A method for brazing skutterudite and copper electrode using copper-tin-phosphorus solder

Abstract

A method for brazing skutterudites and copper electrodes using copper-tin-phosphorus solder relates to the technical field of brazing dissimilar materials. The purpose of the present invention is to solve the problem in the existing brazing process of skutterudites and copper electrodes that the solder reacts with the skutterudites due to the solder legs rising to the periphery of the skutterudites, thereby reducing the connection strength of the joint and the conversion efficiency of the thermoelectric device, resulting in the thermoelectric device being unusable. Method: First, the skutterudite thermoelectric material powder, the barrier layer and the copper powder are integrally hot-pressed and sintered, and then cut, ground, polished, ultrasonically cleaned and dried to obtain the skutterudite thermoelectric material to be welded; the surface to be welded of the copper electrode is ground, polished, ultrasonically cleaned and dried to obtain the copper electrode to be welded; the copper-tin-phosphorus solder is placed between the skutterudite thermoelectric material to be welded and the surface to be welded of the copper electrode to be welded, and the welding is carried out in a vacuum environment, and finally the temperature is lowered to room temperature. The present invention can obtain a method for brazing skutterudites and copper electrodes using copper-tin-phosphorus solder.

Description

Technical Field

[0001] The invention relates to the technical field of brazing dissimilar materials, and in particular to a method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus brazing filler metal. Background Art

[0002] Thermoelectric materials, capable of converting heat and electricity, have significant application value. Among them, skutterudite is the most promising mid-temperature thermoelectric material, exhibiting excellent thermoelectric and mechanical properties. From the perspective of thermoelectric device fabrication, practical application requires not only high-performance thermoelectric materials but also reliable, high-quality connections.

[0003] At present, skutterudite and copper electrodes are mainly connected by brazing. Since the operating temperature of the hot end of the thermoelectric device is 500-550℃, and the decomposition temperature of skutterudite is less than 700℃, the brazing temperature is limited to 550-700℃. Existing work often uses AgCu-based brazing filler metals to braze skutterudite and copper electrodes. Although this method can achieve connection, due to the low melting point of this series of brazing filler metals, the connection strength is low at the actual service temperature of 550℃, and the brazing feet formed during the brazing process will rise along the barrier layer to contact the skutterudite and react chemically with the skutterudite (such as Figure 3 This can severely affect the joint strength of the weld, reducing the conversion efficiency of the thermoelectric device and making it unable to meet the actual long-term use requirements. Therefore, it is very important to design a new and reliable brazing method for connecting the skutterudite thermoelectric material to the copper electrode. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem in the existing brazing process of skutterudites and copper electrodes that the brazing filler metal reacts with the skutterudites due to the brazing feet rising to the periphery of the skutterudites, thereby reducing the connection strength of the joint and the conversion efficiency of the thermoelectric device, making the thermoelectric device unusable. The present invention provides a method for brazing skutterudites and copper electrodes using a copper-tin-phosphorus brazing filler metal.

[0005] A method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder is carried out by the following steps:

[0006] Step 1: First, hot-press and sinter the skutterudite thermoelectric material powder, the barrier layer, and the copper powder to obtain an integrated hot-pressed sintered skutterudite thermoelectric material, which is then cut and then ground, polished, ultrasonically cleaned, and dried on the surface to be welded to obtain the skutterudite thermoelectric material to be welded; the surface to be welded of the copper electrode is ground, polished, ultrasonically cleaned, and dried to obtain the copper electrode to be welded; the skutterudite thermoelectric material to be welded and the copper electrode to be welded are both sealed and stored under inert gas;

[0007] Step 2: Place a copper-tin-phosphorus solder between the to-be-welded surface of the skutterudite thermoelectric material to be welded and the to-be-welded surface of the copper electrode to be welded in step 1 to obtain a connection piece to be welded; heat the connection piece to be welded to 660-700°C in a vacuum environment, and keep it at a temperature of 660-700°C for 5-30 minutes, and then cool it to room temperature to complete the brazing connection between the skutterudite thermoelectric material and the copper electrode.

[0008] Beneficial effects of the present invention:

[0009] (1) The present invention discloses a method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder. A barrier layer and a connecting transition layer (copper layer) are prepared on the surface of the skutterudite by an integrated hot-pressing sintering method, and then the skutterudite and the copper electrode are brazed using the copper-tin-phosphorus solder. The solder can achieve a good connection between the copper metal electrode and the skutterudite material without generating cracks. Moreover, due to the poor wettability of the solder and the barrier layer components, the solder foot will automatically stop rising when it rises to the junction of the connecting transition layer and the barrier layer during the brazing process, thereby effectively solving the problem of contact and reaction between the solder and the skutterudite thermoelectric material, ensuring the connection strength of the weld joint and the conversion efficiency of the thermoelectric device. The shear strength of the joint can reach 30 MPa at room temperature, which is about 100% higher than the strength of the existing AgCu-based solder brazing solution.

