Process for diffusion bonding of titanium / copper dissimilar materials and improving the strength and ductility of the joint

Abstract

Titanium / copper dissimilar material diffusion connection and process method for improving joint strength and plasticity, the present application aims to solve the problem of low joint strength and poor plasticity of titanium / copper dissimilar material direct diffusion connection. The process method for improving the strength and plasticity of the joint is: 1. Grooves or array grooves are processed on the welding surface of at least one of the copper workpiece and the titanium workpiece, and short carbon fibers or whiskers are filled into the grooves or array grooves of the workpiece; 2. The welding surface of the copper workpiece and / or the titanium workpiece is treated by friction stir head; 3. Vacuum diffusion connection is carried out at a temperature of 550-900 DEG C; 4. Low-temperature tempering treatment. The present application forms a tortuous interface structure morphology by the random direction distribution of short carbon fibers at the titanium / copper diffusion connection interface, prolongs the crack propagation path during joint failure process, and improves the plasticity of the joint; the dispersion distribution of carbon fibers enhances the strength of the joint by pinning and strengthening the material organization at the interface.

Description

Technical Field

[0001] The invention belongs to the field of diffusion bonding of dissimilar materials, and in particular relates to a titanium / copper dissimilar material diffusion bonding method for improving the strength and plasticity of a connection joint. Background Art

[0002] Titanium alloy is an excellent lightweight material with excellent corrosion resistance and high specific strength. Copper alloy has excellent thermal and electrical conductivity, and its ease of processing makes it a common industrial material. Heat sinks and heat exchangers constructed by connecting corrosion-resistant titanium alloys with high-thermal-conductivity copper alloys are widely used in industries such as energy, chemical engineering, and thermal power plants.

[0003] Among the current metallurgical bonding methods for titanium and copper alloys, diffusion bonding has become a popular choice due to its advantages, such as high bonding precision and a small heat-affected zone. However, in direct diffusion bonding of titanium / copper dissimilar materials, a relatively high bonding temperature of 800-900°C is typically used to achieve a reliable interface, which in turn guarantees the static load strength of the joint. However, at high temperatures, a thick Ti-Cu intermetallic compound layer, such as TiCu4, Ti2Cu, and TiCu, forms at the diffusion interface. Furthermore, at temperatures above 820°C, TiCu2 and T2Cu3 phases, which have high growth activation energies, may also form. The latter phases are hard and brittle relative to the parent materials, resulting in a large strength-to-ductility gradient within the joint. In the weld seam of the joint, cracks initiated at the straight interface formed by the Ti / compound layer / Cu rapidly propagate through the entire interface during the load-bearing failure phase, exhibiting a typical brittle fracture failure mode and resulting in poor joint ductility. In actual industrial applications and production activities, to ensure component performance, the contradiction between high strength and low plasticity in joints can be alleviated through design redundancy. However, the losses caused by the instantaneous failure of low-plasticity joints are difficult to avoid. Therefore, seeking to develop a solution to synergistically improve the strength and plasticity of titanium / copper dissimilar materials in direct diffusion bonding is of great significance and has good industrial application value. Summary of the Invention

[0004] The present invention aims to solve the current problems of low strength and poor plasticity of direct diffusion bonding joints of titanium / copper dissimilar materials, and provide a method that can achieve synergistic improvement of strength and plasticity of diffusion bonding joints of titanium / copper dissimilar materials, thereby alleviating the contradiction between dual improvement of joint strength and plasticity.

