JP5564827B2 - Thermoelectric material manufacturing method and thermoelectric material - Google Patents

Description

  The present invention relates to a thermoelectric material.

  2. Description of the Related Art Conventionally, a technique for manufacturing a thermoelectric material including rhombohedral crystals, such as a BiTe-based thermoelectric material, by plastic working such as ECAP (Equal Channel Angular Pressing) is known. For example, Patent Document 1 discloses that the extrusion process is performed a plurality of times by ECAP, and that the c-planes of the crystals are aligned in the shear direction by the extrusion process. Further, Non-Patent Document 1 discloses that when extrusion processing is performed a plurality of times so as not to cause shearing in the reverse direction due to ECAP, distortion in a cubic unit increases with the number of extrusion processing.

JP 2003-342613 A

Yoshiharu Hotta, Atsushi Furukawa, Terence G. Langdon, Atsushi Nemoto: “Equal-Channel Angular Pressing (ECAP) as a New Organization Control Method”, Materia Vol. 37, No. 9, 1998, p. 767-774

In the conventional technique, the orientation orientation of the c-plane cannot be accurately controlled by ECAP.
That is, in the prior art, it is assumed that by repeating ECAP, the thermoelectric material is given orientation so as to have the same orientation as the shear direction specified from the shape of the mold (Patent Literature). 1) Or it was assumed that the orientation was given so that the orientation orientation according to the strain in the cubic unit was obtained by repeating ECAP (Non-patent Document 1). However, when a thermoelectric material is manufactured by actually repeating ECAP, the actual orientation direction is different from the shear direction fixedly determined from the shape of the mold, and the theoretical orientation according to the strain in the cubic unit. It turned out to be different from the direction.

  The present invention has been made in view of the above problems, and an object of the present invention is to manufacture a thermoelectric material by accurately controlling the orientation orientation of the c-plane by ECAP.

  In order to solve the above problems, in the present invention, in the process of performing extrusion processing a plurality of times by the ECAP method, the posture of the material when the material is recharged into the pressure passage (hereinafter also simply referred to as the recharging posture). Thus, a thermoelectric material in which the c-plane of the rhombohedral crystal is oriented in a specific convergence direction that is associated with each other is manufactured. That is, the inventor of the present application, in the thermoelectric material manufactured by performing the extrusion process a plurality of times by the ECAP method, the orientation direction depends not only on the geometric shape of the mold but also on the re-injection posture, and It was revealed that the orientation orientation converges to a specific orientation by the extrusion process. Therefore, in the present invention, it is considered that a specific convergence direction is associated with the recharging posture in advance, and a thermoelectric material in which the c-plane is oriented in the specific convergence direction is manufactured according to the recharging posture. That is, since the orientation in which the c-plane is actually oriented is accurately specified in advance as a specific convergence orientation, according to the present invention, the thermoelectric material is manufactured by accurately controlling the orientation orientation of the c-plane by ECAP. Can do.

  Here, the material should just be a composition used as the thermoelectric material containing a rhombohedral crystal. That is, any thermoelectric material having a crystal structure that can align the orientation of the c-plane of the crystal in the material by extruding while applying a shearing force by the ECAP method may be used.

  The mold may be a mold that can perform extrusion processing by the ECAP method. That is, when the pressure shaft and the extrusion shaft are different (not on one axis), a shearing force is applied to the material when being pushed out from the pressure passage around the pressure shaft to the extrusion passage around the extrusion shaft. I can do it. Further, the shape of the pressurizing passage in the cross section perpendicular to the pressurizing axis and the shape of the extrusion passage in the cross section perpendicular to the extruding shaft are the opening shapes of the respective passages in the cross section. Thus, the extrusion process by the ECAP method is realized.

  In the present invention, due to the fact that the shape of the pressure passage in the cross section perpendicular to the pressure axis and the shape of the extrusion passage in the cross section perpendicular to the extrusion axis are the same, the material is rotated around the extrusion axis, In addition, it is possible to determine the re-injection posture by reversing the leading portion when pushed out and perform re-injection. That is, when the material is reintroduced into the pressurizing passage, one of a plurality of selectable reintroduction postures is selected and reintroduced. Therefore, in the present invention, a specific convergence direction is associated with the re-input posture.

  The specific convergence direction is a specific angle indicating the orientation direction of the c-plane of the rhombohedral crystal in the material, and may be defined in a reference coordinate system. For example, a configuration in which an orthogonal coordinate system including an extrusion axis direction in a mold is defined as a reference coordinate system, and an angle from the extrusion axis is defined in the orthogonal coordinate system in a process in which a material is extruded in an extrusion passage. It can be adopted. Moreover, the specific convergence direction should just show the orientation direction of c surface converged by a realistic frequency when an extrusion process is repeated. That is, the orientation does not monotonously increase or monotonously decrease (the angle converges by the infinite number of extrusion processes) as the number of extrusion processes increases, but is repeated by a finite number of times (for example, 2 times or 3 times). When the azimuth converges at a certain angle, the azimuth may be a specific convergence azimuth. It should be noted that one specific convergence direction corresponding to the re-filling posture may be determined in advance, and a different value is set based on the symmetry of the re-filling posture.

