Welding processing control method and device for niobium material workpiece

Abstract

The present invention discloses a welding process control method and device for a niobium material workpiece, wherein the welding process control method for the niobium material workpiece includes: applying a main magnetic field at the welding joint and superimposing a pulse magnetic field and a first oscillating acoustic field to form a composite physical field; performing preheating treatment and high-frequency oscillating magnetic field regulation under the action of the composite physical field; forming a quasi-steady-state organizational structure with chain-grid arrangement characteristics by electron beam welding; adjusting field parameters according to a predetermined rate of change to achieve organizational transformation control; and finally optimizing the organization through the combined action of a pulse magnetic field and low-frequency acoustic vibration. The technical solution of the present invention realizes the homogenization control of the grain orientation in the weld area through the synergistic action of the composite physical field, effectively suppresses the formation of large-angle grain boundaries, and ensures the stability of the superconducting performance of the weld joint in an extremely low temperature environment.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting material welding and manufacturing, and in particular to a welding processing control method and device for a niobium material workpiece. Background Art

[0002] Niobium material workpieces are widely used in the field of superconducting cavity manufacturing due to their excellent superconducting properties, especially in large particle accelerators, quantum computers and nuclear magnetic resonance equipment. Superconducting cavities are the core components for particle acceleration and quantum bit manipulation. In the manufacturing process of superconducting cavities, multiple niobium plates need to be spliced ​​together through welding processes. The most critical welding area is the equatorial weld position. The welding quality of this position directly determines the superconducting performance of the entire cavity in an extremely low temperature environment.

[0003] At present, the welding of niobium material workpieces mainly adopts electron beam welding process, and the welding operation is carried out in a vacuum environment. However, due to the special crystal characteristics of niobium material with body-centered cubic structure, niobium atoms tend to grow preferentially in the lattice during the welding thermal cycle, which makes it easy for the weld metal to form columnar crystals with strong orientation during the solidification process. Large-angle grain boundaries (35-55°) are formed between these grains with strong orientation, which makes the superconducting electron pairs strongly scattered when passing through grains with different orientations, seriously affecting the stability of superconducting performance. Especially in the extremely low temperature working environment below 2 Kelvin, this grain orientation inhomogeneity will lead to significant fluctuations in superconducting performance. What is more serious is that these large-angle grain boundaries often become the enriched areas of low-melting-point liquid film, which are very easy to crack under the action of welding stress, and finally lead to the degradation of superconducting cavity performance. Summary of the invention

[0004] The main purpose of the present invention is to solve the technical problem that in the existing niobium material welding process, due to the preferential growth of grains, large-angle grain boundaries are formed, causing superconducting electron pair scattering.

[0005] A first aspect of the present invention provides a welding process control method for a niobium material workpiece, the welding process control method for a niobium material workpiece comprising:

[0006] Applying a main magnetic field at the weld joint of the niobium material workpiece, and superimposing a pulsed magnetic field and a first oscillating acoustic field on the main magnetic field to form a composite physical field, wherein the main magnetic field forms a predetermined angle with the direction of the weld joint;

[0007] Under the action of the composite physical field, the weld joint is heated to a preset temperature, and a high-frequency oscillating magnetic field is applied to arrange the grains at the weld joint in a predetermined orientation;

[0008] Keeping the composite physical field stable, electron beam welding is used to form a quasi-stable organizational structure with chain-grid arrangement characteristics at the welded joint, wherein the quasi-stable organizational structure includes a low-energy subgrain boundary network and a honeycomb dislocation structure;

[0009] Adjust the main magnetic field strength and the first oscillating sound field frequency according to a predetermined change rate to control the transformation of the quasi-steady-state tissue structure;

[0010] monitoring the transformation parameters of the quasi-steady-state tissue structure, and adjusting the intensities of the main magnetic field and the pulsed magnetic field according to the transformation parameters;

[0011] A combined effect of a pulsed magnetic field of a preset frequency and low-frequency acoustic vibration is applied to the transformed tissue.

[0012] Optionally, applying a main magnetic field at the welding joint of the niobium material workpiece, and superimposing a pulsed magnetic field and a first oscillating acoustic field on the basis of the main magnetic field to form a composite physical field, includes:

[0013] Fixing a niobium material workpiece on a welding platform, wherein the welding joint of the niobium material workpiece is located in the action area of ​​the first electromagnetic coil and the second electromagnetic coil;

[0014] The first electromagnetic coil generates a main magnetic field with a strength of 0.3-0.5T, so that the direction of the main magnetic field forms an angle of 30° with the direction of the welding joint, and the second electromagnetic coil superimposes a pulse magnetic field with a frequency of 100-500Hz, and the intensity of the pulse magnetic field is 20% of the intensity of the main magnetic field;

[0015] A piezoelectric transducer is arranged at the welding joint to generate a first oscillating sound field with a frequency of 18-22 kHz;

[0016] By adjusting the current waveforms of the first electromagnetic coil and the second electromagnetic coil, the main magnetic field and the pulse magnetic field form synchronous oscillations and cooperate with the first oscillating sound field in phase to form a composite physical field.

[0017] Optionally, the step of heating the weld joint to a preset temperature under the action of the composite physical field and applying a high-frequency oscillating magnetic field to arrange the grains at the weld joint in a predetermined orientation includes:

[0018] Generate a guide magnetic field at the welding joint by a third electromagnetic coil, wherein the direction of the guide magnetic field is perpendicular to the direction of the main magnetic field to form a cross magnetic field;

[0019] Under the action of the cross magnetic field, the weld joint is heated to a preset temperature of 1000-1200° C. at a heating rate of 2-5° C. / min, so that a regularly arranged dislocation array is formed inside the grains at the weld joint;

[0020] Applying a high-frequency oscillating magnetic field with a frequency of 1 MHz and a strength of 0.1 T through a fourth electromagnetic coil, wherein the direction of the high-frequency oscillating magnetic field is parallel to the direction of the guiding magnetic field;

[0021] Under the combined action of the guiding magnetic field and the high-frequency oscillating magnetic field, the preset temperature is maintained for 15 minutes, so that a regularly arranged dislocation array is generated inside the grains at the welded joint;

[0022] Adjusting the frequency of the high-frequency oscillating magnetic field to 2 MHz, while reducing the intensity of the guiding magnetic field by 50%, maintaining this condition for 5 minutes, so that the dislocation array migrates and reconstructs along a predetermined direction;

[0023] The preset temperature is gradually reduced to 600°C at a cooling rate of 1-2°C / min, while the parameters of the high-frequency oscillating magnetic field and the guiding magnetic field are kept unchanged, so that the grain orientation at the welding joint is stabilized in the predetermined direction.

[0024] Optionally, the step of maintaining the composite physical field stable and adopting electron beam welding to form a quasi-steady-state organizational structure having a chain-grid arrangement feature at the welded joint includes:

[0025] Adjusting the phase relationship among the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field so that the energy distribution of the composite physical field remains in a stable state;

[0026] The welding joint is divided into a front molten pool area, a middle molten pool area and a rear molten pool area, and the main magnetic field strength of the front molten pool area, the middle molten pool area and the rear molten pool area is controlled within the range of 0.4-0.5T, 0.2-0.3T and 0.1-0.2T respectively;

[0027] Electron beam welding is performed, the temperature of the front molten pool zone is controlled to be 2300-2400° C., the temperature of the middle molten pool zone is controlled to be 2100-2200° C., the temperature of the rear molten pool zone is controlled to be 1900-2000° C., and the solidification rate at the weld joint is controlled within the range of 8-10 mm / s;

[0028] A second oscillating acoustic field with a frequency of 25-30kHz is introduced into the post-molten pool area, and the amplitude of the second oscillating acoustic field is 1.5 times the amplitude of the first oscillating acoustic field. Through the resonance of the second oscillating acoustic field and the first oscillating acoustic field, the chain structures in the quasi-steady-state organizational structure are connected to form a grid structure, and a low-energy subgrain boundary network and a honeycomb dislocation structure are formed in the grid structure.

[0029] Optionally, adjusting the phase relationship among the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field so that the energy distribution of the composite physical field remains in a stable state includes:

[0030] Arranging an annular sensor array at the welding joint, wherein the sensor array is composed of a fluxgate sensor and a piezoelectric sensor to collect energy distribution data of the composite physical field in real time;

[0031] According to the energy distribution data, adjusting the phase difference between the main magnetic field and the pulsed magnetic field, when the energy distribution data fluctuation exceeds a preset threshold, adjusting the phase difference to a range of 60-120°;

[0032] Controlling the phase of the first oscillating acoustic field so that its delay relative to the phase of the main magnetic field fluctuates within a range of 45-60° and the fluctuation amplitude is kept less than ±5°;

[0033] By synchronously adjusting the energy input ratios of the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field, the energy distribution uniformity of the composite physical field is maintained above 90%.

