Brazing part and brazing process of non-compact C / C composite material and low-expansion alloy

Abstract

The invention belongs to the field of ceramic and metal connection, and discloses a brazing part and a brazing process of a non-compact C / C composite material and a low-expansion alloy, the process comprises high-temperature infiltration treatment and brazing connection of the C / C composite material, and the high-temperature infiltration treatment is to carry out infiltration surface modification on the non-compact C / C composite material by adopting a silicon-titanium alloy; according to the high-temperature brazing connection, brazing is conducted through Cu-Sn-Ti brazing filler metal. The method can solve the problems that brazing filler metal easily permeates into the C / C composite material during brazing, the thickness of a welding seam is difficult to control, and the strength of a joint is low, and meanwhile, the density and the strength of the C / C composite material can be improved.

Description

Technical Field

[0001] The invention relates to the field of ceramic and metal connection, and more particularly to a brazing part and a brazing process of a non-dense C / C composite material and a low expansion alloy. Background Art

[0002] C / C composite material is a composite material with long carbon fiber as the reinforcement phase and carbon material as the matrix. It fully combines the advantages of both carbon and graphite, and has higher thermal conductivity, high temperature resistance, lower brittleness, thermal expansion coefficient, etc., and has been used as aerospace engine nozzles, brake discs, nuclear reactor high-temperature components, etc. In order to meet special service environments, C / C composite materials need to be connected with metal materials or themselves as complex shapes or large-sized parts. Low expansion alloys such as Invar and Kovar have lower thermal expansion coefficients and higher melting points. When connected with C / C composite materials, the problem of poor joint performance caused by large residual stress caused by differences in thermal expansion coefficients can be avoided. Therefore, achieving reliable connection between C / C composite materials and low expansion alloys has great application value.

[0003] There are many methods for connecting C / C composites to metals, including instantaneous liquid phase connection, brazing, diffusion welding and self-propagating reaction. Compared with other connection methods, brazing technology has the advantages of short connection time, low pressure on the parent material and simple process, and is a commonly used connection method for C / C composites. The main difficulties in welding C / C composites and metal materials are: (1) The density of C / C composites is low, and the porosity is about 5-15%. Therefore, during the brazing process, the brazing material will excessively penetrate into the parent material due to capillary action, resulting in loss of brazing material, low joint strength, and even connection failure; (2) The thermal expansion coefficient and elastic modulus between C / C composites and metals are very different, and large residual stress is easily formed in the joint, resulting in low joint strength and even joint cracking.

[0004] Therefore, it is urgent to develop a method and process for connecting non-dense carbon fiber reinforced carbon-based composites with low expansion alloys. Summary of the invention

[0005] In view of this, the present invention provides a brazing part and a brazing process of a non-dense C / C composite material and a low expansion alloy.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The first technical purpose of the present invention is to provide a brazing process for a non-dense C / C composite material and a low expansion alloy, comprising the following steps:

[0008] (1) Infiltration of C / C composites: Silicon-titanium alloy is placed around a non-dense C / C composite, and a high-temperature reaction infiltration treatment is performed in a vacuum furnace to obtain a surface-dense C / C composite;

[0009] (2) Brazing connection: The surfaces to be welded of the C / C composite material and the low expansion alloy obtained in step (1) are coated with Cu-Sn-Ti solder paste, and the two are assembled in the sandwich structure of C / C composite material / Cu-Sn-Ti / low expansion alloy. The two are fixed with a graphite mold and placed in a vacuum brazing furnace for brazing to obtain a connector.

[0010] It should be noted that the porosity of the non-dense C / C composite material described in the present invention is 5-15%, which has a relatively high porosity; and the low expansion alloy described in the present invention includes Invar alloy and Kovar alloy.

[0011] Furthermore, in step (1), the silicon content in the silicon-titanium alloy is 70-85wt%, preferably 74-78wt%.

[0012] Furthermore, in step (1), the infiltration atmosphere is a vacuum or a protective atmosphere, the protective gas is argon, preferably a vacuum; the infiltration temperature is 1330-1400°C, preferably 1350-1380°C; and the insulation time is 1-10 min, preferably 2-8 min.

[0013] Furthermore, in step (2), the mass fraction of Cu in the Cu-Sn-Ti solder paste is 70-80%, the mass fraction of Sn is 15-20%, and the mass fraction of Ti is 5-10%.

[0014] Furthermore, in step (2), the coating is performed by screen printing, and the thickness of the coating layer formed after the Cu-Sn-Ti solder paste is coated is 200 to 700 μm, preferably 300 to 600 μm; the use of screen printing technology can effectively solve defects such as the coating layer being too thick and unevenly distributed.

