United States Patent [19J
`Goldstein et al.
`
`[11]
`
`(45]
`
`4,283,233
`Aug. 11, 1981
`
`[54] METHOD OF MODIFYING THE
`TRANSITION TEMPERATURE RANGE OF
`TINI BASE SHAPE MEMORY ALLOYS
`
`[75]
`
`Inventors: David Goldstein, Adelphia; Richard
`E. Jones; Robert S. Sery, both of
`Silver Spring, ·all of Md.
`
`[73] Assignee: The United States of America as
`represented by the Secretary of the
`
`Navy, Washington, D.C. •
`
`[21] Appl. No.: 128,326
`
`(22] Filed:
`
`Mar. 7, 1980
`
`Int. CJ.3 ................................................ C22F 1/10
`[51]
`[52] U.S. CI. .......................... 148/11.5 R; 148/11.5 F;
`148/11.5 N
`[58) Field of Search .......... , .......... 148/11.5 N, 11.5 F,
`148/11.5 R
`
`[56]
`
`3,174,851
`3,753,700
`4,144,057
`
`References Cited
`U.S. PATENT DOCUMENTS
`Buehler et al. ............. ........... 75/170
`Harrison et al. ....................... 75/170
`Melton et al. ......................... 75/170
`
`3/1965
`8/1973
`3/1979
`
`OTHER PUBLICATIONS
`Buehler et al., 55-Nitinol, Unique Wire Alloy with a
`Memory, Wire Journal, Jun. 1969.
`Primary Examiner-R. Dean
`Attorney, Agent, or Firm-R. S. Sciascia; A. L.
`Branning; R.. D. Johnson
`ABSTRACT
`[57]
`A method of changing the shape change transition tem(cid:173)
`perature range (TTR) of an object made from a nickel(cid:173)
`titanium based shape change memory alloy by selection
`of the final annealing temperature.
`
`4 Oaims, 3 Drawing Figures
`
`NIT!NOL WIRE (0.015" DIAMETER)
`53.1 wt.% Ni
`2.0 wt. %Co
`449wt. % Ti
`
`,,,-
`
`---
`
`1
`I
`I 400°C ANNEAL
`I
`I
`I
`
`100
`
`90
`
`80
`
`70
`
`60,
`
`s°f
`40
`
`30
`
`20
`
`10
`
`(I)
`
`0
`~
`Q
`" w
`..J
`(!) z
`<[
`;::'
`a:
`4J >
`§
`a:
`!-z w
`u
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`u.l a.
`
`I
`
`I
`
`O
`
`-190
`
`-160
`
`-130
`
`-100
`
`-70
`
`-40
`
`-10
`
`-5
`
`0
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`TEMPERATURE, °C
`
`GOLD STANDARD EXHIBIT 2046
`US ENDODONTICS v. GOLD STANDARD
`CASE PGR2015-00019
`
`

`
`NITINOL WIRE (0.015 11 DIAMETER)
`53.1 wt.% Ni
`2.0 wt.% Co
`44.9wt. % Ti
`
`, ... --
`
`I
`I
`/ 400°C ANNEAL
`I
`I
`I
`
`I
`
`j
`
`450°C ANNEAL
`
`0
`0
`
`a:, ' 0
`
`0
`)(
`
`w
`...J
`(!) z
`<t
`>-' a:: w
`> 0 u w
`a::
`I-z
`L&J u
`a: w
`
`Cl.
`
`100
`
`90
`
`80
`
`70
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`c::: .
`
`Vl
`•
`~
`
`~ a
`
`t --~ -'° 00 -
`t/l [ -g,
`
`w
`
`O
`
`-190
`
`-160
`
`-130
`
`-100
`
`-10
`
`-40
`
`-10
`
`-5
`
`0
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`FIG. I
`
`TEMPERATURE, °C
`
`~ ...
`N
`00 w
`...
`N w
`w
`
`

`
`NITINOL WIRE (0.031" DIAMETER}
`rv55wt. % Ni
`"'45wt.% Ti
`
`IOOr
`
`' 90
`
`0
`
`.....
`0 80
`!E
`c5
`Q
`)( 70
`w
`...I
`(!) z
`ct 60
`_,.
`>-0::: w
`>
`0 50
`u
`w
`0:::
`I-z 40
`w u
`0:::
`I.LI a.
