Composite brazing material and preparation method and application thereof

Abstract

The invention relates to the technical field of welding materials, and particularly discloses a composite brazing material and a preparation method and application thereof. The composite brazing material comprises 22%-32% of Ti, 22%-32% of Zr, 18%-28% of Ni, 10%-18% of Cu, 2%-5% of Si, 2%-5% of B, 0.5%-0.9% of Sc and 0.5%-0.9% of Y. On the basis of the TiZrNiCu brazing material, non-metallic elements and rare metal elements are introduced. And Si and B elements can react with Ti at the brazing temperature to form a dispersed titanide particle strengthening phase, stress concentration of a weld joint is effectively reduced, and the Si and B elements can also be used as a nucleation center to refine a weld joint organization structure. The trace rare earth elements have the effects of solution strengthening and grain refining, and can form beneficial alloy compounds with elements such as Ni, so that the mechanical property of a joint is improved, and the titanium alloy is suitable for connection between titanium alloys.

Description

Technical Field

[0001] This invention relates to the field of welding materials technology, and in particular to a composite brazing filler metal, its preparation method, and its application. Background Technology

[0002] TC4 alloy (Ti6Al4V) is widely used in aerospace, railway transportation, shipbuilding, and marine engineering industries due to its low density, high melting point, high elastic modulus, high specific strength, corrosion resistance, and excellent high-temperature creep resistance. It is particularly prevalent in industrial and manufacturing sectors, such as in large plate-fin heat exchangers. However, the brittleness of TC4 alloy results in poor room-temperature plasticity, making it difficult to process and form, and hindering the production of large-size or complex shapes of TiAl components, thus limiting its application. Furthermore, processing integral components entirely from TC4 alloy is costly and impractical. To overcome these drawbacks and expand the application range of TC4 alloy, welding is a reliable and feasible method for joining TC4 alloy components. For thin-walled titanium alloy components, traditional welding methods are prone to deformation due to high heat input. Brazing achieves a connection by melting the filler metal without melting the base material, offering advantages such as minimal deformation and easily controllable residual stress, making it suitable for manufacturing complex structures such as plate-fin heat exchangers.

[0003] In the brazing manufacturing of TC4 plate-fin heat exchangers, the brazing filler metal material is the core factor determining the joint performance. Commonly used titanium alloy brazing fillers include Ag-based, Al-based, and Ti-based materials. Ag-based filler metals lack sufficient high-temperature strength and are unsuitable for radiator applications; Al-based filler metals tend to cause joint embrittlement and reduce impact toughness. In contrast, Ti-based filler metals (such as Ti-Cu-Ni and Ti-Zr-Cu-Ni systems) are considered ideal due to their excellent wettability, high-temperature strength, and structural stability. However, elements such as Ni and Cu in Ti-based filler metals easily form brittle intermetallic compounds in the weld, potentially leading to brittle fracture of the joint. Therefore, there is an urgent need to improve Ti-based filler metals to reduce the content of harmful intermetallic compounds or to disperse them to minimize the adverse effects of brittle phases. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a composite brazing alloy, its preparation method, and its application. It uses non-metallic and rare metal elements as reinforcing phases, optimizes the weld microstructure, and improves the mechanical properties of the weld joint, making it suitable for joining titanium alloys.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a composite brazing filler metal comprising the following chemical components in weight percentages: Ti 22%~32%, Zr 22%~32%, Ni 18%~28%, Cu 10%~18%, Si 2%~5%, B 2%~5%, Sc 0.5%~0.9% and Y 0.5%~0.9%.

[0006] Compared to existing technologies, the composite brazing alloy provided by this invention uses non-metallic elements (B and Si) and rare metal elements (Sc and Y) as reinforcing phases. On the one hand, during use (brazing), the metallic elements (such as Ti) react in situ with B and Si to generate TiB. x TiSi x On the one hand, rare earth elements can form metal compounds and on the other hand, during use, they can be added to form metal compounds and dissolved into the metal matrix. Ultimately, the combined effect of grain refinement and solid solution strengthening mechanisms optimizes the weld microstructure and improves the overall mechanical properties of the joint.

[0007] Preferably, the composite brazing filler metal comprises the following chemical components in weight percentage: Ti 25%~30%, Zr 25%~30%, Ni 20%~25%, Cu 13%~15%, Si 3%~5%, B 3%~5%, Sc 0.5%~0.9% and Y 0.5%~0.9%.

