A method for air reaction brazing YSZ ceramic and stainless steel using Ag-Co3O4 filler

Abstract

The application discloses a method for air reaction brazing YSZ ceramic and stainless steel by using Ag-Co3O4 filler, and relates to a method for air reaction brazing YSZ ceramic and stainless steel. The application aims at solving the technical problems that the welding joint obtained by the existing brazing connection method of YSZ ceramic and Crofer22H stainless steel is prone to excessive reaction with the base material, thereby damaging the structure and functional integrity of the base material, and the microstructure and mechanical stability of the joint are poor under a high-temperature air environment for a long time. The application successfully realizes the effective connection of YSZ ceramic and Crofer22H stainless steel under air conditions by using Ag-Co3O4 filler, the filler is well combined with the base materials on both sides, the joint microstructure is dense and defect-free, and the air tightness of the joint is ensured; the filler does not excessively react with the base materials on both sides, thereby ensuring the overall structure and functional integrity of the base materials, and the obtained joint has excellent high-temperature stability.

Description

Technical Field

[0001] The invention relates to a method for air reaction brazing of YSZ ceramics and stainless steel. Background Art

[0002] Electrolysis technology will play a central role in future energy systems, serving as a vital link between electricity, natural gas, and heat grids, and fueling the transportation sector. Solid oxide electrolysis cell technology, a scalable electrolysis technology, holds broad potential for development. Successful operation of solid oxide electrolysis cells requires an effective, sealed connection between the YSZ electrolyte and the stainless steel interconnects.

[0003] Currently, the connection between YSZ and stainless steel includes air reaction brazing, active metal brazing, glass ceramic connection and other methods. Air reaction brazing is currently the most popular method for connecting electrolyte ceramics (YSZ) and stainless steel connectors (Crofer22H). However, although the Ag-CuO brazing filler metals and Ag-Nb2O5 brazing filler metals commonly used in air reaction brazing have good connection effects, they often react severely with ceramics and metal base materials, seriously damaging the base material structure, and the resulting welded joints will seriously degrade in microstructure and performance under long-term high-temperature air conditions. For this reason, it is very necessary to develop a new air reaction brazing filler metal suitable for YSZ ceramics and Crofer22H stainless steel, so as to obtain a joint that does not over-react with the base material during the welding process and has excellent long-term stability in high-temperature air environments. Summary of the Invention

[0004] The present invention aims to solve the technical problems that the welded joint obtained by the existing brazing connection method of YSZ ceramics and Crofer22H stainless steel is prone to excessive reaction with the base material, thereby destroying the structural and functional integrity of the base material, and the joint has poor organizational and mechanical stability in a long-term high-temperature air environment. The present invention provides a method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction.

[0005] The method for brazing YSZ ceramic and stainless steel using Ag-Co3O4 brazing filler metal in air reaction is carried out according to the following steps:

[0006] 1. Ag powder and Co3O4 powder are mixed by ball milling to obtain Ag-Co3O4 solder powder, and then the solder powder is prepared into Ag-Co3O4 solder flakes; the molar ratio of the Ag powder to the Co3O4 powder is (15-99):(1-15);

[0007] 2. Place the Ag-Co3O4 solder sheet prepared in step 1 between the to-be-welded surfaces of the parent material YSZ ceramic and the parent material Crofer22H stainless steel to form a YSZ / Ag-Co3O4 solder / Crofer22H sandwich structure;

[0008] 3. Place the sample to be welded obtained in step 2 into an air muffle furnace, then heat it from room temperature to 960℃~1200℃ and keep it warm for 1min~90min, then cool it to 300℃~310℃, and finally cool it to room temperature with the furnace. This completes the air bonding of YSZ ceramic and Crofer22H stainless steel using Ag-Co3O4 solder.

