Composite brazing filler metal for welding carbon-based materials and titanium-based alloys, brazing filler metal sheet, preparation method thereof, and brazing method

Abstract

The present invention relates to the field of welding, and specifically to a composite brazing filler metal, a brazing filler metal sheet, a preparation method thereof, and a brazing method for brazing carbon-based materials and titanium-based alloys. The composite brazing filler metal provided by the present invention is used for brazing carbon-based materials and titanium-based materials. It has a small amount of brittle compounds, high joint strength, and high-temperature mechanical properties. It solves the bottleneck problems of large joint residual stress, low operating temperature, high brittle compounds, and excessive flow of brazing filler metal in the preparation of carbon-based materials and titanium-based alloy connection components by traditional AgCu brazing, thereby improving the performance of the connection components and the welding accuracy. Experiments have shown that the composite brazing filler metal of the present invention is used for welding carbon-based materials and titanium-based alloys, and the room temperature shear strength of the joint is high, which is 2 to 3 times that of the AgCu28 brazing filler metal joint under the same conditions. In addition, the shear strength of the joint does not decrease under high temperature conditions of 600°C, and it still maintains a high strength at 800°C (close to the welding temperature).

Description

Technical Field

[0001] The invention relates to the field of welding, in particular to a composite brazing filler metal and a brazing filler metal sheet for welding carbon-based materials and titanium-based alloys, and a preparation method and a brazing method thereof. Background Art

[0002] Carbon-based materials and titanium-based alloys are widely used in the automotive, electronics, petrochemical, and aerospace sectors. In practical engineering applications, carbon-based materials and titanium-based alloys are often joined to form structurally and functionally integrated components to meet the demanding requirements of service environments. For example, graphite and titanium alloy components can be used as sealing rings in deep-sea oil and gas pipelines, while SiBCN ceramic and Ti2AlNb components can be used as nozzle transition joints in aircraft engines.

[0003] Currently, brazing with AgCu-based filler metals is one of the main methods for preparing composite components made of carbon-based and titanium-based materials. However, the AgCu filler metal has a high thermal expansion coefficient, resulting in high residual stress in the joint after welding and low joint strength. The AgCu filler metal also has a low melting point and poor oxidation resistance of the Cu-based solid solution, which leads to poor high-temperature mechanical properties of the joint. The Cu and Ti in the AgCu filler metal have a strong reaction tendency, resulting in a large amount of Cu in the filler metal diffusing into the titanium-based alloy and a large amount of Ti dissolving into the filler metal, forming a continuous brittle compound layer and degrading the joint performance. The high chemical affinity between Cu and Ti leads to excessive flow of the filler metal on the titanium-based material surface, affecting the welding precision and aesthetics. The preferential spreading of the filler metal on the titanium-based material also leads to unwelded and non-wetting phenomena on the carbon-based material surface. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a composite brazing filler metal, a brazing filler metal sheet, and a preparation method and a brazing method for welding carbon-based materials and titanium-based alloys. The composite brazing filler metal provided by the present invention is used for brazing carbon-based materials and titanium-based materials, has few brittle compounds, and has high joint strength and high-temperature mechanical properties.

[0005] The present invention provides a composite brazing filler metal for welding carbon-based materials and titanium-based alloys, comprising:

[0006] 3 wt.%~9 wt.% TiH2;

[0007] 20 wt.%~50 wt.% Nb;

[0008] The balance is AgCu28.

[0009] Preferably, the composite brazing filler metal for welding the carbon-based material and the titanium-based alloy comprises:

[0010] 4 wt.%~8 wt.% TiH2;

[0011] 25 wt.%~35 wt.% Nb;

[0012] The balance is AgCu28.

[0013] More preferably, the composite brazing filler metal for welding the carbon-based material and the titanium-based alloy comprises:

[0014] 5 wt.%~7 wt.% TiH2;

[0015] 28 wt.%~32 wt.% Nb;

[0016] The balance is AgCu28.

[0017] The composite solder for welding carbon-based materials and titanium-based alloys described in the present invention comprises TiH2, Nb and AgCu28; wherein the Nb added to the composite solder is Nb particles with a mesh size of 100 to 200 meshes. Nb particles are high-melting-point metals and do not melt during the brazing process, but are retained in the weld in the form of a skeleton. The liquid phase of the solder can be retained in the welding area through capillary action, thereby avoiding excessive flow of the solder and improving the forming accuracy. At the same time, at high temperatures, Nb acts as a high-temperature skeleton to alleviate the softening of the brazing seam, thereby improving the high-temperature mechanical properties of the joint. In addition, the Nb particles added to the composite solder have the characteristic of a low thermal expansion coefficient, which can reduce the thermal expansion coefficient of the solder, reduce the thermal expansion difference between the solder and the carbon-based material, reduce the joint stress, and improve the joint strength.