[0008] Preferably, [B]+[Sc]+[Y]-[Si]=0.8%~1.6%.

[0009] In this invention, [B] represents the mass percentage of B, [Sc] represents the mass percentage of Sc, [Y] represents the mass percentage of Y, and [Si] represents the mass percentage of Si.

[0010] This invention further guarantees the mechanical strength of the joint by limiting the dosage relationship of the four elements B, Si, Sc, and Y. Extensive testing revealed that if the aforementioned relationship of B, Si, Sc, and Y is less than 0.8%, the strengthening phase formed by Si and metallic Ti is prone to aggregation, leading to stress concentration; if the aforementioned relationship of B, Si, Sc, and Y is greater than 1.6%, the rare earth elements Sc and Y will increase porosity defects in the alloy, causing microstructural deterioration and adversely affecting the mechanical strength of the weld joint.

[0011] Secondly, the present invention provides a method for preparing the composite brazing filler metal, comprising the following steps: S1. Weigh each metal powder according to the design ratio, mix the metal powders to obtain mixed brazing filler powder; S2. The mixed brazing powder is subjected to discharge plasma sintering at 730℃~780℃ to obtain composite brazing material.

[0012] The method for preparing composite brazing filler metal provided by this invention involves first mechanically mixing various metal powders, and then sintering them into ingots using spark plasma sintering (SPS) to obtain the composite brazing filler metal. Using SPS sintering can effectively reduce the sintering temperature and shorten the sintering time. Furthermore, a specific sintering temperature (not exceeding 80% of the melting point of the mixed brazing filler metal powder) can yield a dense and fine-grained alloy material.

[0013] Preferably, the specific steps of S1 include: Weigh each metal powder according to the design ratio, mix Ti, Zr, Ni and Cu metal powders for 2h~3h to obtain TiZrNiCu powder; Add B, Si, Sc and Y metal powders to the TiZrNiCu powder and continue mixing for 2h~6h to obtain mixed solder powder.

[0014] Preferably, in S1, the mixing speed is 380 r / h to 420 r / h.

[0015] In example, in S1, mixing is carried out in a stainless steel ball mill jar using vacuum mixing.

[0016] Preferably, in S2, the temperature of the discharge plasma sintering is 730℃~760℃, the pressure is 20MPa~30MPa, and the sintering time is 20min~30min.

[0017] For example, in S2, after the discharge plasma sintering is completed, a cake-shaped composite brazing material is obtained. It can be cut into 5mm×5mm×0.3mm pieces as needed. Both sides of the pieces are polished with 500#, 800# and 2000# sandpaper, and then ultrasonically cleaned with deionized water and anhydrous ethanol respectively.

[0018] Thirdly, the present invention provides an application of the aforementioned composite brazing filler in welding titanium alloys.

[0019] Preferably, the titanium alloy includes TC4 alloy.

[0020] Fourthly, the present invention provides a method for using the aforementioned composite brazing filler metal, comprising the following steps: The composite brazing filler is placed in the gap between the two titanium alloy pieces, and the first brazing is performed at 780℃~820℃, followed by the second brazing at 980℃~1020℃. After cooling, the brazed titanium alloy is obtained.

[0021] The method of using composite brazing alloy provided by the present invention employs stepped brazing (first and second brazing at a specific temperature) to ensure that the temperature of the entire component (composed of composite brazing alloy and two titanium alloys) tends to be consistent, and thermal stress and deformation are controlled to a minimum. At the same time, it can also ensure that the composite brazing alloy and the titanium alloy base material undergo sufficient metallurgical reaction, thereby forming a weld structure with good metallurgical bonding and high joint strength.

[0022] For example, the composite brazing filler metal can be in the form of a solder sheet; both the first and second brazing are performed in a vacuum brazing furnace, with the vacuum level set to 10. -3 Pa.

[0023] Preferably, the method of using the composite brazing filler metal specifically includes the following steps: The composite brazing filler was placed in the gap between two TC4 alloy pieces, and the temperature was raised to 780℃~820℃ at a heating rate of 8℃ / min~12℃ / min for the first brazing. After 20min~35min, the temperature was raised to 980℃~1020℃ at a heating rate of 4℃ / min~6℃ / min for the second brazing. After 20min~35min, the temperature was cooled to room temperature to obtain the brazed titanium alloy.

