CN108568577B - Method for improving strength of carbon fiber reinforced composite material and metal brazing joint - Google Patents
Method for improving strength of carbon fiber reinforced composite material and metal brazing joint Download PDFInfo
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- CN108568577B CN108568577B CN201710134324.8A CN201710134324A CN108568577B CN 108568577 B CN108568577 B CN 108568577B CN 201710134324 A CN201710134324 A CN 201710134324A CN 108568577 B CN108568577 B CN 108568577B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K1/00—Soldering, e.g. brazing, or unsoldering
- B23K1/008—Soldering within a furnace
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K1/00—Soldering, e.g. brazing, or unsoldering
- B23K1/20—Preliminary treatment of work or areas to be soldered, e.g. in respect of a galvanic coating
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Abstract
The invention discloses a method for improving the strength of a carbon fiber reinforced composite material and a metal soldered joint, which comprises the following steps of firstly, carrying out oxidation treatment on the surface of the carbon fiber reinforced composite material at the temperature of 700-800 ℃ so as to form annular holes at the periphery of carbon fibers; and assembling the carbon fiber reinforced composite material, the brazing filler metal and the metal plate according to a sandwich structure by selecting the brazing filler metal, clamping by using a graphite plate to ensure close contact, and then placing the carbon fiber reinforced composite material, the brazing filler metal and the metal plate in a vacuum brazing furnace and vacuumizing for brazing. According to the invention, the carbon fiber reinforced composite material is subjected to surface oxidation treatment before welding to form annular holes, and the brazing filler metal is impregnated into the holes of the carbon fiber reinforced composite material, so that the contact area of the carbon fiber reinforced composite material and the brazing filler metal is increased to increase the area of a reaction layer, thereby reducing the residual stress of the joint and improving the strength of the joint.
Description
Technical Field
The invention relates to a method for improving the strength of a carbon fiber reinforced composite material and a metal brazing joint through surface modification in the field of brazing, in particular to a method for reducing residual stress of the brazing joint and increasing effective connection area by forming micro holes on the surface of the carbon fiber reinforced composite material through a pre-oxidation process, wherein the two aspects jointly improve the strength of the brazing joint.
Background
The carbon fiber reinforced composite material has the advantages of low density, high elastic modulus, large specific strength, low coefficient of thermal expansion, corrosion resistance, good shock absorption, good friction, high thermal conductivity and the like, and in addition, the high-temperature performance of the carbon fiber reinforced composite material is also excellent, such as high temperature resistance, ablation resistance, thermal shock resistance and thermal fatigue resistance, and the carbon fiber reinforced composite material still has high strength, toughness and the like when the temperature is over 2000 ℃. Carbon fiber reinforced composites are therefore considered to be highly desirable high temperature structural materials and have applications in the aerospace field as well as in armor materials for international nuclear reactor experiments. However, due to the limitation of its manufacturing process, it is difficult to manufacture a member having a large size and a complicated shape, and the production cycle is long and the cost is high, which greatly limits its application, so that it is considered to connect it with metal in order to expand its application field.
At present, the connection between carbon fiber reinforced composite material and metal is widely studied, and mainly brazing. However, because the difference between the thermal expansion coefficients of the carbon fiber reinforced composite material and metal is large, the shrinkage degrees of the metal, the brazing filler metal and the carbon fiber reinforced composite material are different in the post-welding cooling process, so that large residual stress exists in the brazed joint, particularly on the side of the carbon fiber reinforced composite material, which greatly reduces the mechanical property of the joint and makes the connecting member difficult to meet the application requirements. Although the residual stress is relieved by a method of machining the surface of the carbon fiber reinforced composite material, the method has the defects of high cost and relatively complex control if a laser grooving method is adopted; and mechanical punching is adopted, so that the uniformity is relatively poor, and the strength of the whole joint is uneven. Therefore, the novel process method for relieving the residual stress of the joint and improving the strength of the joint has good practical significance.
