A brazing connection method for bismuth telluride thermoelectric material and electrode

Abstract

A method for brazing a bismuth telluride thermoelectric material and an electrode, relates to a method for brazing a thermoelectric material and an electrode. The purpose is to solve the problems of element diffusion between bismuth telluride and an electrode and low strength of the brazed joint in the current process of brazing a bismuth telluride thermoelectric material and an electrode. Method: Electroplating a Ni coating on the surface to be welded of the bismuth telluride thermoelectric material, electroplating a NiMo alloy coating on the Ni coating, placing a brazing sheet between the surface to be welded of the bismuth telluride thermoelectric material and the surface to be welded of the electrode for assembly, and brazing. The present invention electroplates a Ni / NiMo composite barrier layer on the surface of bismuth telluride, and uses a tin-based brazing material to braze the bismuth telluride and the electrode. The Ni / NiMo composite barrier layer is densely combined with the bismuth telluride, which effectively solves the problems of element diffusion and low strength of the joint between bismuth telluride and the electrode in the existing welding of bismuth telluride thermoelectric materials and electrodes.

Description

Technical Field

[0001] The invention relates to a method for brazing and connecting a thermoelectric material and an electrode. Background Art

[0002] Bismuth telluride (Bi 2 Te 3 ) has good thermoelectric performance, good conductivity and high stability in the low temperature range (room temperature to 300°C). Brazing connection has low temperature, little damage to the parent material, simple and controllable process and high efficiency, so it is widely used in the connection of bismuth telluride thermoelectric materials and electrodes.

[0003] Reliable metallurgical bonding between bismuth telluride and electrodes is a very important part in the preparation of high-quality thermoelectric devices. Currently, tin-based solder is mostly used to connect bismuth telluride and electrodes. Tin-based solder has a low melting point and good wetting with bismuth telluride thermoelectric materials, but the element diffusion problem needs to be solved urgently. During the brazing process, tin elements diffuse with antimony and tellurium elements in bismuth telluride to form a brittle reaction layer. In actual service, the continuously thickening brittle reaction layer will reduce the connection strength of the joint, and sharply deteriorate the thermoelectric performance of the device, affecting the long-term service stability. Therefore, it is extremely important to design a method to achieve reliable connection between bismuth telluride thermoelectric materials and electrodes. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of element diffusion between bismuth telluride and electrode and low strength of brazed joint in the current process of brazing connection of bismuth telluride thermoelectric material and electrode, and to propose a brazing connection method of bismuth telluride thermoelectric material and electrode.

[0005] The brazing connection method of the bismuth telluride thermoelectric material and the electrode of the present invention is carried out according to the following steps:

[0006] 1. Cutting the bismuth telluride thermoelectric material, then grinding, polishing and ultrasonic cleaning the surface to be welded of the bismuth telluride thermoelectric material in turn, and finally electroplating a Ni coating on the surface to be welded of the bismuth telluride thermoelectric material; the thickness of the Ni coating is 1 to 5 μm;

[0007] In step 1, the process of electroplating the Ni coating on the surface to be welded of the bismuth telluride thermoelectric material is as follows: the electroplating temperature is 45-60°C, the current density is 1-15A / dm 2 , the electroplating time is 1 to 10 minutes;

[0008] In step 1, the electroplating solution used for electroplating the Ni plating layer on the to-be-welded surface of the bismuth telluride thermoelectric material contains 200-400 g / L of nickel sulfate, 20-40 g / L of nickel chloride, 30-40 g / L of boric acid, and 0.05-0.1 g / L of sodium dodecyl sulfate;

[0009] 2. Electroplating a NiMo alloy coating on the Ni coating to obtain a Ni / NiMo composite barrier layer with a thickness of 3 to 20 μm; then polishing and ultrasonically cleaning the Ni / NiMo composite barrier layer to obtain a bismuth telluride thermoelectric material to be welded; grinding and ultrasonically cleaning the surface of the electrode to be welded to obtain an electrode to be welded;

[0010] The process of electroplating the NiMo alloy coating on the Ni coating in step 2 is as follows: the electroplating temperature is 30-50°C, the current density is 4-16A / dm 2 , the electroplating time is 5 to 40 minutes;

