CA1316437C - Method for producing a shape memory alloy member having specific physical and mechanical properties - Google Patents
Method for producing a shape memory alloy member having specific physical and mechanical propertiesInfo
- Publication number
- CA1316437C CA1316437C CA000596022A CA596022A CA1316437C CA 1316437 C CA1316437 C CA 1316437C CA 000596022 A CA000596022 A CA 000596022A CA 596022 A CA596022 A CA 596022A CA 1316437 C CA1316437 C CA 1316437C
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- Prior art keywords
- internal stress
- process according
- mechanical properties
- steps
- temperatures
- Prior art date
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Classifications
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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
-
- 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
Abstract
ABSTRACT OF THE DISCLOSURE
In the present application, a process has been disclosed that controls and adjusts the physical and mechanical properties of a shared memory alloy (SMA). The physical properties include, but are not limited to, trans-formation temperatures of the various SMA phases, the result-ing hysteresis between such phases, suppression of the Martensite phase in relation to the Rhombohedral phase, and the relationship between the start and finish temperatures of the respective phases. Mechanical properties that are controlled and adjusted include, but are not limited to, the yield point, ultimate tensile strength, and ductility. This has been accomplished by the introduction of a known internal stress and the distribution of that stress in the SMA prior to final fabrication of the SMA to a desired shape and prior to imparting memory through a predetermined heat treatment schedule.
In the present application, a process has been disclosed that controls and adjusts the physical and mechanical properties of a shared memory alloy (SMA). The physical properties include, but are not limited to, trans-formation temperatures of the various SMA phases, the result-ing hysteresis between such phases, suppression of the Martensite phase in relation to the Rhombohedral phase, and the relationship between the start and finish temperatures of the respective phases. Mechanical properties that are controlled and adjusted include, but are not limited to, the yield point, ultimate tensile strength, and ductility. This has been accomplished by the introduction of a known internal stress and the distribution of that stress in the SMA prior to final fabrication of the SMA to a desired shape and prior to imparting memory through a predetermined heat treatment schedule.
Description
1 3 ~
A ~ET~OD PUR PROWCING A S~APE MEMORY ALLOY ~EMBER
~AVING SPECIFIC P~YSICAL AND MEC~A~ICAL PROPERTI~S
~ACKGROUND O~ THE INVENTION
Field of the Invention .
The present inventiQn relates to a method for producing a shape memory alloy (SMAJ member having a range of specific physical and mechanical properties and more particularly to the control of the physical and mechanical properties by the introduction of predetermined internal stresses into the alloy prior to a predetermined memory imparting heat treatment.
Descript~on of the Prior Art A nickel-titanium alloyr such as Nitinol (NiTi) is known to have the ability to recover its original shape whe!n deformed in its Martensite and/or Rhombohedral phase(s), and then heated to the Auste~ite phase. This characteristic of shape memory alloy is generally attributed to the basic chemical ~omposition of the alloy, proce3sin9, and-the memory imparting heat treatment.
There are a num~er of articles which describe the aforementioned characteristic of SMA. These include .S. Patent 4,310,354 and 3~174,851 as ~ell a~ an article from ~he Naval Surface Weapons Center entitled ~Effects of Stresses On The Phase Transformation of Nitinol"
~NSWC TR 86-196 1986) and "~fEect of Heat Treatment After Cold Workin~ on the Phase Transformation of TiNi 1316~37 Alloy" Transactions of the Japan Institute of M~tals, Vol. 28, No. 2 (1987) pages 83 - 94.
All of these articles are concerned with the generally known processes for making a SMA alloy. This include~ the steps of initially selecting an alloy of a predetermined composition, forming the alloy to a desired shape, and ~ubjecting the alloy to a predetermined memory imparting heat treatment. Even though close control of the alloy' 5 chemical composition and memory imparting heat treatment is mai~tai~ed, a consid~rable variatio~
in transformation temperatures has been known to occur.
This has generally been attributed to process variables and other unknown factors. This limits ~he use of SMA
alloys in applications where more precise transformation temperatures, and other ~echanical and physical properties are sought.
SUMMARY OF T~E INVENTION
In the present invention, a process has been developed that controls and adjusts the physical and mechanical properties of SMA. The physioal properties include, but are not limited to, transformation temperatures of the various SMA phases, the resulting hysteresis between such phases, suppression of the Martensit:e phase in relation to the Rhombohedral phase, and the relationship between the start and finish temperatures of the respective phases, ~echanical propertie~s that are controlled and adjusted by this invention include, but are not limited to, the yield point, ultimate tensile strength, and ductility. This ha~ been accompli~hed by the introduction of a known internal stress and the di-Rtribution of that stress in the SMA prior to final fabrication ~f the SMA to a desired shape and prior to imparting memory ~hrough a prede~er~ined heat treatment ~ehedule.
