Method for connecting SiGe high-temperature thermoelectric material and metal electrode

Abstract

The invention provides a method for connecting a SiGe high-temperature thermoelectric material and a metal electrode, and relates to the technical field of welding, and the method comprises the steps: preparing a carbon layer on the surface of SiGe, and obtaining carbon-coated SiGe; the carbon-coated SiGe, the multi-principal element alloy brazing filler metal and the metal electrode material are sequentially assembled from top to bottom, and an assembly part is obtained; and under the vacuum condition, the assembly part is heated to the preset temperature at the preset heating rate, heat preservation is conducted for preset time, cooling is conducted to the room temperature, and the connector is obtained. By adopting the method provided by the invention to connect the SiGe thermoelectric material and the metal electrode, not only can a joint be prevented from cracking, but also Si and Ge elements in the SiGe thermoelectric material can be prevented from remarkably diffusing into a welding seam, so that attenuation of the performance of the thermoelectric material and continuous degradation of the bonding performance of a heterogeneous interface are avoided.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, and in particular to a method for connecting a SiGe high-temperature thermoelectric material and a metal electrode. Background Art

[0002] Thermoelectric devices, leveraging the Seebeck and Peltier effects to efficiently convert heat into electricity, hold significant potential for applications in industrial waste heat recovery, deep space exploration power generation, solid-state refrigeration, and micro-area temperature control. Silicon germanium (SiGe) is a common thermoelectric material. Its exceptional mechanical properties and thermal stability at high temperatures make it an ideal choice for long-term energy supply in harsh environments, such as those characterized by extreme heat and radiation. However, improvements in the interface properties between SiGe thermoelectric materials and metal electrodes are hampered by challenges such as poor diffusion and stress coordination at the heterojunction between the SiGe thermoelectric material and the metal electrode, leading to poor connection reliability and a critical bottleneck restricting the energy conversion efficiency of thermoelectric devices. Specifically, due to the inherent brittleness and low thermal expansion coefficient of SiGe, the heterojunction exhibits a thermal expansion mismatch, making post-weld cracking highly susceptible to residual stress. During high-temperature connection and service, Si and Ge elements (particularly Si) in the thermoelectric material diffuse significantly into the weld, resulting in degradation of the thermoelectric material's performance and continuous deterioration of the heterojunction bonding performance, severely impacting the long-term stability of the device. Summary of the Invention

[0003] The present invention solves at least one of the following problems: (1) How to avoid cracking of the connection joint between SiGe thermoelectric material and metal electrode. (2) How to avoid significant diffusion of Si and Ge elements in the SiGe thermoelectric material into the weld seam between SiGe thermoelectric material and metal electrode, thereby avoiding degradation of the thermoelectric material performance and continuous deterioration of the heterogeneous interface bonding performance.

[0004] To solve the above problems, the present invention provides a method for connecting a SiGe high-temperature thermoelectric material to a metal electrode, comprising: Step S1, preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe; Step S2, assembling the carbon-coated SiGe, the multi-principal-element alloy solder, and the metal electrode material in order from top to bottom to obtain an assembly; wherein the multi-principal-element alloy solder includes at least four elements of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu; Step S3: heating the assembly to a preset temperature at a preset heating rate under vacuum conditions, keeping the temperature for a preset time, and cooling to room temperature to obtain a connection joint.

[0005] Optionally, in step S1, preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe includes: Step S11, placing SiGe in a phenolic resin precursor solution for immersion treatment to obtain pretreated SiGe; Step S12: heat-treating the pretreated SiGe under vacuum conditions to obtain the carbon-coated SiGe.

[0006] Optionally, in step S11, the phenolic resin precursor solution is composed of phenolic resin and organic solvent in a mass ratio of 1:(1 to 5).

[0007] Optionally, in step S12, the heating treatment is performed at a temperature of 650° C. to 900° C. for a time of 10 min to 30 min.

[0008] Optionally, in step S2, the metal electrode material is selected from at least one of W, W alloy, Mo, Mo alloy, Cr, Cr alloy, Cu, Cu alloy, Ni and Ni alloy.

[0009] Optionally, in step S1, the thickness of the carbon layer is 0.1 μm to 10 μm.

[0010] Optionally, in step S1, the thickness of the SiGe is 4 mm to 20 mm.

[0011] Optionally, in step S2, the thickness of the multi-principal-component alloy solder is 50 μm to 100 μm.