Disclosure of Invention
The invention aims to overcome the defects of the prior art in the aspect of improving the strength of a joint, and provides a method for increasing the contact area of a carbon fiber reinforced composite material and a brazing filler metal and reducing residual stress, namely, a method for generating uniform microscopic holes on the surface of the carbon fiber reinforced composite material by adopting heating vapor phase oxidation treatment is adopted to change the surface appearance of the carbon fiber reinforced composite material, so that the strength of the brazed joint is improved.
The purpose of the invention is realized by the following technical scheme:
a method for improving the strength of a carbon fiber reinforced composite material and a metal brazing joint comprises the following steps: oxidizing the surface of the carbon fiber reinforced composite material at the temperature of 700-800 ℃ to form annular holes at the periphery of the carbon fibers; then assembling the oxidized carbon fiber reinforced composite material, the brazing filler metal and the metal plate according to a sandwich structure, clamping the carbon fiber reinforced composite material, the brazing filler metal and the metal plate by using a graphite plate to ensure tight contact, placing the carbon fiber reinforced composite material, the brazing filler metal and the metal plate into a vacuum brazing furnace, vacuumizing the vacuum brazing furnace, and enabling the pressure in the furnace to reach 8-9 multiplied by 10-4After MPa, at 5-10 DEG CRaising the temperature rise rate from room temperature of 20-25 ℃ to a temperature 20-150 ℃ higher than the melting point of the brazing filler metal, maintaining the temperature for brazing, and then reducing the temperature to the room temperature of 20-25 ℃ at the temperature reduction rate of 5-10 ℃/min.
In the technical scheme, the temperature is increased from room temperature of 20-25 ℃ to a temperature 50-100 ℃ higher than the melting point of the brazing filler metal at a temperature rising rate of 5-10 ℃/min, the temperature is kept for 5-20 min for brazing, and then the temperature is reduced to the room temperature of 20-25 ℃ at a temperature reducing rate of 5-10 ℃/min.
In the technical scheme, the surface of the sample is cleaned before welding, the sample is polished to 800# by using sand paper, and the sample is ultrasonically cleaned for 5-10 min by using the cleaning agent and is naturally dried.
In the technical scheme, before oxidation, the carbon fiber reinforced composite material is polished to 800# by using sand paper, and then oxidation treatment is carried out in a non-protective gas type resistance furnace such as a muffle furnace.
In the technical scheme, the time for carrying out oxidation treatment on the surface of the carbon fiber reinforced composite material is 5-10 min.
In the technical scheme, the surface of the carbon fiber reinforced composite material is oxidized at the temperature of 700-800 ℃, part of pyrolytic carbon around the carbon fiber is consumed, and the carbon fiber is rarely consumed, so that annular holes with the width of about 1-2 mu m are formed around the carbon fiber.
In the technical scheme, the proper brazing filler metal is selected according to the selection principle of the brazing filler metal, such as ensuring the wettability, the diffusion effect of the brazing filler metal and a base material, the rationality of the melting temperature and the like, and the titanium-containing silver-based or copper-based brazing filler metal is selected according to the principle.
The oxidation treatment of the carbon fiber reinforced composite material is applied to improving the strength of the carbon fiber reinforced composite material and a metal brazing joint, and the surface of the carbon fiber reinforced composite material is subjected to oxidation treatment at the temperature of 700-800 ℃ so as to form annular holes at the periphery of carbon fibers.
According to the invention, the carbon fiber reinforced composite material is subjected to surface oxidation treatment before welding to form annular holes, the brazing filler metal is impregnated into the holes of the carbon fiber reinforced composite material, so that the contact area of the carbon fiber reinforced composite material and the brazing filler metal is increased to increase the reaction layer area, and the residual stress generated by inconsistent shrinkage caused by the difference of thermal expansion coefficients between the carbon fiber reinforced composite material and the metal brazing filler metal and the interface of the metal base metal is released through slight deformation of the parts (shown in figures 2b, c and d) where the carbon fiber reinforced composite material and the brazing filler metal are staggered with each other, so that the residual stress of a joint is reduced, and the strength of the joint is improved.
Drawings
FIG. 1 is an SEM picture of the surface morphology of an original carbon-carbon composite material after being oxidized by heat preservation at 700 ℃, 750 ℃ and 800 ℃ for 5 minutes.
