Flaky composite filler metal for connecting C / C or C / SiC composites with metal, preparation method and brazing process

Abstract

The present invention discloses a flaky composite brazing filler metal for connecting C / C or C / SiC composites and metals, a preparation method and a brazing process, belonging to the field of joining dissimilar materials. The flaky composite brazing filler metal is made of 4-8% Si powder, 3-16% Ti powder and the balance Cu powder by mass percentage. The brazing method is as follows: melting a certain proportion of Cu, Si and Ti elemental substances in a vacuum arc melting furnace to form a Cu-based composite brazing filler metal ingot reinforced with Ti5Si3 phase, cutting the composite brazing filler metal ingot into flakes, and grinding and cleaning to obtain the flaky composite brazing filler metal; assembling the composite material, the brazing filler metal and the metal into a "sandwich" shape and performing vacuum brazing treatment. When using the flaky composite brazing filler metal of the present invention to connect C / C or C / SiC composites and metals, it has the characteristics of high compatibility between the reinforcing phase and the matrix, strong antioxidant ability and good plasticity. The obtained joint has low stress and high strength.

Description

Technical Field

[0001] The present invention relates to the technical field of joining dissimilar materials, and specifically to a flake composite brazing filler metal for joining C / C or C / SiC composites and metals, a preparation method thereof, and a brazing process. Background Art

[0002] C / C and C / SiC composites have a series of excellent properties such as low density, high temperature resistance, low thermal expansion coefficient, high thermal conductivity, high strength and modulus at high temperatures, and wear / erosion resistance, and have important application values in the fields of aviation, aerospace, and thermal protection. However, compared with metal materials, C / C and C f / SiC composites are inherently brittle, have high production costs, poor impact resistance, and are difficult to machine into complex structural parts. In practical applications, C f / SiC composites often need to be combined with metals to form composite parts for use, so as to give full play to the low density and high temperature resistance of C f / SiC composites and the good machining performance and high strength of metals, so as to achieve the purpose of complementary advantages.

[0003] Active brazing has become a widely used joining technology for joining C / C and C f / SiC composites and metals due to its advantages such as simple joining method, high applicability, no need to apply pressure, and good sealing performance. However, due to the large differences in physical and chemical properties between the composite material and the metal, especially the large difference in thermal expansion coefficient between the two, there are large thermal stresses in the traditional active brazing joint, which reduces the mechanical properties of the joint and even leads to joint failure.

[0004] Composite brazing is a joining method proposed on the basis of active brazing to relieve the residual thermal stress in the joint of dissimilar materials. Its process principle is to directly add a reinforcing phase with low thermal expansion coefficient and high temperature resistance (such as TiC, W, etc.) to the conventional powder brazing filler metal, so as to reduce the thermal expansion coefficient of the joining layer and make the thermal expansion coefficient of the joining layer between those of the two base materials, thus effectively relieving the thermal stress of the joint. However, there are currently two problems with composite brazing: one is that the directly added reinforcing phase in the joining material has poor compatibility with the matrix and is prone to porosity; the other is that the joining materials reported for composite brazing currently are all powder brazing filler metals, and there are few reports on composite brazing filler metals in other forms, which to a certain extent limits the application of composite brazing; the third is that the powder brazing filler metal has poor oxidation resistance and requires a high vacuum degree for the equipment.

[0005] Therefore, developing a flake composite brazing filler metal with good compatibility between the reinforcing phase and the matrix and strong oxidation resistance is of great significance for the joining of C / C and C / SiC composites and metals and the popularization and application of composite brazing. Summary of the Invention

[0006] To solve the deficiencies in the prior art, the present invention provides a sheet composite brazing filler metal for connecting C / C or C / SiC composites with metals, a preparation method thereof, and a brazing process. Using the sheet composite brazing filler metal of the present invention for connecting C / C or C / SiC composites with metals can solve the problems of poor compatibility between the reinforcing phase and the matrix in composite brazing and poor oxidation resistance of the powder composite brazing filler metal.

[0007] To achieve the above object, the specific solution adopted by the present invention is as follows:

[0008] A sheet composite brazing filler metal for connecting C / C or C / SiC composites with metals, which is made of 4-8% Si powder, 3-16% Ti powder and the balance Cu powder by mass percentage.

[0009] As a preferred solution, the sheet composite brazing filler metal is made of 5-6% Si powder, 8-10% Ti powder and the balance Cu powder by mass percentage.

