Room-temperature plastic forming method for improving performance of thermoelectric material

Abstract

The invention provides a room-temperature plastic forming method for improving the performance of a thermoelectric material. The room-temperature plastic forming method comprises the following steps that S1, the surface of the columnar thermoelectric material is evenly coated with graphite; and S2, the thermoelectric material coated with graphite is placed in an isolation sleeve with openings in the upper end and the lower end, then the thermoelectric material and the isolation sleeve are integrally placed in a cylindrical mold, the thermoelectric material and the isolation sleeve are compressed downwards at the same time, the thermoelectric material in the isolation sleeve is taken out after compression is finished, and the thermoelectric material subjected to plastic forming is obtained. The thermoelectric material prepared by the preparation method disclosed by the invention can complete the deformation exceeding 70% under the three-dimensional pressure stress greater than 1000MPa, and the forming condition is good; the morphology of the microstructure is changed into a compressed wrinkle shape from an original layered shape; when compression is performed at room temperature, recrystallization does not occur; the whole forming process is simple and efficient, and the mechanical property and the thermoelectric property are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric material forming, and in particular to a room-temperature plastic forming method for improving the performance of thermoelectric materials. Background Art

[0002] Thermoelectric materials (thermoelectricity materials) are functional materials that utilize the movement of carriers inside solids to directly convert thermal energy and electrical energy into each other, and have become key materials for forward-looking and strategic new energy technologies such as thermoelectric refrigeration and thermoelectric power generation. Thermoelectric materials have the advantages of simple structure, small volume, sensitive response, pollution-free, no wear, and low-carbon energy conservation. As the currently optimal thermoelectric material near room temperature, bismuth telluride-based alloy materials have been widely used in fields such as aerospace, microelectronics, and special power supplies. However, how to improve the ZT value, overcome the brittleness of the materials, and improve the compressive properties of the materials remains a research aspect worthy of attention.

[0003] Since thermoelectric materials are brittle materials, during the preparation and operation processes, they exhibit brittle fracture behavior similar to ceramic materials at room temperature and have large processing losses; defects or cracks will inevitably occur in the thermoelectric structure, and internal cracks in the materials will cause an increase in internal thermal resistance and resistance. At the same time, their mechanical properties are highly sensitive to the microstructure and defects of the materials, resulting in a significant decrease in the efficiency of thermoelectric devices and ultimately failure. In the patent with the application publication number CN 116985324A, the compression process is completed at 400-700°C, the provided stress is small, recrystallization will occur when the deformation amount reaches a certain level, and the heating and heat preservation steps greatly increase the time required for forming. Therefore, more stringent requirements are imposed on the mechanical strength and mechanical properties of thermoelectric materials. Therefore, in order to make them widely used, it is necessary to further solve problems such as the mechanical strength and mechanical properties of thermoelectric materials. Summary of the Invention

[0004] In view of this, the present invention proposes a room-temperature plastic forming method for improving the performance of thermoelectric materials to solve problems such as easy cleavage fracture, poor mechanical properties and formability of thermoelectric materials, and improve the mechanical properties and thermoelectric properties.

[0005] The technical solution of the present invention is realized as follows: The present invention provides a room-temperature plastic forming method for improving the performance of thermoelectric materials, which is characterized by including the following steps:

[0006] Step S1: Uniformly coat the surface of the columnar thermoelectric material with graphite;

[0007] Step S2: Place the thermoelectric material coated with graphite in an isolation sleeve with openings at both upper and lower ends, then place the thermoelectric material and the isolation sleeve as a whole in a cylindrical mold, and simultaneously compress the thermoelectric material and the isolation sleeve downward. After completion, take out the thermoelectric material in the isolation sleeve to obtain the plastically formed thermoelectric material.

[0008] Based on the above technical solutions, preferably, in step S1, the coating thickness of the graphite is 0.1% to 1% of the diameter of the thermoelectric material.

[0009] Based on the above technical solutions, preferably, the strain rate of the compression is 1 to 10 s -1 .