The primary object o~ this invention is to control and adjust the transformation te~peratures of S~A by the introduction and distribution vf known 131~7 internal stresses into a SMA member of a known composition pxior to a memory imparting heat treatment.
Another object of the invention is to control other physical properties and the mechanical properties of SMA by the introduction and distribution of known internal stresses in a SMA member of a known composition prior to a memory imparting heat treatment.
A primary feature of the invention is the ability to provide precise transformation temperatures and other physical and the mecbanical properties in an S~A alloy of known composition.
Other principal features and advantages of the invention will become apparent to tho~e skilled in the art upon review of the following detailed description, claims and drawings.
DETAILED DESCRIPTON OF THE DRA~INGS
Figure 1 is a typical DSC curve showing an A to R to M to A (ARMA) transformation reaction for a low amount, under 15% cold reduction in area, of internal stress introduced prior to heat treatment where A, R and M denote Austenite, Rhombohedral and Martensi~e phases, respectively.
Figure la is a typical ~SC curve showing an A to R to A (ARA) transformation reaction for the same ~ample as in Figure 1.
- ~igure 2 is a typical DSC curve ~howin~ the aR~A transfor~ation reaction for a moderate amount, 35%
cold reduction in area, of internal stre~s introduced prior to heat treatment.
Figure 2a is a typical DSC curve showing an ARA transformation reaction for the same 3ample as in Figure 2.
~ igure 3 is a typical DSC curve ~howing an AR~A transforDation reaction for a high amount, 55~
cold reduction in area, o~ internal stre-qs introduced prior ~o heat treatment.
131~37 ~4--~ igure 3a is a typical DSC curve showing an ARA tranformation reaction for the same sample as in Figure 3.
Pigure 4 is a family of curves showing the Austenite peak temperature of the ARMA reactions at different amounts of internal stress and memory imparting temperatures.
Fi~ure S is a family of curves showing the Austenite peak temperature of the ARA reaction at different amounts of internal stress and ~emory imparting temperatures.
Figure 6 is a family of curves showing the Rhombohedral peak te~perature of the ARMA or ARA
reacti3ns at different amounts of internal stress and memory imparting temperatures.
Figure 7 is a family of curves showing the Martensite peak temperature of the ARMA or AMA reactions at different amounts of internal stress and ~emory imparting te~peratures.
Figure 8 is a family of curves -~howing the phase tranformation peak tempertures at different amounts of internal stress and a memory imparting temperature of 475C for l hour.
Figure 9 is a family of curves showing the austenitic and martensi~ic yield strength at different amounts of internal stress at 500C memory imparting te~perature for l hour.
Figure lO is a family of curves showing the Austenite yield strength at different amounts of internal stress and memory imparting temperatures.
Figure 11 is a stress/strain curve o~ both Aus~enite and ~arten3ite at two levels of internal strecs.
Figure 12 is a 3ke~ch of a SMA ~ember having a plur~lity o~ section with different stress levels.
Before the invention is explained in detail, it i5 to be understood that the invention is not limited in its application to the details as set forth in the ~311~437 following description or illustrated in the drawings.
The invention is capable of other embodiments and o' being practiced or being carried out in various ways.
Also, it is to be understood that the phraseology and terminolc)gy used herein i5 for the purpose of description and should not be regarded as limiting.
DESCRIPTION OP T~E INVENTION
The Shape Memory Alloy (SMA) describ~d herein is a near equiatomic alloy of nickel 2nd titanium.
This alloy is used for illustration purposes only, as other SMA alloys will al~o respond in a similar fashion.
The process accordinq to the present invention generally includ~s .he selection of an SMA of a known composition. Annealing of the alloy to a reference stress level ~or a predetermined time. Cold forming of the alloy to introduce a controlled amount of internal stress into the alloy.
The next step includes the forming of the alloy to a desired shape or configuration. Fixuring the alloy to the desired shape memory coniquration.
Heat treating of the alloy at a selected memory imparting temperature for a fixed period of time and allowing the alloy to cool to ambient temperature. The SMA is then re~ved f.rom the fixture. Determining the transformation temperature of the SMA for the Austenite, Rhombohedral and Marte!nsite phases. A amily of curves for these pha~e~ can be establi~hed by repeating the above process at different internal stresses and different memory impartin~ temperatures as described now fully hereinafter.
