US20090218013A1 - High temperature shape memory alloy, actuator and motor - Google Patents

High temperature shape memory alloy, actuator and motor Download PDF

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US20090218013A1
US20090218013A1 US12/235,528 US23552808A US2009218013A1 US 20090218013 A1 US20090218013 A1 US 20090218013A1 US 23552808 A US23552808 A US 23552808A US 2009218013 A1 US2009218013 A1 US 2009218013A1
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mol
alloy
shape memory
concentration
alloys
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Shuichi Miyazaki
Heeyoung Kim
Yoshinari Takeda
Masanari Tomozawa
Buenconsejo Pio
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University of Tsukuba NUC
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C30/00Alloys containing less than 50% by weight of each constituent
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C14/00Alloys based on titanium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C19/00Alloys based on nickel or cobalt
    • C22C19/03Alloys based on nickel or cobalt based on nickel
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C27/00Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
    • C22C27/02Alloys based on vanadium, niobium, or tantalum
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/006Resulting in heat recoverable alloys with a memory effect
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/10Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18High-melting or refractory metals or alloys based thereon
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02KJET-PROPULSION PLANTS
    • F02K1/00Plants characterised by the form or arrangement of the jet pipe or nozzle; Jet pipes or nozzles peculiar thereto
    • F02K1/54Nozzles having means for reversing jet thrust
    • F02K1/76Control or regulation of thrust reversers
    • F02K1/763Control or regulation of thrust reversers with actuating systems or actuating devices; Arrangement of actuators for thrust reversers
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03GSPRING, WEIGHT, INERTIA OR LIKE MOTORS; MECHANICAL-POWER PRODUCING DEVICES OR MECHANISMS, NOT OTHERWISE PROVIDED FOR OR USING ENERGY SOURCES NOT OTHERWISE PROVIDED FOR
    • F03G7/00Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for
    • F03G7/06Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for using expansion or contraction of bodies due to heating, cooling, moistening, drying or the like
    • F03G7/065Mechanical-power-producing mechanisms, not otherwise provided for or using energy sources not otherwise provided for using expansion or contraction of bodies due to heating, cooling, moistening, drying or the like using a shape memory element
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05CINDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
    • F05C2201/00Metals
    • F05C2201/04Heavy metals
    • F05C2201/0433Iron group; Ferrous alloys, e.g. steel
    • F05C2201/0466Nickel
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05CINDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
    • F05C2201/00Metals
    • F05C2201/90Alloys not otherwise provided for
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05DINDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2300/00Materials; Properties thereof
    • F05D2300/50Intrinsic material properties or characteristics
    • F05D2300/505Shape memory behaviour

Definitions

  • the present inventions relate to high temperature shape memory alloys which can be used at temperatures in excess of 100° C., as well as actuators and a motors using the shape memory alloys. More particularly, the present inventions relate to high temperature shape memory alloys with peak and reverse martensite transformation temperatures higher than 100° C., as well as actuators and motors using the shape memory alloys.
  • Ti—Ni base alloys are widely known shape memory alloys consisting of Titanium (Ti) and Nickel(Ni) which revert back to their original configuration upon application of heat up to their prescribed operating temperature, remembering their original shape.
  • Ti—Ni—Cu alloys are generally known to exhibit shape memory effects at temperature in the range of 200K to 360K Kokai publication Tokukai No. 2002-294371).
  • Ti—Ni—Nb alloys with martensite start temperatures (M s ) below 50° C. have also been disclosed (Patent publication No. 2539786).
  • the below mentioned alloys are generally well known as high temperature shape memory alloys obtained by adding additive elements to Ti—Ni base alloys for operation at high temperature exceeding 100° C.
  • Titanium is substituted by 0-20 mol % (atomic percent) Zirconium (Zr) to obtain a corresponding martensite start temperature (M s ) in the range of 373(K) to 550(K).
  • Titanium is substituted by 0-20 mol % Hafnium (Hf) to obtain a corresponding martensite start temperature (M s ) in the range of 373(K) to 560(K).
  • Nickel is substituted by 0-50 mol % Palladium (Pd) to obtain a corresponding martensite start temperature (M s ) from 280(K) to 800(K).
  • Nickel(Ni) is substituted by 0-50 mol % Gold(Au) to obtain a corresponding martensite start temperature (M s ) from 300(K) to 850(K).
  • Nickel is substituted by 0-50 mol % Platinum (Pt) to obtain a corresponding martensite start temperature (M s ) from 280(K) to 1300(K).
  • Ni—Al base alloys comprising 30-36 mol % Aluminum (Al) and a balance of Nickel (Ni)
  • M s martensite start temperature
  • the conventional high temperature shape memory alloys No. 1 and 2 described above are brittle and thus break easily, which results in poor machinability and lead to failure in cold working.
  • shape memory alloy No. 6 in addition to poor machinability, precipitation of Ni5Al3 weakens the structural stability of the alloy and embrittles the alloy. Therefore, repeated operation of the alloy at temperatures over 200° C. is impossible. That is to say, the alloy does not exhibit shape memory effects.
  • embodiments of the present disclosure address the problems of the prior art and provide a high temperature shape memory alloys which have good machinability and, in the meanwhile, are suitable for repeated high temperature operation.
  • a high temperature shape memory alloy is provided in Embodiment 1 to solve these technical problems, where the alloy consists of 34.7 mol %-48.5 mol % Nickel, at least one of Zirconium or Hafnium as transformation temperature increasing additive element, with a total content of 6.8 mol %-22.5 mol %; at least one of Niobium or Tantalum as machinability improving additive element, with a total content of 1 mol %-30 mol %, Boron below 2 mol %, and the balance Titanium; and impurities.
  • Embodiment 1 With respect to high temperature shape memory alloys having the components of Embodiment 1, since the alloys consist of 34.7 mol %-48.5 mol % Nickel at least one of Zirconium or Hafnium as transformation temperature increasing additive element, with a total content of 6.8 mol %-22.5 mol %, at least one of Niobium or Tantalum as machinability improving additive elements, with a total content of 1 mol %-30 mol %, Boron below 2 mol % and the balance Titanium, high transformation temperatures (peak transformation temperature (M*) or peak reverse transformation temperatures (A*)) in excess of 100° C. are obtained, and cold ductility is also improved. Consequently, Embodiment 1 provides a high temperature shape memory alloy for repeated high temperature operation with improved cold working machinability.
  • M* peak transformation temperature
  • A* peak reverse transformation temperatures
  • High temperature shape memory alloys of form 1 in Embodiment 1 consists of 6.8 mol %-22.5 mol % Zirconium as transformation temperature increasing additive elements and 3 mol %-30 mol % Niobium as machinability improving additives.