[0010] A preparation method of a sheet composite brazing filler metal for connecting C / C or C / SiC composites with metals mainly includes the following steps:

[0011] Step 1, raw material calculation and batching: Calculate the masses of elemental Cu powder, Si powder and Ti powder required according to the mass percentages of 4-8% Si powder, 3-16% Ti powder and the balance Cu powder, and weigh the required elemental powders according to the calculation results;

[0012] Step 2, mixing and die-casting: Fully mix the Cu powder, Si powder and Ti powder, and then press the mixed powder into a cylindrical powder blank;

[0013] Step 3, vacuum arc melting: Use an arc melting furnace to melt the cylindrical powder blank under vacuum, melt it repeatedly 6 times, and then cool it to obtain a Cu-based composite brazing filler metal ingot reinforced with Ti5Si3 phase; during the melting process, Ti and Si react in situ to synthesize Ti5Si3 with a low coefficient of thermal expansion, and the brazing filler metal matrix is a Cu solid solution matrix containing the active element Ti;

[0014] Step 4, cutting into sheets: Wire-cut the Cu-based composite brazing filler metal ingot reinforced with Ti5Si3 phase into sheets, and polish its surface to obtain the sheet composite brazing filler metal.

[0015] As a preferred solution, in Step 1, the purities of the Cu powder, Si powder and Ti powder are all above 99.9%.

[0016] As a preferred solution, in Step 1, the size of the Cu powder is -1000 mesh, and the sizes of the Si powder and Ti powder are -300 mesh.

[0017] The brazing process of C / C or C / SiC composites and metals mainly includes the following steps:

[0018] S1. Grind the surfaces to be brazed of the composites and metals, and put the ground composites, metals and sheet composite filler metals into absolute ethanol for ultrasonic cleaning;

[0019] S2. Assemble the composites, sheet composite filler metals and metals into a "sandwich"-shaped workpiece to be brazed;

[0020] S3. Place the workpiece to be brazed in a vacuum furnace. When the vacuum degree is better than 5×10 -3 Pa, start to energize and heat for vacuum brazing. After brazing is completed, cool it to room temperature with the furnace.

[0021] During the brazing process, the active element Ti in the matrix reacts with the composite to achieve connection, and Ti5Si3 with low thermal expansion coefficient acts as a reinforcement phase to relieve the thermal stress of the joint.

[0022] As a preferred solution, in step S3, the specific process of vacuum brazing is: the brazing temperature is 950°C to 1060°C, and the holding time is 5 to 30 minutes.

[0023] Beneficial effects:

[0024] Compared with the existing composite brazing, the present invention has the following advantages: (1) The in-situ synthesized Ti5Si3 phase has good compatibility with the filler metal matrix, and there are few pores in the joint layer after welding; (2) Compared with the powder composite filler metal, the sheet filler metal has higher oxidation resistance, reduces the requirement for vacuum degree, and is easy to obtain high-quality joints; (3) The composite filler metal matrix is a Cu solid solution matrix, which has good plasticity and is used to relieve the thermal stress of the composite and metal joints; (4) The sheet composite filler metal broadens the original concept of composite brazing, increases the form of the composite filler metal, and has important significance for the connection of C / C and C / SiC composites and metals and the popularization and application of composite brazing. Description of the drawings

[0025] Figure 1 It is the microstructure diagram of the sheet composite filler metal obtained by arc melting in Example 1.

[0026] Figure 2 It is the microstructure diagram of the joint of the welded part prepared in Example 1. Detailed implementation manners

[0027] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] A sheet-like composite brazing filler metal for connecting C / C or C / SiC composites with metals, the sheet-like composite brazing filler metal is made of 4-8% of Si powder, 3-16% of Ti powder and the balance of Cu powder by mass percentage.

[0029] A preparation method of a sheet-like composite brazing filler metal for connecting C / C or C / SiC composites with metals mainly includes the following steps:

[0030] Step 1, raw material calculation and batching: Calculate the masses of elemental Cu powder, Si powder and Ti powder required according to the mass percentages of 4-8% of Si powder, 3-16% of Ti powder and the balance of Cu powder, and weigh the required elemental powders according to the calculation results; among them, the purities of Cu powder, Si powder and Ti powder are all above 99.9%, the size of Cu powder is -1000 mesh, and the sizes of Si powder and Ti powder are -300 mesh;

[0031] Step 2, mixing and die-casting: Fully mix Cu powder, Si powder and Ti powder, and then press the mixed powder into a cylindrical powder blank;

[0032] Step 3, vacuum arc melting: Use an arc melting furnace to melt the cylindrical powder blank under vacuum, melt it repeatedly 6 times, and then cool it to obtain a Ti5Si3 phase-reinforced Cu-based composite brazing filler metal ingot;

[0033] Step 4, cutting into sheets: Wire-cut the Ti5Si3 phase-reinforced Cu-based composite brazing filler metal ingot into sheets, and polish its surface to obtain the sheet-like composite brazing filler metal.