[0012] Optionally, in step S2, the thickness of the metal electrode material is 0.3 mm to 4 mm.

[0013] Optionally, in step S3, the preset heating rate is 8°C / min to 12°C / min, the preset temperature is 950°C to 1250°C, and the preset time is 5 min to 60 min.

[0014] Compared with the related art, the present invention first prepares a carbon layer on the surface of SiGe high-temperature thermoelectric material to obtain carbon-coated SiGe, and uses a multi-principal element alloy brazing filler metal to braze the carbon-coated SiGe to the metal electrode. Since the multi-principal element alloy brazing filler metal is composed of at least four elements of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, Cu and other elements with strong affinity for carbon, during the connection process, the carbon layer coating the SiGe surface reacts in situ with the multi-principal element alloy brazing filler metal to form a multi-principal element carbide layer. The multi-principal element carbide layer acts as a diffusion barrier layer for SiGe, which can inhibit the diffusion of Si and Ge elements to the connection interface. The thermal expansion coefficient of the multi-principal element carbide layer is similar to that of SiGe, which can effectively relieve the residual stress of the joint, and finally realize high-temperature and reliable connection between the SiGe thermoelectric material and the metal electrode. In summary, the method provided by the present invention is used to connect SiGe thermoelectric materials and metal electrodes, which can not only avoid cracking of the connection joint, but also prevent the Si and Ge elements in the SiGe thermoelectric material from significantly diffusing into the weld, thereby avoiding the attenuation of the thermoelectric material performance and the continuous deterioration of the heterogeneous interface bonding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the process of connecting SiGe high-temperature thermoelectric material and metal electrode in an embodiment of the present invention; Figure 2 This is a scanning electron microscope image of the connection joint prepared in Example 1; Figure 3 This is a scanning electron microscope image of the connection joint prepared in Comparative Example 1; Figure 4 This is a scanning electron microscope image of the connection joint prepared in Comparative Example 2. DETAILED DESCRIPTION

[0016] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein. Instead, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0018] The term "including" and its variations used in this document are open inclusions, that is, "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0019] Due to the difficulty in coordinating diffusion and stress at the heterojunction interface between SiGe thermoelectric materials and metal electrodes, as well as poor connection reliability, the improvement of the interface characteristics between SiGe thermoelectric materials and metal electrodes has been restricted, becoming a key bottleneck restricting the energy conversion efficiency of thermoelectric devices. Specifically, due to the inherent brittleness and low thermal expansion coefficient of SiGe, there is a thermal expansion coefficient mismatch in the heterojunction connection, which is very prone to post-weld cracking under the influence of residual stress. During high-temperature connection and service, the Si and Ge elements (especially Si) in the thermoelectric material will significantly diffuse into the weld, causing the thermoelectric material performance to degrade and the heterojunction interface bonding performance to continue to deteriorate, seriously affecting the long-term stability of the device.

[0020] Related technologies for connecting SiGe high-temperature thermoelectric materials to metal electrodes rely on diffusion bonding and integrated sintering. Diffusion bonding uses titanium as the intermediate layer, leading to significant diffusion of elements during the bonding process, forming Kirkendall pores. Integrated sintering, on the other hand, uses titanium and silicide powders as transition layers, acting as diffusion barriers. However, the sintered interface is tortuous and uncontrollable, and the intermediate sintered layer is often very thick, introducing additional interface resistance.

[0021] In response to the problems existing in the above-mentioned related technologies, an embodiment of the present invention provides a method for connecting a SiGe high-temperature thermoelectric material and a metal electrode, comprising: Step S1, preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe, which is denoted as SiGe@C; Step S2, assembling the carbon-coated SiGe, the multi-principal alloy solder, and the metal electrode material in order from top to bottom to obtain an assembly; wherein the assembly is a sandwich structure, comprising, from top to bottom, the carbon-coated SiGe, the multi-principal alloy solder, and the metal electrode material, wherein the multi-principal alloy solder includes at least four elements selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu; Step S3: heating the assembly to a preset temperature at a preset heating rate under vacuum conditions, keeping the temperature for a preset time, and cooling to room temperature to obtain a connection joint.