[0015] Furthermore, in step (2), the brazing atmosphere is vacuum, the brazing temperature is 910-950°C, preferably 920-940°C; the holding time is 5-15 min, preferably 2-8 min; the heating rate and cooling rate are both 10°C / min.

[0016] The second technical purpose of the present invention is to provide a brazed part of a non-dense C / C composite material and a low expansion alloy prepared by the brazing process as described above, wherein the room temperature shear strength of the brazed part is greater than 50 MPa.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) Taking advantage of the characteristics of C / C composite materials, which are not dense and have micropores, silicon-titanium alloy with excellent penetration and a melting point lower than that of silicon is used. The liquid phase is formed at a temperature lower than the melting point of silicon, and can quickly penetrate into the C / C composite material and fill the internal fiber bundle pores under the action of capillary force. The improvement of joint performance is reflected in the following aspects:

[0019] 1) Compared with the direct brazing method without infiltration treatment, the density and strength of C / C composite materials after infiltration treatment are greatly improved (flexural strength is increased by 70%), such as Figure 1 As shown in ac, it is helpful for subsequent brazing connection;

[0020] 2) Changing the surface structure of the C / C composite material. Through surface modification of the C / C composite material, the problems of brazing material loss, difficulty in controlling weld thickness, and low joint strength caused by brazing material penetrating into the C / C composite material during brazing are solved.

[0021] (2) The surface modification layer material system constructed by the present invention is SiC+residual silicon titanium, wherein SiC is formed by the reaction of silicon titanium alloy and C / C composite material, and the improvement effect on the joint performance is reflected in the following aspects:

[0022] 1) The thermal expansion coefficient of SiC is between that of the residual silicon-titanium alloy and the C / C composite material. This gradient structure can effectively reduce the influence of the thermal expansion coefficient mismatch between the silicon-titanium alloy and the C / C composite material, and can alleviate the residual stress inside the C / C composite material;

[0023] 2) SiC at the interface can reduce the difference in thermal expansion coefficients between the C / C composite material and the brazing filler metal and Invar alloy, thereby reducing the residual stress of the subsequent brazing joint and improving the joint strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a comparison diagram of the microstructure and flexural strength of the C / C composite material before and after infiltration according to the present invention.

[0025] Figure 2 This is a scanning electron microscope image of the brazed joint prepared in Example 1 of the present invention.

[0026] Figure 3 This is a scanning electron microscope image of the brazed joint prepared in Example 2 of the present invention.

[0027] Figure 4 This is a scanning electron microscope image of the brazed joint prepared in Example 3 of the present invention.

[0028] Figure 5 This is a scanning electron microscope image of the brazed joint prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment is a two-step connection method of a C / C composite material and a low expansion alloy based on first infiltration and then brazing. The porosity of the C / C composite material is 10%, and the low expansion alloy is Invar alloy as an example. The specific steps are as follows:

[0032] (1) The surface-polished C / C composite material was placed in a graphite crucible, and then a silicon-titanium alloy (Si-24wt%Ti) block was placed on the surface of the C / C composite material. Infiltration was performed in a vacuum furnace at a temperature of 1350°C for 2 min and then cooled to room temperature at a heating and cooling rate of 10°C / min to obtain an infiltrated C / C composite material.

[0033] (2) The C / C composite material and Invar alloy after infiltration in step 1 are cut and polished, and a Cu-19Sn-10Ti (wt.%) paste solder with a thickness of 400 μm is applied between the connecting surfaces of the two base materials by screen printing to form a sandwich structure:

[0034] (3) The sample to be welded is placed in a graphite mold and brazed in a vacuum furnace at a brazing temperature of 930°C for 10 min at a heating and cooling rate of 10°C / min to obtain a C / C composite material / Invar alloy connector.

[0035] The microstructure and flexural strength of C / C composites before and after infiltration were tested by scanning electron microscope. Figure 1 As can be seen from the figure, the C / C composite material before infiltration is a structure composed of carbon fibers of different orientations, with some defects such as pores on the surface. After infiltration, the fiber bundle pores inside the C / C composite material are filled with silicon-titanium alloy, and the strength of the C / C composite material after infiltration is greatly improved.

[0036] The joint was subjected to scanning electron microscopy, and the scanning electron microscopy image is shown in Figure 2 As can be seen from the figure, the interface of the brazed joint is well connected and no obvious defects are found.

[0037] Example 2

[0038] This embodiment is the same as the embodiment 1, except that the thickness of the Cu-Sn-Ti solder paste is 300 μm.

[0039] The joint was subjected to scanning electron microscopy, and the scanning electron microscopy image is shown in Figure 3 As can be seen from the figure, the interface of the brazed joint is well connected and no obvious defects are found.

[0040] Example 3

[0041] This embodiment is the same as the embodiment 1, except that the thickness of the Cu-Sn-Ti solder paste is 500 μm.

