A method for joining sapphire and porous silicon nitride ceramic using a gradient thermal expansion glass solder

Abstract

The application relates to a method for connecting sapphire and porous silicon nitride ceramic by using gradient thermal expansion glass solder, and relates to a method for connecting sapphire and porous silicon nitride ceramic by using glass solder. The application aims to solve the technical problem of thermal stress caused by the excessively large difference in the thermal expansion coefficients of sapphire and porous silicon nitride ceramic. In the Z1 glass raw material, part of the ZnO component in the ZnO-B2O3-Al2O3-SiO2 glass solder is replaced by CaO to prepare a microcrystalline glass solder with different thermal expansion coefficients, the sapphire and the porous Si3N4 ceramic are effectively connected under the condition of argon by using the gradient thermal expansion microcrystalline glass solder, a composite gradient thermal expansion intermediate layer is formed, the solder is well combined with the two side base materials, the joint structure appears closed pores, the joint air tightness is not affected, the joint has excellent mechanical properties, and the room temperature mechanical properties of the joint can reach 31 MPa.

Description

Technical Field

[0001] This invention relates to a method for joining sapphire and porous silicon nitride ceramics using glass brazing filler metal. Background Technology

[0002] With rapid economic and social development, a nation's defense and military science and technology have become increasingly important, and infrared guidance technology occupies a crucial position in modern military development. Infrared guidance technology utilizes infrared detectors to capture and track the radiation energy of a target to achieve pursuit. In infrared guidance technology, the infrared radome is one of the key components of an infrared missile. The infrared radome consists of window materials and radome body materials. Sapphire, a single-crystal Al2O3 ceramic, possesses not only excellent mechanical properties and high chemical stability but also superior optical properties, making it an excellent window material for infrared-guided missile radomes. Porous Si3N4 ceramic not only has high temperature resistance, oxidation resistance, and good dielectric properties but also a high specific surface area, highly open and interconnected pores, and controllable pore size, making it suitable for use as the radome body material for infrared-guided missile radomes. Achieving a superior combination of porous Si3N4 ceramic and sapphire not only meets the optical performance requirements of infrared-guided missile radomes but also optimizes their quality and processing technology, contributing to the development of superior infrared guidance technology and realizing the integration of radome structure and function. Currently, there is no suitable method to connect the two. Because infrared-guided missile radomes have high requirements for the dielectric properties of materials, the commonly used metal brazing method for connecting dissimilar materials cannot meet the requirements of this experiment. Therefore, microcrystalline glass brazing filler metal is preferred for connecting the base materials. However, considering the significant difference in their coefficients of thermal expansion (temperature range: 35℃~800℃, sapphire CTE: 7.7×10⁻⁶), this method is not feasible. -6 / ℃; CTE of porous Si3N4 ceramic: 3.6×10 -6 The use of single-layer glass brazing filler metal ( / ℃) cannot effectively alleviate the thermal stress problem caused by the large difference in thermal expansion coefficients between the base materials. Therefore, it is expected that a gradient thermal expansion microcrystalline glass brazing filler metal can be used to effectively connect the two. Summary of the Invention

[0003] The present invention aims to solve the technical problem of thermal stress caused by the large difference in the thermal expansion coefficients of sapphire and porous silicon nitride ceramics, and provides a method for connecting sapphire and porous silicon nitride ceramics using gradient thermal expansion glass solder.

[0004] The method of connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder of the present invention is carried out according to the following steps:

[0005] 1. Weigh the raw material powder according to the following mass percentages:

[0006] The raw material composition of Z1 glass is as follows: ZnO 19%~20% by mass, B2O3 20%~22% by mass, Al2O3 8%~10% by mass, SiO2 34%~36% by mass, CaO 5%~6% by mass, Na2O 5%~5.5% by mass, Li2O 2%~3% by mass, and TiO2 3%~3.5% by mass.

[0007] The raw material composition of Z2 glass is as follows: ZnO 25%~26% by mass, B2O3 18%~20% by mass, Al2O3 8%~10% by mass, SiO2 34%~36% by mass, Na2O 5.5%~6% by mass, Li2O 1.5%~2% by mass, and TiO2 3.5%~4% by mass.

[0008] Then, the Z1 glass raw material powder and the Z2 glass raw material powder were respectively operated as follows: all the weighed raw material powders were ball-milled and mixed, and then put into an Al2O3 crucible for high-temperature melting. The melting temperature was 1450℃~1500℃, and the temperature was held for 2h~2.5h to obtain Z1 glass melt and Z2 glass melt with uniform composition.