  • High temperature shape memory alloys of form 2 in Embodiment 1 consist of 6.8 mol %-18 mol % Hafnium as transformation temperature increasing additive elements and 3 mol %-20 mol % Niobium as machinability improving additive elements.
  • High temperature shape memory alloys of form 3 in Embodiment 1 consists of 6.8 mol %-20 mol % of transformation temperature increasing additive elements and 3 mol %-30 mol % Tantalum as said machinability improving additive elements.
  • Embodiment 2 An actuator is provided in Embodiment 2 to solve the above-mentioned technical problems, where the actuator is made of the high temperature shape memory alloys described in either the Embodiment 1 or forms 1 through 4 of Embodiment 1.
  • the actuator since the actuator is made of the high temperature shape memory alloy of either the Embodiment 1 or forms 1 through 4 of Embodiment 1, it is capable to perform cold working. In addition, high temperature applications are possible with the help of its high transformation temperatures and shape memory effects.
  • a motor is provided in Embodiment 3 to solve the above-mentioned technical problems, where the motor possesses a flux adjustment valve made of the high temperature shape memory alloys described in either Embodiment 1 or forms 1 through 4 of Embodiment 1.
  • the present embodiments provide shape memory alloys capable of repeated high temperature operation with high machinability.
  • FIG. 1 shows a scanning electron microscope image of alloy No. 7 in an embodiment of the present disclosure.
  • FIG. 2 shows a scanning electron microscope image of alloy No. 8 in an embodiment of the present disclosure.
  • each metallic element is measured by mol %, and then molten by means of arc melting method to make alloy ingots.
  • alloy No. 2 Ti—Ni 49.5 —Zr 10
  • alloy No. 2 has a composition expressed as 49.5 mol % Ni, 10 mol % Zr and the balance Ti (40.5 mol %).
  • step 2 the resultant alloy ingots are subjected to homogenization heat treatment for 2 hours (7.2 ks) at 950° C.
  • step 3 billets (test pieces) 15 mm long, 10 mm wide, and 1 mm thick are cut off by electric discharge machining.
  • Machinability evaluation tests were carried out to evaluate the machinability of the alloys manufactured by the above mentioned methods. Machinability evaluation tests were carried out through cold rolling at deformations up to 60%. The break rolling ratio of test pieces, with test pieces breaking down at deformations up to 60%, was measured to evaluate machinability.
  • composition of ternary Ti—Ni—Zr alloys Nos. 1 to 4 along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.) and peak reverse transformation temperature (A*, ° C.) are provided in Table 1.
  • composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 5 to 7, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 2.
  • alloys No. 5-7 are derived by fixing Ti and Zr content (mol %) of alloy No. 3, and then substituting Ni content by Nb.
  • the composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 8 to 12, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 3.
  • alloys No. 8-12 are derived by fixing the mol ratio of Ti, Ni and Zr to 35.5 mol %, 49.5%, and 15 mol % respectively, and then substituting Ti, Ni, and Zr as a whole by Nb.
  • composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 13 to 17, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 4.
  • composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 18 to 26, as well as the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 5.
  • the composition of quaternary Ti—Ni—Hf—Nb alloys and quinary Ti—Ni—Zr—Hf—Nb Nos. 27 to 37, along with the mol ratio of Ti plus Zr and Hf to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.) and peak reverse transformation temperature (A*, ° C.), are given respectively in Table 6.
  • alloys No. 28 and 29 correspond to alloys 9 and 10, respectively, in which Zr is substituted by Hf and alloy No. 30 corresponds to alloy 20 in which Zr, is substituted by Hf.
  • alloy No. 31 corresponds to alloy No. 7 in which Zr is substituted by Hf
  • alloy No. 32 corresponds to alloy No. 19, in which half of Zr content (10 mol %) is substituted by Hf.
  • the total content of Zr and Hf transformation temperature increasing additive elements
  • composition of quaternary Ti—Ni—Zr—Ta alloys Nos. 38 to 42, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 7.
  • alloys 38-42 are derived by fixing the mol ratio of Ti, Ni and Zr to 40.5 mol %, 49.5% and 10 mol % respectively, and then substituting Ti, Ni, and Zr as a whole by Ta.
  • the composition of quaternary Ti—Ni—Zr—Ta alloys and quinary Ti—Ni—Zr—Nb—Ta, Nos. 43 to 48, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 8.
  • the total content of Nb and Ta (machinability improving additive elements) is 10 mol % in alloy No. 48.
  • the composition of quinary Ti—Ni—Zr—Nb—B alloys Nos. 49 to 52, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 9.
  • alloys No. 49 to 52 are derived by adding element B (Boron) into Ti—Ni—Zr—Nb based alloys.
  • the composition of Ti—Ni—Zr—Hf—Nb—Ta—B based multi-component alloys No. 53 to 55, along with the mol ratio of Ti plus Zr and Hf to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.), are shown in Table 10.
  • FIG. 1 shows a scanning electron microscope image of alloy No. 7 in an embodiment of the present disclosure.
  • alloys No. 5 to 7 are suitable for high temperature operation as high temperature shape memory alloys. Furthermore, even with improved break rolling ratio, existence of a large amount of fine cracks are observed in alloys No. 5 to 7. As shown in FIG. 1 of the SEM image by Scanning Electric Microscope, together with the hard brittle Laves phase that forms in alloy No. 7 after rolling, the soft ⁇ phase liable to plastic deformation precipitates, which hinders the development of cracks, appeared on the interfaces of said Laves phase. As a result, machinability is improved.
  • FIG. 2 shows a scanning electron microscope image of alloy No. 8 in embodiment of the present disclosure.
  • alloys Nos. 38 and 39 possess higher transformation temperature; besides, as we compare alloys Nos. 43, 44 and 46 with alloys Nos. 8, 9, 10 and 3, even though adding Ta to alloys No. 43, 44, and 46 exhibits little effect to improve rolling ratio compared with adding Nb to alloys Nos. 8 to 10, better rolling ratio and higher transformation temperature were obtained compared respectively with alloy No. 3 and alloys Nos. 8 to 10 with added Nb.
  • alloy No. 48 was compared with alloys Nos. 44, 9, and 3, in the case of alloy 48 with combined addition of Ta and Nb, the rolling ratio is improved compared with alloy No. 44 with only Ta added, and yet the transformation temperature is increased compared with alloy No. 9 while only Nb is added.
