Method for connecting sapphire and porous silicon nitride ceramic through gradient thermal expansion glass brazing filler metal

Abstract

The invention discloses a method for connecting sapphire and porous silicon nitride ceramic by using gradient thermal expansion glass brazing filler metal, and relates to a method for connecting sapphire and porous silicon nitride ceramic by using glass brazing filler metal. The invention aims to solve the technical problem of thermal stress caused by overlarge thermal expansion coefficient difference between sapphire and porous silicon nitride ceramic. According to the invention, CaO is used for replacing a part of ZnO component in ZnO-B2O3-Al2O3-SiO2 microcrystalline glass brazing filler metal in a Z1 glass raw material to prepare microcrystalline glass brazing filler metal with different thermal expansion coefficients, effective connection of sapphire and porous Si3N4 ceramic under an argon condition is successfully realized through the gradient thermal expansion microcrystalline glass brazing filler metal, and a composite gradient thermal expansion intermediate layer is formed; the brazing filler metal is well combined with base metal on the two sides, closed air holes are formed in a joint structure, the air tightness of a joint is not affected, excellent mechanical performance is achieved, and the room-temperature mechanical performance of the joint can reach 31 MPa.

Description

Technical Field

[0001] The invention relates to a method for connecting sapphire and porous silicon nitride ceramics by using glass solder. Background Art

[0002] With the rapid development of the economy and society, a country's national defense and military science and technology are becoming increasingly important. Infrared guidance technology plays a crucial role in modern military development. Infrared guidance technology uses infrared detectors to capture and track the target's own radiation energy. Infrared fairings are key components of infrared missiles. Infrared fairings consist of window materials and housing materials. Sapphire, a single-crystal Al2O3 ceramic, not only possesses excellent mechanical properties and chemical stability, but also possesses excellent optical properties, making it an excellent material for infrared-guided missile fairing windows. Porous Si3N4 ceramics not only offer high-temperature resistance, oxidation resistance, and excellent dielectric properties, but also possess a high specific surface area, highly open and interconnected pores, and controllable pore size. Porous Si3N4 ceramics are suitable for infrared-guided missile fairing housings. Achieving an excellent combination of porous Si3N4 ceramics and sapphire can not only meet the optical performance requirements of infrared-guided missile fairings, but also optimize their quality and processing technology, contribute to the completion of better infrared guidance technology, and achieve the integration of fairing structure and function. At present, there is no suitable method to connect the two. Since the infrared-guided missile fairing has high requirements for the dielectric properties of the material, the metal brazing method commonly used to connect dissimilar materials cannot meet the requirements of this experiment, so microcrystalline glass brazing is preferred for connecting the base material. However, considering the large difference in thermal expansion coefficients between the two (temperature range: 35℃~800℃, sapphire CTE: 7.7×10 -6 / ℃; Porous Si3N4 ceramic CTE: 3.6×10 -6 / ℃) The use of a single layer of glass solder cannot effectively alleviate the thermal stress problem caused by the large difference in thermal expansion coefficient between the base materials, so it is hoped that the gradient thermal expansion micro-ceramic glass solder 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 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 ceramics using a gradient thermal expansion glass solder of the present invention is carried out according to the following steps:

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

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

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

[0008] Then, the following operations are performed on the Z1 glass raw material powder and the Z2 glass raw material powder respectively: all the weighed raw material powders are ball-milled and mixed, and then placed in an Al2O3 crucible for high-temperature melting at a melting temperature of 1450°C to 1500°C and kept at this temperature for 2 hours to 2.5 hours to obtain Z1 glass melt and Z2 glass melt with uniform composition, respectively;

[0009] 2. Pour the molten Z1 glass melt and the Z2 glass melt into deionized water at room temperature for quenching, remove them from the water to obtain broken glass slag, and then obtain fine glass powder by ball milling. 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. The surface of the sapphire base material to be joined was polished with 1μm diamond paste to obtain the surface to be joined, and then ultrasonically cleaned in alcohol for 15min~20min and dried for later use; the surface of the porous Si3N4 ceramic was not treated;

[0011] 4. The Z1 glass powder solder and Z2 glass powder solder prepared in step 2 are respectively placed in a tablet pressing mold and pressed into a disc structure with a thickness of 0.1mm to 0.3mm. Then, they are placed between two base materials to form a sandwich structure. The sandwich structure is composed 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 in an atmosphere furnace with the sapphire at the top, and achieve pressure-free connection under protective atmosphere conditions. The connection temperature is 820℃~880℃ and the holding time is 10min~40min.

