Welding method for achieving molybdenum alloy and niobium alloy homogeneous connection joint and connection joint

Abstract

The invention discloses a welding method for achieving a molybdenum alloy and niobium alloy homogeneous connection joint and the connection joint, and the method comprises the following steps that Ni foil, Pd foil and Ti foil are placed in a vacuum furnace according to the stacking sequence from top to bottom, and after heating and pressurizing are conducted, NiPdTi composite foil is obtained; the molybdenum alloy and the niobium alloy to be welded are polished; cleaning the NiPdTi composite foil and the polished molybdenum alloy and niobium alloy; the molybdenum alloy, the NiPdTi composite foil and the niobium alloy are sequentially placed from top to bottom, a to-be-welded piece is obtained, and preset pressure is applied to the side, away from the NiPdTi composite foil, of the molybdenum alloy; and the to-be-welded part is placed in a vacuum brazing furnace, heating is started when the vacuum degree in the vacuum brazing furnace reaches 2 * 10 <-3 > Pa to 5.0 * 10 <-3 > Pa, heat preservation is conducted for 1 min to 30 min when the brazing temperature ranges from 1120 DEG C to 1180 DEG C, and therefore the connecting joint is obtained. According to the connecting method, brittle and hard compounds such as Mo-Ni and Ni-Nb can be prevented from being generated on the connecting joint, meanwhile, a homogeneous solid solution structure can be formed in the process of connecting the base materials on the two sides, and therefore the excellent mechanical property of the joint is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dissimilar material connection, in particular to a welding method for realizing homogeneous connection joint of molybdenum alloy and niobium alloy and the connection joint. BACKGROUND

[0002] At present, molybdenum alloy and niobium alloy are often used as structural and functional materials in aerospace and nuclear fields due to their excellent high-temperature performance, corrosion resistance, oxidation resistance and radiation resistance. Some specific components need to realize large-area face-to-face connection of molybdenum alloy and niobium alloy, and brazing is a reliable way to realize such connection.

[0003] When connecting dissimilar materials, the formation of homogeneous solid solution weld is not only beneficial to relieving the residual stress of the heterogeneous joint after welding, but also can avoid the generation of harmful brittle compounds in the joint through microstructure control, thereby improving the strength and toughness of the joint. However, there is no suitable filler metal in the prior art to realize the connection of homogeneous joint of molybdenum alloy and niobium alloy. SUMMARY

[0004] In view of the above, it is necessary to provide a welding method for realizing homogeneous connection joint of molybdenum alloy and niobium alloy and the connection joint. By using NiPdTi composite foil as solder, it can have good metallurgical compatibility with molybdenum alloy base material and niobium alloy base material, can avoid the generation of brittle and hard Mo-Ni, Ni-Nb and other compounds in the connection joint, and can also form homogeneous solid solution structure in the process of connecting the two sides of the base material, thereby obtaining excellent mechanical properties of the joint.

[0005] The first aspect of the embodiment of the present application provides a welding method for realizing homogeneous connection joint of molybdenum alloy and niobium alloy, comprising the following steps:

[0006] Placing Ni foil, Pd foil and Ti foil in a vacuum furnace in the stacking order from top to bottom, and obtaining NiPdTi composite foil after heating and pressing;

[0007] Grinding the molybdenum alloy and the niobium alloy to be welded;

[0008] Cleaning the NiPdTi composite foil and the molybdenum alloy and the niobium alloy after grinding;

[0009] Placing the molybdenum alloy, the NiPdTi composite foil and the niobium alloy in the order from top to bottom to obtain a welding piece, and applying a preset pressure to the side of the molybdenum alloy away from the NiPdTi composite foil;

[0010] Placing the welding piece in a vacuum brazing furnace, and the vacuum degree in the vacuum brazing furnace reaches 2×10 ～3 Pa~5.0×10 ～3Pa, heating is started, and the connection joint is obtained by keeping the brazing temperature at 1120-1180℃ for 1-30 min.

[0011] In some possible embodiments, the step of placing the Ni foil, the Pd foil and the Ti foil in a vacuum furnace in a stacking order from top to bottom, and obtaining the NiPdTi composite foil after heating and pressurizing specifically comprises:

[0012] The Ni foil, the Pd foil and the Ti foil are placed in a vacuum furnace in a stacking order from top to bottom, a pressure of 1.5-2.5 MPa is applied above the Ni foil, and the NiPdTi composite foil is obtained by heating to 750-850℃ for 15-25 min and cooling to room temperature.