[0034] A brazing process for C / C or C / SiC composites and metals mainly includes the following steps:

[0035] S1. Grind the surfaces to be welded of the composite material and the metal, and put the ground composite material, metal and sheet-like composite brazing filler metal into absolute ethanol for ultrasonic cleaning;

[0036] S2. Assemble the composite material, sheet-like composite brazing filler metal and metal into a "sandwich"-shaped workpiece to be welded;

[0037] S3. Place the workpiece to be welded in a vacuum furnace. When the vacuum degree is better than 5×10 -3Power on and start heating at [[Pa]], perform vacuum brazing, the brazing temperature is 950°C to 1060°C, the holding time is 5 to 30 minutes, and after brazing is completed, cool with the furnace to room temperature.

[0038] Example 1

[0039] The sheet composite filler metal is made of 5.9% Si powder, 10% Ti powder and 84.1% Cu powder by mass percentage. The size of the Cu powder is -1000 mesh, and the sizes of the Si powder and Ti powder are -300 mesh.

[0040] The preparation method of the sheet composite filler metal includes the following steps:

[0041] Step 1, raw material calculation and batching: Calculate the masses of elemental Cu powder, Si powder and Ti powder required according to the mass percentages of 5.9% Si powder, 10% Ti powder and 84.1% Cu powder, and weigh the required elemental powders according to the calculation results;

[0042] Step 2, mixing and die-casting: Use mechanical ball milling to fully mix the three elemental powders of Cu, Si and Ti, and then use a powder press to press the powder into a cylindrical powder blank;

[0043] Step 3, vacuum arc melting: Use an arc melting furnace to melt the cylindrical powder blank under vacuum. The melting current is 250 A, the time is 1 minute, melt repeatedly 6 times, and then cool to obtain a Cu-based composite filler metal ingot reinforced with Ti5Si3 phase;

[0044] Step 4, cutting into sheets: Use a wire cutting machine to cut the composite filler metal ingot into 5 mm × 5 mm × 0.5 mm sheet filler metal, and use 400-mesh sandpaper to polish and remove the impurities and oxide film on the surface of the filler metal to obtain the sheet composite filler metal.

[0045] The composite brazing test uses C / C composite material as the composite material and GH3044 superalloy as the metal. The brazing process includes the following steps:

[0046] S1. Use wire cutting to cut the C / C composite material and GH3044 superalloy into specimens of 5 mm × 5 mm × 5 mm and 10 mm × 1 mm × 3 mm respectively;

[0047] S2. Polish the mating surfaces of the base materials successively with 240 - 1000-mesh sandpaper, and then put the polished base materials and sheet composite filler metal into absolute ethanol for ultrasonic cleaning for 5 minutes;

[0048] S3. Assemble the C / C composite material, filler metal and GH3044 into a "sandwich"-shaped workpiece to be brazed in sequence;

[0049] S4. Place the workpiece to be brazed in a vacuum furnace. When the vacuum degree is better than 5×10-3 Power on and heat at 15 °C / min starting from 1 Pa until the holding temperature of 1050 °C is reached. Hold for 30 min, then cool in the furnace to room temperature and take samples after opening the furnace.

[0050] Use a wire cutting machine to cut the composite brazed joint in half to make a metallographic specimen, and observe the joint microstructure with a scanning electron microscope. Figure 1 It is the microstructure diagram of the flaky composite brazing filler metal obtained by arc melting. Figure 1 The medium-dark gray phase is the Ti5Si3 reinforcement phase, and the matrix is the Cu solid solution. Figure 2 It is the microstructure diagram of the joint of the prepared welded part. The upper part is the C / C composite material, the middle part is the Cu + Ti5Si3 composite brazing filler metal (intermediate layer), and the lower part is the GH3044 superalloy.

