A method for connecting a SiGe high-temperature thermoelectric material and a metal electrode

Abstract

The application provides a SiGe high-temperature thermoelectric material and metal electrode connecting method, relates to the field of welding technology, and the connecting method comprises the following steps: preparing a carbon layer on a SiGe surface to obtain carbon-coated SiGe; sequentially assembling the carbon-coated SiGe, multi-main-element alloy filler and metal electrode material from top to bottom to obtain an assembly; under a vacuum condition, heating the assembly to a preset temperature at a preset heating rate, keeping the temperature for a preset time, and cooling to room temperature to obtain a connecting joint. The SiGe thermoelectric material and the metal electrode are connected by the method, which can not only avoid cracking of the connecting joint, but also avoid significant diffusion of Si and Ge elements in the SiGe thermoelectric material into the weld, thereby avoiding performance attenuation of the thermoelectric material and continuous deterioration of the hetero-interface bonding performance.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a method for connecting a SiGe high-temperature thermoelectric material to a metal electrode. Background Technology

[0002] Thermoelectric devices achieve efficient conversion of thermal and electrical energy based on the Seebeck and Peltier effects, and have significant application potential in fields such as industrial waste heat recovery, deep space exploration power supply, solid-state refrigeration, and micro-area temperature control. Silicon-germanium (SiGe) is a common thermoelectric material. Its excellent mechanical properties and thermal stability at high temperatures make it the ideal choice for long-term energy supply in harsh environments such as extreme temperatures and radiation. However, the difficulty in coordinating diffusion and stress at the heterogeneous interface between SiGe thermoelectric materials and metal electrodes, as well as poor connection reliability, restricts the improvement of the interface characteristics between SiGe thermoelectric materials and metal electrodes, becoming a key bottleneck restricting the energy conversion efficiency of thermoelectric devices. Specifically, due to the high intrinsic brittleness and low coefficient of thermal expansion of SiGe, the heterogeneous interface connection suffers from a mismatch in the coefficient of thermal expansion, making it prone to post-weld cracking under residual stress. During high-temperature connection and service, Si and Ge elements (especially Si) in the thermoelectric material diffuse significantly into the weld, causing the performance of the thermoelectric material to degrade and the bonding performance of the heterogeneous interface to continuously deteriorate, seriously affecting the long-term stability of the device. Summary of the Invention

[0003] The problem solved by this invention is at least one of the following: (1) How to avoid cracking of the joint when connecting SiGe thermoelectric material and metal electrode. (2) How to prevent Si and Ge elements in SiGe thermoelectric material from significantly diffusing into the weld when connecting SiGe thermoelectric material and metal electrode, thereby avoiding the degradation of thermoelectric material performance and continuous deterioration of heterogeneous interface bonding performance.

[0004] To address the above problems, this invention provides a method for connecting a SiGe high-temperature thermoelectric material to a metal electrode, comprising: Step S1: Prepare a carbon layer on the SiGe surface to obtain carbon-coated SiGe; Step S2: Assemble the carbon-coated SiGe, multi-principal element alloy brazing filler metal, and metal electrode material in a top-to-bottom order to obtain an assembly; wherein the multi-principal element alloy brazing filler metal includes at least four elements selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu. Step S3: Under vacuum conditions, heat the assembly to a preset temperature at a preset heating rate, hold it at the temperature for a preset time, and cool it to room temperature to obtain the connection joint.

[0005] Optionally, in step S1, the preparation of a carbon layer on the SiGe surface to obtain carbon-coated SiGe includes: Step S11: Place SiGe in a phenolic resin precursor solution and soak it to obtain pretreated SiGe; Step S12: The pretreated SiGe is heated under vacuum 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 temperature of the heat treatment is 650°C to 900°C, and the time is 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 alloy brazing filler metal 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℃ / min to 12℃ / min, the preset temperature is 950℃ to 1250℃, and the preset time is 5min to 60min.