[0013] In some possible embodiments, in the NiPdTi composite foil, the mass fraction of Ni is 25-27 wt.%, the content of Pd is 38-40 wt.%, and the rest is Ti.

[0014] In some possible embodiments, the thickness of the NiPdTi composite foil is 155-175 μm.

[0015] In some possible embodiments, the molybdenum alloy is one of pure Mo, Mo-Re and TZM, and the niobium alloy is one of pure Nb and Nb-Zr.

[0016] In some possible embodiments, the step of polishing the molybdenum alloy and the niobium alloy to be welded comprises:

[0017] The to-be-welded parts of the molybdenum alloy and the niobium alloy are polished in sequence with SiC sandpaper of 400 mesh, 800 mesh, 1200 mesh and 2000 mesh.

[0018] In some possible embodiments, the step of cleaning the NiPdTi composite foil and the polished molybdenum alloy and niobium alloy comprises:

[0019] The NiPdTi composite foil and the polished molybdenum alloy and niobium alloy are immersed in acetone, dried after ultrasonic cleaning for 10-30 min, and then immersed in an ethanol solution, dried after ultrasonic cleaning for 10-20 min.

[0020] In some possible embodiments, the brazing heating rate is 5-20℃ / min.

[0021] In some possible embodiments, the step of keeping the brazing temperature at 1120-1180℃ for 1-30 min further comprises:

[0022] cooling the heat-insulated said welding piece to room temperature, wherein the cooling rate of the said welding piece is 5-10℃ / min.

[0023] The second aspect of the embodiments of the present application provides a connecting joint prepared by the welding method as described in any one of the above.

[0024] The welding method and the connecting joint for realizing the homogeneous connecting joint of molybdenum alloy and niobium alloy, based on thermodynamic calculation, by adding Ti element with larger bonding tendency on the basis of Ni, Pd foil which can be infinitely miscible, the starting melting temperature of the obtained NiPdTi composite foil is 1120℃, which is significantly lower than the melting point of 1240℃ of the NiPd filler. In addition, the use of NiPdTi composite foil for brazing molybdenum alloy and niobium alloy, on the one hand, reduces the bonding tendency of Nb and Ni and Pd, reduces the dissolution of Nb into the brazing seam, and hinders the formation of brittle Ni-Nb compounds in the brazing seam; on the other hand, it is conducive to promoting the formation of (Ni, Pd) Ti solid solution structure in the brazing seam. Further, the preparation of NiPdTi composite foil as the intermediate layer for brazing, in the process of heating to 1120-1180℃, Ti and Ni element form eutectic liquid phase at 1118℃, the filler melts, a small amount of Mo and Nb dissolves and diffuses into the brazing seam, realizing the metallurgical bonding of molybdenum alloy and niobium alloy. In this process, the Ni, Pd, Ti elements in the brazing seam tend to form (Ni, Pd) Ti solid solution structure, and with the dissolution of Nb element in the niobium alloy, part of the (Ni, Pd) Ti solid solution structure is converted into (Ni, Pd) (Ti, Nb) solid solution. When the brazing temperature is lower than 1120℃, the filler is not completely melted, and the connecting joint is prone to form defects such as holes; when the brazing temperature is higher than 1180℃, the dissolution of Nb into the brazing seam is intensified, and a large amount of Nb-based solid solution and Ti2Ni type compounds are formed in the brazing seam. Therefore, within the appropriate brazing temperature range, it is conducive to the formation of homogeneous (Ni, Pd) Ti solid solution structure in the connecting joint, which has excellent strength and toughness. Therefore, the arrangement of the NiPdTi composite foil of the present application regulates the interfacial reaction and avoids the formation of brittle compounds, the connecting method is simple and the cost is low, a uniform solid solution joint can be generated, and the average tensile strength of the molybdenum alloy / NiPdTi / niobium alloy joint obtained is about 270MPa, the connecting joint is almost as strong as the niobium alloy base material, and part of the fracture is on the niobium alloy base material side. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The flow chart of the welding method for realizing the homogeneous connecting joint of molybdenum alloy and niobium alloy provided by the embodiments of the present application.

[0026] Figure 2 is Figure 1 The structure diagram of the NiPdTi composite foil described in the embodiments of the present application.

[0027] Figure 3 is Figure 1 a structural diagram of a welding object.