  Furthermore, the state where the c-plane of the rhombohedral crystal is oriented may be a state indicating that the index indicating whether the orientation of the c-plane is aligned in the thermoelectric material is equal to or greater than a certain reference. . For example, in a crystal occupying an area of X% of a cross section obtained by cutting a thermoelectric material in a direction parallel to a specific direction, the orientation direction of the c plane with respect to the reference direction is included in the specific angle range. It is possible to adopt a configuration in which the orientation value is the mode value of the orientation direction. Here, X or a specific angle range may be set so as to function as an index indicating the orientation of the c-plane. For example, X = 80 and a specific angle range of about 10 ° to 25 ° can be adopted. It is.

  Furthermore, as an example of a configuration in which the c-plane is oriented in a specific convergence direction and a thermoelectric material is manufactured, a configuration is adopted in which the c-plane is oriented in a convergence direction different from the theoretical orientation direction when the extrusion process is performed a plurality of times. May be. For example, the theoretical orientation azimuth f (N) when the extrusion process is executed a total of N times (N is an integer) from the intersection angle between the pressure axis and the extrusion axis is specified, and N is 2 or more by the extrusion process. In addition, it is possible to adopt a configuration for manufacturing a thermoelectric material whose convergence direction is any one of f (1) to f (N-1).

  That is, when the orientation orientation is theoretically specified from the shape of the mold, even if the Nth theoretical orientation orientation is defined as f (N), the actual orientation orientation is less than N 1 to (N−1). It is considered that it is defined by the theoretical orientation orientation of the second time. Then, the thermoelectric material is manufactured with any one of f (1) to f (N-1) as the convergence direction. For example, in the extrusion process in which N is 3 or more, a configuration in which f (1) or f (2) is a convergence direction can be employed.

  Furthermore, as a more specific configuration, the direction in the direction parallel to the extrusion axis of the material in the extrusion passage and the angle around the extrusion axis are the same in the (N-1) th and Nth extrusion processes (so-called Route A: see Non-Patent Document 1), a thermoelectric material in which the convergence orientation of the c-plane of the rhombohedral crystal is f (2) may be manufactured by an extrusion process in which N is 3 or more. In other words, in the case of the so-called route A, even if N is extruded three times or more, the convergence direction does not change monotonously and is considered to converge to the theoretical orientation direction when the extrusion process is performed twice.

  In addition, in the (N-1) -th and N-th extrusion processes, when the portions located in the forward direction of the extrusion direction match, the directions in the direction parallel to the extrusion axis are the same, and the (N-1) -th time In the N-th extrusion process, when the portions located in the front in the extrusion direction do not match, the direction in the direction parallel to the extrusion axis is reversed. Further, in the (N-1) -th and N-th extrusion processes, if the rotation angles around the extrusion shaft of the reference portion in the material viewed from the extrusion shaft are compared, the (N-1) -th and N-th extrusions An angle around the extrusion axis in the process can be defined.

  Also, the direction of the material in the extrusion passage in the direction parallel to the extrusion axis is opposite in the (N-1) -th and N-th extrusion processes, and the angle around the extrusion axis of the material in the extrusion passage is (N-1). ) When the first and N-th extrusion processes differ by 180 °, a thermoelectric material in which the convergence orientation of the c-plane of the rhombohedral crystal is f (1) may be manufactured by an extrusion process in which N is 2 or more. That is, in the case of this route, even if N is extruded twice or more, the convergence direction does not change monotonously, and is considered to converge to the theoretical orientation direction when the extrusion process is performed once.

  Furthermore, the direction in the direction parallel to the extrusion axis of the material in the extrusion passage is opposite in the (N-1) -th and N-th extrusion processes, and the angle around the extrusion axis of the material in the extrusion passage is (N-1). ) When the extrusion process is the same in the first and N-th extrusion processes, a thermoelectric material in which the c-plane convergence orientation of the rhombohedral crystal is f (1) is produced by an extrusion process in which N is an odd number, or an extrusion in which N is an even number It is good also as a structure which manufactures the thermoelectric material whose convergence direction of c plane of a rhombohedral crystal is 0 degree by a process.

  In addition, the direction in the direction parallel to the extrusion axis of the material in the extrusion passage is the same in the (N−1) -th and N-th extrusion processes, and the angle around the extrusion axis of the material in the extrusion passage is (N−1). ) When the first and N-th extrusion processes differ by 180 °, a thermoelectric material in which the convergence orientation of the c-plane of the rhombohedral crystal is f (1) is manufactured by an extrusion process with an odd number of N, or an extrusion with an even number of N It is good also as a structure which manufactures the thermoelectric material whose convergence direction of c plane of a rhombohedral crystal is 0 degree by a process.

  Further, in the thermoelectric material manufactured as described above, since the c-plane is aligned in a specific convergence direction, the thermoelectric material is cut so as to be a rectangular parallelepiped having planes parallel and perpendicular to the convergence direction of the c-plane. A thermoelectric element may be manufactured. According to this configuration, a high figure of merit can be used by using a rectangular parallelepiped surface as an electrode. Moreover, if a thermoelectric conversion module is formed by combining the obtained thermoelectric elements, a high-performance thermoelectric conversion module can be manufactured.

It is a flowchart which shows the manufacturing method of a thermoelectric material. It is a schematic diagram which shows an example of a metal mold | die. It is explanatory drawing for demonstrating a re-injection attitude | position. It is a graph which shows the change of the orientation degree with respect to the frequency | count of an extrusion process.

