JPH10178218A - Thermoelectric semiconductor material, its manufacture, thermoelectric module using the same and hot forging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermoelectric semiconductor material whose orientation can be enhanced by a constitution containing a hot upsetting process wherein a powder sintered body is deformed plastically in a hot manner so as to be rolled and crystal particles in a power sintered texture are oriented to a crystal orientation in which a performance index is excellent. SOLUTION: When an n-type Bi2 Te3 thermoelectric semiconductor material is manufactured, a Bi element simple substance, a Te element simple substance and an Se element simple substance are weighed so as to obtain a stoichiometric ratio of Bi2 Te2.7 Se0.30 , they are sintered, and an ingot 4 is manufactured. An upsetting apparatus is provided with a base 1, with a cylindrical sleeve 2 and with a punch 3 which is formed so as to be passed through the sleeve 2, and the ingot 4 is placed on the base 1 so as to be pressed by the punch 3. The apparatus is made of cemented carbide, and it is heated up to about 450 deg.C by a heating device. By the apparatus, the ingot 4 is pressurized only from two directions, i.e., the upper direction and the lower direction, other directions are set to a free state, and it is formed so as to make the direction of a C-axis uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a thermoelectric semiconductor material,
The present invention relates to a manufacturing method thereof, a thermoelectric module using the same, and a hot forging method.

[0002]

2. Description of the Related Art An electronic cooling element utilizing the Peltier effect or the Etching-Shausen effect, or a thermoelectric power generation element utilizing the Seebeck effect has a simple structure and is easy to handle. Therefore, its wide use is attracting attention because it can maintain stable characteristics. In particular, as the electronic cooling element, it is possible to perform local cooling and precise temperature control around room temperature,
Research is being widely conducted on constant temperature control of optoelectronics and semiconductor lasers.

In a thermoelectric module used for electronic cooling and thermoelectric power generation, as shown in FIG. 12, a p-type semiconductor 5 and an n-type semiconductor 6 are joined via a metal electrode 7 to form a pn element pair. A plurality of element pairs are arranged in series, and one end is heated while the other end is cooled according to the direction of the current flowing through the junction. The material of this thermoelectric element has a Seebeck coefficient α and a specific resistance
And the figure of merit Z (= α ² /
A material having a large ρK) is used. Many thermoelectric semiconductor materials have anisotropy in thermoelectric performance due to their crystal structure.
That is, the performance index Z differs depending on the crystal orientation. Therefore, in the case of a single crystal material, electric current is applied to a crystal orientation having a large thermoelectric performance. In general, since anisotropic crystals have cleavage properties and material strength is weak, single crystals are not used as practical materials, but polycrystals that are unidirectionally solidified by Bridgman method and oriented in a crystal orientation with high thermoelectric performance Is used. However, although the polycrystalline material is not as strong as the single crystal, the material strength is weak, and there is a problem that the element is easily cracked or cracked during element processing. In contrast to these crystalline materials, powdered sintering materials have no cleavability and dramatically improve material strength.However, although the orientation of the crystal orientation is random or crystal orientation, but has a gradual distribution, the thermoelectric performance is low. There was a problem that it was inferior to the material. There has been no thermoelectric semiconductor material having sufficient strength and performance. That is, the crystal materials generally used as the thermoelectric cooler include bismuth telluride (Bi ₂ Te ₃ ), antimony telluride (Sb ₂ Te ₃ ) and bismuth selenide (Bi
₂ Se ₃ ) is a mixed crystal system, but these crystals have remarkable cleavability, and after slicing and dicing processes for obtaining thermoelectric elements from ingots, yields are extremely high due to cracks and chips. There was a problem that it became low.

[0004] Therefore, attempts have been made to form a powder sintered element to improve mechanical strength. Thus, when used as a powdered sintered body instead of as a crystal, the problem of cleavage is eliminated, but as described above, the performance is inferior due to low orientation. That is, there is a problem that the performance index Z is small. The present invention has been made in view of the above circumstances, and has as its object to provide a thermoelectric semiconductor material having sufficient strength and performance and a high production yield.

[0005]

Therefore, in a first aspect of the present invention, a heating step of mixing and heating and melting material powders to have a desired composition, a rhombohedral structure (a hexagonal structure) A) a solidifying step of forming a solid solution ingot of the thermoelectric semiconductor material having: a pulverizing step of pulverizing the solid solution ingot to form a solid solution powder; a sizing step of equalizing the particle diameter of the solid solution powder; The sintering step of pressure-sintering the solid solution powder that has become uniform, and the powder sintered body is plastically deformed hot and spread, whereby the crystal grains of the powder sintered structure have an excellent performance index. A hot upsetting forging step for orienting the crystal in the crystal orientation.

Preferably, the hot upsetting forging step is a hot upsetting forging step in which the powder sintered body is spread only in one axial direction while hot.

[0007] Preferably, the hot upsetting forging step is a step of spreading while pressing in a direction coinciding with the pressing direction in the sintering step.

More preferably, after the hot upsetting forging step, a heat treatment step of performing a heat treatment is further included.

According to a second aspect of the present invention, an ingot forming step of heating and melting a mixture mainly containing bismuth, antimony, tellurium, and selenium having a desired composition to form a solid solution ingot of a Bi ₂ Te ₃ based thermoelectric semiconductor material; A crushing step of crushing the solid solution ingot to form a solid solution powder; a sizing step of uniformizing the particle diameter of the solid solution powder; and a sintering step of pressure sintering the solid solution powder having a uniform particle diameter. And hot-plastically deforming the powder sintered body hot, and expanding, thereby including a hot upsetting forging step in which the crystal grains of the powder sintered structure are oriented in a crystal orientation having an excellent figure of merit. Features.

[0010] Preferably, the hot upsetting forging step is an upsetting forging step in which the powder sintered body is spread only in one axial direction while hot.

Preferably, the hot upsetting forging step is a step of expanding while pressing in a direction corresponding to a pressing direction in the sintering step.

Preferably, the method further comprises a heat treatment step of performing a heat treatment after the hot upsetting forging step.

More preferably, after the sizing step and before the sintering step, the method further comprises a hydrogen reduction step of heat-treating the solid solution powder in a hydrogen atmosphere.

In a third aspect of the present invention, an ingot forming step of forming a solid solution ingot of a BiSb-based thermoelectric semiconductor material by heating and melting a mixture mainly containing bismuth and antimony having a desired composition, and crushing the solid solution ingot A crushing step of forming a solid solution powder, a sizing step of equalizing the particle diameter of the solid solution powder, a sintering step of pressure sintering the solid solution powder having a uniform particle diameter, A hot upsetting forging step in which the body is plastically deformed and spread so that the crystal grains of the powder sintered structure are oriented in a crystal orientation having an excellent figure of merit.

Preferably, the hot upsetting forging step is an upsetting forging step of hot-rolling the powder sintered body in only one axial direction.

Preferably, the hot upsetting forging step is a step of spreading while pressing in a direction coinciding with a pressing direction in the sintering step.

Preferably, the method further comprises a heat treatment step of performing a heat treatment after the hot upsetting forging step.

According to a fourth aspect of the present invention, the powder sintered body of the BiSb-based thermoelectric semiconductor material is hot-inset and forged and plastically deformed, so that the crystal grains of the powder-sintered structure have a crystal orientation with an excellent figure of merit. The present invention is characterized in that a thermoelectric semiconductor material formed so as to be oriented in a direction is provided.

According to a fifth aspect of the present invention, the c-axis of the crystal grains of the powder sintered structure is oriented by hot forging and plastic deformation of the powdered sintered material of the Bi ₂ Te ₃ based thermoelectric semiconductor material and hot deformation. The present invention is characterized in that a thermoelectric semiconductor material formed in such a manner is provided.

In a sixth aspect of the present invention, the powder sintered material of the BiSb-based thermoelectric semiconductor material is hot-upset-forged in a state where it can be spread only in one axial direction, and plastically deformed to obtain a crystal of the powder sintered structure. It is a feature of the present invention to provide a thermoelectric semiconductor material formed such that grains are oriented in a crystal orientation having an excellent figure of merit.

According to a seventh aspect of the present invention, a powder sintered material of a Bi ₂ Te ₃ based thermoelectric semiconductor material is hot upset forged in a state where it can be spread only in one axis direction, and plastically deformed to obtain a powder sintered material. It is characterized by providing a thermoelectric semiconductor material formed such that the c-axis of the crystal grains of the structure is oriented.

According to an eighth aspect of the present invention, a powder sintered material of a p-type and n-type thermoelectric semiconductor material having a rhombohedral structure (hexagonal structure) is hot-upset-forged and plastically deformed to obtain a powder. P-type and n-type thermoelectric semiconductor materials oriented so that the cleavage planes of the crystal grains of the sintered structure are aligned, and fixed to the upper and lower surfaces of the p-type and n-type thermoelectric semiconductor materials so as to face each other. A thermoelectric module comprising a pair of electrodes and a current flowing along the cleavage plane.