In the following example a wire of abou~ 1 to 2 ~m. in diame~er drawn from the ~MA wa~ annealed at temperatures between 3Q0 and 950C for a ~pecific length of time, generally between five minutes and two hours.
The annealin~ prooe~s reduces the amount of internal ~316~37 stress to a reference level in preparation for subsequen~
introduction or addition of internal stress.
The annealed wire is then processed to introduce or add various amounts cf internal stresses by cold reducing the wire by a specific amount.
Calculations are based upon the initial and final diameters cf the cold worked wire. This step in the process is particularly significant since internal stresses make it posible to adjust and control the transition temperatures and other physical and mechanical properties of the alloy. The alloy is then formed to a desired configuration and supported in the desired shape memory configuration. The alloy is then heated at at a 3elected memory imparting temperature and cooled. The following ~igures ~how the transformation phases at various internal stress levels.
Referring to Figures 1 and la, the transformation reactions: Austenite to Rhombohedral to Martensite to Austenite phase changes IARMA) and the Austeni~e to Rhombohedral to Austenite phase changes (ARA) are depicted usin~ Differential Scanning Calorimetry (DSC) plots. The plots show transition temperatures for low amounts of cold reduction (close to 15~) for this alloy at peak temperatures of 53.4, 37.9, 31.7 and 9.6C for the A, A', R and M phases respecti~ely for 1 ho~r at 475C memory imparting temperature.
Referring to Figures 2 and 2a, the transformation reaotion: Austenite to Rhombohedral to Martensite to Austenite phase changes (ARMA) and the ~ustenite to Rhombohedral to Austenite pha~e ch~nges (ARA) are depicted using Differential Scannng Calorimetry (DSC) plots. The plots ~how transition temperatures for moderate amounts of cold reduction (close to 35~) for this alloy with peak temperatures of 44.3, 40.9, 1316~37 34.3 and -10.8C for the A, A', R and M phases respectively for 1 hour at 475C memory imparting temperature.
Referring to Figures 3 and 3a, the transformation reaction: Austenite to Rhombohedral to Martensite to Austenite phase changes (ARMA) and the Austen$te to Rhombohedral to Austensite phase changes (ARA) are depicted using Differential Scannng Calorimetry (DSC) plots. The plots shcw transition temperatures for high amounts of cold reduction, close to 55%, for this alloy with peak temperatures of 43.7, 41.9, 35.6 and -15O3~C for the A, A', R and M pha~es respectively for 1 hour at 475C me~ory imparting temperature.
The process is then repeated for various amounts of cold reduction and memory imparting temperatures, which for this alloy are in the ranges of 5 to 60% and 400 to 600C respectively. Figures 4 through 7 respectively show the family of curv~s obtained for the peak transition temperatures of the Austensite, Ap (M to A); Austenite, A'p (R to A~; Rhombohedral, Rp;
and Martensite, Mp phases. The family of curves for this alloy are sho~n for 475 through 600C memory imparting t~mperatures for 1 hour.
Figure 8 clearly shows the relationship between the degree of internal stress ~cold work) and the transition temperature peaks of this alloy, at 475C
memory imparting temperature for 1 hour.
Figure 9 al50 clearly shows the relationship between the degree of internal stress (cold ~ork~ and the Yield Strength, both Au~tenite and Marten~ite phases, of this alloy, at 500C memory imparting te~perature for 1 hourO
Figure 10 shows the family of curves obtained for the Austenite phase yield strength for 450, 475, 500 and S25C memory imparting temperatures for 1 hour.
In th~ applications of S~A, there are instances where the crucial parameters relate to the physical properties such as the pha~e transition or tran form2tion ~ 3~6~37 temperatures, the start ~nd finish of a particular phase transformation and/or the hysteresis between the formation of one phase and another. The mechanical properties, however, are considered less crucial. In these applications the SMA members usually encounter low applied stresses and strains while requiring precise transition temperatures, narrow hystere~is loop and a small differential between the start and finish of the phase transformation. Such an ~pplication would be that of a thermal disconnect switch as in an overload protection circuit of electric motors.
A second type of SMA application which places more emphasis on the mechanical properties rather than physical would be an actuator with relatively high stresses and strains. Wider tolerances are acceptable on the actuation te~peratures or hysteresis loop such as in the case of proportionally actuating an air damper over a 100P range or 90 of rotation.
A ~hird type of application might involve both high mechanical output as well as clo~e or tight temperature re~uirement as in the case of closing a fire trap door, fire sprinkler system valves, etc.
actuating within several degrees centigrade.