[0034] Optionally, adjusting the main magnetic field strength and the first oscillating sound field frequency according to a predetermined change rate to control the transition of the quasi-steady-state tissue structure includes:

[0035] After the quasi-steady-state tissue structure is formed, the main magnetic field intensity is reduced to 80% of the initial intensity at a rate of change of 0.02 T / min, and the frequency of the first oscillating sound field is increased to 25 kHz according to a linear law;

[0036] Applying a third oscillating sound field to the welding joint, wherein the frequency of the third oscillating sound field is 1.5 times the frequency of the first oscillating sound field, and the amplitude is 0.8 times the amplitude of the first oscillating sound field;

[0037] The phase of the third oscillating sound field is alternately changed according to a 30 s period, and the phase change range is 0-π / 2, and the main magnetic field strength is further reduced to 50% of the initial strength;

[0038] A third pulsed magnetic field perpendicular to the main magnetic field is introduced, wherein the frequency of the third pulsed magnetic field is 200-300 Hz and the peak intensity is 30% of the current intensity of the main magnetic field. Under the action of the third pulsed magnetic field, the orientation of the quasi-steady-state tissue structure is regulated.

[0039] Optionally, monitoring the transformation parameters of the quasi-steady-state tissue structure and adjusting the intensities of the main magnetic field and the pulsed magnetic field according to the transformation parameters includes:

[0040] Using a synchrotron radiation X-ray diffraction device to monitor the quasi-stable organizational structure online, and obtaining the interplanar spacing and crystal orientation index in the quasi-stable organizational structure;

[0041] Calculating an orientation distribution function value based on the interplanar spacing and the crystal direction index, and when the orientation distribution function value is greater than 0.8, reducing the main magnetic field strength at a rate of 0.02 T / min;

[0042] Acquiring an acoustic emission signal of the quasi-steady-state tissue structure by using an acoustic emission sensor, performing spectrum analysis on the acoustic emission signal, and obtaining the position and intensity ratio of a spectrum characteristic peak;

[0043] When the intensity ratio of the characteristic peaks of the spectrum reaches 3:2:1, the first oscillating acoustic field parameters are kept stable, and the frequency of the pulsed magnetic field is increased to 500 Hz until the grain orientation difference in the backscattered electron diffraction pattern of the quasi-steady-state organizational structure is less than 25°.

[0044] Optionally, the combined action of applying a pulsed magnetic field of a preset frequency and low-frequency acoustic vibration to the transformed tissue includes:

[0045] Applying a fourth pulsed magnetic field with a frequency of 200-300 Hz to the transformed tissue, wherein the direction of the fourth pulsed magnetic field forms an angle of 60° with the grain orientation direction, and the pulse duration is 100 μs;

[0046] During the interval of the fourth pulsed magnetic field, a fourth oscillating sound field with a frequency of 10-15 kHz is introduced into the weld joint, wherein the wave propagation direction of the fourth oscillating sound field is perpendicular to the direction of the fourth pulsed magnetic field;

[0047] The frequency of the fourth pulsed magnetic field is increased by 50 Hz every 180 s, and the frequency of the fourth oscillating sound field is decreased by 1 kHz every 240 s until the average width of the grain boundary at the weld joint is less than 100 nm;

[0048] A fifth pulse magnetic field with a frequency of 400-500 Hz is superimposed on the welding joint, wherein the direction of the fifth pulse magnetic field is opposite to the direction of the fourth pulse magnetic field, and the intensity is 60% of the intensity of the fourth pulse magnetic field;

[0049] Introducing a fifth oscillating sound field with a frequency of 20-25 kHz into the weld joint, so that the fifth oscillating sound field and the fourth oscillating sound field generate standing waves, and the node spacing of the standing waves is 1 / 4 of the average grain size at the weld joint;

[0050] The phase difference between the fourth pulsed magnetic field and the fifth pulsed magnetic field is adjusted to change periodically within the range of 0-π, with a change period of 90s, while keeping the node position of the standing wave fixed.

[0051] A second aspect of the present invention provides a welding process control system for a niobium material workpiece, comprising: a memory and at least one processor, wherein instructions are stored in the memory, and the memory and the at least one processor are interconnected via lines; the at least one processor calls the instructions in the memory so that the welding process control system for the niobium material workpiece executes the steps of the above-mentioned welding process control method for the niobium material workpiece.

[0052] The niobium material workpiece welding processing control scheme proposed in the present invention accurately controls the solidification behavior of the weld metal by constructing a composite physical field environment, which effectively solves the problem of unstable superconducting performance caused by preferential growth of grains in the prior art. Before the welding process begins, the main magnetic field is first applied to the welding joint and the pulsed magnetic field and the first oscillating sound field are superimposed to form a composite physical field environment. The main magnetic field and the welding joint are at a predetermined angle. This specific magnetic field layout can provide guidance for the growth direction of the grains at a macroscopic level. Since niobium atoms are paramagnetic, under the action of an external magnetic field, the atomic magnetic moment will be arranged along the direction of the external magnetic field, thereby affecting the arrangement orientation of niobium atoms at the microscopic level, laying the foundation for subsequent grain growth.

[0053] In a composite physical field environment, the grains at the weld joint are arranged in a predetermined orientation through the synergistic effect of preheating and high-frequency oscillating magnetic field. This process actually activates the migration ability of grain boundaries through thermal-magnetic coupling, so that the dislocations in the niobium material obtain sufficient migration power, thereby forming a regular arrangement in a predetermined direction. Subsequently, electron beam welding is carried out under the condition of maintaining the stability of the composite physical field. At this time, the weld metal will form a special quasi-stable organizational structure, that is, an organizational morphology with chain-grid arrangement characteristics. This quasi-stable organization contains a low-energy subgrain boundary network and a honeycomb dislocation structure. Its formation mechanism is that the synergistic effect of the composite physical field causes the niobium atoms to temporarily deviate from the conventional body-centered cubic arrangement during the solidification process and instead form a transitional structure with lower energy.

[0054] In order to transform this quasi-stable structure into the final homogenized oriented structure, the scheme uses a predetermined change rate to adjust the main magnetic field strength and the first oscillation acoustic field frequency. This process actually induces the quasi-stable structure to transform to the final stable state through the gradual change of field strength and frequency modulation. During the transformation process, the controllability of the transformation process is ensured by real-time monitoring of the transformation parameters of the organizational structure and dynamically adjusting the strength of the main magnetic field and the pulsed magnetic field. Finally, the transformed structure is refined and stabilized by applying a pulsed magnetic field of a preset frequency and a composite effect of low-frequency acoustic vibration. This multi-field coupling effect can promote the formation of small-angle grain boundaries and inhibit the generation of large-angle grain boundaries at the microscopic level, thereby ensuring that the weld area has stable superconducting properties in an extremely low temperature environment.

[0055] This whole process control scheme from field regulation, organizational evolution to final stabilization realizes the precise control of grain growth behavior during niobium material welding. By forming a special quasi-steady-state organization as an intermediate state and using a composite physical field to induce its directional transformation, the problem of orientation disorder caused by spontaneous nucleation and growth of niobium atoms in traditional welding is successfully avoided. At the same time, the grain boundary refinement effect produced by the synergistic effect of multiple fields effectively reduces the scattering probability of superconducting electron pairs at the grain boundary, fundamentally solving the problem of unstable superconducting performance in the weld area. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0057] Figure 1 A schematic diagram of an embodiment of a welding process control method for a niobium material workpiece according to an embodiment of the present invention;

[0058] Figure 2 FIG. 1 is a schematic diagram of an embodiment of a welding process control system for a niobium material workpiece according to an embodiment of the present invention.

