Blazing method

Abstract

To provide a blazing method capable of blazing stainless steel and a carbon fiber-reinforced carbon composite material (C / C composite) by using a controlled atmosphere continuous furnace.SOLUTION: Provided is a blazing method of bonding a carbon fiber-reinforced carbon composite material and stainless steel by a blazing material. The blazing material is a nickel blazing material containing chromium.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a brazing method, and particularly to a brazing method suitable for brazing stainless steel to a carbon fiber reinforced carbon composite material (C / C composite). [Background technology]

[0002] Brazing has been known as a method for joining metals, ceramics, etc. In the brazing method, a brazing filler metal applied to the surface of one base material is heated to a temperature at which the brazing filler metal melts but not the base material, causing a thin film of brazing filler metal to diffuse to the joining surface with the other base material by capillary action, solidifying and joining the base materials together.

[0003] In recent years, from the perspective of carbon neutrality, there has been a demand for lighter materials, particularly those used in transportation equipment such as automobiles. Lightweighting means reducing the weight of materials, but in recent years it has become difficult to achieve lighter weight with a single material, and it has become important to combine various different materials in the right places, taking into account the mechanical properties of each material.

[0004] C / C composites, a composite material containing lightweight carbon fiber for weight reduction, have attracted attention because they are lighter and more rigid than metals (especially iron). However, C / C composites have problems with processability, and joining becomes a problem when used in combination with other materials. While mechanical joining is sometimes used, brazing is one of the most effective joining methods to take advantage of the durability and lightweight properties of C / C composites. Regarding the joining of C / C composites and metals (including stainless steel), for example, Non-Patent Documents 1 and 2 disclose brazing methods using active metals such as titanium. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Toshi-Taka IKESHOJI “Brazing between Carbon Fiber Reinforced Composites and Metals” Volume 83 Issue 3 (2014) pp.199-203. [Non-patent document 2] Y. Miyazawa et al. “Preprints of the National Meeting of JWS (Web)” (2019) Vol. 104, pp118-119. Summary of the Invention [Problem to be solved by the invention]

[0006] However, joining between stainless steel and C / C composites using an active metal such as titanium is performed in an active furnace using an active metal such as titanium, which has the problems of high costs associated with joining and low productivity.

[0007] Therefore, an object of the present invention is to provide a brazing method capable of brazing stainless steel and a carbon fiber reinforced carbon composite material (C / C composite) using a controlled atmosphere continuous furnace. [Means for solving the problem]

[0008] In order to achieve the above object, the brazing method of the present invention comprises: A brazing method for joining a carbon fiber reinforced carbon composite material and stainless steel with a brazing filler metal, comprising the steps of: The brazing filler metal is a nickel brazing filler metal containing chromium. [Effects of the Invention]

[0009] According to one embodiment of the present invention, there can be provided a brazing method capable of brazing stainless steel and a carbon fiber reinforced carbon composite material (C / C composite) using a controlled atmosphere continuous furnace. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a test piece used in a brazing method according to an embodiment of the present invention. [Figure 2] 1 is an example of a flowchart of a brazing method according to an embodiment of the present invention. [Figure 3] 1 is a schematic diagram of the overall configuration of a heat treatment furnace used in a brazing method according to an embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing a schematic structure of the heat treatment furnace of FIG. [Figure 5] 1 is an example of a photograph of a fracture surface of the stainless steel side of a test piece after a shear stress test according to one embodiment of the present invention. [Figure 6] 1 is an example of a photograph of a fracture surface on the C / C composite side of a test piece after a shear stress test according to one embodiment of the present invention. [Figure 7] FIG. 2 is a photograph of the surface structure of the C / C composite side of the test piece after the brazing method according to one embodiment of the present invention, illustrating the point analysis locations. [Figure 8] FIG. 8 is a diagram illustrating the results of area analysis of the surface texture shown in FIG. 7. [Figure 9] FIG. 1 is a photograph of the surface structure of the stainless steel side of a test piece after the brazing method according to one embodiment of the present invention, illustrating the point analysis locations. [Figure 10] FIG. 10 is a diagram illustrating the results of area analysis of the surface structure of the stainless steel side of the same test piece as the test piece with the surface structure shown in FIG. 9. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a brazing method according to one embodiment of the present invention will be described with reference to the drawings.

[0012] (Base material and brazing material) First, the base material and brazing material to be brazed by the brazing method according to this embodiment will be described.

[0013] The first base material can be stainless steel. Stainless steel refers to an alloy steel that is mainly composed of iron, contains 10.5 mass% or more of chromium, and contains 1.2 mass% or less of carbon. In this example, SUS304 stainless steel was used as a widely known stainless steel.

