A method for achieving high-quality joints in titanium alloys at ultra-low temperatures

Abstract

This invention discloses a titanium alloy welding method for achieving high-quality joints at ultra-low temperatures, belonging to the field of titanium alloy welding. This invention aims to solve the technical problem of low joint quality in existing diffusion welding methods. The method involves grinding and polishing the surfaces to be welded until the root mean square roughness R is achieved. q Not greater than 1.5 nm or arithmetic mean roughness R a Not greater than 1.0 nm, and the maximum roughness depth R max This invention employs a multi-heat source diffusion welding technique involving pulsed current and radiative heating with a wavelength not exceeding 50 nm, achieving excellent welding results with no microscopic pore defects at ultra-low temperatures (450℃~550℃). The method produces a weld joint with a near 100% weld bonding rate, achieving high-quality welding. Furthermore, the joint exhibits significant yielding and ductile fracture, with a tensile strength reaching 826.8599 MPa.

Description

Technical Field

[0001] This invention belongs to the technical field of titanium alloy welding, specifically, it relates to a titanium alloy welding method for achieving high-quality joints at ultra-low temperatures. Background Technology

[0002] Titanium alloy diffusion welding, as an advanced solid-state joining technology, has shown great application potential in aerospace, medical devices, and high-end manufacturing. However, it still faces many challenges in practical promotion and application. On the one hand, traditional titanium alloy diffusion welding uses hot-press heating, which is extremely sensitive to process parameters (such as temperature, pressure, and time). These conditions must be precisely controlled; even slight deviations can lead to substandard joint quality, resulting in insufficient strength and reduced toughness. Overall high-temperature heating also accelerates the structural evolution of the base material, reducing its plasticity. On the other hand, to achieve ideal welding results, it usually needs to be carried out under high temperature and high pressure, requiring a long holding time to ensure pore closure and interfacial atomic diffusion. This not only increases energy consumption and production costs but may also cause material phase transformation or embrittlement, affecting the performance of the final product. Furthermore, a rough surface condition significantly prolongs the pore closure time, thus greatly increasing the time required for diffusion welding. Summary of the Invention

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

[0004] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0005] The purpose of this invention is to provide a method for welding titanium alloys to achieve high-quality joints at ultra-low temperatures, comprising the following steps:

[0006] Step 1: Grind and polish the two surfaces to be welded separately until the root mean square roughness R is achieved. q Not greater than 1.5 nm or arithmetic mean roughness R a Not greater than 1.0 nm, and the maximum roughness depth R max No larger than 50nm;

[0007] Step 2: Butt the surfaces to be welded after Step 1, then place them in a graphite mold and put 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, thus obtaining the assembly.

[0008] Step 3: Then, vacuum the furnace and perform diffusion bonding. Use pulsed current to heat the assembly. First, raise the temperature of the assembly to 450℃~550℃ at a certain speed and simultaneously increase the pressure to 5MPa~60MPa. Start radiant heating to ensure that the furnace temperature rises and the assembly temperature is maintained at the holding temperature for 5min~10min.

[0009] Step 4: After the heat preservation is completed, stop the operation of the pressure system and the pulse current heating. The radiant heating continues to run, and the furnace temperature is cooled to 200°C at a certain rate. Then, the furnace is cooled to room temperature. The vacuum is broken to remove the mold and assembly parts, and the welding is completed.

[0010] Further specifying, in step 1, the grinding is performed as follows: the surface to be welded is ground sequentially using 400 grit, 600 grit, 800 grit, 1200 grit, 1500 grit, 2000 grit and 3000 grit sandpaper, and then placed in acetone for ultrasonic cleaning.

[0011] To further specify, in step 1, polishing is performed by first rough polishing and then fine polishing. If the surface roughness requirement is not met, both rough and fine polishing need to be repeated.

[0012] To be further specified, the rough polishing is performed by the following steps: the surface to be welded is polished sequentially with diamond spray polishing agents of 7μm and 2.5μm, and then immediately placed in acetone for ultrasonic cleaning.

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

[0014] To further specify, the fine polishing is performed according to the following steps: the surface to be welded is polished sequentially with 50nm and 20nm SiO2 suspensions for 30 minutes and 1 hour respectively. After polishing, it is immediately placed in acetone for ultrasonic cleaning, then wiped with anhydrous ethanol and dried with cold air.

