US3594239A - Method of treating unique martensitic alloys - Google Patents

Method of treating unique martensitic alloys Download PDF

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US3594239A
US3594239A US708300A US3594239DA US3594239A US 3594239 A US3594239 A US 3594239A US 708300 A US708300 A US 708300A US 3594239D A US3594239D A US 3594239DA US 3594239 A US3594239 A US 3594239A
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alloy
temperature
tini
alloys
resistivity
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Frederick E Wang
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US Department of Navy
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US Department of Navy
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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 new method of heat treatment of an alloy whereby its properties are improved in a controlled way. More particularly, the alloy is heated at 650 to 700 C.
  • alloys such as TiNi Prior to this invention, alloys such as TiNi had been heated above its martensite temperature from about 600 C. to 850 C. for a time period slightly longer than that required to heat the material, which was usually less than an hour. The heating was in most cases followed by a cooling rate determined by the mass of the specimen and the normal heat flow to a still air surrounding. The treatment with near-stoichiometric TiNi varied slightly from this procedure in that the heating range was 700 C. to 800 C. for about a few hours.
  • the variations are found to be related to the thermal cycling of the material, which can occur even at room temperature.
  • fluctuations above and below certain critical temperatures cause energy to be stored in the alloy, which, as a result, does not exhibit the same value of resistivity or dimensional recovery among other properties as those which are Ineasured under identical temperature conditions.
  • These deviations closely resemble the hysteresis eifect which is characteristic of alloys.
  • the alloy .exhibits better memory and damping characteristics as it is recycled several hundred times although these properties do reach a maximum value after which they decrease on exposure to further temperature cycles.
  • the variations in properties are found to be substantially eliminated by heating the alloy at 650 to 700 C. and then cooling it slowly to a temperature at which the alloy does not undergo thermal cycling. If the lower critical temperature is below room temperature, the alloy further may be provided with some mechanical stress but not enough to cause plastic deformation or cold working. Such deformation may be detected from a stress-strain curve and it is usually accompanied by slip, twining or dislocation movement. -In this way, it is possible to store the alloy at room temperature without it going through temperature cycles lwhich may have a degrading effect on its properties.
  • the upper critical temperature limit (TB) is the iirst temperature at which the resistivity of the alloy on cooling is equal to that resistivity obtained during heating for a given temperature as the alloy is cooled after being heated to above its martensite temperature.
  • the lower critical temperature limit (TA) is the second point of equal resistivity for a given temperature obtained as the alloy is cooled.
  • TA critical temperature limit
  • an object of the instant invention is to provide a method of eliiciently converting heat energy of an alloy into mechanical energy.
  • Another object of this invention is to provide a method for minimizing the relaxation of alloys.
  • Another object of the invention is to provide a method of treatment whereby an alloy may be stored without degradation of any of its properties.
  • a further object of this invention is to provide an easy yand accurate method to determine the temperatures at which an alloy will not undergo thermal cycling.
  • FIG. l is a proposed phase diagram of TiNi showing the different types of TiNi which exist over specific temperature ranges
  • FIG. 2 contains three plots of electrical resistivity against temperature for TiNi showing the effects of the thermal cycling
  • FIG. 3 contains additional plots of resistivity against temperature showing the effects of stressing T iNi.
  • An example of an alloy which is within the scope of the invention is TiNi which exhibits the most desirable properties, such as energy conversion eiciency, me-
  • TiNi is found to have four distinct crystal structures as set forth in FIG. 1.
  • an ordering process takes place in the crystal structure and the imperfections due to thermal cycling are eliminated.
  • care should be taken in heating the alloy that the temperature does not exceed 700 C. because then the alloy will contain some TiNi (I) at the martensite temperature (Ms) which in turn results in the formation of an undesirable mixture of TiNi states during the martensite reaction.
