A composite electrode and a preparation method of high-uniform niobium-titanium alloy ingot

Abstract

The present application relates to a kind of composite electrode, preparation method of high uniformity niobium titanium alloy ingot, and preparation method includes the following steps: step S1. Provide titanium sponge, titanium sponge is uniformly loaded into pressing device, is formed by radial pressing process, obtain single-section hollow titanium blank, and hollow titanium blank is arranged axially and is circumferentially welded, obtain hollow titanium electrode;Step S2. Provide niobium rod;Step S3. Niobium rod is slowly inserted into the inner hole of hollow titanium electrode along the axial direction, so that niobium rod is coaxially arranged with hollow titanium electrode, and composite electrode is formed, and the both ends of composite electrode are welded and fixed;Step S4. The assembled composite electrode is placed in vacuum arc furnace and is smelted, and high uniformity niobium titanium alloy ingot is obtained.The hollow titanium electrode of the present application is a whole round structure, eliminates the joint defect of half-arc-shaped butt welding electrode, guarantees the assembly fit of niobium rod, avoids the composition segregation and inclusion problem of subsequent smelting from the root, and lays the foundation for ingot uniformity.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal smelting, and specifically discloses a method for preparing highly uniform niobium-titanium alloy ingots. Background Technology

[0002] NbTi alloys are important superconducting materials, and the quality of their ingot preparation directly affects their subsequent performance. Ingots with uniform composition and low impurities are the focus of research in this field.

[0003] Currently, the electrode preparation process for NbTi alloy ingots has significant drawbacks: existing titanium electrodes mostly employ a "two-stage pressing + butt welding" process for semi-arc-shaped sponge titanium blanks, which suffers from lengthy pressing times and high energy loss; the semi-arc blanks tend to be non-circular after butt welding, and the weld joints are prone to defects such as incomplete penetration and porosity, leading to uneven composition distribution during subsequent melting and causing ingot segregation, Nb infusible blocks, and other inclusions; the electrode preparation process is complex and prone to introducing external contamination, affecting the alloy's plasticity and superconducting properties. To address these shortcomings in electrode preparation, a highly efficient and low-defect titanium electrode preparation process is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for preparing composite electrodes and highly uniform niobium-titanium alloy ingots. This method solves the problems of long pressing time, numerous welding defects, and uneven composition of ingots caused by semi-arc titanium electrodes. The process simplifies the electrode preparation process, improves electrode stability, and thus achieves highly uniform and efficient mass production of NbTi alloy ingots.

[0005] The technical solution adopted in this invention is: A method for preparing a highly uniform niobium-titanium alloy ingot, comprising the following steps: Step S1. Provide sponge titanium, uniformly load the sponge titanium into a pressing device, and form it by radial pressing process of hydraulic press to obtain a single-section hollow titanium blank. Arrange multiple hollow titanium blanks axially and weld them circumferentially to obtain a hollow titanium electrode. Step S2. Provide a niobium rod and perform surface cleaning treatment on the niobium rod; Step S3. Slowly insert the niobium rod processed in step S2 into the inner hole of the hollow titanium electrode along the axial direction, so that the niobium rod and the hollow titanium electrode are coaxially arranged to form a composite electrode, and weld and fix the two ends of the composite electrode. Step S4. Place the assembled composite electrode into a vacuum arc furnace for melting to obtain a highly uniform niobium-titanium alloy ingot.

[0006] Preferably, in the method for preparing the highly uniform niobium-titanium alloy ingot, the radial pressing pressure in step S1 is 150-200 MPa, and the holding time is 5-10 min.

[0007] Preferably, in the method for preparing the high-uniformity niobium-titanium alloy ingot, the hollow titanium electrode in step S1 has an inner diameter of 50-300 mm, an outer diameter of 100-600 mm, and a thickness of 100-400 mm.

[0008] Preferably, in the method for preparing the highly uniform niobium-titanium alloy ingot, the vacuum degree of the circumferential welding in step S1 is 5 × 10⁻⁶. -4 ~1×10 -5 The electron beam voltage is 120~150kV, the electron beam current is 250~350mA, the welding speed is 20~40mm / min, the electron beam oscillation amplitude is 8~12mm, the electron beam oscillation frequency is 2~5Hz, and the axial welding adopts a 3~4 layer multi-pass welding process, with each layer held at heat for 10~15min after welding.

[0009] Preferably, in the method for preparing the high-uniformity niobium-titanium alloy ingot, the pressing device in step S1 includes a pressing unit and a demolding unit. The pressing unit includes a multi-column hollow punch assembly and a lower die assembly disposed at the bottom of the multi-column hollow punch assembly; the multi-column hollow punch assembly includes a fixed plate and multiple hollow cylindrical punches disposed at the bottom of the fixed plate, the fixed plate being connected to a driving device; the lower die assembly has multiple circular cavities inside, the number of circular cavities being consistent with the number of hollow cylindrical punches and being inserted one-to-one, and the central axis of the hollow cylindrical punches coinciding with the central axis of the circular cavities, the hollow cylindrical punches being able to move up and down relative to the lower die assembly; The demolding unit includes an independently liftable bottom mold assembly and a mandrel assembly. The mandrel assembly can move up and down relative to the bottom mold assembly. The top of the mandrel assembly can pass through the bottom mold assembly and enter the circular mold cavity, and cooperate with the hollow cylindrical punch to press the raw material in the circular mold cavity into a single-segment hollow titanium billet. Step S1, which involves obtaining a single-segment hollow titanium blank, specifically includes the following steps: Step S11. Control the mandrel assembly to rise to the material feeding position. The top of the mandrel assembly is located above the required cavity height. Raw material is fed into each circular cavity. The drive device drives the multi-column hollow punch assembly to descend synchronously. After reaching the set pressure, the pressure is maintained to form a hollow electrode surrounding the mandrel. Subsequently, the drive device drives the hollow cylindrical punch to reset. Step S12. The mandrel assembly descends synchronously until the top of the mandrel assembly is completely detached from the inner hole of the hollow electrode; the bottom mold assembly descends so that the single-segment hollow titanium blank is detached from the bottom mold assembly; the bottom mold assembly and the mandrel assembly rise and reset to the fabric position to obtain a set of single-segment hollow titanium blanks.