[0009] The present invention has the following beneficial effects:

[0010] The present invention uses Ag-Co3O4 solder to successfully achieve effective connection between YSZ ceramics and Crofer22H stainless steel under air conditions. The solder is well bonded to the parent materials on both sides, and the joint structure is dense and defect-free, ensuring the airtightness of the joint. The solder does not over-react with the parent materials on both sides, thereby ensuring the overall structural and functional integrity of the parent materials. The thickness of the oxide layer on the Crofer22H side of the parent material of the joint is 8μm, and the room temperature shear strength of the joint is 51MPa. After aging in air conditions at 800℃ for 300h, the joint structure did not change significantly. The thickness of the oxide layer on the Crofer22H side of the joint was 9.5μm, which was only 19% thicker than that at room temperature. The shear strength of the joint was 45MPa, which was only 12% lower than the room temperature strength. This shows that the joint obtained by brazing YSZ ceramics and Crofer22H stainless steel using Ag-Co3O4 solder has excellent high-temperature stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a backscattered electron scanning photograph of the joint obtained after the completion of Experiment 1;

[0012] Figure 2 This is a backscattered electron scanning photograph of the joint obtained after the completion of experiment 1 and after oxidation at 800℃ in air for 300h. DETAILED DESCRIPTION

[0013] Specific embodiment 1: This embodiment is a method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction, which is specifically carried out in the following steps:

[0014] 1. Ag powder and Co3O4 powder are mixed by ball milling to obtain Ag-Co3O4 solder powder, and then the solder powder is prepared into Ag-Co3O4 solder flakes; the molar ratio of the Ag powder to the Co3O4 powder is (15-99):(1-15);

[0015] 2. Place the Ag-Co3O4 solder sheet prepared in step 1 between the to-be-welded surfaces of the parent material YSZ ceramic and the parent material Crofer22H stainless steel to form a YSZ / Ag-Co3O4 solder / Crofer22H sandwich structure;

[0016] 3. Place the sample to be welded obtained in step 2 into an air muffle furnace, then heat it from room temperature to 960℃~1200℃ and keep it warm for 1min~90min, then cool it to 300℃~310℃, and finally cool it to room temperature with the furnace. This completes the air bonding of YSZ ceramic and Crofer22H stainless steel using Ag-Co3O4 solder.

[0017] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the particle size of the Ag powder in step 1 is 10 μm. Other aspects are the same as those of specific embodiment 1.

[0018] Specific embodiment 3: This embodiment differs from specific embodiment 2 in that the particle size of the Co3O4 powder in step 1 is 10 μm. Other aspects are the same as those of specific embodiment 2.

[0019] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the molar ratio of Ag powder to Co3O4 powder in step 1 is 19:1. Other aspects are the same as specific embodiments 1 to 3.

[0020] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the Ag-Co3O4 solder flakes described in step 1 are prepared by a tablet press. Other aspects are the same as specific embodiment 4.

[0021] Specific embodiment 6: This embodiment differs from specific embodiment 5 in that in step 3, the temperature is raised from room temperature to 960°C to 1200°C at a heating rate of 1°C / min to 20°C / min and kept at that temperature for 1 minute to 90 minutes. Other aspects are the same as specific embodiment 5.

[0022] Specific embodiment 7: This embodiment differs from specific embodiment 6 in that in step 3, the temperature is raised from room temperature to 1050° C. at a heating rate of 20° C. / min and kept at that temperature for 30 minutes. Other aspects are the same as specific embodiment 6.

[0023] Specific embodiment eight: This embodiment differs from specific embodiment seven in that in step three, the temperature is raised from room temperature to 1050° C. at a heating rate of 20° C. / min and kept at that temperature for 30 minutes, and then cooled to 300° C. The rest is the same as specific embodiment seven.

[0024] Specific embodiment 9: This embodiment differs from specific embodiment 8 in that in step 3, the temperature is raised from room temperature to 1050°C at a heating rate of 20°C / min and kept at that temperature for 30 minutes, and then cooled to 300°C at a cooling rate of 20°C / min. Other aspects are the same as specific embodiment 8.

[0025] Specific embodiment 10: This embodiment differs from specific embodiment 9 in that in step 2, the two base materials need to be ultrasonically cleaned first. Other aspects are the same as specific embodiment 9.