  • the preferred temperature range is 650 to 700 C. for a period of about four days. However, lower temperatures may be used as long as they exceed the martensite temperature but then longer heating times would also be required.
  • the martensite temperature for TiNi varies ⁇ and depends on the relative properties of Ti to Ni as disclosed in copending application Ser. No. 579,185, now abandoned, led on Sept. 9, 1966.
  • the martensite temperature for stoichiometric TiNi is about 170 C.
  • the heating may be done at either "6 mm, pressure or in the presence of a clean dry inert gas such as, for example, helium or argon in order to prevent oxidation and other interstitial contamination.
  • the alloy After the alloy is annealed and substantially all of it is in the TiNi (II) state, the alloy is slowly cooled below the martensite temperature whereupon it undergoes a martensite transition for the next 60 to 70 C.
  • This transition involves both electron and atom changes whereby there occur a localization and delocalization of electrons and also shear moments in a proper sequence and cooperative manner. Accordingly, resistivity measurements are made in order to determine the characteristics of the martensite transition.
  • FIG. 2(a) A graph of resistivity versus temperature is plotted and a TiNi sample which has been heat treated in accordance with the invention yielded the plot described by FIG. 2(a).
  • the triangle part of the resistivity curve is reproducible if the heating and cooling cycles proceed continuously in one direction until the temperatures (TA and TB) are exceeded before reversing the sample temperature direction.
  • FIG. 2(b) which describes the result of a few heating cycles.
  • the displacement and area of the triangle becomes exaggerated after several hundred of these cycles as indicated by FIG. 2(c).
  • the area decreases, thus exhibiting a maximum area for a given number of temperature cycles.
  • the existence of the triangle within the 60 to 70 C. range is thought to be caused by a difference in the atomic shearing Buergers vector, the value of which depends on whether the alloy is heated or cooled. This vector is further affected if the alloy is cycled within this temperature range. In these measurements, the heating and cooling rates should not vary from test to test in order to produce the most meaningful comparisons.
  • the displacement and increase in the area of the triangle is significant in that it is accompanied by an improvement in the properties of the alloy.
  • experimentation has confirmed that there is a gain in the efficiency of converting heat energy into mechanical energy and also an improvement in memory for that alloy which exhibits the largest triangular area in a resistivity plot.
  • This problem may be solved by storing the material either at 20 C. and lower or at 80 C. and higher so that ordinary liuctuations in temperature will not bring it within the triangular area.
  • this solution is not altogether satisfactory because of the cost involved in keeping the temperature at these levels.
  • Another more economical solution consists of mechanically stressing the material at a temperature below Ms but within its martensitic limit, that is, to such an extent that plastic deformation and work hardening will not occur. In this way, the heat treated alloy may be stored at room temperature without any degradation due to thermal cycling.
  • FIG. 3 (a) through (e) Some other effects of stressing are shown in FIG. 3 (a) through (e).
  • FIG. 3(0), (d) and (e) By specic reference to the curves in FIG. 3(0), (d) and (e), it can be seen that not only the triangular area but also the temperature range from TA to TB is reduced. In addition, compression appears to be particularly elfective in reducing the area and the range.
  • alloys such as ZrPd, ZrRh, ZrRu and their ternary intermediates as well as HfPt, HfIr, HfOs and their intermediates are within the scope of the invention. These alloys are found to exhibit characteristics similar to TiNi as disclosed in copending U.S. patent application Ser. No. 579,185, now abandoned and therefore should also display a TiNi-type phase diagram.
  • step (c) subjecting said alloy after step (b) to a mechanical stress at a temperature which is below the martensitic temperature but within its martensitic limit which stress is less than the stress necessary to effect plastic deformation and work hardening.
  • CoxFe1 X lgal Revew 161 126 No' 5 June 1 196:2 PP' denotes cobalt and iron respectively and make up the remaining approximately 50 atomic percent of the 10 lggurgllSgllfgdlgscs, V01- 36, NO- 10 October com osition which com rises:
  • said entire alloy attains the structure of TiNi pp 14754477 (11); (b) cooling it slowly to a temperature below its 15 CHARLES N LOVELL Pnmary Examiner upper critical temperature limit TB; and U S Cl. XR

