A segmented thermoelectric single-arm connection method with high thermal shock resistance

Abstract

A method for connecting segmented thermoelectric single arms with high thermal shock resistance is disclosed, relating to the field of thermoelectric device manufacturing technology. This invention addresses the problem of poor thermal shock resistance in segmented thermoelectric single arms connected by traditional welding methods. The invention includes: cutting sintered thermoelectric material with a connecting layer into thermoelectric particles according to design dimensions and then polishing them; ultrasonically cleaning the thermoelectric particles and air-drying them; cutting metal foam according to design dimensions, ultrasonically cleaning it, and then drying it in an oven; applying solder paste to the surface of the metal foam, ensuring the paste fully fills the pores; simultaneously, uniformly applying solder paste to the surface of the thermoelectric particles to be welded; sequentially placing the treated low-temperature segment of the thermoelectric particles, the metal foam, and the high-temperature segment of the thermoelectric particles into a welding mold, and then placing the mold on a heating table for pressure brazing to obtain the segmented thermoelectric single arm. This invention is used for connecting segmented thermoelectric single arms with high thermal shock resistance.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric device manufacturing technology, and specifically to a segmented thermoelectric single-arm connection method with high thermal shock resistance. Background Technology

[0002] Thermoelectric materials enable the direct conversion of thermal energy into electrical energy. Segmented thermoelectric single arms, composed of thermoelectric materials with optimal performance across different temperature ranges, can significantly improve thermoelectric conversion efficiency. Thermal shock failure is a key factor limiting the long-term reliable operation of high-performance segmented thermoelectric devices in extreme environments such as deep space exploration. Taking the most widely studied cobaltite-Bi2Te3 segmented thermoelectric single arm in this field as an example, the thermoelectric single arm connected with traditional PbSnAg-based solder experiences interface cracking after a single thermal shock due to stress concentration caused by the significant mismatch in the thermal expansion coefficients between the solder and the thermoelectric material. This severely limits the long-term stable operation of high-performance segmented thermoelectric devices under extreme conditions.

[0003] Therefore, developing a segmented thermoelectric single-arm connection technology with high thermal shock resistance, strong interface bonding, and stable process is of great significance for promoting the practical application of high-performance segmented thermoelectric devices. Summary of the Invention

[0004] This invention addresses the problem of poor thermal shock resistance in segmented thermoelectric single-arm connections made using traditional welding methods.

[0005] Furthermore, a segmented thermoelectric single-arm connection method with high thermal shock resistance is proposed.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: This invention proposes a segmented thermoelectric single-arm connection method with high thermal shock resistance, comprising the following steps: Step 1: Cut the sintered thermoelectric material with connecting layer into thermoelectric particles according to the design dimensions, and polish the six sides of the particles. Step 2: Place the thermoelectric particles in anhydrous ethanol for ultrasonic cleaning and allow them to air dry naturally; Step 3: Cut the metal foam to the design size and place it in anhydrous ethanol for ultrasonic cleaning. After cleaning, dry it in an oven. Step 4: Apply solder paste to the surface of the metal foam, ensuring the solder paste fully fills the pores of the metal foam; at the same time, evenly apply solder paste to the surface of the thermoelectric particles to be soldered. Step 5: Place the processed low-temperature thermoelectric particle section, metal foam, and high-temperature thermoelectric particle section into the welding mold in sequence, and place the mold on the heating table for pressure brazing to obtain the segmented thermoelectric single arm.

[0007] Furthermore, the thermoelectric material mentioned in step one includes low-temperature thermoelectric materials and medium-high temperature thermoelectric materials. The low-temperature thermoelectric materials are suitable for 200-300℃, and the medium-high temperature thermoelectric materials are suitable for 500-600℃.

[0008] Furthermore, the low-temperature thermoelectric material is a Bi2Te3-based thermoelectric material, and the medium- and high-temperature thermoelectric material is a squartz-based thermoelectric material.

[0009] Furthermore, the low-temperature end connection layer of the Bi2Te3-based thermoelectric material adopts a Ni barrier layer, and the medium-temperature end connection layer adopts a porous Ti barrier layer and a Ni solderable layer; the medium-temperature end of the cobaltite-based thermoelectric material does not adopt a barrier layer, and the high-temperature end connection layer adopts a NiCr mixed powder barrier layer.

[0010] Furthermore, the sintering method employs spark plasma sintering or hot pressing sintering; the sintering pressure is 50-100 MPa, the sintering time is 5-60 minutes, and the sintering density is above 95%.