[0010] Based on the above technical solutions, preferably, in step S2, the wall thickness of the mold is 30% to 50% of the diameter of the thermoelectric material.

[0011] Based on the above technical solutions, preferably, in step S2, the inner diameter of the isolation sleeve is 0.5% to 1.5% larger than the diameter of the thermoelectric material, and the height of the isolation sleeve is the same as the height of the thermoelectric material coated with graphite.

[0012] Based on the above technical solutions, preferably, the outer diameter of the isolation sleeve is 0.5% to 1% smaller than the inner diameter of the mold, and the height of the isolation sleeve is lower than the height of the mold.

[0013] Based on the above technical solutions, preferably, in step S2, the hardness of the isolation sleeve is less than the hardness of the mold.

[0014] Based on the above technical solutions, preferably, in step S2, the material of the isolation sleeve is selected from at least one of TA1, TA2, TA3, and 45 steel.

[0015] Based on the above technical solutions, preferably, in step S2, the material of the mold is selected from at least one of 40Cr, 42CrMo, and TC4.

[0016] Based on the above technical solutions, preferably, in step S2, during compression, a pressure head and a gasket are respectively placed above and below the isolation sleeve.

[0017] Based on the above technical solutions, preferably, the materials of the pressure head and the gasket are independently selected from H13 and / or GCr15.

[0018] Based on the above technical solutions, preferably, the hardness of the pressure head and the gasket is greater than the hardness of the mold.

[0019] Based on the above technical solutions, preferably, the diameters of the pressure head and the gasket are 0.1% to 0.5% larger than the outer diameter of the isolation sleeve.

[0020] Based on the above technical solutions, preferably, in step S1, the thermoelectric material is selected from at least one of Bi2Te3, lead telluride, and silicon-germanium alloy.

[0021] According to another aspect of the present invention, the present invention provides a plastically formed thermoelectric material prepared by the above-mentioned plastic forming method.

[0022] As an optional implementation manner, the present invention is realized through the following technical solutions:

[0023] A room-temperature plastic forming method for improving the performance of a thermoelectric material, comprising the following steps:

[0024] S1. Repeatedly and uniformly coat the thermoelectric material with graphite;

[0025] S2. Place the thermoelectric material blank coated with graphite in an isolation layer, and then place the whole in a stress plasticizing layer;

[0026] S3. Select a punch and a gasket with appropriate dimensions and materials, and compress at a certain rate at room temperature;

[0027] S4. After compression, peel off the stress plasticizing layer and the isolation layer, take out the punch and the gasket, and thus obtain the plastically formed thermoelectric material.

[0028] The room-temperature plastic forming method of the present invention for improving the thermoelectric performance of a thermoelectric material has the following beneficial effects compared with the prior art:

[0029] The thermoelectric material prepared by this method effectively improves the mechanical properties and thermoelectric properties; among them, graphite has good lubricating properties and can form a lubricating film between two contact surfaces, reducing the frictional resistance, thereby reducing wear; it also has good chemical stability and is not easy to react with the sample, protecting the compression components from damage; coating a certain thickness of graphite on the surface of the thermoelectric material makes there a gap between the thermoelectric material and the isolation layer, thus preventing the thermoelectric material blank from adhering to the isolation layer during the subsequent compression process, and then it can be easily peeled off from under the mold. Among them, using a gasket during compression can ensure uniform stress distribution between the upper and lower contact surfaces of the thermoelectric material and the mold, adapting to its surface irregularity; the stress plasticizing layer and the isolation layer effectively reduce the tendency of the thermoelectric material to appear surface cracks or even breakage during compression; the entire forming process is carried out at room temperature, no recrystallization will occur, a deformation amount exceeding 70% can be completed, the forming condition is good, the hardness is increased by 60% compared with the hardness of the material before deformation, the mechanical properties are improved, the thermoelectric performance is increased by 5%, the energy consumption is reduced, and the productivity is improved.