  • the afore-described shape memory alloys do not lose their shape memory effect during repeated use at high temperature, they can be used as valves inside gas channels of motors (engines of automobiles, aircrafts, or gas turbine) for high temperature operation, when heated, channel area is regulated with the help of the shape memory effect; when cooled, channel area is reversed back by a spring used for deforming the valve. Besides, they can also be used as lubricant supplying valves of high speed rotating shafts. In addition, these alloys can be used as safety devices for power supply of household electric appliance at high temperature operation. Furthermore, they can also be used as actuators for high temperature operation. In the case of actuators, they also exhibit improved responsiveness resulting from increased cooling speed.

Abstract

A high temperature shape memory alloy is provided which possesses high machinability and is suitable for high temperature applications. The high temperature shape memory alloy consists of Ni from 34.7 mol % to 48.5 mol %, at least either Zirconium or Hafnium as transformation temperature increasing additives, with the sum of which 6.8 mol % to 22.5 mol %, and at least either Niobium or Tantalum as machinability improving additives, with the sum of which 1 mol % to 30 mol %; and Boron less than 2 mol %; and Titanium as the balance; and unavoidable impurity.

Description

    RELATED APPLICATIONS
  • This application is a Continuation of PCT Application No. PCT/JP2006/324206, filed Dec. 5, 2006, which claims priority to Japanese Application No. 2006-076560, filed Mar. 20, 2006, the entire contents of both of which are hereby incorporated by reference.
  • BACKGROUND
  • 1. Field of the Inventions
  • The present inventions relate to high temperature shape memory alloys which can be used at temperatures in excess of 100° C., as well as actuators and a motors using the shape memory alloys. More particularly, the present inventions relate to high temperature shape memory alloys with peak and reverse martensite transformation temperatures higher than 100° C., as well as actuators and motors using the shape memory alloys.
  • 2. Description of the Related Art
  • Ti—Ni base alloys are widely known shape memory alloys consisting of Titanium (Ti) and Nickel(Ni) which revert back to their original configuration upon application of heat up to their prescribed operating temperature, remembering their original shape.
  • For example, Ti—Ni—Cu alloys are generally known to exhibit shape memory effects at temperature in the range of 200K to 360K Kokai publication Tokukai No. 2002-294371). In addition, Ti—Ni—Nb alloys with martensite start temperatures (Ms) below 50° C. have also been disclosed (Patent publication No. 2539786).
  • However, in commercial Ti—Ni alloys including the alloys described in the Kokai publication and patent publication No. 2539786, the peak transformation temperature (M*) is below 70° C. (343K), in the meanwhile, the reverse peak transformation temperature (A*) is below 100° C. (373K). Therefore, the operating temperature of shape memory alloy does not exceed 100° C. Accordingly, conventional Ti—Ni base alloys are difficult for use in high temperature operations as shape memory alloys.
  • The below mentioned alloys are generally well known as high temperature shape memory alloys obtained by adding additive elements to Ti—Ni base alloys for operation at high temperature exceeding 100° C.
  • (1) (Ti—Zr)—Ni Alloys
  • In (Ti—Zr)—Ni base alloys, Titanium is substituted by 0-20 mol % (atomic percent) Zirconium (Zr) to obtain a corresponding martensite start temperature (Ms) in the range of 373(K) to 550(K).
  • (2) (Ti—Hf)—Ni Alloys
  • In (Ti—Hf)—Ni base alloys, Titanium is substituted by 0-20 mol % Hafnium (Hf) to obtain a corresponding martensite start temperature (Ms) in the range of 373(K) to 560(K).
  • (3) Ti—(Ni—Pd) Alloys
  • In Ti—(Ni—Pd) base alloys, Nickel is substituted by 0-50 mol % Palladium (Pd) to obtain a corresponding martensite start temperature (Ms) from 280(K) to 800(K).
  • (4) Ti—(Ni—Au) Alloys
  • In Ti—(Ni—Au) base alloys, Nickel(Ni) is substituted by 0-50 mol % Gold(Au) to obtain a corresponding martensite start temperature (Ms) from 300(K) to 850(K).
  • (5) Ti—(Ni—Pt) Alloys
  • In Ti—(Ni—Pt) base alloys, Nickel is substituted by 0-50 mol % Platinum (Pt) to obtain a corresponding martensite start temperature (Ms) from 280(K) to 1300(K).
  • (6) Ti—Al Alloys
  • In Ni—Al base alloys comprising 30-36 mol % Aluminum (Al) and a balance of Nickel (Ni), a corresponding martensite start temperature (Ms) in the range of 273(K) to 1000(K) is obtained.
  • (7) Ti—Nb Alloys
  • In Ti—Nb alloys comprising 10-28 mol % Niobium (Nb) and a balance of Titanium (Ti), a corresponding martensite start temperature (Ms) in the range of 173(K) to 900(K) is obtained.
  • (8) Ti—Pd Alloys
  • As described in Kokai publication Tokukai No. Hei 11-36024 Ti—Pd base alloys comprising 48 at %-50 at % Palladium (Pd) and 50 at %-52 at % Ti possess a reverse transformation finish temperature (Af) in excess of 560° C. (833K).
  • (9) Ti—Ta Alloys
  • As described in Ikeda, et al. (Masahiko Ikeda, Shin-ya Komatsu and Yuichiro Nakamura, Effects of Sn and Zr Additions on Phase Constitution and Aging Behavior Ti-50 mass % Ta Alloys Quenched from β Singe Phase Region, Materials Transactions, The Japan Institute of Metals, page 1106-1112, issue 4, volume 45, 2004), alloys comprising Tantalum 50 mass % (less than 30 mol % if converted to mol percentage) and a balance of Titanium, or Ti—Ta based alloys with 4 mass % Tin (Sn) or 10 mass % Zirconium (Zr) molten into, possess a shape recovery start temperature in excess of 150° C. (423K).
  • SUMMARY OF THE INVENTIONS
  • The conventional high temperature shape memory alloys No. 1 and 2 described above are brittle and thus break easily, which results in poor machinability and lead to failure in cold working.
  • In shape memory alloys Nos. 3-5 and 8, in addition to poor machinability, the addition of high priced additive elements (Pd, Au, Pt) make the alloys quite expensive.
  • With respect to shape memory alloy No. 6, in addition to poor machinability, precipitation of Ni5Al3 weakens the structural stability of the alloy and embrittles the alloy. Therefore, repeated operation of the alloy at temperatures over 200° C. is impossible. That is to say, the alloy does not exhibit shape memory effects.
  • For the above-mentioned shape memory alloy No. 7, even though it possesses good machinability, formation of ω phase, which results in poor structural stability and causes the loss of shape memory property at over 100° C., lowers the transformation temperature. Therefore the alloy fails for repeated operation. That is to say, the alloy does not exhibit shape memory effects.
