A method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite brazing filler metal

Abstract

A method for brazing graphite / copper dissimilar materials using AgCuInTi composite brazing filler metal reinforced with diamond particles relates to a method for brazing graphite / copper dissimilar materials. The present invention aims to solve the technical problem that due to the large difference in thermal expansion coefficients between graphite and copper, the use of direct brazing will generate extremely large residual stress in the joint, resulting in an inability to obtain a reliable joint. The present invention uniformly mixes AgCuInTi brazing filler metal and diamond particles by ball milling to prepare a composite brazing filler metal for brazing graphite / copper dissimilar materials under vacuum. The present invention successfully achieves reliable connection of graphite / copper dissimilar materials, and the room temperature shear strength of the joint can reach 30 MPa, solving the problem of large residual stress in dissimilar material joints, and can realize the application of graphite / copper dissimilar material components in the fields of nuclear power, radiation protection, etc.

Description

Technical Field

[0001] The invention relates to a method for brazing graphite / copper dissimilar materials. Background Art

[0002] The discovery and application of nuclear energy is one of the greatest scientific and technological achievements of the 20th century. Numerous devices and equipment crucial to human development have been developed around nuclear energy, such as controlled nuclear fusion devices and particle accelerators. While these devices and equipment bring benefits to humanity, they also generate significant amounts of radiation, which can cause serious harm to humans and the environment. Radiation protection has become a paramount concern during the operation of nuclear energy equipment and devices. Furthermore, the radiation process often generates significant amounts of heat, requiring radiation protection materials to possess excellent heat transfer properties.

[0003] Carbon materials have long attracted significant attention as promising high-thermal conductivity materials due to their exceptional properties, including high thermal conductivity, low density, low thermal expansion coefficient, and high-temperature resistance. Graphite, in addition to these advantages, offers exceptional thermal properties, lightweight, radiation resistance, and excellent thermal stability, making it an ideal absorber material. However, graphite itself is brittle and relatively weak, making it prone to breakage when used alone. Copper, a traditional metallic thermal management material, boasts a thermal conductivity of up to 400 W / m·K and excellent strength and processability. By joining graphite, a material with high thermal conductivity and radiation resistance, with copper, components such as vapor chambers, radiation heat exchangers, and beam grabbers can be fabricated with excellent overall performance. Currently, non-metallurgical bonding methods, such as adhesive bonding, are commonly used to join graphite to copper. While simple and easy to implement, these bonding methods often lack sufficient strength to achieve a high bond strength, and adhesives are prone to failure in high-temperature environments. In addition, the thermal conductivity of commonly used thermal conductive adhesives is very poor (0.4 to 10 W / m·K), which greatly weakens the thermal conductivity of carbon materials. In addition, some researchers have used direct brazing to connect graphite and copper. Compared with non-metallurgical bonding, direct brazing can better utilize the thermal conductivity of high-thermal-conductivity graphite, while preventing the workpiece from failing in a high-temperature environment and extending the service life of the workpiece. However, due to the large difference in the thermal expansion coefficients of graphite and copper, the use of direct brazing will generate extremely large residual stress in the joint, resulting in the inability to obtain a reliable joint. Therefore, developing a composite brazing material suitable for graphite / copper dissimilar material connection to alleviate the residual stress problem in the joint, thereby achieving metallurgical connection between the two, is of great significance for obtaining a reliable and highly thermally conductive graphite / copper dissimilar material joint component. Summary of the Invention

[0004] The present invention aims to solve the technical problem that due to the large difference in thermal expansion coefficients of graphite and copper, direct brazing will generate extremely large residual stress in the joint, resulting in the inability to obtain a reliable joint. The present invention provides a method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite brazing filler metal.