[0022] In an embodiment of the present invention, a carbon layer is first prepared on the surface of a SiGe high-temperature thermoelectric material to obtain carbon-coated SiGe, and a multi-principal-element alloy brazing material is used to braze the carbon-coated SiGe to a metal electrode. Since the multi-principal-element alloy brazing material is composed of at least four elements including Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu having a strong affinity for carbon, during the connection process, the carbon layer coating the SiGe surface reacts in situ with the multi-principal-element alloy brazing material to form a multi-principal-element carbide layer. The multi-principal-element carbide layer acts as a diffusion barrier layer for SiGe, which can inhibit the diffusion of Si and Ge elements to the connection interface. The thermal expansion coefficient of the multi-principal-element carbide layer is similar to that of SiGe, which can effectively alleviate the residual stress of the joint, and ultimately achieve a high-temperature and reliable connection between the SiGe thermoelectric material and the metal electrode. In summary, the method provided in the embodiment of the present invention is used to connect SiGe thermoelectric materials and metal electrodes, which can not only avoid cracking of the connection joint, but also prevent the Si and Ge elements in the SiGe thermoelectric material from significantly diffusing into the weld, thereby avoiding the attenuation of the thermoelectric material performance and the continuous deterioration of the heterogeneous interface bonding performance.

[0023] In some embodiments of the present invention, illustratively, in step S1, preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe includes: Step S11, placing SiGe in a phenolic resin precursor solution for immersion treatment to obtain pretreated SiGe; Step S12: heat-treating the pretreated SiGe under vacuum conditions to decompose the phenolic resin, thereby forming a uniformly coated carbon layer on the surface of the SiGe to obtain the carbon-coated SiGe.

[0024] In some embodiments of the present invention, in step S11, the phenolic resin precursor solution is composed of phenolic resin and organic solvent in a mass ratio of 1:(1 to 5).

[0025] In some embodiments of the present invention, in step S12, the heating treatment is performed at a temperature of 650° C. to 900° C. for a time of 10 min to 30 min.

[0026] In some embodiments of the present invention, illustratively, in step S1, preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe includes: Carbon is deposited on the surface of SiGe by magnetron sputtering to obtain the carbon-coated SiGe. In some embodiments of the present invention, illustratively, in step S1, preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe includes: SiGe is placed in a glucose precursor solution and subjected to heat treatment to form a uniformly coated carbon layer on the surface of the SiGe to obtain the carbon-coated SiGe; wherein the heating treatment temperature is 120°C to 180°C and the time is 10h to 12h; the mass fraction of the glucose precursor solution is 3% to 10%.

[0027] Optionally, in step S2, the metal electrode material is selected from at least one of W, W alloy, Mo, Mo alloy, Cr, Cr alloy, Cu, Cu alloy, Ni and Ni alloy.

[0028] In some embodiments of the present invention, in step S1 , the thickness of the carbon layer is 0.1 μm to 10 μm.

[0029] In some embodiments of the present invention, in step S1 , the thickness of the SiGe is 4 mm to 20 mm.

[0030] In some embodiments of the present invention, in step S2, the thickness of the multi-principal-component alloy solder is 50 μm to 100 μm.

[0031] In some embodiments of the present invention, in step S2, the thickness of the metal electrode material is 0.3 mm to 4 mm.

[0032] In some embodiments of the present invention, in step S3, the preset heating rate is 8°C / min to 12°C / min, the preset temperature is 950°C to 1250°C, and the preset time is 5 min to 60 min.

[0033] The present invention is further described below with reference to specific embodiments.

[0034] Example 1 A1. Place SiGe in a phenolic resin precursor solution and immerse it to obtain pretreated SiGe; wherein the SiGe is in a sheet shape with a thickness of 4 mm, and the phenolic resin precursor solution is composed of phenolic resin and organic solvent anhydrous ethanol in a mass ratio of 1:1, and the immersion treatment time is 20 minutes.

[0035] A2. Heat-treating the pretreated SiGe under vacuum conditions to obtain the carbon-coated SiGe; wherein the heating temperature is 775° C. and the heating time is 20 min.

[0036] A3. Assemble the carbon-coated SiGe, multi-principal component alloy solder and metal electrode material in sequence from top to bottom to obtain an assembly part; wherein, the multi-principal component alloy solder is composed of Ti, Fe, Cr, Ni and Mo, and the molar ratio of Ti, Fe, Cr, Ni and Mo in the multi-principal component alloy solder is 1:1:1:1:1; the multi-principal component alloy solder is a foil with a thickness of 75 μm; the metal electrode material is made of W, in the shape of a sheet and with a thickness of 2 mm.

