Titanium alloy welding method for realizing high-quality joint at ultralow temperature

Abstract

The invention discloses a titanium alloy welding method for realizing a high-quality joint at an ultralow temperature, and belongs to the field of titanium alloy welding. The invention aims to solve the technical problem of low joint quality in the existing diffusion welding method. According to the method, the to-be-welded surfaces are ground and then polished till the root mean square roughness Rq is not larger than 1.5 nm or the arithmetic mean roughness Ra is not larger than 1.0 nm, the maximum roughness depth Rmax is not larger than 50 nm, and through the multi-heat-source diffusion welding technology of pulse current and radiation heating, the microcosmic good welding effect without hole defects at the ultralow temperature of 450-550 DEG C is achieved. According to the method, the welding rate of a welded joint after welding is nearly 100%, high-quality welding is achieved, the joint has obvious yield and plastic fracture, and the tensile strength can reach 826.8599 MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy welding, and in particular relates to a titanium alloy welding method for achieving high-quality joints at ultra-low temperatures. Background Art

[0002] As an advanced solid-state connection technology, titanium alloy diffusion welding has shown great application potential in aerospace, medical equipment and high-end manufacturing industries, but it still faces many challenges in actual promotion and application. On the one hand, traditional titanium alloy diffusion welding uses hot pressing heating, which is extremely sensitive to process parameters (such as temperature, pressure, time, etc.). These conditions must be precisely controlled. Any deviation may lead to substandard joint quality, insufficient strength, reduced toughness and other problems. Overall high-temperature heating will also accelerate the structural evolution of the parent material and reduce the plastic properties of the material. On the other hand, in order to achieve the ideal welding effect, it is usually necessary to carry out the welding under high temperature and high pressure, and a long insulation time is required to ensure hole closure and interface atomic diffusion. This not only increases energy consumption and production costs, but may also cause phase change or embrittlement of the material, affecting the performance of the final product. In addition, the rough surface state will significantly prolong the time for hole closure, thereby greatly increasing the time required for diffusion welding. Summary of the invention

[0003] The present invention aims to solve the above technical problems and provides a titanium alloy welding method for achieving high-quality joints at ultra-low temperatures.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The object of the present invention is to provide a titanium alloy welding method for achieving high-quality joints at ultra-low temperatures, comprising the following steps:

[0006] Step 1: Grind the two surfaces to be welded separately and then polish them until the root mean square roughness R q Not more than 1.5nm or arithmetic mean roughness R a Not more than 1.0nm, and the maximum roughness depth R max Not more than 50nm;

[0007] Step 2, butt the surfaces to be welded after the treatment in step 1, then place them in a graphite mold, and load them into a vacuum diffusion welding furnace. The pressure system in the vacuum diffusion welding furnace applies vertical pressure to the assembly so that the surfaces to be welded fit together to obtain an assembly;

[0008] Step 3, then evacuate the chamber, perform diffusion bonding, and heat the assembly with pulse current. First, raise the temperature of the assembly to 450°C to 550°C and simultaneously raise the pressure to 5MPa to 60MPa at a certain speed, start radiation heating, ensure that the furnace temperature rises, and the assembly temperature is maintained at the insulation temperature, and keep the temperature and pressure for 5min to 10min;

[0009] Step 4: After the insulation is completed, stop the pressure system, stop the pulse current heating, continue the radiation heating, cool the furnace temperature to 200°C at a certain speed, then cool to room temperature with the furnace, break the vacuum, take out the mold and assembly, and complete the welding.

[0010] It is further defined that in step 1, grinding is carried out according to the following steps: the surface to be welded is ground using 400 mesh, 600 mesh, 800 mesh, 1200 mesh, 1500 mesh, 2000 mesh and 3000 mesh sandpaper in sequence, and then placed in acetone for ultrasonic cleaning.

[0011] Further defined, in step 1, the polishing is rough polishing first and then fine polishing. If the roughness requirement is not met, rough polishing and fine polishing need to be repeated.

[0012] It is further defined that the rough polishing is performed according to the following steps: the surface to be welded is polished with 7 μm and 2.5 μm diamond spray polishing agents in sequence, and then immediately placed in acetone for ultrasonic cleaning.

[0013] The 7 μm and 2.5 μm diamond spray polishing agents are both commercially available products purchased from Harbin Bonding Technology Co., Ltd., with model numbers BD-PG-202202 and BD-PG-202205, respectively.

