A composite interlayer for SiC ceramic joining and brazing method

Abstract

This invention discloses a composite interlayer for SiC ceramic bonding and a brazing method, belonging to the technical field of ceramic welding components. The composite interlayer consists of metal I, an intermediate metal layer, and metal II arranged sequentially; metal I and metal II are both selected from titanium or vanadium, and their thicknesses are both 0.01–0.05 mm; the intermediate metal layer is a NiCoCr medium-entropy alloy with a thickness of 0.1–0.12 mm. The invention also discloses a brazing method for using the composite interlayer for SiC ceramic bonding components. In this invention, the active metal of the composite interlayer combines with the carbon formed by the reaction, forming carbides dispersed in the joint, refining the size of the silicides, reducing the thermal expansion coefficient of the silicide brazing seam, and simultaneously preventing the formation of graphite at the SiC bonding interface, thereby improving the joint strength. Since the joint does not contain low-melting-point phases and low-strength graphite, it has high high-temperature strength, and the SiC ceramic bonding components produced by this invention are expected to be used in high-temperature environments.

Description

Technical Field

[0001] This invention belongs to the field of ceramic welding technology, and more specifically relates to a composite intermediate layer for SiC ceramic bonding and a brazing connection method. Background Technology

[0002] Currently, metal brazing materials for SiC ceramics can be categorized into Ag-based, Cu-based, Ni-based, Co-based, Ti-based, and Si-based brazing alloys. Among these, Ag-based brazing alloys are the most commonly used ceramic bonding alloys. However, their melting point is generally below 800℃, so the operating temperature of SiC ceramic joints brazed with Ag-based brazing alloys is generally no more than 400℃. Cu-based brazing alloys have a melting point of approximately 900℃, and copper has poor high-temperature oxidation resistance, resulting in poor high-temperature performance of SiC ceramic joints brazed with Cu-based brazing alloys. Ni-based, Co-based, and Ti-based brazing alloys are commonly used for high-temperature bonding of ceramics, with melting points between 950℃ and 1100℃. Although typical Ni-based and Co-based high-temperature alloy brazing alloys readily wet SiC ceramics, they often form a large number of large-sized brittle silicides and low-strength graphite phases in the joint, significantly damaging the SiC substrate properties and resulting in low joint strength. Si-based brazing filler metals have advantages such as high melting point and good oxidation resistance. However, they are brittle and the reliability of brazed joints is relatively poor.

[0003] In recent years, high-entropy (medium-entropy) alloys have attracted widespread attention due to their excellent properties. They generally have high melting points, and their high mixing entropy can effectively prevent the precipitation of brittle intermetallic compounds caused by the addition of excessive other elements, promote the formation of simple solid solutions, and thus improve the strength and plasticity of the alloy. Researchers such as Liu (Liu YH, et al. Journal of the European Ceramic Society, 2022, 42(5):1995-2003.) used a high-entropy alloy of CoFeNiCrCuTi with a single-phase solid solution structure as an intermediate layer for brazing SiC ceramics. The interface reaction was obvious, and the typical microstructure of the joint interface was SiC / C+Cr. 23 C6+TiC / HEA / C+Cr 23 The C6+TiC / SiC joint has a maximum bending strength of 54 MPa. Although the CoFeNiCrCuTi high-entropy alloy contains Ti active elements, graphite residues remain at the interface in the joint, which is detrimental to improving the joint strength and its application in high-temperature oxidizing environments.

[0004] Therefore, exploring a novel high-melting-point brazing filler metal using high-entropy (medium-entropy) alloys and obtaining high-strength SiC connectors, thereby promoting the high-temperature application of SiC ceramic connectors, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a composite intermediate layer and brazing connection method for SiC ceramic connectors, which can improve the bending strength of the joint at room temperature and high temperature, thereby promoting the high-temperature application of SiC ceramic connectors.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A composite interlayer for SiC ceramic bonding, the composite interlayer being composed of metal I, an intermediate metal layer, and metal II arranged sequentially.

