitique par l'application d'une charge; et
(b) à faire cesser d'agir la charge de déformation sur l'article tout en s'assurant que la température de l'alliage ne dépasse pas la valeur As'.
2. Procédé suivant la revendication 1, dans lequel la charge de déformation est appliquée à l'article de manière qu'à tous instants entre le début de l'application de la charge à l'article et le moment où la déformation d'au moins 1% non susceptible de reprise a été conférée à l'article, la vitesse d'accroissement de la charge avec augmentation de la déformation n'ait pas une valeur inférieure à zéro.
3. Procédé suivant la revendication 1 ou la revendication 2, dans lequel la température à laquelle l'article est déformé est supérieure à Ms.
4. Procédé suivant l'une quelconque des revendications 1 à 3, dans lequel l'étape de déformation a lieu à une première température, le procédé impliquant l'étape de répétition de la déformation de l'article à une seconde température qui diffère de la première, et qui lui est de préférence supérieure.
5. Procédé suivant l'une quelconque des revendications 1 à 4, dans lequel l'étape de déformation a lieu à une première température, et qui comprend l'étape d'élévation de la température de l'alliage à une seconde température qui est de préférence de l'ordre de la température ambiante, tout en maintenant la déformation exercée.
6. Procédé suivant l'une quelconque des revendications 1 à 5, dans lequel une déformation d'environ 16% est conférée à l'article.
7. Procédé de réalisation d'un raccord composite qui comprend un organe de serrage constitué d'un alliage à mémoire de forme à base de nickel-titane qui a une hystérésis de transformation définie par les températures Ms, Mt, As et A,, et un manchon positionné dans la direction de reprise de l'organe de serrage, procédé qui consiste:
(a) à élargir l'hystérésis de transformation de l'alliage de manière que les températures As et Af soient portées temporairement aux valeurs As' et A,' pour lesquelles la différence entre As' et Ms est supérieure à la différence entre As et Ms, par déformation de l'organe de serrage par application à cet organe d'une charge suffisante pour créer une déformation d'au moins 1% qui ne serait pas susceptible de reprise si, après la déformation, l'article était chauffé sans charge jusqu'à une température au moins égale à la température Af', la charge de déformation étant appliquée à l'organe de serrage de manière qu'à tous instants pendant que la déformation est exercée sur l'organe de serrage, la température de cet organe soit inférieure:
(i) à la température à laquelle l'alliage commence à passer de la phase martensitique à la phase austénitique et
(ii) à la température maximale à laquelle l'alliage peut passer de la phase austénitique à la phase martensitique par l'application d'une charge; et
(b) à retirer la charge de déformation de l'organe de serrage tout en s'assurant que la température de cet organe ne dépasse pas A7';
(c) à positionner le manchon dans le direction de reprise de l'organe de serrage; et
(d) à élever la température de l'organe de serrage jusqu'à une valeur qui est supérieure à la température As' vraie mais inférieure à la température As' de manière à provoquer la reprise de l'organe de serrage et sa mise en contact avec le manchon.
8. Procédé suivant la revendication 7, dans lequel la température à laquelle l'organe de serrage est déformé est supérieure à la valeur Ms.
9. Procédé suivant la revendication 7 ou la revendication 8, dans lequel la déformation de l'organe de serrage a lieu au-dessous de la température ambiante et a pour effet que la température As' est portée à une valeur supérieure à la température ambiante, et dans l'étape (d) du procédé, la température de l'organe de serrage est élevée au voisinage de la température ambiante.
10. Procédé suivant l'une quelconque des revendications 1 à 9, dans lequel la température Ms de l'alliage est inférieure à environ 0°C.
11. Procédé suivant l'une quelconque des revendications 1 à 10, dans lequel l'alliage est essentiellement constitué de nickel, de titane et de niobium.
EP85308080A 1984-11-06 1985-11-06 Procédé pour la mise en oeuvre d'un alliage à mémoire à base de nickel-titane et pièce obtenue par ce procédé Expired - Lifetime EP0187452B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT85308080T ATE60811T1 (de) 1984-11-06 1985-11-06 Verfahren zur behandlung einer formgedaechtnislegierung auf nickel-titan-basis und daraus hergestellter gegenstand.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US668771 1984-11-06
US06/668,771 US4631094A (en) 1984-11-06 1984-11-06 Method of processing a nickel/titanium-based shape memory alloy and article produced therefrom
US06/783,371 US4740253A (en) 1985-10-07 1985-10-07 Method for preassembling a composite coupling
US783371 1985-10-07

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EP0187452A1 EP0187452A1 (fr) 1986-07-16
EP0187452B1 true EP0187452B1 (fr) 1991-02-06

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DE3821066A1 (de) * 1988-06-22 1989-12-28 Bayerische Motoren Werke Ag Sicherheitsgurtschloss in einem kraftwagen
DE68911614T2 (de) * 1988-08-01 1994-05-26 Matsushita Electric Works Ltd Gedächtnislegierung und Schutzvorrichtung für elektrische Stromkreise unter Verwendung dieser Legierung.
DE4006076C1 (fr) * 1989-08-12 1990-12-13 Fried. Krupp Gmbh, 4300 Essen, De
US5366331A (en) * 1993-02-10 1994-11-22 General Electric Company Shape memory lock fastener
EP0648856B1 (fr) * 1993-09-22 1999-04-21 The Furukawa Electric Co., Ltd. Monture de lunettes et méthode de fabrication
JP2847177B2 (ja) * 1994-03-11 1999-01-13 科学技術庁金属材料技術研究所長 ＮｉＴｉ系高比強度耐熱合金
EP1629134B1 (fr) * 2003-03-25 2012-07-18 Questek Innovations LLC Alliages a memoire de forme renforces par nanodispersion et coherents
CN113481443B (zh) * 2021-06-18 2022-02-01 武汉大学 一种制备变形量可调控的金属材料的方法及校核装置

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US3748197A (en) * 1969-05-27 1973-07-24 Robertshaw Controls Co Method for stabilizing and employing temperature sensitive material exhibiting martensitic transistions
US3953253A (en) * 1973-12-21 1976-04-27 Texas Instruments Incorporated Annealing of NiTi martensitic memory alloys and product produced thereby
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DE3581721D1 (de) 1991-03-14
CA1269915A (fr) 1990-06-05
EP0187452A1 (fr) 1986-07-16

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