[0059] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back...), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0062] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, "and / or" in the full text includes three solutions. Taking A and / or B as an example, it includes technical solution A, technical solution B, and technical solution that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, which must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0063] An embodiment of the present application provides a welding process control method for a niobium material workpiece. Figure 1 A flow chart of a welding process control method for a niobium material workpiece provided in an embodiment of the present application. In this embodiment, the method includes:

[0064] See also Figure 1 , applying a main magnetic field at the weld joint of the niobium material workpiece, and superimposing a pulsed magnetic field and a first oscillating acoustic field on the basis of the main magnetic field to form a composite physical field, wherein the main magnetic field forms a predetermined angle with the direction of the weld joint;

[0065] In one embodiment of the present invention, the method of applying a main magnetic field to a welding joint of a niobium material workpiece, and superimposing a pulsed magnetic field and a first oscillating sound field on the main magnetic field to form a composite physical field comprises: fixing the niobium material workpiece on a welding platform, wherein the welding joint of the niobium material workpiece is located in the action area of ​​a first electromagnetic coil and a second electromagnetic coil; generating a main magnetic field with an intensity of 0.3-0.5T by the first electromagnetic coil, so that the direction of the main magnetic field forms an angle of 30° with the direction of the welding joint, and superimposing a pulsed magnetic field with a frequency of 100-500 Hz by the second electromagnetic coil, wherein the intensity of the pulsed magnetic field is 20% of the intensity of the main magnetic field; arranging a piezoelectric transducer at the welding joint to generate a first oscillating sound field with a frequency of 18-22 kHz; and adjusting the current waveforms of the first electromagnetic coil and the second electromagnetic coil so that the main magnetic field and the pulsed magnetic field form synchronous oscillations, and cooperate with the first oscillating sound field in phase to form a composite physical field.

[0066] Specifically, during the welding process of niobium workpieces, since niobium materials are very easy to react with oxygen at high temperatures to form oxides that affect welding quality and superconducting properties, the entire welding process needs to be carried out in a vacuum environment (the vacuum degree should reach The welding platform is installed in the vacuum chamber of the vacuum electron beam welding machine, and the vacuum chamber is evacuated by mechanical pumps and molecular pumps. The welding platform is made of molybdenum material, and a rectangular positioning groove is machined on the surface of the platform. The lateral width of the positioning groove is the same as the width of the niobium material workpiece, and the longitudinal length is 20mm longer than the length of the workpiece to facilitate placement and adjustment. The depth of the positioning groove is precisely controlled. For example, for a niobium workpiece with a thickness of 3mm, the depth of the positioning groove is machined to 3.1mm. Mechanical processing is used to ensure that the surface flatness error is controlled within ±0.02mm. This matching size can not only ensure the positioning accuracy of the workpiece, but also facilitate loading and unloading.

[0067] In the vacuum chamber, the first electromagnetic coil and the second electromagnetic coil are symmetrically arranged on both sides of the welding platform. Since the center temperature of the weld reaches 2300-2400℃ during electron beam welding of niobium materials, in order to prevent high temperature from damaging the coils, the two electromagnetic coils are arranged 80mm away from the center line of the weld. This distance is determined by comprehensively considering the attenuation law of magnetic field intensity and the distribution characteristics of temperature field, which can not only ensure the effective effect of the magnetic field on the welding area, but also avoid the influence of high temperature on the performance of the coil through appropriate cooling measures. The central axes of the first electromagnetic coil and the second electromagnetic coil are parallel to each other and parallel to the horizontal plane. After the niobium material workpiece is placed, the edges of the two workpieces to be welded form a weld. The center line of the weld (i.e., the contact line of the two workpieces) should be located on the perpendicular bisector of the center axes of the two electromagnetic coils, and the positioning accuracy is ensured by the scale lines and alignment devices on the welding platform.

[0068] A direct current is passed through the first electromagnetic coil to generate a main magnetic field of 0.3-0.5T. The direction of the main magnetic field is determined by the magnetic flux lines, which point from the N pole of the first electromagnetic coil to the S pole. This direction is defined as the main magnetic field direction. The direction of the weld is defined as the extension direction of the weld centerline. The angle between the main magnetic field direction and the weld direction (i.e. the angle between the projection of the main magnetic field direction in the horizontal plane and the weld centerline) is 30°. This angle is chosen because the niobium material crystal has a body-centered cubic structure, and the atoms are most closely arranged on the {110} crystal plane family. When the angle between the main magnetic field direction and the normal direction of these crystal planes is close to 30°, it is beneficial to induce the grains to grow along the direction that is beneficial to superconducting electron transport.

[0069] The second electromagnetic coil is fed with an alternating current to generate a pulsed magnetic field with a frequency of 100-500 Hz and an intensity of 20% of the main magnetic field. For example, when the main magnetic field intensity is 0.4 T, the pulsed magnetic field intensity should be set to 0.08 T. The periodic change of the pulsed magnetic field can exert a periodic electromagnetic force on the niobium atoms in the molten pool, which helps to break the spontaneous aggregation of niobium atoms and promote the uniform nucleation of grains.

[0070] The piezoelectric transducer uses a conventional ultrasonic transducer and is fixed on the welding platform through an L-shaped bracket. In order to avoid the influence of high welding temperature on the transducer and ensure the effective transmission of sound wave energy, the sound wave output end of the transducer is connected to the welding area through a stainless steel waveguide rod with a diameter of 6mm and a length of 30mm. The size parameters of the waveguide rod are determined according to the propagation characteristics of sound waves. This size can ensure the directional propagation of sound waves and avoid excessive energy loss. One end of the waveguide rod is in close contact with the transducer, and the other end is 2mm away from the weld.

[0071] To ensure the precise coordination of the acoustic field and the magnetic field, the signal line of the piezoelectric transducer uses a twisted-pair shielded cable and uses a special high-frequency transformer to achieve signal isolation. The control circuit of the transducer uses an independent shielding module to achieve electrical isolation from the magnetic field control circuit while maintaining effective coupling of each physical field.

[0072] The transducer generates an oscillating sound field of 18-22kHz. This frequency range is close to the characteristic frequency of the lattice vibration of niobium atoms. The transmission of sound wave energy can stimulate lattice vibration and enhance the migration ability of atoms.

[0073] The current signals of the required waveforms are provided to the two electromagnetic coils through an ordinary function signal generator, and the current waveforms are monitored in real time through an oscilloscope. The drive circuits of the two electromagnetic coils are designed with independent shielding modules, the drive signals are electrically isolated through optocouplers, and digital phase-locked loop technology is used to ensure that the phase of the generated magnetic field is accurately controllable. Each drive module is equipped with an independent grounding system and EMI filtering circuit to effectively suppress external electromagnetic interference while ensuring the synergy between magnetic fields.

[0074] The phase of the main magnetic field is taken as the reference (0°), the phase of the pulsed magnetic field is adjusted to 60°, and the phase of the oscillating acoustic field is adjusted to 90°. This phase difference setting allows the three physical fields to act on the welding area in a specific time sequence: first, the main magnetic field provides the basic orientation force, then the pulsed magnetic field generates periodic disturbances, and finally the oscillating acoustic field enhances atomic migration. The three form an orderly energy input sequence in time and space, thereby forming a stable composite physical field environment in the molten pool area.

[0075] It should be noted that the system uses a unified clock source and FPGA controller to achieve nanosecond-level precise synchronization of all physical fields. The controller has an adaptive compensation function, which dynamically optimizes control parameters by real-time monitoring of the distribution status of each physical field to ensure the synergistic effect of multiple fields. When the fluctuation of any physical field is detected to exceed the set threshold, the system will automatically perform phase and intensity compensation to maintain the stability of the field distribution.

[0076] Please continue reading Figure 1, under the action of the composite physical field, the weld joint is heated to a preset temperature, and a high-frequency oscillating magnetic field is applied to arrange the grains at the weld joint in a predetermined orientation;

[0077] In one embodiment of the present invention, under the action of the composite physical field, the weld joint is heated to a preset temperature, and a high-frequency oscillating magnetic field is applied to arrange the grains at the weld joint in a predetermined orientation, including: generating a guide magnetic field at the weld joint by a third electromagnetic coil, wherein the direction of the guide magnetic field is perpendicular to the direction of the main magnetic field to form a cross magnetic field; under the action of the cross magnetic field, the weld joint is heated to a preset temperature of 1000-1200°C at a heating rate of 2-5°C / min to form a regularly arranged dislocation array inside the grains at the weld joint; applying a high-frequency oscillating magnetic field with a frequency of 1 MHz and an intensity of 0.1 T by a fourth electromagnetic coil. an oscillating magnetic field, the direction of the high-frequency oscillating magnetic field is parallel to the direction of the guiding magnetic field; under the joint action of the guiding magnetic field and the high-frequency oscillating magnetic field, the preset temperature is maintained for 15 minutes, so that a regularly arranged dislocation array is generated inside the grains at the welding joint; the frequency of the high-frequency oscillating magnetic field is adjusted to 2 MHz, and the intensity of the guiding magnetic field is reduced by 50%, and maintained under this condition for 5 minutes, so that the dislocation array migrates and reconstructs along a predetermined direction; the preset temperature is gradually reduced to 600°C, and the cooling rate is 1-2°C / min, while the parameters of the high-frequency oscillating magnetic field and the guiding magnetic field are kept unchanged, so that the grain orientation at the welding joint is stabilized in the predetermined direction.