[0010] (2) The present invention adopts a brazing method to connect the cobalt ore and the copper electrode, and selects a barrier layer that does not wet with the solder, and its composition can be selected according to actual conditions; the solder uses commercial copper-tin-phosphorus solder, which has a simple process, convenient operation, and low cost.

[0011] The present invention can obtain a method for brazing and connecting skutterudite and a copper electrode by using a copper-tin-phosphorus solder. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The cobalt ore thermoelectric material / Ti in Example 1 80-x Co 20 Nb x SEM image of the barrier layer / Cu layer / Cu-tin-phosphorus solder / Cu electrode interface;

[0013] Figure 2 The cobalt ore thermoelectric material / Ti in Example 1 80-x Co 20 Nb x Schematic diagram of the barrier layer / Cu layer / Cu-tin-phosphorus solder / Cu electrode interface;

[0014] Figure 3 It is the existing technology of cobalt ore thermoelectric material / Ti 80-x Co 20 Nb x Schematic diagram of the barrier layer / CuSnP solder / Cu electrode interface. DETAILED DESCRIPTION

[0015] Specific embodiment 1: This embodiment provides a method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder, which is carried out in the following steps:

[0016] Step 1: First, hot-press and sinter the skutterudite thermoelectric material powder, the barrier layer, and the copper powder to obtain an integrated hot-pressed sintered skutterudite thermoelectric material, which is then cut and then ground, polished, ultrasonically cleaned, and dried on the surface to be welded to obtain the skutterudite thermoelectric material to be welded; the surface to be welded of the copper electrode is ground, polished, ultrasonically cleaned, and dried to obtain the copper electrode to be welded; the skutterudite thermoelectric material to be welded and the copper electrode to be welded are both sealed and stored under inert gas;

[0017] Step 2: Place a copper-tin-phosphorus solder between the to-be-welded surface of the skutterudite thermoelectric material to be welded and the to-be-welded surface of the copper electrode to be welded in step 1 to obtain a connection piece to be welded; heat the connection piece to be welded to 660-700°C in a vacuum environment, and keep it at a temperature of 660-700°C for 5-30 minutes, and then cool it to room temperature to complete the brazing connection between the skutterudite thermoelectric material and the copper electrode.

[0018] Beneficial effects of this embodiment:

[0019] (1) This embodiment provides a method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder. A barrier layer and a connecting transition layer (copper layer) are prepared on the surface of the skutterudite by an integrated hot-pressing sintering method, and then the skutterudite and the copper electrode are brazed using the copper-tin-phosphorus solder. The solder can achieve a good connection between the copper metal electrode and the skutterudite material without generating cracks. Moreover, due to the poor wettability of the solder and the barrier layer components, the solder foot will automatically stop rising when it rises to the junction of the connecting transition layer and the barrier layer during the brazing process, thereby effectively solving the problem of contact and reaction between the solder and the skutterudite thermoelectric material, ensuring the connection strength of the weld joint and the conversion efficiency of the thermoelectric device. The shear strength of the joint can reach 30 MPa at room temperature, which is about 100% higher than the strength of the existing AgCu-based solder brazing solution.

[0020] (2) This embodiment uses a brazing method to connect the cobalt ore and the copper electrode, and selects a barrier layer that does not wet the solder, and its composition can be selected according to actual conditions; the solder uses commercial copper-tin-phosphorus solder, which has a simple process, easy operation, and low cost.

[0021] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the barrier layer in step 1 is a Ti-based alloy material, and the barrier layer is not wettable with the solder component.

[0022] The other steps are the same as those in the first embodiment.

[0023] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the barrier layer is composed of Ti 80-x-y Co 20-y Nb x , 0 <x<20,0<y<20。

[0024] The other steps are the same as those in the first or second embodiment.

[0025] Specific embodiment 4: The difference between this embodiment and specific embodiments 1 to 3 is that the mass fraction ratio of Ti, Co and Nb is (60-90): (10-20): (0-20), Co is a pure metal element powder, and Ti and Nb are atomized TiNb alloy powder.

[0026] The other steps are the same as those in Specific Embodiments 1 to 3.