  • For the above-mentioned shape memory alloy No. 9, it fails for repeated operation due to its relative ease of plastic deformation. Furthermore, easy formation of ω phase during operation results in loss of shape memory property.
  • As a result, based on the conventional high temperature shape memory technology described in alloys (1) and (2), the below-described invention were carried out through large amount of experiments and research work in order to improve machinability of Ti—Ni—Zr alloys and Ti—Ni—Hf alloys.
  • Accordingly, embodiments of the present disclosure address the problems of the prior art and provide a high temperature shape memory alloys which have good machinability and, in the meanwhile, are suitable for repeated high temperature operation.
  • EMBODIMENT 1
  • A high temperature shape memory alloy is provided in Embodiment 1 to solve these technical problems, where the alloy consists of 34.7 mol %-48.5 mol % Nickel, at least one of Zirconium or Hafnium as transformation temperature increasing additive element, with a total content of 6.8 mol %-22.5 mol %; at least one of Niobium or Tantalum as machinability improving additive element, with a total content of 1 mol %-30 mol %, Boron below 2 mol %, and the balance Titanium; and impurities.
  • With respect to high temperature shape memory alloys having the components of Embodiment 1, since the alloys consist of 34.7 mol %-48.5 mol % Nickel at least one of Zirconium or Hafnium as transformation temperature increasing additive element, with a total content of 6.8 mol %-22.5 mol %, at least one of Niobium or Tantalum as machinability improving additive elements, with a total content of 1 mol %-30 mol %, Boron below 2 mol % and the balance Titanium, high transformation temperatures (peak transformation temperature (M*) or peak reverse transformation temperatures (A*)) in excess of 100° C. are obtained, and cold ductility is also improved. Consequently, Embodiment 1 provides a high temperature shape memory alloy for repeated high temperature operation with improved cold working machinability.
  • In addition, the description of Boron below 2 mol % also includes the case of 0 mol % Boron, or no addition of Baron.
  • Form 1 of Embodiment 1
  • High temperature shape memory alloys of form 1 in Embodiment 1 consists of 6.8 mol %-22.5 mol % Zirconium as transformation temperature increasing additive elements and 3 mol %-30 mol % Niobium as machinability improving additives.
  • In the high temperature shape memory alloys of Form 1 in Embodiment 1, since the alloys consist of 6.8 mol %-22.5 mol % Zirconium and 3 mol %-30 mol % Niobium, high peak reverse transformation temperature (A*) in excess of 100° C. is obtained In the meanwhile, cold working can be performed with high ductility.
  • Form 2 of Embodiment 1
  • High temperature shape memory alloys of form 2 in Embodiment 1 consist of 6.8 mol %-18 mol % Hafnium as transformation temperature increasing additive elements and 3 mol %-20 mol % Niobium as machinability improving additive elements.
  • In the high temperature shape memory alloys of Form 2 in Embodiment 1 since the alloys consist of 6.8 mol %-18 mol % Hafnium and 3 mol %-20 mol % Niobium, high peak reverse transformation temperatures (A*) in excess of 100° C. are obtained In the meanwhile, cold working can be performed with improved ductility.
  • Form 3 of Embodiment 1
  • High temperature shape memory alloys of form 3 in Embodiment 1 consists of 6.8 mol %-20 mol % of transformation temperature increasing additive elements and 3 mol %-30 mol % Tantalum as said machinability improving additive elements.
  • In the high temperature shape memory alloys of Form 3 in Embodiment 1, since the alloys consist of 6.8 mol %-20 mol % of transformation temperature increasing additive elements and 3 mol %-30 mol % Tantalum as machinability improving additive elements, machinability is improved compared with the case while no Tantalum is added.
  • Form 4 of Embodiment 1
  • The high temperature shape memory alloy of Form 4 in Embodiment 1 with respect to either of the Embodiment 1 or form 3 of Embodiment 1, where the mol ratio of Titanium plus Zirconium and Hafnium to Nickel is in the range of 0.98 to 1.14.
  • In the high temperature shape memory alloy of Form 4 in Embodiment 1, since the mol ratio of Titanium plus Zirconium and Hafnium to Nickel is in the range of 0.98 to 1.14, high peak reverse transformation temperature (A*) in excess of 100° C. is obtained. In the meanwhile, cold working can be performed with high ductility.
  • EMBODIMENT 2
  • An actuator is provided in Embodiment 2 to solve the above-mentioned technical problems, where the actuator is made of the high temperature shape memory alloys described in either the Embodiment 1 or forms 1 through 4 of Embodiment 1.
  • In the actuator in Embodiment 2, since the actuator is made of the high temperature shape memory alloy of either the Embodiment 1 or forms 1 through 4 of Embodiment 1, it is capable to perform cold working. In addition, high temperature applications are possible with the help of its high transformation temperatures and shape memory effects.
  • EMBODIMENT 3
  • A motor is provided in Embodiment 3 to solve the above-mentioned technical problems, where the motor possesses a flux adjustment valve made of the high temperature shape memory alloys described in either Embodiment 1 or forms 1 through 4 of Embodiment 1.
  • In the motor in Embodiment 3, since the motor possesses a flux adjustment valve made of the high temperature shape memory alloys described in either Embodiment 1 or forms 1 through 4 of Embodiment 1, high temperature operations can be performed with high transformation temperatures and shape memory effects.
  • The present embodiments provide shape memory alloys capable of repeated high temperature operation with high machinability.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 shows a scanning electron microscope image of alloy No. 7 in an embodiment of the present disclosure.
  • FIG. 2 shows a scanning electron microscope image of alloy No. 8 in an embodiment of the present disclosure.
  • DETAILED DESCRIPTION
  • Embodiments of the present disclosure are described in detail below.
  • As embodiments and comparative examples of the present disclosure, 55 alloy specimens, Nos. 1 to 55, were provided as shown in Tables 1 to 10 and corresponding experiments were carried out. Specimens were prepared by the below described process including steps (1) to (3).
  • In step 1, each metallic element is measured by mol %, and then molten by means of arc melting method to make alloy ingots. Namely, alloy No. 2 (Ti—Ni49.5—Zr10) has a composition expressed as 49.5 mol % Ni, 10 mol % Zr and the balance Ti (40.5 mol %).
  • In step 2, the resultant alloy ingots are subjected to homogenization heat treatment for 2 hours (7.2 ks) at 950° C.
  • In step 3, billets (test pieces) 15 mm long, 10 mm wide, and 1 mm thick are cut off by electric discharge machining.
  • Machinability Evaluation Tests
  • Machinability evaluation tests were carried out to evaluate the machinability of the alloys manufactured by the above mentioned methods. Machinability evaluation tests were carried out through cold rolling at deformations up to 60%. The break rolling ratio of test pieces, with test pieces breaking down at deformations up to 60%, was measured to evaluate machinability.