[0014] The general component contents of SUS304 stainless steel are shown in Table 1.

[0015] [Table 1]

[0016] The second base material to be bonded to the first base material can be a C / C composite, which is a carbon fiber reinforced carbon composite material. In this example, a C / C composite (manufactured by CFC Design Co., Ltd., product name: FS240) was used. The physical properties of the C / C composite used (reference values ​​from the pamphlet) are shown in Table 2.

[0017] [Table 2]

[0018] FIG. 1 shows a schematic diagram of a test piece TP used in a brazing method according to one embodiment of the present invention. FIG. 1(a) is a schematic top view of the test piece TP, and FIG. 1(b) is a schematic side view of the test piece TP. The numerical values ​​in FIG. 1 indicate the size of the test piece (unit: mm). As shown in FIG. 1, in the example, SUS304 stainless steel was used as the first base material M1, and a C / C composite was used as the second base material M2. No. 3 test pieces (a set of two) each having a plate thickness of 2.0 mm and an overlap B of 2.0 mm were prepared in accordance with JIS Z 3192:1999.

[0019] As the brazing filler metal according to this embodiment, a nickel (Ni) brazing filler metal can be used. More specifically, a nickel brazing filler metal containing at least chromium (Cr) can be used. Nickel brazing filler metals are classified according to JIS Z 3265, ranging from BNi-1 to BNi-7. As the brazing filler metal according to this embodiment, nickel brazing filler metals containing chromium, specified as BNi-1, BNi-2, BNi-5, and BNi-7, can be used. In addition to nickel brazing filler metals according to these standards, Ni-Cr-silicon (Si)-phosphorus (P)-based nickel brazing filler metals have recently been used for high-temperature and high-corrosion-resistant applications. As the brazing filler metal according to this embodiment, a Ni-Cr-silicon (Si)-phosphorus (P)-based nickel brazing filler metal can also be suitably used.

[0020] In this example, a Ni-Cr-Si-P based paste-like nickel brazing filler metal (manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: FP-613, solidus temperature: 1203 K, liquidus temperature: 1303 K) was used. The component contents of the nickel brazing filler metal used are shown in Table 3.

[0021] [Table 3]

[0022] The flow chart of the brazing method according to this embodiment is not particularly limited, and any known brazing method can be selected. As an example, Fig. 2 shows a flow chart of the brazing method according to one embodiment of the present invention.

[0023] As shown in FIG. 2, the brazing method according to this embodiment includes an intermediate body producing step (S100) and a brazing step (S110).

[0024] The intermediate body fabrication step (S100) is a step of fabricating an intermediate body including the first base material, the brazing material, and the second base material by, for example, placing or applying a brazing material on a first base material and placing a second base material so as to abut against the brazing material. Of course, the brazing material may be placed or applied on the second base material and the first base material may be placed so as to abut against the brazing material.

[0025] The brazing process (S110) is a process in which the intermediate obtained in the intermediate production process (S100) is heated to a predetermined brazing temperature, and then cooled to harden the molten brazing material, thereby brazing the first base material and the second base material.

[0026] There are no particular limitations on the brazing temperature as long as the C / C composite and stainless steel can be joined by brazing, but it is desirable to set the temperature within a range of 50K to 100K higher than the melting point of the brazing material.

[0027] (Controlled atmosphere continuous furnace) In a brazing method according to one embodiment of the present invention, a heat treatment furnace 10 was used. Specifically, an Oxynon furnace (manufactured by Kanto Yakin Kogyo Co., Ltd.) was used as the heat treatment furnace 10. FIG. 3 shows a schematic diagram of the overall configuration of the heat treatment furnace 10 used in the brazing method according to one embodiment of the present invention. FIG. 4 shows a cross-sectional view showing a schematic structure of the heat treatment furnace 10 of FIG. 3. The heat treatment furnace 10 of this example is a controlled atmosphere continuous furnace, and includes a debinding chamber 12, a heating chamber 14, and a cooling chamber 16. In the furnace 10, a test piece TP, which is an object to be treated, enters the furnace through an inlet 10a, passes through the debinding chamber 12, the heating chamber 14, and the cooling chamber 16 in that order, and is then discharged through an outlet 10b.