[0018] The TiH2 added to the composite solder of the present invention is TiH2 powder with a mesh size of 250-300 mesh. The TiH2 powder of the present invention can decompose during the heating process and the first heat-holding stage during welding, forming evenly distributed Ti particles and precipitating H2. H2 has a reducing effect and can clean the oxides on the surfaces of Nb powder and AgCu28 powder, thereby improving the welding quality. During the second heat-holding stage of welding, the evenly distributed Ti particles dissolve in the AgCu28 liquid phase, thereby achieving uniform wetting of the carbon-based material by the liquid phase. At the same time, the Ti particles can reduce the chemical concentration difference between the solder and the titanium-based material, inhibiting the dissolution of the titanium-based material and reducing brittle compounds.

[0019] The AgCu28 added to the composite solder of the present invention is AgCu28 brazing powder with a mesh size of 200-300 mesh. The Cu element in the AgCu28 brazing powder reacts with the Ti in the TiH2 powder to form a Ti-Cu compound, eliminating the Cu-based solid solution with poor oxidation resistance and shifting the liquid phase composition away from the low-melting-point eutectic, thereby raising the melting point of the weld. The Nb particles serve as nucleation sites for the Ti-Cu compound, achieving uniform distribution of the compound, thus transforming waste into valuable material and strengthening the joint using a brittle compound.

[0020] The composite brazing filler metal provided herein is a composite brazing filler metal for welding carbon-based materials and titanium-based alloys. The carbon-based material includes graphite, SiBCN ceramic, or SiC ceramic; and the titanium-based alloy includes TA2, TC4, TiAl, TC18, or Ti2AlNb. In some embodiments of the present invention, the carbon-based material is preferably SiBCN ceramic, and the titanium-based alloy is preferably Ti2AlNb. In other embodiments of the present invention, the carbon-based material is preferably SiC ceramic, and the titanium-based alloy is preferably Ti2AlNb.

[0021] The present invention provides a method for preparing the composite solder, comprising the following steps: grinding TiH2, Nb, and AgCu28 to obtain the composite solder; the TiH2, Nb, and AgCu28 are the same as those described above and will not be described in detail; the grinding speed is 150 rpm to 300 rpm, and the grinding time is 30 min to 60 min. Specifically, TiH2 powder, Nb powder, and AgCu28 solder powder are mechanically ball-milled to obtain the composite solder, and the mechanical ball-milling process comprises: mechanically ball-milling at a speed of 150 rpm to 300 rpm in a planetary ball mill for 30 min to 60 min; using anhydrous ethanol as the mixing medium; using ZrO2 or agate with a diameter of 1 mm to 3 mm as the grinding balls; and the ball-to-material mass ratio ranges from (2 to 4):1.

[0022] The present invention also provides a solder sheet, which is made from the composite solder described in any of the above technical solutions. The solder sheet of the present invention has a thickness of 100 μm to 300 μm, preferably 200 μm.

[0023] The present invention also provides a method for preparing a solder sheet according to any of the above technical solutions, comprising the following steps: pressing and forming the composite solder to obtain a solder sheet; the pressing and forming pressure is between 2 MPa and 5 MPa. Specifically, the present invention adds the composite solder to a mold and performs a pre-pressing process to obtain a preformed solder sheet; the pre-pressing process pressure ranges from 2 MPa to 5 MPa.

[0024] The present invention also provides a method for welding a carbon-based material and a titanium-based alloy, comprising the following steps: placing a brazing sheet according to any of the above technical solutions on the surfaces of the carbon-based material and the titanium-based alloy to be welded, and performing a heat treatment. Specifically, the brazing sheet, the carbon-based material, and the titanium-based alloy are assembled, and during assembly, the brazing sheet is placed on the surfaces of the carbon-based material and the titanium-based alloy to be welded, and then performing a heat treatment. The brazing sheet, the carbon-based material, and the titanium-based alloy described in the present invention are the same as those described above and will not be described in detail.

[0025] More specifically, the above-mentioned brazing sheet, carbon-based material and titanium-based alloy are assembled. During assembly, the brazing sheet is placed on the surface to be welded of the carbon-based material and the titanium-based alloy, and heat treatment is performed. The heat treatment is specifically: heating to 700°C~750°C and keeping warm for 20 min~40 min, then heating to 800°C~860°C and keeping warm for 30 min~60 min.