[0014] Compared with related technologies, this invention first prepares a carbon layer on the surface of SiGe high-temperature thermoelectric material to obtain carbon-coated SiGe, and then uses a multi-principal alloy brazing filler metal to braze the carbon-coated SiGe to the metal electrode. Since the multi-principal alloy brazing filler metal is composed of at least four elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu, which have a strong affinity for carbon, the carbon layer on the surface of SiGe reacts in situ with the multi-principal alloy brazing filler metal during the connection process to form a multi-principal carbide layer. This multi-principal carbide layer acts as a diffusion barrier layer for SiGe, which can inhibit the diffusion of Si and Ge elements to the connection interface. Moreover, the thermal expansion coefficient of the multi-principal carbide layer is similar to that of SiGe, which can effectively alleviate the residual stress of the joint, and finally achieve a high-temperature reliable connection between the SiGe thermoelectric material and the metal electrode. In summary, the method provided by this invention for connecting SiGe thermoelectric materials and metal electrodes can not only avoid cracking of the joint, but also prevent significant diffusion of Si and Ge elements in the SiGe thermoelectric material into the weld, thereby avoiding the degradation of thermoelectric material performance and the continuous deterioration of heterogeneous interface bonding performance. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the connection method between SiGe high-temperature thermoelectric material and metal electrode in an embodiment of the present invention; Figure 2 The image shows a scanning electron microscope (SEM) image of the connector prepared in Example 1. Figure 3 The image shows a scanning electron microscope (SEM) image of the connector prepared in Comparative Example 1. Figure 4 This is a scanning electron microscope image of the connector prepared in Comparative Example 2. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying 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 this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0018] The term "comprising" and its variations as used herein are open-ended, meaning "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 additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the following description. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0019] The poor reliability of the connection, caused by difficulties in coordinating diffusion and stress at the heterogeneous interface between SiGe thermoelectric materials and metal electrodes, hinders the improvement of the interface characteristics between SiGe thermoelectric materials and metal electrodes, becoming a key bottleneck restricting the energy conversion efficiency of thermoelectric devices. Specifically, due to the high intrinsic brittleness and low coefficient of thermal expansion of SiGe, the heterogeneous interface connection suffers from a mismatch in the coefficient of thermal expansion, making it prone to post-weld cracking under residual stress. During high-temperature connection and service, Si and Ge elements (especially Si) in the thermoelectric material diffuse significantly into the weld, causing a degradation in the performance of the thermoelectric material and a continuous deterioration in the bonding performance of the heterogeneous interface, seriously affecting the long-term stability of the device.

[0020] In related technologies, the connection methods between SiGe high-temperature thermoelectric materials and metal electrodes are mainly diffusion bonding and integrated sintering. In diffusion bonding, Ti is used as the intermediate layer for diffusion bonding. During the bonding process, elements diffuse significantly, forming Kirkendal pores. The integrated sintering method uses titanium oxide and silicide powders as transition intermediate layers and plays a diffusion blocking role. However, the sintering interface is tortuous and uncontrollable, and the intermediate sintering layer is often very thick, introducing additional interface resistance problems.

[0021] To address the problems existing in the aforementioned related technologies, embodiments of the present invention provide a method for connecting a SiGe high-temperature thermoelectric material to a metal electrode, comprising: Step S1: Prepare a carbon layer on the SiGe surface to obtain carbon-coated SiGe, denoted as SiGe@C; Step S2: Assemble the carbon-coated SiGe, multi-principal element alloy solder, and metal electrode material in a top-to-bottom order to obtain an assembly; wherein, the assembly has a sandwich structure, and from top to bottom, it consists of carbon-coated SiGe, multi-principal element alloy solder, and metal electrode material, wherein the multi-principal element alloy solder includes at least four elements selected from Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu; Step S3: Under vacuum conditions, heat the assembly to a preset temperature at a preset heating rate, hold it at the temperature for a preset time, and cool it to room temperature to obtain the connection joint.

[0022] In this embodiment of the invention, a carbon layer is first prepared on the surface of the SiGe high-temperature thermoelectric material to obtain carbon-coated SiGe. Then, a multi-principal element alloy solder is used to braze the carbon-coated SiGe to the metal electrode. Since the multi-principal element alloy solder is composed of at least four elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Fe, and Cu, which have a strong affinity for carbon, the carbon layer on the surface of SiGe reacts in situ with the multi-principal element alloy solder during the connection process to form a multi-principal element carbide layer. This 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. Moreover, 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 finally achieve a high-temperature reliable connection between the SiGe thermoelectric material and the metal electrode. In summary, the method provided in this embodiment of the invention for connecting SiGe thermoelectric materials and metal electrodes can not only avoid cracking of the joint, but also prevent Si and Ge elements in the SiGe thermoelectric material from significantly diffusing into the weld, thereby avoiding the degradation of thermoelectric material performance and the continuous deterioration of heterogeneous interface bonding performance.

