Brazing filler metal for connecting C / C composite material and cobalt-based high-temperature alloy, preparation method and brazing method

Abstract

The invention provides brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy, a preparation method and a brazing method, and belongs to the field of dissimilar material connection. The brazing filler metal is prepared by mixing Co-Fe-B alloy powder and Ti powder according to the mass ratio of (6-40): 1. The brazing filler metal is prepared through the steps that firstly, Co-Fe-B alloy powder is designed and prepared; and then Ti powder is added into the Co-Fe-B alloy powder, and the brazing filler metal is formed after sufficient mixing. When the brazing filler metal is used for connecting the C / C composite material and the cobalt-based high-temperature alloy, firstly, the brazing filler metal is prepared into paste through ethylene glycol, and the paste is preset between the polished and cleaned C / C composite material and the cobalt-based high-temperature alloy to form a to-be-welded part; and then the to-be-welded piece is placed in a vacuum furnace to be connected. The connection method is simple, pressure does not need to be applied, the low-stress high-temperature-resistant connector can be obtained, and low-temperature connection / high-temperature service is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of connecting dissimilar materials, in particular to a brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy, a preparation method and a brazing method. Background Art

[0002] C / C composite materials have low density, good mechanical properties and high-temperature ablation resistance, and have been widely used in aerospace, machinery and other fields. However, the complex preparation process and poor processing performance of C / C composite materials make it difficult to process them into complex structural parts. Therefore, C / C composite materials often need to be combined with metals with good processing performance to form composite parts. Cobalt-based high-temperature alloys have high high-temperature strength, good oxidation resistance and corrosion resistance, and are widely used in the aerospace field. Realizing a reliable connection between C / C composite materials and cobalt-based high-temperature alloy structural parts and giving full play to the advantages of both can not only increase the operating temperature of hot end components, but also reduce equipment weight and cost, which is of great significance to the application of C / C composite materials.

[0003] Active brazing is the most suitable method for joining C / C composites and cobalt-based superalloys due to its simplicity, convenience and low cost. However, there are two important difficulties in joining C / C composites and cobalt-based superalloys using traditional active brazing: (1) There are huge differences in structure and performance between C / C composites and cobalt-based superalloys. For example, the thermal expansion coefficient of C / C composites is about 1×10 -6 / K, the thermal expansion coefficient of cobalt-based high-temperature alloy is about (13~16)×10 -6 / K, the large difference in thermal expansion coefficient between the two leads to large residual thermal stress in the joint; (2) The joint is often used in high temperature environment, and the service environment of some components is even above 1200℃, which requires the joint to have high temperature resistance.

[0004] Composite brazing (including reaction-composite brazing) is a joining method proposed to alleviate thermal stress in dissimilar materials. Its process principle is to synthesize a reinforcing phase with a low thermal expansion coefficient in situ reaction within the joining layer, bringing the thermal expansion coefficient of the joining layer between the two parent materials, thereby alleviating joint thermal stress. However, due to the heat resistance temperature of the low-melting-point brazing metal matrix, composite brazing cannot increase the heat resistance of the joint. In theory, using a high-melting-point brazing filler metal can improve the high-temperature performance of the joint, but it will increase the thermal stress of the joint at higher joining temperatures.

[0005] Therefore, in order to give full play to the high temperature resistance of C / C composite materials and cobalt-based high temperature alloys, and solve the problems of connection thermal stress and high temperature resistance of joints, it is necessary to develop a new type of brazing filler metal to obtain low-stress and high-temperature resistant C / C composite materials and cobalt-based high-temperature alloy joints to achieve "low temperature connection / high temperature service". Summary of the Invention

[0006] The present invention provides a brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy, a preparation method and a brazing method, aiming to solve the problems of high thermal stress and poor high-temperature resistance in the connection joints between the C / C composite material and the cobalt-based high-temperature alloy.