[0078] Specifically, after the composite physical field of the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field is established, the grain orientation at the weld joint needs to be preprocessed. First, a guide magnetic field is generated at the weld joint by the third electromagnetic coil. The third electromagnetic coil is arranged at a distance of 80 mm from the weld joint, and its axial direction is perpendicular to the axial direction of the first electromagnetic coil. The direction of the guide magnetic field (that is, the direction in which the magnetic flux lines point from the N pole to the S pole) is perpendicular to the direction of the main magnetic field, forming a cross magnetic field. The setting of this cross magnetic field is based on the magnetic response characteristics of niobium materials, because under the action of two mutually perpendicular magnetic fields, the movement of niobium atoms can be more comprehensively regulated in three-dimensional space.

[0079] In a cross-magnetic field environment, the weld joint is preheated by resistance heating. The heating rate is controlled in the range of 2-5℃ / min. This rate range is selected to ensure uniform temperature distribution and avoid excessive thermal stress. When the temperature reaches the preset temperature of 1000-1200℃, the niobium material is in the recrystallization temperature range. At this time, the lattice atoms have sufficient migration ability, but have not reached the temperature of significant plastic deformation. This temperature range is conducive to the formation and movement of dislocations, thereby forming a regularly arranged dislocation array inside the grains.

[0080] A high-frequency oscillating magnetic field with a frequency of 1MHz and an intensity of 0.1T is applied through the fourth electromagnetic coil, which is arranged in parallel with the third electromagnetic coil and 50mm apart. The frequency of the high-frequency oscillating magnetic field is selected to be 1MHz based on the thermal vibration frequency characteristics of niobium atoms in the lattice. This frequency can effectively excite the vibration of atoms and promote the movement of dislocations. The direction of the high-frequency oscillating magnetic field is parallel to the direction of the guiding magnetic field. This parallel configuration can enhance the control effect of the magnetic field on the movement of dislocations.

[0081] Under the combined action of the guided magnetic field and the high-frequency oscillating magnetic field, the preset temperature is maintained for 15 minutes. This time can ensure that the dislocations are fully moved and reorganized, forming a regularly arranged dislocation array inside the grains. The formation of the dislocation array plays an important role in the subsequent regulation of grain orientation, because the dislocation array can serve as a channel for grain boundary migration and guide the grains to grow in the expected direction.

[0082] The frequency of the high-frequency oscillating magnetic field was then increased to 2MHz, while the intensity of the guiding magnetic field was reduced to 50% of the initial value. The increase in frequency can increase the activity of dislocation movement, while the reduction in the intensity of the guiding magnetic field reduces the constraints on dislocation movement, which is conducive to the reconstruction of the dislocation array. This condition was maintained for 5 minutes, allowing the dislocation array to migrate and reconstruct along the predetermined direction (i.e., the direction that is conducive to superconducting electron transport).

[0083] Finally, the preset temperature is lowered to 600°C at a cooling rate of 1-2°C / min. This cooling rate is slow enough to ensure that the lattice remains stable during the cooling process and avoid the generation of new stresses and defects. During the cooling process, the parameters of the high-frequency oscillating magnetic field and the guiding magnetic field are kept unchanged, which can continuously constrain the orientation of the grains and prevent the disorder of the grain orientation during the annealing process, and finally stabilize the grain orientation at the weld joint in the predetermined direction.

[0084] Through the whole process control of preheating, heat preservation and slow cooling, combined with the synergistic effect of cross magnetic field and high-frequency oscillating magnetic field, the grain orientation foundation that is beneficial to superconducting properties can be established before welding, creating good initial conditions for the subsequent welding process.

[0085] Please continue reading Figure 1, maintaining the stability of the composite physical field, using electron beam welding to form a quasi-stable organizational structure with chain-grid arrangement characteristics at the welded joint, wherein the quasi-stable organizational structure includes a low-energy subgrain boundary network and a honeycomb dislocation structure;

[0086] In one embodiment of the present invention, the composite physical field is kept stable, electron beam welding is used, and a quasi-steady-state organizational structure with chain-grid arrangement characteristics is formed at the weld joint, including: adjusting the phase relationship between the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field so that the energy distribution of the composite physical field remains stable; dividing the weld joint into a front molten pool area, a middle molten pool area and a rear molten pool area, and controlling the main magnetic field strength of the front molten pool area, the middle molten pool area and the rear molten pool area within the range of 0.4-0.5T, 0.2-0.3T and 0.1-0.2T respectively; using electron beam welding to control the front molten pool area to be stable; The temperature of the pool zone is 2300-2400°C, the temperature of the middle molten pool zone is 2100-2200°C, the temperature of the rear molten pool zone is 1900-2000°C, and the solidification rate at the welding joint is controlled within the range of 8-10mm / s; a second oscillating sound field with a frequency of 25-30kHz is introduced into the rear molten pool zone, and the amplitude of the second oscillating sound field is 1.5 times the amplitude of the first oscillating sound field. Through the resonance of the second oscillating sound field and the first oscillating sound field, the chain structure in the quasi-steady-state organizational structure is connected to form a grid structure, and a low-energy subgrain boundary network and a honeycomb dislocation structure are formed in the grid structure.

[0087] Specifically, after completing the pre-orientation of the grains at the welding joint, it is necessary to enter the electron beam welding stage. First, the phase relationship between the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field is adjusted by a function signal generator. The main magnetic field is used as the reference phase (0°), and the phase lag of the pulsed magnetic field is adjusted to 60°, and the phase lag of the first oscillating acoustic field is 90°. This phase configuration is based on the energy transfer characteristics of the physical field: the main magnetic field first provides the basic orientation force, the pulsed magnetic field then generates periodic disturbances, and finally the oscillating acoustic field is used to enhance atomic migration. The waveforms of the three physical fields are monitored in real time by an oscilloscope to ensure that the phase relationship remains stable and the uniformity of the energy distribution of the composite physical field is maintained above 90%.

[0088] According to the dynamic characteristics of the molten pool, the weld joint is divided into the front molten pool area, the middle molten pool area and the rear molten pool area along the welding direction, and the length of each area is about 8-10mm. Main magnetic fields of different intensities are applied to these three areas: the front molten pool area is controlled at 0.4-0.5T for preheating and melting the metal; the middle molten pool area is controlled at 0.2-0.3T, and its main function is to stabilize the flow of the molten pool; the rear molten pool area is controlled at 0.1-0.2T for regulating solidification behavior. This gradient magnetic field setting is based on the magnetic response characteristics of niobium materials at different temperatures: a stronger magnetic field is required in the high-temperature melting area to overcome the influence of thermal motion, while a weaker magnetic field is required in the solidification area so that the grains can grow self-organized.

[0089] When electron beam welding is used, the electron beam acceleration voltage is set to 60kV, and the welding current is controlled within the range of 45-50mA. By controlling the power density distribution of the electron beam, the temperature of the front molten pool area is maintained at 2300-2400℃ to ensure full melting; the temperature of the middle molten pool area is controlled at 2100-2200℃, and this temperature range is conducive to the stable flow of the molten pool; the temperature of the rear molten pool area is controlled at 1900-2000℃, which is in the solidification temperature range of niobium and is conducive to the directional growth of grains. The solidification rate at the weld joint is controlled within the range of 8-10mm / s. This rate is determined based on the thermophysical properties of niobium materials, which can not only ensure the stability of the molten pool, but also provide sufficient time for grain growth.

