Method for air reaction brazing of YSZ ceramic and stainless steel through Ag-Co3O4 brazing filler metal

Abstract

The invention relates to a method for air reaction brazing of YSZ ceramic and stainless steel, in particular to a method for air reaction brazing of YSZ ceramic and stainless steel through Ag-Co3O4 brazing filler metal. The method aims at solving the technical problems that a welded joint obtained through an existing brazing connection method of YSZ ceramic and Crofer22H stainless steel is prone to excessively reacting with base metal, so that the structural and functional integrity of the base metal is damaged, and the tissue and mechanical stability of the joint is poor in the long-time high-temperature air environment. According to the method, effective connection of the YSZ ceramic and the Crofer22H stainless steel under the air condition is successfully achieved through the Ag-Co3O4 brazing filler metal, the brazing filler metal is well combined with base metal on the two sides, the joint structure is compact and free of defects, and the air tightness of the joint is guaranteed; and the brazing filler metal does not have excessive reaction with the base metal on the two sides, so that the overall structure and functional integrity of the base metal are guaranteed, 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 an important link between electricity, gas and heat networks, and providing fuel for the transportation sector. Solid oxide electrolysis cell technology has broad development potential as an electrolysis technology that can be applied on a large scale. The successful operation of solid oxide electrolysis cells requires an effective sealing connection between the YSZ electrolyte and the stainless steel connector.

[0003] At present, 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 metal and Ag-Nb2O5 brazing filler metal commonly used in air reaction brazing have good connection effects, they often react severely with ceramics and metal parent materials and seriously damage the parent material structure, and the resulting welded joints will seriously deteriorate 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 to obtain a joint that does not over-react with the parent material during the welding process and has long-term excellent stability in a high-temperature air environment. 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 easy to over-react with the base material, thereby destroying the structure and functional integrity of the base material, and the organization and mechanical stability of the joint are poor in a long-term high-temperature air environment, and provide a method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal air reaction.

[0005] The method for brazing YSZ ceramic and stainless steel by using Ag-Co3O4 brazing filler metal 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 base material YSZ ceramic and the base material Crofer22H stainless steel to form a YSZ / Ag-Co3O4 solder / Crofer22H sandwich structure;

[0008] 3. Put 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 for 1min~90min, then cool it to 300℃~310℃, and finally cool it to room temperature with the furnace, thus completing the air connection of YSZ ceramic and Crofer22H stainless steel with Ag-Co3O4 brazing filler metal.

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

[0010] The present invention uses Ag-Co3O4 solder to successfully achieve effective connection of YSZ ceramics and Crofer22H stainless steel under air conditions. The solder is well combined with the parent materials on both sides, and the joint structure is dense and defect-free, ensuring the air tightness of the joint; the solder does not over-react with the parent materials on both sides, thereby ensuring the overall structure 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 at 800℃ air conditions 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, which 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 implementation method 1: This implementation method is a method for brazing YSZ ceramics and stainless steel using Ag-Co3O4 brazing filler metal 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 base material YSZ ceramic and the base material Crofer22H stainless steel to form a YSZ / Ag-Co3O4 solder / Crofer22H sandwich structure;

[0016] 3. Put 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 for 1min~90min, then cool it to 300℃~310℃, and finally cool it to room temperature with the furnace, thus completing the air connection of YSZ ceramic and Crofer22H stainless steel with Ag-Co3O4 brazing filler metal.

[0017] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that the particle size of the Ag powder in step 1 is 10 μm. The rest is the same as the specific implementation method 1.

[0018] Specific implementation method 3: This implementation method is different from specific implementation method 2 in that the particle size of the Co3O4 powder in step 1 is 10 μm. The rest is the same as specific implementation method 2.

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

[0020] Specific embodiment 5: This embodiment is different from specific embodiment 4 in that the Ag-Co3O4 solder flakes described in step 1 are prepared by a tablet press. The rest is 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 1min to 90min. The rest is 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. The rest is 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 min, 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. The rest is the same as specific embodiment 8.