[0015] The 50nm SiO2 suspension is made by uniformly dispersing high-purity silica powder with a particle size of 50nm in deionized water at a weight-to-volume ratio of 50g / L. The 20nm SiO2 suspension is made by uniformly dispersing high-purity silica powder with a particle size of 20nm in deionized water at a weight-to-volume ratio of 50g / L. The dispersion is carried out by ultrasonication or stirring.

[0016] Further specifying, in step 3, the vacuum is evacuated until the vacuum level is 5E-3Pa to 1E-2Pa.

[0017] Further specifying, in step 3, the heating rate is 100℃ / min.

[0018] Further specifying, in step 3, the pressurization rate is 4 MPa / min.

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

[0020] Further specifying, in step 4, the cooling rate is 10℃ / min.

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

[0022] This invention achieves high-quality weld joints without the need for an intermediate layer during the welding process, avoiding heterogeneous microscopic phenomena at the weld joint caused by the introduction of an intermediate layer.

[0023] Even with the aid of a multi-heat source diffusion welding method, the pore closure process, atomic diffusion, and interface homogenization process in diffusion welding still require a long time without the use of an intermediate layer. A large surface roughness will lead to a significant reduction in the initial bonding rate during 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 initial bonding rate is not greater than 1.5 nm, it is relatively high in multi-heat source diffusion bonding. Meanwhile, in R... max When the aperture is no larger than 50 nm, in-situ heating with high-frequency pulsed current can ensure complete closure of the aperture in about 5 minutes. Without using an intermediate layer, strict control of surface roughness is required to ensure high-quality welding at extremely low temperatures and in extremely short times.

[0025] This invention achieves excellent welding results with no microscopic pores at ultra-low temperatures (450℃~550℃, preferably 500℃) by combining ultra-fine surface polishing and multi-heat source diffusion welding technology. This is due to the extremely low roughness of the ultra-fine surface treatment, which ensures more thorough plastic deformation in diffusion welding, resulting in smaller and fewer initial pores. In the multi-heat source simultaneous heating diffusion welding technology, pulsed current in-situ heating can rapidly raise the temperature at the interface to be welded, while the non-thermal effect of the pulsed current promotes atomic diffusion, thus facilitating diffusion welding. The multi-heat source simultaneous heating diffusion welding equipment can achieve a slower cooling rate, thereby promoting the pore closure and atomic diffusion processes in diffusion welding. Furthermore, due to the lower temperature, the base material (workpiece) will not undergo severe deformation, thus achieving a high-quality weld joint.

[0026] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0027] Figure 1 This is a surface roughness diagram obtained using an atomic force microscope in Example 1;

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

[0029] Figure 3 Microstructure characterization diagram of welded joint in Comparative Example 1

[0030] Figure 4 Microstructure characterization diagram of welded joint in Comparative Example 2

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

[0032] Figure 6 Comparative Example 1 Joint Strength Diagram

[0033] Figure 7 Comparative Example 2 Joint Strength Diagram

[0034] Figure 8 This is a schematic diagram of a vacuum diffusion welding furnace with pulsed current in-situ heating and molybdenum tube radiation heating. Detailed Implementation

[0035] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, while not limiting the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0036] The vacuum diffusion welding furnace used below ( Figure 8 The system features a multi-source heating system with pulsed current in-situ heating and molybdenum tube radiant heating. Temperature measurements are taken by thermocouples controlling the sample temperature and those controlling the furnace temperature, respectively. The system is regulated by a multi-source temperature control system and also includes a hydraulic pressure system. Furthermore, the equipment mainly comprises a furnace body, vacuum system, gas filling and discharging system, hydraulic system, electrical control system, pulsed DC heating system, water cooling system, and cooling circulation system. A schematic diagram of the vacuum diffusion welding furnace is shown below. Figure 8 As shown. During equipment operation, the vacuum system ensures a high vacuum inside the furnace; the pulsed DC generator generates pulsed current through the upper pressure head, mold, sample, and lower pressure head; radiant heating heats the furnace through molybdenum tubes; and the hydraulic system provides pressure to the mold and sample via the upper pressure head.

[0037] Example 1: The method for achieving high-quality joints in titanium alloy TC4 at ultra-low temperatures in this example is implemented through 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 in sequence with 400 grit, 600 grit, 800 grit, 1200 grit, 1500 grit, 2000 grit and 3000 grit sandpaper, and then place it in acetone for ultrasonic cleaning;

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

[0041] Fine polishing: After rough polishing, the surface to be welded needs to be polished in sequence with 50nm and 20nm SiO2 suspensions. Fine polishing with 50nm SiO2 suspension for 30 minutes and fine polishing with 20nm SiO2 suspension for 1 hour. After polishing, it should be placed in acetone for ultrasonic cleaning, then wiped with alcohol and dried with cold air.