[0008] Both metal I and metal II are selected from titanium, or both metal I and metal II are selected from vanadium;

[0009] The intermediate metal layer is a NiCoCr medium-entropy alloy.

[0010] The thickness of both metal I and metal II is 0.01~0.05mm.

[0011] The atomic percentages of Ni, Co, and Cr in the NiCoCr entropy alloy are (0.9~1.0): (0.9~1.0): (0.9~1.0); the thickness of the intermediate metal layer is 0.1~0.12 mm.

[0012] Its beneficial effects are as follows: NiCoCr medium-entropy alloy is a single-phase face-centered cubic solid solution with a high melting point (around 1350℃), good strength and plasticity and excellent cold and hot working properties. Using it as a connecting material for SiC ceramics is expected to yield SiC ceramic connectors with high-temperature application prospects.

[0013] However, the inventors' research shows that, similar to typical Co-based and Ni-based high-temperature solders, although NiCoCr medium-entropy alloys can wet SiC ceramics well, they will produce a strong interfacial chemical reaction with the SiC ceramic substrate. At the joint interface, a large amount of brittle silicides and graphite are formed. Graphite has low strength and poor high-temperature oxidation resistance; therefore, the graphite present at the joint interface will greatly damage the performance of the SiC ceramic substrate and weaken the joint performance.

[0014] Therefore, the inventors further added active metals such as titanium or vanadium to construct an active metal / NiCoCr / active metal composite interlayer. During welding, the composite interlayer forms a liquid phase at the eutectic temperature, reducing the connection temperature. Simultaneously, the active metal in the composite interlayer combines with the carbon formed by the reaction to form carbides that are dispersed throughout the joint. These carbides refine the size of the silicides, reducing the thermal expansion coefficient of the silicide brazing seam. At the same time, this avoids the formation of graphite at the SiC ceramic connection interface, thereby improving joint strength and high-temperature performance.

[0015] This invention also provides a brazing connection method for applying the aforementioned composite intermediate layer to SiC ceramic connectors, comprising the following steps:

[0016] (1) Grind and polish the surfaces of SiC ceramic, metal I, metal II and intermediate metal layer to be welded;

[0017] (2) The SiC ceramic, metal I, metal II and intermediate metal layer after grinding and polishing are ultrasonically cleaned and dried in sequence;

[0018] (3) Assemble the SiC ceramic, metal I, intermediate metal layer, metal II and SiC ceramic in that order, then place them in a graphite mold and braze them to obtain the SiC ceramic connector.

[0019] The grinding and polishing requirement in step (1) is that the surface roughness Ra ≤ 10 μm.

[0020] In step (2), the ultrasonic cleaning is performed using acetone or anhydrous ethanol; the ultrasonic cleaning time is 20 minutes.

[0021] The brazing described in step (3) is vacuum brazing, and the brazing connection process parameters are: vacuum degree ≤ 5 × 10 -2 Pa, heating rate of 10℃ / min, welding temperature of 1360~1400℃, holding time of 6~10min, then cooling to 300℃ at 5℃ / min, and then cooling to room temperature with the furnace.

[0022] The typical microstructure at the joint of the SiC ceramic connector obtained after brazing is SiC / Cr. 23 C6+Cr5Si3 / TiC+Ni2Si+Co2Si / Cr 23 C6+Cr5Si3 / SiC or SiC / Cr 23 C6+Cr5Si3 / VC+Ni2Si+Co2Si / Cr 23 C6+Cr5Si3 / SiC.

[0023] Its beneficial effects are as follows:

[0024] The active metal (titanium or vanadium) in the composite interlayer combines with the reacted carbon to form carbides, preventing the formation of low-strength graphite at the SiC ceramic interface. Simultaneously, due to the different joint microstructure between the active metal and conventional active brazed SiC ceramics, the reacted carbides (TiC, VC) are uniformly dispersed within the brazed metal matrix, rather than forming a brittle carbide layer at the SiC ceramic interface. From a composite reinforcement perspective, the dispersed carbides in the brazed joint can provide dispersion strengthening to the brazed joint matrix, reducing the thermal expansion coefficient of the silicide brazed joint while preventing the formation of large-sized brittle silicides. Thanks to the absence of low-strength graphite at the interface and the formation of dispersed carbides in the weld, the room temperature and high temperature strength of the SiC ceramic joint are improved.