[0027] Specific embodiment five: The difference between this embodiment and specific embodiments one to four is that: in step one, the integrated hot-pressed and sintered skutterudite thermoelectric material is cut using a diamond wire cutting machine, and the cut size is (2~5) mm×(2~5) mm×(2~10) mm. After the integrated hot-pressed and sintered skutterudite thermoelectric material is cut, its surface to be welded is polished using 800#, 1000#, 1500# and 2000# metallographic sandpaper in sequence, and then placed in an acetone solution for ultrasonic cleaning for 10~20 minutes, and finally blown dry with cold air from a hair dryer.

[0028] The other steps are the same as those in Specific Embodiments 1 to 4.

[0029] Specific embodiment six: The difference between this embodiment and specific embodiments one to five is that in step one, the surface of the copper electrode to be welded is ground step by step using sandpaper between 500 and 5000#, then polished, and then ultrasonically cleaned in an acetone solution for 10 to 20 minutes, and finally dried with cold air from a hair dryer.

[0030] The other steps are the same as those in Specific Embodiments 1 to 5.

[0031] Specific embodiment seven: This embodiment differs from specific embodiments one to six in that the copper-tin-phosphorus solder is composed of Cu, Sn, P and Ni elements, and the mass ratio of Cu, Sn, P and Ni is 83:10.5:4.5:2.

[0032] The other steps are the same as those in Specific Embodiments 1 to 6.

[0033] Specific embodiment eight: The difference between this embodiment and specific embodiments one to seven is that in step two, the connecting piece to be welded is placed on a 2×10 -4 ~3×10 -3Heat it to 660 - 700 °C in a vacuum environment of Pa.

[0034] Other steps are the same as those in the first to seventh specific embodiments.

[0035] Specific Embodiment Nine: The difference between this embodiment and any one of the first to eighth specific embodiments is that in Step 2, the connector to be welded is heated to 660 - 700 °C at a heating rate of 10 - 20 °C / min.

[0036] Other steps are the same as those in the first to eighth specific embodiments.

[0037] Specific Embodiment Ten: The difference between this embodiment and any one of the first to ninth specific embodiments is that in Step 2, the connector after brazing is cooled to room temperature at a cooling rate of 1 - 10 °C / min.

[0038] Other steps are the same as those in the first to ninth specific embodiments.

[0039] The following examples are used to verify the beneficial effects of the present invention:

[0040] Example 1: A method for brazing and connecting skutterudite and copper electrodes using a copper - tin - phosphorus brazing filler metal is carried out according to the following steps:

[0041] Step 1: First, perform one - body hot - pressing sintering on the skutterudite thermoelectric material powder, barrier layer powder, and copper powder to obtain a one - body hot - pressed sintered skutterudite thermoelectric material, and then use a diamond wire cutting machine for cutting. The size after cutting is (2 - 5) mm × (2 - 5) mm × (2 - 10) mm; after cutting the one - body hot - pressed sintered skutterudite thermoelectric material, polish its welding surface successively with 800#, 1000#, 1500#, and 2000# metallographic sandpapers, then place it in an acetone solution for ultrasonic cleaning for 20 min, and finally use a hair dryer to blow - dry it with cold air to obtain the skutterudite thermoelectric material to be welded, which is stored in an inert gas - sealed manner.

[0042] Gradually polish the welding surface of the copper electrode with sandpaper between 500 - 5000#, then polish it, then place it in an acetone solution for ultrasonic cleaning for 20 min, and finally use a hair dryer to blow - dry it with cold air to obtain the copper electrode to be welded, which is stored in an inert gas - sealed manner.

[0043] The composition of the barrier layer powder is Ti 80-x Co 20 Nb x , 0 < x < 10, Co is a pure metal elemental powder, and Ti and Nb are atomized TiNb alloy powders.

[0044] Step 2: Place the copper - tin - phosphorus brazing filler metal between the welding surface of the skutterudite thermoelectric material to be welded and the welding surface of the copper electrode to be welded in Step 1 to obtain a connector to be welded; place the connector to be welded at 3×10-3 Pa vacuum environment, the temperature was raised to 675 ° C at a heating rate of 10 ° C / min, and kept at 675 ° C for 10 minutes, and then cooled to room temperature at a cooling rate of 10 ° C / min to complete the brazing connection between the cobaltite thermoelectric material and the copper electrode.

[0045] The copper-tin-phosphorus solder consists of Cu, Sn, P and Ni elements, and the mass ratio of Cu, Sn, P to Ni is 83:10.5:4.5:2.

[0046] Figure 3 It is the existing technology of cobalt ore thermoelectric material / Ti 80-x Co 20 Nb x Schematic diagram of the barrier layer / CuSnP solder / Cu electrode interface; Figure 3 It is shown in the figure that the brazing feet formed during the brazing process will rise along the barrier layer to contact the skutterudite and react chemically with the skutterudite, which will seriously affect the connection strength of the welding joint, reduce the conversion efficiency of the thermoelectric device, and make the thermoelectric device unable to meet the actual long-term use requirements.