In a ninth aspect of the present invention, p-type and n-type Bi
₂ Te ₃ based thermoelectric semiconductor material powder sintered material was forged each upset hot, by plastic deformation, the thermoelectric semiconductor material of p-type and n-type c-axis of the crystal grains of the powder sintering tissue are oriented A pair of electrodes respectively fixed to the upper and lower surfaces of the p-type and n-type thermoelectric semiconductor materials so as to face each other, so that a current flows in a direction perpendicular to the c-axis. And a thermoelectric module configured as described above.

A tenth aspect of the present invention is characterized in that the hot upsetting forging step is a step of hot upsetting the powder sintered body at a grain growth temperature or lower.

An eleventh aspect of the present invention is characterized in that the hot upsetting forging step is a step of hot upsetting the sintered powder at a temperature of 350 ° C. or more and 550 ° C. or less.

A twelfth aspect of the present invention is characterized in that the hot upsetting forging step is a hot upsetting forging step such that the density ratio of the powder sintered body finally becomes 97% or more. I do.

According to a thirteenth aspect of the present invention, in the hot upsetting forging step, the powder sintered body having a density ratio of 97% or more is subjected to hot upsetting forging, so that the density ratio finally exceeds the density ratio. The process is characterized in that

A fourteenth aspect of the present invention is characterized in that the hot upsetting forging step is a hot upsetting forging step of the powder sintered body at a load pressure of 500 kg / cm ² or less.

[0029] In the fifteenth invention, the forging process upset between the heat, the powder sintered body, 70 kg / cm ² or more 350k
It is characterized in that it is a step of hot upsetting forging at an initial load pressure of g / cm ² or less.

A sixteenth aspect of the present invention is characterized in that the hot upsetting forging step is a step of spreading the powder sintered body in a free direction and then further applying pressure while regulating the free direction. And

A seventeenth aspect of the present invention is characterized in that, after the hot upsetting forging step, a hot die forging step of hot-molding and forging the powder sintered body is further performed. .

An eighteenth aspect of the present invention is characterized in that the hot upsetting forging step is repeated a plurality of times.

A nineteenth aspect of the present invention is characterized in that a powdered sintered material of a BiSb-based thermoelectric semiconductor material is hot-inset and forged and plastically deformed so that the density ratio is 97% or more.

A twentieth aspect of the present invention is characterized in that a powdered sintered material of a Bi ₂ Te ₃ based thermoelectric semiconductor material is hot-inset and forged and plastically deformed to increase the density ratio to 97% or more. And

In the method of the present invention, attention is paid to the anisotropy of thermoelectric performance inherent in a single crystal of a thermoelectric semiconductor material, and a powder sintered ingot having strength but inferior crystal grain orientation is subjected to hot upsetting and forging. The crystal orientation is improved by plastically deforming. This makes it possible to obtain a thermoelectric semiconductor material having good performance while maintaining strength. With the plastic deformation of hot forging, the ingot shrinks in the compression direction, while the ingot expands in the direction of the compression surface. Due to this deformation, the crystal grains in the ingot undergo flat plastic deformation and are oriented so that the cleavage plane is perpendicular to the compression direction. As a result, a thermoelectric semiconductor material having sufficient strength and performance can be obtained. Bi ₂ Te ₃
In a thermoelectric semiconductor material, the c-axis is oriented in the compression direction.

Therefore, it is possible to obtain a thermoelectric module having high mechanical strength, excellent orientation and high reliability.

Further, in the present invention, since a powder sintered body is formed by hot upsetting and forging rather than a single crystal, the composition ratio can be selected relatively freely and a high figure of merit Z can be obtained. Can be.

Further, as compared with a case where a single crystal or polycrystalline ingot is used as it is, a decrease in manufacturing yield due to cracks or the like is greatly reduced. Here, the terms Bi ₂ Te ₃ -based thermoelectric semiconductor material, Bi _{2 over} x Sb _x Te _{3 over yz} Se _y S _z
(0 ≦ x ≦ 2, 0 ≦ y + z ≦ 3), and includes a crystal containing impurities. Similarly, BiSb-based semiconductor refers to Bi _1-x Sb _x (0
<X <1), and includes a crystal containing an impurity as a dopant.

The scope of the present invention is not limited to the range of hot upsetting forging a powder sintered body obtained by hot pressing (pressure sintering).

The pressurized body obtained by pressing the solid solution powder may be hot upset forged, or the sintered body obtained by pressing the solid solution powder and then sintered may be hot upset forged. Moreover,
A material obtained by melting and solidifying the material may be cut out as a desired solid solution block, and this may be directly subjected to hot upsetting forging.

The scope of the present invention is not limited to the case where a thermoelectric semiconductor material is obtained by hot forging.

The material to which the hot forging of the present invention is applied includes a magnetic material having a hexagonal structure, a layer structure, or a tungsten bronze structure, a dielectric material, and a superconductor material. Body, bismuth layered structure high-temperature superconductor, and the like.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described in detail with reference to the drawings.

In the method of the present invention, the sintered ingot obtained by powder sintering is subjected to hot upsetting forging as shown in the conceptual view of FIGS. It is characterized in that it is treated so as to be oriented. FIG. 2 is a micrograph showing the state after free forging, and FIG. 3 is a micrograph showing the state before free forging.

The photographs shown in FIG. 1 and FIG. 2 show that the material after hot upsetting and the material before hot upsetting are embedded in an epoxy resin and polished until the surface of each material becomes a mirror surface. This is a micrograph of the structure etched with an acidic solution after the formation, and the vertical direction of the photograph is the pressing direction during forging and sintering.

In the state before forging in FIG. 3, the structure is observed in a wavy shape. The wavy grains are crystal grains caused by the grains of the powder when forming the powder sintered material.

In the state after forging shown in FIG. 2, the wavy crystal grains shown in FIG. 3 are elongated by forging, and the crystal grains are oriented in a layer perpendicular to the pressing direction. Recognize.

Incidentally, the circular holes in the photograph are generated at the time of etching and do not indicate the structure itself.

FIG. 4 is a flow chart showing the steps of manufacturing an n-type Bi ₂ Te ₃ thermoelectric semiconductor material.

That is, as shown in FIG.
i, tellurium Te, and selenium Se are weighed so that the stoichiometric ratio is Bi ₂ Te _2.7 Se _0.30, and further, an appropriate amount of a compound for adjusting the carrier concentration is added, dissolved, mixed, and solidified. , A soluble material was created. After pulverizing this soluble material with a stamp mill, ball mill or the like,
The mixture is passed through a mesh and a 400-mesh sieve, and those remaining on the 400-mesh sieve are selected, and the powder having a particle size of about 34 to 106 μm is prepared. After sizing, a predetermined volume of powder is supplied into a predetermined volume of glass ampule under vacuum evacuation, hydrogen is injected and sealed to 0.9 atm, and then heat treatment is performed in a heating furnace at 350 ° C. for 10 hours. To perform hydrogen reduction. Then, this powder was sintered by a hot press apparatus in an argon atmosphere at a sintering temperature of 500 ° C. and a pressure of 750 k.
Powder sintering was performed at g / cm ² . The size of the sintered ingot has a cross-sectional area of 32 mm x 32 mm and a thickness of 20 m
m. The ingot has a negative Seebeck coefficient and the material has n-type. This is forged by hot upsetting forging.

In the forging step, as shown in FIG. 5, this ingot was placed in a cemented carbide upsetting apparatus, and was press-sintered from above at 150 kg / cm ² at 450 ° C. in an argon atmosphere. This is done by pressing in the same direction as the pressing direction. As a result, the sintered ingot is compressed. Here, FIG. 5A is a top view, and FIG. 5B is a cross-sectional view. The upsetting device includes a base 1, a cylindrical sleeve 2 erected perpendicular to the base 1, and a punch 3 formed to be inserted through the sleeve 2. 1, and is configured to be pressed by a punch 3. This device is made of carbide and is configured to be heated to about 450 ° C. by a heating device (not shown). According to this apparatus, the ingot 4 is pressurized only from two directions, that is, the upper direction and the lower direction, and is free in the other directions, and is forged so that the c-axis direction is aligned. FIG. 6 is a diagram showing the results of measuring the relationship between forging time and ingot thickness. By the pressing for 12 hours, the thickness of the ingot was reduced to about 8 mm, about 1/2, and the bottom area was doubled to about 48.5 mm square. FIG. 7 shows the distribution of the density ratio with respect to the single crystal in the quarter portion of the ingot. Since the thermoelectric performance decreases as the density decreases and the strength decreases, the usable portion is a portion having a density ratio of 97% or more.

Table 1 shows the thermoelectric performances of the hot forged ingot and the central part of the ingot before forging. In the case of this n-type material, carriers decrease due to crystal defects due to hot forging, and specific resistance and Seebeck constant increase.
By enclosing in a glass ampoule together with 0.9 atm of argon gas and heat-treating at 400 ° C. for 48 hours, lattice defects for forging were eliminated and the carrier concentration became the same as that of the starting ingot. This can be understood by the same Seebeck constant.

[0053] Furthermore, hot forging was performed while changing the compression ratio, and the performance of the material after the heat treatment was compared. Table 2 shows the results.