[0014] It is further defined that the fine polishing is carried out according to the following steps: the surface to be welded is polished using 50nm and 20nm SiO2 suspensions in sequence, the polishing time is 30 minutes and 1 hour respectively, and immediately after polishing, it is placed in acetone for ultrasonic cleaning, and then the surface is wiped with anhydrous ethanol and blown dry with cold air.

[0015] 50nmSiO2 suspension is made by evenly dispersing high-purity silicon dioxide powder with a particle size of 50nm in deionized water, with a weight-volume ratio of 50g / L. 20nmSiO2 suspension is made by evenly dispersing high-purity silicon dioxide powder with a particle size of 20nm in deionized water, with a weight-volume ratio of 50g / L. Dispersion is performed by ultrasonic or stirring.

[0016] It is further defined that in step 3, vacuum is drawn until the vacuum degree is 5E-3Pa to 1E-2Pa.

[0017] It is further defined that in step 3, the heating rate is 100°C / min.

[0018] It is further defined that in step 3, the pressure increasing rate is 4 MPa / min.

[0019] It is further defined that in step 3, the pulse current frequency is 30kHz and the pulse current peak is 10kA; not only can in-situ heating be performed through Joule heat, but the non-thermal effects of high-frequency pulse current (including electroplastic effect, discharge effect, electron wind force, electromigration effect, etc.) can significantly promote atomic diffusion and significantly accelerate the diffusion process.

[0020] It is further defined that in step 4, the cooling rate is 10°C / min.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] In the welding process, the present invention can realize high-quality welding joints without adding an intermediate layer, thereby avoiding the occurrence of heterogeneous microscopic phenomena at the welding joints due to the introduction of the intermediate layer.

[0023] Even with the help of a multi-heat source diffusion welding method, without the use of an intermediate layer, the hole closing process, atomic diffusion, and interface homogenization process in diffusion welding still require a long time. A larger surface roughness will lead to a significant decrease in the initial bonding rate in the plastic deformation stage. Therefore, the method of the present invention promotes diffusion bonding efficiency through extremely low surface roughness.

[0024] When the surface roughness R q When the thickness is not greater than 1.5 nm, the initial bonding rate in multi-heat source diffusion welding is high. max When the hole is not larger than 50nm, the in-situ heating of high-frequency pulse current can ensure that the hole is completely closed in about 5 minutes. Without the use of an intermediate layer, the surface roughness needs to be strictly controlled to ensure high-quality welding at extremely low temperatures and in an extremely short time.

[0025] The present invention combines the ultra-fine surface polishing treatment and the multi-heat source diffusion welding technology to achieve a good welding effect without microscopic hole defects at an ultra-low temperature (450°C to 550°C, preferably 500°C). This is due to the extremely low roughness of the ultra-fine surface treatment, which ensures that the plastic deformation result of the diffusion welding is more thorough, and the initial holes are smaller and fewer. In the diffusion welding technology with simultaneous heating of multiple heat sources, the pulse current in-situ heating can rely on in-situ heating to quickly heat up the interface to be welded, and the non-thermal effect of the pulse current can promote atomic diffusion and promote diffusion welding. The diffusion welding equipment with simultaneous heating of multiple heat sources can achieve a slower cooling rate, thereby promoting the hole closing process and atomic diffusion process of diffusion welding. In addition, due to the low temperature, the parent material (parts to be welded) will not be severely deformed, thereby achieving high-quality welded joints.

[0026] In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and drawings of the present invention. However, the attached drawings are only provided for reference and illustration and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the atomic force microscope surface roughness image of Example 1;

[0028] Figure 2 This is a microstructure characterization diagram of the welded joint of Example 1;

[0029] Figure 3 This is the microstructure characterization diagram of the welded joint of Example 1

[0030] Figure 4 This is the microstructure characterization diagram of the welded joint of Example 2

[0031] Figure 5 is the joint strength diagram of Example 1;