[0010] Preferably, the method for preparing the high-uniformity niobium-titanium alloy ingot is characterized in that positioning grooves are provided on both opposite side walls of the fixing plate, and a lower protrusion is provided at the end of the hollow cylindrical punch away from the fixing plate, the lower protrusion being frustoconical in shape. The bottom mold assembly includes a bottom mold, on which a plurality of protrusions are provided. One end of each protrusion is provided with a frustum-shaped groove, which cooperates with the lower protrusion. The mandrel assembly includes a base and a plurality of mandrels disposed on the base, each mandrel having a hemispherical top, and each base being connected to a lifting hydraulic system; Step S11, which involves feeding raw materials into each circular mold cavity, specifically includes the following steps: the hydraulic press drives the hollow cylindrical punch upward, causing the hollow cylindrical punch to separate from the circular mold cavity, making it easier to feed raw materials into the circular mold cavity; The process of obtaining a set of single-segment hollow titanium blanks in step S12 specifically includes: a driving device driving a hollow cylindrical punch to move downwards, a hydraulic cylinder driving a bottom mold assembly to move upwards, and a lifting hydraulic system driving a mandrel assembly to move upwards. The mandrel in the mandrel assembly can pass through the protrusion of the bottom mold assembly and enter the circular mold cavity, cooperating with the downward-moving hollow cylindrical punch to press the raw material in the circular mold cavity into a single-segment hollow titanium blank.

[0011] Preferably, in the method for preparing the high-uniformity niobium-titanium alloy ingot, the outer diameter of the mandrel is less than the inner diameter of the hollow cylindrical punch and less than the diameter of the circular mold cavity, the diameter of the circular mold cavity is less than the outer diameter of the base, and the height of the circular mold cavity is greater than the pressing stroke of the mandrel assembly.

[0012] Preferably, in the method for preparing the high-uniformity niobium-titanium alloy ingot, the surface cleaning treatment in step S2 specifically involves: first, pickling the niobium rod with a mixed acid solution, then rinsing it with deionized water, followed by dehydration with anhydrous ethanol, and finally drying it; the mixed acid solution includes hydrofluoric acid, nitric acid, and deionized water, with a volume ratio of hydrofluoric acid, nitric acid, and deionized water of 1:3:6; the pickling temperature is 20~25℃, and the pickling time is 15~25 min; the number of times the deionized water is rinsed is 3~5 times; the drying temperature is 100~120℃, and the holding time is 1~3 h.

[0013] Preferably, in the method for preparing the highly uniform niobium-titanium alloy ingot, step S4 specifically includes the following steps: Step S41. Place the assembled composite electrode into a vacuum arc furnace and perform a single melting operation using a DC stabilizing arc method. Before melting, evacuate the vacuum furnace to a vacuum level of ≤5×10⁻⁶. -3Pa, and control the melting voltage to 28~32V, the melting current to 8~12kA, and the arc stabilization current to 4~12A. Use 5kA low power to start the arc, and increase the current to 12kA in the later stage of melting to ensure that the head of the ingot is fully melted. After melting, cool for ≥4h, and flatten the ingot to remove the loose area at the end. Step S42. Turn the flattened ingot over and place it into another suitable crystallizer. Before melting, further increase the vacuum level in the furnace to ≤1×10⁻⁶. -3 Pa, control the melting voltage to 30~34V, the current to 10~14kA, and the arc stabilization current to 4~12A. Use AC arc stabilization method for secondary melting. After melting, extend the cooling time to ≥6h. After cooling, perform flattening treatment again. Step S43. Turn the ingot over again and place it into the crystallizer of the corresponding size. Before melting, evacuate the vacuum in the furnace to ≤5×10. -4 Pa uses an AC arc stabilization method for secondary melting, controlling the melting voltage at 32~36V, the current at 12~15kA, and the arc stabilization current at 4~5kA. During the melting process, the input power is gradually reduced by decreasing 1kA every 10 minutes to maintain a stable molten pool depth. During the feeding stage, the input power is further reduced to ensure that the bottom of the ingot from the previous melting round is completely retained on the auxiliary electrode. After melting is completed, the ingot is cooled for ≥8 hours.

[0014] Preferably, in the method for preparing the highly uniform niobium-titanium alloy ingot, the leakage rate during the first, second, and third melting processes is ≤5×10⁻⁶. -6 Pa·m 3 / s.

[0015] A method for preparing a high-uniformity niobium-titanium alloy ingot includes a composite electrode for preparing the high-uniformity niobium-titanium alloy ingot, comprising a hollow titanium electrode and a niobium rod coaxially disposed in the hollow titanium electrode, wherein the hollow titanium electrode comprises a plurality of hollow titanium blanks arranged axially and circumferentially welded.

[0016] The present invention has the following advantages: (1) The method for preparing the high uniformity niobium-titanium alloy ingot of the present invention has a hollow titanium electrode with a round structure. The round structure reduces the number of welding points and the distance from the round to the crucible wall is equal, which is conducive to the uniform distribution of elements, reduces the joint defects of the semi-arc welding electrode, ensures the fit of the assembly with the niobium rod, and reduces the composition segregation and inclusion problems in the subsequent melting from the root, laying the foundation for the uniformity of the ingot.