[0030] The plastically formed thermoelectric material prepared by the present invention completes a deformation amount exceeding 70% under a triaxial compressive stress greater than 1000 MPa, and the forming condition is good; the morphology of the microstructure changes from the original layered shape to the wrinkled shape after compression; compression is carried out at room temperature, and no recrystallization will occur; the entire forming process is simple and efficient, and the mechanical properties and thermoelectric properties are significantly improved. Brief Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0032] Figure 1 It is a schematic flow chart of a room-temperature plastic forming method for improving the performance of thermoelectric materials provided by the present invention;

[0033] Figure 2 It is a schematic diagram of the forming process of the thermoelectric material in the present invention;

[0034] Figure 3 Among them, a. is the SEM image of the zone-melted bismuth telluride sample, b. is the SEM image of the bismuth telluride sample with a compressive deformation of 70% in Example 2, and c is an example diagram of recrystallization during high-temperature deformation;

[0035] Figure 4 Among them, a-c are thermoelectric materials prepared by traditional high-temperature forming methods, and d is the forming effect diagram of 70% room-temperature compression in Example 2 of the present invention;

[0036] Figure 5 It is a hardness comparison diagram of the undeformed bismuth telluride sample and the hardness with deformation amounts of 30%, 40, 50%, and 70% in the present invention. Detailed Embodiments

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] Refer to Figure 1 、 Figure 2 A room-temperature plastic forming method for improving the performance of thermoelectric materials and a schematic diagram of the forming process of the thermoelectric material provided by the present invention are as follows:

[0039] S1. Repeatedly and evenly coat the thermoelectric material with graphite.

[0040] Preferably, the graphite has good lubrication properties and can form a lubrication film between the two contact surfaces to reduce friction resistance and thus reduce wear; it also has good chemical stability and is not easy to react with the sample, thus protecting the compression components from damage; a layer of graphite of a certain thickness is coated on the surface of the thermoelectric material so that there is a gap between the thermoelectric material and the insulating layer, thereby preventing the thermoelectric material blank from adhering to the insulating layer during the subsequent compression process, and thus the blank can be peeled off from the mold;

[0041] Specifically, the graphite thickness of the graphite repeatedly and evenly coated on the thermoelectric material is 0.1% to 1% of the diameter of the thermoelectric material blank. If the graphite thickness is too small, it is not easy to peel off from the mold after compression, and the ability to protect the thermoelectric material from damage is small, resulting in cracks or even breakage. If the graphite thickness is too large, the cost of use will be increased, and the thickness of the graphite must be adapted to the gap between the thermoelectric material and the insulation layer.

[0042] S2. Placing the thermoelectric material blank coated with graphite in the insulating layer, and then placing the entire blank in the stress plasticization layer.

[0043] Preferably, the material of the insulating layer includes but is not limited to TA1, TA2, TA3 and 45 steel, and the material of the stress plasticizing layer includes but is not limited to 40Cr, 42CrMo and TC4. The hardness of the material selected for the stress plasticizing layer is greater than the hardness of the insulating layer material. The stress plasticizing layer can provide a stress greater than 1000 MPa to complete a compression deformation of more than 70%. If the required hardness requirement is not met, the thermoelectric material will break; the hardness of the insulating layer material is lower than that of the stress plasticizing layer and higher than that of the thermoelectric material, which can make the radial transmission of stress during the compression process more uniform, while bearing part of the compressive stress of the axial pressure head, avoiding the breakage caused by excessive or uneven stress changes on the thermoelectric material.

[0044] Specifically, the wall thickness of the stress plasticizing layer is 30% to 50% of the diameter of the thermoelectric material blank, the inner diameter of the insulating layer is 0.5% to 1.5% larger than the diameter of the thermoelectric material blank, and the outer diameter of the insulating layer is 0.5% to 1% smaller than the inner diameter of the stress plasticizing layer. The wall thickness range of the stress plasticizing layer and the insulating layer is a reasonable range that can provide the desired stress during the compression process. If the wall thickness of the stress plasticizing layer is too small, the ideal plasticizing effect cannot be achieved; if the wall thickness of the stress plasticizing layer is too large, the internal stress of the thermoelectric material will be too large during the compression process, affecting the forming effect. If the wall thickness of the insulating layer is too small, it cannot produce sufficient insulating and buffering effect; if the wall thickness of the insulating layer is too large, the internal stress of the thermoelectric material will be too large during the compression process, affecting the forming effect of the thermoelectric material.