[0042] The joint was subjected to scanning electron microscopy, and the scanning electron microscopy image is shown in Figure 4 As can be seen from the figure, the interface of the brazed joint is well connected and no obvious defects are found.

[0043] Example 4

[0044] This embodiment is the same as the embodiment 1, except that the thickness of the Cu-Sn-Ti solder paste is 600 μm.

[0045] The joint was subjected to scanning electron microscopy, and the scanning electron microscopy image is shown in Figure 5 As can be seen from the figure, the interface of the brazed joint is well connected and no obvious defects are found.

[0046] Example 5

[0047] This embodiment is the same as the embodiment 1, except that the brazing temperature is 910°C.

[0048] Example 6

[0049] This embodiment is the same as the embodiment 1, except that the brazing temperature is 950°C.

[0050] Example 7

[0051] This embodiment is the same as embodiment 1, except that the brazing holding time is 15 minutes.

[0052] Comparative Example 1

[0053] (1) The C / C composite material with a porosity of 10% and the Invar alloy were cut and polished, and a Cu-19Sn-10Ti (wt.%) paste solder with a thickness of 400 μm was applied between the connecting surfaces of the two base materials by screen printing to form a sandwich structure:

[0054] (2) The sample to be welded is placed in a graphite mold and brazed in a vacuum furnace at a brazing temperature of 930°C for 10 min at a heating and cooling rate of 10°C / min to obtain a C / C composite material / Invar alloy connector.

[0055] Comparative Example 2

[0056] This embodiment is the same as Comparative Example 1, except that the thickness of the Cu-Sn-Ti solder paste is 300 μm.

[0057] It was found through testing that the brazing filler metal of the brazed joint obtained in this comparative example penetrated into the pores of the C / C composite material due to capillary action, resulting in joint connection failure.

[0058] Performance Testing:

[0059] In order to compare and analyze the strength of brazed joints under different processes, a shear strength test was performed on the brazed joints using a mechanical testing machine to test the room temperature shear strength of the samples. Three samples were selected from each group for the shear test, and the shear strength was the average shear strength of the three samples. The shear strength data of the brazed joints obtained in Examples 1-7 and Comparative Examples 1-2 are shown in Table 1 below:

[0060] Table 1 Flexural strength test results of C / C composite material / Invar alloy connectors

[0061]

[0062]

[0063] It can be seen from the data in the above table that compared with the C / C composite material brazing sample without infiltration (Comparative Example 1), the use of C / C composite material after infiltration for brazing can effectively reduce the penetration of brazing material into the non-dense C / C composite material during the brazing process, thereby realizing the connection between the C / C composite material and the Invar alloy.

[0064] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A brazing process for a non-dense C / C composite material and a low expansion alloy, characterized in that: The steps include: (1) Infiltration of C / C composites: Silicon-titanium alloy is placed around a non-dense C / C composite, and a high-temperature reaction infiltration treatment is performed in a vacuum furnace to obtain a surface-dense C / C composite; (2) Brazing connection: Coat the surfaces to be welded of the C / C composite material obtained in step (1) and the low expansion alloy with Cu-Sn-Ti solder paste, assemble them in the sandwich structure of C / C composite material / Cu-Sn-Ti / low expansion alloy, fix them with a graphite mold and place them in a vacuum brazing furnace for brazing to obtain a connector.

2. The brazing process of the non-dense C / C composite material and the low expansion alloy according to claim 1, characterized in that: In step (1), the silicon content in the silicon-titanium alloy is 70-85wt%.

3. The brazing process of the non-dense C / C composite material and the low expansion alloy according to claim 1 or 2, characterized in that: In step (1), the infiltration atmosphere is a vacuum or protective atmosphere, and the protective gas is argon; the infiltration temperature is 1330-1400° C., and the insulation time is 1-10 min.

4. The brazing process of the non-dense C / C composite material and the low expansion alloy according to claim 1, characterized in that: In step (2), the mass fraction of Cu in the Cu-Sn-Ti solder paste is 70-80%, the mass fraction of Sn is 15-20%, and the mass fraction of Ti is 5-10%.

5. The brazing process of the non-dense C / C composite material and the low expansion alloy according to claim 1, characterized in that: In step (2), the coating is performed by screen printing, and the thickness of the coating layer formed after the Cu-Sn-Ti solder paste is coated is 200 to 700 μm.

6. The brazing process of the non-dense C / C composite material and the low expansion alloy according to claim 1, characterized in that: In step (2), the brazing atmosphere is vacuum, the brazing temperature is 910-950°C, the holding time is 5-15 minutes, and the heating rate and cooling rate are both 10°C / min.

7. A brazing part of a non-dense C / C composite material and a low expansion alloy, characterized in that: The brazing part is prepared by the method according to any one of claims 1 to 6.

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