[0054] As is apparent from Table 2, when the compression ratio increases, the amount of plastic deformation increases, the orientation is improved, and the thermoelectric performance is also improved. By increasing the pressing force, as shown in FIG. 8, the compression speed (thickness reduction amount) increases, and the processing time is shortened.
Cracks are formed in the peripheral portion during processing, so that high-density portions are reduced and usable portions are reduced. Therefore, it is desirable to set the pressing force to such an extent that cracking cannot be caused. This pressing force also depends on the frictional force at the portion where the ingot contacts the base and the punch. Before the forging, carbon powder, BN powder and the like were applied to the bottom surface of the punch and the top surface of the base for smooth spreading. This facilitates deformation without cracking.

As described above, according to the method of the present invention, it is possible to obtain a thermoelectric semiconductor material which has a high yield without a decrease in density due to cracks or the like during forging and has an extremely good orientation. The hot forging step was performed in an argon atmosphere, but is not limited to this, and may be performed in a vacuum or another inert gas atmosphere.

Next, as a second embodiment of the present invention, an upsetting forging method for freely extending only in one axial direction will be described. In this method, as shown in FIG. 9, the forging process is performed by installing this ingot in a cemented carbide upsetting apparatus,
Pressing is performed at 50 ° C. at 100 to 500 kg / cm ² for 5 hours in the same direction as the pressing direction during pressure sintering. As a result, the sintered ingot is compressed. Here, FIG. 9A shows a state before upsetting forging, and FIG. 9B shows a state after upsetting forging. The upsetting device includes a base 11, a columnar sleeve 12 erected perpendicularly to the base 11, and having a rectangular parallelepiped cavity H therein.
1 formed so as to be inserted into the cavity H of
And the ingot 14 is placed on the base 11 and pressed by the punch 13. This device is made of carbide and is configured to be heated to about 450 ° C. by a heating device (not shown). Here, the ingot had a thickness of 30 mm, a width of 40 mm, and a length in the extending direction of 18 mm. According to this device, the ingot 14 is restricted from the upper and lower sides and the width direction of the cavity in the sleeve, and in the remaining two directions, these directions are free until they contact the wall of the sleeve, and the cleavage plane is It is forged to be aligned. FIG. 10 shows the results of measuring the thickness of the ingot with respect to the pressure applied in this step and the elapsed time. As is apparent from this figure, the thickness of the ingot was reduced to about 7 mm by pressing for 5 hours, and the length was pressed to the wall of the sleeve. It was 80 mm. About 90% of the ingot had a density ratio of 98% or more. FIG. 11 shows the distribution of the density ratio with respect to a half of the ingot single crystal. The thermoelectric performance decreases as the density ratio decreases, and the material strength also decreases. In this example, the usable portion is a portion having a density ratio of 97% or more, so that almost everything can be used.

Table 3 shows the thermoelectric performance of the ingot heat-treated after the hot forging and the center of the ingot before the forging. In the case of this n-type material, carriers decrease due to crystal defects due to hot forging, and specific resistance and Seebeck constant increase. However, as in the first embodiment, forging is performed by heat treatment in an argon gas atmosphere. There is no lattice defect for Forge) and the carrier concentration is the same as in the starting ingot. This can be understood by the same Seebeck constant.

[0058] Next, a method of forming a p-type element will be described as a third embodiment of the present invention. Elemental elements of bismuth Bi, tellurium Te, and antimony Sb were converted to stoichiometric ratios Bi _0.4 Sb _1.6
It was weighed so as to be Te _3, and further, an appropriate amount of Te for adjusting the carrier concentration was dissolved, mixed and solidified to prepare a soluble material. This soluble material is pulverized by a stamp mill, a ball mill, or the like, and then sieved with a 150-mesh or 400-mesh sieve, and the material remaining on the 400-mesh sieve is selected to obtain powder having a particle size of about 34 to 106 μm. In the case of the p-type material, the effect of oxidation of the fine particles and powder was small, so that the hydrogen reduction step was not performed. Then, the powder was sintered at a temperature of 500 ° C. and a pressure of 7 using a hot press.
Powder sintering was performed at 50 kg / cm ² . The size of the sintered ingot is height 30mm, width 40mm, length 18
It is cut into mm and placed in the same upsetting apparatus as used in Example 2, and forged by hot upsetting forging.

In the forging step, this ingot was set in a cemented carbide upsetting device, as shown in FIG.
By pressing at 100 ° C. for 5 hours at 100 to 500 kg / cm ² in the same direction as the pressing direction during pressure sintering,
The sintered ingot is compressed. Table 4 shows the thermoelectric performances of the hot forged ingot and the central part of the ingot before forging. In the case of this p-type material, heat treatment is not performed because the carrier is not reduced by hot forging as compared with the n-type material. When the heat treatment is performed, the carrier concentration becomes lower than that of the starting ingot.

[0060] In the same manner, Bi ₂ Te _2.85 Se _0.15 and Bi _0.5
As for Sb _1.5 Te ₃ , the thermoelectric performance of the hot forged ingot and the central part of the ingot before forging were measured, and the results are shown in Tables 5 and 6, respectively.

[0061] Next, of the n-type Bi ₂ Te _2.7 Se _0.3 ingots formed by the method of the second embodiment, an ingot having a density of 97% or more and 80% of the ingots was used. To form a wafer having a thickness of 1.33 mm. An electrode metal layer was formed on the front and back surfaces of the wafer. Then, dicing was performed to form a 0.64 mm square chip. An n-type element was randomly extracted from these (see Table 3). Further, the p-type Bi _0.4 Sb _1.6 Te ₃ formed by the method of the third embodiment is used.
The ingot was processed into chips of the same size, which were used as p-type elements (see Table 4). And the n-type element and p
A thermoelectric module as shown in FIG. 12 was formed by mounting 18 pn element pairs each composed of a mold element. Then, 16 thermoelectric modules were formed, and the maximum temperature difference was measured. The average value of the maximum temperature difference was calculated, and the relationship between the average value and the heat radiation surface temperature is shown by a curve a in FIG. Also, for comparison, a curve b shows the result of forming a thermoelectric module by performing dicing after hot pressing without hot upsetting and forging without performing hot upsetting, and performing the other steps exactly the same. In the region where the heat radiation surface temperature is in the range of 0 ° C. to 80 ° C., the maximum temperature difference of the thermoelectric module formed by hot upsetting forging is significantly larger than the maximum temperature difference of the module formed by hot pressing. The improvement of the thermoelectric performance by hot upsetting forging in Table 4 is envisaged. Here, the current value giving the maximum temperature difference was 1.5 to 1.6 A for both modules. The standard deviation of the maximum temperature difference was from 0.4 to 0.5 ° C. Furthermore, for example, when the heat radiation surface temperature is 2
At 7 ° C., the maximum temperature difference of the thermoelectric module formed by the hot upsetting forging was 75 ° C. or more, which is an extremely excellent result.

Here, the strength of the thermoelectric module formed as described above will be examined.

When the thermoelectric module is broken, shear stress is applied to the thermoelectric module, and the p-type and n-type elements are often broken.

Therefore, as shown in FIG. 17, a material obtained by soldering a p-type element 5 and an n-type element 6 to one side of a ceramic plate 15 obtained in the process of manufacturing a thermoelectric module was used as a test material. The shear strength of these p-type and n-type elements was measured.

That is, as shown in the side view of FIG. 17A and the partial perspective view of FIG. 17B, the push-pull gauge 16 is applied to the base of the p-type element 5 and the n-type element 6. 10 mm / mi
It measures the shear strength when pulled up at a speed of n.

Table 10 below shows the measurement results of the shear strength of the p-type element and the n-type element generated based on the forged ingot subjected to the hot upsetting forging.

Table 11 below shows the results of measuring the shear strength of a p-type element and an n-type element produced based on a sintered ingot made of the same material and not subjected to hot upsetting after hot pressing.

Table 12 shows that a unidirectionally solidified soluble material was produced by the stock burger method instead of hot pressing with the same material, and the shearing of the p-type element and the n-type element produced based on this soluble material was carried out. The intensity measurement result is shown.

[0069] When these tables are compared, as for the n-type element 6, the shear strength of the element of the hot forging material and the shear strength of the element of the hot press material are both higher than the element of the ingot material (1).
176 to 2185, 1914), it can be seen that the strength of the hot forged material element is higher than that of the hot pressed material element (2185 to 1914). It can also be seen that the standard deviation of the shear strength decreases in the order of the element of the soluble material, the element of the hot press material, and the element of the hot forging material (224 to 347, 347 to 347).
224 vs. 158).

On the other hand, as for the p-type element 5, the magnitude of the shear strength increases in the order of the element of the soluble material, the element of the hot press material, and the element of the hot forging material, though slightly different (see 1413). 1430, 1472 for 1430). The standard deviation of the shear strength also decreases in the order of the element of the soluble material, the element of the hot press material, and the element of the hot forging material (132 for 429, 112 for 132).

Here, the larger the standard deviation of the shear strength, the higher the possibility of breakage even below the average value of the shear strength, and the higher the probability of breakage below the average value of the shear strength.