[0032] Figure 6 This is the joint strength diagram of comparative example 1

[0033] Figure 7 This is the joint strength diagram of comparative example 2

[0034] Figure 8 It is a schematic diagram of the structure of a vacuum diffusion welding furnace with pulse current in-situ heating and molybdenum tube radiation heating. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0036] The vacuum diffusion soldering furnace used below ( Figure 8 ) A multi-heat source heating system with pulse current in-situ heating and molybdenum tube radiation heating, which is measured by the sample temperature control thermocouple and the furnace temperature control thermocouple respectively, and is regulated by the multi-heat source temperature control system, and has a pressure system with hydraulic function. In addition, the equipment mainly includes a furnace body, a vacuum system, a gas charging and discharging system, a hydraulic system, an electronic control system, a pulse DC heating system, a water cooling system, a cooling circulation system, etc. The structural diagram of the vacuum diffusion welding furnace is shown in the figure below. Figure 8 When the equipment is running, the vacuum system ensures high vacuum in the furnace; the pulse DC generator generates pulse current through the upper pressure head, mold, sample, and lower pressure head; the radiation heating heats the furnace through the molybdenum tube; the hydraulic system provides pressure to the mold and sample with the help of the upper pressure head.

[0037] Embodiment 1: In this embodiment, the titanium alloy TC4 welding method for achieving high-quality joints at ultra-low temperatures is achieved by the following steps:

[0038] Step 1: Grind and polish the surface to be welded. The specific steps are as follows:

[0039] Grinding: Grind the surface to be welded with 400 mesh, 600 mesh, 800 mesh, 1200 mesh, 1500 mesh, 2000 mesh and 3000 mesh sandpaper in sequence, and then place it in acetone for ultrasonic cleaning;

[0040] Rough polishing: The cleaned specimens to be welded were polished with 7 μm diamond spray polishing agent (diamond spray polishing agent purchased from Harbin Bonding Technology Co., Ltd., model BD-PG-202202) and 2.5 μm diamond spray polishing agent (diamond spray polishing agent purchased from Harbin Bonding Technology Co., Ltd., model BD-PG-202205) in turn, and then immediately placed in acetone for ultrasonic cleaning;

[0041] Fine polishing: After the rough polishing is completed, the surface to be welded needs to be polished with 50nm and 20nm SiO2 suspensions in turn. The 50nm SiO2 suspension is fine polished for 30 minutes, and the 20nm SiO2 suspension is fine polished for 1 hour. After polishing, it is immediately placed in acetone for ultrasonic cleaning, and then the surface is wiped with alcohol and blown dry with cold air;

[0042] The 50nmSiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 50nm in deionized water, with a weight-to-volume ratio of 50g / L. The 20nmSiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 20nm in deionized water, with a weight-to-volume ratio of 50g / L.

[0043] The roughness of the surface to be welded after grinding and polishing was tested by using AFM (atomic force microscope) to randomly select three areas and measure the root mean square roughness R of the welded part. q They are 1.22nm and 1.08nm respectively, and the corresponding maximum roughness depth R max They are 44.3nm and 30.2nm respectively, meeting the roughness requirements;

[0044] Step 2: The root mean square roughness R q The surfaces to be welded are 1.22nm and 1.08nm respectively, and then placed in a graphite mold and loaded into a vacuum diffusion welding furnace ( Figure 8 As shown in the figure, the pressure system in the vacuum diffusion welding furnace applies vertical pressure to the assembly so that the surfaces to be welded are fitted together to obtain an assembly (specimen);

[0045] Step 3: Then, evacuate the vacuum to 5E-3Pa and run the diffusion bonding process. The specific process is as follows:

[0046] First, the pulse current in-situ heating system was operated, and the sample temperature was raised to 550°C at a rate of 100°C / min;

[0047] The pulse current in-situ heating system keeps the sample warm for 10 minutes, during which the pressure is 20 MPa. At the same time, the radiation heating system is started to ensure that the furnace temperature rises and the sample temperature is maintained at the insulation temperature.

[0048] The pulse current frequency is 30kHz, and the pulse current and radiation heating power are controlled by a multi-heat source temperature control system to ensure that the temperature at the measuring point conforms to the process curve.

[0049] Step 4: After the insulation is completed, the pressure system stops running, the pulse current in-situ heating system stops running, and the radiation heating system continues to run, maintaining a furnace cooling rate of 10°C / min, cooling to 200°C, and then cooling to room temperature with the furnace, breaking the vacuum to take out the mold and sample, and completing the welding.

[0050] After welding, the samples were subjected to microstructure characterization and mechanical property tests. Microstructure characterization showed that the welding rate of the welded joint after welding was nearly 100%, achieving high-quality welding. Mechanical property tests showed that the joint showed obvious yielding and plastic fracture, and the tensile strength reached 826.8599MPa.