  • Transformation Temperature Measurement Tests
  • In this test, cold rolled test pieces were heat-treated for 1 hour at 700° C. to measure the martensite peak transformation temperature (M*) and peak reverse transformation temperature (A*) of each alloy by means of Differential Scanning Calorimetry (DSC).
  • As comparative examples, the composition of ternary Ti—Ni—Zr alloys Nos. 1 to 4, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.) and peak reverse transformation temperature (A*, ° C.) are provided in Table 1.
  • TABLE 1
    Machinability of Ti—Ni—Zr alloys and transformation temperatures
    Break transformation
    Component(mol %) (Ti + Zr)/ rolling temperature
    No. composition Ti Ni Zr Nb Ni ratio (%) M* A*
    Comparative 1 Ti—Ni49.5—Zr7 balance 49.5 7 1.02 42 81 132
    example 2 Ti—Ni49.5—Zr10 balance 49.5 10 1.02 30 102 155
    3 Ti—Ni49.5—Zr15 balance 49.5 15 1.02 10 179 219
    4 Ti—Ni49.5—Zr20 balance 49.5 20 1.02 9 270 325
  • As embodiments of the present disclosure, the composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 5 to 7, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 2.
  • Furthermore, alloys No. 5-7 are derived by fixing Ti and Zr content (mol %) of alloy No. 3, and then substituting Ni content by Nb.
  • TABLE 2
    Machinability of Ti—Ni—Zr—Nb alloys and transformation temperature
    Break transformation
    Component(mol %) (Ti + Zr)/ rolling temperature
    No. composition Ti Ni Zr Nb Ni ratio (%) M* A*
    Embodiment 5 Ti—Ni48.5—Zr15—Nb1 balance 48.5 15 1 1.04 17 149 190
    6 Ti—Ni46.5—Zr15—Nb3 balance 46.5 15 3 1.09 50 140 184
    7 Ti—Ni44.5—Zr15—Nb5 balance 44.5 15 5 1.14 46 131 171
  • As embodiments and comparative examples of the present invention, the composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 8 to 12, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 3.
  • Furthermore, alloys No. 8-12 are derived by fixing the mol ratio of Ti, Ni and Zr to 35.5 mol %, 49.5%, and 15 mol % respectively, and then substituting Ti, Ni, and Zr as a whole by Nb.
  • TABLE 3
    Machinability of Ti—Ni—Zr—Nb alloys and transformation temperatures
    Break transformation
    Component(mol %) (Ti + Zr)/ rolling temperature
    No. Composition Ti Ni Zr Nb Ni ratio (%) M* A*
    Embodiment 8 (Ti—Ni49.5—Zr15)95—Nb5 balance 47.0 14.3 5 1.02 35 134 180
    9 (Ti—Ni49.5—Zr15)90—Nb10 balance 44.6 13.5 10 1.02 Over 60 110 162
    10 (Ti—Ni49.5—Zr15)80—Nb20 balance 39.6 12.0 20 1.02 Over 60 90 139
    11 (Ti—Ni49.5—Zr15)70—Nb30 balance 34.7 10.5 30 1.02 Over 60 72 122
    Comparative 12 (Ti—Ni49.5—Zr15)99—Nb1 balance 49.0 14.9 1 1.02 10 157 198
    example
  • As embodiments and comparative examples of the present disclosure, the composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 13 to 17, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 4.
  • Additionally, with regard to the alloys No. 16 and 17, since the transformation temperature is not identified in the experiment, it can be concluded that transformation temperature is too low to be observed.
  • TABLE 4
    Machinability of Ti—Ni—Zr—Nb alloys and transformation temperatures
    Break transformation
    Component(mol %) (Ti + Zr)/ rolling temperature
    No. Composition Ti Ni Zr Nb Ni ratio (%) M* A*
    Embodiment 13 (Ti—Ni50.5—Zr15)90—Nb10 balance 45.5 13.5 10 0.98 Over 60 74 121
    14 (Ti—Ni48.5—Zr15)95—Nb5 balance 46.1 14.3 5 1.06 23 132 177
    15 (Ti—Ni50.5—Zr15)95—Nb5 balance 48 14.3 5 0.98 30 104 145
    Comparative 16 (Ti—Ni55.0—Zr15)90—Nb10 balance 49.5 13.5 10 0.82 5
    17 (Ti—Ni35.0—Zr15)90—Nb10 balance 31.5 13.5 10 1.86 8
  • As embodiments and comparative examples of the present disclosure, the composition of quaternary Ti—Ni—Zr—Nb alloys Nos. 18 to 26, as well as the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 5.
  • TABLE 5
    Machinability of Ti—Ni—Zr—Nb alloys and transformation temperatures
    Break transformation
    Content(mol %) (Ti + Zr)/ rolling temperature
    No. Composition Ti Ni Zr Nb Ni ratio (%) M* A*
    Embodiment 18 (Ti—Ni49.5—Zr10)95—Nb5 balance 47.0 9.5 5 1.02 Over 60 52 124
    19 (Ti—Ni49.5—Zr10)90—Nb10 balance 44.6 9.0 10 1.02 Over 60 41 109
    20 (Ti—Ni49.5—Zr20)90—Nb10 balance 44.6 18.0 10 1.02 38 182 236
    21 (Ti—Ni49.5—Zr25)90—Nb10 balance 44.6 22.5 10 1.02 28 325 408
    22 (Ti—Ni49.5—Zr25)70—Nb30 balance 34.7 17.5 30 1.02 Over 60 450 580
    23 (Ti—Ni49.5—Zr7)97—Nb3 balance 48.0 6.8 3 1.02 Over 60 41 102
    Comparative 24 (Ti—Ni49.5—Zr30)90—Nb10 balance 44.6 27.0 10 1.02 5
    example 25 (Ti—Ni49.5—Zr20)50—Nb50 balance 24.8 10.0 50 1.02 Over 60
    26 (Ti—Ni49.5—Zr5)90—Nb10 balance 44.6 4.5 10 1.02 Over 60 5 75
  • As embodiments and comparative examples of the present invention, the composition of quaternary Ti—Ni—Hf—Nb alloys and quinary Ti—Ni—Zr—Hf—Nb Nos. 27 to 37, along with the mol ratio of Ti plus Zr and Hf to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.) and peak reverse transformation temperature (A*, ° C.), are given respectively in Table 6.