[0090] A second piezoelectric transducer is introduced into the post-molten pool area to generate a second oscillating acoustic field with a frequency of 25-30kHz and an amplitude of 1.5 times that of the first oscillating acoustic field. The frequency range of the second oscillating acoustic field is selected based on the natural vibration frequency of the niobium lattice, and the amplitude ratio is set to generate sufficiently strong acoustic field disturbances in the solidification area. When the second oscillating acoustic field meets the first oscillating acoustic field (18-22kHz), an acoustic field resonance is formed in the post-molten pool area. The mechanical vibration generated by this resonance can promote atomic rearrangement during solidification, so that the initially formed chain-like grain structure is connected into a grid-like structure under the action of the acoustic field. At the nodes of the grid-like structure, a subgrain boundary network with lower energy is formed due to stress concentration and atomic rearrangement. At the same time, the periodic stress field generated by the acoustic field resonance also induces the directional movement and reorganization of dislocations, forming a honeycomb dislocation structure inside the grains. The formation process of this organizational feature can be compared to the acoustic cavitation effect of liquid metal under the action of an ultrasonic field, but the difference is that this scheme achieves precise control of the organization through acoustic field resonance in a semi-solid state.

[0091] In one embodiment of the present invention, the phase relationship among the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field is adjusted so that the energy distribution of the composite physical field remains in a stable state, including: arranging an annular sensor array at the welding joint, wherein the sensor array is composed of a fluxgate sensor and a piezoelectric sensor, and real-time collecting energy distribution data of the composite physical field; adjusting the phase difference between the main magnetic field and the pulsed magnetic field according to the energy distribution data, and when the energy distribution data fluctuates beyond a preset threshold, adjusting the phase difference to a range of 60-120°; controlling the phase of the first oscillating acoustic field so that its delay relative to the main magnetic field phase fluctuates within a range of 45-60°, and maintaining a fluctuation amplitude less than ±5°; maintaining the uniformity of the energy distribution of the composite physical field above 90% by synchronously adjusting the energy input ratio of the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field.

[0092] Specifically, in order to achieve precise control of the energy distribution of the composite physical field, a ring sensor array needs to be arranged at the weld joint. The ring sensor array consists of 8 fluxgate sensors and 8 piezoelectric sensors arranged alternately, evenly distributed around the weld joint in a circular shape, with an installation radius of 30 mm.

[0093] The layout of the sensors adopts an anti-interference design. Each sensor is equipped with an independent signal conditioning circuit and analog filter to ensure accurate signal acquisition in strong magnetic and acoustic fields. The fluxgate sensor adopts an orthogonal structure design to measure the horizontal and vertical magnetic field components at the same time. The piezoelectric sensor effectively isolates electromagnetic interference through the shielding structure. The signal lines between adjacent sensors adopt differential transmission to further improve the anti-interference ability.

[0094] The choice of 30mm installation radius is the result of a trade-off between measurement accuracy and temperature influence: if the distance is too close, it will be interfered by the high temperature of welding, and if the distance is too far, the measurement sensitivity will be reduced. The fluxgate sensor adopts an orthogonal structure design, with a measurement range of 0-1T and a sensitivity better than 0.1mT, which is used to detect magnetic field distribution; the piezoelectric sensor is made of high-frequency piezoelectric ceramic material, with an operating frequency range of 1kHz-50kHz and a sensitivity better than 0.1mV / Pa, which is used to detect sound field distribution.

[0095] The data collected by the annular sensor array is collected through a 16-channel synchronous sampling system, and the sampling frequency is set to 1MHz to ensure that the changing characteristics of high-frequency oscillations can be accurately captured. After analog-to-digital conversion, the sampling data of each sensor is input into the field programmable gate array (FPGA) for real-time processing. The processing process includes three steps: signal filtering, Fourier transform, and energy calculation, and finally the energy distribution data of the composite physical field is obtained. The energy distribution data includes two parts: magnetic field energy density and acoustic field energy density. These data can be used to monitor the spatial distribution state of the composite physical field in real time.

[0096] According to the energy distribution data, the system calculates the energy fluctuation amplitude in real time. When the energy value of a certain measurement point deviates from the average value by more than ±10% (i.e., the preset threshold), it indicates that the spatial distribution of the composite physical field is uneven and phase adjustment is required. At this time, the control system first adjusts the phase difference between the main magnetic field and the pulsed magnetic field to control it within the range of 60-120°. The selection of this phase difference range is based on the principle of electromagnetic field superposition: when the phase difference is within this range, the superposition effect of the two magnetic fields is most conducive to maintaining the stability of the field strength distribution. The specific adjustment process uses a gradient descent algorithm, with a step size of 5° each time, until the energy distribution tends to be uniform.

[0097] At the same time, the phase of the first oscillating sound field is controlled so that its delay relative to the main magnetic field phase is kept within the range of 45-60°. The determination of this delay range is based on the acoustic-electric coupling effect: there is energy conversion between sound waves and electromagnetic fields, and when the phase delay is within this range, the energy conversion efficiency is the highest. In order to avoid energy fluctuations caused by phase jitter, the system uses a proportional-integral-differential (PID) control algorithm to control the phase fluctuation amplitude within ±5°. The response time of the control loop is set to 1ms, which is fast enough to track and compensate for various disturbances in the welding process.

[0098] The programmable gate array is used to achieve synchronous adjustment of the power of the main magnetic field, pulsed magnetic field and first oscillating acoustic field to maintain the energy input ratio among the three. The energy input of the main magnetic field is used as the reference value, the energy input of the pulsed magnetic field is controlled within the range of 20%-25% of the main magnetic field, and the energy input of the first oscillating acoustic field is controlled within the range of 15%-20% of the main magnetic field. The system calculates the energy distribution uniformity index of the composite physical field every 10μs, which is defined as the inverse of the ratio of the maximum energy density to the minimum energy density in the field area. This index is maintained above 90% through real-time adjustment, that is, to ensure that the energy density difference between any two points in the field area does not exceed 10%. This precise energy distribution control is essential to ensure the uniformity of grain growth during welding.

[0099] Please continue reading Figure 1, adjusting the main magnetic field intensity and the first oscillating sound field frequency according to a predetermined change rate to control the transformation of the quasi-steady-state tissue structure;

[0100] In one embodiment of the present invention, the main magnetic field strength and the first oscillating acoustic field frequency are adjusted according to a predetermined change rate to control the transformation of the quasi-steady-state organizational structure, including: after the quasi-steady-state organizational structure is formed, the main magnetic field strength is reduced to 80% of the initial strength at a change rate of 0.02T / min, and the first oscillating acoustic field frequency is increased to 25kHz according to a linear law; a third oscillating acoustic field is applied to the welding joint, the frequency of the third oscillating acoustic field is 1.5 times the frequency of the first oscillating acoustic field, and the amplitude is 0.8 times the amplitude of the first oscillating acoustic field; the phase of the third oscillating acoustic field is alternately changed according to a 30s period, and the phase change range is 0-π / 2, and the main magnetic field strength is further reduced to 50% of the initial strength; a third pulsed magnetic field perpendicular to the direction of the main magnetic field is introduced, the frequency of the third pulsed magnetic field is 200-300Hz, and the peak intensity is 30% of the current intensity of the main magnetic field, and the quasi-steady-state organizational structure is oriented and regulated under the action of the third pulsed magnetic field.

[0101] Specifically, after the quasi-steady-state microstructure is formed, it is necessary to precisely control its transformation. First, a programmable DC power supply is used to reduce the main magnetic field intensity at a rate of change of 0.02T / min. The selection of this rate of change is based on the characteristics of the niobium material grains responding to magnetic field changes: too fast a change in magnetic field intensity will lead to grain boundary stress concentration, while too slow a change will extend the process cycle. When the main magnetic field intensity is reduced to 80% of the initial intensity (for example, if the initial intensity is 0.4T, it is reduced to 0.32T), the frequency of the first oscillating sound field is linearly increased to 25kHz by a function signal generator. The linear increase in frequency ensures a smooth transition of the sound field energy and avoids tissue disturbances caused by mutations.

[0102] Subsequently, a third oscillating acoustic field is applied to the weld joint through a third piezoelectric transducer. The third piezoelectric transducer is installed at a position opposite to the first piezoelectric transducer and is also 2 mm away from the weld joint. The frequency of the third oscillating acoustic field is set to 1.5 times the frequency of the first oscillating acoustic field (about 37.5 kHz at this time), and the amplitude is 0.8 times the amplitude of the first oscillating acoustic field. This design of frequency and amplitude ratio is based on the propagation characteristics of sound waves in metals: higher frequencies are conducive to grain refinement, while smaller amplitudes avoid excessive mechanical stress.