Figures 9 through 11 show the data that one obtains as a result of utilizing the process of adjusting the de~ree of internal stresses. From the physical parameter data, such as shown in ~igures 1 through 8, and the mechanical parameter data, such as shown in ~igures ~ and 10, one can ~elect the appropriate amount of internal stress for a specific application. A sample calculation is shown in Figure 11.
In SMA applications, the amount of work output delivered or produ~ed by the elements, is proportional to ~he difference between the Austenitic and ~artensitic strengths in A to M to A reactions and to the difference between the ~ustenitic and Rhombohedral strengths in A
to R to A reactions. Referring to Figur@ 9, the strength differential for this alloy at 30% cold work ~s shown ~3~$~37 .9 to be approximately 750 Mpa (9oO - 150); whereas the differential is only about 250 Mpa (350 -100) at 6%
cold work. The work output is best illustrated by Figure 11 showing two stress/strain curves at two different degrees of internal stress levels (I and II). Referring to Figure 11, two applications utilizing this process can be identified. In the first application of high strain/low stress, (I), for an ARMA reaction, the Martensite phase is strained to 1O75~ and a stress of 15 KSI. In a second application of high stress/low strain, (II~, for an ARA reaction, the Rhombohedral phase stres~ and strain are 15 XSI and 0.75%
respectively. The corresponding Austenitic phase stress/strains are 40 KSI and 0.5% for the ARMA reaction (I), and 70 KSI and 0.5% for the ARA reaction. ~ence, the energy product (work output~ is (40 - 15) x (1.75 -0~5) or 31.25 for the ARMA reaction and (70 -15) x (O.75 - O.S) or 13.75 for the ARA reaction.
In some specific applications it i desireable to have a progressively variable amount of internal stress and more particularly to widen hystersis loop of a SMA member.
In a step function application, it is desireable to stop the motion as a function of temperature in two or more steps. In this case, a plurality of integral sections of the SMA member have different internal stress levels, as shown in figure 12, leading to actuation of such sections in a predeterminled ~equence.
Thus it is apparent that there has been provided in accordance with the invention a method for controlling the transformation temperatures of S~A that fully ~atisfies the aims and advantages ~et forth above~
While the inventisn has been described in conjunction with specific embodi~ents thereof, it is evident that there are many alternatives, modifications and variations that will be apparent to those skilled in the art.
Accordingly, it is intended to embrace all such 13~6437 alternatives, modifications and variations as fall within the spirit and broad scope of the appen~ed claims.
A ~ET~OD PUR PROWCING A S~APE MEMORY ALLOY ~EMBER
~AVING SPECIFIC P~YSICAL AND MEC~A~ICAL PROPERTI~S
~ACKGROUND O~ THE INVENTION
Field of the Invention .
The present inventiQn relates to a method for producing a shape memory alloy (SMAJ member having a range of specific physical and mechanical properties and more particularly to the control of the physical and mechanical properties by the introduction of predetermined internal stresses into the alloy prior to a predetermined memory imparting heat treatment.
Descript~on of the Prior Art A nickel-titanium alloyr such as Nitinol (NiTi) is known to have the ability to recover its original shape whe!n deformed in its Martensite and/or Rhombohedral phase(s), and then heated to the Auste~ite phase. This characteristic of shape memory alloy is generally attributed to the basic chemical ~omposition of the alloy, proce3sin9, and-the memory imparting heat treatment.
There are a num~er of articles which describe the aforementioned characteristic of SMA. These include .S. Patent 4,310,354 and 3~174,851 as ~ell a~ an article from ~he Naval Surface Weapons Center entitled ~Effects of Stresses On The Phase Transformation of Nitinol"
~NSWC TR 86-196 1986) and "~fEect of Heat Treatment After Cold Workin~ on the Phase Transformation of TiNi 1316~37 Alloy" Transactions of the Japan Institute of M~tals, Vol. 28, No. 2 (1987) pages 83 - 94.
All of these articles are concerned with the generally known processes for making a SMA alloy. This include~ the steps of initially selecting an alloy of a predetermined composition, forming the alloy to a desired shape, and ~ubjecting the alloy to a predetermined memory imparting heat treatment. Even though close control of the alloy' 5 chemical composition and memory imparting heat treatment is mai~tai~ed, a consid~rable variatio~
in transformation temperatures has been known to occur.
This has generally been attributed to process variables and other unknown factors. This limits ~he use of SMA
alloys in applications where more precise transformation temperatures, and other ~echanical and physical properties are sought.