  • Furthermore, alloys No. 28 and 29 correspond to alloys 9 and 10, respectively, in which Zr is substituted by Hf and alloy No. 30 corresponds to alloy 20 in which Zr, is substituted by Hf. Besides, alloy No. 31 corresponds to alloy No. 7 in which Zr is substituted by Hf, and alloy No. 32 corresponds to alloy No. 19, in which half of Zr content (10 mol %) is substituted by Hf. In other words, the total content of Zr and Hf (transformation temperature increasing additive elements) is 9 mol % in alloy No. 32 and 12 mol % in alloy No. 33 respectively.
  • TABLE 6
    Machinability of Ti—Ni—Zr—Nb alloys and transformation temperatures
    Break transformation
    Content(mol %) (Ti + Zr + rolling temperature
    No. composition Ti Ni Zr Hf Nb Hf)/Ni ratio (%) M* A*
    Embodiment 27 (Ti—Ni49.5—Hf7)97—Nb3 balance 48.0 6.8 3 1.02 Over 60 75 125
    28 (Ti—Ni49.5—Hf15)90—Nb10 balance 44.6 13.5 10 1.02 Over 60 152 206
    29 (Ti—Ni49.5—Hf15)80—Nb20 balance 39.6 12 20 1.02 Over 60 95 158
    30 (Ti—Ni49.5—Hf20)90—Nb10 balance 44.6 18 10 1.02 33 193 255
    31 Ti—Ni44.5—Hf15—Nb5 balance 44.5 15 5 1.14 48 136 185
    32 (Ti—Ni49.5—Zr5—Hf5)90—Nb10 balance 44.6 4.5 4.5 10 1.02 Over 60 52 121
    33 (Ti—Ni49.5—Zr7.5—Hf7.5)80—Nb20 balance 39.6 6 6 20 1.02 Over 60 77 141
    Comparative 34 Ti—Ni49.5—Hf7 balance 49.5 7 1.02 40 94 153
    example 35 Ti—Ni49.5—Hf15 balance 49.5 15 1.02 15 183 228
    36 Ti—Ni49.5—Hf20 balance 49.5 20 1.02 10 265 307
    37 Ti—Ni49.5—Zr7.5—Hf7.5 balance 49.5 7.5 7.5 1.02 12 179 223
  • As embodiments the present disclosure, the composition of quaternary Ti—Ni—Zr—Ta alloys Nos. 38 to 42, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 7.
  • Furthermore, alloys 38-42 are derived by fixing the mol ratio of Ti, Ni and Zr to 40.5 mol %, 49.5% and 10 mol % respectively, and then substituting Ti, Ni, and Zr as a whole by Ta.
  • TABLE 7
    Machinability of Ti—Ni—Zr—Ta alloys and transformation temperatures
    Break transformation
    Component(mol %) (Ti + Zr)/ rolling temperature
    No. composition Ti Ni Zr Nb Ta Ni ratio (%) M* A*
    Embodiment 38 (Ti—Ni49.5—Zr10)95—Ta5 balance 47.0 9.5 5 1.02 40 97 155
    39 (Ti—Ni49.5—Zr10)90—Ta10 balance 44.6 9 10 1.02 Over 60 98 156
    40 (Ti—Ni49.5—Zr10)85—Nb15 balance 42.1 8.5 15 1.02 Over 60 98 161
    41 (Ti—Ni49.5—Zn10)80—Ta20 balance 39.6 8 20 1.02 Over 60 111 171
    42 (Ti—Ni49.5—Zr10)70—Ta30 balance 34.7 7 30 1.02 Over 60 117 175
  • As embodiments of the present disclosure, the composition of quaternary Ti—Ni—Zr—Ta alloys and quinary Ti—Ni—Zr—Nb—Ta, Nos. 43 to 48, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 8.
  • Furthermore, the total content of Nb and Ta (machinability improving additive elements) is 10 mol % in alloy No. 48.
  • TABLE 8
    Machinability of Ti—Ni—Zr—Ta—(Nb) alloys and transformation temperatures
    Break transformation
    Content(mol %) (Ti + Zr)/ rolling temperature
    No. composition Ti Ni Zr Nb Ta Ni ratio (%) M* A*
    Embodiment 43 (Ti—Ni49.5—Zr15)95—Ta5 balance 47.0 14.3 5 1.02 15 180 229
    44 (Ti—Ni49.5—Zr15)90—Ta10 balance 44.6 13.5 10 1.02 23 165 219
    45 (Ti—Ni49.5—Zr15)85—Ta15 balance 42.1 12.8 15 1.02 30 169 224
    46 (Ti—Ni49.5—Zr15)80—Ta20 balance 39.6 12.0 20 1.02 Over 179 231
    60
    47 (Ti—Ni49.5—Zr25)80—Ta20 balance 39.6 20.0 20 1.02 45 327 412
    48 (Ti—Ni49.5—Zr15)90—Nb5—Ta5 balance 44.6 13.5 5 5 1.02 40 142 203
  • As embodiments and comparative examples of the present disclosure, the composition of quinary Ti—Ni—Zr—Nb—B alloys Nos. 49 to 52, along with the mol ratio of Ti plus Zr to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.) are shown respectively in Table 9.
  • Furthermore, alloys No. 49 to 52 are derived by adding element B (Boron) into Ti—Ni—Zr—Nb based alloys.
  • TABLE 9
    Machinability of Ti—Ni—Zr—Nb—B alloys and transformation temperatures
    Break transformation
    Content(mol %) (Ti + Zr)/ rolling temperature
    No. composition Ti Ni Zr Nb B Ni ratio (%) M* A*
    Embodiment 49 (Ti—Ni49.5—Zr15)94.8—Nb5—B0.2 balance 46.9 14.2 5 0.2 1.02 40 140 185
    50 (Ti—Ni49.5—Zr15)93—Nb5—B2 balance 46.0 14.0 5 2 1.02 36 144 191
    51 (Ti—Ni49.5—Zr20)89.5—Nb10—B0.5 balance 44.3 17.9 10 0.5 1.02 40 217 271
    Comparative 52 (Ti—Ni49.5—Zr15)92—Nb5—B3 balance 45.5 13.8 5 3 1.02 20 135 179
    example
  • As embodiments of the present invention, the composition of Ti—Ni—Zr—Hf—Nb—Ta—B based multi-component alloys No. 53 to 55, along with the mol ratio of Ti plus Zr and Hf to Ni, break rolling ratio (%), martensite peak transformation temperature (M*, ° C.), and peak reverse transformation temperature (A*, ° C.), are shown in Table 10.