[0037] A4. Under vacuum conditions, heat the assembly to a preset temperature at a preset heating rate, keep the temperature for a preset time, cool to 400°C at a preset cooling rate, and then furnace cool to room temperature to obtain a connection joint; wherein the preset heating rate is 10°C / min, the preset temperature is 1100°C, the preset time is 30 minutes, and the preset cooling rate is 7.5°C / min.

[0038] Example 2 A1. Place SiGe in a phenolic resin precursor solution and immerse it to obtain pretreated SiGe; wherein the SiGe is in a sheet shape with a thickness of 20 mm, the phenolic resin precursor solution is composed of phenolic resin and organic solvent anhydrous ethanol in a mass ratio of 1:1, and the immersion time is 20 minutes.

[0039] A2. Heat-treating the pretreated SiGe under vacuum conditions to obtain the carbon-coated SiGe; wherein the heating temperature is 900° C. and the heating time is 5 minutes.

[0040] A3. Assemble the carbon-coated SiGe, multi-principal component alloy solder and metal electrode material in sequence from top to bottom to obtain an assembly part; wherein, the multi-principal component alloy solder is composed of Ti, Fe, Cr, Ni and Mo, and the molar ratio of Ti, Fe, Cr, Ni and Mo in the multi-principal component alloy solder is 1:1:1:1:1; the multi-principal component alloy solder is a foil material with a thickness of 100 μm; the metal electrode material is made of W, in the shape of a sheet and with a thickness of 4 mm.

[0041] A4. Under vacuum conditions, heat the assembly to a preset temperature at a preset heating rate, keep the temperature for a preset time, cool to 400°C at a preset cooling rate, and then furnace cool to room temperature to obtain a connection joint; wherein the preset heating rate is 12°C / min, the preset temperature is 1250°C, the preset time is 5 minutes, and the preset cooling rate is 7.5°C / min.

[0042] Example 3 A1. Place SiGe in a phenolic resin precursor solution and immerse it to obtain pretreated SiGe; wherein the SiGe is in a sheet shape with a thickness of 20 mm, the phenolic resin precursor solution is composed of phenolic resin and organic solvent anhydrous ethanol in a mass ratio of 1:1, and the immersion time is 20 minutes.

[0043] A2. Heat-treating the pretreated SiGe under vacuum conditions to obtain the carbon-coated SiGe; wherein the heating temperature is 650° C. and the heating time is 30 minutes.

[0044] A3. Assemble the carbon-coated SiGe, multi-principal component alloy solder and metal electrode material in sequence from top to bottom to obtain an assembly part; wherein, the multi-principal component alloy solder is composed of Ti, Fe, Cr, Ni and Mo, and the molar ratio of Ti, Fe, Cr, Ni and Mo in the multi-principal component alloy solder is 1:1:1:1:1; the multi-principal component alloy solder is a foil material with a thickness of 50 μm; the metal electrode material is made of W, in the shape of a sheet and with a thickness of 0.3 mm.

[0045] A4. Under vacuum conditions, heat the assembly to a preset temperature at a preset heating rate, keep the temperature for a preset time, cool to 400°C at a preset cooling rate, and then furnace cool to room temperature to obtain a connection joint; wherein the preset heating rate is 8°C / min, the preset temperature is 950°C, the preset time is 60 minutes, and the preset cooling rate is 7.5°C / min.

[0046] Comparative Example 1 SiGe, a multi-principal component alloy solder and a metal electrode material are assembled in sequence from top to bottom to obtain an assembly part; wherein, the SiGe is in the shape of a sheet and has a thickness of 4 mm; the multi-principal component alloy solder is composed of Ti, Fe, Cr, Ni and Mo; the molar ratio of Ti, Fe, Cr, Ni and Mo in the multi-principal component alloy solder is 1:1:1:1:1; the multi-principal component alloy solder is a foil material with a thickness of 75 μm; the metal electrode material is made of W, has a sheet shape and a thickness of 2 mm.

[0047] Under vacuum conditions, the assembly is heated to a preset temperature at a preset heating rate, kept at that temperature for a preset time, cooled to 400°C at a preset cooling rate, and then furnace-cooled to room temperature to obtain a connection joint; wherein, the preset heating rate is 10°C / min, the preset temperature is 1100°C, the preset time is 30 minutes, and the preset cooling rate is 7.5°C / min.