SUMMARY OF T~E INVENTION
In the present invention, a process has been developed that controls and adjusts the physical and mechanical properties of SMA. The physioal properties include, but are not limited to, transformation temperatures of the various SMA phases, the resulting hysteresis between such phases, suppression of the Martensit:e phase in relation to the Rhombohedral phase, and the relationship between the start and finish temperatures of the respective phases, ~echanical propertie~s that are controlled and adjusted by this invention include, but are not limited to, the yield point, ultimate tensile strength, and ductility. This ha~ been accompli~hed by the introduction of a known internal stress and the di-Rtribution of that stress in the SMA prior to final fabrication ~f the SMA to a desired shape and prior to imparting memory ~hrough a prede~er~ined heat treatment ~ehedule.
The primary object o~ this invention is to control and adjust the transformation te~peratures of S~A by the introduction and distribution vf known 131~7 internal stresses into a SMA member of a known composition pxior to a memory imparting heat treatment.
Another object of the invention is to control other physical properties and the mechanical properties of SMA by the introduction and distribution of known internal stresses in a SMA member of a known composition prior to a memory imparting heat treatment.
A primary feature of the invention is the ability to provide precise transformation temperatures and other physical and the mecbanical properties in an S~A alloy of known composition.
Other principal features and advantages of the invention will become apparent to tho~e skilled in the art upon review of the following detailed description, claims and drawings.
DETAILED DESCRIPTON OF THE DRA~INGS
Figure 1 is a typical DSC curve showing an A to R to M to A (ARMA) transformation reaction for a low amount, under 15% cold reduction in area, of internal stress introduced prior to heat treatment where A, R and M denote Austenite, Rhombohedral and Martensi~e phases, respectively.
Figure la is a typical ~SC curve showing an A to R to A (ARA) transformation reaction for the same ~ample as in Figure 1.
- ~igure 2 is a typical DSC curve ~howin~ the aR~A transfor~ation reaction for a moderate amount, 35%
cold reduction in area, of internal stre~s introduced prior to heat treatment.
Figure 2a is a typical DSC curve showing an ARA transformation reaction for the same 3ample as in Figure 2.
~ igure 3 is a typical DSC curve ~howing an AR~A transforDation reaction for a high amount, 55~
cold reduction in area, o~ internal stre-qs introduced prior ~o heat treatment.
131~37 ~4--~ igure 3a is a typical DSC curve showing an ARA tranformation reaction for the same sample as in Figure 3.
Pigure 4 is a family of curves showing the Austenite peak temperature of the ARMA reactions at different amounts of internal stress and memory imparting temperatures.
Fi~ure S is a family of curves showing the Austenite peak temperature of the ARA reaction at different amounts of internal stress and ~emory imparting temperatures.
Figure 6 is a family of curves showing the Rhombohedral peak te~perature of the ARMA or ARA
reacti3ns at different amounts of internal stress and memory imparting temperatures.
Figure 7 is a family of curves showing the Martensite peak temperature of the ARMA or AMA reactions at different amounts of internal stress and ~emory imparting te~peratures.
Figure 8 is a family of curves -~howing the phase tranformation peak tempertures at different amounts of internal stress and a memory imparting temperature of 475C for l hour.
Figure 9 is a family of curves showing the austenitic and martensi~ic yield strength at different amounts of internal stress at 500C memory imparting te~perature for l hour.
Figure lO is a family of curves showing the Austenite yield strength at different amounts of internal stress and memory imparting temperatures.
Figure 11 is a stress/strain curve o~ both Aus~enite and ~arten3ite at two levels of internal strecs.
Figure 12 is a 3ke~ch of a SMA ~ember having a plur~lity o~ section with different stress levels.
Before the invention is explained in detail, it i5 to be understood that the invention is not limited in its application to the details as set forth in the ~311~437 following description or illustrated in the drawings.
The invention is capable of other embodiments and o' being practiced or being carried out in various ways.
Also, it is to be understood that the phraseology and terminolc)gy used herein i5 for the purpose of description and should not be regarded as limiting.
DESCRIPTION OP T~E INVENTION
The Shape Memory Alloy (SMA) describ~d herein is a near equiatomic alloy of nickel 2nd titanium.
This alloy is used for illustration purposes only, as other SMA alloys will al~o respond in a similar fashion.
The process accordinq to the present invention generally includ~s .he selection of an SMA of a known composition. Annealing of the alloy to a reference stress level ~or a predetermined time. Cold forming of the alloy to introduce a controlled amount of internal stress into the alloy.
The next step includes the forming of the alloy to a desired shape or configuration. Fixuring the alloy to the desired shape memory coniquration.