Here, embodiments of the present invention will be described in the following order.
(1) Thermoelectric material manufacturing method:
(2) Theoretical orientation direction and specific convergence direction of the extrusion process:
(3) Example:
(3-1) Route A:
(3-2) Route C ^* :
(4) Other embodiments:

(1) Thermoelectric material manufacturing method:
FIG. 1 is a flowchart showing an embodiment of a method for producing a thermoelectric material. In the present embodiment, first, an element that is a raw material of the BiTe thermoelectric material is weighed and melted to create an ingot (step S100). That is, an ingot of at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se is weighed, and (Bi, Sb) ₂ (Te, Se) The composition is ₃ .

  After weighing, these elements are once melted and cooled by various means, thereby producing an alloy ingot having a desired composition. Next, the ingot of the alloy is rapidly cooled by a roll type liquid quenching method to produce a thin film powder (step S105). That is, an alloy ingot is melted and sprayed onto a rotating roll to form a thin film powder. Of course, the liquid quenching method may be a single roll method or a twin roll method. Further, after melting each weighed element, the step of cooling to ingot may be omitted, and the molten alloy may be liquid quenched.

  When an alloy powder material is prepared, the powder is set in a mold in a chamber (not shown) (step S110). FIG. 2 is a schematic diagram showing an example of a mold for performing an extrusion process by the ECAP method. In this embodiment, the mold 10 is a rectangular parallelepiped, and a rectangular hole 11 a is formed in the surface 11, and a rectangular hole 12 a is formed in the surface 12 adjacent to the surface 11. The hole 11 a is formed from the opening in the surface 11 in a direction perpendicular to the surface 11 and extends to a predetermined position inside the mold 10. The hole 12 a is formed in a direction perpendicular to the surface 12 from the opening in the surface 12, and is connected to the hole 11 a inside the mold 10.

  In the present embodiment, the inner wall formed in the mold 10 by extending the hole 11a constitutes the pressurizing passage 11b, and the inner wall formed in the mold 10 by extending the hole 12a becomes the extrusion passage 12b. An imaginary straight line extending in the same direction as the direction in which the pressurizing passage 11b extends in the center of the pressurizing passage 11b is called a pressurizing shaft, and a virtual line extending in the same direction as the direction in which the extruding passage 12b extends in the center of the extrusion passage 12b. A straight line is called an extrusion shaft. In the present embodiment, the pressure axis and the extrusion axis are orthogonal to each other. In FIG. 2, the pressure axis is indicated as the Z axis, and the extrusion axis is indicated as the X axis. Also, the Y axis is set in a direction perpendicular to the Z axis and the X axis, and the intersection of each axis is set as the origin. The pressing direction of the material in the pressurizing passage 11b is opposite to the direction of the Z axis, and the extruding direction of the material in the extrusion passage 12b is the same as the direction of the X axis.

  That is, the mold 10 can perform an extrusion process in which a material to be pressurized is set and pressurized on the pressure passage 11b side and the material is pushed out through the extrusion passage 12b. Further, the cross section of the pressurizing passage 11b in the direction perpendicular to the pressurizing shaft has the same shape as the hole 11a, the cross section of the pushout passage 12b in the direction perpendicular to the extruding shaft is the same shape as the hole 12a, and the holes 11a and 12a have the same shape. It is. Therefore, it is possible to perform extrusion processing by the ECAP method using the mold 10.

  In step S110, in order to perform the extrusion process by the ECAP method, materials are laminated so as to be aligned in the thickness direction of the thin film. That is, since the c-plane is aligned in the direction parallel to the film thickness direction in the thin film-like powder prepared by the roll quenching method, by laminating so as to align in the thickness direction of the thin film, The deformation resistance is reduced, and the processing pressure in the extrusion process can be reduced.

  When the powder is set in the mold 10, the inside of the chamber is evacuated, and after the evacuation is completed, argon gas is introduced into the chamber (step S115). That is, the atmosphere of the mold 10 is replaced with argon gas. Thereafter, the mold 10 is heated by a heater (not shown) (step S120), and the mold 10 is set to a predetermined set temperature. In the present embodiment, this set temperature is set in a range from a temperature 100 ° C. lower than the melting point of the material to a temperature 20 ° C. lower than the melting point.

  When the mold 10 reaches the set temperature, an extrusion process by the ECAP method is executed by pushing the material in the pressurizing passage 11b with a plunger (not shown) (step S125). That is, the extrusion process is performed at a predetermined extrusion speed while applying a shearing force to the material. According to the extrusion process, a bulk material in which the c-planes of the rhombohedral crystals of the material are aligned can be manufactured. Thereafter, the bulk material is reintroduced into the pressure passage 11b and the extrusion process by the ECAP method is repeated. Thus, a thermoelectric material in which the c-plane is oriented in a specific convergence direction is manufactured.

  In order to repeat the extrusion process by the ECAP method, in this embodiment, the mold 10 is cooled by a cooling mechanism (not shown) (step S130), and the mold 10 is cooled to a temperature at which the material can be taken out. The material 20 is taken out from 10 (step S135). In this embodiment, the number of times of extrusion processing by the ECAP method is determined in advance, and it is determined whether or not the predetermined number of repetitions has been completed (step S140). Re-injects the material into the pressure passage 11b (step S145).