[0026] In certain embodiments of the present invention, the above-mentioned brazing sheet, carbon-based material and titanium-based alloy are assembled. During assembly, the brazing sheet is placed on the surface to be welded of the carbon-based material and the titanium-based alloy and subjected to heat treatment. The heat treatment is specifically as follows: heating to 700°C~750°C at a heating rate of 8°C / min~12°C / min and keeping warm for 20 min~40 min, then heating to 800°C~860°C at a heating rate of 3°C / min~5°C / min and keeping warm for 30 min~60 min, and finally cooling to below 250°C at a cooling rate of 3°C / min~5°C / min to complete precision welding.

[0027] The present invention provides a composite brazing filler metal, a brazing filler metal sheet, and a preparation and brazing method for welding carbon-based materials and titanium-based alloys. The composite brazing filler metal provided by the present invention is used for brazing carbon-based and titanium-based materials. It contains fewer brittle compounds, exhibits high joint strength, and exhibits high-temperature mechanical properties. This overcomes bottlenecks such as high joint residual stress, low operating temperature, high brittle compounds, and excessive brazing filler metal flow, which are common in brazing carbon-based and titanium-based alloy components using conventional AgCu brazing filler metals. This improves the performance of connected components and welding precision. Tests have shown that the composite brazing filler metal of the present invention, whether used for welding SiBCN to Ti2AlNb or SiC to Ti2AlNb, achieves room-temperature shear strength exceeding 65 MPa, three times that of joints made with AgCu28 brazing filler metal under the same conditions. Furthermore, the shear strength of the joints remains unchanged at 600°C, and the strength remains high at 800°C (close to the welding temperature). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a microstructure morphology of a joint at a scale of 50 microns obtained by brazing SiBCN ceramic and Ti2AlNb alloy with the composite brazing filler metal of Example 1 of the present invention;

[0029] Figure 2 This is a microstructure morphology of a joint at a scale of 10 microns obtained by brazing SiBCN ceramic and Ti2AlNb alloy with a composite brazing filler metal according to Example 1 of the present invention;

[0030] Figure 3 The microstructure and mapping diagram of the joint at a scale of 20 microns obtained by brazing SiBCN ceramic and Ti2AlNb alloy with the composite brazing filler metal according to Example 1 of the present invention;

[0031] Figure 4 This is a microstructure morphology of a joint at a scale of 5 microns obtained by brazing SiBCN ceramic and Ti2AlNb alloy with the composite brazing filler metal according to Example 1 of the present invention;

[0032] Figure 5 This is a microstructure morphology of a joint obtained by brazing Ti2AlNb and SiC with a composite brazing filler metal according to Example 2 of the present invention;

[0033] Figure 6 This is the microstructure morphology of the joint of Ti2AlNb and SiC brazed with AgCu28 solder of the present invention. DETAILED DESCRIPTION

[0034] The present invention discloses a composite brazing filler metal, a brazing filler metal sheet, a preparation method thereof, and a brazing method for welding carbon-based materials and titanium-based alloys. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications of this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0035] The present invention will be further described below with reference to the embodiments:

[0036] Example 1

[0037] The carbon-based material is SiBCN ceramic, the titanium-based alloy is Ti2AlNb alloy, and the carbon-based material and the titanium-based alloy are precisely welded using a composite brazing filler metal. The composite brazing filler metal is obtained by ball milling a mixture of 300-mesh TiH2 powder with a mass fraction of 6 wt.%, 200-mesh Nb powder with a mass fraction of 30 wt.%, and 200-mesh AgCu28 brazing powder with a remainder of 200 mesh. The ball milling mixing process includes: mechanical ball milling at a speed of 200 rpm for 45 minutes in a planetary ball mill; using anhydrous ethanol as a mixing medium; using ZrO2 with a diameter of 1 mm as a grinding ball; and the ball-to-material mass ratio range includes 3:1.

[0038] The composite solder is pre-pressed to form a 200 μm thick solder sheet under a pressure of 2.5 MPa. The pre-pressed sheet is assembled with the polished and cleaned carbon-based material and titanium-based alloy, and placed on the surface to be welded. The welding process involves heating to 750°C at a rate of 10°C / min, holding for 20 minutes, heating to 820°C at a rate of 3°C / min and holding for 30 minutes, and cooling to below 250°C at a rate of 3°C / min to complete the precision welding.

[0039] like Figures 1 to 4 As shown, Figure 1 This is a 50-micron joint microstructure diagram of the composite brazing filler metal brazing SiBCN ceramic and Ti2AlNb alloy according to Example 1 of the present invention. Figure 2 This is a 10-micron scale joint microstructure diagram of the composite brazing filler metal brazing SiBCN ceramic and Ti2AlNb alloy according to Example 1 of the present invention. Figure 3 The morphology and mapping diagram of the joint at a scale of 20 microns of SiBCN ceramic and Ti2AlNb alloy brazed with the composite brazing filler metal of Example 1 of the present invention are shown. Figure 4 This is a 5-micron joint microstructure morphology of SiBCN ceramic and Ti2AlNb alloy brazed with the composite brazing filler metal of Example 1 of the present invention.

