High-temperature shape memory alloy, method for producing the same, actuator and engine using the same

Abstract

To provide a high temperature shape memory alloy subject to martensite transformation at a high temperature.SOLUTION: A high temperature shape memory alloy contains a total amount of Ti (titanium), Zr (zirconium), and V (vanadium) of 45 atom% or more and 55 atom% or less, each of Ti, ZR, and V of at least 10 atom% or more, and the balance of Pd (palladium), Ni (nickel), and inevitable impurities. A ratio of Pd and Ni is 1:2 or more and 2:1 or less. In the high temperature shape memory alloy, among martensite transformation temperatures, a martensite finishing temperature (Mf) satisfies a temperature range of 350°C or higher and 990°C or lower, and an austenite finishing temperature (Af) satisfies a temperature range of 550°C or higher and 1,105°C or lower.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a high-temperature shape memory alloy, a method for manufacturing the same, and uses thereof, and more particularly to a high-temperature shape memory alloy having improved work capacity and repeated characteristics at high temperatures, a method for manufacturing the same, and uses thereof.

Background Art

[0002] Shape memory alloys typified by TiNi are used as actuators and the like that operate by sensing temperature changes without requiring power. There are various performance requirements for such shape memory alloys. For parts such as actuators used in high-temperature parts in the order of several hundred °C to 1000 °C, such as automobile engines and jet engines, a shape memory alloy that operates even in such a high-temperature use environment is required.

[0003] Therefore, attempts have been made to increase the martensite transformation temperature related to the shape memory effect by adding Zr, Hf, Pd, Pt, etc. to TiNi. For example, Patent Document 1 discloses a high-temperature shape memory alloy in which Ti is 50 to 52 atomic%, Pt is 10 to 25 atomic%, contains one or more of Au, Pd, Cu at 5 atomic% or less, contains C at 2 atomic% or less, and the balance is Ni, and precipitates of the Ti4(Ni,Pt)3 type are formed.

[0004] On the other hand, the development of high-temperature shape memory alloys using alloys based on TiPt or TiPd has also been carried out. For example, Patent Document 2 discloses an alloy having shape memory characteristics and pseudoelasticity in which Ir is added to a Pt-42 to 63 atomic% Ti alloy and part of Pt is replaced with Ir of less than 50 atomic%. Patent Document 3 discloses an alloy in which Pd is 45 to 55 atomic%, one or more of Hf, Zr, Ta, Nb, V, Mo, W is 0.1 to 15 atomic%, and the balance is Ti and inevitable impurities, and shows shape recovery in the temperature range from 200 °C to 550 °C. Patent Document 4 discloses a TiPd-based high-temperature shape memory alloy consisting of 45 to 55 atomic% of Pd and the balance being Ti and inevitable impurities, wherein a part of the Ti is substituted with one or more of Zr, Hf, Nb, Ta, Mo, and W in the range of 0.1 to 15 atomic% with respect to the overall composition, and which has a characteristic martensite twin structure.

[0005] Patent Document 5 discloses a TiPd-based high-temperature shape memory alloy consisting of 30 to 50 atomic% of Pd and the balance being Ti and inevitable impurities, wherein a part of the Ti is substituted with Zr in the range of 0.1 to 18 atomic% with respect to the overall composition, and a part of the Pd is substituted with Ni in the range of 0.1 to 15 atomic% with respect to the overall composition. Incidentally, instead of Ni, a part of the Pd may be substituted with Co in the range of 0.1 to 22 atomic% with respect to the overall composition. Patent Document 6 discloses a high-temperature shape memory alloy containing Ti, Pd, Pt, Zr, X (X is Ni and / or Co), and inevitable impurities, satisfying the following conditions: the total of the Pd and the Pt is more than 35 atomic% and less than 55 atomic%, the Zr is 0.1 atomic% or more and less than 15 atomic%, and the X is 0.1 atomic% or more and less than 15 atomic%, and the balance is the Ti and the inevitable impurities.

[0006] Non-Patent Document 1 shows that substituting 25 atomic% of Pd for Pt in a TiPt-based high-temperature shape memory alloy causes the same martensitic transformation as TiPt. Non-Patent Document 2 mentions Ni 35 Pd 15 Ti 30 Hf 20 , and a high-entropy alloy Ni 25 Pd 25 Ti 25 Hf 25 , Ni 25 Pd 25 Ti 16.6 Hf 16.7 Zr 16.7 , are shown to transform at a high temperature of 400 °C or higher, and Ni 35 Pd 15 Ti 30 Hf20 has been shown to recover its shape.

[0007] When a shape memory alloy is deformed in a state having a martensite phase and then heated to a temperature above the martensite transformation temperature, it transforms from the martensite phase to the austenite phase, which is the parent phase, and recovers its shape. Therefore, in order to cause shape recovery at a high temperature, it is necessary to increase the martensite transformation temperature.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made to solve the above problems in conventional high-temperature shape memory alloys, and an object thereof is to provide a high-temperature shape memory alloy that causes a martensitic transformation at high temperatures, a method for manufacturing the same, and applications using the same.