[0017] (2) The method for preparing the high uniformity niobium-titanium alloy ingot of the present invention replaces two pressing and welding with a single radial pressing, avoiding double pressing time and energy loss, simplifying the electrode preparation process, shortening the overall production cycle and reducing costs.

[0018] (3) The preparation method of the high uniformity niobium-titanium alloy ingot of the present invention is different from the conventional method of using semi-arc pressing and butt welding for titanium electrodes. The present invention breaks through the conventional method of using radial pressing to directly prepare hollow titanium electrodes, which effectively improves the uniformity of the ingot composition, simplifies the process, reduces energy consumption, and has good prospects for industrial production. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the circular hollow titanium electrode of the present invention.

[0020] Figure 2 This is a top view of the single-segment hollow titanium blank of the present invention.

[0021] Figure 3 This is a side view of the single-segment hollow titanium blank of the present invention.

[0022] Figure 4 This is a schematic diagram of the pressing device of the present invention.

[0023] Figure 5 This is a schematic diagram of the structure of the multi-column hollow punch assembly of the present invention.

[0024] Figure 6 This is a cross-sectional view of the multi-column hollow punch assembly of the present invention.

[0025] Figure 7 This is a cross-sectional view of the bottom mold assembly of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Unless otherwise stated, the terminology used herein should be understood in accordance with the conventional usage of those skilled in the art.

[0027] Example 1 like Figures 1-7 A method for preparing a highly uniform niobium-titanium alloy ingot, comprising the following steps: Step S1. Provide sponge titanium, uniformly load the sponge titanium into a pressing device, and form it using a radial pressing process with a hydraulic press. The radial pressing pressure is 180 MPa, and the holding time is 8 min, resulting in a single-section hollow titanium billet. Multiple hollow titanium billets are then axially arranged and circumferentially welded. The vacuum degree of the circumferential welding is 2 × 10⁻⁶. -5 The electron beam voltage was 135kV, the electron beam current was 300mA, the welding speed was 30mm / min, the electron beam oscillation amplitude was 10mm, the electron beam oscillation frequency was 3Hz, and the axial welding adopted a 3-layer multi-pass welding process. After each layer was welded, the temperature was maintained for 12min to obtain a hollow titanium electrode with an inner diameter of 180mm, an outer diameter of 350mm, and a thickness of 170mm. The pressing device includes a pressing unit and a demolding unit; the pressing unit includes a multi-column hollow punch assembly 1 and a lower die assembly 2 disposed at the bottom of the multi-column hollow punch assembly; the pressing unit is located inside the hydraulic press host, the multi-column hollow punch assembly 1 includes a fixed plate 12 and multiple hollow cylindrical punches 11 disposed at the bottom of the fixed plate 12, the fixed plate 12 is connected to a driving device; the driving device can be a hydraulic press, the lower die assembly 2 is provided with multiple circular mold cavities 21 inside, the number of circular mold cavities 21 is consistent with the number of hollow cylindrical punches 11 and they are inserted one by one, and the central axis of the hollow cylindrical punches 11 coincides with the central axis of the circular mold cavity 21, the hollow cylindrical punches 11 can move up and down relative to the lower die assembly 2 under the drive of the movable crossbeam; The demolding unit includes an independently liftable bottom mold assembly 3 and a mandrel assembly 4. The bottom mold assembly 3 can move up and down relative to the lower mold assembly 2, and the mandrel assembly 4 can move up and down relative to the bottom mold assembly 3. The top of the mandrel assembly 4 can pass through the bottom mold assembly 3 and enter the circular mold cavity 21, and cooperate with the hollow cylindrical punch 11 to press the raw material in the circular mold cavity 21 into a hollow electrode. The fixed plate 12 is provided with positioning grooves 14 on both opposite side walls. The fixed plate 12 is fastened to the movable crossbeam with bolts, and the fixed plate 12 is positioned by the positioning grooves 14 and positioning pins to ensure that the hollow cylindrical punch 11 corresponds one-to-one with the circular mold cavity 21. The diameter of the circular mold cavity 21 is compatible with the outer diameter of the hollow cylindrical punch 11, and the hollow cylindrical punch 11 can move up and down in the circular mold cavity 21. Step S1, obtaining a single-segment hollow titanium blank, specifically includes the following steps: Step S11. The servo hydraulic cylinder drives the mandrel assembly 4 to rise to the material feeding position, and sponge titanium particles are put into each circular mold cavity 21. The hydraulic press drives the hollow cylindrical punch 11 to descend synchronously. After reaching the set pressure, the pressure is maintained to form a hollow electrode surrounding the mandrel 41. The mandrel assembly is then reset by the hydraulic press driving the movable crossbeam to move the hollow cylindrical punch 11. Step S12. The mandrel assembly 4 descends synchronously under the drive of the servo hydraulic cylinder until the top of the mandrel assembly 4 is completely separated from the inner hole of the hollow electrode; the bottom mold assembly 3 descends so that the single-segment hollow titanium blank is separated from the bottom mold assembly 3; the bottom mold assembly 3 and the mandrel assembly 4 rise and reset to the fabric position to obtain a set of single-segment hollow titanium blanks.