[0005] The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity of the present invention is achieved by the following steps:

[0006] Step 1: machining grooves or array grooves on the surface to be welded of at least one of the copper workpiece and the titanium workpiece, cleaning and drying the copper workpiece and the titanium workpiece, and uniformly filling the grooves or array grooves of the copper workpiece and / or the titanium workpiece with short carbon fibers or whiskers having a length of 0.1 to 60 μm to obtain a fiber-filled copper workpiece and / or titanium workpiece;

[0007] Step 2: Clamp the fiber-filled copper workpiece and / or titanium workpiece on the workbench of the friction stir device, and perform friction stir surface treatment on the surface to be welded of the copper workpiece and / or titanium workpiece by the friction stir head to obtain a copper workpiece and / or titanium workpiece with composite fiberized surface;

[0008] Step 3: Grinding and polishing the surface of the copper workpiece and / or titanium workpiece to be welded, the surfaces of the copper workpiece and the titanium workpiece to be welded are brought into contact with each other, and a connecting pressure is applied. Vacuum diffusion bonding is performed in a vacuum diffusion furnace at a temperature of 550 to 900° C. to obtain a connecting piece.

[0009] Step 4: Perform multiple low-temperature tempering treatments on the connector, control the tempering temperature to 300-550°C, complete the diffusion bonding of titanium / copper dissimilar materials and improve the strength and plasticity of the joint.

[0010] The present invention adopts the method of pre-setting grooves to fill short carbon fibers and combines stir friction surface treatment to achieve surface composite fiberization of solid copper and titanium alloy plates. The fiberized plates are cut according to the required size for diffusion connection and the surface roughness is polished, and then assembled for vacuum diffusion connection. After connection, the joints are subjected to multiple low-temperature tempering treatments according to the plasticity index requirements to obtain joints with high strength and high plasticity.

[0011] In the friction stir process, the original grains of the metal plate surface material undergo friction heat and plastic flow driven by the rigid treatment tool, dynamic recrystallization occurs to form fine grain structure, the high proportion of grain boundary characteristics of fine grain structure is beneficial to improve the atomic diffusion coefficient in the diffusion bonding process, and good metallurgical bonding of titanium and copper alloy is realized. The dispersed micron-sized short carbon fibers in the friction stir process increase the nucleation sites of recrystallization, further refine the grain size, and then improve the interdiffusion coefficient of titanium and copper alloy, so that titanium / copper low-temperature diffusion bonding can be realized, thereby avoiding the excessive generation of a large number of and various hard and brittle Ti-Cu intermetallic compounds. In addition, the carbon fibers distributed on the surface of the alloy plate are retained at the titanium / copper interface after diffusion bonding, the pinning strengthening mechanism of the short carbon fibers to the material improves the strength of the joint, and the random distribution of the fiber direction shapes the tortuous interface structure morphology, prolongs the crack propagation path during the failure process, and improves the plasticity of the joint. Through the multiple tempering heat treatment of the joint after welding, the residual stress can be reduced, and the dislocation defects of the material can be eliminated, which is helpful to obtain a high plasticity joint. The present application can realize the synergistic improvement of the strength and plasticity of the titanium / copper dissimilar material diffusion bonding joint, and has good technical application prospect and value.

[0012] The titanium / copper dissimilar material diffusion bonding and joint strength and plasticity improving process method disclosed by the present application has the following beneficial effects:

[0013] 1、The present application realizes the ultra-fining of the parent material surface grains through the friction stir surface fiberization process, improves the titanium / copper surface interface interdiffusion coefficient, thereby helps to realize low-temperature diffusion bonding, reduces the types and thickness of hard and brittle Ti-Cu intermetallic compounds, and realizes the double improvement of joint strength and plasticity.

[0014] 2、The present application shapes the tortuous interface structure morphology by the random direction distribution of the short carbon fibers at the titanium / copper diffusion bonding interface, prolongs the crack propagation path during the joint failure process, and improves the plasticity of the joint; the pinning strengthening mechanism of the dispersed carbon fibers to the material organization at the interface improves the strength of the joint.

[0015] 3、The multiple tempering heat treatment of the joint after welding can reduce the residual stress and eliminate the dislocation defects of the material, which is helpful to obtain a titanium / copper diffusion bonding joint with higher plasticity.