[0011] The electroplating solution used for electroplating the NiMo alloy coating on the Ni coating in step 2 contains 25-55 g / L of basic sodium carbonate, 5-15 g / L of sodium molybdate, 30-70 g / L of sodium citrate, 10-30 g / L of sodium chloride, 1.0-3.0 g / L of saccharin and 20-25 mL / L of concentrated ammonia water;

[0012] The electrode material in step 2 is Cu-based alloy, Fe-based alloy, Ni-based alloy, or Co-based alloy;

[0013] 3. placing the brazing sheet between the to-be-welded surface of the bismuth telluride thermoelectric material and the to-be-welded surface of the electrode for assembly, brazing, and then cooling with the furnace to complete the brazing connection between the bismuth telluride thermoelectric material and the electrode;

[0014] The brazing connection process in step 3 is: heating to 160-200° C. in an atmospheric environment, keeping the temperature at 160-200° C. for 1-10 min, and then cooling to room temperature at a cooling rate of 1-10° C. / min to complete the brazing connection between the bismuth telluride thermoelectric material and the electrode;

[0015] The solder sheet in step three is SnIn solder, SnBi solder or SnBiAg solder.

[0016] The principles and beneficial effects of the present invention are:

[0017] 1. The present invention electroplates a Ni / NiMo composite barrier layer on the surface of bismuth telluride, and uses a tin-based solder to braze the bismuth telluride and the electrode, so that the Ni / NiMo composite barrier layer is densely combined with the bismuth telluride. Among them, the Ni layer plays a role in adjusting the linear expansion coefficient of the joint and relieving the residual stress of the joint; and the high-melting-point Mo element in the NiMo layer increases the energy barrier for the elements in the bismuth telluride thermoelectric material to diffuse into the composite barrier layer, which is conducive to the diffusion of barrier elements. At the same time, the solder wets the composite barrier layer well, no holes or cracks are generated, and the diffusion reaction layer is very thin. The shear strength of the obtained joint can reach 18MPa at room temperature, and the diffusion of interface elements is slow, which effectively solves the problem of easy element diffusion and low joint strength between bismuth telluride and electrodes in the existing welding of bismuth telluride thermoelectric materials and electrodes.

[0018] 2. The present invention adopts a soft soldering method to connect bismuth telluride and the electrode, and uses a tin-based solder. The soldering temperature is low, the linear expansion coefficient is well matched, the residual stress in the joint is small, and the connection strength is high.

[0019] 3. The present invention can obtain a brazing connection method for bismuth telluride thermoelectric material and electrode, realize direct welding of bismuth telluride thermoelectric material and electrode, and the process control is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the Bi obtained in Example 1 2 Te 3 / Ni / NiMo / SnBi joint interface structure SEM image. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any reasonable combination of the specific implementation modes.

[0022] Specific implementation method 1: In this implementation method 1, the bismuth telluride thermoelectric material is cut, and then the surface to be welded of the bismuth telluride thermoelectric material is grinded, polished and ultrasonically cleaned in sequence, and finally a Ni coating is electroplated on the surface to be welded of the bismuth telluride thermoelectric material; the thickness of the Ni coating is 1 to 5 μm;

[0023] In step 1, the process of electroplating the Ni coating on the surface to be welded of the bismuth telluride thermoelectric material is as follows: the electroplating temperature is 45-60°C, the current density is 1-15A / dm 2 , the electroplating time is 1 to 10 minutes;

[0024] In step 1, the electroplating solution used for electroplating the Ni plating layer on the to-be-welded surface of the bismuth telluride thermoelectric material contains 200-400 g / L of nickel sulfate, 20-40 g / L of nickel chloride, 30-40 g / L of boric acid, and 0.05-0.1 g / L of sodium dodecyl sulfate;

[0025] 2. Electroplating a NiMo alloy coating on the Ni coating to obtain a Ni / NiMo composite barrier layer with a thickness of 3 to 20 μm; then polishing and ultrasonically cleaning the Ni / NiMo composite barrier layer to obtain a bismuth telluride thermoelectric material to be welded; grinding and ultrasonically cleaning the surface of the electrode to be welded to obtain an electrode to be welded;