[0028] The hollow cylindrical punch 11 has a lower protrusion 13 at one end away from the fixed plate 12. The lower protrusion 13 is frustum-shaped, and its size decreases from top to bottom. The bottom mold assembly 3 includes a bottom mold with multiple protrusions 31. One end of each protrusion 31 has a frustum-shaped groove 32. The frustum-shaped groove 32 cooperates with the lower protrusion 13. The outer diameter of the protrusion 31 is less than or equal to the diameter of the circular mold cavity 21. The protrusion 31 can be fully accommodated in the circular mold cavity 21 and is engaged and fixed to the lower end of the circular mold cavity 21. The size of the frustum-shaped groove 32 decreases from top to bottom. The frustum-shaped groove 32 is adapted to the lower protrusion 13, and the two can be spliced ​​together. The shape of the frustum-shaped groove 32 is adapted to the lower end of the circular mold cavity 21. The size of the frustum-shaped groove 32 decreases from top to bottom, while the size of the lower end of the circular mold cavity 21 increases from top to bottom. This fit prevents material leakage.

[0029] The mandrel assembly 4 includes a base 42 and a plurality of mandrels 41 disposed on the base 42. The top of each mandrel 41 is hemispherical. Each base 42 is connected to an 80-ton servo hydraulic cylinder. The four servo hydraulic cylinders are precisely synchronized through a closed-loop servo control system.

[0030] The hollow part 15 of the hollow cylindrical punch 11 and the core rod 41 are both cylindrical, and the two together can produce a cylindrical hollow electrode.

[0031] Step S11, which involves feeding raw materials into each circular mold cavity 21, specifically includes the following steps: the hydraulic press drives the hollow cylindrical punch 11 to move upward, so that the hollow cylindrical punch 11 separates from the circular mold cavity 21, making it easier to feed raw materials into the circular mold cavity 21; The process of obtaining a set of single-segment hollow titanium blanks in step S12 specifically includes: the hydraulic press controlling the movable crossbeam to drive the hollow cylindrical punch 11 to move downwards, the hydraulic cylinder driving the bottom mold assembly 3 to move upwards, and at the same time, the servo hydraulic cylinder driving the mandrel assembly 4 to move upwards. The mandrel 41 in the mandrel assembly 4 can pass through the protrusion 31 of the bottom mold assembly 3 and enter the circular mold cavity 21, cooperating with the downward-moving hollow cylindrical punch 11 to press the raw material in the circular mold cavity 21 into a single-segment hollow titanium blank.

[0032] The diameter of the circular mold cavity 21 is matched with the outer diameter of the hollow cylindrical punch 11, so that the hollow cylindrical punch 11 can move up and down in the circular mold cavity 21.

[0033] The outer diameter of the mandrel 41 is less than the inner diameter of the hollow cylindrical punch 11 and less than the diameter of the circular mold cavity 21. The diameter of the circular mold cavity 21 is less than the outer diameter of the base 42. The height of the circular mold cavity 21 is greater than the pressing stroke of the mandrel assembly 4.

[0034] The lower mold assembly 2 is connected to the lower worktable via T-slots, T-bolts, and positioning blocks. The T-bolts are located at the bottom of the lower mold assembly 2 and are tightened with nuts after passing through the T-slots. The positioning blocks fit against the side of the lower worktable to ensure that the center of the circular mold cavity 21 is aligned with the center of the hollow cylindrical punch 11. A heat insulation pad is provided between the bottom of the lower mold assembly 2 and the lower worktable. The bottom mold assembly 3 is bolted to the lifting platform and positioned by guide posts. The guide posts are fixed on the lower worktable, and the guide sleeves are embedded in the lifting platform to ensure that the bottom mold assembly 3 does not tilt when it is raised or lowered.

[0035] The method of using the pressing device includes the following steps: Step a, Initialization and Material Placement: Calculate the required height of the mold cavity to accommodate the material, and control all mandrel assemblies 4 to rise to the material placement position. At this time, the top of the mandrel assembly 4 is located above the required mold cavity. Quantitatively add 40.6 kg of sponge titanium particles to each circular mold cavity 21. Since the top of the mandrel 41 is hemispherical, the sponge titanium particles are naturally distributed around the mandrel. Step b, Multi-station Synchronous Pressing: The hydraulic press (pressure of 12,000 tons) drives the multi-column hollow punch assembly 1 to descend synchronously, compacting the sponge titanium particles. After reaching the set pressure of 600 MPa, the pressure is held for 12 seconds before returning to form a titanium hollow electrode surrounding the mandrel assembly 4. Subsequently, the hydraulic press drives the movable crossbeam to reset the hollow cylindrical punch 11. Step c, Secondary linkage demolding: The mandrel assembly 4 descends synchronously by 500mm under the drive of an independent hydraulic system until the top of the mandrel assembly 4 is completely detached from the inner hole of the titanium hollow electrode; the bottom mold assembly 3 and the lifting platform descend as a whole by 300mm, and the titanium hollow electrode falls smoothly into the corresponding transport platform under the action of gravity; the bottom mold assembly 3 and the mandrel assembly 4 rise and reset to the material placement position, ready to prepare for the preparation of the next set of electrode blocks; Step d: Repeat steps a-c to obtain a preset number of single-segment hollow titanium billets. Place multiple single-segment hollow titanium billets on a stacking rack and stack them neatly.