[0023] In some embodiments of the present invention, exemplarily, step S1, which involves preparing a carbon layer on the SiGe surface to obtain carbon-coated SiGe, includes: Step S11: Place SiGe in a phenolic resin precursor solution and soak it to obtain pretreated SiGe; Step S12: The pretreated SiGe is heated under vacuum conditions to decompose the phenolic resin, thereby forming a uniformly coated carbon layer on the surface of SiGe, thus obtaining 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 temperature of the heat treatment is 650°C to 900°C, and the time is 10 min to 30 min.

[0026] In some embodiments of the present invention, exemplarily, step S1, which involves preparing a carbon layer on the SiGe surface to obtain carbon-coated SiGe, includes: Carbon was deposited on the surface of SiGe by magnetron sputtering to obtain carbon-coated SiGe. In some embodiments of the present invention, exemplarily, step S1, which involves preparing a carbon layer on the SiGe surface to obtain carbon-coated SiGe, includes: SiGe is placed in a glucose precursor solution and heated to form a uniformly coated carbon layer on the surface of SiGe, thereby obtaining the carbon-coated SiGe; wherein the heating 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 alloy brazing filler metal 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 5min to 60min.

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

[0034] Example 1 A1. SiGe is placed in a phenolic resin precursor solution and soaked to obtain pretreated SiGe; wherein, the SiGe is in the shape of a sheet with a thickness of 4mm, the phenolic resin precursor solution is composed of phenolic resin and anhydrous ethanol in an organic solvent at a mass ratio of 1:1, and the soaking time is 20min.

[0035] A2. The pretreated SiGe is heated under vacuum to obtain carbon-coated SiGe; wherein the heating temperature is 775℃ and the time is 20min.

[0036] A3. Assemble the carbon-coated SiGe, multi-principal element alloy solder, and metal electrode material in a top-to-bottom order to obtain an assembly; wherein, the multi-principal element 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 element alloy solder is 1:1:1:1:1, the multi-principal element alloy solder is a foil with a thickness of 75 μm; the metal electrode material is made of W, and its shape is sheet-like with a thickness of 2 mm.

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

[0038] Example 2 A1. SiGe is placed in a phenolic resin precursor solution and soaked to obtain pretreated SiGe; wherein, the SiGe is in the shape of a sheet with a thickness of 20mm, the phenolic resin precursor solution is composed of phenolic resin and anhydrous ethanol in an organic solvent at a mass ratio of 1:1, and the soaking time is 20min.

[0039] A2. The pretreated SiGe is heated under vacuum to obtain the carbon-coated SiGe; wherein the heating temperature is 900℃ and the time is 5min.

[0040] A3. Assemble the carbon-coated SiGe, multi-principal element alloy solder, and metal electrode material in a top-to-bottom order to obtain an assembly; wherein, the multi-principal element 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 element alloy solder is 1:1:1:1:1, the multi-principal element alloy solder is a foil with a thickness of 100 μm; the metal electrode material is made of W, and its shape is sheet-like with a thickness of 4 mm.

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

[0042] Example 3 A1. SiGe is placed in a phenolic resin precursor solution and soaked to obtain pretreated SiGe; wherein, the SiGe is in the shape of a sheet with a thickness of 20mm, the phenolic resin precursor solution is composed of phenolic resin and anhydrous ethanol in an organic solvent at a mass ratio of 1:1, and the soaking time is 20min.

[0043] A2. The pretreated SiGe is heated under vacuum to obtain carbon-coated SiGe; wherein the heating temperature is 650℃ and the time is 30min.

[0044] A3. Assemble the carbon-coated SiGe, multi-principal element alloy solder, and metal electrode material in a top-to-bottom order to obtain an assembly; wherein, the multi-principal element 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 element alloy solder is 1:1:1:1:1, the multi-principal element alloy solder is a foil with a thickness of 50 μm; the metal electrode material is made of W, is in sheet shape, and has a thickness of 0.3 mm.

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

[0046] Comparative Example 1 SiGe, multi-principal component alloy solder, and metal electrode material are assembled sequentially from top to bottom to obtain an assembly. The SiGe is in sheet form with a thickness of 4 mm. The multi-principal component alloy solder is composed of Ti, Fe, Cr, Ni, and Mo, with a molar ratio of 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 sheet form, and has a thickness of 2 mm.