[0045] S3. Select the indenter and gasket with appropriate size and material, and compress at a certain rate at room temperature;

[0046] Preferably, the materials of the indenter and the gasket include but are not limited to H13 and GCr15. The diameter ratio of the indenter and the gasket is 0.1% - 0.5% larger than the outer diameter of the isolation layer. The gasket can ensure uniform stress distribution between the upper and lower contact surfaces of the thermoelectric material and the mold, and adapt to surface irregularities. The minimum value of the diameter range of the indenter and the gasket is the summary of experience in the actual operation process, and the maximum value is the calculation result for adapting to the above stress plasticizing layer and isolation layer; if the diameter of the indenter and the gasket is too small, it cannot ensure uniform stress on the thermoelectric material and the gasket, and if it is too large, it will affect the stress plasticizing layer.

[0047] Specifically, "at a certain rate" means that the thermoelectric material is compressed at a strain rate of 1 - 10 s -1 . If the strain rate is too small, the forming is slow and the efficiency is low; if the strain rate is too large, the internal stress of the thermoelectric material changes violently, and there will be a phenomenon of fragmentation.

[0048] S4. After compression, peel off the stress plasticizing layer and the isolation layer, remove the indenter and the gasket, and then the plastically formed thermoelectric material can be obtained.

[0049] Through experimental verification, the thermoelectric material prepared by this method effectively improves the mechanical properties and thermoelectric properties. Graphite has good lubrication performance, can form a lubricating film between the two contact surfaces, reduce the frictional resistance, and thus reduce wear; it also has good chemical stability, is not easy to react with the specimen, and protects the compression components from damage; applying a certain thickness of graphite on the surface of the thermoelectric material creates a gap between the thermoelectric material and the isolation layer, thus preventing the thermoelectric material blank from adhering to the isolation layer during the subsequent compression process, and then it can be easily peeled off from the mold. Using a gasket during compression can ensure uniform stress distribution between the upper and lower contact surfaces of the thermoelectric material and the mold, and adapt to its surface irregularities; the stress plasticizing layer and the isolation layer effectively reduce the tendency of the thermoelectric material to have surface cracks or even fragmentation during compression; the entire forming process is carried out at room temperature, no recrystallization occurs, a deformation amount of more than 70% can be completed, the forming condition is good, the hardness is 60% higher than that of the material before deformation, the mechanical properties are improved, the thermoelectric properties are increased by 5%, the energy consumption is reduced, and the productivity is improved.

[0050] The following further elaborates on the present invention with specific embodiments.

[0051] Example 1

[0052] The present invention provides a room-temperature plastic forming method for improving the performance of thermoelectric materials. Using a P-type Bi2Te3 blank as the forming material, it specifically includes the following steps:

[0053] Step 1. Pretreat the thermoelectric material Bi2Te3: Use the thermoelectric material Bi2Te3 with a diameter of 19.8 mm and a height of 20 mm. First, place the Bi2Te3 thermoelectric material coated with 0.0198 mm graphite into an isolation sleeve with open upper and lower ends made of 45 steel, having an inner diameter of 20 mm, an outer diameter of 25 mm, and a height of 20 mm. Then, place it into a mold made of 42CrMo with an inner diameter of 25.2 mm, an outer diameter of 40 mm, a height of 25 mm, and a wall thickness of 7.4 mm. The selected punch is made of H13 die steel, with a diameter of 25.1 mm and a height of 27.5 mm. The selected gasket is made of H13 die steel, with a diameter of 25.1 mm and a thickness of 2 mm. H13 die steel can reach the required hardness level and has good fatigue and creep resistance. H13 die steel is harder than the stress plasticizing layer made of 40CrMo, thus preventing the punch from being damaged during compression.