[0025] As can be seen from the above technical solution, compared with the prior art, the advantages of the present invention are:

[0026] (1) Applying NiCoCr medium-entropy alloy to connect SiC, and inserting pure titanium (or pure vanadium) foil between SiC ceramic and NiCoCr medium-entropy alloy, can form a liquid phase at the eutectic temperature of NiCoCr medium-entropy alloy and titanium or vanadium. The active elements of titanium or vanadium in the liquid phase combine with the carbon formed by the decomposition of SiC ceramic. The resulting carbides are dispersed in the joint, which refines the size of silicides and reduces the thermal expansion coefficient of the brazing metal. At the same time, it avoids the formation of graphite at the SiC ceramic connection interface, thereby improving the joint strength.

[0027] (2) Because the interfacial reaction and joint microstructure can be easily controlled by adjusting the thickness of each layer in the composite intermediate layer, without having to change the composition of the solder by the traditional method of smelting to prepare the solder, the present invention has the advantages of flexible operation and low cost.

[0028] (3) Since the connecting layer of the connector has a high melting point and does not contain low-strength graphite, it has high high-temperature strength and the present invention has good high-temperature application prospects. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0030] Figure 1 The image shows a scanning electron microscope (SEM) image of the connector obtained in Example 2 of this invention. It can be seen from the image that the connection interface is well bonded, the carbides are dispersed in the weld, and no graphite formed by the reaction is found.

[0031] Figure 2 The image shows a scanning electron microscope (SEM) image of the connector obtained in Example 3 of this invention. It can be seen from the image that the connection interface is well bonded, the carbides are dispersed in the weld, and no graphite formed by the reaction is found.

[0032] Figure 3 The image shows a scanning electron microscope (SEM) image of the connector obtained in Example 4 of this invention. It can be seen from the image that the connection interface is well bonded, the carbides are dispersed in the weld, and no graphite formed by the reaction is found.

[0033] Figure 4 The image shows a scanning electron microscope (SEM) image of the connector obtained in Comparative Example 1 of this invention. As can be seen from the image, a large amount of graphite is distributed at the connection interface. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] The brazing connection method for SiC ceramic connectors includes the following specific steps:

[0037] (1) SiC ceramics, NiCoCr medium-entropy alloy and pure titanium foil are processed into dimensions of 8mm×8mm×8mm, 8mm×8mm×0.12mm and 8mm×8mm×0.03mm respectively; the atomic percentages of Ni, Co and Cr in NiCoCr medium-entropy alloy are 1:1:1;

[0038] (2) Polish the surfaces of SiC ceramic, NiCoCr medium-entropy alloy, and pure titanium foil to be welded until the surface roughness Ra≤10μm;

[0039] (3) SiC ceramic, NiCoCr medium-entropy alloy and pure titanium foil were placed in anhydrous ethanol for ultrasonic cleaning for 20 min and then dried for later use.

[0040] (4) Combine the materials in the order of SiC / Ti / NiCoCr / Ti / SiC, and then place the combination in a graphite mold; place the graphite mold containing the sample to be welded into a vacuum brazing furnace, with a heating rate of 10℃ / min and a vacuum degree ≤5×10 -2 Pa is heated to the brazing temperature of 1370℃, held for 10 min, and then cooled to 300℃ at a rate of 5℃ / min, and then cooled to room temperature in the furnace to obtain the SiC ceramic connector.

[0041] Example 2

[0042] The brazing temperature was changed to 1380℃, and the rest was the same as in Example 1.