Therefore, the element made of the hot forged material not only has a higher shear strength than elements of other materials, but also has a lower probability of fracture at an average value of the shear strength or less, and has a higher reliability. It can be concluded.

For this reason, by using a hot forging material for the thermoelectric module, damage during module assembly can be reduced, durability can be increased, and reliability can be improved.

Similarly, Bi ₂ Te _2.85 Se _0.15
And Bi _0.5 Sb _1.5 Te ₃ (Tables 5 and 6)
Reference) Similarly, an n-type element and a p-type element were formed, respectively, to produce a thermoelectric module. The average value of the maximum temperature difference of the thermoelectric module was calculated, and the relationship between the average value and the heat radiation surface temperature is shown by a curve a in FIG. Also, for comparison, a curve b shows the result of forming a thermoelectric module by performing dicing after hot pressing without hot upsetting and forging without performing hot upsetting, and performing the other steps exactly the same. In the region where the heat radiation surface temperature is in the range of 0 ° C. to 80 ° C., the maximum temperature difference of the thermoelectric module formed by hot upsetting forging exceeds the maximum temperature difference of the module formed by hot pressing. The current value giving the maximum temperature difference was 1.3 to 1.4 A for both modules.

From the comparison between FIG. 13 and FIG. 14, it can be seen that the present invention is effective, although there are some changes depending on the material.

The present inventors have further conducted experiments, and as a result, the following parameters have been found to have an effect on the performance. A brief description is as follows.

(1) Density Ratio When the density ratio of the sintered ingot is low, the thermal conductivity decreases, but the thermoelectric performance decreases due to an increase in electric resistance. Also, the strength of the material is reduced.

After all, the thermoelectric performance can be improved,
There is a range of density ratios that does not impair the strength of the material, and it has become clear that the sintered ingot only needs to have a density of 97% or more by hot forging. Alternatively, it has been clarified that the sintered ingot having a density ratio of 97% or more may be finally hot-forged to have the density ratio or more.

Here, the density ratio is the ratio of the green density to the true density (ideal density) of a substance having the same composition as the green compact (a single crystal before being pulverized).

(2) Plastic Working Temperature In hot forging and warm forging, the recovery of the crystal proceeds simultaneously with the progress of the plastic working in addition to the crystal distortion. In the hot plastic working of the thermoelectric semiconductor, it is considered that this crystal distortion and recovery, and furthermore, the flow of the powder grain boundaries and the crystal grain boundaries of the sintered material occur, but the details are still unknown.

However, it is clear that the larger the hot forge ratio, the more uniform the structure as viewed with a polarizing microscope, and that the crystal distortion and recovery by plastic working greatly contribute to the improvement of the orientation. Here, when the temperature increases, crystal distortion and recovery are promoted, but at a temperature higher than the recrystallization temperature, the crystal grains grow regardless of orientation, the degree of orientation decreases, and the material strength decreases. I will. The higher the temperature, the faster the deformation speed of the ingot. In other words, if the temperature is high, the structure becomes fluid, plastically deforms before the alignment becomes uniform, and the orientation does not progress further.

Conversely, if the temperature is too low, there is a problem that the plastic deformation itself becomes slow, which is not suitable for practical working.

After all, it is clear that there is a temperature range that is optimal for plastic working of a sintered ingot, and it is necessary that the temperature be lower than the grain growth temperature at which crystallites increase and orientation is lost. Was.

More specifically, it was found that the temperature should be 550 ° C. or lower, and 350 ° C. or higher in which plastic deformation can be performed at a practical speed.

It is considered that the temperature range of the hot press and the temperature range of the plastic working are desirably the same.

(3) Plastic Working Load The greater the load applied to the sintered ingot, the higher the deformation speed. However, as the load increases, the frictional resistance increases and the ingot buckles. In addition, when the deformation speed was reduced by reducing the load, no significant improvement in the orientation was observed, probably because only the flow at the grain boundaries occurred. The rate of deformation is determined by the initial load pressure initially applied to the sintered ingot. Also, the initial load pressure needs to be a force equal to or higher than the yield stress of the sintered ingot.

After all, there is a range of an appropriate initial load pressure, and the range is 70 kg / cm ^{2 to} 350 k.
g / cm ² or less.

(4) Forging Process Although the present invention basically presupposes the upsetting forging step, the above-mentioned (1) is obtained by appropriately adding a die forging process to the upsetting forging step. It has been found that the density ratio can be improved.

That is, after the sintered ingot is spread in the free direction by upsetting forging, the pressure is further increased in a state where the free direction is regulated by a jig or the like, so that the lowered density ratio can be recovered. It was found that the density ratio could be improved.

Also, by performing a hot die forging process after hot upsetting and forging the sintered ingot,
It became clear that the density ratio which once decreased can be recovered or the density ratio can be improved.

(5) Number of Forgings It has also been clarified that by increasing the number of forging steps and sequentially increasing the compression ratio, the orientation can be improved and the thermoelectric performance can be improved.

The above (1) to (5) will be described below with reference to specific examples.

Fourth Embodiment First, a description will be given of a specific example of performance improvement when the density ratio of (1) is 97% or more.

In this embodiment, an n-type thermoelectric semiconductor of Bi ₂ Te _2.7 Se _0.30 having the same composition as that of the second embodiment is used.
Pulverized with an average particle size of 20 μm, and the sintering temperature is 500 °
C, powder sintering was performed by hot pressing at a pressure of 750 kg / cm ² . The average particle size (20 μm) used was smaller than that of the second example.

Thereafter, in the same manner as in the second embodiment, hot forging was performed by applying a load pressure shown in FIG. 15 at 400 ° C. by using an upsetting device shown in FIG. . That is, as the load pressure, the initial load was set to 100 kg / cm ^2, and finally 450 kg / cm ²
Increased.

Then, the forged ingot after forging is
Annealing was performed at 400 ° C. for 48 hours in an argon-reduced glass sealed tube.

Table 7 below shows the result of comparison between the second embodiment and the fourth embodiment. In Table 7, the term "hot press 1" refers to the case where only the hot press is performed in the second embodiment, and the step of hot forging (hot forging) is omitted. The term "hot forge 1" refers to the second embodiment. Shows the case where the hot forge process was performed. The hot press 2 refers to the case where only the hot press is performed in the fourth embodiment, and the hot forging (hot forging) step is omitted. The hot forge 2 refers to the hot forge according to the fourth embodiment. 3 shows the case where the process of FIG.

[0098] Here, the anisotropy ratio of the resistance is a value indicating the directionality of the resistance, and the larger the value is, the more remarkable the effect of improving the crystal orientation is.

The evaluation criterion of the performance index Z is as follows.
The threshold value was 2.45. When the performance index Z is 2.45 or more, it is determined that the thermoelectric performance has been improved.

As is clear from the table, in the fourth embodiment, since a relatively fine powder (average particle size: 20 μm) was used, the density ratio of the sintered ingot subjected to hot forging was low (96%). 0.8%), and the anisotropy ratio of the resistance indicating the degree of crystal orientation is also low (1.01).

When the sintered ingot is forged in a uniaxial direction, the forging temperature is lower than that of the second embodiment (400 ° C. compared to 450 ° C. of the second embodiment).
It can be seen that the processing speed is high (see FIGS. 10 and 15).

In the fourth embodiment, the density ratio of the forged ingot after hot forging is the same as that of the sintered ingot before forging (96.8%), but the figure of merit is improved (2.45). ). This is considered to be because the crystal orientation was improved by forging. This is why the anisotropy ratio of the resistance has increased (2.42).

However, since the density ratio is lower than that of the forged ingot after hot forging in the second embodiment, the figure of merit is low (2.45 as compared with 2.81 in the second embodiment). You can see that.

As described above, in the fourth embodiment, although the anisotropy ratio of the resistance is improved, the figure of merit is lower than that of the second embodiment. It is explained as follows.

That is, the figure of merit Z is determined by both factors of the resistance anisotropy ratio and the density ratio. The contribution ratio of the density ratio is larger than the contribution ratio of the resistance anisotropy ratio.

Therefore, in the case of the fourth embodiment in which the density ratio is smaller than 97%, the figure of merit Z is 2.45, which is an evaluation criterion, although the anisotropy ratio of resistance is improved.
Will not rise to values far above

From the above, it was concluded that setting the density ratio of the sintered ingot before hot forging to 97% or more is desirable for improving the thermoelectric performance. And the density ratio of the forged ingot finally obtained by hot forging is 97%
It was concluded that this was desirable. Then, it was finally concluded that it is desirable that the sintered ingot having a density ratio of 97% or more be hot-forged to have a density ratio equal to or higher than the density of the sintered ingot before forging.

Fifth Embodiment Next, a specific example of performance improvement by increasing the number of times of the forging step (5) will be described.

In this embodiment, a Bi ₂ Te _2.7 Se _0.30 n-type thermoelectric semiconductor material having the same composition as that of the above-described second embodiment was sintered by the same manufacturing method as that of the second embodiment. The sintered ingot 14 obtained at this time is, as shown in FIG.
The height (thickness) was 60 mm, the width was 40 mm, and the length in the extending direction was 40 mm.

