A brazing connection method of bismuth telluride and copper with NiCoFeMo as barrier layer

Abstract

A brazing connection method of bismuth telluride and copper with NiCoFeMo as barrier layer relates to the technical field of brazing connection. The present application is to solve the problem of the thermal electric joint of bismuth telluride and copper, which is caused by the element diffusion and finally leads to the joint fracture and the failure of the thermal electric device when serving at 200 DEG C or above. Method: the brazing filler metal is placed between the bismuth telluride and the copper to be welded to obtain the joint to be welded; the joint to be welded is placed in the heating furnace and heated to 300-320 DEG C, and kept at 300-320 DEG C for 5-30 min, and then cooled to room temperature, to complete the brazing connection of bismuth telluride and copper. The present application can obtain a brazing connection method of bismuth telluride and copper with NiCoFeMo as barrier layer.

Description

Technical Field

[0001] This invention relates to the field of brazing technology, and specifically to a brazing method for connecting bismuth telluride to copper using NiCoFeMo as a barrier layer. Background Technology

[0002] Bismuth telluride thermoelectric materials exhibit excellent thermoelectric properties at room temperature, are well-researched, and have wide applications. Copper, with its low resistivity and good thermal conductivity, is an ideal electrode material offering high economic efficiency. The junction between bismuth telluride and copper is a core component of thermoelectric devices; improving its connection quality helps to enhance the thermoelectric conversion efficiency and lifespan of the thermoelectric device.

[0003] In the joining of bismuth telluride and copper, brazing is the most commonly used method due to its low joining temperature, minimal damage to the base material, and high connection quality. During brazing, the metallurgical bond between bismuth telluride and the brazing filler metal is crucial for achieving a reliable connection. In practical applications of thermoelectric devices, even at operating temperatures below the melting point of the brazing filler metal, interdiffusion of elements still occurs between bismuth telluride and the brazing seam, leading to a continuous thickening of the reaction layer. This results in decreased joint performance and ultimately joint failure.

[0004] The current main approach is to prepare a barrier layer on the bismuth telluride surface to suppress excessive interfacial reactions and ensure good wetting between the solder and the barrier layer. However, the service temperature of the barrier layer materials currently widely used is below 200°C; when the temperature is above 200°C, excessive diffusion and interfacial reactions between the barrier layer and bismuth telluride will continuously consume the barrier layer, resulting in unstable joint operation.

[0005] Currently, no barrier layer material has been reported that can ensure stable operation of bismuth telluride-copper joints above 200°C. Therefore, designing a suitable barrier layer material to achieve stable operation of bismuth telluride-copper joints above 200°C has become a pressing technical challenge for the industry. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of excessively thick reaction layer, low shear strength (<5MPa), and excessively high interfacial resistivity (>20μΩ·cm) caused by intense interdiffusion of elements in bismuth telluride-copper thermoelectric joints during long-term service at temperatures above 200°C. 2 This leads to problems such as joint breakage and thermoelectric device failure. Therefore, a brazing connection method for bismuth telluride and copper with NiCoFeMo as the barrier layer is provided.

[0007] A brazing method for connecting bismuth telluride to copper using NiCoFeMo as a barrier layer comprises the following steps:

[0008] Step S1: Prepare bismuth telluride to be soldered;

[0009] The bismuth telluride thermoelectric material is cut, and then the surface of the bismuth telluride thermoelectric material to be soldered is ground, polished and ultrasonically cleaned. Then, a NiCoFeMo coating is electroplated on the surface of the bismuth telluride thermoelectric material to be soldered. The NiCoFeMo coating is polished and ultrasonically cleaned, and then a metal coating is prepared on the surface of the NiCoFeMo coating to obtain the bismuth telluride to be soldered.

[0010] Step S2: Prepare the copper to be soldered;

[0011] The copper electrode is cut, and then the surface of the copper electrode to be soldered is ground, polished and ultrasonically cleaned to obtain the copper to be soldered.

[0012] Step S3: Brazing the bismuth telluride to be soldered to the copper to be soldered;

[0013] The brazing filler metal is placed between the bismuth telluride surface to be brazed obtained in step S1 and the copper surface to be brazed obtained in step S2 to form a weldable component. The weldable component is placed in a heating furnace and heated to 300-320°C. It is then held at 300-320°C for 5-30 minutes. After the holding period, it is cooled to room temperature to complete the brazing connection between bismuth telluride and copper.