[0043] The microstructure of the brazed joint obtained in Example 2 was examined by scanning electron microscopy, and the scanning electron micrograph is shown in the figure. Figure 1 It can be seen that the brazed joint interface is well connected, with no graphite and carbides (TiC) dispersed in the weld.

[0044] Example 3

[0045] The dimensions of the NiCoCr medium-entropy alloy were changed to 8mm×8mm×0.1 mm, the dimensions of the pure titanium foil were changed to 8mm×8mm×0.015mm, the brazing temperature was changed to 1380℃, the holding time was changed to 6min, and the rest were the same as in Example 1.

[0046] The microstructure of the brazed joint obtained in Example 3 was examined by scanning electron microscopy, and the scanning electron micrograph is shown in the figure. Figure 2 It can be seen that the brazed joint interface is well connected, and no graphite or titanium carbide (TiC) was found to be dispersed in the weld.

[0047] Example 4

[0048] The brazing connection method for SiC ceramic connectors includes the following specific steps:

[0049] (1) SiC ceramics, NiCoCr medium-entropy alloy and pure vanadium foil are processed into dimensions of 8mm×8mm×8mm, 8mm×8mm×0.12mm and 8mm×8mm×0.03mm respectively; the atomic percentage of Ni, Co and Cr in NiCoCr medium-entropy alloy is 0.9:1:0.9;

[0050] (2) Polish the surfaces of SiC ceramic, NiCoCr medium-entropy alloy, and pure vanadium foil to be welded until the surface roughness Ra≤10μm;

[0051] (3) SiC ceramic, NiCoCr medium-entropy alloy and pure vanadium foil were placed in anhydrous ethanol for ultrasonic cleaning for 20 min and then dried for later use.

[0052] (4) Assemble the materials in the order of SiC / V / NiCoCr / V / SiC, and then place the assembly in a graphite mold; place the graphite mold containing the sample to be welded into a vacuum brazing furnace, with a heating rate of 10℃ / min and a vacuum degree ≤5×10 - 2Pa is heated to the brazing temperature of 1380℃, held for 10 min, and then cooled to 300℃ at a rate of 5℃ / min, and then cooled to room temperature in the furnace to obtain the SiC ceramic connector.

[0053] The microstructure of the brazed joint obtained in Example 4 was examined by scanning electron microscopy, and the scanning electron micrograph is shown below. Figure 3 It can be seen that the brazed joint interface is well connected, and no graphite or vanadium carbide (VC) was found to be dispersed in the weld.

[0054] Example 5

[0055] The dimensions of the pure vanadium foil were changed to 8mm×8mm×0.05mm, and the rest were the same as in Example 4.

[0056] Comparative Example 1

[0057] The brazing connection method for SiC ceramic connectors includes the following specific steps:

[0058] (1) The SiC ceramic and NiCoCr medium-entropy alloy sheets are processed into dimensions of 8mm×8mm×8mm and 8mm×8mm×0.12mm respectively; the atomic percentages of Ni, Co and Cr in the NiCoCr medium-entropy alloy are 1:1:1;

[0059] (2) Grind and polish the surfaces of SiC ceramic and NiCoCr medium-entropy alloy sheets to be welded until the surface roughness Ra≤10μm;

[0060] (3) SiC ceramic and NiCoCr medium-entropy alloy sheet were placed in anhydrous ethanol for ultrasonic cleaning for 20 min, and then dried for later use.

[0061] (4) Assemble the materials in the order of SiC ceramic, NiCoCr medium-entropy alloy sheet, and SiC ceramic, and then place the assembly in a graphite mold; place the graphite mold containing the sample to be welded into a vacuum furnace, and heat it at a rate of 10℃ / min with a vacuum degree ≤5×10 -2 The furnace is heated to the brazing temperature of 1380℃ and held for 10 minutes. Then, it is cooled to 300℃ at a rate of 5℃ / min and then cooled to room temperature in the furnace. A SiC ceramic connector is obtained.