Means for Solving the Problems

[0011] [1] In the high-temperature shape memory alloy of the present invention, the total of Ti (titanium), Zr (zirconium), and V (vanadium) is 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and V is at least 10 atomic % or more, the balance consists of Pd (palladium), Ni (nickel), and inevitable impurities, and the ratio of Pd to Ni is 1:2 or more and 2:1 or less. [2] In the high-temperature shape memory alloy [1] of the present invention, preferably, the ratio of Pd to Ni is 1:1.5 or more and 1.5:1 or less. Next, the actions of the constituent elements in the high-temperature shape memory alloys [1] and [2] of the present invention will be described. When the total of Ti, Zr, and V is less than 45 atomic % or exceeds 55 atomic %, the martensitic transformation required for a shape memory alloy does not occur. When each of Ti, Zr, and V is less than at least 10 atomic %, the characteristics as a high-entropy alloy are not exhibited. More preferably, the total of Ti, Zr, and V is 48 atomic % or more and 52 atomic % or less, and each of Ti, Zr, and V is at least 14 atomic % or more. Here, a high-entropy alloy is a solid-solution material in which the mixing entropy is increased by mixing substantially equal amounts of five or more constituent elements. When this is regarded as a casting alloy, (1) a material in which a solid solution is formed as cast and is not basically brittle can be obtained, (2) high strength can be expected as cast, and (3) it has excellent characteristics such as being able to be produced using general-purpose melting and casting equipment.

[0012] [3] The high-temperature shape memory alloy of the present invention has a total of Ti (titanium), Zr (zirconium), and Hf (hafnium) of 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and Hf being at least 10 atomic % or more, and the balance consisting of Pd (palladium), Pt (platinum), and inevitable impurities, and the ratio of Pd to Pt being 1:2 or more and 2:1 or less. [4] In the high-temperature shape memory alloy [3] of the present invention, preferably, Pd is 5 atomic % or more and 20 atomic % or less, and the balance consists of Pt and inevitable impurities. Next, the actions of the constituent elements in the high-temperature shape memory alloys [3] and [4] of the present invention will be described. When the total of Ti, Zr, and Hf is less than 45 atomic % or exceeds 55 atomic %, the martensitic transformation required for the shape memory alloy does not occur. When each of Ti, Zr, and Hf is less than at least 10 atomic %, the characteristics as a high-entropy alloy are not exhibited. More preferably, the total of Ti, Zr, and Hf is 48 atomic % or more and 52 atomic % or less, and each of Ti, Zr, and Hf is at least 14 atomic % or more.

[0013] [5] The high-temperature shape memory alloy of the present invention has a total of Ti (titanium) and Zr (zirconium) of 45 atomic % or more and 55 atomic % or less, the ratio of Ti to Zr being 1:2 or more and 2:1 or less, and the balance consisting of Pd (palladium), Pt (platinum), and Ni (nickel), and inevitable impurities, each of Pd, Pt, and Ni being at least 10 atomic % or more. [6] In the high-temperature shape memory alloy [5] of the present invention, preferably, the ratio of Ti to Zr is 1:1.5 or more and 1.5:1 or less. Next, the actions of the constituent elements in the high-temperature shape memory alloys [5] and [6] of the present invention will be described. When the total of Ti and Zr is less than 45 atomic % or exceeds 55 atomic %, the martensitic transformation required for the shape memory alloy does not occur. More preferably, the total of Ti and Zr is 48 atomic % or more and 52 atomic % or less. When at least one of Pd, Pt, and Ni is less than 10 atomic %, it will not exhibit the characteristics of a high-entropy alloy. More preferably, each of Pd, Pt, and Ni is at least 14 atomic % or more.

[0014] [7] The high-temperature shape memory alloy of the present invention has a total of Ti (titanium), Zr (zirconium), and V (vanadium) of 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and V being at least 10 atomic % or more, and the balance being composed of Pd (palladium), Pt (platinum), and inevitable impurities, and the ratio of Pd to Pt being 1:2 or more and 2:1 or less. [8] In the high-temperature shape memory alloy [7] of the present invention, preferably, the ratio of Ti to Zr is 1:1.5 or more and 1.5:1 or less. Next, the actions of the constituent elements in the high-temperature shape memory alloys [7] and [8] of the present invention will be described. When the total of Ti, Zr, and V is less than 45 atomic % or exceeds 55 atomic %, the martensitic transformation required for a shape memory alloy will not occur. More preferably, the total of Ti, Zr, and V is 48 atomic % or more and 52 atomic % or less. When at least one of Ti, Zr, and V is less than 10 atomic %, it will not exhibit the characteristics of a high-entropy alloy. More preferably, each of Ti, Zr, and V is at least 14 atomic % or more.