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

[0014] The present invention prepares glass-ceramic solders with different thermal expansion coefficients by replacing part of the ZnO component in the ZnO-B2O3-Al2O3-SiO2 glass-ceramic solder with CaO in the Z1 glass raw material. This gradient thermal expansion glass-ceramic solder successfully achieves effective bonding of sapphire and porous Si3N4 ceramics under argon conditions, forming a composite gradient thermal expansion interlayer. The solder bonds well with the parent materials on both sides, creating closed pores in the joint structure that do not affect the joint's airtightness and exhibiting excellent mechanical properties. The thermal expansion coefficients of sapphire, Z1 glass layer, Z2 glass layer, and porous Si3N4 ceramic show a decreasing relationship, being 6.94×10 -6 / ℃、6.01×10 -6 / ℃、5.45×10 -6 / ℃ and 2.74×10 -6 / °C, creating a thermal expansion gradient interlayer and effectively alleviating residual stress in the joint. Energy dispersive spectrum analysis and X-ray analysis revealed a ZnAl2O4 reaction layer at the sapphire interface. The Z1 glass layer's primary crystalline phase is ZnAl2O4, while the Z2 glass layer's crystalline phase is a mixture of Zn2SiO4 and ZnAl2O4. An infiltration layer appears on the porous Si3N4 ceramic side, demonstrating good interfacial bonding. After heating to 840°C and holding for 30 minutes in an argon atmosphere, the joint's mechanical properties reached 31 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The X-ray diffraction pattern of the weld of the joint obtained after the completion of the test 1;

[0016] Figure 2 This is a backscattered electron scanning photograph and a partial magnified view of the joint obtained after the completion of the first test;

[0017] Figure 3 The thermal expansion curves of the test base material and two types of glass measured by a thermal expansion tester in step 2 of the experiment are shown in FIG. DETAILED DESCRIPTION

[0018] Specific embodiment 1: This embodiment is a method for connecting sapphire and porous silicon nitride ceramics using gradient thermal expansion glass solder, which is specifically carried out in the following steps:

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

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

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

[0022] Then, the following operations are performed on the Z1 glass raw material powder and the Z2 glass raw material powder respectively: all the weighed raw material powders are ball-milled and mixed, and then placed in an Al2O3 crucible for high-temperature melting at a melting temperature of 1450°C to 1500°C and kept at this temperature for 2 hours to 2.5 hours to obtain Z1 glass melt and Z2 glass melt with uniform composition, respectively;

[0023] 2. Pour the molten Z1 glass melt and the Z2 glass melt into deionized water at room temperature for quenching, remove them from the water to obtain broken glass slag, and then obtain fine glass powder by ball milling. 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 grinding paste to grind and polish the surface of the sapphire base material to obtain the surface to be connected, then ultrasonically clean it in alcohol for 15min~20min, blow dry and set aside;

[0025] 4. The Z1 glass powder solder and Z2 glass powder solder prepared in step 2 are respectively placed in a tablet pressing mold and pressed into a disc structure with a thickness of 0.1mm to 0.3mm. Then, they are placed between two base materials to form a sandwich structure. The sandwich structure is composed 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 in an atmosphere furnace with the sapphire at the top, and achieve pressure-free connection under protective atmosphere conditions. The connection temperature is 820℃~880℃ and the holding time is 10min~40min.

[0027] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the raw material composition of the Z1 glass described in step 1 is: 20% by mass of ZnO, 20% by mass of B2O3, 8% by mass of Al2O3, 36% by mass of SiO2, 5% by mass of CaO, 5.5% by mass of Na2O, 2% by mass of Li2O, and 3.5% by mass of TiO2. Other components are the same as those in specific embodiment 1.

[0028] Specific embodiment 3: This embodiment differs from specific embodiments 1 or 2 in that the raw material composition of the Z2 glass described in step 1 is: 25% by mass of ZnO, 20% by mass of B2O3, 8% by mass of Al2O3, 36% by mass of SiO2, 5.5% by mass of Na2O, 2% by mass of Li2O, and 3.5% by mass of TiO2. Other components are the same as those in specific embodiments 1 or 2.

[0029] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the melting temperature in step 1 is 1450° C. The rest is the same as specific embodiments 1 to 3.

[0030] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the sieve in step 2 is 300 mesh. Other aspects are the same as specific embodiment 4.

[0031] Specific embodiment 6: This embodiment differs from specific embodiment 5 in that the drying temperature in step 2 is 70° C. The rest is the same as specific embodiment 5.