[0028] Figure 4 a backscattered electron image of a connection joint obtained by the present application. DETAILED DESCRIPTION

[0029] Embodiments of the present application are described in detail below with reference to the attached drawing figures, wherein the same or like component have the same or similar designations throughout the attaching figures. The embodiments described below are presented by way of example only, and are not intended to limit the present application as defined by the appended claims.

[0030] The disclosure that follows provides many different embodiments, or examples, for implementing different structures of the present application. For the purpose of simplicity, the elements of the specific examples below are described in a manner that is intended to convey the essential nature of the features of the embodiments. It will be appreciated that the description set forth is intended as a description of various embodiments of the application, and is not intended to limit the scope of the application in any way. Furthermore, the

[0031] The embodiments of the present application are further described below with reference to the accompanying drawings.

[0032] At present, when the Ni-based filler and the Ti-based filler for high-temperature brazing are used to braze molybdenum alloy and niobium alloy, respectively, the interface will generate Mo-Ni and Nb-Ni brittle compounds, excessive dissolution of Nb into the brazing seam will cause premature failure of the joint and degradation of the high-temperature joint performance, and the like.

[0033] To solve the above problems, please see Figure 1 The embodiments of the present application provide a welding method for realizing a homogeneous connection joint of molybdenum alloy and niobium alloy, comprising the following steps:

[0034] S10, placing the Ni foil, Pd foil and Ti foil in a vacuum furnace in a stacking order from top to bottom, and obtaining a NiPdTi composite foil after heating and pressurizing.

[0035] In some possible embodiments, the step of placing the Ni foil, Pd foil and Ti foil in a vacuum furnace in a stacking order from top to bottom, and obtaining a NiPdTi composite foil after heating and pressurizing specifically comprises:

[0036] As Figure 2As shown, the Ni foil, Pd foil and Ti foil are placed in a vacuum furnace in the order from top to bottom, a pressure of 1.5 MPa to 2.5 MPa is applied above the Ni foil, heated to 750°C to 850°C for 15 min to 25 min, and after cooling to room temperature, the NiPdTi composite foil is obtained. Preferably, a pressure of 2 MPa is applied above the Ni foil, heated to 800°C for 20 min, and after cooling to room temperature, the NiPdTi composite foil is obtained.

[0037] In the NiPdTi composite foil, the mass fraction of Ni is 25wt.% to 27wt.%, the content of Pd is 38wt.% to 40wt.%, and the rest is Ti.

[0038] In the NiPdTi composite foil, the thickness is 155μm to 175μm. Preferably, the thickness of the NiPdTi composite foil is 165μm.

[0039] In the NiPdTi composite foil, the thickness is 155μm to 175μm. Preferably, the thickness of the NiPdTi composite foil is 165μm.

[0040] S20, polishing the molybdenum alloy and the niobium alloy to be welded.

[0041] In some possible embodiments, the step of polishing the molybdenum alloy and the niobium alloy to be welded includes:

[0042] The molybdenum alloy and the niobium alloy to be welded are polished with SiC sandpaper of 400 mesh, 800 mesh, 1200 mesh and 2000 mesh in sequence.

[0043] S30, cleaning the NiPdTi composite foil and the polished molybdenum alloy and niobium alloy.

[0044] In some possible embodiments, the step of cleaning the NiPdTi composite foil and the polished molybdenum alloy and niobium alloy includes:

[0045] The NiPdTi composite foil and the polished molybdenum alloy and niobium alloy are immersed in acetone, dried after ultrasonic cleaning for 10 min to 30 min, and then immersed in an ethanol solution, dried after ultrasonic cleaning for 10 min to 20 min.

[0046] S40, placing the molybdenum alloy, the NiPdTi composite foil and the niobium alloy in sequence from top to bottom to obtain a welding piece (as shown in Figure 3 As shown, a predetermined pressure is applied to the side of the molybdenum alloy away from the NiPdTi composite foil.

[0047] S50, placing the welding piece in a vacuum brazing furnace, and when the vacuum degree in the vacuum brazing furnace reaches 2×10 ～3 Pa to 5.0×10 ～3Pa, heating is started, and the brazing temperature is kept at 1120-1180 DEG C for 1-30 min, so as to obtain the connecting joint.

[0048] The brazing temperature is kept at 1120-1180 DEG C for 1-30 min.