[0051] Example 2

[0052] The differences between Example 2 and Example 1 are as follows: (1) The flaky composite brazing filler metal is made of 4.5% Si powder, 4% Ti powder, and 91.5% Cu powder by mass percentage; (2) In the brazing process, the composite material is the C / SiC composite material, and the metal is 304 stainless steel; (3) In the brazing process, in step S4, the holding time is 20 min. The rest are the same as in Example 1.

[0053] Comparative Example 1

[0054] The only difference between Comparative Example 1 and Example 1 is that the flaky composite brazing filler metal is made of 2.8% Si powder, 1.6% Ti powder, and 95.6% Cu powder by mass percentage, and the rest are the same as in Example 1.

[0055] Comparative Example 2

[0056] The only difference between Comparative Example 2 and Example 2 is that the flaky composite brazing filler metal is made of 3.7% Si powder, 1.6% Ti powder, and 94.7% Cu powder by mass percentage, and the rest are the same as in Example 2.

[0057] Shear strength analysis

[0058] Use the joint shear strength to characterize the mechanical properties of the joint. Place the welded parts prepared in Examples 1-2 and Comparative Examples 1-2 in a shear die and conduct a shear test on an electronic universal testing machine. The loading rate of the testing machine is 2 mm / min, record the maximum applied load, and finally convert it into the joint shear strength. The results are shown in Table 1.

[0059] Table 1 Shear strength results of welded joints prepared in Examples 1-2 and Comparative Examples 1-2

[0060]

[0061] The shear strength of the joints shown in Table 1 is the average of the shear strength data of five specimens. From the data in the table, it can be seen that the shear strengths of the joints in Examples 1 and 2 are 37.6 MPa and 125.6 Pa respectively, while the shear strengths of the joints in Comparative Examples 1 and 2 are 18.3 MPa and 65.6 MPa respectively, showing a significant decrease. Therefore, the composite filler metal of the present invention has a better proportioning.

[0062] The above are only the preferred embodiments of the present invention, and do not impose any formal limitations on the present invention. Any equivalent transformation or modification made according to the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. Brazing process of C / C or C / SiC composites and metals, characterized in that, The brazing process mainly includes the following steps: S1. Grinding the surfaces of the composite material and the metal to be welded, and placing the ground composite material, the metal and the sheet-shaped composite solder into anhydrous ethanol for ultrasonic cleaning; S2, assembling the composite material, the sheet-shaped composite solder and the metal into a "sandwich"-shaped part to be welded; S3. Place the workpiece to be welded in a vacuum furnace. Start power-on heating for vacuum brazing when the vacuum degree is better than 5×10 -3 Pa. After the brazing is completed, cool it in the furnace to room temperature; The metal is GH3044 high temperature alloy or 304 stainless steel; the sheet-shaped composite solder is made of 4-8% Si powder, 3-16% Ti powder and the balance Cu powder by mass percentage; The preparation method of the flaky composite solder is as follows: Step 1: Calculate and prepare raw materials: Calculate the mass of the required elemental Cu powder, Si powder and Ti powder according to the above mass percentage, and weigh the required elemental powder according to the calculated result; Step 2: Mixing and die casting: fully mix the Cu powder, Si powder and Ti powder, and then press the mixed powder into a cylindrical powder blank; Step 3, vacuum arc melting: using an arc melting furnace to melt the cylindrical powder blank under vacuum, repeatedly melting for 6 times, and then cooling to obtain a Ti5Si3 phase-reinforced Cu-based composite solder ingot; Step 4: Cutting into sheets: Cutting the Ti5Si3 phase-reinforced Cu-based composite solder ingot into sheets, and grinding the surface thereof to obtain a sheet-like composite solder.

2. The brazing process of C / C or C / SiC composite material and metal according to claim 1, characterized in that, The sheet-shaped composite solder is made of 5-6% Si powder, 8-10% Ti powder and the balance Cu powder in terms of mass percentage.

3. The brazing process of C / C or C / SiC composite material and metal according to claim 1, characterized in that, In step 1, the purity of Cu powder, Si powder and Ti powder is above 99.9%.

4. The brazing process of C / C or C / SiC composite material and metal according to claim 1, characterized in that, In step 1, the size of Cu powder is -1000 mesh, and the size of Si powder and Ti powder is -300 mesh.

5. The brazing process of C / C or C / SiC composite material and metal according to claim 1, characterized in that, In step S3, the specific process of vacuum brazing is as follows: the brazing temperature is 950°C to 1060°C, and the holding time is 5 to 30 minutes.

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