  When the material is reintroduced into the pressurizing passage 11b, the material is adjusted so as to have a predetermined reintroduction posture. When the extrusion process is performed with the mold 10 having the rectangular holes 11a and 12a as in the present embodiment, four types of re-injection postures can be assumed. FIG. 2 schematically shows the material 20 to be extruded through the extrusion passage 12b. In this example, the material 20 is perpendicular to the Z axis in the extrusion passage 12b in the extrusion processing of the powder material (first extrusion processing). In addition, of the surfaces parallel to the X-axis and the Y-axis, the surface located on the upper side (the positive side of the Z-axis) is defined as a reference surface, and the vertexes are indicated as vertices A, B, C, and D.

  The four types of recharging postures can be specified by the reference plane and the vertices A, B, C, and D when the material 20 is recharged into the pressurizing passage 11b. That is, when the material 20 is re-entered into the pressurizing passage 11b, there are two cases where the vertexes located in front of the material 20 are the vertexes A and D and the vertexes B and C. There are two cases where the reference surface is located on the positive side of the X axis and the negative side of the X axis in the material that has been re-entered into the pressurizing passage 11b and reached the extrusion passage 12b. Therefore, four types of re-entry postures can be selected depending on the combination in each case. Of course, the material is distorted by the shearing force in the extrusion process, but here, the direction of the leading vertex and the rotation angle of the reference surface are considered without considering the change in the size of the reference surface. In FIG. 2, the apexes A and D are positioned forward when the material is re-entered into the pressurizing passage 11b, and the reference plane is positioned on the plus side of X when reaching the extrusion passage 12b. An example of the recharging posture is shown as the material 21. Further, the recharging posture like the material 21 is referred to as a route A.

  In step S145, a predetermined recharging posture is selected from the four types of recharging postures, the material is recharged into the pressurizing passage 11b, and step S115 is repeated. That is, the extrusion process by the ECAP method is repeated with a specific re-input posture. On the other hand, when it is determined in step S140 that the predetermined number of repetitions have been completed, the c-plane of the rhombohedral crystal is oriented in a specific convergence direction corresponding to the re-input posture in the extruded material. Therefore, a thermoelectric material in which the c-plane of the rhombohedral crystal is oriented in a specific convergence direction is manufactured.

  Therefore, the thermoelectric material is cut so as to have a plane parallel to and perpendicular to the specific convergence direction, and a rectangular parallelepiped thermoelectric element is manufactured (step S150). According to the above manufacturing process, a thermoelectric element in which the c-plane is aligned in a direction parallel to one of the outer surfaces of the rectangular parallelepiped can be manufactured from the thermoelectric material having the c-plane aligned in a specific convergence direction.

(2) Theoretical orientation direction and specific convergence direction of the extrusion process:
In the present embodiment, the specific convergence direction when the extrusion process is executed N times is as follows. The extrusion process is performed N times (N is a positive value) by the mold 10 whose crossing angle between the pressure axis and the extrusion axis is a specific angle. (Integer) orientation orientation different from the theoretical orientation orientation f (N) when executed. That is, even if the extrusion process by the ECAP method is repeated, the present inventor can orient the c-plane according to the theoretical orientation direction f (N) determined according to the shape of the mold 10 and the number of extrusion processes. It was impossible, and in fact, the orientation direction was found to converge to a specific direction. The present invention determines a specific convergence direction based on this finding.

In the re-injection posture called route A like the material 21 shown in FIG. 2, the theoretical orientation azimuth f (N) when the extrusion process is executed N times is the intersection angle θ between the pressing axis and the extrusion axis in the mold. And f (N) = arctan (tan (θ / 2) / (2N))
It can be expressed as. The theoretical orientation azimuth f (N) is an angle with respect to the X axis when the c-plane rotates counterclockwise about the Y axis in the XYZ axes shown in FIG.

Table 1 shows the theoretical orientation azimuth f (N) when the crossing angles are 90 °, 120 °, and 135 °. As shown in Table 1, the number of extrusion processes at any crossing angle. As the value increases, the theoretical orientation azimuth f (N) decreases. For example, when the crossing angle between the pressure axis and the extrusion axis is 90 ° as in the mold 10 shown in FIG. 2, the theoretical orientation directions f (1), f (2), and f (3) are 26. 6 °, 14.0 °, and 9.5 °, and the angle value decreases with increasing N even after f (4).

  In the route A, the direction of the material in the extrusion passage 12b in the direction parallel to the extrusion axis and the angle around the extrusion axis are the same in the (N-1) th and Nth extrusion processes. 3A and 3B are explanatory views for explaining the posture of the material in the extrusion passage 12b in the (N-1) th extrusion process in the route A, and FIGS. 3C and 3D show the Nth extrusion process in the route A. It is explanatory drawing explaining the attitude | position of the material in the extrusion channel | path 12b in.

  3A and 3C show a state in which the material 20 existing in the extrusion passage 12b is viewed from the tip end side of the X axis in the direction of viewing the ZY plane. 3B and 3D show a state in which the material 20 existing in the extrusion passage 12b is viewed from the front end side of the Y-axis in the direction of viewing the XZ plane. 3A to 3D, the reference plane surrounded by the vertices A, B, C, and D shown in FIG. 2 is indicated by a bold line, and among the vertices, the vertex close to the viewpoint is indicated by a lead line.

  As shown in FIG. 3B, when the material 20 existing in the extrusion passage is extruded with the apex D side as the head in the (N-1) th extrusion process, according to the route A, also in the Nth extrusion process The material 20 existing in the extrusion passage is extruded with the apex D side as the head as shown in FIG. 3D. Accordingly, the direction of the material 20 in the direction parallel to the extrusion axis (X axis) is the same in the (N-1) th and Nth extrusion processes.