[0026] The process of electroplating the NiMo alloy coating on the Ni coating in step 2 is as follows: the electroplating temperature is 30-50°C, the current density is 4-16A / dm 2 , the electroplating time is 5 to 40 minutes;

[0027] The electroplating solution used for electroplating the NiMo alloy coating on the Ni coating in step 2 contains 25-55 g / L of basic sodium carbonate, 5-15 g / L of sodium molybdate, 30-70 g / L of sodium citrate, 10-30 g / L of sodium chloride, 1.0-3.0 g / L of saccharin and 20-25 mL / L of concentrated ammonia water;

[0028] The electrode material in step 2 is Cu-based alloy, Fe-based alloy, Ni-based alloy, or Co-based alloy;

[0029] 3. placing the brazing sheet between the to-be-welded surface of the bismuth telluride thermoelectric material and the to-be-welded surface of the electrode for assembly, brazing, and then cooling with the furnace to complete the brazing connection between the bismuth telluride thermoelectric material and the electrode;

[0030] The brazing connection process in step 3 is: heating to 160-200° C. in an atmospheric environment, keeping the temperature at 160-200° C. for 1-10 min, and then cooling to room temperature at a cooling rate of 1-10° C. / min to complete the brazing connection between the bismuth telluride thermoelectric material and the electrode;

[0031] The solder sheet in step three is SnIn solder, SnBi solder or SnBiAg solder.

[0032] 1. In this embodiment, a Ni / NiMo composite barrier layer is electroplated on the surface of bismuth telluride, and tin-based solder is used to braze the bismuth telluride and the electrode, so that the Ni / NiMo composite barrier layer is densely bonded to the bismuth telluride. Among them, the Ni layer plays a role in adjusting the linear expansion coefficient of the joint and relieving the residual stress of the joint; and the high-melting-point Mo element in the NiMo layer increases the energy barrier for the elements in the bismuth telluride thermoelectric material to diffuse into the composite barrier layer, which is conducive to the diffusion of barrier elements. At the same time, the solder wets the composite barrier layer well, no holes or cracks are generated, and the diffusion reaction layer is very thin. The shear strength of the resulting joint can reach 18MPa at room temperature, and the diffusion of interface elements is slow, which effectively solves the problem of easy element diffusion and low joint strength between bismuth telluride and electrodes in the existing welding of bismuth telluride thermoelectric materials and electrodes.

[0033] 2. This embodiment uses a soft soldering method to connect bismuth telluride and the electrode, using tin-based solder, with a low brazing temperature, good linear expansion coefficient matching, small residual stress in the joint, and high connection strength.

[0034] 3. This embodiment can obtain a brazing connection method for bismuth telluride thermoelectric material and electrode, realize direct welding of bismuth telluride thermoelectric material and electrode, and the process control is simple.

[0035] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that: in step 1, the bismuth telluride thermoelectric material is cut using a diamond cutting machine, and the size of the cut bismuth telluride thermoelectric material is 4 mm×4 mm×4 mm.

[0036] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that: in step one, the surface to be welded of the bismuth telluride thermoelectric material is polished using 1000#, 1500#, 2000#, 3000# and 5000# metallographic sandpaper in sequence, and then polished using a polishing agent with a particle size of 1.0μm, and then ultrasonically cleaned in acetone for 10 to 20 minutes.

[0037] Specific implementation method 4: This implementation method is different from any one of specific implementation methods 1 to 3 in that: in step 2, the Ni / NiMo composite barrier layer is polished using a polishing paste with a particle size of 1.5 μm, and then ultrasonically cleaned in acetone for 10 to 20 minutes.

[0038] Specific implementation method 5: This implementation method is different from specific implementation methods 1 to 4 in that: in step 2, the surface of the electrode to be welded is polished with 2000# metallographic sandpaper and then ultrasonically cleaned in acetone for 10 to 20 minutes.

[0039] Specific implementation method 6: This implementation method is different from any one of specific implementation methods 1 to 5 in that: the thickness of the solder in step 3 is 0.09 to 0.11 mm.