[0036] Step S2. Provide a niobium rod and perform surface cleaning treatment on the niobium rod. The surface cleaning treatment is as follows: first, pickle the niobium rod with a mixed acid solution, then rinse it with deionized water, then dehydrate it with anhydrous ethanol, and finally dry it. The mixed acid solution includes hydrofluoric acid, nitric acid and deionized water, and the volume ratio of hydrofluoric acid, nitric acid and deionized water is 1:3:6. The pickling temperature is 22℃ and the pickling time is 20min. The deionized water is rinsed 4 times. The drying temperature is 110℃ and the holding time is 2h. Step S3. Slowly insert the niobium rod processed in step S2 into the inner hole of the hollow titanium electrode along the axial direction, so that the niobium rod and the hollow titanium electrode are coaxially arranged to form a composite electrode, and weld and fix the two ends of the composite electrode. Step S4. Place the assembled composite electrode into a vacuum arc furnace for melting to obtain a highly uniform niobium-titanium alloy ingot; Step S4 specifically includes the following steps: Step S41. Place the assembled composite electrode into a vacuum arc furnace and perform a single melting operation using a DC stabilizing arc method. Before melting, evacuate the vacuum arc furnace to a vacuum level of 3×10⁻⁶. -3 Pa, and control the melting voltage at 30V, the melting current at 10kA, and the arc stabilization current at 5A. Use 5kA low-power arc initiation, and increase the current to 12kA in the later stage of melting to ensure that the head of the ingot is fully melted. After melting, cool for 6 hours and then flatten the ingot to remove the loose area at the end. Step S42. Turn the flattened ingot over and place it into another suitable crystallizer. Before melting, further increase the vacuum level in the furnace to 8×10. -4 Pa, control the melting voltage to 32V, the current to 10kA, and the arc stabilization current to 8A, and use AC arc stabilization method for secondary melting. After melting, extend the cooling time to 8h, and after cooling, perform flattening treatment again. Step S43. Turn the ingot over again and place it into the crystallizer of the corresponding size. Before melting, evacuate the vacuum in the furnace to 3×10. - 4 Pa was used for secondary melting using an AC arc-stabilized method, controlling the melting voltage at 34V, the current at 12kA, and the arc-stabilizing current at 10A. During the melting process, the input power was gradually reduced by decreasing 1kA every 10 minutes to maintain a stable molten pool depth. The input power was further reduced during the feeding stage to ensure that the bottom of the ingot from the previous melting round remained completely on the auxiliary electrode. After melting, the ingot was cooled for 8 hours. The leakage rate for the first, second, and third melting processes was all 3×10⁻⁶. -6 Pa·m 3 / s.

[0037] The niobium-titanium alloy ingot prepared in Example 1 was subjected to performance testing, and the results are as follows: Compositional uniformity: Nb element segregation degree 0.6%, Ti element segregation degree 0.4%, no regional element enrichment.

[0038] Inclusion content: Oxygen content 0.002%, nitrogen content 0.001%, no Nb infusible metal inclusions.

[0039] Ingot density: 99.8%, free from porosity and looseness defects.

[0040] Example 2 like Figures 1-7 A method for preparing a highly uniform niobium-titanium alloy ingot, comprising the following steps: Step S1. Provide sponge titanium, uniformly load the sponge titanium into a pressing device, and form it using a radial pressing process with a hydraulic press. The radial pressing pressure is 160 MPa, and the holding time is 6 min, resulting in a single-section hollow titanium billet. Multiple hollow titanium billets are then axially arranged and circumferentially welded. The vacuum degree of the circumferential welding is 5 × 10⁻⁶. -4 The electron beam voltage was 125kV, the electron beam current was 280mA, the welding speed was 25mm / min, the electron beam oscillation amplitude was 9mm, the electron beam oscillation frequency was 2.5Hz, and the axial welding adopted a 4-layer multi-pass welding process. After each layer was welded, the temperature was maintained for 11min to obtain a hollow titanium electrode with an inner diameter of 150mm, an outer diameter of 300mm, and a thickness of 150mm. The pressing device includes a pressing unit and a demolding unit; the pressing unit includes a multi-column hollow punch assembly 1 and a lower die assembly 2 disposed at the bottom of the multi-column hollow punch assembly; the pressing unit is located inside the hydraulic press host, the multi-column hollow punch assembly 1 includes a fixed plate 12 and multiple hollow cylindrical punches 11 disposed at the bottom of the fixed plate 12, the fixed plate 12 is connected to a driving device; the driving device can be a hydraulic press, the lower die assembly 2 is provided with multiple circular mold cavities 21 inside, the number of circular mold cavities 21 is consistent with the number of hollow cylindrical punches 11 and they are inserted one by one, and the central axis of the hollow cylindrical punches 11 coincides with the central axis of the circular mold cavity 21, the hollow cylindrical punches 11 can move up and down relative to the lower die assembly 2 under the drive of the driving device; The demolding unit includes an independently liftable bottom mold assembly 3 and a mandrel assembly 4. The mandrel assembly 4 can move up and down relative to the bottom mold assembly 3. The top of the mandrel assembly 4 can pass through the bottom mold assembly 3 and enter the circular mold cavity 21, and cooperate with the hollow cylindrical punch 11 to press the raw material in the circular mold cavity 21 into a hollow electrode. The fixed plate 12 is provided with positioning grooves 14 on both opposite side walls. The fixed plate 12 is fastened to the movable crossbeam by bolts and positioned by positioning grooves 14 and positioning pins to ensure that the hollow cylindrical punch 11 corresponds one-to-one with the circular mold cavity 21. The diameter of the circular mold cavity 21 is compatible with the outer diameter of the hollow cylindrical punch 11, and the hollow cylindrical punch 11 can move up and down in the circular mold cavity 21.

[0041] Step S1, obtaining a single-segment hollow titanium blank, specifically includes the following steps: Step S11. Control the mandrel assembly 4 to rise to the material feeding position. The top of the mandrel assembly 4 is located above the required cavity height. Raw material is fed into each circular cavity 21. The driving device drives the multi-column hollow punch assembly 1 to descend synchronously. After reaching the set pressure, the pressure is maintained to form a hollow electrode surrounding the mandrel 41. Subsequently, the driving device drives the hollow cylindrical punch 11 to reset. Step S12. The mandrel assembly 4 descends synchronously under the drive of the servo hydraulic cylinder until the top of the mandrel assembly 4 is completely separated from the inner hole of the hollow electrode; the bottom mold assembly 3 descends so that the single-segment hollow titanium blank is separated from the bottom mold assembly 3; the bottom mold assembly 3 and the mandrel assembly 4 rise and reset to the fabric position to obtain a set of single-segment hollow titanium blanks.