[0009] 2. The molten Z1 glass melt and Z2 glass melt are poured into deionized water at room temperature for water quenching. They are then removed from the water to obtain broken glass slag. The slag is then ball-milled to obtain fine glass powder. The glass powder is sieved to remove unbroken glass pieces and then dried in an oven to obtain Z1 glass powder solder and Z2 glass powder solder respectively.

[0010] 3. Polish the sapphire substrate surface to be joined using 1μm diamond polishing paste to obtain the joint surface. Then, place it in alcohol for ultrasonic cleaning for 15-20 minutes and blow it dry for later use. The porous Si3N4 ceramic surface is not treated.

[0011] 4. Place the Z1 glass powder solder and Z2 glass powder solder prepared in step 2 into a pressing mold and press them into circular sheet structures with a thickness of 0.1mm~0.3mm. Then place them between two base materials to form a sandwich structure. The sandwich structure consists of sapphire, Z1 glass solder, Z2 glass solder and porous Si3N4 ceramic from top to bottom.

[0012] 5. Place the sandwich structure assembled in step 4 into an atmosphere furnace, with the sapphire at the top. Achieve pressureless connection under a protective atmosphere. The connection temperature is 820℃~880℃, and the holding time is 10min~40min.

[0013] The present invention has the following beneficial effects:

[0014] This invention prepares microcrystalline glass solders with different coefficients of thermal expansion by replacing part of the ZnO component in the ZnO-B2O3-Al2O3-SiO2 microcrystalline glass solder with CaO in the Z1 glass raw material. The gradient thermal expansion microcrystalline glass solder successfully achieves effective bonding between sapphire and porous Si3N4 ceramic under argon conditions, forming a composite gradient thermal expansion intermediate layer. The solder bonds well with the base materials on both sides, and the joint structure exhibits closed pores without affecting the joint's airtightness, resulting in excellent mechanical properties. The coefficients of thermal expansion of sapphire, Z1 glass layer, Z2 glass layer, and porous Si3N4 ceramic decrease in that order, being 6.94 × 10⁻⁶. -6 / ℃, 6.01×10 -6 / ℃, 5.45×10 -6 / ℃ and 2.74×10 -6 The temperature was / ℃, achieving a gradient intermediate layer for thermal expansion, effectively alleviating residual stress in the joint. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis revealed a ZnAl2O4 reaction layer at the sapphire interface. The main crystalline phase of the Z1 glass layer was ZnAl2O4, while the Z2 glass layer consisted of a mixture of Zn2SiO4 and ZnAl2O4. A penetration layer appeared on the porous Si3N4 ceramic side, indicating good interfacial bonding. After heating to 840℃ and holding for 30 min in an argon atmosphere, the joint's mechanical properties reached 31 MPa. Attached Figure Description

[0015] Figure 1 The X-ray diffraction pattern of the weld seam of the joint obtained after Experiment 1 was completed;

[0016] Figure 2 The backscattered electron scanning image and a magnified view of the connector obtained after Experiment 1 were completed;

[0017] Figure 3 The graph shows the thermal expansion curves of the test base material and the two types of glass, measured by a thermal expansion tester in step two of the experiment. Detailed Implementation

[0018] Specific Implementation Method 1: This implementation method is a method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder, specifically carried out according to the following steps:

[0019] 1. Weigh the raw material powder according to the following mass percentages:

[0020] The raw material composition of Z1 glass is as follows: ZnO 19%~20% by mass, B2O3 20%~22% by mass, Al2O3 8%~10% by mass, SiO2 34%~36% by mass, CaO 5%~6% by mass, Na2O 5%~5.5% by mass, Li2O 2%~3% by mass, and TiO2 3%~3.5% by mass.

[0021] The raw material composition of Z2 glass is as follows: ZnO 25%~26% by mass, B2O3 18%~20% by mass, Al2O3 8%~10% by mass, SiO2 34%~36% by mass, Na2O 5.5%~6% by mass, Li2O 1.5%~2% by mass, and TiO2 3.5%~4% by mass.

[0022] Then, the Z1 glass raw material powder and the Z2 glass raw material powder were respectively operated as follows: all the weighed raw material powders were ball-milled and mixed, and then put into an Al2O3 crucible for high-temperature melting. The melting temperature was 1450℃~1500℃, and the temperature was held for 2h~2.5h to obtain Z1 glass melt and Z2 glass melt with uniform composition.