FIG. 2 is an SEM image of the original carbon-carbon composite material and the microstructure of the original carbon-carbon composite material, wherein the microstructure is formed by oxidizing the original carbon-carbon composite material at 700 ℃, 750 ℃ and 800 ℃ and then preserving the heat of the original carbon-carbon composite material for 10min when the brazing temperature is 880 ℃.
FIG. 3 is a graph of the shear strength of the original carbon-carbon composite material and the soldered joint after oxidation at 700 deg.C, 750 deg.C, 800 deg.C.
Detailed Description
The technical solution of the present invention will be described in detail with reference to the following specific examples.
The first implementation mode comprises the following steps:
the brazing experiments used 3D carbon-carbon composites (purchased from Changshan Boyun New materials Co., Ltd., used as carbon fiber reinforced composites, consisting of carbon fiber and pyrolytic carbon), 100 μm thick Ag-21Cu-4.5Ti (21 wt% Cu, 4.5 wt% Ti, remainder Ag, totaling 100 wt%) foil (as brazing solder), and pure Nb plates (purity: 100 wt%) foil (as brazing solder)>99.9% as a metal plate). The size of the carbon-carbon composite material is 4mm multiplied by 6mm, the carbon-carbon composite material is polished to 800# by SiC sand paper before oxidation, then the material is put into a canoe and placed into a furnace after being heated to 700 ℃, 750 ℃ and 800 ℃ in a muffle furnace at the heating rate of 10 ℃/min and is insulated for 5min for oxidation treatment, and the carbon-carbon composite material is divided into four groups which are not treated and are respectively treated at 700 ℃, 750 ℃ and 800 ℃ for 5 min. Cutting Ag-21Cu-4.5Ti foil into pieces with the size of 4mm multiplied by 6mm and the size of Nb plate as 15mm multiplied by 10mm multiplied by 2mm, grinding the pieces to 800# by using SiC sand paper, ultrasonically cleaning all the samples in an acetone cleaning agent for ten minutes, naturally airing, assembling four groups of samples according to a sandwich pattern, and carrying out ultrasonic cleaning on the four groups of samplesClamping with graphite plate, placing in vacuum brazing furnace, and vacuumizing until the pressure in furnace reaches 8.8 × 10-4After Pa, the temperature is raised to 880 ℃ at the heating rate of 10 ℃/min, the temperature is kept for 10min, then the temperature is reduced to 500 ℃ at the speed of 5 ℃/min, then the temperature is reduced to the room temperature along with the furnace, and finally the product is taken out.
The microscopic morphology of the carbon-carbon composite material after oxidation at different temperatures is shown in fig. 1, two carbon fiber weaving directions can be seen on the section of each figure, the left side is parallel to the surface, the right side is perpendicular to the surface, after oxidation treatment at different temperatures, pyrolytic carbon filled around the carbon fibers is partially oxidized and consumed to form annular holes, and the size and the depth of the annular holes around the carbon fibers are increased along with the increase of the temperature.
Cutting and inlaying the welded sample, sanding and polishing by using sand paper, observing the micro-morphology of the welded sample under different oxidation conditions by using a scanning electron microscope (SEM; NanoSEM430), and as shown in figure 2, forming a reaction layer at the interface of the carbon-carbon composite material and the brazing filler metal can be seen in the partial enlarged views of figures 2a and b, and obtaining that the sample consists of TiC according to energy spectrum data. Comparing fig. 2a, b, c and d, it is found that as the degree of oxidation increases, the length and amount of the micro-cavities of the carbon-carbon composite infiltrated by the brazing filler metal increase, which increases the contact area between the carbon-carbon composite and the brazing metal, and the area of the TiC reaction layer also increases. In addition, the interface of the carbon-carbon composite material and the metal brazing filler metal has a layer in which carbon fibers and the immersed brazing filler metal are staggered, and the carbon-carbon composite material is easier to generate tiny deformation compared with a flat interface of a base material of the carbon-carbon composite material, so that the residual stress is reduced, and the purpose of improving the joint strength can be achieved by combining the two aspects.