[0042] The 50nm SiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 50nm in deionized water at a weight-to-volume ratio of 50g / L. The 20nm SiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 20nm in deionized water at a weight-to-volume ratio of 50g / L.

[0043] The surface roughness of the workpiece after grinding and polishing was tested by randomly selecting three areas using AFM (atomic force microscopy) and measuring the root mean square roughness R of the workpiece. q The corresponding maximum roughness depths R are 1.22 nm and 1.08 nm, respectively. max The wavelengths are 44.3 nm and 30.2 nm respectively, which meet the roughness requirements;

[0044] Step 2: Set the root mean square roughness R q The surfaces to be soldered are 1.22nm and 1.08nm respectively, then placed in a graphite mold and loaded into a vacuum diffusion soldering furnace. Figure 8 Inside the vacuum diffusion welding furnace (as shown), the pressure system applies vertical pressure to the assembly to make the surfaces to be welded fit together, thus obtaining the assembly (sample).

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

[0046] First, the pulsed current in-situ heating system was operated, and the sample temperature was raised at a rate of 100℃ / min, reaching 550℃.

[0047] The pulsed current in-situ heating system maintains the sample temperature for 10 minutes, with a pressure of 20 MPa during the holding period. At the same time, the radiation heating system is activated to ensure that the furnace temperature rises and the sample temperature is maintained at the holding temperature.

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

[0049] Step 4: After the heat preservation 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 cooling rate of 10℃ / min in the furnace until it reaches 200℃. Then, the furnace is cooled down to room temperature. The vacuum is broken to remove the mold and sample, and the welding is completed.

[0050] After welding, the samples underwent microstructural characterization and mechanical property testing. Microstructural characterization showed that the weld joint achieved a near 100% fusion rate, demonstrating high-quality welding. Mechanical property testing showed that the joint exhibited significant yielding and ductile fracture, with a tensile strength of 826.8599 MPa.

[0051] Comparative Example 1 was welded using the following steps:

[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 in sequence with 400 grit, 600 grit, 800 grit, 1200 grit, 1500 grit, 2000 grit and 3000 grit sandpaper, and then place it in acetone for ultrasonic cleaning;

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

[0055] Fine polishing: After rough polishing, the surface to be welded needs to be polished in sequence with 50nm and 20nm SiO2 suspensions. Fine polishing with 50nm SiO2 suspension for 30 minutes and fine polishing with 20nm SiO2 suspension for 1 hour. After polishing, it should be placed in acetone for ultrasonic cleaning, then wiped with alcohol and dried with cold air.

[0056] The 50nm SiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 50nm in deionized water at a weight-to-volume ratio of 50g / L. The 20nm SiO2 suspension is made by ultrasonically dispersing high-purity (99.999% mass purity) silica powder with a particle size of 20nm in deionized water at a weight-to-volume ratio of 50g / L.

[0057] The surface roughness of the workpiece after grinding and polishing was tested by randomly selecting three areas using AFM (atomic force microscopy) and measuring the root mean square roughness R of the workpiece. q The corresponding maximum roughness depths R are 1.34 nm and 1.17 nm, respectively. max The wavelengths are 37.9 nm and 41.1 nm respectively, which meet the roughness requirements;

[0058] Step 2: Set the root mean square roughness R q The surfaces to be soldered are 1.34nm and 1.17nm respectively, then placed in a graphite mold and loaded into a vacuum diffusion soldering furnace. Figure 8 Inside the vacuum diffusion welding furnace (as shown), the pressure system applies vertical pressure to the assembly to make the surfaces to be welded fit together, thus obtaining the assembly (sample).

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

[0060] First, the pulsed current in-situ heating system was operated, and the sample temperature was raised at a rate of 100℃ / min, reaching 550℃.

[0061] The single-pulse current in-situ heating system maintained the sample temperature for 10 minutes, with a pressure of 20 MPa during the holding period.

[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 heat preservation is completed, the pressure system stops running, the pulse current in-situ heating system stops running, and then the furnace is cooled down to room temperature. The vacuum is broken to remove the mold and sample, and the welding is completed.