[0016] 4、Since the distribution direction of the short carbon fibers at the joint interface has random characteristics, the joint has uniform mechanical performance in all directions, and the anisotropy interference can be excluded in the welding structure mechanical calculation or joint actual use. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a process schematic diagram for filling short carbon fibers in the prefabricated groove.

[0018] Figure 2 Schematic diagram of the structure of the friction stir head described in the seventh embodiment;

[0019] Figure 3 Schematic diagram of the friction stir surface composite fiberization process in the present invention;

[0020] Figure 4 Schematic diagram of the process of diffusion bonding and tempering treatment in the present invention;

[0021] Figure 5 This is a temperature process curve diagram of diffusion bonding and tempering treatment in Example 1;

[0022] Figure 6 This is a microscopic electron microscope photograph of the titanium / copper diffusion interface obtained in Example 1;

[0023] Figure 7 is the tensile test curve of the joint obtained in Example 1;

[0024] Figure 8 This is a schematic diagram of the process method for diffusion bonding titanium / copper dissimilar materials and improving the strength and plasticity of the joint according to the present invention. DETAILED DESCRIPTION

[0025] Specific embodiment 1: The process method for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity in this embodiment is implemented according to the following steps:

[0026] Step 1: machining grooves or array grooves on the surface to be welded of at least one of the copper workpiece and the titanium workpiece, cleaning and drying the copper workpiece and the titanium workpiece, and uniformly filling the grooves or array grooves of the copper workpiece and / or the titanium workpiece with short carbon fibers or whiskers having a length of 0.1 to 60 μm to obtain a fiber-filled copper workpiece and / or titanium workpiece;

[0027] Step 2: Clamp the fiber-filled copper workpiece and / or titanium workpiece on the workbench of the friction stir device, and perform friction stir surface treatment on the surface to be welded of the copper workpiece and / or titanium workpiece by the friction stir head to obtain a copper workpiece and / or titanium workpiece with composite fiberized surface;

[0028] Step 3: Grinding and polishing the surface of the copper workpiece and / or titanium workpiece to be welded, the surfaces of the copper workpiece and the titanium workpiece to be welded are brought into contact with each other, and a connecting pressure is applied. Vacuum diffusion bonding is performed in a vacuum diffusion furnace at a temperature of 550 to 900° C. to obtain a connecting piece.

[0029] Step 4: Perform multiple low-temperature tempering treatments on the connector, control the tempering temperature to 300-550°C, complete the diffusion bonding of titanium / copper dissimilar materials and improve the strength and plasticity of the joint.

[0030] In this embodiment, the surface materials of the titanium and copper alloy plates undergo parent material grain crushing and dynamic recrystallization under the action of stir friction treatment, and the short carbon fibers introduced through the pre-set grooves and dispersedly distributed under the drive of the rigid stir friction treatment tool increase the crystal nucleation sites during the structural recrystallization process, thereby improving the grain refinement effect and facilitating the acquisition of an ultrafine grain structure. As a result, the fine-grained structure obtained on the surface of the alloy plate provides more channels for titanium / copper diffusion connection due to the high volume fraction of grain boundaries, improves the interdiffusion coefficient of interface atoms, and facilitates the realization of a more reliable metallurgical bonding at the interface. The fiber pinning effect at the joint interface improves the joint strength. At the same time, the random distribution of the fiber direction shapes a more tortuous interface structure morphology, prolongs the crack transmission path of joint failure, and improves the joint plasticity. Multiple tempering heat treatments of the joint after welding can reduce residual stress, eliminate defects such as material dislocations, and help to obtain a high-plasticity joint.

[0031] This embodiment is applicable to the diffusion bonding of titanium / copper dissimilar materials, and is also applicable to the bonding of the same copper alloy materials and the same titanium alloy materials.

[0032] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that the material of the copper workpiece in step 1 is pure copper, brass or bronze.

[0033] Specific embodiment three: The difference between this embodiment and specific embodiment one or two is that the material of the titanium workpiece in step one is pure titanium (TA1, TA2, TA3), TC4, TC9, TC10 or TC11.