  • TABLE 10
    Machinability of Ti—Ni—Zr—Hf—Nb—Ta—B alloys and transformation temperatures
    Break transformation
    Content(mol %) (Ti + Zr + rolling temperature
    No. composition Ti Ni Zr Hf Nb Ta B Hf)/Ni ratio (%) M* A*
    Em- 53 (Ti—Ni49.5—Hf15)85—Nb5—Ta10 Balance 42.1 12.8 5 10 1.02 Over 125 178
    bodi- 60
    ment 54 (Ti—Ni49.5—Zr7.5—Hf7.5)90—Nb5—Ta5 Balance 44.6 6.8 6.8 5 5 1.02 45 112 168
    55 (Ti—Ni49.5—Zr7.5—Hf7.5)91.5—Nb5—Ta3—B0.5 Balance 45.3 6.9 6.9 5 3 0.5 1.02 42 118 171
  • FIG. 1 shows a scanning electron microscope image of alloy No. 7 in an embodiment of the present disclosure.
  • The following conclusion can be drawn from the forgoing description of the experiment results. The relatively low rolling ratio of Ti—Ni—Zr based ternary alloys No. 1 to 4 in the comparative examples indicates poor machinability. Besides, while the transformation temperature (M* and A*) increases with increasing Zr (Zr, transformation temperature increasing additive) content, the rolling ratio decreases, resulting in reduced machinability.
  • In comparison to the forgoing result, as shown in Table 2, in the case of the quaternary Ti—Ni—Zr—Nb base alloys Nos. 5 to 7 derived from substitution of Ni in alloy No. 3 of the comparative example by Nb (machinability improvement additive element), rolling ratio increases thus machinability improves accordingly. In addition, transformation temperature (M* and A*) in excess of 100° C. makes it possible for high temperature operation 100° C. Particularly, even though the transformation temperature tends to decrease with increasing Nb content, it exhibits a small change in amplitude indicating no drastic drop of transformation temperature occurred.
  • As a result, with improved machinability, alloys No. 5 to 7 are suitable for high temperature operation as high temperature shape memory alloys. Furthermore, even with improved break rolling ratio, existence of a large amount of fine cracks are observed in alloys No. 5 to 7. As shown in FIG. 1 of the SEM image by Scanning Electric Microscope, together with the hard brittle Laves phase that forms in alloy No. 7 after rolling, the soft β phase liable to plastic deformation precipitates, which hinders the development of cracks, appeared on the interfaces of said Laves phase. As a result, machinability is improved.
  • FIG. 2 shows a scanning electron microscope image of alloy No. 8 in embodiment of the present disclosure.
  • In Table 3, in the case of quaternary Ti—Ni—Zr—Nb alloys Nos. 8 to 12, embodiments of which are derived by fixing the mol ratio of Ti—Ni49.5—Zr15 and then substituting Ti, Ni, and Zr as a whole by Nb, high peak reverse transformation temperature (A*) exceeding 100° C. and relatively high martensite transformation temperature (A*) are obtained. Moreover, even though no significant improvement in ductility was observed with 1 mol % Nb added (alloy No. 11 of comparative example), ductility increases when Nb content is greater than 3 mol %. In particular, when Nb content exceeds 10 mol %, rolling ratio reached 60% for alloys No. 9 to 11. Furthermore, with respect to alloys No. 8 to 11, compared to alloys No. 5 to 7, machinability was improved while no significant fine crack developed. In the SEM image of FIG. 2, soft β phase precipitated on crystal interfaces, as well as within the crystal grains, for alloy No. 8 after rolling. Consequently machinability is improved.
  • In Tables 1 to 4, in the case of alloys Nos. 13 to 15 and alloy No. 7, when the mol ratio of metallic components to Nickel is about 1, compared with alloys No. 3 and 12 while Zr content is 15 mol %, ductility increases. However, when the mol ratio of metallic components to Nickel is 0.82, which deviates substantially from the value 1 for alloy No. 16, or 1.86 as for alloy No. 17, ductility decreases and machinability is reduced. At the same time it is identified a drastic drop in transformation temperature (M* and A*)
  • In Table 5, with respect to alloys No. 18 to 23, even though the content of Zr which is added to increase the transformation temperature (M* and A*) reaches the degree that may reduce machinability, through addition of Nb by 3 to 30 mol %, machinability is able to be improved without reducing transformation temperature. Particularly in the case of alloy No. 22, an extremely high transformation temperature, exceeding 400° C., is obtained with 60% of extremely high machinability. In alloy No. 24, when the content of added Zr reaches 27%, the test piece broke at merely 5% deformation, even with 10 mol % Nb added. As shown with alloy No. 25, rolling ratio is in excess of 60% when 50 mol % Nb was added, which indicates extraordinarily high machinability; however, transformation temperature was not identified. On the other hand, when 4.5 mol % Zr was added in the case of alloy No. 26, high machinability of over 60% in rolling ratio was obtained with 10 mol % addition of Nb, transformation temperature was lowered to below 100° C.
  • As shown in Table 6 with respect to alloys No. 27 to 37, in the case of Ti—Ni—Hf based alloys, which possess approximately the same properties as Ti—Ni—Zr based alloys and are also poor in machinability, high temperature shape memory alloys having high transformation temperature with improved machinability are obtained through addition of Nb. Particularly, in the case of alloy No. 27, compared with alloys Nos. 1, 23 and 34, equal or better physical properties (transformation temperature and rolling ratio) are obtained even when Zr is substituted by Hf (transformation temperature increasing additive), same as the case of Zr. Similarly, it can also be seen that equal or better properties (transformation temperature and rolling ratio) are obtained when Zr was substituted by Hf (transformation temperature increasing additive) as we compare alloy No. 28 compare with alloys Nos. 3, 9 and 35, alloy No. 29 with alloys No. 10, alloy No. 30 with alloys Nos. 20 and 36, alloy No. 31 with alloy 7, alloy 32 with alloys Nos. 2 and 19, alloy No. 33 with alloys Nos. 10, 29 and 37, which indicates that by adding Nb the same improvement effect is achieved.
  • As a result, it is understood that by adding Nb to Ti—Ni—Zr (or Hf) based alloys, high temperature shape memory alloys with high machinability and high transformation temperature are obtained.
  • As shown in Tables 7 and 8 with respect to alloys Nos. 38 to 48, by adding Ta (machinability improving additive) or the combination of Ta and Nb instead of Nb, to Ti—Ni—Zr based alloys, high temperature shape memory alloys of high machinability with high transformation temperature are obtained. In addition, it shows that with increasing Ta content, rolling ratio increases and transformation temperature increases as well.
  • In particular, comparing alloys Nos. 38 and 39 with alloys Nos. 18 and 19 in which Nb is added, it can be seen that alloys Nos. 38 and 39 possess higher transformation temperature; besides, as we compare alloys Nos. 43, 44 and 46 with alloys Nos. 8, 9, 10 and 3, even though adding Ta to alloys No. 43, 44, and 46 exhibits little effect to improve rolling ratio compared with adding Nb to alloys Nos. 8 to 10, better rolling ratio and higher transformation temperature were obtained compared respectively with alloy No. 3 and alloys Nos. 8 to 10 with added Nb.