Heat treating of the alloy at a selected memory imparting temperature for a fixed period of time and allowing the alloy to cool to ambient temperature. The SMA is then re~ved f.rom the fixture. Determining the transformation temperature of the SMA for the Austenite, Rhombohedral and Marte!nsite phases. A amily of curves for these pha~e~ can be establi~hed by repeating the above process at different internal stresses and different memory impartin~ temperatures as described now fully hereinafter.
In the following example a wire of abou~ 1 to 2 ~m. in diame~er drawn from the ~MA wa~ annealed at temperatures between 3Q0 and 950C for a ~pecific length of time, generally between five minutes and two hours.
The annealin~ prooe~s reduces the amount of internal ~316~37 stress to a reference level in preparation for subsequen~
introduction or addition of internal stress.
The annealed wire is then processed to introduce or add various amounts cf internal stresses by cold reducing the wire by a specific amount.
Calculations are based upon the initial and final diameters cf the cold worked wire. This step in the process is particularly significant since internal stresses make it posible to adjust and control the transition temperatures and other physical and mechanical properties of the alloy. The alloy is then formed to a desired configuration and supported in the desired shape memory configuration. The alloy is then heated at at a 3elected memory imparting temperature and cooled. The following ~igures ~how the transformation phases at various internal stress levels.
Referring to Figures 1 and la, the transformation reactions: Austenite to Rhombohedral to Martensite to Austenite phase changes IARMA) and the Austeni~e to Rhombohedral to Austenite phase changes (ARA) are depicted usin~ Differential Scanning Calorimetry (DSC) plots. The plots show transition temperatures for low amounts of cold reduction (close to 15~) for this alloy at peak temperatures of 53.4, 37.9, 31.7 and 9.6C for the A, A', R and M phases respecti~ely for 1 ho~r at 475C memory imparting temperature.
Referring to Figures 2 and 2a, the transformation reaotion: Austenite to Rhombohedral to Martensite to Austenite phase changes (ARMA) and the ~ustenite to Rhombohedral to Austenite pha~e ch~nges (ARA) are depicted using Differential Scannng Calorimetry (DSC) plots. The plots ~how transition temperatures for moderate amounts of cold reduction (close to 35~) for this alloy with peak temperatures of 44.3, 40.9, 1316~37 34.3 and -10.8C for the A, A', R and M phases respectively for 1 hour at 475C memory imparting temperature.
Referring to Figures 3 and 3a, the transformation reaction: Austenite to Rhombohedral to Martensite to Austenite phase changes (ARMA) and the Austen$te to Rhombohedral to Austensite phase changes (ARA) are depicted using Differential Scannng Calorimetry (DSC) plots. The plots shcw transition temperatures for high amounts of cold reduction, close to 55%, for this alloy with peak temperatures of 43.7, 41.9, 35.6 and -15O3~C for the A, A', R and M pha~es respectively for 1 hour at 475C me~ory imparting temperature.
The process is then repeated for various amounts of cold reduction and memory imparting temperatures, which for this alloy are in the ranges of 5 to 60% and 400 to 600C respectively. Figures 4 through 7 respectively show the family of curv~s obtained for the peak transition temperatures of the Austensite, Ap (M to A); Austenite, A'p (R to A~; Rhombohedral, Rp;
and Martensite, Mp phases. The family of curves for this alloy are sho~n for 475 through 600C memory imparting t~mperatures for 1 hour.
Figure 8 clearly shows the relationship between the degree of internal stress ~cold work) and the transition temperature peaks of this alloy, at 475C
memory imparting temperature for 1 hour.
Figure 9 al50 clearly shows the relationship between the degree of internal stress (cold ~ork~ and the Yield Strength, both Au~tenite and Marten~ite phases, of this alloy, at 500C memory imparting te~perature for 1 hourO
Figure 10 shows the family of curves obtained for the Austenite phase yield strength for 450, 475, 500 and S25C memory imparting temperatures for 1 hour.
In th~ applications of S~A, there are instances where the crucial parameters relate to the physical properties such as the pha~e transition or tran form2tion ~ 3~6~37 temperatures, the start ~nd finish of a particular phase transformation and/or the hysteresis between the formation of one phase and another. The mechanical properties, however, are considered less crucial. In these applications the SMA members usually encounter low applied stresses and strains while requiring precise transition temperatures, narrow hystere~is loop and a small differential between the start and finish of the phase transformation. Such an ~pplication would be that of a thermal disconnect switch as in an overload protection circuit of electric motors.
A second type of SMA application which places more emphasis on the mechanical properties rather than physical would be an actuator with relatively high stresses and strains. Wider tolerances are acceptable on the actuation te~peratures or hysteresis loop such as in the case of proportionally actuating an air damper over a 100P range or 90 of rotation.