`
`30
`
`20L.....----------------::::::::::::::
`10
`
`FIG. 2
`
`040
`
`42
`
`44
`
`46
`
`48
`
`50
`
`5·2
`
`54
`
`56
`
`58
`
`60
`
`62
`
`64
`
`66
`
`68
`
`TEMPERATURE, °C
`
`~ .
`en .
`
`~
`
`~ a (I) a
`(!Cl --~ -'° 00 -
`
`Cll
`::r
`(l)
`~
`N
`0 -..
`w
`
`~ .. tv
`00 w
`'" N w
`w
`
`

`
`IOOr
`;;--
`~ 90
`~
`Q
`,c
`UJ
`.J
`(!) z
`
`80
`
`~ -ft
`UJ
`6
`frl a::
`.... z
`UJ 40
`u
`0:: w a..
`
`30
`
`20
`
`10
`
`FIG. 3
`
`0'----.J'-----J'---'---'--'----.J'-----J'---'-----'----'---L---'----'----'-----'----L---L---'-----
`18
`20
`22
`24
`26
`28
`30
`32
`34
`36
`38
`40
`42
`44
`46
`48
`50
`16
`12
`14
`
`TEMPERATURE, °C
`
`70
`
`60
`
`50
`
`NITINOL WIRE
`53.I wt.% Ni
`2.0 wt.% Co
`44.9wt. % Ti
`
`0.015'.1 DIA.
`500°C ANNEAL
`
`0.01911 01A .
`520°C ANNEAL
`
`C .
`VJ .
`"'C
`~ a
`
`t --~ -\0
`
`00 -·
`
`Cll
`::r'
`(1)
`.....
`(1)
`w
`0
`~
`w
`
`~ ...
`N
`00
`...
`vJ
`N w
`w
`
`

`
`1
`
`4,283,233
`
`METHOD OF MODIFYING THE TRANSITION
`TEMPERATURE RANGE OF TINI BASE SHAPE
`MEMORY ALLOYS
`
`2
`however, is not desirable in some cases. Therefore, it is
`desirable to have another method of adjusting the TTR.
`Moreover, even when copper is used, it is desirable to
`have means of further fine tuning the TTR.
`
`15
`
`BACKGROUND OF THE INVENTION
`This invention relates to metal alloys and more par(cid:173)
`ticularly to nickel-titanium base metal alloys which
`have shape change
`The Nitinol alloys are nickel-titanium-base metal 10
`alloys having shape change memories. The general
`method for using the memory properties of these alloys
`is to:
`(1) shape the alloy into a permanent form at a temper-
`ature below the temperature transition range (TTR);
`(2) constrain the alloy in this shape;
`(3) anneal the alloy at 500° C.;
`(4) cool the alloy to a temperature below the TTR;
`(5) remove the constraint; and
`(6) shape the alloy into an another form.
`The alloy can then be converted from its other shape to
`its permanent shape by heating it to a temperature
`above the TTR. An excellent discussion about the theo(cid:173)
`ries and properties of Nitinol is given by William J.
`Buehler and William B. Cross, "55-Nitinol: Unique 25
`Wire Alloy with a Memory," Wire Journal, June 1969.
`Methods of preparing Nitinol are disclosed in U.S. Pat.
`No. 3,174,851, entitled "Nickel-Base Alloys," which
`issued to Buehler and Wiley on Mar. 23, 1965. The
`shape change memory properties of nickel-titanium 30
`alloys containing from 53.5 to 56.5 weight percent
`nickel, the remainder being titanium, are disclosed in
`U.S. Pat. No. 3,403,238 entitled "Conversion of Heat
`Energy to Mechanical Energy," which issued to Wil(cid:173)
`liam J. Buehler and David M. Goldstein on Sept. 24, 35
`1968.
`In the prior art, the usual method of changing the
`TTR was to change the ratio of nickel to titanium or to
`substitute cobalt or iron for nickel. A limitation of this
`previous method of alloying, has been the requirement 40
`to prepare by melting a different composition of alloy
`for each different transition temperature desired. This
`limitation presents significant economic disadvantages
`to the manufacturer of these alloys. In addition to an
`infinite number of TTR possibilities, it is difficult to 45
`precision alloy to control to a pre-selected composition.
`For example, a shift in total cobalt on the order of0.2%
`of the total composition can change the midpoint (50%
`recovery) of the TTR by 8° C., an unacceptable amount
`in many applications. Even worse from the standpoint SO
`of reproducibility, a shift of 0.2 weight percent nickel
`·
`can shift the midpoint of the TTR by 25° C.