[0054] Step 2. Compress the thermoelectric material Bi2Te3 at room temperature under a triaxial compressive stress of 372 MPa with a strain rate of 1 s -1 to make the Bi2Te3 thermoelectric material specimen complete a 50% deformation amount and have good forming conditions.

[0055] Step 3. Take out the thermoelectric material: After compression, peel off the mold made of 42CrMo and the isolation sleeve made of 45 steel, and take out the punch and gasket made of H13 die steel, then the plastically formed thermoelectric material is obtained.

[0056] After testing, the surface of the plastically formed thermoelectric material has no cracks, no recrystallization occurs, the hardness is 59.6 HV, which is 45% higher than that of the undeformed specimen, and the thermoelectric performance remains at the same level as the base material.

[0057] Example 2

[0058] The present invention provides a room-temperature plastic forming method for improving the performance of thermoelectric materials. Using a P-type Bi2Te3 blank as the forming material, it specifically includes the following steps:

[0059] Step 1. Pretreat the thermoelectric material Bi2Te3: Use the thermoelectric material Bi2Te3 with a diameter of 24.6 mm and a height of 20 mm. First, place the Bi2Te3 thermoelectric material coated with 0.0246 mm of graphite into an open-ended isolation sleeve made of TA1 with an inner diameter of 24.969 mm, an outer diameter of 35.046 mm, and a height of 20 mm, and then place it into a mold made of 42CrMo with an inner diameter of 35.4 mm, an outer diameter of 55 mm, a height of 25 mm, and a wall thickness of 9.8 mm; The selected indenter is made of GCr15, with a diameter of 35.1 mm and a height of 27.5 mm; The gasket is also made of GCr15, with a diameter of 35.1 mm and a thickness of 2 mm.

[0060] Step 2. Compress the thermoelectric material Bi2Te3 at room temperature under a triaxial compressive stress of 601.3 MPa with a strain rate of 10 s -1 so that the Bi2Te3 thermoelectric material specimen can complete a 70% deformation amount and has a good forming condition.

[0061] Step 3. Take out the thermoelectric material: After compression, peel off the mold made of 40CrMo and the isolation sleeve made of TA1, and take out the indenter and gasket made of GCr15, then the plastically formed thermoelectric material can be obtained.

[0062] After testing, the surface of the plastically formed thermoelectric material has no cracks, no recrystallization occurs, the hardness is 65.7 HV, which is 60% higher than that of the undeformed specimen, and the thermoelectric performance is improved by 5%. As Figure 3 shown, a. is the SEM image of the zone-melted bismuth telluride sample, b. is the SEM image of the bismuth telluride sample with a 70% compression deformation amount in Example 2, c. is an example diagram of recrystallization during high-temperature deformation; In Figure 3 a, the microscopic tissue morphology diagram of the bismuth telluride sample before deformation can be seen. A typical layered structure can be observed, and the direction is consistent with the seed crystal growth direction. Figure 3 b is the microscopic tissue morphology diagram parallel to the pressure direction of the bismuth telluride specimen at room temperature with a strain rate of 0.001 s -1 and a deformation amount of 70%. It can be seen that the internal layered structure turns into a wrinkled shape after plastic deformation. Figure 3 c is the microscopic tissue morphology diagram of the bismuth telluride specimen at 550 °C with a strain rate of 0.001 s -1 and a deformation amount of 32.7%. The recrystallization morphology can be observed. During the recrystallization process, the grains grow, which may reduce the thermoelectric performance and mechanical properties of the material.

[0063] As Figure 4 shown, from Figure 4It can be seen that cracks appear in the plastically formed thermoelectric materials prepared by traditional high-temperature forming methods (a-c), while there are no cracks in the thermoelectric materials formed by the room-temperature compression forming method of the present invention.