[0011] Furthermore, the cross-sectional dimensions of the thermoelectric particles are 4 mm × 4 mm, the height of the low-temperature thermoelectric material is 1.2 mm, and the height of the medium- and high-temperature thermoelectric material is 8.8 mm.

[0012] Furthermore, in step three, the metal foam is Ni foam; the thickness of the metal foam is 300 µm, the pore size is 50-150 µm, and the porosity is 83%; the cross-sectional dimensions of the metal foam are 4 mm × 4 mm.

[0013] Furthermore, in step four, the solder paste is a medium-high temperature solder paste with the composition Pb92.5Sn5Ag2.5; the particle size of the solder paste is 20-38 μm.

[0014] Furthermore, the heating table in step five is set to a temperature of 370 ℃, the welding process is carried out in an air atmosphere, and the pressure of the pressure brazing is 0.1-0.3 MPa.

[0015] Furthermore, the welding mold mentioned in step five is made of graphite. When in use, the low-temperature thermoelectric material, foam metal and high-temperature thermoelectric material are stacked vertically on the mold in sequence, and pressure is applied in the vertical direction.

[0016] The beneficial effects of this invention are: This invention employs a pressure brazing process, filling solder paste into a metal foam. The three-dimensional network structure of the metal foam creates a global confinement effect on the solder, significantly reducing the coefficient of thermal expansion of the weld layer and minimizing residual stress during welding and thermal stress during thermal shock. Furthermore, during thermal shock, the metal foam undergoes plastic deformation, actively absorbing and dissipating strain energy, preventing the rigid transfer of stress to vulnerable interfaces. These combined effects result in a significant improvement in the thermal shock resistance of the segmented thermoelectric single arm.

[0017] The thermoelectric single arm with a metal foam composite weld layer, prepared using the welding technology of this invention, maintained its interface integrity and exhibited excellent electrical contact performance after seven severe thermal shocks. It is predicted to withstand 79-90 cold start cycles in service, far exceeding the predicted maximum of 11 cold start cycles for thermoelectric single arms with traditional solder layers. These results demonstrate that the thermoelectric single arm with a metal foam composite weld layer prepared using this invention possesses outstanding thermal shock resistance and stability. Attached Figure Description

[0018] Figure 1 The images show the actual thermoelectric single arm with the metal foam composite weld layer in the embodiment after undergoing different numbers of thermal shocks. After seven rapid thermal shocks from 250 °C to room temperature, the interface remained intact. After the eighth thermal shock, the Ti barrier layer-Bi2Te3 interface cracked.

[0019] Figure 2 These are the interface secondary electron scanning images of the thermoelectric single arm with the metal foam composite weld layer in the embodiment, and the energy dispersive X-ray spectral surface scanning images of each component element.

[0020] Figure 3 The curve shows the change in the coefficient of thermal expansion of the traditional PbSnAg solder and metal foam composite welding layer with temperature in the implementation method. The addition of metal foam significantly reduces the coefficient of thermal expansion of the solder, which helps to improve the welding residual stress and thermal shock stress caused by thermal mismatch.

[0021] Figure 4 The images are secondary electron scanning images of the interface of the thermoelectric single arm with metal foam composite weld layer in the embodiment after experiencing different numbers of thermal shocks. Within seven thermal shocks, the interface remained intact and no macroscopic holes or cracks were observed. After the eighth thermal shock, the interface cracked at the Ti barrier layer-Bi2Te3 interface.

[0022] Figure 5 This is a diagram showing the displacement changes of interface markers in the thermoelectric single arm with a metal foam composite weld layer after welding and after three thermal shocks in the embodiment. (a) Region 1, containing markers 1, 2 and 3; (b) Region 2, containing markers 4, 5 and 6.

[0023] Figure 6 This is a bar graph showing the displacement changes of the interface markers of the thermoelectric single arm with the metal foam composite weld layer before and after thermal shock in the embodiment. The displacement changes originate from... Figure 5 The relative displacement changes of the markers after welding and thermal shock reveal that the markers underwent significant irreversible plastic deformation, which plays a role in absorbing and buffering interfacial thermal stress during thermal shock.

[0024] Figure 7 The images show the changes in interfacial contact resistivity of the thermoelectric single arm with the metal foam composite weld layer after experiencing different numbers of thermal shocks in the implementation method. After the second thermal shock, the interfacial resistivity shows an upward trend, which means that microscopic defects may appear at the interface.