[0051] Comparative Example 1 uses the following steps for welding:

[0052] Step 1: Grind and polish the surface to be welded. The specific steps are as follows:

[0053] Grinding: Grind the surface to be welded with 400 mesh, 600 mesh, 800 mesh, 1200 mesh, 1500 mesh, 2000 mesh and 3000 mesh sandpaper in sequence, and then place it in acetone for ultrasonic cleaning;

[0054] Rough polishing: The cleaned specimens to be welded were polished with 7 μm diamond spray polishing agent (diamond spray polishing agent purchased from Harbin Bonding Technology Co., Ltd., model BD-PG-202202) and 2.5 μm diamond (diamond spray polishing agent purchased from Harbin Bonding Technology Co., Ltd., model BD-PG-202205) spray polishing agent in turn, and then immediately placed in acetone for ultrasonic cleaning;

[0055] Fine polishing: After the rough polishing is completed, the surface to be welded needs to be polished with 50nm and 20nm SiO2 suspensions in turn. The 50nm SiO2 suspension is fine polished for 30 minutes, and the 20nm SiO2 suspension is fine polished for 1 hour. After polishing, it is immediately placed in acetone for ultrasonic cleaning, and then the surface is wiped with alcohol and blown dry with cold air;

[0056] The 50nmSiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 50nm in deionized water, with a weight-to-volume ratio of 50g / L. The 20nmSiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 20nm in deionized water, with a weight-to-volume ratio of 50g / L.

[0057] The roughness of the surface to be welded after grinding and polishing was tested by using AFM (atomic force microscope) to randomly select three areas and measure the root mean square roughness R of the welded part. q They are 1.34nm and 1.17nm respectively, and the corresponding maximum roughness depth R max They are 37.9nm and 41.1nm respectively, meeting the roughness requirements;

[0058] Step 2: The root mean square roughness R q The surfaces to be welded are 1.34nm and 1.17nm respectively, and then placed in a graphite mold and loaded into a vacuum diffusion welding furnace ( Figure 8 As shown in the figure, the pressure system in the vacuum diffusion welding furnace applies vertical pressure to the assembly so that the surfaces to be welded are fitted together to obtain an assembly (specimen);

[0059] Step 3: Then, evacuate the vacuum to 5E-3Pa and run the diffusion bonding process. The specific process is as follows:

[0060] First, the pulse current in-situ heating system was operated, and the sample temperature was raised to 550°C at a rate of 100°C / min;

[0061] The single pulse current in-situ heating system maintains the sample temperature for 10 min, and the pressure during the temperature maintenance period is 20 MPa;

[0062] The pulse current frequency is 30kHz, and the pulse current is controlled by a multi-heat source temperature control system to ensure that the temperature at the measuring point conforms to the process curve.

[0063] Step 4: After the insulation is completed, the pressure system stops running, the pulse current in-situ heating system stops running, and then the temperature is cooled down to room temperature with the furnace, the vacuum is broken, the mold and the sample are taken out, and the welding is completed.

[0064] After welding, the samples were subjected to microstructure characterization and mechanical property tests. Microstructure characterization showed that the welding rate of the welded joint after welding was nearly 80%, and several single holes and some flat holes appeared in the joint. Mechanical property tests showed that the joint showed yielding phenomenon, and the tensile strength reached 651.5072MPa.

[0065] Comparative Example 2 uses the following steps for welding:

[0066] Step 1: Grind and polish the surface to be welded. The specific steps are as follows:

[0067] Grinding: The surface to be welded is ground with 400 mesh, 600 mesh, 800 mesh, 1200 mesh, and 1500 mesh sandpaper in sequence, and then ultrasonically cleaned in acetone; no rough polishing or fine polishing is performed. No roughness test is performed.

[0068] Step 2: Butt the surfaces to be welded, place them in a graphite mold, and load them into a vacuum diffusion welding furnace ( Figure 8 As shown in the figure, the pressure system in the vacuum diffusion welding furnace applies vertical pressure to the assembly so that the surfaces to be welded are fitted together to obtain an assembly (specimen);

[0069] Step 3: Then, evacuate the vacuum to 5E-3Pa and run the diffusion bonding process. The specific process is as follows:

[0070] First, the pulse current in-situ heating system was operated, and the sample temperature was raised to 550°C at a rate of 100°C / min;

[0071] The pulse current in-situ heating system keeps the sample warm for 10 minutes, during which the pressure is 20 MPa. At the same time, the radiation heating system is started to ensure that the furnace temperature rises and the sample temperature is maintained at the insulation temperature.