[0007] In order to achieve the above object, the specific scheme adopted by the present invention is: On the one hand, the present invention discloses a brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy. The brazing filler metal is prepared by mixing Co-Fe-B alloy powder and Ti powder in a mass ratio of (6 to 40):1, wherein the mass ratio of Co, Fe and B elements in the Co-Fe-B alloy powder is 60.9:34.6:4.5.

[0008] Furthermore, the particle size of the Co-Fe-B alloy powder is -300 mesh, and the particle size of the Ti powder is 25-75 μm.

[0009] On the other hand, the present invention discloses a method for preparing a brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy, which mainly comprises the following steps: Step (1), calculating and weighing the Co block, the Fe block and the Fe-B master alloy block; Step (2), using a vacuum suspension melting furnace to melt the Co block, Fe block and Fe-B intermediate alloy block into a Co-34.6Fe-4.5B alloy rod; Step (3), using a vacuum furnace to perform a composition homogenization heat treatment on the Co-34.6Fe-4.5B alloy rod; Step (4), using electromagnetic induction atomization to make spherical Co-Fe-B alloy powder from the heat-treated Co-34.6Fe-4.5B alloy rod; Step (5): adding Ti powder to the Co-Fe-B alloy powder, wherein the mass ratio of the Co-Fe-B alloy powder to the Ti powder is (6-40):1, and mixing them thoroughly to obtain the solder.

[0010] Furthermore, in step (3), the specific process of heat treatment is: keeping the temperature at 600° C. for 3 hours under a vacuum environment, and cooling with the furnace.

[0011] In another aspect, the present invention discloses a brazing method for a C / C composite material and a cobalt-based high-temperature alloy, which is characterized by mainly comprising the following steps: Step 1: Grind the C / C composite material and the cobalt-based high-temperature alloy with 1500-mesh and 240-mesh sandpaper, respectively, and then ultrasonically clean the polished base materials with anhydrous ethanol for 5 minutes; Step 2: Prepare the solder into a paste with ethylene glycol, and place it between the C / C composite material and the cobalt-based high-temperature alloy to obtain a part to be welded; Step 3: Place the parts to be welded in a vacuum brazing furnace without applying pressure and perform brazing. After the insulation is completed, a connection sample is obtained.

[0012] Furthermore, in step 3, the specific process of brazing is as follows: the vacuum degree is lower than 5×10 -3 Pa, heating rate is 10℃ / min, connection temperature is 1050-1300℃, and holding time is 60-180min.

[0013] Beneficial effects:

[0014] (1) The present invention uses a mixed powder of Co-Fe-B alloy powder and Ti powder with eutectic composition as a brazing filler metal to connect a C / C composite material and a cobalt-based high-temperature alloy. The added Ti particles combine with the C atoms from the C / C composite material to form a TiC reinforcement phase, which can relieve thermal stress. At the same time, the Co-Fe-B and the cobalt-based high-temperature alloy can undergo mutual atomic diffusion, and the B atoms with small atomic radius diffuse into the high-temperature alloy. The matrix composition of the connecting layer changes with the eutectic composition point, causing the connecting layer to undergo isothermal solidification. As the holding time increases, the heat resistance of the connecting layer gradually increases, and ultimately a low-stress, ultra-high-temperature resistant joint is obtained.

[0015] (2) The brazing method of the present invention combines the advantages of reaction-composite brazing and TLP connection. The connection method is simple and can obtain low-stress and high-temperature resistant joints, realizing "low-temperature connection / high-temperature service". BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Microstructure diagrams of Co-Fe-B alloy powder (a) and Ti powder (b) in the solder.

[0017] Figure 2 This is the organizational diagram of the joint obtained in Example 1, Figure 2 (a) The upper part is C / C composite material, the middle is the intermediate layer, and the lower part is GH5188 cobalt-based high-temperature alloy. Figure 2 (b) The TiC reinforcement phase synthesized by in-situ reaction in the intermediate layer. DETAILED DESCRIPTION

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] The present invention is further described below with reference to the accompanying drawings and examples, but the protection scope of the present invention is not limited thereto.