[0015] [9] The high-temperature shape memory alloy of the present invention has a total of Ti (titanium) and Zr (zirconium) of 45 atomic % or more and 55 atomic % or less, the ratio of Ti to Zr being 1:2 or more and 2:1 or less, and the balance being composed of Pd (palladium), Ni (nickel), and inevitable impurities, and the ratio of Pd to Ni being 1:2 or more and 2:1 or less. Next, the actions of the constituent elements in the high-temperature shape memory alloy [9] of the present invention will be described. When the total of Ti and Zr is less than 45 atomic % or exceeds 55 atomic %, the martensitic transformation required for a shape memory alloy will not occur. More preferably, the total of Ti and Zr is 48 atomic % or more and 52 atomic % or less. The total of Pd and Ni is the balance of Ti and Zr. When the total of Pd and Ni is less than 45 atomic % or more than 55 atomic %, the martensitic transformation required for the shape memory alloy does not occur. More preferably, the total of Pd and Ni is 48 atomic % or more and 52 atomic % or less.

[0016]

[10] In the high-temperature shape memory alloy of the present invention, the total of (titanium), Zr (zirconium), and Hf (hafnium) is 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and Hf is at least 10 atomic % or more, and the balance consists of Pd (palladium), Pt (platinum), and Ni (nickel), and inevitable impurities. It is a high-temperature shape memory alloy in which each of Pd, Pt, and Ni is at least 10 atomic % or more. Next, the action of the constituent elements in the high-temperature shape memory alloy

[10] of the present invention will be described. When the total of Ti, Zr, and Hf is less than 45 atomic % or more than 55 atomic %, the martensitic transformation required for the shape memory alloy does not occur. When each of Ti, Zr, and Hf is less than at least 10 atomic %, the characteristics as a high-entropy alloy are not exhibited. More preferably, the total of Ti, Zr, and Hf is 48 atomic % or more and 52 atomic % or less, and each of Ti, Zr, and Hf is at least 14 atomic % or more. When the total of Pd, Pt, and Ni is less than 45 atomic % or more than 55 atomic %, the martensitic transformation required for the shape memory alloy does not occur. When each of Pd, Pt, and Ni is less than at least 10 atomic %, the characteristics as a high-entropy alloy are not exhibited. More preferably, the total of Pd, Pt, and Ni is 48 atomic % or more and 52 atomic % or less, and each of Pd, Pt, and Ni is at least 14 atomic % or more.

[0017]

[11] In the high-temperature shape memory alloy [1], [3], [5], [7], [9], or

[10] of the present invention, preferably, among the martensitic transformation temperatures, the martensite finish temperature (Mf) satisfies a temperature range of 350 °C or more and 990 °C or less, and the austenite finish temperature (Af) satisfies a temperature range of 550 °C or more and 1105 °C or less.

[0018]

[12] In the high-temperature shape memory alloy [2], [4], [6], [8], or

[10] of the present invention, preferably, among the martensitic transformation temperatures, the martensite finish temperature (Mf) satisfies a temperature range of 630°C or higher and 990°C or lower, and the austenite finish temperature (Af) satisfies a temperature range of 850°C or higher and 1105°C or lower.

[0019]

[13] In the high-temperature shape memory alloy [1] to

[12] of the present invention, preferably, at a temperature below the martensitic transformation temperature, it may have one or more of B19-type orthorhombic crystal, B19'-type monoclinic crystal, orthorhombic crystal of space group 63, and R-phase of space group 147.

[14] In the high-temperature shape memory alloy [1] to

[12] of the present invention, preferably, it has a B2-type cubic crystal at a temperature above the martensitic transformation temperature.

[15] In the high-temperature shape memory alloy

[12] to

[13] of the present invention, preferably, the martensitic transformation temperature is the midpoint temperature [(Ms + Mf) / 2] between the martensite start temperature (Ms) and the martensite finish temperature (Mf).

[16] In the high-temperature shape memory alloy

[12] to

[13] of the present invention, preferably, the martensitic transformation temperature is the midpoint temperature [(As + Af) / 2] between the austenite start temperature (As) and the austenite finish temperature (Af).

[0020]

[17] A method for manufacturing the high-temperature shape memory alloy [1] to

[12] of the present invention, comprising preparing a melted material containing at least 5 compositional elements of Ti, Zr, Hf, V, Pd, Pt, and Ni that satisfy the composition described in any one of [1] to

[12] , and heat-treating the melted material within a range from a temperature above the martensitic transformation temperature and above the temperature in the B2-type cubic crystal region to a temperature 100°C lower than the temperature at which the liquid phase of the high-temperature shape memory alloy occurs.

[18] In the method for manufacturing a high-temperature shape memory alloy of the present invention

[17] , preferably, in the heat treatment step, the melted material may be heat-treated at a temperature in the range of not less than the martensite transformation temperature and not more than 1300 °C for a time of not less than 15 minutes and not more than 24 hours.

[19] In the method for manufacturing a high-temperature shape memory alloy of the present invention

[17] or

[18] , preferably, the melted material may have a substantially uniform composition ratio of at least five compositional elements among Ti, Zr, Hf, V, Pd, Pt, and Ni that satisfy the composition described in any one of [1] to

[12] in a range larger than the crystal grains.