[0049] In some possible embodiments, the step of keeping the brazing temperature at 1120-1180 DEG C for 1-30 min further comprises:

[0050] The brazed workpiece is cooled to room temperature, and the cooling speed of the workpiece is 5-10 DEG C / min.

[0051] The second aspect of the embodiments of the present application provides a connecting joint prepared by using the welding method of any one of the above.

[0052] The welding method and the connecting joint for realizing the homogeneous connecting joint of molybdenum alloy and niobium alloy, based on thermodynamic calculation, by adding Ti element with larger bonding tendency on the basis of the Ni and Pd foil which can be infinitely miscible, the starting melting temperature of the obtained NiPdTi composite foil is 1120 DEG C, which is significantly lower than the melting point 1240 DEG C of the NiPd filler. In addition, the molybdenum alloy and the niobium alloy are brazed by using the NiPdTi composite foil, on the one hand, the bonding tendency of Nb and Ni and Pd is reduced, the dissolution of Nb into the brazing seam is reduced, and the formation of the brittle Ni-Nb compound in the brazing seam is hindered; on the other hand, it is conducive to promoting the formation of the (Ni, Pd) Ti solid solution structure in the brazing seam. Further, as Figure 4As shown, the NiPdTi composite foil is prepared as the intermediate layer for brazing. During the heating to 1120-1180°C, the eutectic liquid phase of Ti and Ni is formed at 1118°C, the brazing filler is melted, a small amount of Mo and Nb is dissolved and diffused into the brazing seam, and the metallurgical bonding of the molybdenum alloy and the niobium alloy is achieved. In this process, the elements of Ni, Pd and Ti in the brazing seam tend to form a (Ni, Pd) Ti solid solution structure, and with the dissolution of the Nb element in the niobium alloy, part of the (Ni, Pd) Ti solid solution structure is converted into a (Ni, Pd)(Ti, Nb) solid solution. When the brazing temperature is lower than 1120°C, the brazing filler is not completely melted, and the connected joint is prone to form defects such as holes. When the brazing temperature is higher than 1180°C, the dissolution of Nb into the brazing seam is intensified, and a large amount of Nb-based solid solution and Ti2Ni type compound is formed in the brazing seam. Therefore, within the appropriate brazing temperature range, it is beneficial to form a homogeneous (Ni, Pd) Ti solid solution structure in the connected joint, which has excellent strength and toughness. Thus, the arrangement of the NiPdTi composite foil of the present application controls the interfacial reaction and avoids the formation of brittle compounds, the connection method is simple and low in cost, a uniform solid solution joint can be generated, and the average tensile strength of the molybdenum alloy / NiPdTi / niobium alloy joint obtained is about 270 MPa, the connected joint is almost as strong as the niobium alloy base material, and part of the fracture is on the niobium alloy base material side.

[0053] The technical solution of the present application is not limited to the specific embodiments exemplified below, but also includes any combination between the specific embodiments.

[0054] Embodiment 1

[0055] The present embodiment provides a welding method for realizing a homogeneous connected joint of a molybdenum alloy and a niobium alloy, comprising the following steps:

[0056] Step one, place the Ni foil with a thickness of 35 μm, the Pd foil with a thickness of 40 μm and the Ti foil with a thickness of 100 μm in the vacuum furnace in the stacking order from top to bottom, apply a pressure of 2 MPa on the top of the Ni foil, heat to 800°C and keep for 20 min, and after cooling to room temperature, obtain the NiPdTi composite foil.

[0057] Step two, polish the to-be-welded parts of the pure Mo and Nb1Zr alloy in turn with 400 mesh, 800 mesh, 1200 mesh and 2000 mesh SiC sandpaper.

[0058] Step three, immerse the NiPdTi composite foil and the polished molybdenum alloy and niobium alloy in acetone, ultrasonic clean for 10 min and then dry, then immerse in an ethanol solution, ultrasonic clean for 10 min and then dry with a hair dryer or oven dry.

[0059] Step four, place the molybdenum alloy, the NiPdTi composite foil and the niobium alloy in turn in the order from top to bottom,

[0060] The pieces to be welded are obtained, and a graphite block with a pressure of 0.5 x 10 3 Pa is applied to the side of the molybdenum alloy away from the NiPdTi composite foil.

[0061] Step five, the pieces to be welded are placed into a vacuum brazing furnace, heated to 1140℃ under a vacuum of 5.0 x 10 ～3 Pa, the heating rate is set to 15℃ / min, and the holding time is 10 min. After brazing, the cooling rate is 5℃ / min until room temperature is reached, thereby obtaining a connected joint.