[0032] Specific embodiment 7: This embodiment differs from specific embodiment 6 in that: in step 3, the sample is ultrasonically cleaned in alcohol for 15 minutes. Other aspects are the same as specific embodiment 6.

[0033] Specific embodiment eight: This embodiment differs from specific embodiment seven in that in step four, the Z1 glass powder solder and Z2 glass powder solder prepared in step two are placed in a tableting mold and pressed into a disc structure with a thickness of 0.2 mm. Other aspects are the same as specific embodiment seven.

[0034] Specific embodiment 9: This embodiment differs from specific embodiment 8 in that the protective atmosphere in step 5 is argon. Other aspects are the same as specific embodiment 8.

[0035] Specific embodiment 10: This embodiment differs from specific embodiment 9 in that the connection temperature in step 5 is 840° C. and the holding time is 30 minutes. Other aspects are the same as specific embodiment 9.

[0036] The present invention is verified by the following test:

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

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

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

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

[0041] Then, the following operations were performed on the Z1 glass raw material powder and the Z2 glass raw material powder: all the weighed raw material powders were ball-milled and mixed, and then placed in an Al2O3 crucible for high-temperature melting at a melting temperature of 1450°C and kept at this temperature for 2 hours to obtain Z1 glass melt and Z2 glass melt with uniform composition, respectively;

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

[0043] Another portion of the Z1 glass melt and another portion of the Z2 glass melt were poured into graphite molds to prepare glass blocks. The resulting glass blocks were placed in a muffle furnace preheated to 500°C for 2 hours and then cooled to room temperature to eliminate the thermal internal stress formed during the glass preparation and forming process. The two glass blocks were cut into 4mm×4mm×12mm rectangular blocks to measure their thermal expansion.

[0044] 3. The surface of the sapphire base material to be joined was polished with 1μm diamond paste to obtain the surface to be joined, and then ultrasonically cleaned in alcohol for 15 minutes and dried for later use; the surface of the porous Si3N4 ceramic was not treated;

[0045] 4. The Z1 glass powder solder and Z2 glass powder solder prepared in step 2 are placed in a tablet pressing mold and pressed into a disc structure with a thickness of 0.2 mm. Then, the disc structure is placed between two base materials to form a sandwich structure. The sandwich structure is composed 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 in an atmosphere furnace with the sapphire at the top, and achieve pressureless connection under argon atmosphere. The connection temperature is 840°C and the holding time is 30 minutes.

[0047] Experiment 2: This experiment differs from Experiment 1 in that the connection temperature in step 5 is 820° C. The rest is the same as Experiment 1.

[0048] Experiment 3: This experiment differs from Experiment 1 in that the connection temperature in step 5 is 860° C. The rest is the same as Experiment 1.

[0049] Test 4: This test differs from Test 1 in that the connection temperature in step 5 is 880° C. Other aspects are the same as Test 1.

[0050] Experiment 5: This experiment differs from Experiment 1 in that the holding time in step 5 is 10 minutes. Other conditions are the same as Experiment 1.

[0051] Experiment 6: This experiment differs from Experiment 1 in that the holding time in step 5 is 20 minutes. Other conditions are the same as Experiment 1.

[0052] Experiment 7: This experiment differs from Experiment 1 in that the holding time in step 5 is 40 minutes. Other conditions are 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 strengths of the joints obtained under different connection processes in Tests 1 to 7 are shown in Table 1. The results show that the use of the gradient thermal expansion glass solder of the present invention can obtain joints with excellent mechanical properties, among which the room temperature shear strength of the joint obtained in Test 1 reached 31 MPa.

[0054] Table 1 test Shear strength at room temperature (MPa) Experiment 1 31 Experiment 2 24 Experiment 3 21 Test 4 18 Test 5 12 Test 6 25 Test 7 26

[0055] Figure 1The weld of the joint obtained after the completion of the experiment was analyzed by X-ray diffraction pattern to analyze its phase composition. It was found that the weld was mainly composed of glass phase, ZnAl2O4 phase and Zn2SiO4 phase.

[0056] Figure 2 The backscattered electron scanning photo and local magnification of the joint obtained after the completion of experiment 1. Figure b is a local magnification of area b in Figure a, and Figure c is a local magnification of area c in Figure a. It can be seen from the figure that the solder is well bonded to the base materials on both sides, and the joint structure has closed pores, which will not affect the airtightness of the joint. ZnAl2O4 and Zn2SiO4 phases are distributed in the weld, among which there are many nanocrystalline phases. The thickness of the reaction layer on the sapphire side of the joint is about 0.5μm. X-ray diffraction ( Figure 1 ) Combined with Table 2, it is analyzed that it is ZnAl2O4 phase (point A in Figure b).