`Hence the alloy manufacturer may find it necessary
`to remanufacture the alloy or to prepare several melts
`of slightly different compositions to achieve his in- 55
`tended final composition. Normal melting losses make it
`exceedingly difficult to anticipate the final composition
`with adequate precision. The alloy manufacturer can
`encounter high scrap losses.
`U.S. Pat. No. 4,144,057, entitled "Shape Memory 60
`Alloys," issued on Mar. 13, 1979, to Keith Melton and
`Olivier Mercier, discloses Nickel-the use of from 0.5
`to 30 weight percent of copper and from 0.01 to 5
`weight percent of at least one element selected from the
`group consisting of aluminum zirconium, cobalt, 65
`chrome, and iron in nickel-titanium alloys. They report
`that the transition temperatures in these alloys are less
`sensitive to compositional changes. The use of copper,
`
`5
`
`SUMMARY OF THE INVENTION
`Accordingly, one object of this invention is to pro(cid:173)
`vide a new method of changing the temperature transi(cid:173)
`tion range (TTR) of a nickel-titanium alloy having a
`shape change memory (Nitinol).
`Another object of this invention is to provide a
`method of changing the TTR of a nickel-titanium alloy
`(Nitinol) having a shape change memory without
`changing the composition of the alloy.
`Still another object of this invention is to provide an
`easier method of obtaining a nickel-titanium shape
`change memory alloy (Nitinol) having a given TTR.
`Yet another object of this invention is to reduce the
`amount of waste occurring in the production of a nick-
`20 el-titanium shape change memory alloy having a spe(cid:173)
`cific TTR.
`A further object of this invention is to provide a
`method of providing a nickel-titanium shape change
`memory alloy (Nitinol) having a more accurate TTR.
`These and other objects of this invention are accom(cid:173)
`plished by providing:
`in the process of forming an article with a shape
`change memory from a nickel-titanium based shape
`memory alloy by annealing the object at a temperature
`above the transition temperature range (TTR) while the
`object is restrained in its permanent shape and then
`reshaping the object into its intermediate shape at a
`temperature below ·the transition temperature range, the
`improvement comprising:
`selecting the annealing temperature to obtain a de(cid:173)
`sired transition temperature range.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`A more complete appreciation of the invention and
`many of the attendant advantages thereof will be
`readily appreciated as the same becomes better under(cid:173)
`stood by reference to the following detailed description
`when considered in connection with the accompanying
`drawing wherein:
`FIG. 1 contains three plots of percent shape recovery
`versus temperature for 3 Nitinol wires having the same
`composition of nickel, titanium, and cobalt but which
`have been anealed at 400° C., 450° C., and 500° C.,
`respectively;
`FIG. 2 contains 3 plots of percent shape change ver(cid:173)
`sus temperature for 3 Nitinol wires having the same
`composition of nickel and titanium but which are an(cid:173)
`nealed at 400° C., 450° C., and 500° C., respectively; and
`FIG. 3 contains 2 plots of percent shape change ver(cid:173)
`sus temperature for 2 Nitinol wires having the same
`composition as the wires in FIG. 1, one of the wires was
`annealed at 500° C. and the other at 520° C.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`The present invention provides a method by which
`the shape change temperature range (TTR) of Nitinol
`(nickel-titanium based) alloys can be varied by selecting
`the final annealing conditions. Broadly, the method may
`be applied to all nickel-titanium based alloys which
`possess shape change memory properties. U.S. Pat. No.
`4,144,057 discloses shape memory alloys which may be
`
`

`
`4,283,233
`
`3
`used which comprise from 23 to 55 weight percent of
`nickel, 40 to 46.5 weight percent of titanium, 0.5 to 30
`weight percent of copper, with the remainder being
`0.01 to 5 weight percent of at least one of the following
`elements: aluminium, zirconium, cobalt, chromium, and 5
`iron. Preferred are alloys comprising from 43 to 47
`weight percent of titanium, from more than zero to 6
`weight percent of cobalt, with the remainder being
`nickel. More preferred are alloy composed of from 43
`to 47 weight percent of titanium with the remainder 10
`being nickel. These alloys are prepared by convention
`means such as arc casting.