[0062] Testing shows that the average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 270 MPa at room temperature.

[0063] Example 2

[0064] The difference between this embodiment and Example 1 is that the pure Mo base material used in Step two is changed to Mo5Re, and the other steps are the same as in Example 1.

[0065] Testing shows that the average tensile strength of the Mo5Re / NiPdTi / Nb1Zr joint obtained in this embodiment is 263 MPa at room temperature.

[0066] Example 3

[0067] The difference between this embodiment and Example 1 is that the thickness of the Ti foil in Step one is 80 μm, and the other steps are the same as in Example 1.

[0068] Testing shows that the average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 210 MPa at room temperature.

[0069] Example 4

[0070] The difference between this embodiment and Example 1 is that the Nb1Zr base material used in Step two is changed to pure Nb, and the other steps are the same as in Example 1.

[0071] Testing shows that the average tensile strength of the Mo / NiPdTi / Nb joint obtained in this embodiment is 267 MPa at room temperature.

[0072] Example 5

[0073] The difference between this embodiment and Example 1 is that a graphite block with a pressure of 3.0 x 10 3 Pa is applied to the pieces to be welded in Step three, and the other steps are the same as in Example 1.

[0074] The average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 256 MPa at room temperature.

[0075] Example 6

[0076] The difference between this embodiment and Example 1 is that the brazing temperature in step five is 1120°C, and the other steps are the same as those in Example 1.

[0077] The average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 260 MPa at room temperature.

[0078] Example 7

[0079] The difference between this embodiment and Example 1 is that the brazing temperature in step five is 1120°C, and the other steps are the same as those in Example 1.

[0080] The average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 260 MPa at room temperature.

[0081] Example 8

[0082] The difference between this embodiment and Example 1 is that the brazing temperature in step five is 1120°C, and the other steps are the same as those in Example 1.

[0083] The average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 247 MPa at room temperature.

[0084] Example 9

[0085] The difference between this embodiment and Example 1 is that the brazing temperature in step five is 1180°C, and the other steps are the same as those in Example 1.

[0086] The average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 244 MPa at room temperature.

[0087] Example 10

[0088] The difference between this embodiment and Example 1 is that the brazing temperature in step five is 1180°C, and the other steps are the same as those in Example 1.

[0089] The average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 212 MPa at room temperature.

[0090] Example 11

[0091] The difference between this embodiment and embodiment 1 is that the vacuum degree in step five is 2x10 ～3 Pa, and other steps are the same as those in embodiment 1.

[0092] It can be obtained through testing that the average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 216 MPa at room temperature.

[0093] Embodiment 12

[0094] The difference between this embodiment and embodiment 11 is that the vacuum degree in step five is 2x10 ～3 Pa, and other steps are the same as those in embodiment 11.

[0095] It can be obtained through testing that the average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 240 MPa at room temperature.

[0096] Embodiment 13

[0097] The difference between this embodiment and embodiment 11 is that the vacuum degree in step five is 2x10 ～3 Pa, and other steps are the same as those in embodiment 11.

[0098] It can be obtained through testing that the average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 206 MPa at room temperature.

[0099] Embodiment 14

[0100] The difference between this embodiment and embodiment 1 is that the heating in step five is to 1140℃ for 1 min, and other steps are the same as those in embodiment 1.

[0101] It can be obtained through testing that the average tensile strength of the Mo / NiPdTi / Nb1Zr joint obtained in this embodiment is 236 MPa at room temperature.

[0102] Comparative Example 1

[0103] The difference between this comparative example and embodiment 1 is that the brazing filler metal in step one is a Ni-based brazing filler metal, and other steps are the same as those in embodiment 1.

[0104] It can be obtained through testing that the average tensile strength of the joint obtained in this embodiment is 93 MPa at room temperature.

[0105] Comparative Example 2

[0106] The difference between this comparative example and embodiment 1 is that the brazing filler metal in step one is a Ti-based brazing filler metal, and other steps are the same as those in embodiment 1.

[0107] The average tensile strength of the joint obtained in this example is 147 MPa at room temperature.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 1 is that the brazing filler metal in Step 1 is PdNi foil, and the other steps are the same as those in Example 1.

[0110] The average tensile strength of the joint obtained in this example is 135 MPa at room temperature.