[0072] The pulse current frequency is 30kHz, and the pulse current and radiation heating power are controlled by a multi-heat source temperature control system to ensure that the temperature at the measuring point conforms to the process curve.

[0073] Step 4: After the insulation is completed, the pressure system stops running, the pulse current in-situ heating system stops running, and the radiation heating system continues to run, maintaining a furnace cooling rate of 10°C / min, cooling to 200°C, and then cooling to room temperature with the furnace, breaking the vacuum to take out the mold and sample, and completing the welding.

[0074] After welding, the samples were subjected to microstructure characterization and mechanical property tests. Microstructure characterization showed that the welding rate of the welded joint after welding was nearly 40%, and several long coin-shaped unwelded areas appeared in the joint. Mechanical property tests showed that the joint did not undergo plastic deformation, the fracture mode was brittle fracture, and the tensile strength reached 93.0471MPa.

[0075] By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the method of the present invention achieves high-quality welding of titanium alloy at ultra-low temperature, with a joint welding rate of nearly 100% and a tensile strength of 826.8599 MPa.

[0076] The above describes the specific embodiments of the present invention. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essential content of the present invention.

Claims

1. A titanium alloy welding method for achieving high-quality joints at ultra-low temperatures, characterized in that: The following steps are involved: Step 1: Grind the two surfaces to be welded separately and then polish them until the root mean square roughness R q Not more than 1.5nm or arithmetic mean roughness R a Not more than 1.0nm, and the maximum roughness depth R max Not more than 50nm; Step 2, butt the surfaces to be welded after the treatment in step 1, then place them in a graphite mold, and load them into a vacuum diffusion welding furnace. The pressure system in the vacuum diffusion welding furnace applies vertical pressure to the assembly so that the surfaces to be welded fit together to obtain an assembly; Step 3, then evacuate the chamber, perform diffusion bonding, and heat the assembly with pulse current. First, raise the temperature of the assembly to 450°C to 550°C and simultaneously raise the pressure to 5MPa to 60MPa at a certain speed, start radiation heating, ensure that the furnace temperature rises, and the assembly temperature is maintained at the insulation temperature, and keep the temperature and pressure for 5min to 10min; Step 4: After the insulation is completed, stop the pressure system, stop the pulse current heating, continue the radiation heating, cool the furnace temperature to 200°C at a certain speed, then cool to room temperature with the furnace, break the vacuum, take out the mold and assembly, and complete the welding.

2. The method according to claim 1, characterized in that: The grinding was carried out according to the following steps: the surface to be welded was ground using 400 mesh, 600 mesh, 800 mesh, 1200 mesh, 1500 mesh, 2000 mesh and 3000 mesh sandpaper in sequence, and then placed in acetone for ultrasonic cleaning.

3. The method according to claim 1, characterized in that: Polishing is rough polishing first and then fine polishing.

4. The method according to claim 3, characterized in that: Rough polishing was performed as follows: the surface to be welded was polished with 7 μm and 2.5 μm diamond spray polishes in sequence, and then immediately placed in acetone for ultrasonic cleaning.

5. The method according to claim 3, characterized in that: Fine polishing is carried out according to the following steps: 50nm and 20nm SiO2 suspensions are used to polish the surface to be welded, the polishing time is 30 minutes and 1 hour respectively, and immediately after polishing, it is placed in acetone for ultrasonic cleaning, and then the surface is wiped with anhydrous ethanol and blown dry with cold air.

6. The method according to claim 1, characterized in that: The vacuum degree is 5E-3Pa~1E-2Pa.

7. The method according to claim 1, characterized in that: The holding temperature was 550°C and the pressure during the holding period was 20 MPa.

8. The method according to claim 1, characterized in that: The heating rate was 100°C / min, and the pressure increase rate was 4 MPa / min.

9. The method according to claim 1, characterized in that: The pulse current frequency is 30kHz and the pulse current peak value is 10kA.

10. The method according to claim 1, characterized in that: The cooling rate is 10℃ / min.

Images