[0014] The beneficial effects of this invention are:

[0015] (1) This invention discloses a brazing method for connecting bismuth telluride to copper using NiCoFeMo as a barrier layer. A NiCoFeMo plating layer is electroplated on the surface of bismuth telluride, and soft solder or nano-silver solder paste is used to connect the bismuth telluride to copper. The NiCoFeMo plating layer contains elements ranging from 5% to 35%, conforming to the composition of a high-entropy alloy. High-entropy alloys exhibit a hysteresis diffusion effect, and the NiCoFeMo barrier layer provides good diffusion barrier properties. Simultaneously, the plating layer contains the refractory element Mo, which further enhances the thermal stability of the barrier layer. The NiCoFeMo plating layer bonds well with bismuth telluride, and the pure metal plating layer (such as Ni, Co, Ag, etc.) prepared on the NiCoFeMo plating layer exhibits good wetting of the solder and a thin reaction layer. After annealing and aging, the mechanical properties and interfacial resistivity of the joint remain stable. The brazing connection method of this invention can achieve a joint shear strength of up to 20 MPa at room temperature. When in service at temperatures above 200°C, the joint remains stable with a shear strength of over 15 MPa and a low interface resistivity. This solves the problems of excessively thick brittle reaction layer and poor thermal stability in existing thermoelectric joints between bismuth telluride and copper.

[0016] (2) The present invention uses soft solder or nano silver solder paste to connect bismuth telluride and copper. The connection temperature is low, the damage to the base material is small, the thermal expansion coefficient is well matched, the joint shear strength is high, and the interface resistivity is low.

[0017] (3) The present invention provides a method for connecting bismuth telluride with copper using NiCoFeMo as a barrier layer, thereby achieving brazing connection between bismuth telluride and copper. The process is simple and has good repeatability.

[0018] This invention provides a brazing method for connecting bismuth telluride to copper using NiCoFeMo as a barrier layer. Attached Figure Description

[0019] Figure 1 This image shows the SEM image of the interface structure of the copper / AuSn / Ni / NiCoFeMo / bismuth telluride joint obtained in Example 1.

[0020] Figure 2 The image shows the SEM image of the AuSn / Ni / NiCoFeMo / bismuth telluride interface structure obtained in Example 1. Detailed Implementation

[0021] Specific Implementation Method 1: This implementation method describes a brazing connection method between bismuth telluride and copper using NiCoFeMo as a barrier layer, which is carried out according to the following steps:

[0022] Step S1: Prepare bismuth telluride to be soldered;

[0023] The bismuth telluride thermoelectric material is cut, and then the surface of the bismuth telluride thermoelectric material to be soldered is ground, polished and ultrasonically cleaned. Then, a NiCoFeMo coating is electroplated on the surface of the bismuth telluride thermoelectric material to be soldered. The NiCoFeMo coating is polished and ultrasonically cleaned. Then, a pure metal coating is prepared on the surface of the NiCoFeMo coating to improve the wettability of the solder on the metal coating, and finally the bismuth telluride to be soldered is obtained.

[0024] Step S2: Prepare the copper to be soldered;

[0025] The copper electrode is cut, and then the surface of the copper electrode to be soldered is ground, polished and ultrasonically cleaned to obtain the copper to be soldered.

[0026] Step S3: Brazing the bismuth telluride to be soldered to the copper to be soldered;

[0027] The brazing filler metal is placed between the bismuth telluride surface to be brazed obtained in step S1 and the copper surface to be brazed obtained in step S2 to form a weldable component. The weldable component is placed in a heating furnace and heated to 300-320°C. It is then held at 300-320°C for 5-30 minutes. After the holding period, it is cooled to room temperature to complete the brazing connection between bismuth telluride and copper.

[0028] Specific Implementation Method Two: The difference between this implementation method and Specific Implementation Method One is that the ultrasonic cleaning time in both steps S1 and S2 is 10 to 20 minutes.

[0029] The other steps are the same as in Specific Implementation Method 1.