[0024] The present invention has the following beneficial effects: This invention introduces non-metallic and rare metal elements into TiZrNiCu brazing filler metal to create a composite brazing filler metal. Si and B elements can react with Ti at the brazing temperature to form dispersed TiB. x TiSi x The addition of titanium oxide particles as strengthening phases can effectively reduce stress concentration in the weld and, as nucleation centers, refine the weld microstructure. The addition of trace amounts of rare earth elements can also play a positive role in solid solution strengthening and grain refinement, and can form beneficial alloying compounds with elements such as Ni (e.g., Ni3Y and Ni3Sc phases), inhibiting the formation of harmful metallic compounds and thus improving the mechanical properties of the joint.

[0025] This invention involves brazing a composite brazing alloy between two layers of TC4 alloy. Compared to traditional brazing alloys, the composite brazing alloy has better wetting effect. Through a stepped temperature brazing process, the overall mechanical properties of the weld joint can be significantly improved. Attached Figure Description

[0026] Figure 1 The images show the XRD patterns of the brazed titanium alloy weld seams in Application Example 1 (black line) and Comparative Application Example 1 (red line) of this invention.

[0027] Figure 2 This is a microstructure diagram of the brazed titanium alloy weld in Application Example 1 of the present invention.

[0028] Figure 3 This is a microstructure diagram of the brazed titanium alloy weld in Comparative Application Example 1 of the present invention.

[0029] Figure 4 This is a microstructure diagram of the brazed titanium alloy weld in Comparative Application Example 2 of the present invention.

[0030] Figure 5 This is a microstructure diagram of the brazed titanium alloy weld in Comparative Application Example 3 of the present invention.

[0031] Figure 6 This is a microstructure diagram of the brazed titanium alloy weld in Comparative Application Example 4 of the present invention.

[0032] Figure 7 This is a microstructure diagram of the fracture surface at the brazed titanium alloy weld in Application Example 1 of the present invention.

[0033] Figure 8 This is a microstructure diagram of the fracture surface of the brazed titanium alloy weld in Comparative Application Example 1 of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Unless otherwise specified in the embodiments of the present invention, the raw materials used in the preparation of these materials are all commercially available products.

[0036] Example 1 This embodiment provides a composite brazing filler metal comprising the following chemical composition by mass percentage: Ti 27.5%, Zr 27%, Ni 24%, Cu 14.5%, Si 3%, B 3%, Sc 0.5%, and Y 0.5%. [B]+[Sc]+[Y]-[Si]=1.0%.

[0037] The preparation method of the above-mentioned composite brazing alloy includes the following steps: S1. Weigh the metal powders according to the designed proportions. Place the Ti, Zr, Ni, and Cu metal powders into a stainless steel ball mill jar and mix at 400 r / h under vacuum for 3 h to obtain TiZrNiCu powder. Add B, Si, Sc, and Y metal powders to the TiZrNiCu powder and continue mixing at 400 r / h under vacuum for 4 h to obtain mixed solder powder.

[0038] S2. The mixed brazing filler powder is subjected to discharge plasma sintering at 750℃ and 30MPa pressure. After 30 minutes, it is cooled to room temperature, sliced, and the composite brazing filler is obtained.

[0039] Example 2 This embodiment provides a composite brazing filler metal comprising the following chemical composition by weight percentage: Ti 27.6%, Zr 27.6%, Ni 23%, Cu 13.8%, Si 3.2%, B 3.2%, Sc 0.8%, and Y 0.8%. [B]+[Sc]+[Y]-[Si]=1.6%.

[0040] The preparation method of the above-mentioned composite brazing alloy includes the following steps: S1. Weigh the metal powders according to the designed proportions. Place the Ti, Zr, Ni, and Cu metal powders into a stainless steel ball mill jar and mix at 380 r / h under vacuum for 3 h to obtain TiZrNiCu powder. Add B, Si, Sc, and Y metal powders to the TiZrNiCu powder and continue mixing at 380 r / h under vacuum for 5 h to obtain mixed solder powder.

[0041] S2. The mixed brazing powder was subjected to discharge plasma sintering at 760℃ and 30MPa pressure. After 20 minutes, it was cooled to room temperature and sliced ​​to obtain the composite brazing material.