[0042] The hollow cylindrical punch 11 has a lower protrusion 13 at one end away from the fixed plate 12, and the lower protrusion 13 is frustum-shaped; the bottom mold assembly 3 includes a bottom mold, and the bottom mold has a plurality of protrusions 31, and one end of the protrusion 31 has a frustum-shaped groove 32, which cooperates with the lower protrusion 13; the mandrel assembly 4 includes a base 42 and a plurality of mandrels 41 disposed on the base 42, the top of each mandrel 41 is hemispherical, and each base 42 is connected to an 80-ton servo hydraulic cylinder, and the four servo hydraulic cylinders are precisely synchronized through a closed-loop servo control system.

[0043] Step S11, which involves feeding raw materials into each circular mold cavity 21, specifically includes the following steps: the hydraulic press drives the hollow cylindrical punch 11 to move upward, so that the hollow cylindrical punch 11 separates from the circular mold cavity 21, making it easier to feed raw materials into the circular mold cavity 21; The process of obtaining a set of single-segment hollow titanium blanks in step S12 specifically includes: the hydraulic press controlling the movable crossbeam to drive the hollow cylindrical punch 11 to move downwards, the hydraulic cylinder driving the bottom mold assembly 3 to move upwards, and at the same time, the servo hydraulic cylinder driving the mandrel assembly 4 to move upwards. The mandrel 41 in the mandrel assembly 4 can pass through the protrusion 31 of the bottom mold assembly 3 and enter the circular mold cavity 21, cooperating with the downward-moving hollow cylindrical punch 11 to press the raw material in the circular mold cavity 21 into a single-segment hollow titanium blank.

[0044] The outer diameter of the mandrel 41 is less than the inner diameter of the hollow cylindrical punch 11 and less than the diameter of the circular mold cavity 21. The diameter of the circular mold cavity 21 is less than the outer diameter of the base 42. The height of the circular mold cavity 21 is greater than the pressing stroke of the mandrel assembly 4.

[0045] The pressing device also includes a lower worktable and a lifting platform. The lower die assembly 2 is connected to the lower worktable via a T-slot, a T-bolt, and a positioning block. The T-bolt is located at the bottom of the lower die assembly 2 and is tightened with a nut after passing through the T-slot. The positioning block fits against the side of the lower worktable to ensure that the center of the circular die cavity 21 is aligned with the center of the hollow cylindrical punch 11. A heat insulation pad is provided between the bottom of the lower die assembly 2 and the lower worktable. The bottom die assembly 3 is bolted to the lifting platform and positioned by a guide post. The guide post is fixed on the lower worktable, and the guide sleeve is embedded in the lifting platform to ensure that the bottom die assembly 3 does not tilt when it is raised or lowered. Driven by the lifting platform, the bottom die assembly 3 can move up and down relative to the lower die assembly 2.

[0046] In one implementation, the lifting platform of the bottom mold assembly 3 is driven by a 500-ton hydraulic cylinder.

[0047] The method of using the pressing device includes the following steps: Step a, Initialization and Clothing: Calculate the required height of the mold cavity to accommodate the cloth, and control all mandrel assemblies 4 to rise to the cloth position. At this time, the top of the mandrel assembly 4 is located above the required mold cavity. Quantitatively add 40.6 kg of sponge titanium particles to each circular mold cavity 21. Since the top of the mandrel 41 is hemispherical, the sponge titanium particles are naturally distributed around the mandrel. Step b, Multi-station synchronous pressing: The hydraulic press (pressure of 12,000 tons) drives the multi-column hollow punch assembly 1 to descend synchronously, compacting the sponge titanium particles. After reaching the set pressure of 600MPa, it holds the pressure for 12 seconds and returns to form a titanium hollow electrode surrounding the mandrel assembly 4. Subsequently, the hydraulic press drives the movable crossbeam to reset the hollow cylindrical punch 11. Step c, Secondary linkage demolding: The mandrel assembly 4 descends synchronously by 500mm under the drive of an independent hydraulic system until the top of the mandrel assembly 4 is completely detached from the inner hole of the titanium hollow electrode; the bottom mold assembly 3 and the lifting platform descend as a whole by 300mm, and the titanium hollow electrode falls smoothly into the corresponding transport platform under the action of gravity; the bottom mold assembly 3 and the mandrel assembly 4 rise and reset to the material placement position, ready to prepare for the preparation of the next set of electrode blocks; Step d: Repeat steps a-c to obtain a preset number of single-segment hollow titanium billets. Place multiple single-segment hollow titanium billets on a stacking rack and stack them neatly.