[0062] The microstructure of the brazed joint obtained in Comparative Example 1 was examined by scanning electron microscopy, and the scanning electron micrograph is shown below. Figure 4 It can be seen that a large amount of graphite formed by the reaction is distributed at the interface of the SiC ceramic.

[0063] Performance testing

[0064] To compare and analyze the strength of SiC ceramic joints under different processes, a mechanical testing machine was used to test the SiC ceramic brazed connectors. The three-point bending strength of the samples was tested at room temperature and high temperature. Three samples were selected for each group for bending tests, and the bending strength was the average of the three samples. The room temperature bending strength data of the SiC ceramic brazed connectors obtained in Examples 1-5 and Comparative Example 1 are shown in Table 1. The atmospheric high temperature bending strength test data of the SiC ceramic brazed connectors obtained in Example 2 and Comparative Example 1 are shown in Table 2.

[0065] Table 1. Room temperature flexural strength test results of SiC ceramic brazed joints

[0066] Table 2. High-temperature bending strength test results of SiC ceramic brazed joints

[0067] As can be seen from the data in the table above, the room temperature and high temperature bending strength of the connector obtained by the scheme of the present invention are significantly higher than those of the connector obtained by the scheme of Comparative Example 1, and it has high practical value.

[0068] This invention inserts a pure titanium (or pure vanadium) foil between a NiCoCr medium-entropy alloy sheet and a SiC ceramic. This allows a liquid phase to form at the eutectic temperature of the NiCoCr medium-entropy alloy and titanium or vanadium. The active titanium or vanadium elements in the liquid phase combine with the carbon formed from the decomposition of the SiC ceramic to form carbides that are dispersed throughout the joint. This reduces the thermal expansion coefficient of the silicide weld joint and refines the size of the silicides. Simultaneously, it avoids graphite formation at the interface, thereby improving the joint strength. Compared to a single NiCoCr medium-entropy alloy interlayer, the composite interlayer effectively suppresses graphite formation at the joint interface, while the reacted carbide reinforcing phase is dispersed throughout the joint, improving the connection strength of the connector. Furthermore, because the connector layer has a high melting point and does not contain low-strength graphite, it exhibits high high-temperature strength.

[0069] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0070] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A brazing connection method for applying a composite interlayer to SiC ceramic connectors, characterized in that, The composite intermediate layer is composed of metal I, an intermediate metal layer, and metal II arranged in sequence. Metal I and metal II are both selected from titanium or metal I and metal II are both selected from vanadium. The intermediate metal layer is a NiCoCr medium-entropy alloy. Includes the following steps: (1) Grind and polish the surfaces of SiC ceramic, metal I, metal II and intermediate metal layer to be welded; (2) The SiC ceramic, metal I, metal II and intermediate metal layer after grinding and polishing are ultrasonically cleaned and dried in sequence; (3) Assemble the SiC ceramic, metal I, intermediate metal layer, metal II and SiC ceramic in that order, then place them in a graphite mold and braze them to obtain the SiC ceramic connector.

2. The brazing connection method according to claim 1, characterized in that, The thickness of both metal I and metal II is 0.01~0.05mm.

3. The brazing connection method according to claim 1, characterized in that, The atomic ratio of Ni, Co and Cr is (0.9~1.0): (0.9~1.0): (0.9~1.0); the thickness of the intermediate metal layer is 0.1~0.12 mm.

4. The brazing connection method according to claim 1, characterized in that, The grinding and polishing requirement in step (1) is that the surface roughness Ra ≤ 10 μm.

5. The brazing connection method according to claim 1, characterized in that, In step (2), acetone or anhydrous ethanol is used for ultrasonic cleaning; the ultrasonic cleaning time is 20 min.

6. The brazing connection method according to claim 1, characterized in that, The brazing described in step (3) is vacuum brazing, and the brazing connection process parameters are: vacuum degree ≤ 5 × 10 -2 Pa, heating rate of 10℃ / min, welding temperature of 1360~1400℃, holding time of 6~10min, then cooling to 300℃ at 5℃ / min, and then cooling to room temperature with the furnace.

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