[0110] The sintered ingot 14 was
By performing hot forging once and three times, forging materials having a large compression ratio are sequentially generated. That is, by the first forging, the compression ratio becomes 1/2, by the second forging, the compression ratio becomes 1/8, and by the third forging,
The compression ratio becomes 1/16.

Then, the forged ingot after the final forging was subjected to a heat treatment at 400 ° C. for 24 hours in an atmosphere substituted with argon.

Table 8 shows the average value of the thermoelectric performance and the resistance anisotropy of the portion where the density ratio is 97% or more in the forged ingot.

[0113] The data of the forging frequency of 1 (compression ratio 1/5) shown in Table 8 uses the average value of the portion with the density ratio of 97% or more in the forged ingot obtained in the second embodiment.

As shown in the table, when the compression ratio increases, the amount of plastic deformation increases, the orientation is further improved, and the thermoelectric performance is improved (from a performance index of 2.19 to 2.52, from 2.52 to 2.55). To).

Further, a slight change in carrier concentration occurs due to an increase in the compression ratio. This can be understood from the fact that the Seebeck constant changes according to the compression ratio.

Although the anisotropy ratio of the resistance is large for the forged ingot which has been forged a plurality of times (2.52, 2.55 with respect to 2.19 of the first forged ingot), the figure of merit is obtained. Is not so much increased (2.61 and 2.62 compared to 2.56 for the first forged ingot) because the composition of the sintered ingot as the starting material is the optimum carrier concentration at which the thermoelectric performance can be maximized. This is considered to be due to the fact that the forged ingot that has been forged a plurality of times while being formed has a composition that deviates from this optimum carrier concentration.

However, this can be solved by changing the carrier of the sintered ingot of the starting material to a concentration suitable for the compression ratio.

Sixth Embodiment Next, a specific example of performance improvement by the number of forgings performed on a p-type material will be described in the same manner as in the fifth embodiment. In this embodiment, a p-type thermoelectric semiconductor material of Bi _0.4 Sb _1.6 Te ₃ having the same composition as that of the third embodiment described above is used.
Was sintered by the same manufacturing method as that of the above example. As shown in FIG. 16, the sintered ingot 14 obtained at this time had a height (thickness) of 60 mm, a width of 40 mm, and a length in the extending direction of 40 mm.

[0119] The sintered ingot 14 was
By performing hot forging once and three times, forging materials having a large compression ratio are sequentially generated. That is, by the first forging, the compression ratio becomes 1/2, by the second forging, the compression ratio becomes 1/8, and by the third forging,
The compression ratio becomes 1/16.

Thereafter, the forged ingot after the final forging was subjected to a heat treatment at 400 ° C. for 24 hours in an atmosphere substituted with argon.

Table 9 shows the average value of the thermoelectric performance and the resistance anisotropy of the portion where the density ratio is 97% or more in the forged ingot.

[0122] The data in Table 9 where the number of times of forging is 1 (compression ratio 1/5) uses the average value of the portion having a density ratio of 97% or more in the forged ingot obtained in the third embodiment.

As shown in the table, when the compression ratio increases, the plastic deformation increases, the orientation is further improved, and the thermoelectric performance is improved (from 3.2 to 3.22, 3.2 to 3.2.
(To 35).

Seventh Example Next, the effect of the sintering temperature of the hot press on the performance will be examined.

In this embodiment, an n-type thermoelectric semiconductor of Bi ₂ Te _2.7 Se _0.30 having the same composition as that of the second embodiment is used.
Pulverized with an average particle size of 40 μm,
The powder was sintered by hot pressing at ² cm ² . Hot press 400 ° C, 450 ° C, 500 ° C, 550 ° C
The sintering was performed under the following four conditions:

Thereafter, as in the second embodiment, the loading pressure at 450 ° C. is 100 kg / cm ^{2 to} 45 ° C. by the upsetting device shown in FIG.
Pressure was applied at 0 kg / cm ² .

Thereafter, the forged ingot after forging is
Annealing was performed at 400 ° C. for 24 hours in an argon reduced glass sealed tube.

The physical properties of the central portion of the resulting forged ingot (“forged product” in the table) and the sintered ingot after hot pressing (“pressed product” in the table) were measured at each sintering temperature of 4%.
The values are shown in the following Tables 13, 14, 15, and 16 for each of 00 ° C, 450 ° C, 500 ° C, and 550 ° C.

[0129] As is clear from these tables, the forged ingot subjected to hot upsetting forging has a density of 99% or more regardless of the production conditions (sintering temperature conditions) of the sintered ingot which is the starting material of the forging process. It can be seen that the material strength and the thermoelectric performance are improved. Furthermore, the sintered ingot of the starting material having a density ratio of about 98% after hot pressing (when the sintering temperature is 400 ° C. and 450 ° C.)
It can be seen that the density ratio is increased by hot upsetting forging (in the case of a sintering temperature of 400 ° C., 9
(From 8.4% to 99.6%, at a sintering temperature of 450 ° C, from 98.5% to 99.9%).

Regarding the crystal orientation (resistance anisotropy ratio), hot upsetting forging is performed irrespective of the production conditions (sintering temperature conditions) of the sintered ingot which is the starting material of the forging process. It can be seen that there is improvement and improvement.

When the hot pressing temperature is high, the structure changes due to recrystallization during hot pressing, and the anisotropy ratio of the resistance decreases (the resistance of the sintered ingot when the sintering temperature is 550 ° C.). The anisotropy ratio is 1.34). For this reason, when hot forging is performed using a sintered ingot having a reduced resistance anisotropy ratio, although the orientation is improved (from 1.34 to 2.25), forging is started. Since the orientation itself at the time is low (the anisotropy ratio of the resistance of the sintered ingot is low), the figure of merit becomes low (2.43 or less, evaluation criteria of 2.45 or less). For example, sintering temperature of 550 ° C
Has a performance index of 2.43 (the resistance anisotropy ratio of the sintered ingot is 1.34) and a sintering temperature of 50.
The figure of merit of the forged ingot at 0 ° C. is lower than 2.65 (the anisotropy ratio of the resistance of the sintered ingot is 1.83). Eighth Embodiment Next, as described in (4) above, by adding a die-forging process to the upsetting forging process, it is possible to improve the density ratio and improve the thermoelectric performance. An example will be described.

In the present embodiment, an n-type thermoelectric semiconductor material of Bi ₂ Te _2.7 Se _0.30 having the same composition as that of the above-described first embodiment is manufactured by the same manufacturing method (firing) as in the first and second embodiments. Sintering was performed at a sintering temperature of 500 ° C and a pressure of 750 kg / cm ² ). Two sintered ingots having a height (thickness) of 30 mm, a width of 40 mm, and a length in the extending direction of 18 mm were cut out from the powder sintered body obtained in the same manner as in the second embodiment. Then, the forging process was made different for each, and hot forging was performed at 450 ° C. using the upsetting device shown in FIG.

FIG. 18 shows that one of the two sintered ingots is restricted in the direction of spreading by a jig (wall) added to the upsetting device in the middle of the spreading, and the hot ingot is further heated. 3 shows a change in the height of the ingot (solid line) and a change in the load pressure (broken line) when the pressurization is continued. That is, in the latter half of the upset forging, the load pressure is further increased to 450 kg / cm ² for about 5 hours after the extended end of the ingot is restrained by the jig wall (about 315 minutes after the start of forging). The pressure is continued, and the latter half of the forging process is performed by die forging.

As shown in the figure, in the latter half of the forging process,
It can be seen that there is no change in the height of the ingot because no spreading takes place.

On the other hand, FIG. 19 shows that the other sintered ingot of the two sintered ingots was similarly spread,
It shows a change in ingot height and a change in load pressure when the spread is stopped (forging is stopped) before the spread end is brought into contact with the jig. 18 and 19, the initial load pressure was 250 kg / cm ² .

Observation of the forged ingot obtained in the forging step shown in FIG. 18 revealed that the end portion was formed in a square shape and the surface was smooth because the ingot was pressed for a long time using a forging die. On the other hand, the end of the forged ingot obtained by the process of stopping the forging in the middle shown in FIG. 19 was in an arc shape, and many fine cracks were observed on the surface.

The measurement pieces shown in FIG. 20 are cut out from the two forged ingots 14 obtained in these different forging steps, and the resistivity, density ratio, resistivity anisotropy ratio, Seebeck constant, Physical properties such as power factor were measured. Table 17 below shows the results.
18. The power factor is a value obtained by dividing the square of the Seebeck constant by the resistivity, and the larger the value, the better the thermoelectric performance. As a criterion for evaluation, a hot-pressed product (before forging) having an n-type power factor of 3.2 or more, which is a comparative example, was evaluated as “good thermoelectric performance”.

Although there was almost no variation in the physical property values in the height direction and the width direction of the measurement piece (forged ingot 14), there was variation in the distribution of the physical property values in the spreading direction D. Tables 17 and 18 show average values in the width direction and show the physical property values for each position in the spreading direction D.