[0021]

[20] The actuator of the present invention is a high-temperature shape memory alloy actuator using a high-temperature shape memory alloy, and the high-temperature shape memory alloy is the high-temperature shape memory alloy described in any one of [1] to

[16] .

[21] The engine of the present invention is an engine provided with an actuator, and the actuator is the high-temperature shape memory alloy actuator described in

[20] .

[22] In the engine

[21] of the present invention, preferably, the engine may be selected from the group consisting of a jet engine, an automobile engine, a marine engine, and an aircraft engine.

Advantages of the Invention

[0022] The high-temperature shape memory alloy of the present invention is composed of specific elements that satisfy the alloy compositions of [1], [3], [5], [7], [9], or

[10] , so that among the martensite transformation temperatures, the martensite finish temperature (Mf) satisfies the temperature range of 350 °C or higher and 990 °C or lower, and the austenite finish temperature (Af) satisfies the temperature range of 550 °C or higher and 1105 °C or lower, and a shape memory alloy that exhibits shape recovery at a high temperature (for example, exceeding 350 °C) can be provided. The high-temperature shape memory alloy of the present invention is composed of specific elements satisfying the alloy compositions of [2], [4], [6], [8], or

[10] . As a result, among the martensitic transformation temperatures, the martensite finish temperature (Mf) satisfies the temperature range of 630°C or higher and 990°C or lower, and the austenite finish temperature (Af) satisfies the temperature range of 850°C or higher and 1105°C or lower, thus providing a shape memory alloy capable of exhibiting shape recovery at high temperatures.

[0023] According to the manufacturing method of the high-temperature shape memory alloy of the present invention, by melting a raw material composed of the above-mentioned specific elements and having a specific composition, and performing heat treatment within the range from the temperature of the B2-type cubic crystal region to a temperature 100°C lower than the temperature at which the liquid phase of the shape memory alloy is generated, a shape memory alloy capable of exhibiting shape recovery at high temperatures can be provided.

Embodiments for Carrying Out the Invention

[0024] <Alloy Composition of High-Temperature Shape Memory Alloy> The inventors of the present application focused on TiPd compounds and TiPt compounds and conducted intensive research. According to the binary phase diagram of Ti (titanium) and Pd (palladium), it can be confirmed that TiPd compounds stably exist in the composition range where the ratio of Pd is 45 atomic% or more and 55 atomic% or less, and it can be seen that the preferred composition range of Pd is 45 to 55 atomic%. Similarly, according to the binary phase diagram of Ti and Pt (platinum), it can be confirmed that TiPt compounds stably exist in the composition range where the ratio of Pt is 48 atomic% or more and 52 atomic% or less.

[0025] Furthermore, according to Non-Patent Document 1, it is known that martensitic transformation occurs even when 25 atomic% of Pd in TiPd compounds is replaced with Pt, suggesting that TiPd compounds and TiPt compounds are completely solid-soluble.

[0026] In addition, since the martensitic transformation temperature of the TiPt compound is as high as around 1000°C, in order to maintain a high martensitic transformation temperature as a high-temperature shape memory alloy, for the TiPdPt compound in which the TiPd compound and the TiPt compound are completely solid-solved, Pt is required to be 5 atomic % or more. On the other hand, according to Non-Patent Document 1, it has been shown that when 40 atomic % or more of Pt is added, plastic strain is introduced and complete recovery becomes difficult, and it should not exceed 40 atomic %.

[0027] On the other hand, Ni (nickel), which is an additive element typified by Patent Document 5, also forms a compound with Ti to produce TiNi. The crystal structure of TiNi shows a B2 structure in the high-temperature stable austenite phase, similar to TiPd and TiPt. This fact indicates the possibility that Pd, Pt, and Ni are completely solid-solved when considering Ti-Pd-Pt, Ti-Pd-Ni, Ti-Pt-Ni, or Ti-Pd-Pt-Ni. That is, when Ti is 50 atomic %, it can be said that it shows a B2 structure if Pd + Pt + Ni is 50 atomic %. Therefore, when Ti is 45 to 55 atomic %, it can be extended that it shows a B2 structure if the remainder is Pd + Pt + Ni and is 55 to 45 atomic %.