A ~hird type of application might involve both high mechanical output as well as clo~e or tight temperature re~uirement as in the case of closing a fire trap door, fire sprinkler system valves, etc.
actuating within several degrees centigrade.
Figures 9 through 11 show the data that one obtains as a result of utilizing the process of adjusting the de~ree of internal stresses. From the physical parameter data, such as shown in ~igures 1 through 8, and the mechanical parameter data, such as shown in ~igures ~ and 10, one can ~elect the appropriate amount of internal stress for a specific application. A sample calculation is shown in Figure 11.
In SMA applications, the amount of work output delivered or produ~ed by the elements, is proportional to ~he difference between the Austenitic and ~artensitic strengths in A to M to A reactions and to the difference between the ~ustenitic and Rhombohedral strengths in A
to R to A reactions. Referring to Figur@ 9, the strength differential for this alloy at 30% cold work ~s shown ~3~$~37 .9 to be approximately 750 Mpa (9oO - 150); whereas the differential is only about 250 Mpa (350 -100) at 6%
cold work. The work output is best illustrated by Figure 11 showing two stress/strain curves at two different degrees of internal stress levels (I and II). Referring to Figure 11, two applications utilizing this process can be identified. In the first application of high strain/low stress, (I), for an ARMA reaction, the Martensite phase is strained to 1O75~ and a stress of 15 KSI. In a second application of high stress/low strain, (II~, for an ARA reaction, the Rhombohedral phase stres~ and strain are 15 XSI and 0.75%
respectively. The corresponding Austenitic phase stress/strains are 40 KSI and 0.5% for the ARMA reaction (I), and 70 KSI and 0.5% for the ARA reaction. ~ence, the energy product (work output~ is (40 - 15) x (1.75 -0~5) or 31.25 for the ARMA reaction and (70 -15) x (O.75 - O.S) or 13.75 for the ARA reaction.
In some specific applications it i desireable to have a progressively variable amount of internal stress and more particularly to widen hystersis loop of a SMA member.
In a step function application, it is desireable to stop the motion as a function of temperature in two or more steps. In this case, a plurality of integral sections of the SMA member have different internal stress levels, as shown in figure 12, leading to actuation of such sections in a predeterminled ~equence.
Thus it is apparent that there has been provided in accordance with the invention a method for controlling the transformation temperatures of S~A that fully ~atisfies the aims and advantages ~et forth above~
While the inventisn has been described in conjunction with specific embodi~ents thereof, it is evident that there are many alternatives, modifications and variations that will be apparent to those skilled in the art.
Accordingly, it is intended to embrace all such 13~6437 alternatives, modifications and variations as fall within the spirit and broad scope of the appen~ed claims.
Claims (25)
1. A process for adjusting the physical and mechanical properties of a shape memory alloy member of a known chemical composition, said process comprising the steps of annealing said member to a reference internal stress level, introducing a controlled amount of internal stress into said member forming said member into a desired configuration, fixturing said member in the final desired configuration, the shape said member reverts to upon heating, and heat treating said member to obtain the desired physical and mechanical properties
2. The process according to claim 1 including the step of determining the transformation temperatures of said member for the Austenite, Martensite and Rhombohedral phases.
3. The process according to claim 2 including the step of generating a family of phase transformation curves by repeating the steps of claim 2 at different internal stress levels and different memory imparting temperatures.
4. The process according to claim 1 including the step of determining the stress/strain behavior for the Austenite, Martensite and Rhombohedral phases.
5. The process according to claim 4 including the step of generating a family of stress/strain behavior curves by repeating the steps of claim 4 at different internal stress levels and different memory imparting temperatures.
6. The process according to claim 1 wherein said introducing step includes the additional step of introducing a progressively variable internal stress into said member.
7. The process according to claim 1 wherein said introducing step includes the introduction of a variety of different amount of internal stress into selective portions of said member.
8. A process for adjusting the physical and mechanical properties of a shape memory Alloy member of a known chemical composition and known internal stress level, said process comprising the steps of increasing the internal stress level of said member, and forminq said member to a desired configuration, fixturing said member in the final desired configuration, the shape said member reverts to upon heating, and heat treating said member a selected memory imparting temperature.
9. The process according to claim 8 including the step of determining the transformation temperatures of said member for the Austenite, Martensite and Rhombohedral phases.
10. The process according to claim 9 including the step of generating a family of phase transformation curves by repeating the steps of claim 9 at different internal stress levels and different memory imparting temperatures.
11. The process according to claim 8 including the step of determining the stress/strain behavior for the Austenite, Martensite and Rhombohedral phases.