[0026] The present invention is verified by the following test:

[0027] Experiment 1: This experiment is a method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction. The specific steps are as follows:

[0028] 1. Ag powder with a particle size of 10 μm and Co3O4 powder with a particle size of 10 μm were mixed by ball milling to obtain Ag-Co3O4 solder powder, and then the solder powder was prepared into Ag-Co3O4 solder flakes by a tablet press; the molar ratio of the Ag powder to the Co3O4 powder was 19:1;

[0029] 2. First, ultrasonically clean the YSZ ceramic and Crofer 22H stainless steel substrates. Then, place the Ag-Co3O4 solder sheet prepared in step 1 between the surfaces to be welded of the YSZ ceramic and Crofer 22H stainless steel substrates to form a YSZ / Ag-Co3O4 solder / Crofer 22H sandwich structure.

[0030] 3. Place the sample to be welded obtained in step 2 into an air muffle furnace, then heat it from room temperature to the joining temperature at a heating rate of 20°C / min and keep it at that temperature for 30 minutes, then cool it to 300°C at a cooling rate of 20°C / min, and finally cool it to room temperature with the furnace, thus completing the air joining of YSZ ceramic and Crofer22H stainless steel with Ag-Co3O4 solder; the joining temperature is 1050°C.

[0031] Experiment 2: This experiment differs from Experiment 1 in that the molar ratio of Ag powder to Co3O4 powder in step 1 is 99:1. Other steps are the same as Experiment 1.

[0032] Experiment 3: This experiment differs from Experiment 1 in that the molar ratio of Ag powder to Co3O4 powder in step 1 is 93:7. Other steps are the same as Experiment 1.

[0033] Experiment 4: This experiment differs from Experiment 1 in that the molar ratio of Ag powder to Co3O4 powder in step 1 is 88:12. Other steps are the same as Experiment 1.

[0034] Test 5: This test differs from Test 1 in that the connection temperature in step 3 is 970° C. Other aspects are the same as Test 1.

[0035] Test 6: This test differs from Test 1 in that the connection temperature in step 3 is 1010° C. Other steps are the same as Test 1.

[0036] Test 7: This test differs from Test 1 in that the connection temperature in step 3 is 1090° C. Other steps are the same as Test 1.

[0037] Test 8: This test differs from Test 1 in that the connection temperature in step 3 is 1130° C. Other conditions are the same as Test 1.

[0038] Experiment 9: This experiment differs from Experiment 1 in that the holding time in step 3 is 5 minutes. Other conditions are the same as Experiment 1.

[0039] Experiment 10: This experiment differs from Experiment 1 in that the holding time in step 3 is 15 minutes. Other conditions are the same as Experiment 1.

[0040] Experiment 11: This experiment differs from Experiment 1 in that the holding time in step 3 is 45 minutes. Other conditions are the same as Experiment 1.

[0041] Experiment 12: This experiment differs from Experiment 1 in that the holding time in step 3 is 60 minutes. Other conditions are the same as Experiment 1.

[0042] The mechanical properties of the joints obtained in the above tests were evaluated by shear strength. The shear strengths of the joints obtained under different connection processes in Tests 1 to 12 are shown in Table 1. The results show that the Ag-Co3O4 solder of the present invention can be used to obtain joints with excellent mechanical properties, among which the shear strength of the joint obtained in Test 1 reached 51 MPa.

[0043] Table 1

[0044] test Shear strength (MPa) Experiment 1 51 Experiment 2 23 Experiment 3 19 Test 4 10 Test 5 8 Test 6 19 Test 7 26 Test 8 5 Test Nine 29 Test 10 31 Test 11 28 Test 12 21

[0045] Figure 1 This is a backscattered electron scanning photo of the joint obtained after the completion of the experiment 1. It can be seen from the figure that the joint is dense and has no defects such as pores and cracks. The thickness of the oxide layer on the Crofer22H side of the base material is 8μm. Table 2 Figure 1 The chemical composition of the phases at each point in the figure shows that the phases of the entire joint are Co3O4, (Ag+Co3O4) weld middle layer, (CoCr2O4+Cr2O3) oxide layer from left to right. The thickness of the oxide layer on the Crofer 22H stainless steel side is only 8μm.