`Prior to the annealing step, the alloy is cold worked
`to bring it to a convenient size and shape and to remove
`any prior shape memory effect which may be present in 15
`the alloy. The alloys undergo conventional plastic de(cid:173)
`formation when they are cold worked. Lattice vacan(cid:173)
`cies (holes where atoms should be) are created. Cold
`working a minimum of 15% is sufficient to enable the
`annealing process to control the transition temperature. 20
`Next, the material is formed into its permanent shape.
`Some additional cold working may occur during this
`forming step. The material is restrained in this perma(cid:173)
`nent shape during the annealing step.
`The critical feature of this invention is the selection of 25
`the final annealing temperature. This is based on the
`discovery that by adjusting the final annealing tempera(cid:173)
`ture, the transition temperature range (TTR) can be
`changed. In general, for a given composition raising the
`annealing temperature raises the TTR.
`The procedure, as illustrated in examples 1-3, is to
`anneal the shape change objects at different tempera(cid:173)
`tures and measure the resulting TTR's. In this manner
`the optimum annealing temperature to achieve the
`desired TTR can determined. Because the TTR is 35
`sensitive to even small changes in composition, the
`annealing temperature must be redetermined for each
`new batch of alloy. Moreover, the TTR depends on the
`permanent shape of the object. Therefore, the exact
`shape must be used in determining the relationship 40
`between the annealing temperature and the TTR.
`The annealing is performed in a dry, inert atmosphere
`(e.g., dry helium or argon) to prevent contamination of
`the alloy. The shape change memory object is heated at
`the annealing temperature until all of the object is at the 45
`annealing temperature; the object is then heated an
`additional 5 minutes. Heating the alloy beyond this time
`will have little if any effect. An object may be annealed
`again at a higher temperature to exhibit a TTR corre(cid:173)
`sponding to that higher annealing temperature; how- 50
`ever, the reverse is not true. Thus, an object which had
`been annealed first at 400° C. and then at 500° C. will
`exhibit a TTR corresponding to the 500° C. annealing,
`but an object annealed first at 500° C. and then 400° C.
`will still exhibit a TTR corresponding to the 500° C. 55
`anneal.
`After the annealing step, the object is cooled down
`below the TTR, during which it is still restrained in its
`permanent shape. After this, the restraint is removed.
`Next, by using conventional techniques the nickel- 60
`titanium based shape change alloy object is formed into
`another shape, taking care not to cause more than 7 or
`8 percent deformation in the material. If the object is
`heated or allowed to warm to above the transition tem(cid:173)
`perature range (TTR) it will regain its permanent shape. 65
`The TTR of the shape change memory produced by
`the process· of this invention will change if the material
`is worked. Therefore, the alloys are not to be used in
`
`4
`dynamic devices such as nitinol motors. The alloys are
`useful, however, in prosthetic devices such as artificial
`knee or elbow joints. Typically, the intermediate form
`of the device will be easy to insert. Body heat will raise
`the temperature of the device above the TTR, causing
`the device to change to its final shape.
`To more clearly illustrate this invention, the follow(cid:173)
`ing examples are presented. It should be understood,
`however, that these examples are presented merely as a
`means of illustration and are not intended to limit the
`scope of the invention in any way.
`
`EXAMPLE 1
`An alloy (A-137) of composition 53.1 weight percent
`nickel 2.0 weight percent cobalt, and 44.9 weight per(cid:173)
`cent titanium was arc melted into j inch diameter bar
`under an inert atmosphere. This bar was hot swagged
`and subsequently drawn into wire at -30° C. The wire
`was then reduced in diameter to 0.015 inch and separate
`lengths of it were annealed at temperatures of 400°,
`450°, and 500° C. The transition temperatures of the
`alloy as annealed at the various temperatures are shown
`in FIG. 1.
`It is apparent in the example of A-137 that the final
`annealing procedure causes a shift in the midpoint of the
`transition temperature range, for an alloy of given com(cid:173)
`position, from - 70° to + 27° C. for the 400° and 500° C.
`anneals, respectively. As expected, the 450° C. anneal
`produced an intermediate transition temperature. The
`30 percent recovery ordinate on FIG. 1 is the proportional
`recovery from a "U" bend to a straight wire.
`
`EXAMPLE 2
`An alloy composed of approximately 55 weight per(cid:173)
`cent nickel and 45 weight percent titanium was cold
`drawn into a wire 0.031 inches in diameter. Three indi(cid:173)
`vidual sections of this wire were annealed respectively
`at temperatures between 400° and 600° C. The transition
`temperature range of this alloy varied as shown in FIG.