[0030] Specific Implementation Method Three: The difference between this implementation method and Specific Implementation Method One or Two is that the electroplating process parameters for electroplating a NiCoFeMo coating on the surface of the bismuth telluride thermoelectric material to be soldered in step S1 are: electroplating solution temperature is 35-60℃, and current density is 1-12 A / dm³. 2 The electroplating time is 1 to 60 minutes.

[0031] The other steps are the same as in Specific Implementation Method 1 or 2.

[0032] Specific Implementation Method Four: The difference between this implementation method and Specific Implementation Methods One to Three is that the electroplating solution used in step S1 for electroplating the NiCoFeMo coating on the surface to be soldered of the bismuth telluride thermoelectric material is composed of 50-350 g / L nickel sulfate, 10-100 g / L nickel chloride, 10-100 g / L cobalt sulfate, 10-100 g / L ferrous sulfate, 10-40 g / L sodium molybdate, 30-100 g / L sodium citrate, and 20-40 g / L boric acid.

[0033] The other steps are the same as those in Specific Implementation Methods One to Three.

[0034] Specific Implementation Method 5: The difference between this implementation method and Specific Implementation Methods 1 to 4 is that the elemental contents of Ni, Co, Fe and Mo in the NiCoFeMo coating described in step S1 are all between 5% and 35%, and the sum of the elemental contents of Ni, Co, Fe and Mo is 100%.

[0035] The other steps are the same as those in Specific Implementation Methods One through Four.

[0036] Specific Implementation Method Six: The difference between this implementation method and Specific Implementation Methods One to Five is that the thickness of the NiCoFeMo coating in step S1 is 1 to 30 μm.

[0037] The other steps are the same as those in Specific Implementation Methods 1 to 5.

[0038] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the metal coating mentioned in step S1 is Ni, Co, Fe, Ag or Au.

[0039] The other steps are the same as those in Specific Implementation Methods 1 to 6.

[0040] Specific Implementation Method Eight: The difference between this implementation method and one of the specific implementation methods one to seven is that the solder mentioned in step S3 is tin-based solder, lead-based solder, gold-based solder, or nano silver solder paste.

[0041] The other steps are the same as those in Specific Implementation Methods 1 to 7.

[0042] Specific Implementation Method Nine: The difference between this implementation method and Specific Implementation Methods One to Eight is that the thickness of the brazing filler metal mentioned in step S3 is 0.05 to 0.2 mm.

[0043] The other steps are the same as those in Specific Implementation Methods 1 to 8.

[0044] Specific Implementation Method 10: The difference between this implementation method and Specific Implementation Methods 1 to 9 is that in step S3, the connecting parts to be welded are placed in a heating furnace and heated to 300-320°C at a heating rate of 5-15°C / min.

[0045] The other steps are the same as those in Specific Implementation Methods 1 to 9.

[0046] The beneficial effects of the present invention are verified using the following embodiments:

[0047] Example 1: A brazing method for connecting bismuth telluride to copper using NiCoFeMo as a barrier layer, comprising the following steps:

[0048] Step S1: Prepare bismuth telluride to be soldered;

[0049] The bismuth telluride thermoelectric material was cut, and then the surface of the bismuth telluride thermoelectric material to be soldered was sanded, polished, and ultrasonically cleaned for 15 minutes. Finally, it was plated at a bath temperature of 45℃ and a flux of 5A / dm. 2 Electroplating was performed for 5 minutes under the current density conditions. A NiCoFeMo coating with a thickness of 3 μm was electroplated on the surface of the bismuth telluride thermoelectric material to be soldered. The NiCoFeMo coating was polished and ultrasonically cleaned. Then, a Ni coating was prepared on the surface of the NiCoFeMo coating to obtain the bismuth telluride to be soldered.

[0050] In step S1, the electroplating solution used for electroplating the NiCoFeMo coating on the surface of the bismuth telluride thermoelectric material to be soldered consists of 200 g / L nickel sulfate, 50 g / L nickel chloride, 50 g / L cobalt sulfate, 50 g / L ferrous sulfate, 30 g / L sodium molybdate, 100 g / L sodium citrate, and 30 g / L boric acid.

[0051] Step S2: Prepare the copper to be soldered;

[0052] The copper electrode is cut, and then the surface of the copper electrode to be soldered is sanded, polished and ultrasonically cleaned for 15 minutes to obtain the copper to be soldered.