[0042] Example 3 This embodiment provides a composite brazing filler metal comprising the following chemical composition by weight percentage: Ti 26.7%, Zr 26.7%, Ni 22.2%, Cu 13.4%, Si 5%, B 5%, Sc 0.5%, and Y 0.5%. [B]+[Sc]+[Y]-[Si]=1.0%.

[0043] The preparation method of the above-mentioned composite brazing alloy includes the following steps: S1. Weigh the metal powders according to the designed proportions. Place the Ti, Zr, Ni, and Cu metal powders into a stainless steel ball mill jar and mix at 420 r / h under vacuum for 2 hours to obtain TiZrNiCu powder. Add B, Si, Sc, and Y metal powders to the TiZrNiCu powder and continue mixing at 420 r / h under vacuum for 2 hours to obtain mixed solder powder.

[0044] S2. The mixed brazing powder was subjected to discharge plasma sintering at 730℃ and 20MPa pressure. After 30 minutes, it was cooled to room temperature and sliced ​​to obtain the composite brazing material.

[0045] Example 4 This embodiment provides a composite brazing filler metal comprising the following chemical composition by weight percentage: Ti 30%, Zr 30%, Ni 20%, Cu 13%, Si 3%, B 2.8%, Sc 0.6%, and Y 0.6%. [B]+[Sc]+[Y]-[Si]=1.0%.

[0046] The preparation method of the above-mentioned composite brazing alloy is the same as that in Example 1, and will not be repeated here.

[0047] Example 5 This embodiment provides a composite brazing filler metal comprising the following chemical composition by mass percentage: Ti 25%, Zr 25%, Ni 25%, Cu 15%, Si 4.2%, B 4.6%, Sc 0.6%, and Y 0.6%. [B]+[Sc]+[Y]-[Si]=1.6%.

[0048] The preparation method of the above-mentioned composite brazing alloy is the same as that in Example 1, and will not be repeated here.

[0049] Example 6 This embodiment provides a composite brazing filler metal comprising the following chemical composition by weight percentage: Ti 26.4%, Zr 26.5%, Ni 22.1%, Cu 13.2%, Si 5%, B 5%, Sc 0.9%, and Y 0.9%. [B]+[Sc]+[Y]-[Si]=1.8%.

[0050] The preparation method of the above-mentioned composite brazing alloy is the same as that in Example 1, and will not be repeated here.

[0051] Comparative Example 1 This comparative example provides a composite brazing filler metal comprising the following chemical composition in weight percentages: Ti 30%, Zr 25%, Ni 25%, and Cu 20%.

[0052] The preparation method of the above composite brazing alloy is similar to that of Example 1 (B, Si, Sc and Y metal powders are not added during mixing in S1, and TiZrNiCu powder is replaced in S2), and will not be described again.

[0053] Comparative Example 2 This comparative example provides a composite brazing filler metal comprising the following chemical composition in weight percentages: Ti 27%, Zr 27%, Ni 22.5%, Cu 13.5%, Si 5%, and B 5%.

[0054] The preparation method of the above composite brazing alloy is similar to that of Example 1 (Sc and Y metal powders are not added during mixing in S1), and will not be described again.

[0055] Comparative Example 3 This comparative example provides a composite brazing filler metal comprising the following chemical composition by weight percentage: Ti 29%, Zr 29%, Ni 24.5%, Cu 15.7%, Sc 0.9%, and Y 0.9%.

[0056] The preparation method of the above composite brazing filler is similar to that of Example 1 (B and Si metal powders are not added during mixing in S1), and will not be described again.

[0057] Comparative Example 4 This comparative example provides a composite brazing filler metal comprising the following chemical composition in weight percentages: Ti 27.5%, Zr 27%, Ni 24%, Cu 14.5%, Si 6%, and Y 1%.

[0058] The preparation method of the above composite brazing alloy is similar to that of Example 1 (B and Sc metal powders are not added during mixing in S1), and will not be described again.

[0059] Comparative Example 5 This comparative example provides a composite brazing filler metal comprising the following chemical composition in weight percentages: Ti 27.5%, Zr 27%, Ni 24%, Cu 14.5%, B 6%, and Sc 1%.

[0060] The preparation method of the above composite brazing alloy is similar to that of Example 1 (Si and Y metal powders are not added during mixing in S1), and will not be described again.