[0005] The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder of the present invention is carried out by the following steps:

[0006] 1. Preparation of composite solder: AgCuInTi solder powder and diamond particles were preliminarily mixed in an agate mortar, and then the mixed powder was placed in a ball mill and milled at a low speed using a ball mill until fully mixed to obtain composite solder powder;

[0007] The volume fraction of diamond particles in the composite solder is 5% to 15%;

[0008] 2. Pretreatment of graphite and copper base materials;

[0009] 3. Assembling the parts to be welded: Mix the composite solder powder prepared in step 1 with a binder to form a paste solder, apply the paste solder to the surface of the copper base material to be welded by screen printing, and then place the surface of the graphite base material to be welded on the paste solder, thereby assembling a graphite / diamond particle reinforced AgCuInTi composite solder / copper part to be welded;

[0010] 4. Brazing: Place the parts to be welded in step 3 into a graphite mold, and then put them into a vacuum furnace. First, heat them to 300℃~310℃ and keep them warm for 30min~35min to remove the binder, then heat them to 680℃, and then heat them to the brazing temperature of 680℃~800℃ and keep them warm for 5min~20min; finally, cool them to 300℃ and then cool them to room temperature with the furnace to complete the entire brazing process. The entire brazing process is carried out under vacuum.

[0011] Compared with the prior art, the present invention provides an easy-to-prepare, low-cost diamond particle reinforced composite brazing material, and realizes the connection of graphite / copper under low-temperature vacuum conditions. The specific beneficial effects are as follows:

[0012] 1. The composite brazing filler metal provided by the present invention is used for the connection method of graphite / copper dissimilar materials. The composite brazing filler metal reinforced with diamond particles is used as the intermediate layer, and the graphite / copper dissimilar materials are connected by direct brazing. The AgCuInTi composite brazing filler metal has good fluidity, a low melting point, and excellent wettability with the base material. At the same time, the connection layer has few defects and the joint reliability is high.

[0013] 2. AgCuInTi solder itself is one of the best solders with the best thermal conductivity (thermal conductivity is about 100-180W / m·K), while diamond is one of the materials with the highest thermal conductivity in nature (thermal conductivity is about 1000-2000W / m·K). The addition of diamond particles can further improve the heat transfer performance of the solder. In addition, diamond has the advantages of low thermal expansion coefficient, high strength, and low density. The addition of diamond particle reinforcement can also reduce the thermal expansion coefficient of the solder layer, thereby forming a buffer layer between the two base materials, which greatly alleviates the problem of excessive stress in the joint caused by the mismatch of the thermal expansion coefficients of the base materials.

[0014] 3. During the joining process, the brazing filler metal interacts with the parent metal. After the graphite parent metal surface contacts the composite brazing filler metal, the composite brazing filler metal penetrates into the pores of the graphite parent metal, forming a penetration layer similar to a "pinning" effect, which helps improve the joint strength. The brazing filler metal reacts with the graphite parent metal to form a TiC reaction layer, while a diffusion layer forms on the copper parent metal side. Finally, after holding at 740°C for 10 minutes, the resulting joint has a maximum room temperature shear strength of approximately 30 MPa. Therefore, the present invention uses a diamond particle-reinforced AgCuInTi composite brazing filler metal as an intermediate layer for graphite / copper dissimilar material joining, achieving good wetting and interfacial bonding with the parent metal, thereby enabling the fabrication of large-scale, complex-shaped structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the SEM image of the composite solder powder prepared by ball milling in step 1 of experiment 1;

[0016] Figure 2 This is the EDS image of the carbon element in the composite solder powder prepared by ball milling in step 1 of experiment 1;

[0017] Figure 3 This is the SEM image of the graphite / copper dissimilar material joint prepared in comparative test 1;

[0018] Figure 4 This is the XRD pattern of the graphite / copper dissimilar material joint prepared in comparative experiment 1;

[0019] Figure 5 This is the EDS image of the graphite / copper dissimilar material joint prepared in comparative experiment 1, where the scale bar is 2.5 μm;

[0020] Figure 6 SEM image of the graphite / copper dissimilar material joint prepared in experiment 2. DETAILED DESCRIPTION

[0021] Specific embodiment 1: This embodiment is a method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder, which is specifically carried out in the following steps:

[0022] 1. Preparation of composite solder: AgCuInTi solder powder and diamond particles were preliminarily mixed in an agate mortar, and then the mixed powder was placed in a ball mill and milled at a low speed using a ball mill until fully mixed to obtain composite solder powder;

[0023] The volume fraction of diamond particles in the composite solder is 5% to 15%;

[0024] 2. Pretreatment of graphite and copper base materials;

[0025] 3. Assembling the parts to be welded: Mix the composite solder powder prepared in step 1 with a binder to form a paste solder, apply the paste solder to the surface of the copper base material to be welded by screen printing, and then place the surface of the graphite base material to be welded on the paste solder, thereby assembling a graphite / diamond particle reinforced AgCuInTi composite solder / copper part to be welded;

[0026] 4. Brazing: Place the parts to be welded in step 3 into a graphite mold, and then put them into a vacuum furnace. First, heat them to 300℃~310℃ and keep them warm for 30min~35min to remove the binder, then heat them to 680℃, and then heat them to the brazing temperature of 680℃~800℃ and keep them warm for 5min~20min; finally, cool them to 300℃ and then cool them to room temperature with the furnace to complete the entire brazing process. The entire brazing process is carried out under vacuum.

[0027] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the mass fraction of Ti element in the AgCuInTi solder powder in step 1 is 3% to 7%. Other aspects are the same as specific embodiment 1.

[0028] Specific embodiment 3: This embodiment differs from specific embodiment 2 in that the AgCuInTi solder powder in step 1 is AgCuInTi3. Other aspects are the same as specific embodiment 2.

[0029] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the diameter of the diamond particles in step 1 is W7 to W20. Other aspects are the same as specific embodiments 1 to 3.

[0030] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the rotation speed of the low-speed ball mill in step 1 is 200 to 300 rpm. Other aspects are the same as specific embodiment 4.

[0031] Specific Embodiment 6: This embodiment differs from Specific Embodiment 5 in that the pretreatment method for the graphite and copper base materials described in step 2 is as follows: the two base materials are cut into the required size, the surface of the copper base material to be welded is polished with 600#, 1200#, and 2000# wet sandpaper in sequence, and the graphite base material is polished with 2000# sandpaper until the surface is smooth. The polished base materials are placed in anhydrous ethanol and ultrasonically vibrated for 5 to 10 minutes, then removed and air-dried. Other aspects are the same as Specific Embodiment 5.

[0032] Specific embodiment 7: This embodiment differs from specific embodiment 6 in that the binder in step 3 is a 2% by mass hydroxyethyl cellulose aqueous solution. Other aspects are the same as specific embodiment 6.

[0033] Specific embodiment eight: This embodiment differs from specific embodiment seven in that the vacuum degree in step four is 6×10 -3 Pa. Other aspects are the same as those of the seventh embodiment.

[0034] Specific embodiment 9: This embodiment differs from specific embodiment 8 in that in step 4, the temperature is first raised to 300° C. at 10° C. / min and kept at that temperature for 30 minutes to remove the binder. Other aspects are the same as specific embodiment 8.

[0035] Specific embodiment 10: This embodiment differs from specific embodiment 9 in that in step 4, the temperature is raised to 680°C at a rate of 10°C / min, then raised to the brazing temperature of 680°C to 800°C at a rate of 5°C / min and held at that temperature for 5 to 20 minutes; finally, the temperature is lowered to 300°C at a rate of 5°C / min, and then cooled to room temperature in the furnace to complete the brazing process. The entire brazing process is performed under vacuum. 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 brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder. The specific steps are as follows:

[0038] 1. Preparation of composite solder: AgCuInTi solder powder and diamond particles were preliminarily mixed in an agate mortar, and then the mixed powder was placed in a ball mill and milled at a low speed using a ball mill until fully mixed to obtain composite solder powder;

[0039] The AgCuInTi solder powder described in step 1 is AgCuInTi3;

[0040] The volume fraction of diamond particles in the composite solder is 10%;

[0041] The particle size of the diamond particles described in step 1 is W7;

[0042] The rotation speed of the low-speed ball mill described in step 1 is 200 rpm;

[0043] 2. Pretreatment of graphite and copper base materials: Cut the two base materials into the required size. The surface of the copper base material to be welded is polished with 600#, 1200# and 2000# water sandpaper in sequence. The graphite base material is polished with 2000# sandpaper until the surface is smooth. Place the polished two base materials in anhydrous ethanol and ultrasonically vibrate for 5min to 10min, then take them out and blow dry.