[0064] Example 3

[0065] The present invention provides a room-temperature plastic forming method for improving the performance of thermoelectric materials. Using a P-type Bi2Te3 blank as the forming material, it specifically includes the following steps:

[0066] Step 1: Pretreat the thermoelectric material Bi2Te3. Use a thermoelectric material Bi2Te3 with a diameter of 19.8 mm and a height of 20 mm. First, place the Bi2Te3 thermoelectric material coated with 0.198 mm of graphite into an open-ended isolation sleeve made of 45 steel with an inner diameter of 20 mm, an outer diameter of 25 mm, and a height of 20 mm. Then, place it into a mold made of 42CrMo with an inner diameter of 25.2 mm, an outer diameter of 40 mm, a height of 25 mm, and a wall thickness of 7.4 mm. The selected punch is made of H13 die steel, with a diameter of 25.1 mm and a height of 27.5 mm. The selected gasket is made of H13 die steel, with a diameter of 25.1 mm and a thickness of 2 mm. H13 die steel can reach the required hardness level and has good anti-fatigue and anti-creep properties. H13 die steel is harder than the stress plasticizing layer made of 40CrMo, thus preventing the punch from being damaged during compression.

[0067] Step 2: Compress the thermoelectric material Bi2Te3 at room temperature under a triaxial compressive stress of 372 MPa at a strain rate of 5 s -1 so that the Bi2Te3 thermoelectric material specimen can complete a 40% deformation amount and the forming condition is good.

[0068] Step 3: Take out the thermoelectric material. After compression, peel off the mold made of 42CrMo and the isolation sleeve made of 45 steel, and take out the punch and gasket made of H13 die steel, then the plastically formed thermoelectric material is obtained.

[0069] After testing, the surface of the plastically formed thermoelectric material has no cracks, no recrystallization occurs, the hardness is 53.43 HV, which is 30% higher than that of the undeformed specimen, and the thermoelectric performance remains at the same level as the base material.

[0070] Example 4

[0071] The present invention provides a room-temperature plastic forming method for improving the performance of thermoelectric materials. Using a P-type Bi2Te3 blank as the forming material, it specifically includes the following steps:

[0072] Step 1. Pretreat the thermoelectric material Bi2Te3: Use the thermoelectric material Bi2Te3 with a diameter of 19.8 mm and a height of 20 mm. First, place the Bi2Te3 thermoelectric material coated with 0.1 mm of graphite into an open-ended isolation sleeve made of 45 steel with an inner diameter of 20 mm, an outer diameter of 25 mm, and a height of 20 mm. Then, place it into a mold made of 42CrMo with an inner diameter of 25.2 mm, an outer diameter of 40 mm, a height of 25 mm, and a wall thickness of 7.4 mm. The selected punch is made of H13 die steel, with a diameter of 25.1 mm and a height of 27.5 mm. The selected gasket is made of H13 die steel, with a diameter of 25.1 mm and a thickness of 2 mm. H13 die steel can reach the required hardness level and has good anti-fatigue and anti-creep properties. H13 die steel is harder than the stress plasticizing layer made of 40CrMo, thus preventing the punch from being damaged during the compression process.

[0073] Step 2. Compress the thermoelectric material Bi2Te3 at room temperature under a triaxial compressive stress of 372 MPa with a strain rate of 8 s -1 so that the Bi2Te3 thermoelectric material specimen can complete a 30% deformation amount and has a good forming condition.

[0074] Step 3. Remove the thermoelectric material: After compression, peel off the mold made of 42CrMo and the open-ended isolation sleeve made of 45 steel at both ends, and remove the punch and gasket made of H13 die steel, then the plastically formed thermoelectric material can be obtained.

[0075] After testing, the surface of the plastically formed thermoelectric material has no cracks, no recrystallization occurs, the hardness is 52.6 HV, and the hardness is 28% higher than that of the undeformed specimen. The thermoelectric performance remains at the same level as that of the base material.

[0076] As Figure 5 shown, it can be seen from Figure 5 that the hardness of the undeformed bismuth telluride is the lowest, and its hardness increases with the increase of the deformation amount.