[0047] In this embodiment, copper-tin-phosphorus solder is used to braze skutterudite and copper electrodes, and a barrier layer composition that is not wettable by the copper-tin-phosphorus solder is selected. Figure 1 The cobalt ore thermoelectric material / Ti in Example 1 80-x Co 20 Nb x SEM image of the barrier layer / Cu layer / Cu-tin-phosphorus solder / Cu electrode interface. Figure 2 The cobalt ore thermoelectric material / Ti in Example 1 80-x Co 20 Nb x Schematic diagram of barrier layer / Cu layer / Cu-tin-phosphorus solder / Cu electrode interface; Figure 1-2 As shown in the figure, the copper-tin-phosphorus solder is well bonded with the Cu layer and the Cu electrode, and no obvious cracks are observed. The solder foot automatically stops rising when it reaches the junction of the Cu layer and the barrier layer, thus effectively avoiding the problem of contact and reaction between the solder and the skutterudite thermoelectric material.

[0048] In summary, the method of brazing skutterudites and copper electrodes using copper-tin-phosphorus solder in this embodiment is highly effective. Furthermore, performance testing of the brazed joints of skutterudites and copper electrodes using copper-tin-phosphorus solder in this embodiment showed that the joints achieved a shear strength of 30 MPa at room temperature, compared to a maximum shear strength of 15 MPa at room temperature achieved with conventional silver-copper solder.

Claims

1. A method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder, characterized in that The brazing connection method is carried out in the following steps: Step 1: First, hot-press and sinter the skutterudite thermoelectric material powder, the barrier layer, and the copper powder to obtain an integrated hot-pressed sintered skutterudite thermoelectric material, which is then cut and then ground, polished, ultrasonically cleaned, and dried on the surface to be welded to obtain the skutterudite thermoelectric material to be welded; the surface to be welded of the copper electrode is ground, polished, ultrasonically cleaned, and dried to obtain the copper electrode to be welded; the skutterudite thermoelectric material to be welded and the copper electrode to be welded are both sealed and stored under inert gas; The barrier layer described in Step 1 is a Ti-based alloy material, and the composition of the barrier layer is Ti 80-x-y Co 20-y Nb x , where 0 < x < 20, 0 < y < 20, and the mass fraction ratio of Ti, Co, and Nb is (60-90):(10-20):(0-20). Co is a pure metal elemental powder, and Ti and Nb are atomized TiNb alloy powders; Step 2: placing a copper-tin-phosphorus brazing filler metal between the to-be-welded surface of the skutterudite thermoelectric material to be welded and the to-be-welded surface of the copper electrode to be welded in step 1 to obtain a connection piece to be welded; heating the connection piece to be welded to 660-700° C. in a vacuum environment, and keeping the temperature at 660-700° C. for 5-30 minutes, and then cooling to room temperature to complete the brazing connection between the skutterudite thermoelectric material and the copper electrode; The copper-tin-phosphorus solder consists of Cu, Sn, P and Ni elements, and the mass ratio of Cu, Sn, P to Ni is 83:10.5:4.5:

2.

2. The method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder according to claim 1, characterized in that In step 1, the integrated hot-pressed sintered skutterudite thermoelectric material is cut using a diamond wire cutting machine, and the cut size is (2-5) mm × (2-5) mm × (2-10) mm. After the integrated hot-pressed sintered skutterudite thermoelectric material is cut, the surface to be welded is polished using 800#, 1000#, 1500# and 2000# metallographic sandpaper in sequence, and then placed in an acetone solution for ultrasonic cleaning for 10-20 minutes, and finally blown dry with cold air from a hair dryer.

3. The method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder according to claim 1, characterized in that In step 1, the surface of the copper electrode to be welded is ground step by step using sandpaper between 500# and 5000#, then polished, and then ultrasonically cleaned in an acetone solution for 10 to 20 minutes, and finally dried with cold air from a hair dryer.

4. The method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder according to claim 1, characterized in that In step 2, place the connector to be welded on a 2×10 -4 ~3×10 -3 Pa in a vacuum environment and heat to 660-700°C.

5. A method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder according to claim 1 or 4, characterized in that In step 2, the connection piece to be welded is heated to 660-700° C. at a heating rate of 10-20° C. / min.

6. The method for brazing skutterudite and a copper electrode using a copper-tin-phosphorus solder according to claim 1, characterized in that In step 2, the brazed connection piece is cooled to room temperature at a cooling rate of 1 to 10° C. / min.

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