[0061] Comparative Example 6 This comparative example provides a method for preparing a composite brazing alloy, similar to Example 1, except that in S2, the temperature of the spark plasma sintering is replaced with 800°C. The remaining steps and parameter settings are the same as in Example 1 and will not be repeated here.

[0062] The chemical composition of the composite brazing alloy in this comparative example is the same as that in Example 1, and will not be repeated here.

[0063] Verification Experiment 1 According to the national standard GB / T 11363-2008 "Test Method for Strength of Brazed Joints", the shear strength of the composite brazing materials of Examples 1-6 and Comparative Examples 1-6 was tested using a universal testing machine at a speed of 50 mm / min. Three samples of the same composite brazing material were tested, and the average value of the measurement results (as shown in Table 1) was taken.

[0064] Table 1. Shear strength of composite brazing fillers in the examples and comparative examples.

[0065] Application Example 1 This application example provides a method for using the composite solder of Example 1, including the following steps: The composite brazing filler (5mm×5mm×0.3mm) was placed in the gap between two pieces of TC4 alloy (5mm×5mm×5mm). The temperature was raised to 800℃ at a rate of 10℃ / min for the first brazing. After 30 minutes, the temperature was raised to 1000℃ at a rate of 5℃ / min for the second brazing. After 30 minutes, the temperature was cooled to room temperature to obtain the brazed titanium alloy.

[0066] Application Example 2 This application example provides a method for using the composite solder of Example 2, including the following steps: The composite brazing filler (5mm×5mm×0.3mm) was placed in the gap between two pieces of TC4 alloy (5mm×5mm×5mm). The temperature was raised to 780℃ at a rate of 8℃ / min for the first brazing. After 25 minutes, the temperature was raised to 980℃ at a rate of 4℃ / min for the second brazing. After 25 minutes, the temperature was cooled to room temperature to obtain the brazed titanium alloy.

[0067] Application Example 3 This application example provides a method for using the composite solder of Example 4, including the following steps: The composite brazing filler (5mm×5mm×0.3mm) was placed in the gap between two pieces of TC4 alloy (5mm×5mm×5mm). The temperature was raised to 820℃ at a rate of 12℃ / min for the first brazing. After 35 minutes, the temperature was raised to 1020℃ at a rate of 6℃ / min for the second brazing. After 35 minutes, the temperature was cooled to room temperature to obtain the brazed titanium alloy.

[0068] Compare and contrast examples 1-5 Comparative Examples 1-5 provide a method for using a composite solder, similar to Application Example 1, except that the composite solder of Example 1 is replaced with the composite solder of Comparative Examples 1-5. The remaining steps and parameters are the same as in Application Example 1 and will not be repeated.

[0069] Verification Experiment 2 X-ray diffraction tests were performed on the weld seams of the brazed titanium alloys prepared in Example 1 and Comparative Application Example 1, respectively. The results are as follows: Figure 1 As shown. From Figure 1 As can be seen from this, compared to the weld in Comparative Application Example 1 ( Figure 1 (Red line in the diagram), after introducing the four elements B, Si, Sc, and Y, the weld seam of Example 1 is applied ( Figure 1 The black lines in the figure show a significant reduction in brittle alloy compounds such as CuZr, and the formation of reinforcing phases such as Ti5Si3 and TiB2, indicating that the weld structure of the composite brazing filler metal provided by this invention has been significantly optimized.

[0070] Microstructure tests were performed on the weld seams of the brazed titanium alloys prepared in Example 1 and Comparative Application Examples 1-4, respectively. The results are as follows: Figures 2-6 As shown. From Figures 2-6 As can be seen from Table 1, (1) compared with the weld of Application Example 1 (which only uses TiZrNiCu alloy sintered powder), there is a thick etched layer on the TC4 alloy base material, and the weld microstructure is coarse, with brittle intermetallic compounds and pores, which ultimately leads to a lower joint strength. (2) compared with the welds of Application Examples 2-3 (which use TiZrNiCu+Si+B and TiZrNiCu+Sc+Y alloy sintered powder respectively), the weld microstructure is uniform and fine, without obvious large brittle intermetallic compounds, indicating that the addition of these elements has suppressed the precipitation of intermetallic compounds to a certain extent, but the grain size is still coarser than that of Application Example 1. (3) Compared with the weld of Application Example 4 (using TiZrNiCu+Si+Y alloy sintered powder), the excessive Si element caused the growth of the strengthening phase, forming coarse Ti5Si3 aggregates, which increased stress concentration and fracture sites; the addition of excessive Y led to the formation of more pore defects in the weld, resulting in reduced microstructure uniformity and significantly reduced fracture strength. (4) Under the combined action of elements such as B, Si, Sc, and Y, the weld structure of Application Example 1 was further refined, and it reacted with Ni, Ti and other metals in TiZrNiCu to form fine, trace and dispersed strengthening phases Ti5Si3 and TiB2. While suppressing the precipitation of brittle alloy compounds, it can also serve as nucleation sites to further refine the microstructure, thereby significantly improving the mechanical strength of the joint.