[0020] Example 1

[0021] A brazing method for a C / C composite material and a cobalt-based high-temperature alloy, wherein the specific connection process is as follows: S1. Use wire cutting to cut the C / C composite material and GH5188 cobalt-based superalloy into 5 mm × 5 mm × 5 mm and 10 mm × 10 mm × 4 mm specimens, respectively. Then, use 400-mesh, 800-mesh, and 1500-mesh sandpaper to polish the C / C composite material, and 240-mesh sandpaper to polish the superalloy. The polished parent metal to be welded is ultrasonically cleaned with anhydrous ethanol for 5 minutes. S2. Prepare a solder paste (Co-Fe-B:Ti=10:1) with ethylene glycol and pre-place it between the C / C composite material and the GH5188 high-temperature alloy to form a welded part, with the upper part being the C / C composite material and the lower part being the GH5188 high-temperature alloy. S3. Place the workpiece to be welded in a vacuum furnace and wait until the vacuum degree is better than 5×10 -3 Pa, turn on the heating, the heating rate is 10℃ / min, the connection temperature of the welded parts is 1140℃, the holding time is 90min, and after the holding is completed, the joint is obtained by cooling with the furnace.

[0022] Figure 1 The microstructure of Co-Fe-B alloy powder (a) and Ti powder (b) in the solder is shown. Figure 1 It can be seen that the Co-Fe-B alloy powder is spherical with a particle size of -300 mesh. The Ti powder is spherical with a particle size of 25-75μm. The microstructure of the joint was observed and analyzed. Figure 2 For the overall organizational structure of the joint, Figure 2 The enlarged image in the middle is an enlarged image of the interface reaction layer on the C / C composite material side. Figure 2 It can be seen that in the obtained joint, the C / C composite material and the GH5188 cobalt-based high-temperature alloy are firmly connected through the intermediate layer, and the TiC reinforcement phase is in situ synthesized in the intermediate layer, which can relieve thermal stress.

[0023] Example 2

[0024] The difference between this embodiment and embodiment 1 is that the solder used in step S2 has a ratio of (Co-Fe-B):Ti=15:1.

[0025] Example 3

[0026] The difference between this embodiment and embodiment 1 is that the solder used in step S2 has a ratio of (Co-Fe-B):Ti=20:1.

[0027] Comparative Example 1

[0028] The difference between this comparative example and Example 1 is that the solder used in step S2 is a single Co-Fe-B.

[0029] Comparative Example 2

[0030] The difference between this comparative example and Example 1 is that the holding time in step S3 is 15 minutes.

[0031] Comparative Example 3

[0032] The difference between this comparative example and Example 1 is that the ratio of (Co-Fe-B):Ti in the solder used in step S2 is 5:1.

[0033] The joints obtained in Examples 1-3 and Comparative Examples 1-3 were tested below, and the test results were examined.

[0034] To characterize the mechanical properties of the joint, a shear strength test was performed on the joint. The joint was placed in a homemade shear mold and a shear test was performed on an electronic universal testing machine with a loading rate of 0.5 mm / min. The maximum compressive load was recorded and converted into the joint shear strength. To characterize the heat resistance of the joint, the heat resistance temperature of the joint connection layer was tested. The connection layer specimens were prepared using wire cutting and grinding, and the initial liquefaction temperature of the connection layer was tested using a TG-DSC comprehensive analyzer. The test results of shear strength and initial liquefaction temperature are shown in Table 1.