[0040] Specific implementation method 7: This implementation method is different from any one of specific implementation methods 1 to 6 in that the heating rate in step 3 is 5 to 10° C. / min.

[0041] Specific embodiment 8: This embodiment differs from any one of specific embodiments 1 to 7 in that: in step 1, the process of electroplating the Ni coating on the surface to be welded of the bismuth telluride thermoelectric material is as follows: the electroplating temperature is 50°C, the current density is 15A / dm 2 , the electroplating time is 1min.

[0042] Specific embodiment nine: This embodiment differs from any one of specific embodiments one to eight in that: in step one, the plating solution used for electroplating the Ni plating layer on the surface to be welded of the bismuth telluride thermoelectric material contains 400 g / L nickel sulfate, 40 g / L nickel chloride, 40 g / L boric acid, and 0.1 g / L sodium dodecyl sulfate.

[0043] Specific embodiment ten: This embodiment differs from any one of specific embodiments one to nine in that: the brazing connection process in step three is: heating to 190°C in an atmospheric environment at a heating rate of 8°C / min, keeping at 190°C for 3 minutes, and then cooling to room temperature at a cooling rate of 5°C / min.

[0044] Embodiment 1:

[0045] The brazing connection method of the bismuth telluride thermoelectric material and the electrode in this embodiment is carried out according to the following steps:

[0046] 1. Cut the bismuth telluride thermoelectric material, then grind, polish and ultrasonically clean the surface to be welded, and then electroplate at 50°C and 15A / dm 2 At a current density of , a Ni coating is electroplated on the surface to be welded of the bismuth telluride thermoelectric material for 1 minute. The thickness of the Ni coating is 3 μm. The electroplating solution used contains 400 g / L nickel sulfate, 40 g / L nickel chloride, 40 g / L boric acid, and 0.1 g / L sodium dodecyl sulfate. The surface to be welded of the bismuth telluride thermoelectric material is polished with 1000#, 1500#, 2000#, 3000#, and 5000# metallographic sandpapers in sequence, and then polished with a polishing agent with a particle size of 1.0 μm, and then ultrasonically cleaned in acetone for 15 minutes.

[0047] 2. Plate the bismuth telluride thermoelectric material with Ni coating on the surface to be welded, and then electroplate it at 40℃ and 8A / dm 2 At a current density of , a NiMo alloy coating is electroplated on the surface to be welded for 10 min. The thickness of the NiMo alloy coating is 5 μm. The electroplating solution used contains 40 g / L of basic sodium carbonate, 10 g / L of sodium molybdate, 50 g / L of sodium citrate, 20 g / L of sodium chloride, 2.0 g / L of saccharin and 24 mL / L of concentrated ammonia water; finally, the surface of the NiMo alloy coating is polished and ultrasonically cleaned to obtain the bismuth telluride thermoelectric material to be welded; the surface of the copper electrode to be welded is polished and ultrasonically cleaned to obtain the copper electrode to be welded;

[0048] The Ni / NiMo composite barrier layer was polished with a polishing paste having a particle size of 1.5 μm, and then ultrasonically cleaned in acetone for 15 minutes; the surface to be welded of the copper electrode was polished with 2000# metallographic sandpaper, and then ultrasonically cleaned in acetone for 15 minutes;

[0049] 3. Place the SnBi solder sheet between the bismuth telluride thermoelectric material to be welded and the copper electrode to be welded to obtain the welded connection. Heat the connection to be welded to 190°C in an atmospheric environment at a heating rate of 8°C / min, and keep it at 190°C for 3 minutes, then cool it to room temperature at a cooling rate of 5°C / min to complete the brazing connection between the bismuth telluride thermoelectric material and the copper electrode; the size of the solder sheet in step 3 is 6mm×6mm×0.1mm;