[0023] 2. The molten Z1 glass melt and Z2 glass melt are poured into deionized water at room temperature for water quenching. They are then removed from the water to obtain broken glass slag. The slag is then ball-milled to obtain fine glass powder. The glass powder is sieved to remove unbroken glass pieces and then dried in an oven to obtain Z1 glass powder solder and Z2 glass powder solder respectively.

[0024] 3. Use 1μm diamond polishing paste to polish the sapphire base material to be joined, and then place it in alcohol for ultrasonic cleaning for 15min~20min, and blow dry for later use.

[0025] 4. Place the Z1 glass powder solder and Z2 glass powder solder prepared in step 2 into a pressing mold and press them into circular sheet structures with a thickness of 0.1mm~0.3mm. Then place them between two base materials to form a sandwich structure. The sandwich structure consists of sapphire, Z1 glass solder, Z2 glass solder and porous Si3N4 ceramic from top to bottom.

[0026] 5. Place the sandwich structure assembled in step 4 into an atmosphere furnace, with the sapphire at the top. Achieve pressureless connection under a protective atmosphere. The connection temperature is 820℃~880℃, and the holding time is 10min~40min.

[0027] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the raw material composition of the Z1 glass mentioned in step one is as follows: ZnO mass percentage 20%, B2O3 mass percentage 20%, Al2O3 mass percentage 8%, SiO2 mass percentage 36%, CaO mass percentage 5%, Na2O mass percentage 5.5%, Li2O mass percentage 2%, and TiO2 mass percentage 3.5%. Everything else is the same as in Specific Implementation Method One.

[0028] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the raw material composition of the Z2 glass mentioned in step one is: ZnO 25% by mass, B2O3 20% by mass, Al2O3 8% by mass, SiO2 36% by mass, Na2O 5.5% by mass, Li2O 2% by mass, and TiO2 3.5% by mass. Everything else is the same as in Specific Implementation Method One or Two.

[0029] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the melting temperature described in step one is 1450℃. Everything else is the same as in Specific Implementation Methods One to Three.

[0030] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the sieve used in step two is 300 mesh. Everything else is the same as in Specific Implementation Method Four.

[0031] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the drying temperature in step two is 70℃. Everything else is the same as in Specific Implementation Method Five.

[0032] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that: in step three, the sample is ultrasonically cleaned in alcohol for 15 minutes. Everything else is the same as in Specific Implementation Method Six.

[0033] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that, in step four, the Z1 glass powder solder and Z2 glass powder solder prepared in step two are respectively placed into a pressing mold and pressed into a circular sheet structure with a thickness of 0.2 mm. Everything else is the same as in Specific Implementation Method Seven.

[0034] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the protective atmosphere described in step five is argon. Everything else is the same as in Specific Implementation Method Eight.

[0035] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the connection temperature in step five is 840℃, and the heat preservation time is 30 minutes. Everything else is the same as in Specific Implementation Method Nine.

[0036] The invention was verified using the following experiments:

[0037] Experiment 1: This experiment demonstrates a method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder. The specific steps are as follows:

[0038] 1. Weigh the raw material powder according to the following mass percentages:

[0039] The raw material composition of Z1 glass is as follows: ZnO 20% by mass, B2O3 20% by mass, Al2O3 8% by mass, SiO2 36% by mass, CaO 5% by mass, Na2O 5.5% by mass, Li2O 2% by mass, and TiO2 3.5% by mass.

[0040] The raw material composition of Z2 glass is as follows: ZnO 25% by mass, B2O3 20% by mass, Al2O3 8% by mass, SiO2 36% by mass, Na2O 5.5% by mass, Li2O 2% by mass, and TiO2 3.5% by mass.

[0041] Then, the following operations were performed on the Z1 glass raw material powder and the Z2 glass raw material powder respectively: all the weighed raw material powders were ball-milled and mixed, and then placed into an Al2O3 crucible for high-temperature melting. The melting temperature was 1450℃ and the temperature was held for 2 hours to obtain Z1 glass melt and Z2 glass melt with uniform composition respectively.

[0042] 2. A portion of the molten Z1 glass and a portion of the molten Z2 glass are poured into deionized water at room temperature for water quenching. The glass is then removed from the water to obtain broken glass slag. The slag is then ball-milled to obtain fine glass powder. The glass powder is then sieved (300 mesh) to remove unbroken glass pieces. Finally, it is dried in an oven at 70°C to obtain Z1 glass powder solder and Z2 glass powder solder, respectively.