[0025] Figure 8 The curve showing the relationship between the number of thermal shock test failures and the expected cold start cycle life calculated by the Coffin-Manson model in the implementation method shows that the thermoelectric single arm with the metal foam composite weld layer is expected to withstand 79-90 cold start cycles, which is much higher than the expected number of cold start cycles that the thermoelectric single arm with traditional solder connection can only withstand less than 11 cold start cycles. Detailed Implementation

[0026] This embodiment proposes a segmented thermoelectric single-arm connection method with high thermal shock resistance, the method comprising the following steps: Step 1: Cut the sintered thermoelectric material with connecting layer into thermoelectric particles according to the design dimensions, and polish the six sides of the particles, specifically including: Step 1.1: In a glove box with an argon atmosphere and an oxygen content of less than 1 ppm, according to the chemical formula Yb 0.3 Co4Sb 12 Weigh out Yb blocks, Co blocks, Sb particles and Si blocks in a stoichiometric ratio of / 0.05CoSi to obtain the weighed raw materials; Step 1.2: In an argon atmosphere with a water oxygen content of less than 1 ppm, place the weighed raw material into a quartz tube, use a vacuum pump to evacuate the quartz tube and seal it with a high-temperature flame, and place the sealed quartz tube containing the raw material into a muffle furnace. Step 1.3: Raise the temperature to 1150 ℃ at a heating rate of 5 ℃ / min~10 ℃ / min, hold at 1150 ℃ for 5 hours, then lower the temperature to 700 ℃ at a cooling rate of 5 ℃ / min~10 ℃ / min, and hold at 700 ℃ for 7 days. Step 1.4: Then cool with the furnace to obtain the smelted ingot. Place the smelted ingot in anhydrous ethanol for ultrasonic cleaning, and then grind it in an agate mortar to obtain N-type cobaltite powder. Step 1.5: Place an appropriate amount of powder into a graphite mold, and transfer the graphite mold to a hot pressing sintering furnace. Apply a uniaxial pressure of 60~80 MPa, and heat to 750 ℃ ​​at a rate of 80 ℃ / min~120 ℃ / min in a vacuum environment below 10 Pa. Hold at this temperature for 1 hour, and then cool to room temperature with the furnace to obtain N-type cobaltite blocks. Step 1.6: After grinding and cleaning the top and bottom ends of the block, place it in a graphite mold. Spread an appropriate amount of NiCr mixed powder on one end, where the mass ratio of Ni to Cr is 0.95. Transfer the graphite mold to a hot pressing sintering furnace, apply a uniaxial pressure of 60~80 MPa, and heat to 630 ℃ at a rate of 80 ℃ / min~120 ℃ / min in a vacuum environment below 10 Pa. Hold at this temperature for 20 minutes, and then cool to room temperature with the furnace to obtain an N-type cobaltite thermoelectric material with a NiCr barrier layer. Step 1.7: Cut the commercially available N-type Bi2Te3 extruded rods into appropriate sizes, place them in a graphite mold, cover one end with Ni powder, and cover the other end with Ti powder and Ni powder in turn. Step 1.8: Transfer the graphite mold to a spark plasma sintering furnace, apply a uniaxial pressure of 60~80 MPa, heat to 400 ℃ at a rate of 80 ℃ / min~120 ℃ / min in a vacuum environment below 10 Pa, hold for 5 minutes, and cool to room temperature with the furnace to obtain an N-type Bi2Te3 thermoelectric material with a Ti-Ni barrier layer at one end and a Ni barrier layer at the other end. Step 1.9: Cut the sintered thermoelectric material with connecting layer into thermoelectric particles with a cross-sectional size of 4 mm × 4 mm, and polish the six sides of the particles.

[0027] Step 2: Place the thermoelectric particles in anhydrous ethanol for ultrasonic cleaning for minutes, and then let them air dry naturally.

[0028] Step 3: Cut the Ni foam with a thickness of 300 µm, a pore size of 50-150 µm, and a porosity of 83% into 4 mm × 4 mm pieces, place them in anhydrous ethanol for ultrasonic cleaning, and then dry them in an oven at 60 °C. Step 4: Apply solder paste with a composition of Pb92.5Sn5Ag2.5 to the surface of Ni foam, so that the solder paste fully fills the pores of Ni foam, and then evenly apply the solder paste to the surface of the thermoelectric particles to be soldered. Step 5: Place the processed N-type Bi2Te3 thermoelectric particles, Ni foam, and N-type scotite thermoelectric particles layer by layer into the welding mold, and place the mold on the heating table. Set the heating table temperature to 370 ℃ and braze under pressure of 0.1-0.3 MPa to obtain the segmented thermoelectric single arm.