[0053] Step S3: Brazing the bismuth telluride to be soldered to the copper to be soldered;

[0054] The AuSn foil is placed between the bismuth telluride surface to be soldered obtained in step S1 and the copper surface to be soldered obtained in step S2 to form a soldering connector. The thickness of the AuSn foil is 0.1 mm. The soldering connector is placed in a heating furnace and heated to 320°C at a heating rate of 10°C / min. It is then held at 320°C for 5 min. After the holding period, it is cooled to room temperature with the furnace to complete the brazing connection between bismuth telluride and copper.

[0055] Figure 1 This shows the SEM image of the interface microstructure of the copper / AuSn / Ni / NiCoFeMo / bismuth telluride joint obtained in Example 1; as shown. Figure 1 As shown in the figure, from left to right, the alloys are copper, AuSn, Ni, NiCoFeMo, and bismuth telluride. The weld microstructure of the joint is well-formed and defect-free. AuSn brazing filler metal exhibits good thermal stability and excellent mechanical properties, with a joint shear strength of 20 MPa at room temperature.

[0056] Figure 2 This shows the SEM image of the AuSn / Ni / NiCoFeMo / bismuth telluride interface microstructure obtained in Example 1; as shown. Figure 2 As shown, the NiCoFeMo coating exhibits good bonding with bismuth telluride, and the diffusion reaction layer is very thin, demonstrating that the NiCoFeMo barrier layer effectively inhibits the growth of the brittle reaction layer. The excellent matching of the thermal expansion coefficients between the coating and bismuth telluride effectively reduces thermal stress caused by connection and aging, improving the reliability of the joint. The Ni prepared on the NiCoFeMo coating effectively enhances the metallurgical bonding force between the AuSn solder and the coating. The Ni / NiCoFeMo composite layer achieves good connection with both bismuth telluride and AuSn solder, with no unbonded areas. Shear strength and interfacial resistivity tests were conducted on the bismuth telluride / copper thermoelectric joint aged at 250℃ for 1000h. The test results show that the joint shear strength reaches 17MPa, and the interfacial resistivity is 11μΩ·cm. 2 Compared with thermoelectric joints using conventional barrier layers and aged materials, the shear strength (<5MPa) and interfacial resistivity (>20μΩ·cm) are significantly higher. 2 Compared to other methods, it has a clear advantage.

[0057] Example 2: A brazing method for connecting bismuth telluride to copper using NiCoFeMo as a barrier layer, comprising the following steps:

[0058] Step S1: Prepare bismuth telluride to be soldered;

[0059] The bismuth telluride thermoelectric material was cut, and then the surface of the bismuth telluride thermoelectric material to be soldered was sanded, polished, and ultrasonically cleaned for 10 minutes. Finally, it was plated at a bath temperature of 45℃ and a flux of 5A / dm. 2Electroplating was performed for 5 minutes under the current density conditions. A NiCoFeMo coating with a thickness of 3 μm was electroplated on the surface of the bismuth telluride thermoelectric material to be soldered. The NiCoFeMo coating was polished and ultrasonically cleaned. Then, a Ni coating was prepared on the surface of the NiCoFeMo coating to obtain the bismuth telluride to be soldered.

[0060] In step S1, the electroplating solution used for electroplating the NiCoFeMo coating on the surface of the bismuth telluride thermoelectric material to be soldered consists of 200 g / L nickel sulfate, 50 g / L nickel chloride, 50 g / L cobalt sulfate, 50 g / L ferrous sulfate, 30 g / L sodium molybdate, 100 g / L sodium citrate, and 30 g / L boric acid.

[0061] Step S2: Prepare the copper to be soldered;

[0062] The copper electrode is cut, and then the surface of the copper electrode to be soldered is sanded, polished and ultrasonically cleaned for 10 minutes to obtain the copper to be soldered.

[0063] Step S3: Brazing the bismuth telluride to be soldered to the copper to be soldered;

[0064] Nano-silver solder paste is applied between the solderable surface of the bismuth telluride obtained in step S1 and the solderable surface of the copper obtained in step S2 to obtain a solderable connector. The thickness of the nano-silver solder paste is 0.05 mm. The solderable connector is placed in a heating furnace and heated to 300°C at a heating rate of 15°C / min. It is then held at 300°C for 30 min. After the holding time is completed, it is cooled to room temperature with the furnace to complete the connection between bismuth telluride and copper.