[0028] Ti, Zr, Hf, and V are elements in Groups 4 and 5 of the periodic table and have similar properties. When considering Ti-Pd-Pt, Ti-Pd-Ni, Ti-Pt-Ni, or Ti-Pd-Pt-Ni, it is considered that the structure will not change even if Zr, Hf, or V is added to Ti. In fact, Patent Document 3 shows a shape memory alloy in which Zr, Hf, and V are added to Ti in the range of 0.1 to 15 atomic %, Patent Document 4 shows a shape memory alloy in which Zr and Hf are added to Ti in the range of 0.1 to 15 atomic %, Patent Document 5 shows a shape memory alloy in which Zr is added to Ti in the range of 0.1 to 18 atomic %, and Patent Document 6 shows a shape memory alloy in which Zr is added to Ti in the range of 0.1 to 15 atomic %. It can be said that the structure does not change even if Zr, Hf, and V are added to Ti up to about 18 atomic %. In addition, Zr, Hf, and V are elements effective in improving the high-temperature strength of Ti-Pd-Pt, Ti-Pd-Ni, Ti-Pt-Ni, and Ti-Pd-Pt-Ni compounds. On the premise of the above, embodiments of the high-temperature shape memory alloy of the present invention will be described in more detail below.

[0029] Note that the high-temperature shape memory alloy of the present invention is mainly composed of a compound containing two or more of Pd, Pt, and Ni, which is a compound in which the TiPd compound, the TiPt compound, and the TiNi compound are completely solid-solved as described above. It can also be said that two or more of Zr, Hf, and V are added to Ti. Therefore, the high-temperature shape memory alloy of the present invention has a B2-type cubic crystal in the high-temperature stable austenite phase. Below the transformation temperature, it has one or more of a B19-type orthorhombic crystal, a B19'-type monoclinic crystal, an orthorhombic crystal of space group 63, and an R phase of space group 147. Also, if the amount of the main component is at least 50% by mass, preferably 80% by mass or more, it can function as a high-temperature shape memory alloy.

[0030] <Properties of High-Temperature Shape Memory Alloy> The high-temperature shape memory alloy of the present invention preferably exhibits a martensite transformation temperature (martensite transformation end temperature Mf) in the range of 350°C or higher and 840°C or lower and a martensite transformation temperature (austenite end temperature Af) in the temperature range of 550°C or higher and 1105°C or lower. Thereby, shape recovery can be exhibited in the temperature range of 350°C to 1105°C.

[0031] <Manufacturing Method of High-Temperature Shape Memory Alloy> An embodiment of the manufacturing process of the high-temperature shape memory alloy of the present invention will be described below. The high-temperature shape memory alloy of the present invention contains Ti, Zr, Hf, V, Pd, Pt, Ni, and inevitable impurities, and the total is 100 atomic%. A melting material with a predetermined composition is heat-treated (also called solution treatment) within a range from a temperature in the B2-type cubic crystal region above the martensite transformation temperature to a temperature 100°C lower than the temperature at which the liquid phase of the high-temperature shape memory alloy is generated.

[0032] The martensitic transformation temperature varies depending on the alloy composition. However, since the high-temperature shape memory alloy of the present invention is composed of high-melting-point elements, it is desirable to perform heat treatment at the temperature in the B2-type cubic crystal region, which is the austenite phase, so that sufficient diffusion and homogenization can be achieved. Also, although the B2-type cubic crystal region extends up to the melting point, heat treatment near the melting point may cause the regular state of the crystal to be lost. Therefore, the solution treatment temperature is set to be below the temperature at which the liquid phase of the alloy occurs by 100 °C as the upper limit.

[0033] The heat treatment varies depending on the alloy composition as described above. Exemplarily, the heat treatment is performed on the melted material in the temperature range of 1100 °C or higher and 1300 °C or lower for 15 minutes or longer and 24 hours or shorter. The heat treatment atmosphere is preferably an inert atmosphere such as nitrogen or a noble gas (argon, etc.).

[0034] Also, the melted material having the above composition is manufactured by adopting various melting methods used for melting general Ti materials. Although not particularly limited, exemplary melting methods include an arc melting method, an electron beam melting method, and a high-frequency melting method. Needless to say, the composition of the melted material is appropriately selected so as to satisfy the composition of the high-temperature shape memory alloy described above.

[0035] By the above manufacturing method, the high-temperature shape memory alloy of the present invention, which is excellent in work amount and repeatability at high temperatures, can be manufactured. The high-temperature shape memory alloy of the present invention is used for an actuator. Since the high-temperature shape memory alloy of the present invention exhibits shape recovery at a high temperature exceeding 250 °C and is particularly excellent in its work amount and repeatability at high temperatures, such an actuator is suitable for high-temperature engines such as jet engines, automobile engines, ship engines, and aircraft engines.

Examples

[0036] [From Example 1 to Example 9 and from Comparative Example 1 to Comparative Example 6] Examples 1 to 9 and Comparative Examples 1 to 6 produced alloys to meet the compositions shown in Table 1 and evaluated their martensitic transformation temperatures. Table 1 is a list of the alloy compositions (atomic %) of Examples 1 to 9 and Comparative Examples 1 to 6. Here, the alloy compositions of Comparative Example 1 and Comparative Example 2 are substantially equal to those disclosed in Non-Patent Document 2.