The shear strength test of the test specimens was carried out in a Condor150 push-pull test machine, and the results are shown in FIG. 3, where the strength is an average value calculated from three test specimens. The average strength of the soldered joint of the unoxidized carbon-carbon composite material and metal is about 35MPa, and the joint strength is gradually improved along with the increase of the oxidation degree, which is consistent with the analysis of a micro interface. The average strength of the oxidized joint reaches 55MPa under the condition of keeping the temperature at 800 ℃ for 5min, and is improved by 57 percent compared with the joint which is not oxidized.
The second embodiment:
the difference between this embodiment and the specific embodiment is that the carbon-carbon composite material is changed to a carbon/silicon carbide composite material (obtained from new materials of Changshan Boyun Co., Ltd., used as a carbon fiber reinforced composite material, composed of carbon fibers and silicon carbide). The rest is the same as the first embodiment.
Through a shear test, the shear strength of the joint before and after oxidation at the temperature of 800 ℃ for 5min is 82MPa and 135MPa respectively, and the strength is improved by 65 percent.
The third concrete implementation mode:
the present embodiment is different from the first embodiment in that the Nb plate is changed to the TC4 plate, and the rest is the same as the first embodiment.
Through a shear test, the shear strength of the joint before and after oxidation at the temperature of 800 ℃ for 5min is 31MPa and 48MPa respectively, and the strength is improved by 55%.
The fourth concrete implementation mode:
the third difference between the present embodiment and the specific embodiment is that the carbon-carbon composite material is changed to a carbon/silicon carbide composite material. The rest is the same as the third embodiment.
Through a shear test, the shear strength of the joint before and after oxidation at the temperature of 800 ℃ for 5min is respectively 88MPa and 146MPa, and the strength is improved by 54 percent.
The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.
Claims (3)
1. A method for improving the strength of a carbon fiber reinforced composite material and metal brazing joint is characterized by comprising the following steps: oxidizing the surface of the carbon fiber reinforced composite material at the temperature of 700-800 ℃ to form annular holes at the periphery of the carbon fibers; then assembling the oxidized carbon fiber reinforced composite material, the brazing filler metal and the metal plate according to a sandwich structure, and clamping the carbon fiber reinforced composite material, the brazing filler metal and the metal plate by using a graphite plate to ensure thatClosely contacting, placing in a vacuum brazing furnace, vacuumizing, and making the pressure in the furnace reach 8-9 × 10-4And after the temperature is MPa, raising the temperature from room temperature of 20-25 ℃ to a temperature 20-150 ℃ higher than the melting point of the brazing filler metal at a temperature rise rate of 5-10 ℃/min, preserving the temperature for brazing, and then reducing the temperature to the room temperature of 20-25 ℃ at a temperature drop rate of 5-10 ℃/min.
2. The method for improving the strength of the joint between the carbon fiber reinforced composite material and the metal, which is claimed in claim 1, is characterized in that the temperature is increased from room temperature of 20-25 ℃ to a temperature which is 50-100 ℃ higher than the melting point of the brazing filler metal at a temperature rising rate of 5-10 ℃/min, the temperature is kept for 5-20 min for brazing, and then the temperature is reduced to room temperature of 20-25 ℃ at a temperature reducing rate of 5-10 ℃/min.
3. The method for improving the strength of the joint between the carbon fiber reinforced composite material and the metal, which is recited in claim 1, wherein the time for performing the oxidation treatment on the surface of the carbon fiber reinforced composite material is 5-10 min.
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| CN111069726B (en) * | 2018-10-19 | 2021-04-30 | 天津大学 | Carbon-carbon composite material and metal brazing connection method based on electrophoretic deposition of SiC nanowires |
| CN112548253B (en) * | 2020-11-30 | 2022-03-25 | 哈尔滨工业大学 | Method for brazing fiber reinforced composite material and metal in selective hot corrosion auxiliary mode |
| CN112548252B (en) * | 2020-11-30 | 2022-06-21 | 哈尔滨工业大学 | Method for regulating and controlling surface structure of carbon fiber reinforced composite material and metal brazing through electric corrosion |
| CN112975031A (en) * | 2021-02-05 | 2021-06-18 | 北京科技大学 | Surface honeycombed modified auxiliary brazing CfMethod for preparing/SiC composite material and metal |
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