Table 17 shows forged ingot 1 shown in FIG.
FIG. 19 shows the physical property values of the forged ingot obtained in the forging step shown in FIG. 18 for each distance in the spreading direction D from the center C of No. 4.

Table 18 shows the physical property values of the forged ingot obtained in the forging step shown in FIG. 19 for each distance in the extending direction D from the center portion C of the forged ingot 14.

[0141] As shown in these tables, Table 17 was obtained by die forging in the latter half.
Forged ingots have a density ratio of 98% for each part of the ingot
As described above, it can be seen from these results that the material strength and the thermoelectric performance are improved.

However, it can be seen that the anisotropy ratio of the resistance decreases from the center of the ingot to the end, and the orientation of the crystallites gradually becomes less uniform. Also, as with the anisotropy ratio of resistance, it can be seen that the absolute value of the Seebeck constant decreases from the center of the ingot to the end, and the resistivity increases from the end to the end.

It is considered that the reason why the Seebeck constant decreases toward the end portion is that lattice defects due to forging increase toward the end portion. Also, it is considered that the reason why the resistivity increases toward the end is that the orientation of crystal grains deteriorates toward the end.

Further, the power factor decreases from the center of the ingot to the end, indicating that the crystal orientation deteriorates toward the end and the thermoelectric performance decreases. However, up to a distance of 26 mm from the center of the ingot, the power factor exceeded 3.2, which was the evaluation criterion, and was maintained at a value of 3.6 or more, indicating that the range usable as a thermoelectric material is wide.

On the other hand, it can be seen that the density ratio of the forged ingot of Table 18 obtained by stopping the forging before the die forging is lower than that of Table 17. Note that the density ratio at a distance exceeding 22 mm from the center of the ingot is too low (density ratio less than 97%).
In the figure, data at a distance exceeding 22 mm is omitted.

In the central part of the ingot (for example, a part at a distance of 2 mm from the center of the ingot), although the anisotropy ratio of resistance and the Seebeck constant are almost the same as those in Table 17, the resistivity increases. What is (0.94
8 is 0.993) and the density ratio is lower than that in Table 17 (98.7 versus 98.8). The reason why the power factor is lower than that in Table 17 (3.82 vs. 3.99) is also considered to be due to the effect of the decrease in the density ratio. Only at a distance of 10 mm from the center of the ingot, the value of the power factor is 3.6.
The above cannot be maintained, and it can be seen that the range that can be used as a thermoelectric material is narrower than Table 17.

[0147] From these comparison results, it is understood that the density ratio, in addition to the orientation, greatly affects the thermoelectric performance.

If the density ratio shown in Table 18 is considered to be the density ratio in the middle of the spreading, and the density ratio shown in Table 17 is the density ratio in the case of further die forging in the middle of the spreading, It can be seen that even if the density ratio is lowered in the middle, the density ratio can be improved and recovered by further die forging.

The recovery of the density ratio is caused by the p
The same was confirmed for the mold material.

Further, in the above description, it is assumed that the ingot is freely extended in one axial direction and then restrained in the uniaxial direction. However, as in the first embodiment, the ingot is extended in two axial directions. After the free spreading, the spreading in these two directions may be restricted at the same time.

FIGS. 30 and 31 show the structure of the upsetting device for restraining the spreading in both directions. FIG. 30 is a view showing a free spreading state in which the sintered ingot 14 is not restrained, and FIG. 31 is a state in which the spreading of the sintered ingot 14 is restrained in both upper, lower, left and right directions in the drawing. FIG. FIGS. 30 and 31A are top views of the upsetting device, and FIGS. 30 and 31B are side views of the upsetting device.

That is to say, the upsetting device is not shown in FIG.
0, as shown in FIG. 31, a die 20 on which the sintered ingot 14 is placed, a punch 18 for compressing the sintered ingot 14 from above, and a sintering ingot 14 by being driven as indicated by an arrow. It comprises four side walls 19 that contact each side surface and prevent free spreading.

In the first half of the forging process, hot forging is performed in the free spreading state shown in FIG.
As shown in FIG. 1, the four side walls 19 are driven, and hot forging is continued in a state where the biaxial direction free extension of the sintered ingot 14 is prevented by these four side walls 19 (the punch 18 is lowered). State).

As described above, even when the free spreading in the biaxial direction is prevented in the latter half of the forging process, the density of the forged ingot is reduced in the same manner as in the embodiment in which the free spreading in the single axial direction is prevented in the latter half of the forging process. The ratio can be increased to 97% or more, and the thermoelectric performance can be improved.

In the above-described embodiment, the latter half of the forging process is performed by die forging. However, it is also possible to perform the die forging process after performing the upsetting forging process.

A case in which this is performed using the upsetting device shown in FIGS. 30 and 31 will be described below.

That is, in the first upsetting forging process,
As shown in FIG. 30, hot upsetting forging is performed in a free spreading state. Then, the punch 18 is once raised to bring the sintered ingot 14 into a non-compressed state. In the next die forging process, as shown in FIG. 31, the four side walls 19 are driven, and the punch 18 is again moved in a state in which the biaxial direction free extension of the sintered ingot 14 is prevented by the four side walls 19. Descended. Thus, the sintered ingot 14 is compressed in the vertical direction, and hot die forging is performed.

The hot upsetting forging step and the hot die forging step may be repeated a plurality of times.

Even when the die forging step is performed following the upsetting forging step, the density ratio of the forged ingot is 97% or more, as in the above-described embodiment in which free spreading is prevented in the latter half of the forging step. The thermoelectric performance can be improved.

Ninth Embodiment Next, the range of the plastic working temperature at which the thermoelectric performance described in (2) can be improved, and the plastic working temperature at which the thermoelectric performance described in (3) can be improved The range of the load will be described with a specific example.

Table 19 below shows the ingot deformation speed when hot forging was performed under the conditions 1 to 7 in which the temperature and the initial load pressure were changed. The hot pressing process is the same as in the second embodiment. In the hot forging process, the height (thickness) is 30 mm, the width is 40 mm, and the hot pressing process is the same as in the second embodiment.
A sintered ingot having a length of 18 mm in the extending direction was cut out and hot forged under the conditions shown in Table 19 below using an upsetting device that freely extends only in one axial direction shown in FIG.

[0162] Here, condition 1 is data when the hot forging process is performed under the same conditions as in the second embodiment. The change in load pressure and the change in ingot height during the forging process are as shown in FIG.

Table 20 below shows the physical property values of the sintered ingot as a starting material for forging under each of the conditions 1 to 7.

[0164] FIG. 21 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 3;
FIG. 22 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 4;
FIG. 23 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 5;
FIG. 24 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 6;
FIG. 25 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 7.

As is clear from Table 19, the higher the temperature, the higher the ingot deformation speed. If the initial load pressure is the same, the deformation speed of the ingot becomes almost the same. It can be seen from FIGS. 21 to 25 that buckling occurs depending on the shape of the ingot.

In particular, when the deformation speed of the ingot was high, large buckling was observed.

For example, under the conditions 3 and 7 in which the ingot deformation speed is high, as apparent from FIGS. 21 and 25, it is understood that large buckling occurs.

In buckling, the vicinity of the upper and lower surfaces becomes a rigid region due to the frictional force between the upper and lower surfaces of the ingot, and the vicinity of the unconstrained surface becomes a deformation region. Therefore, a discontinuity in the deformation speed occurs at the boundary of the region. , Resulting from the ingot becoming barrel-shaped and eventually being sheared at this boundary. Cracking due to shearing is recovered by subsequent pressing or forming pressing (die forging) after free forging described in the eighth embodiment, but shearing must be prevented in advance to prevent buckling. There is.

[0169] Buckling can be avoided in advance by using a sintered ingot having a low ingot height with respect to the pressurized area as a starting material for forging. However, when it is desired to increase the forge ratio, using a sintered ingot having such a shape has a disadvantageous effect.

Tables 21 to 27 below show the physical properties of the forged ingots after forging under the above conditions 1 to 7.

[0171] That is, the measurement pieces shown in FIG. 20 were cut out from the forged ingots 14 obtained by performing the heat treatment at 400 ° C. for 24 hours after forging under the respective conditions 1 to 7, and the resistivity, density, Physical properties such as ratio, anisotropy ratio of resistivity, Seebeck constant, and power factor were measured. The results are shown in Tables 21 to 27 above.

[0172] Although there was almost no variation in the physical property values in the height direction and the width direction of the measurement piece (forged ingot 14), there was variation in the distribution of the physical property values in the spreading direction D. In Tables 21 to 27, physical properties are shown for each distance in the spreading direction D by averaging in the width direction.

The resistance anisotropy ratio of the sintered ingot which is the starting material for forging in Table 20 is compared with the anisotropy ratio of the resistance of the forged ingot after forging shown in Tables 21 to 27. As described above, in each of the conditions 1 to 7, the anisotropy ratio of the resistance is larger at the center of the forged ingot than before the forging, and it is understood that the orientation of the crystal grains is improved by the forging. For example, in the case of the condition 2, the anisotropy ratio of the resistance increases from 1.70 to 2.38 at a position 2 mm from the center of the ingot.