[0047] The assembly is heated to a preset temperature at a preset heating rate under vacuum conditions, held 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 connecting joint; wherein the preset heating rate is 10°C / min, the preset temperature is 1100°C, the preset time is 30 min, and the preset cooling rate is 7.5°C / min.

[0048] Comparative Example 2 SiGe was placed in a phenolic resin precursor solution and immersed to obtain pretreated SiGe. The SiGe was in the form of flakes with a thickness of 4 mm. The phenolic resin precursor solution was composed of phenolic resin and anhydrous ethanol in a mass ratio of 1:1. The immersion time was 20 min.

[0049] The pretreated SiGe was heated under vacuum conditions to obtain carbon-coated SiGe; wherein the heating temperature was 775°C and the time was 20 min.

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

[0051] The assembly is heated to a preset temperature at a preset heating rate under vacuum conditions, held 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 connecting joint; wherein the preset heating rate is 10°C / min, the preset temperature is 1100°C, the preset time is 30 min, and the preset cooling rate is 7.5°C / min.

[0052] Experimental Example Scanning electron microscopy analysis was performed on the connectors prepared in Example 1, Comparative Example 1, and Comparative Example 2. The results are shown in the figure. Figures 2 to 4 ,from Figure 2 It can be seen that a black multi-principal element carbide layer forms on the surface of SiGe in the connector prepared in Example 1, and SiGe and tungsten form a good bond without cracking. Furthermore, the multi-principal element carbide layer acts as a diffusion barrier layer for SiGe, inhibiting the diffusion of Si and Ge elements to the interface. Its coefficient of thermal expansion is similar to that of SiGe, effectively alleviating the residual stress in the connector. Figure 3 It can be seen that significant cracking occurred between SiGe and tungsten in the joint prepared in Comparative Example 1, resulting in a poor connection. From... Figure 4 It can be seen that significant cracking occurred between SiGe and tungsten in the joint prepared in Comparative Example 2, resulting in a poor connection. It should be noted that... Figure 3 Image 'a' in the middle is a scanning electron microscope image in secondary electron mode. Figure 3Image b in the middle is a scanning electron microscope image in backscatter mode.

[0053] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for connecting a SiGe high temperature thermoelectric material to a metal electrode, characterized by, include: Step S1: Prepare a carbon layer on the SiGe surface to obtain carbon-coated SiGe; wherein the thickness of the carbon layer is 0.1 μm to 10 μm; Step S2: Assemble the carbon-coated SiGe, multi-principal alloy brazing filler metal, and metal electrode material in a top-to-bottom order to obtain an assembly; wherein the multi-principal alloy brazing filler metal includes Ti, Fe, Cr, Ni, and Mo, and the molar ratio of Ti, Fe, Cr, Ni, and Mo in the multi-principal alloy brazing filler metal is 1:1:1:1:1; Step S3: Under vacuum conditions, heat the assembly to a preset temperature at a preset heating rate, hold it at the temperature for a preset time, and cool it to room temperature to obtain the connection joint.

2. The method of connecting a SiGe high temperature thermoelectric material to a metal electrode of claim 1, wherein, In step S1, the preparation of a carbon layer on the SiGe surface to obtain carbon-coated SiGe includes: Step S11: Place SiGe in a phenolic resin precursor solution and soak it to obtain pretreated SiGe; Step S12: The pretreated SiGe is heated under vacuum to obtain the carbon-coated SiGe.

3. The method of connecting a SiGe high temperature thermoelectric material to a metal electrode of claim 2, wherein, 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).

4. The method for connecting the SiGe high-temperature thermoelectric material and the metal electrode according to claim 2, characterized in that, In step S12, the temperature of the heat treatment is 650°C to 900°C, and the time is 10 min to 30 min.

5. The method for connecting the SiGe high-temperature thermoelectric material and the metal electrode according to claim 1, characterized in that, 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, Ni alloy.

6. The method for connecting the SiGe high-temperature thermoelectric material and the metal electrode according to claim 1, characterized in that, In step S1, the thickness of the SiGe is 4 mm to 20 mm.

7. The method for connecting the SiGe high-temperature thermoelectric material and the metal electrode according to claim 1, characterized in that, In step S2, the thickness of the multi-principal alloy brazing filler metal is 50 μm to 100 μm.

8. The method for connecting the SiGe high-temperature thermoelectric material and the metal electrode according to claim 1, characterized in that, In step S2, the thickness of the metal electrode material is 0.3 mm to 4 mm.

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

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