  Further, as shown in FIG. 3A, when the material 20 existing in the extrusion passage is extruded with the reference surface on the upper side (the positive side of the Z axis) in the (N-1) th extrusion process, the route According to A, even in the N-th extrusion process, the material 20 existing in the extrusion passage is extruded with the reference surface on the upper side (the positive side of the Z axis) as shown in FIG. 3C. Therefore, the angle around the extrusion axis of the material 20 (the angle with respect to the Z axis when a perpendicular extending from the X axis to the reference plane is rotated around the X axis) is the same in the (N-1) th and Nth extrusion processes. It is.

Further, among the above four types of re-injection postures, a re-injection posture (referred to as route C ^* in this specification) in which the relationship between the direction in which the shear force acts and the orientation direction is the same as that of route A is selected. It is also possible to do. In the route C ^* , the portion located at the head in the (N-1) th extrusion process is arranged on the rear side, and the surface located on the upper side in the (N-1) th extrusion process is placed below Adjust the posture so that it is placed on the side. Conventionally, with respect to the route C ^* , the theoretical orientation azimuth f (N) was thought to decrease gradually as the number N of extrusion treatments increased, as with the route A.

3E and 3F are explanatory diagrams for explaining the posture of the material in the extrusion passage 12b in the N-th extrusion process in the route C ^* . 3E and FIG. 3F show a state in which the material 20 is viewed from the same direction as FIG. 3A and FIG. 3B, and FIG. 3E and FIG. 3F are in the posture shown in FIG. 3A and FIG. It is a figure explaining the Nth extrusion process in the case of performing the extrusion process of the 1st time.

That is, in the (N-1) th extrusion process, when the material 20 existing in the extrusion passage is extruded starting from the apex D side as shown in FIG. 3B, the route C ^* is the Nth extrusion process. As shown to 3F, the material 20 which exists in an extrusion channel | path is extruded by using the vertex C side as the head. In this case, the direction of the material 20 in the direction parallel to the extrusion axis (X axis) is reversed in the (N-1) th and Nth extrusion processes.

  Furthermore, as shown in FIG. 3A, when the material 20 existing in the extrusion passage is extruded in the (N-1) th extrusion process with the reference surface on the upper side (the positive side of the Z axis), As shown in 3E, in the N-th extrusion process, the material 20 present in the extrusion passage is extruded with the reference surface on the lower side (minus side of the Z axis). In this case, the angle around the extrusion axis of the material 20 differs by 180 ° in the (N−1) -th and N-th extrusion processes.

In the extrusion process in the route A and the route C ^* as described above, shear in a direction in which the c-plane is oriented in the X-axis direction with respect to the c-plane of the rhombohedral crystal oriented in the material 20 every time the extrusion process is repeated. Apply force. For this reason, as described above, it has been thought that the orientation orientation gradually decreases as the number of extrusion processes increases. However, even if the extrusion process by the ECAP method is repeated, the actual orientation direction does not decrease according to the number N of extrusion processes, and the actual orientation direction becomes f (1) to f (f) by the extrusion process in which the number N of extrusion processes is 2 or more. N-1) can be produced.

(3) Example:
(3-1) Route A:
Next, a specific convergence direction and characteristics of the thermoelectric material will be described using a BiTe thermoelectric material having a specific composition as an example. In Table 2, by the process shown in FIG. 1, the orientation direction when the material having a composition of Bi _1.9 Sb _0.1 Te _2.7 Se _0.3 is subjected to extrusion treatment by the ECAP method at a setting temperature of 500 ° C. at 0.5 mm / min ( °). In Table 2, the orientation azimuth of the number of extrusion processes N = 1 to 10 is shown for each re-input posture. The orientation direction in Table 2 is measured with an EBSD (Electron Back Scatter Diffraction) device manufactured by TSL, and a cross section obtained by cutting the material 20 in a direction parallel to the XZ plane shown in FIG. Name: specified by analyzing in OIM, version 3.5).

That is, according to the analysis software, the crystal orientation distribution in the cross section can be specified based on the reflection of the irradiated electron beam. In this embodiment, the angle at which the frequency of the orientation distribution is the largest is the orientation direction. The orientation direction is measured by the crossing angle (α shown in FIG. 3B) between the X axis and the c-plane shown in FIG. In this specification, the orientation direction is the rotation with respect to the X axis when the c-plane is rotated counterclockwise around the Y axis when the X-Z plane is viewed from the Y-axis side. It is shown in a coordinate system in which the angle is a positive angle.

  In the material shown in this example, when the extrusion process by the ECAP method is repeated in the route A, the orientation direction converges at 14 ° as shown in Table 2. Therefore, even if the number N of extrusion processes increases, the actual orientation direction converges to the theoretical orientation direction f (2) in the case of two extrusion processes. For this reason, when the thermoelectric material is manufactured by repeating the extrusion process by the ECAP method in the route A, in step S150 shown in FIG. 1 described above, in the coordinate system shown in FIG. And cut in a direction perpendicular to and parallel to the cut surface to obtain a rectangular parallelepiped thermoelectric element. As a result, it is possible to manufacture a thermoelectric element in which the c-planes of rhombohedral crystals in the thermoelectric element are aligned in parallel to a specific surface of the rectangular parallelepiped.