[0057] Table 2 is 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 sapphire, ZnAl2O4 reaction layer, glass phase + ZnAl2O4 + Zn2SiO4, infiltration layer (glass phase in Z2 layer) and porous Si3N4 ceramics from left to right.

[0058] Figure 3 The thermal expansion curves of the test base material and the two glasses measured by the thermal expansion tester in step 2 of the experiment show that in the range of 35℃~450℃, the thermal expansion coefficients of sapphire, Z1 glass layer, Z2 glass layer and porous Si3N4 ceramics are in a decreasing relationship, which are 6.94×10 -6 / ℃、6.01×10 -6 / ℃、5.45×10 -6 / ℃ and 2.74×10 -6 / ℃, realizing a gradient middle layer of thermal expansion and effectively alleviating the residual stress of the joint.

[0059] Table 2 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 connecting sapphire and porous silicon nitride ceramics using a 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 in the following steps:

1. Weigh the raw material powders according to the following mass percentages: The raw material composition of Z1 glass is as follows: the mass percentage of ZnO is 19%~20%, the mass percentage of B2O3 is 20%~22%, the mass percentage of Al2O3 is 8%~10%, the mass percentage of SiO2 is 34%~36%, the mass percentage of CaO is 5%~6%, the mass percentage of Na2O is 5%~5.5%, the mass percentage of Li2O is 2%~3%, and the mass percentage of TiO2 is 3%~3.5%; The raw material composition of Z2 glass: the mass percentage of ZnO is 25%~26%, the mass percentage of B2O3 is 18%~20%, the mass percentage of Al2O3 is 8%~10%, the mass percentage of SiO2 is 34%~36%, the mass percentage of Na2O is 5.5%~6%, the mass percentage of Li2O is 1.5%~2%, and the mass percentage of TiO2 is 3.5%~4%; Then, the following operations are performed on the Z1 glass raw material powder and the Z2 glass raw material powder respectively: all the weighed raw material powders are ball-milled and mixed, and then placed in an Al2O3 crucible for high-temperature melting at a melting temperature of 1450°C to 1500°C and kept at this temperature for 2 hours to 2.5 hours to obtain Z1 glass melt and Z2 glass melt with uniform composition, respectively; 2. Pour the molten Z1 glass melt and the Z2 glass melt into deionized water at room temperature for quenching, remove them from the water to obtain broken glass slag, and then obtain fine glass powder by ball milling. 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 grinding paste to grind and polish the surface of the sapphire base material to obtain the surface to be connected, then ultrasonically clean it in alcohol for 15min~20min, blow dry and set aside; 4. The Z1 glass powder solder and Z2 glass powder solder prepared in step 2 are respectively placed in a tablet pressing mold and pressed into a disc structure with a thickness of 0.1mm to 0.3mm. Then, they are placed between two base materials to form a sandwich structure. The sandwich structure is composed 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 in an atmosphere furnace with the sapphire at the top, and achieve pressure-free connection under protective atmosphere conditions. The connection temperature is 820℃~880℃ and the holding time is 10min~40min.

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

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

4. The method for joining sapphire and porous silicon nitride ceramics using a gradient thermal expansion glass solder according to claim 1, characterized in that The smelting temperature in step 1 is 1450°C.

5. The method for joining sapphire and porous silicon nitride ceramics using a gradient thermal expansion glass solder according to claim 1, characterized in that The sieve in step 2 is 300 mesh.

6. The method for joining sapphire and porous silicon nitride ceramics using a gradient thermal expansion glass solder according to claim 1, characterized in that The drying temperature in step 2 is 70°C.

7. The method for joining sapphire and porous silicon nitride ceramics using a gradient thermal expansion glass solder according to claim 1, characterized in that In step 3, ultrasonic cleaning was performed in alcohol for 15 minutes.

8. The method for joining sapphire and porous silicon nitride ceramics using a gradient thermal expansion glass solder according to claim 1, characterized in that In step 4, the Z1 glass powder solder and the Z2 glass powder solder prepared in step 2 are placed in a tablet pressing mold and pressed into a disc structure with a thickness of 0.2 mm.

9. The method for joining sapphire and porous silicon nitride ceramics using a gradient thermal expansion glass solder according to claim 1, characterized in that The protective atmosphere described in step 5 is argon.

10. The method for joining sapphire and porous silicon nitride ceramics using a gradient thermal expansion glass solder according to claim 1, characterized in that In step 5, the connection temperature is 840° C. and the holding time is 30 min.

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