[0029] The pressure brazing process of this invention, which fills solder paste into a metal foam, utilizes the three-dimensional network structure of the metal foam to create a global confinement effect on the solder, significantly reducing the coefficient of thermal expansion of the weld layer and minimizing residual stress during welding and thermal stress during thermal shock. Furthermore, during thermal shock, the metal foam undergoes plastic deformation to actively absorb and dissipate strain energy, preventing the rigid transfer of stress to vulnerable interfaces. These combined effects result in a significant improvement in the thermal shock resistance of the segmented thermoelectric single arm.

[0030] Performance test results demonstrate that the thermoelectric single arm with a metal foam composite weld layer prepared using the welding technology of this invention maintains interface integrity and exhibits excellent electrical contact performance after seven severe thermal shocks. It is predicted to withstand 79-90 cold start cycles in service environments, far exceeding the predicted maximum of 11 cold start cycles for thermoelectric single arms with traditional solder layers. These results indicate that the thermoelectric single arm with a metal foam composite weld layer prepared using this technology possesses outstanding thermal shock resistance and stability.

[0031] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for connecting a segmented thermoelectric single arm with high thermal shock resistance, characterized in that, The method includes the following steps: Step 1: Cut the sintered thermoelectric material with connecting layer into thermoelectric particles according to the design dimensions, and polish the six sides of the particles. Step 2: Place the thermoelectric particles in anhydrous ethanol for ultrasonic cleaning and allow them to air dry naturally; Step 3: Cut the metal foam to the design size and place it in anhydrous ethanol for ultrasonic cleaning. After cleaning, dry it in an oven. Step 4: Apply solder paste to the surface of the metal foam, ensuring the solder paste fully fills the pores of the metal foam; at the same time, evenly apply solder paste to the surface of the thermoelectric particles to be soldered. Step 5: Place the processed low-temperature thermoelectric particle section, metal foam, and high-temperature thermoelectric particle section into the welding mold in sequence, and place the mold on the heating table for pressure brazing to obtain the segmented thermoelectric single arm.

2. The segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 1, characterized in that, The thermoelectric materials mentioned in step one include low-temperature thermoelectric materials and medium-high temperature thermoelectric materials. The low-temperature thermoelectric materials are suitable for 200-300℃, and the medium-high temperature thermoelectric materials are suitable for 500-600℃.

3. The segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 2, characterized in that, The low-temperature thermoelectric material is a Bi2Te3-based thermoelectric material, and the medium- and high-temperature thermoelectric material is a squartz-based thermoelectric material.

4. The segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 3, characterized in that, The low-temperature end connection layer of the Bi2Te3-based thermoelectric material adopts a Ni barrier layer, and the medium-temperature end connection layer adopts a porous Ti barrier layer and a Ni solderable layer; the medium-temperature end of the cobaltite-based thermoelectric material does not adopt a barrier layer, and the high-temperature end connection layer adopts a NiCr mixed powder barrier layer.

5. A segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 4, characterized in that, The sintering method is either spark plasma sintering or hot pressing sintering; the sintering pressure is 50-100 MPa, the sintering time is 5-60 minutes, and the sintering density is above 95%.

6. The segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 5, characterized in that, The cross-sectional dimensions of the thermoelectric particles are 4 mm × 4 mm, the height of the low-temperature thermoelectric material is 1.2 mm, and the height of the medium- and high-temperature thermoelectric material is 8.8 mm.

7. A segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 6, characterized in that, In step three, the metal foam is Ni foam; the thickness of the metal foam is 300 µm, the pore size is 50-150 µm, and the porosity is 83%; the cross-sectional dimensions of the metal foam are 4 mm × 4 mm.

8. A segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 7, characterized in that, In step four, the solder paste is a medium-high temperature solder paste with the composition Pb92.5Sn5Ag2.5 and a particle size of 20-38 μm.

9. A segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 8, characterized in that, The heating table in step five is set to a temperature of 370 ℃, the welding process is carried out in an air atmosphere, and the pressure of the pressure brazing is 0.1-0.3 MPa.

10. A segmented thermoelectric single-arm connection method with high thermal shock resistance according to claim 9, characterized in that, The welding mold mentioned in step five is made of graphite. When using it, the low-temperature thermoelectric material, foam metal and high-temperature thermoelectric material are stacked vertically on the mold in sequence, and pressure is applied in the vertical direction.

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