[0103] The phase of the third oscillating acoustic field is alternately changed with a timing controller at a period of 30 seconds, and the phase varies within the range of 0-π / 2 (0-90°). This periodic phase change can produce the slapping effect of the acoustic field and promote the rearrangement of atoms in the quasi-steady-state tissue. During this process, the main magnetic field strength is further reduced to 50% of the initial strength (if the initial strength is 0.4T, it will eventually drop to 0.2T). The further reduction of the main magnetic field strength weakens the constraints on the grain orientation, creating conditions for subsequent tissue regulation.

[0104] Finally, a third pulsed magnetic field is introduced through the fifth electromagnetic coil, and the coil is arranged so that the direction of the magnetic field it generates is perpendicular to the direction of the main magnetic field. The frequency of the third pulsed magnetic field is controlled in the range of 200-300 Hz, which is close to the relaxation frequency of niobium atoms in the lattice and is conducive to inducing grain boundary migration. The peak intensity of the third pulsed magnetic field is set to 30% of the current intensity of the main magnetic field (for example, when the main magnetic field is reduced to 0.2 T, the peak intensity of the third pulsed magnetic field is about 0.06 T). Under the action of this cross-magnetic field, the atoms in the quasi-steady-state structure are affected by multi-directional magnetic forces, prompting the grains to reorganize along the predetermined orientation direction. This orientation regulation process is actually achieved by inducing the directional migration of grain boundaries through an external field, and ultimately forming a uniformly oriented grain structure.

[0105] Please continue reading Figure 1 , monitoring the transformation parameters of the quasi-steady-state tissue structure, and adjusting the intensities of the main magnetic field and the pulsed magnetic field according to the transformation parameters;

[0106] In one embodiment of the present invention, the monitoring of the transformation parameters of the quasi-stable organizational structure and adjusting the strength of the main magnetic field and the pulsed magnetic field according to the transformation parameters include: using a synchrotron radiation X-ray diffraction device to perform online monitoring of the quasi-stable organizational structure to obtain the crystal plane spacing and crystal direction index in the quasi-stable organizational structure; calculating the orientation distribution function value based on the crystal plane spacing and crystal direction index, and when the orientation distribution function value is greater than 0.8, reducing the main magnetic field strength at a rate of 0.02T / min; collecting the acoustic emission signal of the quasi-stable organizational structure through an acoustic emission sensor, performing spectral analysis on the acoustic emission signal, and obtaining the position and intensity ratio of the spectral characteristic peak; when the intensity ratio of the spectral characteristic peak reaches 3:2:1, keeping the first oscillating acoustic field parameters stable, and at the same time increasing the frequency of the pulsed magnetic field to 500Hz, until the grain orientation difference in the backscattered electron diffraction pattern of the quasi-stable organizational structure is less than 25°.

[0107] Specifically, in order to accurately monitor the transformation process of the quasi-stable organizational structure, a synchrotron radiation X-ray diffraction device is required for online monitoring. The X-ray source of the device operates at an energy of 15keV, and the spot size is 100μm×100μm. The selection of this energy and spot size can ensure that the X-ray has sufficient penetration ability for niobium materials, while ensuring that the spatial resolution meets the requirements of crystal structure analysis. The diffractometer collects diffraction patterns in the range of 20-80° (2θ) at a scanning speed of 2° / min to obtain the crystal plane spacing and crystal direction index data in the quasi-stable organizational structure.

[0108] For niobium materials with a body-centered cubic structure, the main focus is on the diffraction peaks of the three crystal plane families {110}, {200} and {211}. The crystal plane spacing d value can be calculated by the position of the diffraction peak. For example, the standard d value of the {110} crystal plane is 2.338Å. The crystal direction index reflects the orientation characteristics of the grains. By comparing the diffraction intensity of each crystal plane, the preferred orientation of the grains can be determined. Based on these data, the spherical harmonic function expansion method is used to calculate the orientation distribution function (ODF) value. When the ODF value is greater than 0.8, it indicates that the grains in the quasi-stable structure have formed an obvious orientation trend. At this time, the main magnetic field intensity is reduced at a rate of 0.02T / min to provide conditions for further orientation rearrangement of the grains.

[0109] At the same time, 6 acoustic emission sensors are evenly arranged around the weld joint. The frequency response range of the sensor is 100kHz-1MHz, and the sensitivity is better than 55dB (reference 1V / μbar). The acoustic emission sensor converts the elastic waves inside the material into electrical signals through the piezoelectric effect. These elastic waves mainly come from the grain boundary migration and dislocation movement process. The collected acoustic emission signal is amplified by the preamplifier (gain 40dB) and enters the multi-channel signal analyzer. The spectrum characteristics are obtained by fast Fourier transform (FFT) of the acoustic emission signal. In the spectrum, three characteristic peaks are mainly concerned, which correspond to the grain boundary migration (about 200kHz), dislocation slip (about 400kHz) and lattice reconstruction (about 600kHz) processes.

[0110] When the intensity ratio of these three spectral characteristic peaks reaches 3:2:1, it indicates that the quasi-steady-state organization is undergoing an orderly structural transformation. At this time, the frequency and amplitude parameters of the first oscillating acoustic field need to be kept unchanged to maintain the stabilizing effect of the acoustic field on the organizational transformation. At the same time, the frequency of the pulsed magnetic field is increased to 500Hz. This frequency increase helps to enhance the regulatory effect of the magnetic field on grain boundary migration. This process continues until the orientation difference between the grains is detected to be less than 25° using backscattered electron diffraction (EBSD) technology. The EBSD test is carried out at an accelerating voltage of 20kV, and the step size is set to 0.5μm. These parameter settings can ensure the accurate characterization of the grain orientation of the niobium material. An orientation difference of less than 25° means that the grain boundaries are mainly small-angle grain boundaries. This grain boundary structure is conducive to the transport of superconducting electron pairs and is an important guarantee for obtaining stable superconducting properties.

[0111] Please continue reading Figure 1 , a combined effect of a pulsed magnetic field of a preset frequency and low-frequency acoustic vibration is applied to the transformed tissue.

[0112] In one embodiment of the present invention, the combined action of applying a pulsed magnetic field of a preset frequency and low-frequency acoustic vibration to the transformed tissue includes: applying a fourth pulsed magnetic field with a frequency of 200-300 Hz to the transformed tissue, the direction of the fourth pulsed magnetic field is at an angle of 60° to the grain orientation direction, and the pulse duration is 100 μs; during the gap between the fourth pulsed magnetic field, introducing a fourth oscillating acoustic field with a frequency of 10-15 kHz to the weld joint, the wave propagation direction of the fourth oscillating acoustic field being perpendicular to the direction of the fourth pulsed magnetic field; increasing the frequency of the fourth pulsed magnetic field by 50 Hz every 180 s, and reducing the frequency of the fourth oscillating acoustic field by 1 kHz every 240 s. , until the average width of the grain boundary at the weld joint is less than 100nm; a fifth pulse magnetic field with a frequency of 400-500Hz is superimposed on the weld joint, the direction of the fifth pulse magnetic field is opposite to the direction of the fourth pulse magnetic field, and the intensity is 60% of the intensity of the fourth pulse magnetic field; a fifth oscillating sound field with a frequency of 20-25kHz is introduced into the weld joint, so that the fifth oscillating sound field and the fourth oscillating sound field generate standing waves, and the node spacing of the standing wave is 1 / 4 of the average grain size at the weld joint; the phase difference between the fourth pulse magnetic field and the fifth pulse magnetic field is adjusted to change periodically in the range of 0-π, with a change period of 90s, while keeping the node positions of the standing wave fixed.

[0113] Specifically, after the structural transformation is completed, the weld structure needs to be finally optimized. First, the fourth pulsed magnetic field is applied to the transformed structure through the sixth electromagnetic coil, and the frequency is controlled in the range of 200-300Hz. The arrangement of the sixth electromagnetic coil needs to ensure that the direction of the magnetic field it generates is at an angle of 60° to the orientation direction of the formed grains. The selection of this angle is based on the elastic anisotropy of niobium crystals. At this angle, the stress induced by the magnetic field is most conducive to the refinement of the grain boundaries. The fourth pulsed magnetic field adopts a narrow pulse form with a pulse width of 100μs. This short-term strong magnetic field can locally adjust the grain boundary structure without destroying the basic orientation of the grains.