Further, it is presumed that the power factor is increased by forging under each of the conditions 1 to 7, and that the thermoelectric performance is improved by improving the orientation of crystal grains.
For example, in the case of Condition 2, the power factor is increased from 3.22 to 3.63 at a position 2 mm from the center of the ingot.

In this respect, in the case of the conditions 3 and 7, the orientation was improved only in a part of the center of the forged ingot. The results of comparison between Tables 20 and 23 and Tables 20 and 27 It is clear from the result of comparison. For example, the reason why the power factor of the condition 3 is larger than the value before the forging (3.53) after forging is that the power factor is 6 mm from the center of the forged ingot.
(3.79) only.

This means that, as described above, large buckling occurs during the hot forging process (see FIGS. 21 and 25), and the ingot breaks and separates. It is considered that the orientation of the crystal changed.

However, even under such forging conditions in which buckling is likely to occur, buckling can be avoided and the orientation can be improved by using a sintered ingot having a shape that does not easily cause buckling as described above. Is possible. This is because the orientation of the center of the ingot which is not easily affected by buckling is originally good.

The higher the temperature, the easier the plastic deformation proceeds, but it is necessary that the forging temperature is lower than the temperature at which the crystal grains grow and the orientation is lost. Specifically, the result of the ninth embodiment and the first to eighth embodiments is 55
It is desirable that the temperature be 0 ° C or less.

Conversely, when the forging temperature is low, the plastic deformation becomes slow and is not practical, but forging is possible at a temperature at which hot press sintering is possible. Specifically, from the results of the ninth embodiment and the first to eighth embodiments, the temperature is desirably 350 ° C. or more.

Regarding the load pressure during forging, it is necessary that the initial load pressure is a force equal to or higher than the yield stress of the sintered ingot. In addition, the load pressure must be such that the ingot deformation speed is lower than the ingot deformation speed at which buckling occurs. Specifically, from the results of the ninth embodiment and the first to eighth embodiments, it is desirable that the pressure is in the range of 70 kg / cm ^{2 to} 350 kg / cm ² .

As shown in FIGS. 21 to 25, in this embodiment, the buckling is minimized by changing the load pressure according to the shape (height) change of the ingot during forging. I have to. From the results of the ninth embodiment and the first to eighth embodiments, in order to avoid buckling, etc.
It has been found that the sintered ingot should not be pressed with an initial load pressure exceeding 00 kg / cm ² .

Next, a description will be given of an embodiment in which forging conditions are similarly changed for a p-type material.

That is, Bi of the same composition as in the third embodiment
A p-type thermoelectric semiconductor material of _0.4 Sb _1.6 Te ₃ was sintered by the same manufacturing method as in the third embodiment. Then, similarly to the third embodiment, a sintered ingot having a height (thickness) of 30 mm, a width of 40 mm, and a length of 18 mm in the extending direction is cut out, and is free only in the uniaxial direction shown in FIG. Hot forging was performed under the conditions 8 to 12 shown in Table 28 below using a spreading upsetting device.

Table 28 below shows the ingot deformation speed when hot forging was performed under the conditions 8 to 12 in which the temperature and the initial load pressure were changed.

[0185] Here, condition 8 is data when the hot forging process is performed under the same conditions as in the third embodiment.

Table 29 below shows the physical property values of the sintered ingot as a starting material for forging under each of the conditions 8 to 12.

[0187] FIG. 26 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 9;
FIG. 27 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 10;
FIG. 28 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 11;
FIG. 29 shows a change in load pressure (broken line) and a change in ingot height (solid line) during the forging process under the condition 12.

In particular, when the deformation speed of the ingot was high, large buckling was observed.

For example, in the case of the condition 10 in which the ingot deformation speed is high, it can be seen that large buckling occurs as is clear from FIG.

Tables 30 to 34 below show the physical property values of the forged ingot after forging under the above conditions 8 to 12.

[0191] That is, after forging under each of the conditions 8 to 12, the measuring pieces shown in FIG. 20 are cut out from the obtained forged ingots 14 and the resistivity, density ratio, resistivity anisotropy ratio, Seebeck Physical properties such as constants and power factors were measured. The results are shown in Tables 30 to 34 above.

Although there was almost no variation in the physical property values in the height direction and the width direction of the measuring piece (forged ingot 14), there was variation in the distribution of each physical property value in the extending direction D. In Tables 30 to 34, physical properties are shown for each distance in the spreading direction D by averaging in the width direction.

It can be seen by comparing the anisotropy ratio of the resistance of the sintered ingot as the starting material for forging in Table 29 with the anisotropy ratio of the resistance of the forged ingot after forging shown in Tables 30 to 34. As described above, in each of the conditions 8 to 12, the anisotropy ratio of the resistance is larger at the center of the forged ingot than before the forging, and it is understood that the orientation of the crystallite is improved by the forging.

Also, in the case of the p-type material, the range in which the orientation is improved extends to the end of the forged ingot in the case of the p-type material, and the influence of buckling is smaller for the n-type material. It can be seen that the orientation is more improved.

In the fourth to ninth embodiments described above,
Although the description has been made mainly with reference to a Bi ₂ Te ₃ -based thermoelectric semiconductor material as an example, a similar result can be obtained when the present invention is applied to a BiSb-based thermoelectric semiconductor material.

In the first to ninth embodiments described above,
Although the Bi ₂ Te ₃ -based thermoelectric semiconductor and the BiSb-based thermoelectric semiconductor have been described, the present invention is also applicable to other thermoelectric semiconductor materials having rhombohedrals.

In the present embodiment, the description has been made mainly on the assumption that the powder sintered body obtained by hot pressing (pressure sintering) is hot upset forged. It is not limited to.

The pressurized body obtained by pressing the solid solution powder may be hot upset forged, or the sintered body obtained by pressing the solid solution powder and then sintering may be hot upset forged. Moreover,
As shown in the comparative example, a material obtained by melting and solidifying a material (melted material) may be cut out as a desired solid solution block, and this may be directly subjected to hot upsetting forging.

Further, in the present embodiment, the description has been made on the assumption that the thermoelectric semiconductor material is obtained by hot forging. However, the hot forging method described in the present embodiment can be applied to any material.

The material to which the hot forging of the present invention is applied includes a magnetic material having a hexagonal structure, a layered structure, or a tungsten bronze structure, a dielectric material, and a superconductor material. Body, bismuth layered structure high-temperature superconductor, and the like.

[0201]

As described above, according to the method of the present invention, a thermoelectric semiconductor material having a high orientation and a high production yield can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing hot upsetting forging in a method of manufacturing a thermoelectric semiconductor according to the present invention.

FIG. 2 is a micrograph of a thermoelectric semiconductor material after hot upsetting forging according to the present invention.

FIG. 3 is a micrograph of a thermoelectric semiconductor material before hot upsetting forging according to the present invention.

FIG. 4 is a flowchart showing a method of manufacturing a thermoelectric semiconductor according to the present invention.

FIG. 5 is a diagram showing an upsetting device used in the method of the first embodiment of the present invention.

FIG. 6 is a view showing a result of measuring a relationship between forging time and ingot thickness in hot upsetting forging of the present invention.

FIG. 7 is a diagram showing a distribution of a density ratio of a quarter portion of the ingot to a single crystal.

FIG. 8 is a diagram showing the relationship between the pressing force and the thickness reduction of the ingot in the hot upsetting forging of the present invention.

FIG. 9 is a diagram showing an upsetting device used in the method according to the second embodiment of the present invention.

FIG. 10 is a diagram showing the relationship between pressure, time, and ingot thickness in the method according to the embodiment of the present invention.

FIG. 11 is a diagram showing a distribution of a density ratio of a quarter part of the ingot to a single crystal.

FIG. 12 shows a thermoelectric module.

FIG. 13 is a diagram showing a relationship between a heat radiation surface temperature and a maximum temperature difference of a thermoelectric module formed using a thermoelectric element material formed by the method of the present invention.

FIG. 14 is a diagram showing a relationship between a heat radiation surface temperature and a maximum temperature difference of a thermoelectric module formed using a thermoelectric element material formed by the method of the present invention.

FIG. 15 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 16 is a diagram showing a state where a forging process according to an embodiment of the present invention is repeatedly performed.

FIG. 17 is a view for explaining how to measure the strength of the thermoelectric module created in the example of the present invention.

FIG. 18 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 19 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 20 is a view showing a measuring piece for measuring physical properties of a forged ingot.

FIG. 21 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 22 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 23 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 24 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 25 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 26 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 27 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 28 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 29 is a diagram showing changes over time in pressure and ingot height in the method according to the embodiment of the present invention.

FIG. 30 is a diagram illustrating an upsetting device according to an embodiment of the present invention.

FIG. 31 is a diagram illustrating an upsetting device according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 base 2 sleeve 3 punch H cavity 5 p-type element 6 n-type element 7 bonding electrode 11 base 12 sleeve 13 punch

Continued on the front page (72) Inventor Takeshi Kajiwara 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture, Komatsu Ltd.