12. The process according to claim 11 including the step of generating a family of stress/strain behavior curves by repeating the steps of claim 11 at different internal stress levels and different memory imparting temperatures.
13. The process according to claim 8 wherein said increasing step includes the additional step of introducing a progressively variable internal stress into said member.
14. The process according to claim a wherein the increasing step includes the additional step of introducing a variety of different amounts of internal stress into selected portions of said member.
15. A process for adjusting the physical and mechanical properties of a shape memory alloy member of a known chemical composition and known internal stress level, said process comprising the steps of annealing said member at a predetermined temperature and time to establish a lower reference internal stress level, increasing the internal stress level of said member, forming said member to a desired configuration, fixturing said member in the desired configuration, the shape said member reverts to upon heating, and heat treating said member at a selected memory imparting temperature.
16. The process according to claim 15 including the step of determining the transformation temperatures of said member for the Austenite, Martensite and Rhombohedral phases.
17. The process according to claim 16 including the step of generating a family of phase transformation curves by repeating the steps of claim 16 at different internal stress levels and different memory imparting temperatures.
18. The process according to claim 15 including the step of determining the stress/strain behavior for the Austenite, Martensite and Rhombohedral phases.
19. The process according to claim 18 including the step of generating a family of stress/strain behavior curves by repeating the steps of claim 18 at different internal stress levels and different memory imparting temperatures.
20. The process according to claim 15 wherein said increasing step includes the additional step of introducing a progressively variable internal stress into said member.
21. The process according to claim 15 wherein said increasing step includes the introduction of a variety of different amounts of internal stress into selected portions of said member.
22. A process for adjusting the physical and mechanical properties of a shape memory alloy member or a known chemical composition, said process comprising the steps of annealing said member to a reference internal stress level, introducing a progressively variable internal stress into said member and heat treating said member to obtain the desired physical and mechanical properties.
23. A process for adjusting the physical and mechanical properties of a shape memory alloy member of a known chemical composition, said process comprising the steps of annealing said member to a reference internal stress level, introducing a variety of different amounts of internal stress into selected portions of said member, and heat treating said member to obtain the desired physical and mechanical properties.
24. A process for adjusting the physical and mechanical properties of a shape memory alloy member of a known chemical composition and known internal stress level, said process comprising the steps of increasing the internal stress level of said member by introducing a progressively variable internal stress into said alloy member, and heat treating said member at a selected memory imparting temperature.
25. A process for adjusting the physical and mechanical properties of a shape memory alloy member of a known chemical composition and known internal stress level, said process comprising the steps of increasing the internal stress level of said member by introducing a variety of different amounts of internal stress into selected portions of said member, and heat treating said member at a selected memory imparting temperature.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US183,818 | 1988-04-20 | ||
| US07/183,818 US4881981A (en) | 1988-04-20 | 1988-04-20 | Method for producing a shape memory alloy member having specific physical and mechanical properties |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1316437C true CA1316437C (en) | 1993-04-20 |
Family
ID=22674408
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000596022A Expired - Fee Related CA1316437C (en) | 1988-04-20 | 1989-04-07 | Method for producing a shape memory alloy member having specific physical and mechanical properties |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4881981A (en) |
| EP (1) | EP0374209A1 (en) |
| JP (1) | JPH02501579A (en) |
| KR (1) | KR930007143B1 (en) |
| AU (1) | AU616514B2 (en) |
| CA (1) | CA1316437C (en) |
| WO (1) | WO1989010421A1 (en) |
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-
1988
- 1988-04-20 US US07/183,818 patent/US4881981A/en not_active Expired - Fee Related
-
1989
- 1989-04-04 AU AU34241/89A patent/AU616514B2/en not_active Ceased
- 1989-04-04 KR KR1019890702420A patent/KR930007143B1/en not_active IP Right Cessation
- 1989-04-04 WO PCT/US1989/001414 patent/WO1989010421A1/en not_active Application Discontinuation
- 1989-04-04 JP JP1504380A patent/JPH02501579A/en active Pending
- 1989-04-04 EP EP89904664A patent/EP0374209A1/en not_active Withdrawn
- 1989-04-07 CA CA000596022A patent/CA1316437C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| WO1989010421A1 (en) | 1989-11-02 |
| AU616514B2 (en) | 1991-10-31 |
| JPH02501579A (en) | 1990-05-31 |
| AU3424189A (en) | 1989-11-24 |
| KR930007143B1 (en) | 1993-07-30 |
| EP0374209A1 (en) | 1990-06-27 |
| KR900700647A (en) | 1990-08-16 |
| US4881981A (en) | 1989-11-21 |
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