[0044] 3. Assembling the parts to be welded: Mix the composite solder powder prepared in step 1 with a binder to form a paste solder, apply the paste solder to the surface of the copper base material to be welded by screen printing, and then place the surface of the graphite base material to be welded on the paste solder, thereby assembling a graphite / diamond particle reinforced AgCuInTi composite solder / copper part to be welded;

[0045] The binder described in step 3 is a 2% by mass aqueous solution of hydroxyethyl cellulose. There is no specific requirement for the amount of binder. Just add the binder until it is completely mixed into a paste.

[0046] 4. Brazing: Place the parts to be welded in step 3 into a graphite mold, and then put them into a vacuum furnace. First, heat them to 300℃ at 10℃ / min and keep them warm for 30min to remove the binder. Then heat them to 680℃ at 10℃ / min, and then heat them to 740℃ brazing temperature at 5℃ / min and keep them warm for 10min. Finally, cool them to 300℃ at 5℃ / min, and then cool them to room temperature with the furnace to complete the whole brazing process. The whole brazing process is carried out under vacuum with a vacuum degree of 6×10 -3 Pa, and the room temperature shear strength of the joint is 23 MPa.

[0047] Figure 1 This is the SEM image of the composite solder powder prepared by ball milling in step 1 of experiment 1. Figure 2 This is the EDS image of the C element in the composite solder powder prepared by the ball milling method in step 1 of experiment 1. The figure shows that the composite solder obtained by the ball milling method is uniformly mixed.

[0048] Experiment 2: This experiment differs from Experiment 1 in that the diamond particles in step 1 have a particle size of W20. All other conditions are the same as Experiment 1. The resulting room temperature shear strength of the joint is 30 MPa.

[0049] Experiment 3: This experiment differed from Experiment 2 in that the AgCuInTi solder powder used in Step 1 was replaced with AgCuInTi5 and the volume fraction of diamond particles in the composite solder was 5%. All other conditions were the same as Experiment 2. The resulting joint had a room-temperature shear strength of 18 MPa.

[0050] Experiment 4: This experiment differs from Experiment 2 in that the volume fraction of diamond particles in the composite solder in step 1 is 15%. All other conditions are the same as Experiment 2. The resulting joint has a room temperature shear strength of 10 MPa.

[0051] Experiment 5: This experiment differed from Experiment 2 in that the brazing temperature in step 4 was 740°C and held for 5 minutes. All other conditions were the same as Experiment 2. The resulting room-temperature shear strength of the joint was 16 MPa.

[0052] Experiment 6: This experiment differed from Experiment 2 in that the brazing temperature in step 4 was 740°C and held for 15 minutes. All other conditions were the same as Experiment 2. The resulting room-temperature shear strength of the joint was 21 MPa.

[0053] Comparative Experiment 1: This experiment differed from Experiment 1 in that no diamond particles were added to the brazing filler metal in Step 1, and ball milling was not performed. In Step 4, the brazing temperature was 780°C and held for 10 minutes. All other conditions were the same as Experiment 1. The resulting joint had a room-temperature shear strength of 19 MPa.

[0054] Figure 3 For comparison, the SEM image of the graphite / copper dissimilar material joint prepared in test 1 is shown. Figure 4 For comparison, the XRD pattern of the graphite / copper dissimilar material joint prepared in experiment 1 is shown. Figure 5 For comparison, the EDS diagram of the graphite / copper dissimilar material joint prepared in experiment 1, combined with XRD and EDS, can determine that the weld mainly contains Ag-based solid solution, Cu-based solid solution and Ag-Cu eutectic structure, and a thin TiC reaction layer will be formed on the graphite side of the joint.