[0065] In Examples 1 and 2, the purity of nickel sulfate, nickel chloride, cobalt sulfate, ferrous sulfate, sodium molybdate, sodium citrate, and boric acid in the electroplating solutions was all above 99.9%.

[0066] The bismuth telluride and copper nano-silver sintered thermoelectric joint prepared in this embodiment has a dense structure and good stability. The joint's room temperature shear strength can reach 16 MPa, and after aging at 250℃ for 1000 h, the shear strength is 15 MPa, which is much higher than that of traditional barrier layer thermoelectric joints (<5 MPa); the interface resistivity is 13 μΩ·cm. 2 Lower than traditional barrier layer thermoelectric joints (>20μΩ·cm) 2 ).

Claims

1. A method for brazing bismuth telluride to copper using NiCoFeMo as a barrier layer, characterized in that... The brazing connection method is performed according to the following steps: Step S1: Prepare bismuth telluride to be soldered; The bismuth telluride thermoelectric material is cut, and then the surface of the bismuth telluride thermoelectric material to be soldered is ground, polished and ultrasonically cleaned. Then, a NiCoFeMo coating is electroplated on the surface of the bismuth telluride thermoelectric material to be soldered. The NiCoFeMo coating is polished and ultrasonically cleaned, and then a metal coating is prepared on the surface of the NiCoFeMo coating to obtain the bismuth telluride to be soldered. In step S1, the elemental contents of Ni, Co, Fe and Mo in the NiCoFeMo coating are all between 5% and 35%, and the sum of the elemental contents of Ni, Co, Fe and Mo is 100%; the thickness of the NiCoFeMo coating in step S1 is 1 to 30 μm. The metal coating mentioned in step S1 is Ni, Co, Fe, Ag, or Au; Step S2: Prepare the copper to be soldered; The copper electrode is cut, and then the surface of the copper electrode to be soldered is ground, polished and ultrasonically cleaned to obtain the copper to be soldered. Step S3: Brazing the bismuth telluride to be soldered to the copper to be soldered; The brazing filler metal is placed between the bismuth telluride surface to be brazed obtained in step S1 and the copper surface to be brazed obtained in step S2 to obtain the brazing connector; the brazing connector is placed in a heating furnace and heated to 300~320℃, and held at 300~320℃ for 5~30 minutes. After the holding time is completed, it is cooled to room temperature to complete the brazing connection between bismuth telluride and copper. The solder mentioned in step S3 is tin-based solder, lead-based solder, gold-based solder, or nano-silver solder paste.

2. The brazing connection method between bismuth telluride and copper using NiCoFeMo as a barrier layer according to claim 1, characterized in that... The ultrasonic cleaning time in both steps S1 and S2 is 10-20 minutes.

3. The brazing connection method between bismuth telluride and copper using NiCoFeMo as a barrier layer according to claim 1, characterized in that... In step S1, the electroplating process parameters for electroplating a NiCoFeMo coating on the surface of the bismuth telluride thermoelectric material to be soldered are as follows: electroplating bath temperature is 35~60℃, and current density is 1~12A / dm³. 2 The electroplating time is 1~60min.

4. A brazing connection method for bismuth telluride and copper with NiCoFeMo as the barrier layer according to claim 1 or 3, characterized in that... In step S1, the electroplating solution used for electroplating the NiCoFeMo coating on the surface of the bismuth telluride thermoelectric material to be soldered consists of 50~350g / L nickel sulfate, 10~100g / L nickel chloride, 10~100g / L cobalt sulfate, 10~100g / L ferrous sulfate, 10~40g / L sodium molybdate, 30~100g / L sodium citrate, and 20~40g / L boric acid.

5. The brazing connection method between bismuth telluride and copper using NiCoFeMo as a barrier layer according to claim 1, characterized in that... The thickness of the brazing filler metal mentioned in step S3 is 0.05~0.2mm.

6. The brazing connection method between bismuth telluride and copper using NiCoFeMo as a barrier layer according to claim 1, characterized in that... In step S3, the connector to be welded is placed in a heating furnace and heated to 300-320°C at a heating rate of 5-15°C / min.

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