[0028] The heat treatment furnace 10 includes an outer wall 18 having a metal outer wall 18a that seals the entire heat treatment furnace 10 from the atmosphere and a graphite insulation material 18b that contacts the inside of the metal outer wall 18a and keeps the heating chamber 14 warm. A tunnel-shaped graphite outer muffle 20 made of graphite is disposed within the cavity surrounded by the graphite insulation material 18b. A tunnel-shaped graphite inner muffle 22 also made of graphite is disposed within the graphite outer muffle 20, and the interior of this graphite inner muffle 22 forms the heating chamber 14 in which the workpiece W is heat-treated. Above and below the graphite inner muffle 22, graphite heaters 24 for heating the heating chamber 14 are disposed, each penetrating the graphite outer muffle 20 approximately horizontally and attached to the outer wall 18 via bushings 26. A mesh belt 28 made of a C / C composite is disposed within the heating chamber 14 so as to be movable longitudinally along the lower edge of the graphite inner muffle 22. The material W to be treated is placed on the mesh belt 28 and moves through the heating chamber 14 at a set speed in a direction perpendicular to the plane of the drawing. Heater boxes 32, sealed with metal plates 30, are provided on both sides of the outer wall 18. These heater boxes 32 are provided with gas supply ports 34 for supplying neutral or inert gas to the heating chamber 14. Note that the gas supply pipes and various sensors to the heat treatment furnace 10 are omitted from FIG. 4 . Neutral or inert gas is supplied to the heater box 32 under pressure slightly higher than 1 atmosphere. This gas is supplied into the graphite outer muffle 20 through a gap between the graphite outer muffle 20 and the bushing 26, and then further supplied to the heating chamber 14 through a gap (not shown) in the graphite inner muffle 22. The material W to be treated placed on the mesh belt 28 is then heat-treated at high temperatures—in this case, brazing—in a low-oxygen atmosphere of a neutral gas, such as nitrogen gas, or an inert gas, such as argon or helium gas.

[0029] (Example) Nitrogen gas or argon gas was introduced into the above-mentioned heat treatment furnace, and the furnace was heated to 1393 K. At 1393 K, the reaction is thought to proceed according to the following formula (1).

[0030] [ka] Assuming that the above formula (1) is in an equilibrium state, the oxygen partial pressure in the heat treatment furnace can be estimated as shown in the following formula (2).

[0031] [ka] In equation (2), R is the gas constant (JK -1 mol -1 ) and T is the temperature (K).

[0032] Here, ΔG (1) is the Gibbs free energy change associated with the reaction of equation (1), and ΔG (1) is the standard Gibbs energy change of formation for this reaction system, and K is the reaction constant.

[0033] At equilibrium, ΔG (1) Since is zero, equation (1) can be expressed as equation (3).

[0034] [ka] On the other hand, the reaction constant K is given by (4).

[0035] [ka] In formula (4), a c is the activity of carbon, and P O2 is the partial pressure of oxygen (atm), and P CO is the partial pressure of carbon monoxide (atm).

[0036] Since the activity of the solid (carbon muffle) can be considered to be 1, by measuring the carbon monoxide partial pressure, the oxygen partial pressure in the heat treatment furnace can be calculated using the following equation (5).

[0037] [ka] Based on the above theory, the brazing method according to this embodiment was carried out in the following examples.

[0038] 0.2 g of the brazing filler metal described above was applied to the No. 3 test piece and forced dried in air at 473 K for 20 minutes. The heat treatment furnace was filled with argon gas, and the debinding chamber was set to 873 K and the heating chamber to 1393 K. The test piece was held in the debinding chamber for 10 minutes and then in the heating chamber for 30 minutes. The carbon monoxide content in the heat treatment furnace during heating was 8 to 10 ppm.

[0039] From known thermodynamic data, the standard Gibbs energy change of formation in this reaction system, ΔG° (1) is expressed by the following equation (6).

[0040] [ka] Gas constant R is 8.314(JK -1 mol -1 ), and the temperature T is set to 1393K, equation (7) can be derived from equations (5) and (6) above.

[0041] [ka] According to the above formula (7), the carbon monoxide content in the heat treatment furnace is 8 to 10 ppm (8 to 10 × 10 -6 Since the maximum oxygen content in the heat treatment furnace was 100% atm, the maximum oxygen content in the heat treatment furnace was calculated using the following formula (8).

[0042] [ka] At 1393K, various iron oxides exist, but thermodynamically, ferrous oxide (FeO) forms at the lowest oxygen partial pressure.

[0043] For example, in the reaction of the following formula (9), the equilibrium oxygen partial pressure at 1393 K is 10 -14 atm(10 -9 Pa).

[0044] [ka] In addition, the oxygen partial pressure at which chromium oxide (Cr2O3) is produced is thermodynamically about 10 -19 atm(10 -14 Pa). Therefore, it is estimated that no oxidation of iron or chromium occurs in the heat treatment furnace in the above experiment.