[0050] Figure 1 is the Bi obtained in Example 1 2 Te 3 / Ni / NiMo / SnBi joint interface microstructure SEM image; Figure 1 From left to right in the table are Bi 2 Te 3, Ni coating, NiMo alloy coating, SnBi solder. It can be seen that the Ni / NiMo composite coating is well bonded to the bismuth telluride, and no holes or cracks are found between the layers, achieving a good transition of the linear expansion coefficient. The SnBi solder and the composite coating are well wetted, and no brittle reaction layer appears, forming a reliable metallurgical bond, which improves the thermoelectric properties of the bismuth telluride brazed joint. In summary, the brazing connection effect between the bismuth telluride thermoelectric material and the copper electrode in this embodiment is very excellent. At the same time, the mechanical properties of the brazed connection between the bismuth telluride thermoelectric material and the copper electrode were tested, and the test results showed that the shear strength of the joint can reach 14MPa at room temperature.

[0051] Embodiment 2: A method for brazing a bismuth telluride thermoelectric material and an electrode, which is carried out according to the following steps:

[0052] 1. Cut the bismuth telluride thermoelectric material, then grind, polish and ultrasonically clean the surface to be welded, and then electroplate at 50°C and 15A / dm 2 At a current density of , a Ni coating is electroplated on the surface to be welded of the bismuth telluride thermoelectric material for 1 minute. The thickness of the Ni coating is 3 μm. The electroplating solution used contains 400 g / L nickel sulfate, 40 g / L nickel chloride, 40 g / L boric acid, and 0.1 g / L sodium dodecyl sulfate. The surface to be welded of the bismuth telluride thermoelectric material is polished with 1000#, 1500#, 2000#, 3000#, and 5000# metallographic sandpapers in sequence, and then polished with a polishing agent with a particle size of 1.0 μm, and then ultrasonically cleaned in acetone for 15 minutes.

[0053] 2. Plate the bismuth telluride thermoelectric material with Ni coating on the surface to be welded, and then electroplate it at 40℃ and 8A / dm 2 At a current density of , a NiMo alloy coating is electroplated on the surface to be welded for 10 minutes. The thickness of the NiMo alloy coating is 5 μm. The electroplating solution used contains 40 g / L of basic sodium carbonate, 10 g / L of sodium molybdate, 50 g / L of sodium citrate, 20 g / L of sodium chloride, 2.0 g / L of saccharin and 24 mL / L of concentrated ammonia water; finally, the surface of the NiMo alloy coating is polished and ultrasonically cleaned to obtain the bismuth telluride thermoelectric material to be welded; the surface of the copper electrode to be welded is polished and ultrasonically cleaned to obtain the copper electrode to be welded;

[0054] The Ni / NiMo composite barrier layer was polished with a polishing paste having a particle size of 1.5 μm, and then ultrasonically cleaned in acetone for 15 minutes; the surface to be welded of the copper electrode was polished with 2000# metallographic sandpaper, and then ultrasonically cleaned in acetone for 15 minutes;

[0055] 3. Place the SnBi solder sheet coated with flux between the bismuth telluride thermoelectric material to be welded and the copper electrode to be welded to obtain a welded connection. Heat the connection to be welded to 200°C in an atmospheric environment at a heating rate of 8°C / min, and keep it at 200°C for 3 minutes, then cool it down to room temperature at a cooling rate of 5°C / min to complete the brazing connection between the bismuth telluride thermoelectric material and the copper electrode;

[0056] The size of the solder sheet in step 3 is 6mm×6mm×0.1mm;

[0057] The brazed joint between the bismuth telluride thermoelectric material and the copper electrode in this embodiment has a dense structure and high stability, and the room temperature shear strength of the joint is as high as 18 MPa.

Claims

1. A method for brazing a bismuth telluride thermoelectric material and an electrode, Features: The brazing connection method of bismuth telluride thermoelectric material and electrode is carried out in the following steps:

