Ti—Ni-based alloy; wire, electrically conductive actuator, and temperature sensor, each using this alloy; and method of producing a Ti—Ni-based alloy

1. A Ti—Ni-based alloy, which has a torsion angle for Interface I, which is a junction plane between habit plane variants of a martensitic phase, of less than 1.00°,

wherein the Ti—Ni-based alloy comprises 25.0 to 35.0 atom % of Ni, 0.0 to 10.0 atom % of Hf, and 15.0 to 25.0 atom % of Cu, with a balance being Ti and unavoidable impurities, in which a content of each unavoidable impurity is 0.1 atom % or less, and wherein the Ti—Ni-based alloy has a recrystallized structure, and is a Ti—Ni-based shape memory alloy or a Ti—Ni-based superelastic alloy,

wherein a crystal structure of the martensitic phase is a single phase of B19′ or B19, or is a mixed phase in which the B19′ phase or the B19 phase co-exists simultaneously with another phase, and

wherein the torsion angle is determined by X-ray diffraction measurement under conditions of CuKα as an X-ray source, a tube voltage of 45 kV, a tube current of 40 mA, and a measurement range of 15° to 120°.

2. The Ti—Ni-based alloy according to claim 1 , in which a transformation temperature after 10 cycles in a thermal cycle test is lowered by 1.0° C. or less, and

the thermal cycle test is performed by Differential Scanning Calorimeter under conditions of a temperature rising or lowering speed of 10° C./min, α-Al 2 O 3 as a reference sample, and a temperature range of −130° C. to 250° C.

3. A wire, which is composed of the Ti—Ni-based alloy according to claim 1 .

4. An electrically conductive actuator, in which the wire according to claim 3 is applied.

5. A temperature sensor, in which the wire according to claim 3 is applied.

6. A method of producing the Ti—Ni-based alloy according to claim 1 , with the method comprising: a step of melting the Ti—Ni-based alloy having an alloy composition as defined in claim 1 , and casting the thus-molten alloy at a cooling speed of 10° C./second or higher; and a step of homogenization treatment,

wherein:

the melting is vacuum arc melting, vacuum dielectric melting, plasma melting, or electron beam melting,

the casting is done using a mold with a thermal conductivity of 12 W/(m·K) or higher, and

the homogenization treatment is carried out at a temperature of 800° C. or higher for one hour or longer.

7. A method of producing the Ti—Ni-based alloy according to claim 1 , with the method comprising the following Steps (a) to (d):

Step (a): a step of melting the Ti—Ni-based alloy having an alloy composition as defined in claim 1 , and casting the thus-molten alloy at a cooling speed of 10° C./second or higher;

Step (b): a step of hot working the resultant alloy at a temperature higher than a recrystallization temperature;

Step (c): a step of performing intermediate annealing, and cold working at a cumulative working ratio of 15% or higher; and

Step (d): a step of forming a desired shape, by imparting a shape memory effect, and imparting a shape memory effect at a temperature at which a desired shape memory effect is obtained when the resultant alloy is re-heated to a temperature higher than or equal to a reverse martensitic transformation finish temperature (A f temperature),

wherein:

the melting of Step (a) is vacuum arc melting, vacuum dielectric melting, plasma melting, or electron beam melting, and

the casting of Step (a) is done using a mold with a thermal conductivity of 12 W/(m·K) or higher.

8. A Ti—Ni-based alloy, which has a torsion angle for Interface I, which is a junction plane between habit plane variants of a martensitic phase, of less than 1.00°,

wherein the Ti—Ni-based alloy comprises 25.0 to 35.0 atom % of Ni, 3.0 to 10.0 atom % of Hf, and 15.0 to 25.0 atom % of Cu, with a balance being Ti and unavoidable impurities, in which a content of each unavoidable impurity is 0.1 atom % or less, and wherein the Ti—Ni-based alloy has a recrystallized structure, and is a Ti—Ni-based shape memory alloy or a Ti—Ni-based superelastic alloy,

wherein a crystal structure of the martensitic phase is a mixed phase in which a B19′ phase co-exists simultaneously with another phase, and

wherein the torsion angle is determined by X-ray diffraction measurement under conditions of CuKα as an X-ray source, a tube voltage of 45 kV, a tube current of 40 mA, and a measurement range of 15° to 120°.

9. The Ti—Ni-based alloy according to claim 1 , in which the crystal structure of the martensitic phase is a mixed phase having the B19′ phase and a Cm structure, or a mixed phase having the B19′ phase and the B19 phase.