[0048] Comparative Example 2 SiGe is placed in a phenolic resin precursor solution and immersed to obtain pretreated SiGe; wherein the SiGe is in a sheet shape with a thickness of 4 mm, the phenolic resin precursor solution is composed of phenolic resin and organic solvent anhydrous ethanol in a mass ratio of 1:1, and the immersion treatment time is 20 minutes.

[0049] The pretreated SiGe is heat-treated under vacuum conditions to obtain the carbon-coated SiGe; wherein the heating temperature is 775° C. and the heating time is 20 minutes.

[0050] The carbon-coated SiGe and the metal electrode material are assembled in sequence from top to bottom to obtain an assembly part; wherein the metal electrode material is made of W, has a sheet shape, and has a thickness of 2 mm.

[0051] Under vacuum conditions, the assembly is heated to a preset temperature at a preset heating rate, kept at that temperature for a preset time, cooled to 400°C at a preset cooling rate, and then furnace-cooled to room temperature to obtain a connection joint; wherein, the preset heating rate is 10°C / min, the preset temperature is 1100°C, the preset time is 30 minutes, and the preset cooling rate is 7.5°C / min.

[0052] Experimental example The connection joints prepared in Example 1, Comparative Example 1 and Comparative Example 2 were analyzed by scanning electron microscopy. Figures 2 to 4 ,from Figure 2 It can be seen that a black multi-element carbide layer is formed on the surface of the SiGe in the connection joint prepared in Example 1, and SiGe forms a good connection with tungsten without cracking. In addition, the multi-element carbide layer acts as a diffusion barrier for SiGe, which can inhibit the diffusion of Si and Ge elements to the interface, and its thermal expansion coefficient is similar to that of SiGe, which can effectively relieve the residual stress of the connection joint. Figure 3 It can be seen that in the connection joint prepared in Comparative Example 1, significant cracks occurred between SiGe and tungsten, and no good connection was formed. Figure 4 It can be seen that significant cracking occurred between SiGe and tungsten in the connection joint prepared in Comparative Example 2, and a good connection was not formed. Figure 3 Figure a is a scanning electron microscope image in secondary electron mode. Figure 3Figure b is a scanning electron microscope image in backscattering mode.

[0053] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for connecting a SiGe high-temperature thermoelectric material to a metal electrode, characterized in that: include: Step S1, preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe; Step S2, assembling the carbon-coated SiGe, the multi-principal-element alloy solder, and the metal electrode material in order from top to bottom to obtain an assembly; wherein the multi-principal-element alloy solder includes at least four elements of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu; Step S3: heating the assembly to a preset temperature at a preset heating rate under vacuum conditions, keeping the temperature for a preset time, and cooling to room temperature to obtain a connection joint.

2. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 1, characterized in that: In step S1, the step of preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe includes: Step S11, placing SiGe in a phenolic resin precursor solution for immersion treatment to obtain pretreated SiGe; Step S12: heat-treating the pretreated SiGe under vacuum conditions to obtain the carbon-coated SiGe.

3. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 2, characterized in that: In the step S11, the phenolic resin precursor solution is composed of phenolic resin and organic solvent in a mass ratio of 1: (1 to 5).

4. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 2, wherein: In the step S12, the heating treatment is performed at a temperature of 650° C. to 900° C. and for a time of 10 min to 30 min.

5. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 1, wherein: In step S2, the metal electrode material is selected from at least one of W, W alloy, Mo, Mo alloy, Cr, Cr alloy, Cu, Cu alloy, Ni and Ni alloy.

6. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 1, characterized in that: In the step S1 , the thickness of the carbon layer is 0.1 μm to 10 μm.

7. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 1, wherein: In the step S1 , the thickness of the SiGe is 4 mm to 20 mm.

8. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 1, wherein: In the step S2, the thickness of the multi-principal-component alloy solder is 50 μm to 100 μm.

9. The method for connecting a SiGe high-temperature thermoelectric material to a metal electrode according to claim 1, wherein: In step S2, the thickness of the metal electrode material is 0.3 mm to 4 mm.

10. The method for connecting a SiGe high-temperature thermoelectric material and a metal electrode according to claim 1, characterized in that: In step S3, the preset heating rate is 8°C / min to 12°C / min, the preset temperature is 950°C to 1250°C, and the preset time is 5 min to 60 min.

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