[0034] Specific embodiment 4: The difference between this embodiment and any one of specific embodiments 1 to 3 is that the groove in step 1 is a rectangular groove, a V-shaped groove or a trapezoidal groove, and the shape of the groove is circular, square or triangular.

[0035] Specific embodiment 5: This embodiment differs from any one of specific embodiments 1 to 4 in that the short carbonaceous fibers in step 1 are one or a mixture of short carbon fibers, short silicon carbide fibers, short silicon nitride fibers, silicon carbide whiskers and silicon nitride whiskers.

[0036] Specific embodiment 6: This embodiment differs from any one of specific embodiments 1 to 5 in that the diameter of the short carbonaceous fibers in step 1 is 0.5 to 5 μm.

[0037] Specific embodiment seven: The difference between this embodiment and any one of specific embodiments one to six is ​​that in step two, the friction stir surface treatment controls the rotation speed of the friction stir head to be 200-600 rpm, the travel speed to be 20-100 mm / min, and the inclination angle to be 0-3.5°.

[0038] The friction stir head in this embodiment is in the form of a needleless flat shoulder, a needleless shoulder with an inner concave angle, and a stirring head with a stirring needle. The structures of various friction stir heads are as follows: Figure 2 shown.

[0039] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that the connection pressure applied in step three is 2-10 MPa.

[0040] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 7 in that in step 3, vacuum diffusion bonding is performed at a temperature of 650-750° C. for 20-60 minutes.

[0041] Specific embodiment ten: This embodiment differs from any one of specific embodiments one to seven in that in step four, the connecting piece is subjected to two to three low-temperature tempering treatments.

[0042] Example 1: The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity in this embodiment is implemented according to the following steps:

[0043] Step 1: Rectangular grooves with a width of 1 mm and a depth of 0.15 mm were processed on the surfaces to be welded of the C10000 copper alloy workpiece and the TC4 titanium alloy workpiece, respectively. The C10000 copper alloy workpiece and the TC4 titanium alloy workpiece were cleaned and dried, and T1000 short carbon fiber powder (such as 1000 carbon fiber powder) was evenly filled into the grooves of the C10000 copper alloy workpiece and the TC4 titanium alloy workpiece. Figure 1 As shown), the average diameter of the carbon fiber is 3 μm and the length is 20 μm, and a copper workpiece and a titanium workpiece filled with fibers are obtained;

[0044] Step 2: Clamp the copper workpiece and titanium workpiece after fiber filling on the workbench of the friction stir device, and perform friction stir surface treatment on the surfaces to be welded of the copper workpiece and titanium workpiece respectively by the friction stir head (such as Figure 3 As shown), the rotation speed of the friction stir head was controlled to be 300 rpm, the travel speed was 50 mm / min, the inclination angle was 0.4°, and the shoulder plunge depth was 0.2 mm to obtain copper and titanium workpieces with composite fiberized surfaces;

[0045] Step 3: Grind and polish the surfaces of the copper workpiece and the titanium workpiece to be welded, and then place the surfaces of the copper workpiece and the titanium workpiece to be welded together. Figure 4As shown, a connection pressure of 4 MPa was applied, and vacuum diffusion bonding was performed in a vacuum diffusion furnace at a temperature of 700° C. for 40 min to obtain a connection piece;

[0046] Step 4: Perform two low-temperature tempering treatments on the connector, control the tempering temperature to 400℃, and the tempering holding time to 30min. The process temperature curves of diffusion bonding and tempering treatment are as follows: Figure 5 As shown, a process method for completing diffusion bonding of titanium / copper dissimilar materials and improving the strength and plasticity of the joint.