[0055] Figure 6 This is an SEM image of the graphite / copper dissimilar joint prepared in Experiment 2. 1 and 5 represent the graphite and copper base materials, respectively; 2 is the infiltration layer; 3 is the composite brazing filler metal layer; and 4 is the diamond particles. The composite brazing filler metal layer has a structure similar to that of the AgCuInTi3 filler metal layer, except that the diamond particles are also uniformly distributed throughout.

[0056] Comparative Experiment 2: This experiment differed from Experiment 1 in that no diamond particles were added to the brazing filler metal in Step 1, and ball milling was not performed. In Step 4, the brazing temperature was 760°C and held for 10 minutes. All other conditions were the same as in Experiment 1. The resulting joint had a room-temperature shear strength of 15 MPa.

[0057] Comparative Experiment 3: This experiment differed from Experiment 1 in that no diamond particles were added to the brazing filler metal in Step 1, and ball milling was not performed. In Step 4, the brazing temperature was 740°C and held for 10 minutes. All other conditions were the same as Experiment 1. The resulting joint had a room-temperature shear strength of 17 MPa.

Claims

1. A method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder, characterized in that The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder is carried out in the following steps:

1. Preparation of composite solder: AgCuInTi solder powder and diamond particles were preliminarily mixed in an agate mortar, and then the mixed powder was placed in a ball mill and milled at a low speed using a ball mill until fully mixed to obtain composite solder powder; The volume fraction of diamond particles in the composite solder is 5% to 15%; The mass fraction of Ti element in the AgCuInTi solder powder is 3% to 7%; 2. Pretreatment of graphite and copper base materials; The pretreatment method of the graphite and copper base materials is as follows: cut the two base materials into the required size, polish the surface of the copper base material to be welded with 600#, 1200#, and 2000# water sandpaper in sequence, and polish the graphite base material with 2000# sandpaper until the surface is smooth, place the polished two base materials in anhydrous ethanol and ultrasonically oscillate for 5min~10min, take them out and blow dry; 3. Assembling the parts to be welded: Mix the composite solder powder prepared in step 1 with a binder to form a paste solder, apply the paste solder to the surface of the copper base material to be welded by screen printing, and then place the surface of the graphite base material to be welded on the paste solder, thereby assembling a graphite / diamond particle reinforced AgCuInTi composite solder / copper part to be welded; 4. Brazing: Place the parts to be welded in step 3 into a graphite mold, and then put them into a vacuum furnace. First, heat them to 300℃~310℃ and keep them warm for 30min~35min to remove the binder, then heat them to 680℃, and then heat them to the brazing temperature of 680℃~800℃ and keep them warm for 5min~20min; finally, cool them to 300℃ and then cool them to room temperature with the furnace to complete the entire brazing process. The entire brazing process is carried out under vacuum.

2. The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder according to claim 1, characterized in that The AgCuInTi solder powder described in step 1 is AgCuInTi3.

3. The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder according to claim 1, characterized in that The particle size of the diamond particles described in step 1 is W7~W20.

4. The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder according to claim 1, characterized in that The rotation speed of the low-speed ball mill described in step 1 is 200-300 rpm.

5. The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder according to claim 1, characterized in that The binder described in step three is a 2% by mass hydroxyethyl cellulose aqueous solution.

6. The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder according to claim 1, characterized in that The vacuum degree in step 4 is 6×10 -3 Pa.

7. The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder according to claim 1, characterized in that In step 4, the temperature is first raised to 300°C at a rate of 10°C / min and kept at this temperature for 30 minutes to remove the binder.

8. The method for brazing graphite / copper dissimilar materials using diamond particle reinforced AgCuInTi composite solder according to claim 1, characterized in that In step 4, the temperature is raised to 680°C at 10°C / min, then raised to the brazing temperature of 680°C~800°C at 5°C / min and kept at this temperature for 5min~20min; finally, the temperature is lowered to 300°C at 5°C / min, and then cooled to room temperature with the furnace to complete the entire brazing process. The entire brazing process is carried out under vacuum.

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