[0025] Specific embodiment 10: This embodiment is different from specific embodiment 9 in that in step 2, two base materials need to be ultrasonically cleaned first. The rest is the same as specific embodiment 9.

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

[0027] Experiment 1: This experiment is a method for brazing YSZ ceramic and stainless steel using Ag-Co3O4 brazing filler metal air reaction, which is specifically carried out in the following steps:

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

[0029] 2. First, the YSZ ceramic and Crofer22H stainless steel are ultrasonically cleaned, and then the Ag-Co3O4 solder sheet prepared in step 1 is placed between the surfaces to be welded of the YSZ ceramic and Crofer22H stainless steel to form a YSZ / Ag-Co3O4 solder / Crofer22H sandwich structure;

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

[0031] Experiment 2: This experiment is different from Experiment 1 in that the molar ratio of Ag powder to Co3O4 powder in step 1 is 99:1. The rest is the same as Experiment 1.

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

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

[0034] Test 5: This test is different from Test 1 in that the connection temperature in step 3 is 970° C. The rest is the same as Test 1.

[0035] Test 6: This test is different from Test 1 in that the connection temperature in step 3 is 1010° C. The rest is the same as Test 1.

[0036] Test 7: This test is different from Test 1 in that the connection temperature in step 3 is 1090° C. The rest is the same as Test 1.

[0037] Test 8: This test is different from Test 1 in that the connection temperature in step 3 is 1130° C. The rest is the same as Test 1.

[0038] Test 9: This test is different from Test 1 in that the holding time in step 3 is 5 minutes. The rest is the same as Test 1.

[0039] Test 10: This test differs from Test 1 in that the holding time in step 3 is 15 minutes. The rest is the same as Test 1.

[0040] Test 11: This test differs from Test 1 in that the holding time in step 3 is 45 minutes. The rest is the same as Test 1.

[0041] Test 12: This test differs from Test 1 in that the heat preservation time in step 3 is 60 minutes. The rest is the same as Test 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, and the shear strength of the joints obtained in Test 1 reaches 51 MPa.

[0043] Table 1

[0044] test Shear strength(MPa) Test 1 51 Test 2 23 Test 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 From the chemical composition of the phases at each point in the figure, we can see 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 photo of the joint obtained after the completion of the experiment 1 after oxidation at 800℃ in air for 300h. It can be seen from the figure that the joint has no defects, and the thickness of the oxide layer on the side of the base material Crofer22H has only increased to 9.5μm, which is only 19% thicker than at room temperature. Table 3 Figure 2 From the chemical composition of the phases at each point, it can be seen that the phases of the entire joint are still Co3O4, (Ag+Co3O4) weld middle layer, (CoCr2O4+Cr2O3) oxide layer from left to right, and the organization has not changed compared with Table 2. The thickness of the oxide layer on one side of the base material Crofer22H is only increased to 9.5μm. The shear strength test shows that its shear strength is 45MPa, which is only 12% lower than the room temperature strength, ensuring the stability of the organization and mechanical properties of the joint at high temperature for a long time.

[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 - - <![CDATA[Co3O4]]> 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 <![CDATA[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 ceramic 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 base material YSZ ceramic and the base material Crofer22H stainless steel to form a YSZ / Ag-Co3O4 solder / Crofer22H sandwich structure; 3. Put 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 for 1min~90min, then cool it to 300℃~310℃, and finally cool it to room temperature with the furnace, thus completing the air connection of YSZ ceramic and Crofer22H stainless steel with Ag-Co3O4 brazing filler metal.

2. A 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. A method for brazing YSZ ceramic 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 ceramic 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 ceramic 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 ceramic 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 increased from room temperature to 960°C to 1200°C at a heating rate of 1°C / min to 20°C / min and maintained for 1min to 90min.

7. A method for brazing YSZ ceramic and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 6, characterized in that In step 3, the temperature is increased 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 ceramic and stainless steel using Ag-Co3O4 brazing filler metal in air reaction according to claim 7, characterized 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 this temperature for 30 minutes, and then cooled to 300°C.

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

10. The method for brazing YSZ ceramic 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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