[0047] The interface microstructure of the titanium / copper dissimilar alloy diffusion bonded joint obtained in this embodiment is as follows: Figure 6 As shown, it can be observed that Figure 6 There are two layers of Ti-Cu intermetallic compound layers formed by reaction on the titanium / copper diffusion interface (diffusion bonding at -700°C / 4MPa / 40min after surface stir friction composite fiberization) obtained in this embodiment shown in a. During the diffusion bonding process, the compound layer gradually grows from the interface to both sides. On the copper side, since its surface has undergone a carbon short fiber composite stir friction treatment, the compound contacts the carbon fibers inside the copper matrix after generation and continues to grow. The carbon fibers in the interface formed after the diffusion bonding is completed span the copper alloy matrix and the intermetallic compound layer. According to experimental research, the strength of conventional direct diffusion bonding of titanium / copper below 700°C is extremely low, so the titanium / copper interface with conventional direct diffusion bonding at 850°C, which has relatively high bonding strength, was selected for comparison. The conventional direct diffusion bonding is unfilled with fibers and no stir friction surface treatment is performed. By Figure 6 b It can be seen that due to the high connection temperature, the atomic diffusion of the titanium / copper interface is intensified, the Ti-Cu intermetallic compound with higher growth activation energy is overgrown, and a thicker 4-layer intermetallic compound is generated at the interface. According to mechanical experiments, the tensile strength of the titanium / copper joint obtained in Example 1 is 154MPa, and the tensile strength of the 850°C direct diffusion joint used as a reference comparison group is 113MPa. In addition, compared with the latter, the engineering strain increase rate of the tensile specimen at the same gauge length of the former reaches 314.2%, which verifies the synergistic improvement effect of the present invention on the plasticity and strength of the titanium / copper joint.

[0048] Combine Figure 8The schematic diagram shown further illustrates the beneficial effects of the present invention. After the friction stir surface composite fiberization treatment, the titanium / copper dissimilar material diffusion bonding interface forms a form in which short carbon fibers are embedded with the matrix and the titanium-copper reaction layer. When the joint fails to bear the load, crack propagation is relatively difficult, and the joint fracture presents a brittle-tough mixed fracture with the compound layer and the parent material peeling off and the fiber being pulled out. Correspondingly, the titanium / copper direct diffusion interface that is not treated by diffusion bonding according to the present invention presents a straight interface microstructure of titanium / intermetallic compound / copper, and the joint fails in a brittle fracture mode with poor plasticity. In addition, the pinning strengthening mechanism of the carbon fibers at the interface of the joint obtained in Example 1 for the alloy parent material organization has a promoting effect on the joint strength.

[0049] Example 2: The difference between this example and Example 1 is that in step 1, V-shaped grooves are processed on the surfaces to be welded of the H59 copper alloy workpiece and the TA2 titanium alloy workpiece, respectively. The groove width is 1 mm and the depth is 0.15 mm. The H59 copper alloy workpiece and the TA2 titanium alloy workpiece are cleaned and dried, respectively, and silicon carbide short fiber powder is evenly filled into the grooves of the H59 copper alloy workpiece and the TA2 titanium alloy workpiece.

[0050] Example 3: The difference between this example and Example 1 is that in step 1, an array of circular grooves with a diameter of 2 mm and a depth of 0.2 mm are processed on the surfaces to be welded of the C10000 copper alloy workpiece and the TC4 titanium alloy workpiece, with a hole pitch of 2 mm. The C10000 copper alloy workpiece and the TC4 titanium alloy workpiece are cleaned and dried respectively, and silicon nitride whiskers are evenly filled in the grooves of the C10000 copper alloy workpiece and the TC4 titanium alloy workpiece.