[0043] Another portion of Z1 glass melt and a portion of Z2 glass melt were poured into graphite molds to prepare block glass. The block glass obtained after casting was placed in a muffle furnace that had been preheated to 500°C and kept at that temperature for 2 hours. Then, it was cooled to room temperature with the furnace to eliminate the thermal internal stress formed during the glass preparation process. The two glass blocks were cut into 4mm×4mm×12mm cuboids to measure their thermal expansion.

[0044] 3. Polish the sapphire substrate surface to be joined using 1μm diamond polishing paste to obtain the joint surface. Then, ultrasonically clean it in alcohol for 15 minutes and blow it dry for later use. The porous Si3N4 ceramic surface is not treated.

[0045] 4. Place the Z1 glass powder solder and Z2 glass powder solder prepared in step 2 into a pressing mold and press them into a circular sheet structure with a thickness of 0.2 mm. Then place them between two base materials to form a sandwich structure. The sandwich structure consists of sapphire, Z1 glass solder, Z2 glass solder and porous Si3N4 ceramic from top to bottom.

[0046] 5. Place the sandwich structure assembled in step 4 into an atmosphere furnace, with the sapphire on top. Achieve pressureless connection under argon atmosphere conditions. The connection temperature is 840℃ and the holding time is 30 minutes.

[0047] Experiment 2: This experiment differs from Experiment 1 in that the connection temperature mentioned in step five is 820℃. Everything else is the same as Experiment 1.

[0048] Experiment 3: This experiment differs from Experiment 1 in that the connection temperature mentioned in step five is 860℃. Everything else is the same as Experiment 1.

[0049] Experiment 4: This experiment differs from Experiment 1 in that the connection temperature mentioned in step 5 is 880℃. Everything else is the same as Experiment 1.

[0050] Experiment 5: This experiment differs from Experiment 1 in that the heat preservation time mentioned in step 5 is 10 minutes. Everything else is the same as Experiment 1.

[0051] Experiment Six: This experiment differs from Experiment One in that the heat preservation time mentioned in step five is 20 minutes. Everything else is the same as Experiment One.

[0052] Experiment 7: This experiment differs from Experiment 1 in that the heat preservation time mentioned in step 5 is 40 minutes. Everything else is the same as Experiment 1.

[0053] The mechanical properties of the joints obtained in the above tests were evaluated by shear strength. The room temperature shear strength of the joints obtained under different connection processes in tests one through seven is shown in Table 1. The results show that the gradient thermal expansion glass brazing filler metal of the present invention can be used to obtain joints with excellent mechanical properties. Among them, the room temperature shear strength of the joint obtained in test one reached 31 MPa.

[0054] Table 1

[0055] test Shear strength at room temperature (MPa) Experiment 1 31 Experiment 2 24 Experiment 3 21 Experiment 4 18 Experiment 5 12 Experiment 6 25 Experiment 7 26

[0056] Figure 1X-ray diffraction analysis was performed on the weld of the joint obtained after Experiment 1 to analyze its phase composition. It was found that the weld was mainly composed of glass phase, ZnAl2O4 phase and Zn2SiO4 phase.

[0057] Figure 2 The images show backscattered electron scanning images and magnified views of the joint obtained after Experiment 1. Figure b is a magnified view of region b in Figure a, and Figure c is a magnified view of region c in Figure a. The images show good bonding between the solder and the base materials on both sides. The joint microstructure exhibits closed pores, which do not affect the joint's airtightness. ZnAl2O4 and Zn2SiO4 phases are distributed in the weld, containing many nanocrystalline phases. The reaction layer thickness on the sapphire side of the joint is approximately 0.5 μm. X-ray diffraction (XRD) is also shown. Figure 1 Based on the analysis in Table 2, it is identified as the ZnAl2O4 phase (point A in Figure b).

[0058] Table 2 is... Figure 1 The chemical composition of each phase in the joint shows that the phases of the entire joint, from left to right, are sapphire, ZnAl2O4 reaction layer, glass phase + ZnAl2O4 + Zn2SiO4, infiltrated layer (the glass phase in the Z2 layer), and porous Si3N4 ceramic.

[0059] Figure 3 The graph shows the thermal expansion curves of the test substrate and the two types of glass, measured by a thermal expansion tester in step two of the experiment. The graph reveals that within the temperature range of 35℃ to 450℃, the coefficients of thermal expansion of sapphire, Z1 glass layer, Z2 glass layer, and porous Si3N4 ceramic decrease in that order, with values ​​of 6.94 × 10⁻⁶. -6 / ℃, 6.01×10 -6 / ℃, 5.45×10 -6 / ℃ and 2.74×10 -6 / ℃, achieving a gradient intermediate layer for thermal expansion, effectively alleviating residual stress in the joint.