[0037] Specifically, seven types of Ti metal (purity 99.5%), Zr metal (purity 99.5%), Hf metal (purity 99.5%), V metal (purity 99.5%), Pd metal (purity 99.99%), Pt metal (purity 99.99%), and Ni metal (purity 99.9%) as shown in Table 1 were prepared. Then, four to six of the above seven types of elements were weighed to obtain the alloy compositions (atomic %) of Examples 1 to 9 and Comparative Examples 1 to 6, and mixed as fine powders so as to have a substantially uniform composition ratio in a range larger than the crystal grains, and melted by arc melting under vacuum to produce 20 g button-shaped alloys, respectively. Next, the melted alloys (melted materials) were placed in a silica tube filled with argon gas, heat-treated at 1000 °C for 3 hours, and water-cooled.

[0038]

Table 1

[0039] When the composition of each obtained alloy was measured by energy dispersive X-ray spectroscopy (EDS), although there were slight errors in the values after the decimal point, it was substantially the same as the designed composition in Table 1. From this, it was confirmed that an alloy satisfying the designed composition can be obtained by implementing the production method of the present invention. Further, when X-ray diffraction measurements were performed on each obtained alloy at room temperature (25 °C) and above the transformation temperature, the XRD pattern at room temperature was identified as one or more of orthorhombic B19 type, monoclinic B19' type, orthorhombic space group No. 63, and R phase of space group 147, and the XRD pattern above the transformation temperature was identified as cubic B2 type.

[0040] Each alloy was cut into specimens having a diameter of 4 mm and a thickness of 1 mm, and differential thermal analysis was performed using a differential scanning calorimeter (DSC, SETRAM) to measure the martensitic transformation temperature. The measurement conditions were heating and cooling rates of 10 °C per minute in the atmosphere. The results are shown in Table 2. Table 2 is a list of the transformation temperatures (°C) of the alloys of Examples 1 to 9 and Comparative Examples 1 to 6.

[0041]

Table 2

[0042] In Table 2, As, Af, Ms, and Mf are the austenite transformation start temperature, austenite transformation end temperature, martensite transformation start temperature, and martensite transformation end temperature, respectively. Since the alloys of Comparative Examples 4 to 9 did not show a clear transformation temperature in the DSC measurement, the transformation temperature is considered to be below room temperature. The alloys of Examples 1 to 6 showed higher transformation temperatures with Mf of 630 °C or higher and Af up to 1105 °C as compared with the alloys of Comparative Examples 1 to 6. The alloys of Examples 7 to 9 showed transformation temperatures as high as those of the alloys of Comparative Examples 1 and 2, with Mf of 360 °C or higher and Af up to 1105 °C. Comparative Examples 1 and 2 are those shown in Non-Patent Document 2, and among the alloys of Comparative Examples 1 to 6, they show high transformation temperatures, exhibit shape recovery at temperatures above 250 °C, and are excellent in the work amount and repetition characteristics at that high temperature.

[0043] Next, the alloy compositions of the examples and comparative examples shown in Tables 1 and 2 are classified into the following four types for further details. (1) (Quinary alloy of Ti, Zr, V, Pd, Ni) Example 6 (2) (Quinary alloy of Ti, Zr, Hf, Pd, Pt) Examples 2, 5, 9 (3) (Quinary alloy of Ti, Zr, Pd, Pt, Ni) Examples 1, 8 (4) (Quinary alloy of Ti, Zr, V, Pd, Pt) Example 3 (5) (Hexanary alloy of Ti, Zr, Hf, Pd, Pt, Ni) Example 4 (6) (Quaternary alloy of Ti, Zr, Pd, and Ni) Example 7

[0044] (1) (Quinary alloy of Ti, Zr, V, Pd, and Ni) This type of alloy composition corresponds to Example 6 shown in Table 1. Since this type of alloy composition does not contain Pt, it is not necessary to use Pt, which is in high demand for catalysts etc., and is preferable in terms of element strategy. In Example 6, As was 835 °C, Af was 935 °C, Ms was 815 °C, and Mf was 715 °C, showing a higher martensitic transformation temperature compared to Comparative Examples 1 and 2.

[0045] (2) (Quinary alloy of Ti, Zr, Hf, Pd, and Pt) This type of alloy composition corresponds to Examples 2, 5, and 9 shown in Table 1. In Example 2, As was 1055 °C, Af was 1105 °C, Ms was 980 °C, and Mf was 840 °C, showing a higher martensitic transformation temperature compared to Comparative Examples 1 and 2. Also, Example 2 showed the highest martensitic transformation temperature among Examples 1 - 6. In Example 5, As was 995 °C, Af was 1100 °C, Ms was 1045 °C, and Mf was 990 °C, showing a higher martensitic transformation temperature compared to Comparative Examples 1 and 2. In Example 9, As was 640 °C, Af was 770 °C, Ms was 640 °C, and Mf was 510 °C, showing a martensitic transformation temperature similar to that of Comparative Examples 1 and 2.