Table 3 shows the measurement results obtained by cutting the thermoelectric material manufactured by re-inputting the material by route A and performing extrusion processing a total of 4 times at different cutting angles (inclination angle with respect to the X axis in the coordinate system shown in FIG. 2). Shows the material properties. That is, the thermoelectric material manufactured by performing extrusion processing a total of four times in the process of re-inputting the material by route A and repeating the extrusion processing is cut at each of the cutting angles shown in Table 3, and is perpendicular and parallel to the cut surface. A rectangular parallelepiped thermoelectric element is manufactured by further cutting in the direction. In Table 4, S is the Seebeck coefficient (μV / K), ρ is the electrical resistivity (× 10 ⁻⁵ Ωcm), κ is the thermal conductivity (W / (K · m)), and Z is the figure of merit (× 10 ^−3). / K). The thermal conductivity κ was measured by a steady method, and the electrical resistivity ρ was measured by a four-terminal method. The Seebeck coefficient S gives a temperature difference of 1 to 2 ° C. at room temperature to both ends of the thermoelectric material in the direction parallel to the energizing direction during ρ measurement and the heat flow direction during κ measurement in a thermoelectric material of 5 mm cubic. It was specified by dividing the electromotive force V generated between both ends by the temperature difference. The figure of merit Z was calculated as Z = S ² / (ρ × κ).

  As shown in Table 3, when the cutting angle is changed every 10 ° from 4 ° to 44 °, the characteristics gradually improve in any of Seebeck coefficient S, electrical resistivity ρ, thermal conductivity κ, and figure of merit. However, the characteristics deteriorate after reaching the best value. In addition, the Seebeck coefficient S is the best value at the cutting angles of 14 ° and 24 °, the electrical resistivity ρ is the best value at the cutting angle of 14 °, and the thermal conductivity κ is the best value at the cutting angles of 4 ° to 24 °. The figure of merit Z is the best value at a cutting angle of 14 °. Therefore, Table 3 confirms that the material characteristics at the cutting angle of 14 ° are the best even when the extrusion process is performed four times.

  In addition, when the number of extrusion processes N is increased, the orientation direction converges to a specific convergence direction, but the degree to which the c-plane of the rhombohedral crystal is oriented to the specific convergence direction (the degree that the c-plane is aligned: Hereinafter, it is considered that the degree of orientation also converges to a specific degree as the number of extrusion processes N increases. The degree of orientation may be an index indicating the degree of orientation of the c-plane in a specific convergence direction, and can be specified based on, for example, the measurement result of the above-described EBSD device. That is, in the EBSD apparatus, the orientation orientation of the c-plane of the rhombohedral crystal at each measurement point can be measured, and the degree of alignment of the c-plane is greater as the frequency distribution of the orientation orientation is steeper, It can be said that the degree of alignment of the c-plane orientation is smaller as the frequency distribution of the orientation is gentler. Therefore, in this embodiment, the frequency of the orientation direction is specified based on the measurement result of the EBSD device, the mode value φ of the orientation direction is specified, and the absolute value of the deviation of the orientation direction from the mode value φ is calculated. Δφ is specified, and the cumulative value of the orientation azimuth in the range of φ to Δφ is specified. Then, Δφ where the cumulative value of the frequency is 80% of all the measurement points is defined as the orientation degree.

  FIG. 4 is a graph showing changes in the degree of orientation with respect to the number N of extrusion treatments. In FIG. 4, the horizontal axis indicates the number of extrusion processes N, the vertical axis indicates the degree of orientation, and the change in the degree of orientation due to the increase in the number of times of extrusion process N for each recharging posture. According to FIG. 4, in the route A, the degree of orientation improves as the number of extrusion processes N increases (the value of the degree of orientation decreases), but the change for each extrusion process gradually decreases. A material having an orientation degree of 20 ° or less in the above definition is a material having good characteristics, and a material having an orientation degree of about 10 ° to 15 ° is a material having extremely good characteristics. Accordingly, the orientation orientation of the c-plane converges with a theoretical orientation orientation of 2 extrusion treatments, but the extrusion treatment is preferably performed 3 times or more, and preferably about 4 to 7 times in total.

(3-2) Route C ^* :
In the material shown in this example, when the extrusion process by the ECAP method is repeated in the route C ^* , the orientation direction converges at 26 ° as shown in Table 2. Therefore, even if the number N of extrusion processes increases, the actual orientation direction converges to the theoretical orientation direction f (1) in the case of the number of extrusion processes 1. For this reason, when the thermoelectric material is manufactured by repeating the extrusion process by the ECAP method at the route C ^* , in the above-described step S150 shown in FIG. 1, 26 ° with respect to the X axis in the coordinate system shown in FIG. Cut in an inclined direction and cut in a direction perpendicular to and parallel to the cut surface to obtain a rectangular parallelepiped thermoelectric element. As a result, it is possible to manufacture a thermoelectric element in which the c-planes of rhombohedral crystals in the thermoelectric element are aligned in parallel to a specific surface of the rectangular parallelepiped.

Table 4 shows different cutting angles (inclination angles with respect to the X axis in the coordinate system shown in FIG. 2 above) of the thermoelectric materials manufactured by re-injecting the material by route C ^* and performing extrusion processing four times in total as described above. It shows the material properties measured after cutting. The measurement method and units are the same as in Table 3.