[0114] During the pulse gap of the fourth pulsed magnetic field (i.e., during the pulse off period), a fourth oscillating acoustic field with a frequency of 10-15kHz is introduced into the weld joint through the fourth piezoelectric transducer. The installation position of the fourth piezoelectric transducer must ensure that the propagation direction of the sound waves it generates is perpendicular to the direction of the fourth pulsed magnetic field. This vertical configuration can form an acoustic-magnetic cross field and enhance the regulation effect on grain boundary migration. The frequency range of the fourth oscillating acoustic field is selected based on the characteristic frequency of the grain boundary vibration of the niobium material. This frequency range can effectively excite the grain boundary vibration without causing instability of the overall structure.

[0115] The frequency of the fourth pulsed magnetic field is increased by 50Hz every 180s by program control, while the frequency of the fourth oscillating acoustic field is reduced by 1kHz every 240s. This alternating rhythm is designed to maintain the synergistic effect of the acoustic and magnetic fields. When the frequency of the magnetic field increases, its force on the atoms increases, while the reduction in the frequency of the acoustic field provides the time required for atomic rearrangement. This process continues until the transmission electron microscope observes that the average width of the grain boundary at the weld joint is less than 100nm. The measurement of the grain boundary width is carried out at an accelerating voltage of 200kV using high-resolution imaging. This sub-nanometer scale grain boundary structure is beneficial to improving the mechanical properties and superconducting properties of the weld.

[0116] Next, the fifth pulsed magnetic field with a frequency of 400-500 Hz is superimposed on the weld joint through the seventh electromagnetic coil. The seventh electromagnetic coil is arranged so that the direction of the magnetic field it generates is opposite to the direction of the fourth pulsed magnetic field, and the magnetic field intensity is set to 60% of the fourth pulsed magnetic field intensity. This reverse magnetic field setting can generate alternating magnetic stress at the grain boundary, further promoting the refinement and stabilization of the grain boundary.

[0117] At the same time, a fifth oscillating sound field with a frequency of 20-25kHz is introduced through the fifth piezoelectric transducer. The fifth oscillating sound field meets the fourth oscillating sound field in space to form a standing wave, and the node spacing of the standing wave is controlled to be 1 / 4 of the average grain size at the weld joint. Taking the grain size of 10μm as an example, the standing wave node spacing should be set to 2.5μm. This precise spatial scale matching allows the acoustic wave energy to be maximized at the grain boundary, because the stress field at the standing wave node can effectively clamp the movement of the grain boundary.

[0118] Finally, the phase difference between the fourth pulse magnetic field and the fifth pulse magnetic field is controlled by a function signal generator to change periodically in the range of 0-π (0-180°), and the change period is set to 90s. This periodic change of the phase difference can produce a scanning magnetic field control effect, so that the magnetic field effect is evenly distributed in the entire weld joint area. In this process, the node position of the standing wave is kept fixed through real-time monitoring and feedback control system, which is crucial to maintaining the stability of the grain boundary structure. The entire process continues until a stable fine-grained structure is formed in the weld area.

[0119] In addition, it should be noted that since the center temperature of the weld reaches 2300-2400°C when the niobium material is welded, in some embodiments, corresponding cooling protection measures can be taken for each key component. The first electromagnetic coil and the second electromagnetic coil adopt a double-layer structure design, and a water cooling channel is provided inside the coil. The cooling water temperature is controlled at 15-20°C, and the flow rate is maintained at 8-10L / min to ensure that the working temperature of the coil does not exceed 40°C. The third and fourth electromagnetic coils adopt an indirect cooling method, and a water cooling plate is set on the support frame. The water cooling plate and the coil are connected by a heat-conducting copper block, and the heat generated by the coil is taken away by heat conduction.

[0120] The piezoelectric transducer is cooled by a closed-loop cooling system. For example, the transducer housing is designed with a spiral cooling water channel, and the cooling water circulates at a flow rate of 5L / min. The waveguide rod adopts a segmented structure with radial heat sinks in the middle to quickly dissipate the conducted heat. During the welding process, the temperature of each component is monitored in real time by a temperature sensor. When the temperature exceeds the preset threshold, the control system automatically increases the cooling water flow rate. For example, when the temperature of the first electromagnetic coil exceeds 35°C, its cooling water flow rate is automatically increased to 12L / min until the temperature drops to the normal range. All cooling water pipelines are connected with vacuum-sealed joints to ensure that the sealing of the vacuum chamber is not affected.

[0121] The cooling system uses non-magnetic materials to make pipelines, and the pipeline layout is optimized to avoid affecting the distribution of the physical field. Each coil and transducer cooling circuit is equipped with independent temperature and flow sensors, and the temperature is accurately adjusted through the PLC controller to ensure that each component operates stably within the optimal operating temperature range.

[0122] The welding process control system of the niobium material workpiece in the embodiment of the present invention is described in detail from the perspective of hardware processing.

[0123] Figure 2 3 is a schematic diagram of the structure of a welding process control system for a niobium material workpiece provided by an embodiment of the present invention. The welding process control system 300 for the niobium material workpiece may have relatively large differences due to different configurations or performances, and may include one or more processors (central processing units, CPU) 310 (for example, one or more processors) and a memory 320, and one or more storage media 330 (for example, one or more mass storage device terminals) storing application programs 333 or data 332. Among them, the memory 320 and the storage medium 330 may be temporary storage or permanent storage. The program stored in the storage medium 330 may include one or more modules (not shown in the figure), and each module may include a series of instruction operations in the welding process control system 300 for the niobium material workpiece. Furthermore, the processor 310 may be configured to communicate with the storage medium 330, and execute a series of instruction operations in the storage medium 330 on the welding process control system 300 for the niobium material workpiece to implement the steps of the above-mentioned welding process control method for the niobium material workpiece.

[0124] The welding process control system 300 of the niobium material workpiece may also include one or more power supplies 340, one or more wired or wireless network interfaces 350, one or more input and output interfaces 360, and / or one or more operating systems 331, such as Windows Serve, Mac OS X, Unix, Linux, FreeBSD, etc. It can be understood by those skilled in the art that Figure 2 The structure of the welding process control system for niobium material workpieces shown does not constitute a limitation on the welding process control system for niobium material workpieces provided by the present invention, and may include more or less components than shown in the figure, or combine certain components, or arrange the components differently.

[0125] The present invention also provides a computer-readable storage medium, which may be a non-volatile computer-readable storage medium or a volatile computer-readable storage medium. Instructions are stored in the computer-readable storage medium. When the instructions are executed on a computer, the computer executes the steps of the welding process control method for a niobium material workpiece.

[0126] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-described system, device, or unit can refer to the corresponding process in the aforementioned method embodiment and will not be repeated here.

[0127] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or the whole or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk and other media that can store program code.

[0128] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A welding process control method for a niobium material workpiece, characterized in that: include: A main magnetic field is applied to the welding joint of the niobium material workpiece, and a pulsed magnetic field and a first oscillating sound field are superimposed on the main magnetic field to form a composite physical field, wherein the main magnetic field forms a predetermined angle with the direction of the welding joint; the method of applying the main magnetic field to the welding joint of the niobium material workpiece, and superimposing the pulsed magnetic field and the first oscillating sound field on the main magnetic field to form a composite physical field comprises: fixing the niobium material workpiece on a welding platform, wherein the welding joint of the niobium material workpiece is located in the action area of ​​the first electromagnetic coil and the second electromagnetic coil; generating a main magnetic field with an intensity of 0.3-0.5T by the first electromagnetic coil, so that the direction of the main magnetic field forms an angle of 30° with the direction of the welding joint, and superimposing a pulsed magnetic field with a frequency of 100-500Hz by the second electromagnetic coil, and the intensity of the pulsed magnetic field is 20% of the intensity of the main magnetic field; arranging a piezoelectric transducer at the welding joint to generate a first oscillating sound field with a frequency of 18-22kHz; by adjusting the current waveforms of the first electromagnetic coil and the second electromagnetic coil, the main magnetic field and the pulsed magnetic field form synchronous oscillation, and cooperate with the first oscillating sound field in phase to form a composite physical field; Under the action of the composite physical field, the weld joint is heated to a preset temperature, and a high-frequency oscillating magnetic field is applied to arrange the grains at the weld joint in a predetermined orientation; Keeping the composite physical field stable, electron beam welding is used to form a quasi-stable organizational structure with chain-grid arrangement characteristics at the welded joint, wherein the quasi-stable organizational structure includes a low-energy subgrain boundary network and a honeycomb dislocation structure; Adjust the main magnetic field strength and the first oscillating sound field frequency according to a predetermined change rate to control the transformation of the quasi-steady-state tissue structure; monitoring the transformation parameters of the quasi-steady-state tissue structure, and adjusting the intensities of the main magnetic field and the pulsed magnetic field according to the transformation parameters; A combined effect of a pulsed magnetic field of a preset frequency and low-frequency acoustic vibration is applied to the transformed tissue.