[0060] Table 2

[0061] Location O Na Al Si Ca Ti Zn phase of matter A 47.15 5.09 27.58 5.50 0.80 0.71 13.17 <![CDATA[ZnAl2O4]]> B 58.57 5.36 9.02 19.19 2.57 0.93 4.36 Glass C 41.49 - 7.2 14.17 - 0.82 26.53 <![CDATA[Zn2SiO4]]>

Claims

1. A method for joining sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder, characterized in that... The method for joining sapphire and porous silicon nitride ceramics using gradient thermal expansion glass solder is carried out according to the following steps:

1. Weigh the raw material powder according to the following mass percentages: The raw material composition of Z1 glass is as follows: ZnO 19%~20% by mass, B2O3 20%~22% by mass, Al2O3 8%~10% by mass, SiO2 34%~36% by mass, CaO 5%~6% by mass, Na2O 5%~5.5% by mass, Li2O 2%~3% by mass, and TiO2 3%~3.5% by mass. The raw material composition of Z2 glass is as follows: ZnO 25%~26% by mass, B2O3 18%~20% by mass, Al2O3 8%~10% by mass, SiO2 34%~36% by mass, Na2O 5.5%~6% by mass, Li2O 1.5%~2% by mass, and TiO2 3.5%~4% by mass. Then, the Z1 glass raw material powder and the Z2 glass raw material powder were respectively operated as follows: all the weighed raw material powders were ball-milled and mixed, and then put into an Al2O3 crucible for high-temperature melting. The melting temperature was 1450℃~1500℃, and the temperature was held for 2h~2.5h to obtain Z1 glass melt and Z2 glass melt with uniform composition.

2. The molten Z1 glass melt and Z2 glass melt are poured into deionized water at room temperature for water quenching. They are then removed from the water to obtain broken glass slag. The slag is then ball-milled to obtain fine glass powder. The glass powder is sieved to remove unbroken glass pieces and then dried in an oven to obtain Z1 glass powder solder and Z2 glass powder solder respectively.

3. Use 1μm diamond polishing paste to polish the sapphire base material to be joined, and then place it in alcohol for ultrasonic cleaning for 15min~20min, and blow dry for later use.

4. Place the Z1 glass powder solder and Z2 glass powder solder prepared in step 2 into a pressing mold and press them into circular sheet structures with a thickness of 0.1mm~0.3mm. Then place them between two base materials to form a sandwich structure. The sandwich structure consists of sapphire, Z1 glass solder, Z2 glass solder and porous Si3N4 ceramic from top to bottom.

5. Place the sandwich structure assembled in step 4 into an atmosphere furnace, with the sapphire at the top. Achieve pressureless connection under a protective atmosphere. The connection temperature is 820℃~880℃, and the holding time is 10min~40min.

2. The method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... The raw material composition of the Z1 glass mentioned in step one is as follows: ZnO has a mass percentage of 20%, B2O3 has a mass percentage of 20%, Al2O3 has a mass percentage of 8%, SiO2 has a mass percentage of 36%, CaO has a mass percentage of 5%, Na2O has a mass percentage of 5.5%, Li2O has a mass percentage of 2%, and TiO2 has a mass percentage of 3.5%.

3. The method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... The raw material composition of the Z2 glass mentioned in step one is as follows: ZnO has a mass percentage of 25%, B2O3 has a mass percentage of 20%, Al2O3 has a mass percentage of 8%, SiO2 has a mass percentage of 36%, Na2O has a mass percentage of 5.5%, Li2O has a mass percentage of 2%, and TiO2 has a mass percentage of 3.5%.

4. The method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... The melting temperature mentioned in step one is 1450℃.

5. The method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... The sieve used in step two is 300 mesh.

6. The method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... The drying temperature in step two is 70℃.

7. The method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... In step three, place the sample in alcohol and ultrasonically clean it for 15 minutes.

8. The method for connecting sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... In step four, the Z1 glass powder solder and Z2 glass powder solder prepared in step two are placed into a pressing mold and pressed into a circular sheet structure with a thickness of 0.2 mm.

9. A method for joining sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... The protective atmosphere described in step five is argon.

10. A method for joining sapphire and porous silicon nitride ceramic using gradient thermal expansion glass solder according to claim 1, characterized in that... In step five, the connection temperature is 840℃ and the holding time is 30 minutes.

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