As shown in Table 4, when the cutting angle is changed every 10 ° from 16 ° to 56 °, the Seebeck coefficient S, the electrical resistivity ρ, and the performance index Z are the best values at the cutting angle of 26 °. Therefore, Table 4 confirms that the material characteristics at the cutting angle of 26 ° are the best even when the extrusion process is performed four times. The tendency of the orientation degree in the route C ^* with respect to the number N of extrusion treatments is the same as the tendency of the orientation degree in the route A. Therefore, the orientation orientation of the c-plane converges with the theoretical orientation orientation of the number of extrusion treatments of 1, but the extrusion treatment is preferably performed a total of 3 times or more, preferably about 4 to 7 times in total.

(4) Other embodiments:
In the present invention, it is only necessary to be able to utilize the fact that the c-plane of the rhombohedral crystal is oriented in a specific convergence orientation associated with the re-injection posture, and when the thermoelectric element is manufactured, the specific convergence orientation The orientation orientation may be adjusted so that a high-performance thermoelectric element can be manufactured by cutting in a different orientation.

For example, in the mold 10, in addition to a re-injection posture (route A and route C ^* ) that applies a shearing force that contributes to inclining the c-plane in a specific direction, the c-plane is set in the opposite direction every time the extrusion process is repeated. It is also possible to select a recharging posture that applies a shearing force that contributes to tilting.

3G and 3H, and FIGS. 3I and 3J show the material 20 viewed from the same direction as in FIGS. 3A and 3B. FIGS. 3G and 3H, FIGS. 3I and 3J It is a figure explaining the extrusion process of the Nth time when the (N-1) th extrusion process is performed with the attitude | position shown to 3A and FIG. 3B. That is, after the extrusion process is performed in the posture shown in FIGS. 3A and 3B in the (N-1) th extrusion process, the material present in the extrusion passage as shown in FIGS. 3G and 3H in the Nth extrusion process. It is possible to perform the extrusion process in a posture in which 20 is the apex B on the opposite side of the apex D and the reference surface is directed upward. In the (N + 1) th extrusion process, the posture again becomes the same as the posture shown in FIGS. 3A and 3B. In this specification, the re-input posture for realizing this posture is referred to as route A ^* . Further, after the extrusion process is performed in the posture shown in FIGS. 3A and 3B in the (N-1) th extrusion process, the material existing in the extrusion passage in the Nth extrusion process as shown in FIGS. 3I and 3J. It is possible to perform the extrusion process in a posture in which 20 is the top on the same side as the vertex D, and the reference surface is directed downward by 180 ° with respect to FIG. 3A. In the (N + 1) th extrusion process, the posture again becomes the same as the posture shown in FIGS. 3A and 3B. In this specification, the re-input posture for realizing this posture is referred to as a route C.

When extrusion processing by the ECAP method is repeated through these routes A ^* or C, as shown in Table 2, the orientation orientation of the c-plane oscillates and does not converge to a specific convergence orientation as the number of extrusion treatments N increases. . Therefore, according to these route A ^* or route C, a desired orientation direction can be selected from either of two kinds of orientation directions. Specifically, when the number of extrusion processes N is an odd number, the orientation direction of the material is the theoretical orientation direction f (1), and when the number of extrusion processes N is an even number, the orientation direction of the material is 0 °. Therefore, when the extrusion process by the ECAP method is performed in the route A ^* or the route C, a thermoelectric material in which the c-plane orientation direction is aligned with either the theoretical orientation direction f (1) or 0 ° can be manufactured. .

Table 5 shows the material properties measured by cutting the thermoelectric material manufactured by performing the extrusion process by the route A ^* an odd number of times (three times) at different cutting angles, and Table 6 shows the extrusion process by the route A ^* by an even number. The material characteristic measured by cutting the thermoelectric material manufactured by performing it 4 times (cutting) at different cutting angles is shown. Table 7 shows the material properties measured by cutting the thermoelectric material manufactured by performing the extrusion process by the route C odd number of times (three times) at different cutting angles, and Table 8 shows the even number of the extrusion process by the route C. The material characteristic measured by cutting the thermoelectric material manufactured by performing it 4 times (cutting) at different cutting angles is shown. The measuring method and unit of each characteristic are the same as in Table 3. According to these tables, when the extrusion process is performed an odd number of times in the route A ^* or the route C, the material properties when cutting at the theoretical orientation azimuth f (1) = 26 ° are the best, and when the even number of times is performed, the material property is 0 °. It is proved that the material properties are the best when cut. Therefore, when the c-plane is aligned in a specific orientation direction different from 0 ° and the material is re-introduced through route A ^* or route C and extrusion is performed again, the c-plane is oriented at 0 °. it is conceivable that. In addition, according to FIG. 4, it is possible to improve the degree of orientation in the route A ^* and the route C as the number of extrusion processes N increases, and the thermoelectric material having an orientation degree of 20 ° to 25 ° when the number of extrusion processes is 3 or more. It can be seen that can be manufactured.