[0071] The brazed titanium alloys prepared in Application Example 1 and Comparative Application Example 1 were subjected to shear strength tests using a universal testing machine at a speed of 50 mm / min according to the national standard GB / T 11363-2008 "Test Method for Strength of Brazed Joints". The microstructure at the weld fracture surface was observed, and the results are as follows. Figures 7-8 As shown. From Figures 7-8 As can be seen from the above, (1) compared with the weld of Application Example 1 (which only uses TiZrNiCu alloy sintered powder), its fracture morphology does not have obvious tearing ridges, and the fracture surface shows significant brittle cleavage cracking morphology. Furthermore, precipitated metal compounds were found at the fracture surface, which indicates that the coarse microstructure and the presence of a large number of brittle phases led to a decrease in strength. (2) Under the combined action of elements such as B, Si, Sc, and Y, the weld of Application Example 1 has obvious river-like patterns at its fracture surface, and the cracks are relatively fine, exhibiting a mixed structural characteristic of ductile fracture and cleavage cracking. This indicates that the mechanical properties of the weld joint using the composite brazing filler provided by this invention are significantly improved.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite brazing filler metal, characterized in that, The chemical composition includes the following percentages by mass: Ti 22%~32%, Zr 22%~32%, Ni 18%~28%, Cu 10%~18%, Si 2%~5%, B 2%~5%, Sc 0.5%~0.9%, and Y 0.5%~0.9%.

2. The composite brazing filler metal as described in claim 1, characterized in that, The composite brazing filler metal comprises the following chemical components in weight percentages: Ti 25%~30%, Zr 25%~30%, Ni 20%~25%, Cu 13%~15%, Si 3%~5%, B 3%~5%, Sc 0.5%~0.9%, and Y 0.5%~0.9%.

3. The composite brazing filler metal as described in claim 1 or 2, characterized in that, [B]+[Sc]+[Y]-[Si]=0.8%~1.6%.

4. The method for preparing the composite brazing alloy according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Weigh each metal powder according to the design ratio, mix the metal powders to obtain mixed brazing filler powder; S2. The mixed brazing powder is subjected to discharge plasma sintering at 730℃~780℃ to obtain composite brazing material.

5. The method for preparing the composite brazing filler metal as described in claim 4, characterized in that, In S1, the mixing speed is 380 r / h to 420 r / h.

6. The method for preparing the composite brazing filler metal as described in claim 4, characterized in that, In S2, the temperature of the discharge plasma sintering is 730℃~760℃, the pressure is 20MPa~30MPa, and the sintering time is 20min~30min.

7. The application of the composite brazing alloy according to any one of claims 1 to 3 or the composite brazing alloy prepared by the method of any one of claims 4 to 6 in welding titanium alloys.

8. The application of the composite brazing filler metal as described in claim 7 in welding titanium alloys, characterized in that, The titanium alloy includes TC4 alloy.

9. The method of using the composite brazing filler metal according to any one of claims 1 to 3, characterized in that, Includes the following steps: The composite brazing filler is placed in the gap between the two titanium alloy pieces, and the first brazing is performed at 780℃~820℃, followed by the second brazing at 980℃~1020℃. After cooling, the brazed titanium alloy is obtained.

10. The method of using the composite brazing filler metal as described in claim 9, characterized in that, The method of using the composite brazing filler specifically includes the following steps: The composite brazing filler was placed in the gap between two TC4 alloy pieces, and the temperature was raised to 780℃~820℃ at a heating rate of 8℃ / min~12℃ / min for the first brazing. After 20min~35min, the temperature was raised to 980℃~1020℃ at a heating rate of 4℃ / min~6℃ / min for the second brazing. After 20min~35min, the temperature was cooled to room temperature to obtain the brazed titanium alloy.

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