[0051] The present invention aims at the problem of low strength and poor plasticity of direct diffusion bonding of titanium / copper at the current stage. By introducing short carbon fibers into the metal sheet through a stir friction process, the metal sheet is subjected to surface composite fiberization treatment, and then titanium / copper vacuum diffusion bonding is performed to achieve a synergistic improvement in the strong plasticity of titanium / copper dissimilar material diffusion bonding joints. In this process, the stir friction surface treatment breaks the relatively coarse original grains in the metal matrix, and dynamic recrystallization occurs under the heat-mechanical conditions of friction heat and large plastic deformation of the metal. The short fibers filled into the tissue are helpful for multi-point nucleation of the grains and refine the grain size. There is a high volume fraction of grain boundary diffusion channel on the surface of the fine-grained metal obtained after the treatment, which is conducive to realizing titanium / copper diffusion bonding and metallurgical bonding at a lower temperature, thereby reducing the thickness and compound type of the hard and brittle Ti-Cu intermetallic compound layer generated by excessive high-temperature reaction at the interface. In addition, the fiber pinning effect in the joint improves the joint strength, and the interface shapes a more tortuous interface structure morphology due to the random distribution of the fiber direction, prolongs the crack transmission path of the joint failure, and improves the joint plasticity. Multiple post-weld tempering heat treatments can reduce residual stress and eliminate defects such as material dislocations, helping to achieve highly ductile joints. This invention can achieve a synergistic improvement in the strength and ductility of titanium / copper dissimilar material diffusion bonded joints, demonstrating promising technical results and application prospects.

Claims

1. A process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity, characterized by The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity is achieved by the following steps: Step 1: machining grooves or array grooves on the surface to be welded of at least one of the copper workpiece and the titanium workpiece, cleaning and drying the copper workpiece and the titanium workpiece, and uniformly filling the grooves or array grooves of the copper workpiece and / or the titanium workpiece with short carbon fibers or whiskers having a length of 0.1 to 60 μm to obtain a fiber-filled copper workpiece and / or titanium workpiece; Step 2: Clamp the fiber-filled copper workpiece and / or titanium workpiece on the workbench of the friction stir device, and perform friction stir surface treatment on the surface to be welded of the copper workpiece and / or titanium workpiece by the friction stir head to obtain a copper workpiece and / or titanium workpiece with composite fiberized surface; Step 3: Grinding and polishing the surface of the copper workpiece and / or titanium workpiece to be welded, the surfaces of the copper workpiece and the titanium workpiece to be welded are brought into contact with each other, and a connecting pressure is applied. Vacuum diffusion bonding is performed in a vacuum diffusion furnace at a temperature of 550 to 900° C. to obtain a connecting piece. Step 4: Perform multiple low-temperature tempering treatments on the connector, control the tempering temperature to 300-550°C, complete the diffusion bonding of titanium / copper dissimilar materials and improve the strength and plasticity of the joint.

2. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1 is characterized in that The material of the copper workpiece in step 1 is pure copper, brass or bronze.

3. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1 is characterized in that The material of the titanium workpiece in step 1 is pure titanium, TC4, TC9, TC10 or TC11.

4. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1 is characterized in that The groove in step 1 is a rectangular groove, a V-shaped groove or a trapezoidal groove, and the shape of the groove is circular, square or triangular.

5. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1 is characterized in that In step 1, the short carbon fibers are one or a mixture of short carbon fibers, short silicon carbide fibers, short silicon nitride fibers, silicon carbide whiskers and silicon nitride whiskers.

6. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1, characterized in that In step 1, the diameter of the short carbon fibers is 0.5 to 5 μm.

7. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1 is characterized in that In step 2, the friction stir surface treatment controls the rotation speed of the friction stir head to be 200-600 rpm, the travel speed to be 20-100 mm / min, and the inclination angle to be 0-3.5°.

8. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1 is characterized in that In step 3, the connection pressure applied is 2 to 10 MPa.

9. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1, characterized in that In step 3, vacuum diffusion bonding is performed at a temperature of 650-750° C. for 20-60 minutes.

10. The process for diffusion bonding titanium / copper dissimilar materials and improving joint strength and plasticity according to claim 1, characterized in that In step 4, the connecting parts are subjected to 2 to 3 low-temperature tempering treatments.

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