[0111] In summary, the average tensile strength of the joint obtained in Examples 1 to 14 ranges from 206 MPa to 270 MPa, and the average tensile strength of the joint obtained in Comparative Examples 1 to 3 ranges from 93 MPa to 147 MPa. It can be seen that the average tensile strength of the joint obtained in Examples 1 to 14 is much higher than that of the joint obtained in Comparative Examples 1 to 3. The NiPdTi composite foil brazing filler metal of the present application is used to braze connect molybdenum alloy and niobium alloy, and a homogeneous (Ni, Pd) Ti solid solution joint structure can be obtained, and the connection method is simple, and the average tensile strength of the molybdenum alloy / NiPdTi / niobium alloy joint obtained is high, and the optimal average shear tensile strength at room temperature can reach 270 MPa, and the mechanical properties are better.

[0112] It is apparent for those skilled in the art that the present application is not limited to the details of the foregoing exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the present application is defined by the appended claims rather than the foregoing description, and it is intended to embrace all changes and modifications that fall within the meaning and range of equivalents of the claims.

[0113] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for achieving a homogeneous joint connection between a molybdenum alloy and a niobium alloy, characterized in that: The steps include: Ni foil, Pd foil and Ti foil are placed in a vacuum furnace in a stacking order from top to bottom, and heated and pressurized to obtain NiPdTi composite foil; Grinding of molybdenum alloys and niobium alloys to be welded; cleaning the NiPdTi composite foil and the polished molybdenum alloy and niobium alloy; Placing the molybdenum alloy, the NiPdTi composite foil, and the niobium alloy in order from top to bottom to obtain a workpiece to be welded, and applying a preset pressure to a side of the molybdenum alloy facing away from the NiPdTi composite foil; The workpiece to be welded is placed in a vacuum brazing furnace, and the vacuum degree in the vacuum brazing furnace reaches 2×10 ～3 Pa~5.0×10 ～3 Pa, start heating, and keep the brazing temperature at 1120℃~1180℃ for 1min~30min to obtain a connection joint.

2. The welding method according to claim 1, wherein: The steps of placing Ni foil, Pd foil and Ti foil in a vacuum furnace in a stacking order from top to bottom, heating and pressurizing, and obtaining NiPdTi composite foil specifically include: Ni foil, Pd foil and Ti foil are placed in a vacuum furnace in a stacking order from top to bottom, a pressure of 1.5MPa to 2.5MPa is applied on the Ni foil, and the Ni foil is heated to 750°C to 850°C and kept warm for 15min to 25min. After cooling to room temperature, a NiPdTi composite foil is obtained.

3. The welding method according to claim 1, wherein: In the NiPdTi composite foil, the mass fraction of Ni is 25 wt.% to 27 wt.%, the content of Pd is 38 wt.% to 40 wt.%, and the remainder is Ti.

4. The welding method according to claim 1, wherein: The NiPdTi composite foil has a thickness of 155 μm to 175 μm.

5. The welding method according to claim 1, wherein: The molybdenum alloy is one of pure Mo, Mo-Re, and TZM, and the niobium alloy is one of pure Nb and Nb-Zr.

6. The welding method according to claim 1, wherein: The step of grinding the molybdenum alloy and the niobium alloy to be welded comprises: The parts to be welded of the molybdenum alloy and the niobium alloy were polished in sequence using SiC sandpapers of 400 mesh, 800 mesh, 1200 mesh and 2000 mesh.

7. The welding method according to claim 1, wherein: The step of cleaning the NiPdTi composite foil and the polished molybdenum alloy and the niobium alloy comprises: The NiPdTi composite foil and the polished molybdenum alloy and niobium alloy are immersed in acetone, ultrasonically cleaned for 10 to 30 minutes, and then dried. They are then placed in an ethanol solution for ultrasonic cleaning for 10 to 20 minutes and then dried.

8. The welding method according to claim 1, wherein: The brazing heating rate is 5°C / min to 20°C / min.

9. The welding method according to claim 1, wherein: The step of keeping the brazing temperature at 1120° C. to 1180° C. for 1 to 30 minutes further comprises: The workpiece to be welded after heat preservation is cooled to room temperature, wherein the cooling rate of the workpiece to be welded is 5° C. / min to 10° C. / min.

10. A connecting joint, characterized in that: The method is prepared by the welding method according to any one of claims 1 to 9.

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