[0040] The room temperature shear strength of the joint obtained above is 69±9 MPa, which is three times that of the AgCu28 solder joint under the same conditions (24±3 MPa). In addition, the shear strength of the joint does not decrease under high temperature conditions of 600°C, and it still maintains a strength of 24±1 MPa at 800°C (close to the welding temperature).

[0041] Example 2

[0042] The carbon-based material is SiC, the titanium-based alloy is Ti2AlNb, and the carbon-based material and the titanium-based alloy are precisely welded using a composite brazing filler metal. The composite brazing filler metal is obtained by ball milling a mixture of 300-mesh TiH2 powder with a mass fraction of 6 wt.%, 200-mesh Nb powder with a mass fraction of 30 wt.%, and 200-mesh AgCu28 brazing powder as the remainder. The ball milling mixing process includes: mechanical ball milling at a speed of 300 rpm for 60 min in a planetary ball mill; using anhydrous ethanol as a mixing medium; using agate with a diameter of 3 mm as a grinding ball; and a ball-to-material mass ratio ranging from 2:1.

[0043] The composite solder is pre-pressed to form a 200 μm thick solder sheet at a pressure of 3 MPa. The pre-pressed sheet is assembled with the polished and cleaned carbon-based material and titanium-based alloy, and then placed on the surface to be welded. The welding process involves heating to 750°C at a rate of 10°C / min, holding for 20 minutes, heating to 820°C at a rate of 3°C / min and holding for 30 minutes, and cooling to below 250°C at a rate of 3°C / min to complete the precision welding.

[0044] like Figure 5 and Figure 6 As shown, Figure 5This is a microstructure diagram of a joint obtained by brazing Ti2AlNb and SiC with a composite brazing filler metal according to Example 2 of the present invention. Figure 6 This is the morphology of the joint structure of Ti2AlNb and SiC brazed with AgCu28 solder of the present invention. Figure 5 and Figure 6 It can be seen that the amount of brittle compounds in the joint of Ti2AlNb and SiC brazed with the composite brazing filler metal of Example 2 of the present invention is greatly reduced, and the room temperature shear strength of the obtained joint is 65±4 MPa, and the strength of the joint does not decrease under high temperature conditions of 600°C.

[0045] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A composite brazing filler metal for welding carbon-based materials and titanium-based alloys, characterized in that: include: 3 wt.%~9 wt.% TiH2; 20 wt.%~50 wt.% Nb; The balance is AgCu28.

2. The composite brazing filler metal for welding carbon-based materials and titanium-based alloys according to claim 1, characterized in that: include: 4 wt.%~8 wt.% TiH2; 25 wt.%~35 wt.% Nb; The balance is AgCu28.

3. The composite brazing filler metal for welding carbon-based materials and titanium-based alloys according to claim 1, characterized in that: The mesh number of the TiH2 is 250-300 mesh; The mesh number of the Nb is 100-200 mesh; The mesh size of the AgCu28 is 200-300 meshes.

4. The composite brazing filler metal for welding carbon-based materials and titanium-based alloys according to any one of claims 1 to 3, characterized in that: The carbon-based material includes graphite, SiBCN ceramic or SiC ceramic; The titanium-based alloy includes TA2, TC4, TiAl, TC18 or Ti2AlNb.

5. A solder sheet, characterized in that: The composite solder is made from the composite solder according to any one of claims 1 to 4.

6. The brazing sheet according to claim 5, wherein: The thickness of the solder sheet is 100 μm to 300 μm.

7. The method for preparing a solder sheet according to claim 5 or 6, characterized in that: The following steps are involved: Pressing the composite solder into shape to obtain a solder sheet; The pressure of the compression molding is 2 MPa to 5 MPa.

8. A method for welding carbon-based materials and titanium-based alloys, characterized in that: The following steps are involved: The brazing sheet according to claim 5 or 6 is placed on the surfaces to be welded of the carbon-based material and the titanium-based alloy, and subjected to heat treatment.

9. The welding method according to claim 8, characterized in that: The heat treatment is specifically as follows: heating to 700° C. to 750° C. and keeping the temperature for 20 min to 40 min, then heating to 800° C. to 860° C. and keeping the temperature for 30 min to 60 min.

10. The welding method according to claim 8, characterized in that: The heat treatment is specifically as follows: heating to 700°C~750°C at a heating rate of 8°C / min~12°C / min and keeping warm for 20 min~40 min, then heating to 800°C~860°C at a heating rate of 3°C / min~5°C / min and keeping warm for 30 min~60 min, and finally cooling to below 250°C at a cooling rate of 3°C / min~5°C / min.

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