[0046] (3) (Quinary alloy of Ti, Zr, Pd, Pt, and Ni) This type of alloy composition corresponds to Examples 1, 8, Comparative Examples 4, and 5 shown in Table 1. In Example 1, As was 910 °C, Af was 1010 °C, Ms was 805 °C, and Mf was 675 °C, showing a higher martensitic transformation temperature compared to Comparative Examples 1 and 2. In Example 8, As was 690 °C, Af was 815 °C, Ms was 702 °C, and Mf was 573 °C, showing a martensitic transformation temperature similar to that of Comparative Examples 1 and 2.

[0047] (4) (Quinary alloy of Ti, Zr, V, Pd, and Pt) This type of alloy composition corresponds to Example 3 shown in Table 1. Example 3 showed a higher martensitic transformation temperature of As at 835 °C, Af at 935 °C, Ms at 815 °C, and Mf at 715 °C compared to Comparative Examples 1 and 2.

[0048] (5) (Hexanary alloy of Ti, Zr, Hf, Pd, Pt, and Ni) This type of alloy composition corresponds to Example 4 shown in Table 1. Example 4 showed a higher martensitic transformation temperature of As at 845 °C, Af at 910 °C, Ms at 835 °C, and Mf at 735 °C compared to Comparative Examples 1 and 2.

[0049] (6) (Quaternary alloy of Ti, Zr, Pd, and Ni) This type of alloy composition corresponds to Example 7 shown in Table 1. Example 7 showed a martensitic transformation temperature of As at 713 °C, Af at 824 °C, Ms at 706 °C, and Mf at 590 °C, which was as high as that of Comparative Examples 1 and 2.

[0050] From the above, the alloy that satisfies the composition of the present invention is a high-temperature shape memory alloy and undergoes martensitic transformation at a high temperature comparable to or higher than that of Comparative Examples 1 and 2.

Industrial Applicability

[0051] The high-temperature shape memory alloy of the present invention is a material that causes shape recovery by utilizing martensitic transformation occurring at a high temperature, and can be used for actuators in high-temperature parts such as automobiles and jet engines. In addition to these, it can also be used for actuators operating in the temperature range of 350 °C or higher and 1100 °C or lower, flow rate and pressure control units for high-temperature fluids, etc.

Claims

1. A high-temperature shape memory alloy in which the total of Ti (titanium), Zr (zirconium), and V (vanadium) is 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and V is 10 atomic % or more, the balance consists of Pd (palladium), Ni (nickel), and inevitable impurities, and the ratio of Pd to Ni is 1:2 or more and 2:1 or less.

2. The high-temperature shape memory alloy according to Claim 1, wherein the ratio of Pd to Ni is 1:1.5 or more and 1.5:1 or less.

3. A high-temperature shape memory alloy in which the total of Ti (titanium), Zr (zirconium), and Hf (hafnium) is 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and Hf is 10 atomic % or more, the balance consists of Pd (palladium), Pt (platinum), and inevitable impurities, and the ratio of Pd to Pt is 1:2 or more and 2:1 or less.

4. The total of Ti, Zr, and Hf is 45 atomic % or more and 55 atomic % or less, and each of Ti, Zr, and Hf is 10 atomic % or more, Pd is 15 atomic % or more and 20 atomic % or less, and the balance consists of Pt and inevitable impurities. The high-temperature shape memory alloy according to Claim 3.

5. A high-temperature shape memory alloy in which the total of Ti (titanium) and Zr (zirconium) is 45 atomic % or more and 55 atomic % or less, the ratio of Ti to Zr is 1:2 or more and 2:1 or less, the balance consists of Pd (palladium), Pt (platinum), Ni (nickel), and inevitable impurities, and each of Pd, Pt, and Ni is 10 atomic % or more.

6. The high-temperature shape memory alloy according to Claim 5, wherein the ratio of Ti to Zr is 1:1.5 or more and 1.5:1 or less.

7. A high-temperature shape memory alloy in which the total of Ti (titanium), Zr (zirconium), and V (vanadium) is 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and V is 10 atomic % or more, the balance consists of Pd (palladium), Pt (platinum), and inevitable impurities, and the ratio of Pd to Pt is 1:2 or more and 2:1 or less.

8. The high-temperature shape memory alloy according to Claim 7, wherein the ratio of Pd to Pt is 1:1.5 or more and 1.5:1 or less.

9. A high-temperature shape memory alloy in which the total of Ti (titanium) and Zr (zirconium) is 45 atomic % or more and 55 atomic % or less, the ratio of Ti to Zr is 1:2 or more and 2:1 or less, the balance consists of Pd (palladium), Ni (nickel), and inevitable impurities, and the ratio of Pd to Ni is 1:2 or more and 2:1 or less.

10. A high-temperature shape memory alloy in which the total of Ti (titanium), Zr (zirconium), and Hf (hafnium) is 45 atomic % or more and 55 atomic % or less, each of Ti, Zr, and Hf is 10 atomic % or more, and the balance consists of Pd (palladium), Pt (platinum), Ni (nickel), and inevitable impurities, A high-temperature shape memory alloy in which each of Pd, Pt, and Ni is 10 atomic % or more.