[0064] After welding, the samples underwent microstructural characterization and mechanical property testing. Microstructural characterization showed that the weld joint had a weld fusion rate of nearly 80%, with several single pores and some flat pores appearing in the joint. Mechanical property testing showed that the joint exhibited yielding behavior, with a tensile strength of 651.5072 MPa.

[0065] Comparative Example 2 was welded using the following steps:

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

[0067] Grinding: The surfaces to be welded are successively ground with 400-grit, 600-grit, 800-grit, 1200-grit, and 1500-grit sandpaper, and then ultrasonically cleaned in acetone; no coarse or fine polishing is performed. No roughness test is performed.

[0068] Step 2: Butt the surfaces to be welded together, then place them in a graphite mold and load them into a vacuum diffusion welding furnace. Figure 8 Inside the vacuum diffusion welding furnace (as shown), the pressure system applies vertical pressure to the assembly to make the surfaces to be welded fit together, thus obtaining the assembly (sample).

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

[0070] First, the pulsed current in-situ heating system was operated, and the sample temperature was raised at a rate of 100℃ / min, reaching 550℃.

[0071] The pulsed current in-situ heating system maintains the sample temperature for 10 minutes, with a pressure of 20 MPa during the holding period. At the same time, the radiation heating system is activated to ensure that the furnace temperature rises and the sample temperature is maintained at the holding temperature.

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

[0073] Step 4: After the heat preservation 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 cooling rate of 10℃ / min in the furnace until it reaches 200℃. Then, the furnace is cooled down to room temperature. The vacuum is broken to remove the mold and sample, and the welding is completed.

[0074] After welding, the samples were characterized by microstructure and tested for mechanical properties. Microstructure characterization showed that the weld joint had a weld fusion rate of nearly 40%, with several long, coin-shaped unwelded areas appearing at the joint. Mechanical property testing showed that the joint did not undergo plastic deformation, and the fracture mode was brittle fracture, with a tensile strength of 93.0471 MPa.

[0075] 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 alloys at ultra-low temperatures, with a joint welding rate of nearly 100% and a tensile strength of 826.8599 MPa.

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

Claims

1. A method for welding titanium alloys to achieve high-quality joints at ultra-low temperatures, characterized in that, Includes the following steps: Step 1: Grind and polish the two surfaces to be welded separately until the root mean square roughness R is achieved. q Not greater than 1.5 nm or arithmetic mean roughness R a Not greater than 1.0 nm, and the maximum roughness depth R max No larger than 50nm; Step 2: Butt the surfaces to be welded after Step 1, then place them in a graphite mold and put 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, thus obtaining the assembly. Step 3: Then, vacuum the furnace and perform diffusion bonding. Use pulsed current to heat the assembly. First, raise the temperature of the assembly to 450℃~550℃ at a certain speed and simultaneously increase the pressure to 5MPa~60MPa. Start radiant heating to ensure that the furnace temperature rises and the assembly temperature is maintained at the holding temperature for 5min~10min. Step 4: After the heat preservation is completed, stop the operation of the pressure system and the pulse current heating. The radiant heating continues to run, and the furnace temperature is cooled to 200°C at a certain rate. Then, the furnace is cooled to room temperature. The vacuum is broken to remove the mold and assembly parts, and the welding is completed. The grinding is performed as follows: the surface to be welded is ground sequentially with 400 grit, 600 grit, 800 grit, 1200 grit, 1500 grit, 2000 grit and 3000 grit sandpaper, and then placed in acetone for ultrasonic cleaning; Polishing involves first rough polishing and then fine polishing; Rough polishing is performed as follows: the surface to be welded is polished sequentially with 7μm and 2.5μm diamond spray polishing agent, and then immediately placed in acetone for ultrasonic cleaning; Fine polishing is performed as follows: the surface to be welded is polished sequentially with 50nm and 20nm SiO2 suspensions for 30 minutes and 1 hour respectively. After polishing, it is immediately placed in acetone for ultrasonic cleaning, then wiped with anhydrous ethanol and dried with cold air. The insulation temperature is 550℃, and the pressure during the insulation period is 20MPa; The heating rate is 100℃ / min, and the pressure increase rate is 4MPa / min; The pulse current frequency is 30kHz, and the peak pulse current is 10kA. The cooling rate is 10℃ / min.

2. The method according to claim 1, characterized in that, The vacuum level is 5E-3Pa to 1E-2Pa.

Images