1. Cutting the bismuth telluride thermoelectric material, then grinding, polishing and ultrasonic cleaning the surface to be welded of the bismuth telluride thermoelectric material in turn, and finally electroplating a Ni coating on the surface to be welded of the bismuth telluride thermoelectric material; the thickness of the Ni coating is 1 to 5 μm; In step 1, the process of electroplating the Ni coating on the surface to be welded of the bismuth telluride thermoelectric material is as follows: the electroplating temperature is 45-60°C, the current density is 1-15A / dm 2 , the electroplating time is 1 to 10 minutes; In step 1, the electroplating solution used for electroplating the Ni plating layer on the to-be-welded surface of the bismuth telluride thermoelectric material contains 200-400 g / L of nickel sulfate, 20-40 g / L of nickel chloride, 30-40 g / L of boric acid and 0.05-0.1 g / L of sodium dodecyl sulfate; 2. Electroplating a NiMo alloy coating on the Ni coating to obtain a Ni / NiMo composite barrier layer with a thickness of 3 to 20 μm; then polishing and ultrasonically cleaning the Ni / NiMo composite barrier layer to obtain a bismuth telluride thermoelectric material to be welded; grinding and ultrasonically cleaning the surface of the electrode to be welded to obtain an electrode to be welded; The process of electroplating the NiMo alloy coating on the Ni coating in step 2 is as follows: the electroplating temperature is 30-50°C, the current density is 4-16A / dm 2 , the electroplating time is 5 to 40 minutes; The electroplating solution used for electroplating the NiMo alloy coating on the Ni coating in step 2 contains 25-55 g / L of basic sodium carbonate, 5-15 g / L of sodium molybdate, 30-70 g / L of sodium citrate, 10-30 g / L of sodium chloride, 1.0-3.0 g / L of saccharin and 20-25 mL / L of concentrated ammonia water; The electrode material in step 2 is Cu-based alloy, Fe-based alloy, Ni-based alloy or Co-based alloy; 3. placing the brazing sheet between the to-be-welded surface of the bismuth telluride thermoelectric material and the to-be-welded surface of the electrode for assembly, brazing, and then cooling with the furnace to complete the brazing connection between the bismuth telluride thermoelectric material and the electrode; The brazing connection process in step 3 is: heating to 160-200° C. in an atmospheric environment, keeping the temperature at 160-200° C. for 1-10 min, and then cooling to room temperature at a cooling rate of 1-10° C. / min to complete the brazing connection between the bismuth telluride thermoelectric material and the electrode; The solder sheet in step three is SnIn solder, SnBi solder or SnBiAg solder.

2. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: In step 1, the bismuth telluride thermoelectric material is cut using a diamond cutting machine, and the size of the cut bismuth telluride thermoelectric material is 4 mm×4 mm×4 mm.

3. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: In step 1, the surface to be welded of the bismuth telluride thermoelectric material is polished using 1000#, 1500#, 2000#, 3000# and 5000# metallographic sandpaper in sequence, and then polished using a polishing agent with a particle size of 1.0 μm, and then ultrasonically cleaned in acetone for 10 to 20 minutes.

4. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: In step 2, the Ni / NiMo composite barrier layer is polished using a polishing paste with a particle size of 1.5 μm, and then ultrasonically cleaned in acetone for 10 to 20 minutes.

5. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: In step 2, the surface of the electrode to be welded is polished with 2000# metallographic sandpaper, and then ultrasonically cleaned in acetone for 10 to 20 minutes.

6. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: The thickness of the solder in step 3 is 0.09-0.11 mm.

7. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: In step 3, the heating rate is 5-10°C / min.

8. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: In step 1, the process of electroplating Ni on the surface of the bismuth telluride thermoelectric material to be welded is as follows: the electroplating temperature is 50°C, the current density is 15A / dm 2 , the electroplating time is 1min.

9. The brazing connection method of the bismuth telluride thermoelectric material and the electrode according to claim 1, Features: In step 1, the electroplating solution used for electroplating the Ni plating layer on the to-be-welded surface of the bismuth telluride thermoelectric material contains 400 g / L of nickel sulfate, 40 g / L of nickel chloride, 40 g / L of boric acid, and 0.1 g / L of sodium dodecyl sulfate.

10. The brazing connection method of bismuth telluride thermoelectric material and electrode according to claim 1, Features: The brazing connection process in step 3 is: heating to 190°C in an atmospheric environment at a heating rate of 8°C / min, keeping at 190°C for 3 minutes, and then cooling to room temperature at a cooling rate of 5°C / min.

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