  • Furthermore, as alloy No. 48 was compared with alloys Nos. 44, 9, and 3, in the case of alloy 48 with combined addition of Ta and Nb, the rolling ratio is improved compared with alloy No. 44 with only Ta added, and yet the transformation temperature is increased compared with alloy No. 9 while only Nb is added.
  • As shown in Table 9, with respect to alloys Nos. 49 to 52, by adding Nb and further adding B (Boron, temperature increasing and machinability improving additive element), rolling ratio is improved with increased transformation temperature compared with alloys Nos. 8 and 20 while no B is added. In addition, comparing alloys Nos. 49, 50, and 52 with alloy No. 8, it can be seen that the improving effect tends to be weakened with increasing B content, indicating a small amount of B addition is preferable.
  • As shown in Table 10 with respect to alloys Nos. 53 to 55, by adding Nb, Ta and B to Ti—Ni—Hf or Ti—Ni—Zr—Hf alloys, a transformation temperature exceeding 100° C. is obtained and rolling ratio is also improved compared with alloys No. 35 and 37.
  • In the above description, the preferred exemplary embodiments of the present invention were set forth, it will be understood that the invention is not limited to the specific forms shown, modification may be made without departing from the scope of the present invention as expressed in the claims.
  • INDUSTRIAL APPLICATIONS
  • Since the afore-described shape memory alloys do not lose their shape memory effect during repeated use at high temperature, they can be used as valves inside gas channels of motors (engines of automobiles, aircrafts, or gas turbine) for high temperature operation, when heated, channel area is regulated with the help of the shape memory effect; when cooled, channel area is reversed back by a spring used for deforming the valve. Besides, they can also be used as lubricant supplying valves of high speed rotating shafts. In addition, these alloys can be used as safety devices for power supply of household electric appliance at high temperature operation. Furthermore, they can also be used as actuators for high temperature operation. In the case of actuators, they also exhibit improved responsiveness resulting from increased cooling speed.

Claims (20)

1. A high temperature shape memory alloy, wherein said alloy consists of 34.7 mol %-48.5 mol % Ni, at least either Zirconium or Hafnium as transformation temperature increasing additive elements, with the sum of which 6.8 mol % to 22.5 mol %; at least either Niobium or Tantalum as machinability improving additives, with the sum of which 1 mol % to 30 mol %; and Boron less than 2 mol %; and Titanium and impurities as the balance.
2. A high temperature shape memory alloy according to claim 1, wherein said alloy consists of 6.8 mol % to 22.5 mol % Zirconium as said transformation temperature increasing additives; and 3 mol % to 30 mol % Niobium as said machinability improving additives.
3. A high temperature shape memory alloy according to claim 1, wherein said alloy consists of 6.8 mol % to 18 mol % Hafnium as said transformation temperature increasing additives; and 3 mol % to 20 mol % Niobium as said machinability improving additives.
4. A high temperature shape memory alloy according to claim 1, wherein said alloy consists of 6.8 mol % to 20 mol % said transformation temperature increasing additives; and 3 mol % to 30 mol % Tantalum as said machinability improving additives.
5. A high temperature shape memory alloy according to claim 1, wherein the mol ratio of Titanium plus Zirconium and Hafnium to Nickel is in the range of 0.98 to 1.14.
6. An actuator, wherein the said actuator is made of the high temperature shape memory alloy described in claim 1.
7. A motor equipped with a flux adjusting valve, wherein the said flux adjusting valve is made of the high temperature shape memory alloy described in claim 1.
8. A shape memory alloy, comprising:
nickel (Ni);
at least one of zirconium (Zr) and hafnium (Hf) as transformation temperature increasing additive elements;
at least one of niobium (Nb) and tantalum (Ta) as machinability improving additives; and
boron (B) in a concentration ranging between 0 mol %-2 mol %;
wherein the mol ratio of Titanium plus Zirconium and Hafnium to Nickel is between 0.98 to 1.14.
9. The alloy of claim 8, wherein nickel is present in a concentration ranging between 34.7 mol %-48.5 mol %.
10. The alloy of claim 8, wherein the sum of the concentration of zirconium and hafnium ranges between 6.8 mol %-22.5 mol %.
11. The alloy of claim 8, wherein the sum of the concentration of niobium and tantalum ranges between 1 mol %-30 mol %.
12. The alloy of claim 8, wherein the concentration of zirconium ranges between 6.8 mol %-22.5 mol % and the concentration of niobium ranges between 3 mol %-30 mol %.
13. The alloy of claim 8, wherein the concentration of hafnium ranges between 6.8 mol %-18 mol % and the concentration of niobium ranges between 3 mol %-20 mol %.
14. The alloy of claim 8, wherein the sum of the concentration of zirconium and hafnium ranges between 6.8 mol %-20 mol % and the concentration of tantalum ranges between 3 mol %-30 mol %.
15. The alloy of claim 8, wherein the peak reverse transformation temperature (A*) is greater than 100° C.
16. A method of making a shape memory alloy part, comprising:
providing a shape memory alloy composition comprising:
nickel in a concentration ranging between 34.7 mol %-48.5 mol %;
at least one of zirconium and hafnium, wherein the total concentration zirconium plus hafnium ranges between 1 mol %-30 mol %;
at least one of niobium and tantalum, wherein the total concentration niobium plus tantalum ranges between 6.8 mol %-22.5 mol %; and
boron (B) in a concentration below 2 mol %;
wherein the concentration of the elements is selected such that the mol ratio of Titanium plus Zirconium and Hafnium to Nickel is between 0.98 to 1.14; and
forming the shape memory alloy composition into the part.
17. The method of claim 16, wherein the concentration of zirconium ranges between 6.8 mol %-22.5 mol % and the concentration of niobium ranges between 3 mol %-30 mol %.
18. The method of claim 16, wherein the concentration of hafnium ranges between 6.8 mol %-18 mol % and the concentration of niobium ranges between 3 mol %-20 mol %.
19. The method of claim 16, wherein the sum of the concentration of zirconium and hafnium ranges between 6.8 mol %-20 mol % and the concentration of tantalum ranges between 3 mol %-30 mol %.
20. The method of claim 16, wherein the part comprises at least one of an actuator and a flux adjusting value configured for use with a motor.
US12/235,528 2006-03-20 2008-09-22 High temperature shape memory alloy, actuator and motor Abandoned US20090218013A1 (en)

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