Claims (32)

[Claims] 1. A heating step of mixing and heating and melting material powders to have a desired composition; a solidification step of forming a solid solution ingot of a thermoelectric semiconductor material having a rhombohedral structure (hexagonal structure); A crushing step of crushing the solid solution ingot to form a solid solution powder; a sizing step of equalizing the particle diameter of the solid solution powder; and a sintering step of pressure sintering the solid solution powder having a uniform particle diameter. Hot powder plastic deformation of the powder sintered body by hot, and by spreading, the hot upsetting forging step of orienting the crystal grains of the powder sintered structure in the crystal orientation of excellent figure of merit, characterized by comprising Of producing thermoelectric semiconductor materials. 2. The production of a thermoelectric semiconductor material according to claim 1, wherein the hot upsetting forging step is an upsetting forging step in which the powder sintered body is spread only in a uniaxial direction while hot. Method. 3. The method according to claim 1, wherein the hot upsetting forging step is a step of expanding while pressing in a direction coinciding with a pressing direction in the sintering step. A method for producing the thermoelectric semiconductor material according to the above. 4. After the hot upsetting forging step,
The method for producing a thermoelectric semiconductor material according to claim 1, further comprising a heat treatment step of performing a heat treatment. 5. The heating step and the solidifying step heat and melt a mixture mainly containing bismuth, antimony, tellurium, and selenium to form a solid solution ingot of a Bi ₂ Te ₃ thermoelectric semiconductor material. The method for producing a thermoelectric semiconductor material according to claim 1, wherein 6. The method for producing a thermoelectric semiconductor material according to claim 5, further comprising a hydrogen reduction step of heat-treating the solid solution powder in a hydrogen atmosphere after the sizing step and prior to the sintering step. . 7. A heating method according to claim 1, wherein said heating step and said solidifying step heat and melt a mixture mainly composed of bismuth and antimony having a desired composition to form a solid solution ingot of a BiSb-based thermoelectric semiconductor material. The method for producing a thermoelectric semiconductor material according to claim 1. 8. A powder sintered material of a BiSb-based thermoelectric semiconductor material is hot-upset-forged and plastically deformed so that the crystal grains of the powder-sintered structure are oriented in a crystal orientation having an excellent figure of merit. A thermoelectric semiconductor material characterized in that it is formed. 9. A powder sintered material of a Bi ₂ Te ₃ based thermoelectric semiconductor material is hot-pressed and forged, and plastically deformed, so that the c-axis of the crystal grains of the powder sintered structure is oriented. A thermoelectric semiconductor material, characterized in that: 10. The powder sintered body of BiSb-based thermoelectric semiconductor material is hot upset forged in a state where it can be spread only in one axis direction and plastically deformed, whereby the crystal grains of the powder sintered structure have a figure of merit of performance index. A thermoelectric semiconductor material formed to be oriented in an excellent crystal orientation. 11. A powder sintered material of a Bi ₂ Te ₃ based thermoelectric semiconductor material is hot-upset forged in a state where it can be spread only in one axis direction and plastically deformed, whereby crystal grains of the powder sintered structure are reduced. A thermoelectric semiconductor material formed so that a c-axis is oriented. 12. p having a rhombohedral structure (hexagonal structure)
The p-type and n-type p-type and n-type thermoelectric semiconductor material powder sintered materials are hot-upset forged and plastically deformed, so that the cleaved faces of the crystal grains of the powder sintered structure are aligned. A thermoelectric semiconductor material; and a pair of electrodes fixed to the upper and lower surfaces of the p-type and n-type thermoelectric semiconductor materials so as to face each other, so that a current flows along the cleavage plane. A thermoelectric module characterized in that: 13. A hot upholstered forging of p-type and n-type Bi ₂ Te ₃ -based thermoelectric semiconductor material powders, respectively.
By plastically deforming, the p-type and n-type thermoelectric semiconductor materials in which the c-axis of the crystal grains of the powder sintered structure are oriented, and the upper and lower surfaces of the p-type and n-type thermoelectric semiconductor materials are opposed to each other. A thermoelectric module, comprising: a pair of electrodes fixed to each other; and a current flowing along a direction perpendicular to the c-axis. 14. The method for producing a thermoelectric semiconductor material according to claim 1, wherein the hot upsetting forging step is a step of hot upsetting the powder sintered body at a grain growth temperature or lower. . 15. The thermoelectric semiconductor according to claim 1, wherein the hot upsetting forging step is a step of hot upsetting the powder sintered body at 350 ° C. or more and 550 ° C. or less. Material manufacturing method. 16. The hot upsetting forging step, wherein the hot upsetting forging step is a step of hot upsetting so that the density ratio of the powder sintered body finally becomes 97% or more. Production method of thermoelectric semiconductor material. 17. The hot upsetting forging step is a step of hot upsetting the powder sintered body having a density ratio of 97% or more to finally make the density ratio or more. A method for producing a thermoelectric semiconductor material according to claim 1. 18. The hot upsetting forging step is a step of hot upsetting forging the powder sintered body at a load pressure of 500 kg / cm ² or less. Production method of thermoelectric semiconductor material. 19. The hot upsetting forging step is a step of hot upsetting forging the powder sintered body at an initial load pressure of 70 kg / cm ² or more and 350 kg / cm ² or less. 16. The method for producing a thermoelectric semiconductor material according to 5 or 7 or 15. 20. The hot upsetting forging step is a step of, after spreading the powder sintered body in a free direction, further applying pressure while regulating the free direction.
Or the method for producing a thermoelectric semiconductor material according to 7. 21. The hot die forging step of hot-molding and forging the powder sintered body after the hot upsetting forging step. A method for producing a thermoelectric semiconductor material. 22. The method of manufacturing a thermoelectric semiconductor material according to claim 1, wherein the hot upsetting forging step is repeated a plurality of times. 23. A powder sintered material of a BiSb-based thermoelectric semiconductor material is hot-injected and forged, and plastically deformed.
A thermoelectric semiconductor material having a density ratio of 97% or more. 24. A thermoelectric semiconductor material characterized by having a density ratio of 97% or more by hot upsetting and forging a plastic sintered material of a Bi ₂ Te ₃ thermoelectric semiconductor material and plastically deforming it. . 25. A heating step of mixing and heating and melting material powders to have a desired composition; a solidification step of forming a solid solution ingot of a thermoelectric semiconductor material having a rhombohedral structure (hexagonal structure); A pulverizing step of pulverizing the solid solution ingot to form a solid solution powder; a sizing step of making the particle diameter of the solid solution powder uniform; a pressurizing step of pressing the solid solution powder having a uniform particle diameter; A hot upsetting forging process in which the sintered compact is plastically deformed at the same time as hot sintering and spread, thereby sintering the crystal grains of the powder sintered structure while orienting them in a crystal orientation with an excellent figure of merit. A method for producing a thermoelectric semiconductor material, comprising: 26. A heating step of mixing and heating and melting material powders to have a desired composition; a solidification step of forming a solid solution ingot of a thermoelectric semiconductor material having a rhombohedral structure (hexagonal structure); A pulverizing step of pulverizing the solid solution ingot to form a solid solution powder; a sizing step of making the particle diameter of the solid solution powder uniform; a pressurizing step of pressing the solid solution powder having a uniform particle diameter; A sintering step of sintering the sintered body, and a plastic deformation of the sintered body by heating and spreading, whereby the crystal grains of the powder sintered structure are oriented in a crystal orientation having an excellent figure of merit. A method for producing a thermoelectric semiconductor material, comprising: an upset forging step. 27. A heating step of mixing and heating and melting material powders to have a desired composition; a solidification step of forming a solid solution ingot of a thermoelectric semiconductor material having a rhombohedral structure (hexagonal structure); A cutting step of cutting a solid solution ingot into a solid solution block of a desired size, and a hot swaging process in which the solid solution block is plastically deformed hot and spread to thereby orient crystal grains in a crystal orientation having an excellent figure of merit. A method for producing a thermoelectric semiconductor material, comprising: a forging step. 28. The hot upsetting forging step is a step of hot upsetting at a grain growth temperature or lower.
28. The method for producing a thermoelectric semiconductor material according to 26 or 27. 29. The hot upsetting forging step comprises the steps of:
28. The method for producing a thermoelectric semiconductor material according to claim 25, which is a step of hot upsetting and forging at a temperature of not less than 550C and not more than 550C. 30. The hot upsetting forging step comprises the steps of:
30. A hot upsetting forging process under a load pressure of not more than kg / cm ^2.
A method for producing the thermoelectric semiconductor material according to the above. 31. A step of hot-spreading a material having a desired composition in a free direction, and a step of, after spreading in the free direction, further applying pressure while regulating the free direction. By plastically deforming and spreading hot,
A hot forging method, wherein crystal grains of the structure of the material are oriented and a density ratio is set to a predetermined value or more. 32. A step of hot-spreading a material having a desired composition in a free direction; and a hot-die forging step of hot-molding and forging the spread material. A hot forging method, which comprises plastically deforming and spreading hot to orient the crystal grains of the structure of the material and increasing the density ratio to a predetermined value or more.