11. The high-temperature shape memory alloy according to any one of claims 1, 3, 5, 7, 9, or 10, wherein among the martensitic transformation temperatures, the martensite finish temperature (Mf) satisfies a temperature range of 350°C or more and 990°C or less, and the austenite finish temperature (Af) satisfies a temperature range of 550°C or more and 1105°C or less.

12. The high-temperature shape memory alloy according to any one of claims 2, 4, 6, 8, or 10, wherein among the martensitic transformation temperatures, the martensite finish temperature (Mf) satisfies a temperature range of 630°C or more and 990°C or less, and the austenite finish temperature (Af) satisfies a temperature range of 850°C or more and 1105°C or less.

13. The high-temperature shape memory alloy according to any one of claims 1 to 12, having one or more of B19-type orthorhombic crystal, B19'-type monoclinic crystal, orthorhombic crystal of space group 63, and R phase of space group 147 at a temperature below the martensitic transformation temperature.

14. The high-temperature shape memory alloy according to any one of claims 1 to 12, having a B2-type cubic crystal at a temperature above the martensitic transformation temperature.

15. The high-temperature shape memory alloy according to claim 13 or 14, wherein the martensitic transformation temperature is the midpoint temperature [(Ms + Mf) / 2] between the martensite start temperature (Ms) and the martensite finish temperature (Mf).

16. The high-temperature shape memory alloy according to claim 13 or 14, wherein the martensitic transformation temperature is the midpoint temperature [(As + Af) / 2] between the austenite start temperature (As) and the austenite finish temperature (Af).

17. A method for manufacturing the high-temperature shape memory alloy according to any one of claims 1 to 8, Prepare a melted material containing five compositional elements selected from Ti, Zr, Hf, V, Pd, Pt, and Ni that satisfy the composition according to any one of claims 1 to 8, A method including a step of heat-treating the melted material within a range from a temperature equal to or higher than the martensitic transformation temperature and equal to or higher than the temperature in the B2-type cubic crystal region to a temperature lower by 100 °C than the temperature at which the liquid phase of the high-temperature shape memory alloy is formed.

18. The method according to claim 17, wherein the step of heat-treating is to heat-treat the melted material within a temperature range of equal to or higher than the martensitic transformation temperature and equal to or lower than 1300 °C for a time of equal to or longer than 15 minutes and equal to or shorter than 24 hours.

19. The melted material according to claim 17 or 18 has five compositional elements selected from Ti, Zr, Hf, V, Pd, Pt, and Ni that satisfy the composition according to any one of claims 1 to 8 and has a substantially uniform composition ratio in a range larger than the crystal grains.

20. A method for manufacturing a high-temperature shape memory alloy according to claim 9, Prepare a melted material containing four compositional elements of Ti, Zr, Pd, and Ni that satisfy the composition according to claim 9, A method including a step of heat-treating the melted material within a range from a temperature equal to or higher than the martensitic transformation temperature and equal to or higher than the temperature in the B2-type cubic crystal region to a temperature lower by 100 °C than the temperature at which the liquid phase of the high-temperature shape memory alloy is formed.

21. The method according to claim 20, wherein the step of heat-treating is to heat-treat the melted material within a temperature range of equal to or higher than the martensitic transformation temperature and equal to or lower than 1300 °C for a time of equal to or longer than 15 minutes and equal to or shorter than 24 hours.

22. The melted material according to claim 20 or 21 has four compositional elements of Ti, Zr, Pd, and Ni that satisfy the composition according to claim 9 and has a substantially uniform composition ratio in a range larger than the crystal grains.

23. A method for manufacturing a high-temperature shape memory alloy according to claim 10, Prepare a melted material containing six compositional elements of Ti, Zr, Hf, Pd, Pt, and Ni that satisfy the composition according to claim 10, A method including a step of heat-treating the melted material within a range from a temperature equal to or higher than the martensitic transformation temperature and equal to or higher than the temperature in the B2-type cubic crystal region to a temperature lower by 100 °C than the temperature at which the liquid phase of the high-temperature shape memory alloy is formed.

24. The method according to claim 23, wherein the step of heat-treating is to heat-treat the melted material within a temperature range of equal to or higher than the martensitic transformation temperature and equal to or lower than 1300 °C for a time of equal to or longer than 15 minutes and equal to or shorter than 24 hours.

25. The melting material is the method according to claim 23 or 24, which has six compositional elements of Ti, Zr, Hf, Pd, Pt, and Ni satisfying the composition described in claim 10 and has a substantially uniform composition ratio in a range larger than the crystal grains.

26. A high-temperature shape memory alloy actuator using a high-temperature shape memory alloy, wherein the high-temperature shape memory alloy is the high-temperature shape memory alloy according to any one of claims 1 to 16.

27. An engine equipped with an actuator, wherein the actuator is the high-temperature shape memory alloy actuator according to claim 26.

28. The engine according to claim 27, wherein the engine is selected from the group consisting of a jet engine, an automobile engine, a marine engine, and an aircraft engine.

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