2. The welding process control method of niobium material workpiece according to claim 1, characterized in that: The step of heating the weld joint to a preset temperature under the action of the composite physical field and applying a high-frequency oscillating magnetic field to arrange the grains at the weld joint in a predetermined orientation includes: Generate a guide magnetic field at the welding joint by a third electromagnetic coil, wherein the direction of the guide magnetic field is perpendicular to the direction of the main magnetic field to form a cross magnetic field; Under the action of the cross magnetic field, the weld joint is heated to a preset temperature of 1000-1200° C. at a heating rate of 2-5° C. / min, so that a regularly arranged dislocation array is formed inside the grains at the weld joint; Applying a high-frequency oscillating magnetic field with a frequency of 1 MHz and a strength of 0.1 T through a fourth electromagnetic coil, wherein the direction of the high-frequency oscillating magnetic field is parallel to the direction of the guiding magnetic field; Under the combined action of the guiding magnetic field and the high-frequency oscillating magnetic field, the preset temperature is maintained for 15 minutes, so that a regularly arranged dislocation array is generated inside the grains at the welded joint; Adjusting the frequency of the high-frequency oscillating magnetic field to 2 MHz, while reducing the intensity of the guiding magnetic field by 50%, maintaining this condition for 5 minutes, so that the dislocation array migrates and reconstructs along a predetermined direction; The preset temperature is gradually reduced to 600°C at a cooling rate of 1-2°C / min, while the parameters of the high-frequency oscillating magnetic field and the guiding magnetic field are kept unchanged, so that the grain orientation at the welding joint is stabilized in the predetermined direction.

3. The welding process control method of niobium material workpiece according to claim 1, characterized in that: The method of maintaining the stability of the composite physical field and adopting electron beam welding to form a quasi-steady-state organizational structure having a chain-grid arrangement feature at the welded joint comprises: Adjusting the phase relationship among the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field so that the energy distribution of the composite physical field remains in a stable state; The welding joint is divided into a front molten pool area, a middle molten pool area and a rear molten pool area, and the main magnetic field strength of the front molten pool area, the middle molten pool area and the rear molten pool area is controlled within the range of 0.4-0.5T, 0.2-0.3T and 0.1-0.2T respectively; Electron beam welding is performed, the temperature of the front molten pool zone is controlled to be 2300-2400° C., the temperature of the middle molten pool zone is controlled to be 2100-2200° C., the temperature of the rear molten pool zone is controlled to be 1900-2000° C., and the solidification rate at the weld joint is controlled within the range of 8-10 mm / s; A second oscillating acoustic field with a frequency of 25-30kHz is introduced into the post-molten pool area, and the amplitude of the second oscillating acoustic field is 1.5 times the amplitude of the first oscillating acoustic field. Through the resonance of the second oscillating acoustic field and the first oscillating acoustic field, the chain structures in the quasi-steady-state organizational structure are connected to form a grid structure, and a low-energy subgrain boundary network and a honeycomb dislocation structure are formed in the grid structure.

4. The welding process control method of niobium material workpiece according to claim 3, characterized in that: The step of adjusting the phase relationship between the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field so that the energy distribution of the composite physical field remains in a stable state comprises: Arranging an annular sensor array at the welding joint, wherein the sensor array is composed of a fluxgate sensor and a piezoelectric sensor to collect energy distribution data of the composite physical field in real time; According to the energy distribution data, adjusting the phase difference between the main magnetic field and the pulsed magnetic field, when the energy distribution data fluctuation exceeds a preset threshold, adjusting the phase difference to a range of 60-120°; Controlling the phase of the first oscillating acoustic field so that its delay relative to the phase of the main magnetic field fluctuates within a range of 45-60° and the fluctuation amplitude is kept less than ±5°; By synchronously adjusting the energy input ratios of the main magnetic field, the pulsed magnetic field and the first oscillating acoustic field, the energy distribution uniformity of the composite physical field is maintained above 90%.

5. The welding process control method of niobium material workpiece according to claim 1, characterized in that: The step of adjusting the main magnetic field strength and the first oscillating sound field frequency according to a predetermined change rate to control the transition of the quasi-steady-state tissue structure includes: After the quasi-steady-state tissue structure is formed, the main magnetic field intensity is reduced to 80% of the initial intensity at a rate of change of 0.02 T / min, and the frequency of the first oscillating sound field is increased to 25 kHz according to a linear law; Applying a third oscillating sound field to the welding joint, wherein the frequency of the third oscillating sound field is 1.5 times the frequency of the first oscillating sound field, and the amplitude is 0.8 times the amplitude of the first oscillating sound field; The phase of the third oscillating sound field is alternately changed according to a 30 s period, and the phase change range is 0-π / 2, and the main magnetic field strength is further reduced to 50% of the initial strength; A third pulsed magnetic field perpendicular to the main magnetic field is introduced, wherein the frequency of the third pulsed magnetic field is 200-300 Hz and the peak intensity is 30% of the current intensity of the main magnetic field. Under the action of the third pulsed magnetic field, the orientation of the quasi-steady-state tissue structure is regulated.

6. The welding process control method of niobium material workpiece according to claim 1, characterized in that: The monitoring of the transformation parameters of the quasi-steady-state tissue structure and adjusting the intensities of the main magnetic field and the pulsed magnetic field according to the transformation parameters include: Using a synchrotron radiation X-ray diffraction device to monitor the quasi-stable organizational structure online, and obtaining the interplanar spacing and crystal orientation index in the quasi-stable organizational structure; Calculating an orientation distribution function value based on the interplanar spacing and the crystal direction index, and when the orientation distribution function value is greater than 0.8, reducing the main magnetic field strength at a rate of 0.02 T / min; Acquiring an acoustic emission signal of the quasi-steady-state tissue structure by an acoustic emission sensor, performing spectrum analysis on the acoustic emission signal, and obtaining the position and intensity ratio of a characteristic peak of the spectrum; When the intensity ratio of the characteristic peaks of the spectrum reaches 3:2:1, the first oscillating acoustic field parameters are kept stable, and the frequency of the pulsed magnetic field is increased to 500 Hz until the grain orientation difference in the backscattered electron diffraction pattern of the quasi-steady-state organizational structure is less than 25°.

7. The welding process control method of a niobium material workpiece according to claim 1, characterized in that: The combined action of applying a pulsed magnetic field of a preset frequency and low-frequency acoustic vibration to the transformed tissue includes: Applying a fourth pulsed magnetic field with a frequency of 200-300 Hz to the transformed tissue, wherein the direction of the fourth pulsed magnetic field forms an angle of 60° with the grain orientation direction, and the pulse duration is 100 μs; During the interval of the fourth pulsed magnetic field, a fourth oscillating sound field with a frequency of 10-15 kHz is introduced into the weld joint, wherein the wave propagation direction of the fourth oscillating sound field is perpendicular to the direction of the fourth pulsed magnetic field; The frequency of the fourth pulsed magnetic field is increased by 50 Hz every 180 s, and the frequency of the fourth oscillating sound field is decreased by 1 kHz every 240 s until the average width of the grain boundary at the weld joint is less than 100 nm; A fifth pulse magnetic field with a frequency of 400-500 Hz is superimposed on the welding joint, wherein the direction of the fifth pulse magnetic field is opposite to the direction of the fourth pulse magnetic field, and the intensity is 60% of the intensity of the fourth pulse magnetic field; Introducing a fifth oscillating sound field with a frequency of 20-25 kHz into the weld joint, so that the fifth oscillating sound field and the fourth oscillating sound field generate standing waves, and the node spacing of the standing waves is 1 / 4 of the average grain size at the weld joint; The phase difference between the fourth pulsed magnetic field and the fifth pulsed magnetic field is adjusted to change periodically within the range of 0-π, with a change period of 90s, while keeping the node position of the standing wave fixed.

8. A welding process control system for a niobium material workpiece, characterized in that: The welding process control system of the niobium material workpiece includes: a memory and at least one processor, wherein the memory stores instructions; The at least one processor calls the instructions in the memory to enable the welding process control system of the niobium material workpiece to execute the steps of the welding process control method of the niobium material workpiece according to any one of claims 1-7.

Images