[0035] Table 1 Test results of joint shear strength and initial liquefaction temperature of the connecting layer obtained in Examples 1-3 and Comparative Examples 1-3 (Co-Fe-B):Ti Brazing process Shear strength / MPa Initial liquefaction temperature / ℃ Example 1 10:1 1140℃×90min 50.8 1145 Example 2 15:1 1140℃×90min 48.9 1155 Example 3 20:1 1140℃×90min 48.6 1160 Comparative Example 1 1:0 1140℃×90min 45.7 1165 Comparative Example 2 10:1 1140℃×15min 20.1 1110 Comparative Example 3 5:1 1140℃×90min 32.5 1130

[0036] As can be seen from Table 1, under the 1140℃×90min joining process, when (Co-Fe-B):Ti=(10~20):1, the mechanical properties of the joints are all above 40MPa, and the initial liquefaction temperature of the joining layer is higher than the joining temperature, and "low temperature joining / high temperature service" is achieved. And with the increase of the amount of Ti powder added in the solder, the mechanical properties of the joint first increase and then decrease, while the heat resistance of the joining layer gradually decreases. In Comparative Example 1, since the solder only uses a single Co-Fe-B powder, the shear strength of the joint is lower than 48MPa. In Comparative Example 2, due to the short holding time, the mechanical properties and heat resistance of the joint are both low. In Comparative Example 3, since (Co-Fe-B):Ti=5:1, the shear strength is not high, and the initial liquefaction temperature of the joining layer is lower than the joining temperature, "low temperature joining / high temperature service" is not achieved.

[0037] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any equivalent changes or modifications made based on the essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy, characterized in that: The brazing filler metal is prepared by mixing Co-Fe-B alloy powder and Ti powder in a mass ratio of (6-40):1, wherein the mass ratio of Co, Fe and B elements in the Co-Fe-B alloy powder is 60.9:34.6:4.

5.

2. The brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy according to claim 1, characterized in that: The particle size of the Co-Fe-B alloy powder is -300 mesh, and the particle size of the Ti powder is 25-75 μm.

3. A method for preparing a brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy, characterized in that: The main steps are as follows: Step (1), calculating and weighing the Co block, the Fe block and the Fe-B master alloy block; Step (2), using a vacuum suspension melting furnace to melt the Co block, the Fe block and the Fe-B intermediate alloy block into a Co-34.6Fe-4.5B alloy rod; Step (3), using a vacuum furnace to perform a composition homogenization heat treatment on the Co-34.6Fe-4.5B alloy rod; Step (4), using electromagnetic induction atomization method to make spherical Co-Fe-B alloy powder from the heat-treated Co-34.6Fe-4.5B alloy rod; Step (5), adding Ti powder to the Co-Fe-B alloy powder, the mass ratio of the Co-Fe-B alloy powder to the Ti powder being (6-40):1, and mixing thoroughly to obtain a solder.

4. The method for preparing a brazing filler metal for connecting a C / C composite material and a cobalt-based high-temperature alloy according to claim 3, characterized in that: In step (3), the specific process of heat treatment is: in a vacuum environment, keep warm at a temperature of 600° C. for 3 hours, and cool with the furnace.

5. A brazing method for a C / C composite material and a cobalt-based high-temperature alloy, characterized in that: The main steps are as follows: Step 1: Grind the C / C composite material and the cobalt-based high-temperature alloy with 1500-mesh and 240-mesh sandpaper respectively, and then ultrasonically clean the polished base materials with anhydrous ethanol for 5 minutes; Step 2: The solder according to any one of claims 1 to 2 is mixed with ethylene glycol to form a paste, and placed between the C / C composite material and the cobalt-based high-temperature alloy to obtain a part to be welded; Step 3: Place the parts to be welded in a vacuum brazing furnace without applying pressure, and perform brazing. After the insulation is completed, a connection sample is obtained.

6. The brazing method of a C / C composite material and a cobalt-based high-temperature alloy according to claim 5, characterized in that: In step 3, the specific process of brazing is: the vacuum degree is less than 5×10 -3 Pa, heating rate is 10℃ / min, connection temperature is 1050-1300℃, and holding time is 60-180min.

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