[0045] (evaluation) The test pieces obtained after heating were subjected to shear stress tests using an INSTRON® 5900R universal testing machine. The test was performed on four test pieces prepared using the above method, and the tensile speed was 1 mm / min. The results of the shear stress tests are shown in Table 4.

[0046] [Table 4]

[0047] For example, in a non-patent document (Okamura, H., Kajiura, S., and Akiba, M.: Bonding between carbon fiber / carbon composite and copper alloy, Quarterly Journal of Japan Welding Society, 14 (1) (1996), 39-46.), the shear stress of C / C composite / copper joints brazed with various metal fillers is reported (see Table 5 below).

[0048] [Table 5]

[0049] From a comparison of the shear stress values ​​shown in Tables 4 and 5, it was found that although the types of base materials to be joined are different, the brazing method according to this embodiment produced test pieces with shear stresses similar to those produced by conventional brazing methods after brazing.

[0050] Next, the microstructure of the test specimens obtained after the shear stress test was observed using an electron probe microanalyzer (EPMA) (EPMA-8050G (Shimadzu Corporation)). Figure 5 shows an example of a photograph of the fracture surface of the C / C composite side of the test specimen after the shear stress test, and Figure 6 shows an example of a photograph of the fracture surface of the stainless steel side of the test specimen after the shear stress test.

[0051] Since the C / C composite has a porous structure, it was found that the brazing method according to this embodiment allows the brazing material to permeate the pore regions of the C / C composite.

[0052] Furthermore, to examine the distribution of each component after brazing, the test piece was subjected to a component analysis using an electron probe microanalyzer (EPMA) (EPMA-8050G (Shimadzu Corporation)). FIG. 7 shows a surface structure photograph of the C / C composite side of the test piece after brazing according to one embodiment of the present invention, illustrating the point analysis locations. FIG. 8 shows a diagram illustrating the results of area analysis of the surface structure shown in FIG. 8. Note that FIG. 8 shows the surface structure photograph, area distribution of chromium, area distribution of phosphorus, area distribution of iron, area distribution of carbon, area distribution of silicon, area distribution of nickel, and area distribution of oxygen in the order of top left, top center, top right, middle left, middle center, middle right, bottom left, and bottom center.

[0053] Furthermore, the point analysis results for each component corresponding to each point in Figure 7 are shown in Table 6.

[0054] [Table 6]

[0055] Positions 4-6 in Figure 7 and Table 6 correspond to the boundary between the C / C composite and the brazing filler metal, and show high chromium and carbon contents, suggesting that chromium and carbon compounds may be formed at the boundary between the C / C composite and the brazing filler metal.

[0056] Fig. 9 shows a surface structure photograph of the stainless steel side of a test piece after a brazing method according to an embodiment of the present invention, illustrating the location of point analysis. Fig. 10 shows a diagram illustrating the results of area analysis of the surface structure of the stainless steel side of the same test piece as the test piece with the surface structure shown in Fig. 9. In Fig. 10, the surface structure photograph, area distribution of chromium, area distribution of phosphorus, area distribution of iron, area distribution of carbon, area distribution of silicon, area distribution of nickel, and area distribution of oxygen are shown in the order of top left, top center, top right, middle left, middle center, middle right, bottom left, and bottom center.

[0057] Furthermore, the point analysis results for each component corresponding to each point in Figure 9 are shown in Table 7.

[0058] [Table 7]

[0059] From the above results, it was found that chromium and carbon segregated at the boundary between the C / C composite and stainless steel.

[0060] In the brazing method according to this embodiment, a nickel brazing filler metal containing chromium is used to join the C / C composite and stainless steel. This produces chromium and carbon compounds in the gaps caused by the porous structure of the C / C composite, which are thought to fill the gaps, thereby enabling the brazing.

[0061] The brazing method according to this embodiment does not require the use of conventional titanium-containing active brazing filler metal, and therefore can use a controlled atmosphere continuous furnace. It can be said that this brazing method is lower in cost and more productive than conventional brazing methods.

[0062] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configurations should not be considered to be limited to these embodiments. The scope of the present invention is defined not only by the description of the above embodiments but also by the claims, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0063] S100 Intermediate production process S110 Brazing process TP test specimen M1 First base material M2 Second base material 10 Heat treatment furnace 12 Debinding chamber 14 Heating chamber 16 Cooling room 18 Exterior Wall 20 Graphite outer muffle 22 Graphite inner muffle 24 Graphite heater 28 Mesh Belt 32 Heater Box 34 Gas supply opening

Claims

[Claim 1] A brazing method for joining a carbon fiber reinforced carbon composite material and stainless steel with a brazing filler metal, comprising the steps of: A brazing method characterized in that the brazing material is a nickel brazing material containing chromium.

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