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Investigating Or Analyzing Materials Using Thermal Means (AREA)
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US708300A 1968-02-26 1968-02-26 Method of treating unique martensitic alloys Expired - Lifetime US3594239A (en)

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US (1) US3594239A (de)
AT (1) AT295177B (de)
BE (1) BE728968A (de)
CH (1) CH536361A (de)
DE (1) DE1909176A1 (de)
FR (1) FR2002596A1 (de)
GB (1) GB1282883A (de)
NL (1) NL6902899A (de)
NO (1) NO127406B (de)
SE (1) SE368231B (de)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3748197A (en) * 1969-05-27 1973-07-24 Robertshaw Controls Co Method for stabilizing and employing temperature sensitive material exhibiting martensitic transistions
US3977913A (en) * 1972-12-01 1976-08-31 Essex International Wrought brass alloy
US3989551A (en) * 1969-11-12 1976-11-02 Fulmer Research Institute Limited Method of making a heat-recoverable article
US3989552A (en) * 1969-11-12 1976-11-02 Fulmer Research Institute Limited Method of making a heat-recoverable article
US4019925A (en) * 1974-05-04 1977-04-26 Osaka University Metal articles having a property of repeatedly reversible shape memory effect and a process for preparing the same
US4095999A (en) * 1972-11-17 1978-06-20 Raychem Corporation Heat-treating method
US4304613A (en) * 1980-05-12 1981-12-08 The United States Of America As Represented By The Secretary Of The Navy TiNi Base alloy shape memory enhancement through thermal and mechanical processing
EP0060575A1 (de) * 1981-03-13 1982-09-22 BBC Aktiengesellschaft Brown, Boveri & Cie. Verfahren zur Herstellung von Halbzeug aus einer kupferhaltigen Gedächtnislegierung
US4919177A (en) * 1987-03-30 1990-04-24 Dai Homma Method of treating Ti-Ni shape memory alloy
US6548013B2 (en) 2001-01-24 2003-04-15 Scimed Life Systems, Inc. Processing of particulate Ni-Ti alloy to achieve desired shape and properties

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58151445A (ja) * 1982-02-27 1983-09-08 Tohoku Metal Ind Ltd 可逆形状記憶効果を有するチタンニツケル合金およびその製造方法
DE69324587T2 (de) * 1993-09-22 1999-11-18 Horikawa Inc., Sabae Brillengestell und Verfahren zur Herstellung

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3748197A (en) * 1969-05-27 1973-07-24 Robertshaw Controls Co Method for stabilizing and employing temperature sensitive material exhibiting martensitic transistions
US3989551A (en) * 1969-11-12 1976-11-02 Fulmer Research Institute Limited Method of making a heat-recoverable article
US3989552A (en) * 1969-11-12 1976-11-02 Fulmer Research Institute Limited Method of making a heat-recoverable article
US4095999A (en) * 1972-11-17 1978-06-20 Raychem Corporation Heat-treating method
US3977913A (en) * 1972-12-01 1976-08-31 Essex International Wrought brass alloy
US4019925A (en) * 1974-05-04 1977-04-26 Osaka University Metal articles having a property of repeatedly reversible shape memory effect and a process for preparing the same
US4304613A (en) * 1980-05-12 1981-12-08 The United States Of America As Represented By The Secretary Of The Navy TiNi Base alloy shape memory enhancement through thermal and mechanical processing
EP0060575A1 (de) * 1981-03-13 1982-09-22 BBC Aktiengesellschaft Brown, Boveri & Cie. Verfahren zur Herstellung von Halbzeug aus einer kupferhaltigen Gedächtnislegierung
US4919177A (en) * 1987-03-30 1990-04-24 Dai Homma Method of treating Ti-Ni shape memory alloy
US6548013B2 (en) 2001-01-24 2003-04-15 Scimed Life Systems, Inc. Processing of particulate Ni-Ti alloy to achieve desired shape and properties

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DE1909176A1 (de) 1969-09-18
NO127406B (de) 1973-06-18
SE368231B (de) 1974-06-24
BE728968A (de) 1969-08-01
GB1282883A (en) 1972-07-26
FR2002596A1 (de) 1969-10-31
NL6902899A (de) 1969-08-28
CH536361A (de) 1973-04-30
AT295177B (de) 1971-12-27

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