`2. The results show that the midpoint of the transition
`temperature range for the wire can be shifted from 47°
`to 65° C. by selection of the final annealing temperature.
`As in example 1 (FIG. 1), the percent recovery ordinate
`on FIG. 2 is the proportionate recovery from a "U"
`bend to straight wire.
`
`EXAMPLE 3
`The alloy used in example 1 (53.1 wt % Ni, 2.0 wt %
`Co, and 44.9 wt% Ti) was cold drawn into a wire 0.019
`in diameter. A segment of the wire was annealed at 520°
`C. The transition temperature range for the wire is
`shown in FIG. 3. As in example 1 (FIG. 1), the percent
`recovery ordinate on FIG. 2 is the proportionate recov(cid:173)
`ery from a "U" bend to a straight wire. The recovery
`curve for the wire which was annealed at 500° C. in
`example 1 (FIG. 1) has also been included in FIG. 3 for
`purposes of comparison.
`The curves in FIG. 3 illustrate the usefulness of the
`present method of controlling the transition tempera(cid:173)
`ture range by adjusting the final annealing temperature.
`The wire (0.019" diameter) annealed at 520° C., com(cid:173)
`pletes its memory response (TTR) at 45° C. This alloy,
`if used in vivo (37° C.) will have recovered only 37% of
`its shape capability at body temperature. Hence, in this
`condition it would be useless as an internal body device
`such as a blood clot filter designed to reform itself at 37°
`C. in vivo. If, however, it were annealed at 500° C., it
`would be effective in the body since its recovers 98% of
`
`

`
`4,283,233
`
`6
`5
`(6) forming the article into an intermediate shape
`its prior shape at 37° C., as is shown for the 0.015 inch
`taking care not to cause more than 7 percent defor(cid:173)
`diameter wire in FIG. 3.
`mation in the material;
`Obviously, numerous modifications and variations of
`7) determining the TTR by slowly heating up the
`the present invention are possible in light of the above
`teachings. It is therefore to be understood that within 5
`article and observing the temperature range over
`which it recovers its permanent shape; and
`the scope of the appended claims the invention may be
`(8) deciding the next steps as follows:
`than as specifically described
`practiced otherwise
`(a) if the TTR is lower than that desired, steps (2)
`herein.
`through (8) are repeated using a higher annealing
`What is claimed as new and desired to be secured by 10
`temperature in step (3);
`Letters Patent of the United States is:
`(b) if the TTR is higher than that desired, steps (I)
`1. In the process of forming an article with a shape
`through (8) are repeated using fresh alloy and a
`change memory from a nickel-titanium based shape
`lower annealing temperature in step (3); but
`change memory alloy by annealing the object at a tem(cid:173)
`(c) if the TTR is that desired, the annealing temper(cid:173)
`perature above the transition temperature range (TTR) 15
`ature last used in step (3) is used in the process.
`2. The process of claim 1 wherein the nickel-titanium
`while the object is restrained in its permanent shape and
`base shape change memory alloy comprises from 43 to
`then reshaping the object into another shape at a tem(cid:173)
`47 weight percent of titanium, from more than zero to 6
`perature below the transition temperature range, the
`weight percent of cobalt, the remainder of the alloy
`improvement comprising:
`being nickel.
`determining the annealing temperature which pro- 20
`3. The process of claim 1 wherein the nickel-titanium
`duces the desired transition temperature range for
`shape change memory alloy comprises from 47 to 53
`the article by performing the following steps in
`weight percent of titanium, the remainder of the alloy
`order:
`being nickel.
`(1) forming the alloy into the desired permanent 25
`4. The process of claim 1 wherein the titanium-nickel
`shape of the article;
`based shape change memory alloy comprises a mixture
`(2) restraining the article in this permanent shape;
`of 23 to 55 wt. % nickel, from 40 to 46.5 wt. % titanium
`(3) annealing the article at a temperature above the
`and 0.5 to 30 wt. % copper with the balance being from
`TTR;
`0.01 to 5 wt % of at least one element selected from the
`(4) cooling the alloy down to a temperature below 30 group consisting of aluminum, zirconium, cobalt, chro-
`mium and iron.
`the TTR;
`(5) removing the restraint from the article;
`
`* * * * *
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65