[0048] Step S2. Provide a niobium rod and perform surface cleaning treatment on the niobium rod. The surface cleaning treatment is as follows: first, pickle the niobium rod with a mixed acid solution, then rinse it with deionized water, then dehydrate it with anhydrous ethanol, and finally dry it. The mixed acid solution includes hydrofluoric acid, nitric acid and deionized water, and the volume ratio of hydrofluoric acid, nitric acid and deionized water is 1:3:6. The pickling temperature is 20℃ and the pickling time is 18min. The deionized water is rinsed 3 times. The drying temperature is 100℃ and the holding time is 1.5h. Step S3. Slowly insert the niobium rod processed in step S2 into the inner hole of the hollow titanium electrode along the axial direction, so that the niobium rod and the hollow titanium electrode are coaxially arranged to form a composite electrode, and weld and fix the two ends of the composite electrode. Step S4. Place the assembled composite electrode into a vacuum arc furnace for melting to obtain a highly uniform niobium-titanium alloy ingot; Step S4 specifically includes the following steps: Step S41. Place the assembled composite electrode into a vacuum arc furnace and perform a single melting operation using a DC stabilizing arc method. Before melting, evacuate the vacuum arc furnace to a vacuum level of 4 × 10⁻⁶. -3Pa, and control the melting voltage at 29V, the melting current at 9kA, and the arc stabilization current at 6A. Use 5kA low-power arc initiation. Increase the current to 12kA in the later stage of melting to ensure that the head of the ingot is fully melted. After melting, cool for 5 hours and flatten the ingot to remove the loose area at the end. Step S42. Turn the flattened ingot over and place it into another suitable crystallizer. Before melting, further increase the vacuum level in the furnace to 9×10. -4 Pa, control the melting voltage 31V, current 11kA, and arc stabilization current 7A, and use AC arc stabilization method for secondary melting. After melting, extend the cooling time to 7h, and after cooling, perform flattening treatment again. Step S43. Turn the ingot over again and place it into the crystallizer of the corresponding size. Before melting, evacuate the vacuum in the furnace to 4×10. - 4 Pa was used for secondary melting using an AC arc-stabilized method, controlling the melting voltage at 32~36V, the current at 12.5kA, and the arc-stabilizing current at 6A. During the melting process, the input power was gradually reduced by decreasing 1kA every 10 minutes to maintain a stable molten pool depth. During the feeding stage, the input power was further reduced to ensure that the bottom of the ingot from the previous melting round was completely retained on the auxiliary electrode. After melting, the ingot was cooled for 9 hours. The leakage rate for the first, second, and third melting processes was all 4×10⁻⁶. -6 Pa·m 3 / s.

[0049] After the three melting processes are completed and the ingot cools to room temperature in the furnace, the ingot is removed. The oxide scale, spatter, and end face burrs on the surface of the ingot are removed by mechanical grinding. Then, the ingot is subjected to ultrasonic non-destructive testing to ensure that the ingot is free from defects such as porosity, inclusions, cracks, and compositional segregation, and finally, a large-size, high-quality NbTi alloy ingot is obtained.

[0050] The niobium-titanium alloy ingot prepared in Example 2 was subjected to performance testing, and the results are as follows: Compositional uniformity: Nb element segregation degree 0.5%, Ti element segregation degree 0.3%, no regional element enrichment.

[0051] Inclusion content: Oxygen content 0.002%, nitrogen content 0.0012%, no Nb infusible metal inclusions.

[0052] Ingot density: 99.7%, free from porosity and looseness defects.

[0053] Example 3 A method for preparing a high-uniformity niobium-titanium alloy ingot includes a composite electrode for preparing the high-uniformity niobium-titanium alloy ingot, comprising a hollow titanium electrode and a niobium rod coaxially disposed in the hollow titanium electrode, wherein the hollow titanium electrode comprises a plurality of hollow titanium blanks arranged axially and circumferentially welded.

[0054] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a highly uniform niobium-titanium alloy ingot, characterized in that, Includes the following steps: Step S1. Provide sponge titanium, uniformly load the sponge titanium into a pressing device, and form it through a radial pressing process to obtain a single-segment hollow titanium blank. Arrange multiple hollow titanium blanks axially and weld them circumferentially to obtain a hollow titanium electrode. Step S2. Provide a niobium rod and perform surface cleaning treatment on the niobium rod; Step S3. Slowly insert the niobium rod processed in step S2 into the inner hole of the hollow titanium electrode along the axial direction, so that the niobium rod and the hollow titanium electrode are coaxially arranged to form a composite electrode, and weld and fix the two ends of the composite electrode. Step S4. Place the assembled composite electrode into a vacuum arc furnace for melting to obtain a highly uniform niobium-titanium alloy ingot.

2. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 1, characterized in that, In step S1, the radial pressing pressure is 150-200 MPa, and the holding time is 5-10 min.

3. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 1, characterized in that, In step S1, the hollow titanium electrode has an inner diameter of 50-300 mm, an outer diameter of 100-600 mm, and a thickness of 100-400 mm.

4. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 1, characterized in that, The vacuum degree for circumferential welding in step S1 is 5×10⁻⁶. -4 ~1×10 -5 The electron beam voltage is 120~150kV, the electron beam current is 250~350mA, the welding speed is 20~40mm / min, the electron beam oscillation amplitude is 8~12mm, the electron beam oscillation frequency is 2~5Hz, and the axial welding adopts a 3~4 layer multi-pass welding process, with each layer held at heat for 10~15min after welding.

5. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 1, characterized in that, The pressing device in step S1 includes a pressing unit and a demolding unit; The pressing unit includes a multi-column hollow punch assembly (1) and a lower die assembly (2) disposed at the bottom of the multi-column hollow punch assembly; the multi-column hollow punch assembly (1) includes a fixing plate (12) and a plurality of hollow cylindrical punches (11) disposed at the bottom of the fixing plate (12), the fixing plate (12) being connected to a driving device; the lower die assembly (2) has a plurality of circular cavities (21) inside, the number of circular cavities (21) being consistent with the number of hollow cylindrical punches (11) and being inserted one-to-one, and the central axis of the hollow cylindrical punches (11) being aligned with the central axis of the circular cavities (21). With the central axis coincident, the hollow cylindrical punch (11) can move up and down relative to the lower die assembly (2); the demolding unit includes a bottom die assembly (3) and a mandrel assembly (4) that can be raised and lowered independently. The bottom die assembly (3) can move up and down relative to the lower die assembly (2), and the mandrel assembly (4) can move up and down relative to the bottom die assembly (3). The top of the mandrel assembly (4) can pass through the bottom die assembly (3) and enter the circular mold cavity (21), and cooperate with the hollow cylindrical punch (11) to press the raw material in the circular mold cavity (21) into a single-segment hollow titanium billet; Step S1, which involves obtaining a single-segment hollow titanium blank, specifically includes the following steps: Step S11. Control the mandrel assembly (4) to rise to the fabric position. The top of the mandrel assembly (4) is above the required cavity height. Raw material is put into each circular cavity (21). The driving device drives the multi-column hollow punch assembly (1) to descend synchronously. After reaching the set pressure, the pressure is maintained to form a hollow electrode surrounding the mandrel (41). Subsequently, the driving device drives the hollow cylindrical punch (11) to reset. Step S12. The mandrel assembly (4) descends synchronously until the top of the mandrel assembly (4) is completely detached from the inner hole of the hollow electrode; the bottom mold assembly (3) descends so that the hollow electrode is detached from the bottom mold assembly (3); the bottom mold assembly (3) and the mandrel assembly (4) rise and reset to the fabric position to obtain a set of single-segment hollow titanium blanks.

6. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 5, characterized in that, The fixing plate (12) has positioning grooves (14) on both opposite side walls. The hollow cylindrical punch (11) has a lower protrusion (13) at one end away from the fixing plate (12). The lower protrusion (13) is in the shape of a frustum. The bottom mold assembly (3) includes a bottom mold, on which a plurality of protrusions (31) are provided. One end of each protrusion (31) is provided with a frustum-shaped groove (32), which cooperates with the lower protrusion (13). The mandrel assembly (4) includes a base (42) and a plurality of mandrels (41) disposed on the base (42). The top of each mandrel (41) is hemispherical, and each base (42) is connected to a lifting hydraulic system. The specific steps of feeding raw materials into each circular mold cavity (21) in step S11 include the following steps: the hydraulic press drives the hollow cylindrical punch (11) to move upward, so that the hollow cylindrical punch (11) separates from the circular mold cavity (21), making it easier to feed raw materials into the circular mold cavity (21); The process of obtaining a set of single-segment hollow titanium blanks in step S12 specifically includes: the driving device drives the hollow cylindrical punch (11) to move downward, the oil cylinder drives the bottom mold assembly (3) to move upward, and at the same time the lifting hydraulic system drives the mandrel assembly (4) to move upward. The mandrel (41) in the mandrel assembly (4) can pass through the protrusion (31) of the bottom mold assembly (3) and enter the circular mold cavity (21), and cooperate with the downward-moving hollow cylindrical punch (11) to press the raw material in the circular mold cavity (21) into a single-segment hollow titanium blank.

7. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 6, characterized in that, The outer diameter of the mandrel (41) is less than the inner diameter of the hollow cylindrical punch (11) and less than the diameter of the circular mold cavity (21). The diameter of the circular mold cavity (21) is less than the outer diameter of the base (42). The height of the circular mold cavity (21) is greater than the pressing stroke of the mandrel assembly (4).

8. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 1, characterized in that, The surface cleaning treatment in step S2 is as follows: the niobium rod is first pickled with a mixed acid solution, then rinsed with deionized water, then dehydrated with anhydrous ethanol, and finally dried. The mixed acid solution includes hydrofluoric acid, nitric acid and deionized water, with a volume ratio of 1:3:

6. The pickling temperature is 20~25℃ and the pickling time is 15~25min. The number of times the deionized water is rinsed is 3~5 times. The drying temperature is 100~120℃ and the holding time is 1~3h.

9. The method for preparing a highly uniform niobium-titanium alloy ingot as described in claim 1, characterized in that, Step S4 specifically includes the following steps: Step S41. Place the assembled composite electrode into a vacuum arc furnace and perform a single melting operation using a DC stabilizing arc method. Before melting, evacuate the vacuum furnace to a vacuum level of ≤5×10⁻⁶. -3 Pa, and control the melting voltage to 28~32V, the melting current to 8~12kA, and the arc stabilization current to 4~12A. Use 5kA low power to start the arc, and increase the current to 12kA in the later stage of melting to ensure that the head of the ingot is fully melted. After melting, cool for ≥4h, and flatten the ingot to remove the loose area at the end. Step S42. Turn the flattened ingot over and place it into another suitable crystallizer. Before melting, further increase the vacuum level in the furnace to ≤1×10⁻⁶. -3 Pa, control the melting voltage to 30~34V, the current to 10~14kA, and the arc stabilization current to 4-12A. Use AC arc stabilization method for secondary melting. After melting, extend the cooling time to ≥6h. After cooling, perform flattening treatment again. Step S43. Turn the ingot over again and place it into the crystallizer of the corresponding size. Before melting, evacuate the vacuum in the furnace to ≤5×10. -4 Pa uses an AC arc stabilization method for secondary melting, controlling the melting voltage at 32~36V, the current at 12~15kA, and the arc stabilization current at 4~12A. During the melting process, the input power is gradually reduced by decreasing 1kA every 10 minutes to maintain a stable molten pool depth. During the feeding stage, the input power is further reduced to ensure that the bottom of the ingot from the previous melting round is completely retained on the auxiliary electrode. After melting is completed, the ingot is cooled for ≥8 hours.

10. A composite electrode for preparing a high-uniformity niobium-titanium alloy ingot using a method for preparing a high-uniformity niobium-titanium alloy ingot as described in any one of claims 1 to 9, characterized in that, It includes a hollow titanium electrode and a niobium rod coaxially disposed in the hollow titanium electrode. The hollow titanium electrode comprises a plurality of hollow titanium blanks arranged axially and circumferentially welded.

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