[0077] Comparative Example 1

[0078] Adopt the traditional high-temperature forming method, that is, without coating graphite, without adding a mold and an isolation sleeve, at a temperature of 500 - 600 °C and a strain rate of 0.001 s -1For downwards compression forming with a deformation amount of 10%, the sample will break, and its hardness and thermoelectric properties cannot be measured. However, for the thermoelectric material prepared by the method provided in the present invention, a deformation amount exceeding 70% can be completed under a triaxial compressive stress greater than 1000 MPa, and the forming condition is good; the morphology of the microstructure changes from the original layered shape to the folded shape after compression; when compressed at room temperature, recrystallization will not occur; the entire forming process is simple and efficient, and the mechanical properties and thermoelectric properties are significantly improved.

[0079] Comparative Example 2

[0080] Using the preparation method in Patent CN 116985324 A, by loading the thermoelectric brittle material blank into a hollow metal sleeve, filling bentonite in the gap between the thermoelectric brittle material blank and the hollow metal sleeve, and laying bentonite at both ends of the thermoelectric brittle material; heating the obtained hollow metal sleeve filled with the thermoelectric brittle material and bentonite to 400 - 700 °C and holding for 1 - 60 min, the compression process is completed at 400 - 700 °C. The provided stress is small, and recrystallization will occur when the deformation amount reaches a certain level. The heating and holding steps greatly increase the time required for forming. However, for the thermoelectric material prepared by the method provided in the present invention, a deformation amount exceeding 70% can be completed under a triaxial compressive stress greater than 1000 MPa, and the forming condition is good; the morphology of the microstructure changes from the original layered shape to the folded shape after compression; when compressed at room temperature, recrystallization will not occur; the entire forming process is simple and efficient, and the mechanical properties and thermoelectric properties are significantly improved.

[0081] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A room-temperature plastic forming method for improving the performance of thermoelectric materials, characterized in that, It includes the following steps: Step S1: Uniformly coat the surface of the columnar thermoelectric material with graphite; Step S2: Place the thermoelectric material coated with graphite into an isolation sleeve with openings at both upper and lower ends, then place the thermoelectric material and the isolation sleeve as a whole into a cylindrical mold, and simultaneously compress the thermoelectric material and the isolation sleeve downward. After completion, take out the thermoelectric material in the isolation sleeve to obtain the plastically formed thermoelectric material.

2. The plastic forming method according to claim 1, characterized in that, In the said step S1, the coating thickness of the graphite is 0.1% - 1% of the diameter of the thermoelectric material.

3. The plastic forming method according to claim 1, characterized in that, In the step S2, the compression strain rate is 1 to 10 s -1 .

4. The plastic forming method according to claim 1, characterized in that, In the said step S2, the wall thickness of the mold is 30% - 50% of the diameter of the thermoelectric material.

5. The plastic forming method according to claim 1, characterized in that, In the said step S2, the inner diameter of the isolation sleeve is 0.5% - 1.5% larger than the diameter of the thermoelectric material, and the height of the isolation sleeve is the same as the height of the thermoelectric material coated with graphite; The outer diameter of the isolation sleeve is 0.5% - 1% smaller than the inner diameter of the mold, and the height of the isolation sleeve is lower than the height of the mold.

6. The plastic forming method according to claim 1, characterized in that, In the said step S2, the hardness of the isolation sleeve is less than the hardness of the mold.

7. The plastic forming method according to claim 1, characterized in that In the said step S2, the material of the isolation sleeve is selected from at least one of TA1, TA2, TA3, and 45 steel; The material of the mold is selected from at least one of 40Cr, 42CrMo, and TC4.

8. The plastic forming method according to claim 1, characterized in that, In the said step S2, during compression, a punch and a gasket are respectively placed above and below the isolation sleeve; The materials of the punch and the gasket are independently selected from H13 and / or GCr15; The hardness of the punch and the gasket is greater than the hardness of the mold; The diameters of the punch and the gasket are 0.1% - 0.5% larger than the outer diameter of the isolation sleeve.

9. The plastic forming method according to claim 1, characterized in that, In the said step S1, the thermoelectric material is selected from at least one of Bi2Te3, lead telluride, and silicon-germanium alloy.

10. The plastically formed thermoelectric material prepared by the plastic forming method according to any one of claims 1 - 9.

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