Therefore, when a thermoelectric material having the c-plane aligned in a specific convergence direction by route A and route C ^* is subjected to extrusion processing by route A ^* or route C, the thermoelectric with the c-plane alignment direction aligned at 0 °. The material can be manufactured. For example, when the extrusion process is performed four times by the route A and then the extrusion process by the route C, the orientation direction of the c-plane is 0 ° and the orientation degree is 15 ° based on the measurement result by the above-mentioned EBSD device. It was confirmed that. Further, when the thermoelectric material after the extrusion treatment by the route C was cut at a cutting angle of 0 ° and the same material properties as described above were measured, the Seebeck coefficient S was 202 μV / K and the electrical resistivity ρ was 0.96 × 10 ^{−. 5} Ωcm, thermal conductivity κ was 1.25 W / (K · m), and the figure of merit Z was 3.40 × 10 ⁻³ / K, confirming that a high-performance thermoelectric element was manufactured.

Furthermore, when the extrusion process is performed four times by the route C ^* and then the extrusion process by the route C ^* , the orientation direction of the c-plane is 0 ° and the degree of orientation is 16 based on the measurement result by the above-mentioned EBSD device. It was confirmed to be °. Further, when the thermoelectric material after the extrusion treatment by the route C was cut at a cutting angle of 0 ° and the same material characteristics as described above were measured, the Seebeck coefficient S was 203 μV / K and the electric resistivity ρ was 0.97 × 10 ^{−. 5} Ωcm, thermal conductivity κ was 1.24 W / (K · m), and the figure of merit Z was 3.43 × 10 ⁻³ / K, confirming that a high-performance thermoelectric element was manufactured. As described above, when the extrusion process according to the route A or the route C ^* is repeated and finally the extrusion process according to the route A ^* or the route C is performed, the orientation direction of the c-plane can be set to 0 °. It is possible to easily perform the cutting process when the thermoelectric element is manufactured by cutting the substrate.

Furthermore, the crossing angle between the pressing shaft and the extrusion shaft in the mold 10 is not limited to 90 °, and various crossing angles can be set. For example, when the crossing angle is 120 °, as shown in Table 1, the theoretical orientation directions f (1) and f (2) corresponding to the extrusion processing times 1 and 2 are 40.9 ° and 23.4 °, respectively. . On the other hand, when the extrusion process is actually performed once in route A, the orientation direction of the c-plane is 41 °, and when the extrusion process is performed twice or more, the orientation direction of the c-plane is 23 °. Therefore, in the case of route A, the specific convergence direction is 23 °. In the case of the route C ^* , the orientation direction of the c-plane when the extrusion process is performed once or more is 41 °, and the specific convergence direction is 41 °. In the route A ^* or the route C, the orientation direction becomes 41 ° by the odd number of extrusion processes, and the orientation direction becomes 0 ° by the even number of extrusion processes.

When the crossing angle is 135 °, as shown in Table 1, the theoretical orientation directions f (1) and f (2) corresponding to the extrusion processing times 1 and 2 are 50.4 ° and 31.1 °, respectively. On the other hand, when the extrusion process is actually performed once in route A, the orientation direction of the c-plane is 50 °, and when the extrusion process is performed twice or more, the orientation direction of the c-plane is 31 °. Therefore, in the case of route A, the specific convergence direction is 31 °. In the case of the route C ^* , the orientation direction of the c plane when the extrusion process is performed once or more is 50 °, and the specific convergence direction is 50 °. In the route A ^* or the route C, the orientation direction becomes 50 ° by the odd number of extrusion processes, and the orientation direction becomes 0 ° by the even number of extrusion processes.

DESCRIPTION OF SYMBOLS 10 ... Mold 11a ... Hole 11b ... Pressurization passage 12a ... Hole 12b ... Extrusion passage 20 ... Thermoelectric material

Claims (4)

A material having a composition to be a thermoelectric material containing rhombohedral crystals is obtained by changing the shape of the pressurization passage in the cross section perpendicular to the pressurization axis and the cross section of the extrusion passage perpendicular to the extrusion shaft. By performing the extrusion process of extruding with a mold having the same shape, a plurality of times in a state where the re-injection posture when performing re-injection of the material into the pressure passage is a specific re-injection posture,
A thermoelectric material manufacturing method for manufacturing a thermoelectric material in which the c-plane of the rhombohedral crystal is oriented in a specific convergence orientation corresponding to the specific re-input attitude ,
When f (N) is the theoretical orientation direction when the extrusion process specified from the intersection angle between the pressure axis and the extrusion axis is performed N times (N is a positive integer),
A thermoelectric material in which the specific convergence direction is any one of f (1) to f (N-1) is produced by an extrusion process in which N is 2 or more.
Thermoelectric material manufacturing method.   When the direction in the direction parallel to the extrusion axis of the material in the extrusion passage and the angle around the extrusion axis are the same in the (N-1) -th and N-th extrusion processes,
  A thermoelectric material in which the specific convergence direction is f (2) is produced by an extrusion process in which N is 3 or more.
  The manufacturing method of the thermoelectric material of Claim 1.   The direction in the direction parallel to the extrusion axis of the material in the extrusion passage is reversed in the (N-1) -th and N-th extrusion processes.
  When the angle around the extrusion axis of the material in the extrusion passage differs by 180 ° in the (N−1) th and Nth extrusion processes,
  The thermoelectric material having the specific convergence direction f (1) is manufactured by an extrusion process in which N is 2 or more.
  The manufacturing method of the thermoelectric material of Claim 1.   The thermoelectric material according to any one of claims 1 to 3 is manufactured by cutting so as to be a rectangular parallelepiped having a plane parallel and perpendicular to the specific convergence direction.
Thermoelectric element.

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