[0046] Figure 2This is a backscattered electron scanning photograph of the joint obtained after the completion of experiment 1 and oxidation at 800℃ in air for 300 hours. It can be seen from the figure that the joint has no defects. The thickness of the oxide layer on the Crofer22H side of the base material has only increased to 9.5μm, which is only 19% thicker than at room temperature. Table 3 Figure 2 The chemical composition of the phases at each point in the figure shows that the phases of the entire joint, from left to right, remain Co3O4, (Ag+Co3O4) weld intermediate layer, and (CoCr2O4+Cr2O3) oxide layer, with no change in structure compared to Table 2. The thickness of the oxide layer on the Crofer22H side of the base material increases only to 9.5 μm. Shear strength testing revealed a shear strength of 45 MPa, only 12% lower than the room temperature strength, ensuring the stability of the joint's structure and mechanical properties at high temperatures for extended periods.

[0047] Table 2

[0048] Location Ag Co O Fe Cr phase of matter 1 1.85 42.25 55.90 - - <![CDATA[Co3O4]]> 2 98.2 - 1.8 - - Ag 3 3.87 38.11 58.02 - - <![CDATA[Co3O4]]> 4 - 16.60 58.69 0.65 24.06 <![CDATA[CoCr2O4]]> 5 - 0.66 59.98 1.79 37.57 <![CDATA[Cr2O3]]>

[0049] Table 3

[0050] Location Ag Co O Fe Cr phase of matter 1 1.85 39.11 59.04 - - Co304 2 96.8 - 3.2 - - Ag 3 3.87 40.35 55.78 - - <![CDATA[Co3O4]]> 4 - 12.77 60.22 0.65 26.36 <![CDATA[CoCr2O4]]> 5 - 0.26 58.78 2.79 38.17 Cr2O3

Claims

1. A method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction, characterized in that The method of brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction is carried out in the following steps:

1. Ag powder and Co3O4 powder are mixed by ball milling to obtain Ag-Co3O4 solder powder, and then the solder powder is prepared into Ag-Co3O4 solder flakes; the molar ratio of the Ag powder to the Co3O4 powder is (15-99):(1-15); 2. Place the Ag-Co3O4 solder sheet prepared in step 1 between the to-be-welded surfaces of the parent material YSZ ceramic and the parent material Crofer22H stainless steel to form a YSZ / Ag-Co3O4 solder / Crofer22H sandwich structure; 3. Place the sample to be welded obtained in step 2 into an air muffle furnace, then heat it from room temperature to 960℃~1200℃ and keep it warm for 1min~90min, then cool it to 300℃~310℃, and finally cool it to room temperature with the furnace. This completes the air bonding of YSZ ceramic and Crofer22H stainless steel using Ag-Co3O4 solder.

2. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 1, characterized in that The particle size of the Ag powder described in step 1 is 10 μm.

3. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 2, characterized in that The particle size of the Co3O4 powder described in step 1 is 10 μm.

4. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 3, characterized in that The molar ratio of Ag powder to Co3O4 powder in step 1 is 19:

1.

5. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 1, characterized in that The Ag-Co3O4 solder flakes described in step 1 are prepared by a tablet press.

6. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 1, characterized in that In step 3, the temperature is raised from room temperature to 960°C to 1200°C at a heating rate of 1°C / min to 20°C / min and kept at this temperature for 1min to 90min.

7. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 6, characterized in that In step 3, the temperature was raised from room temperature to 1050°C at a heating rate of 20°C / min and kept at this temperature for 30 minutes.

8. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 7, characterized in that In step 3, the temperature was raised from room temperature to 1050°C at a heating rate of 20°C / min and kept at that temperature for 30 minutes, and then cooled to 300°C.

9. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 8, characterized in that In step 3, the temperature was raised from room temperature to 1050°C at a heating rate of 20°C / min and kept at that temperature for 30 minutes, and then cooled to 300°C at a cooling rate of 20°C / min.

10. The method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 1, characterized in that In step 2, the two base materials first need to be ultrasonically cleaned.

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