Preparation method of high-uniformity superfine tungsten-rhenium wire

Abstract

This invention discloses a method for preparing highly uniform ultrafine tungsten rhenium wire based on multi-mode composite plastic deformation and online annealing control, aiming to solve the problems of severe work hardening, small deformation per pass, frequent annealing leading to uneven grain size, large wire diameter fluctuation, and high wire breakage rate in the drawing process. The steps include: (1) pre-treating the sintered billet using a composite billet opening technology of equal diameter angular extrusion and rotary forging to obtain a billet wire with ultra-high dislocation; (2) applying axial ultrasonic vibration during wire drawing to reduce drawing force and suppress microcracks, while integrating pulse current behind the deformation zone for millisecond-level rapid annealing to achieve dynamic recrystallization and recovery, and eliminate work hardening; (3) using a laser online diameter measurement and closed-loop feedback system to monitor the wire diameter in real time, automatically adjusting the drawing parameters and annealing intensity to ensure uniform diameter throughout the wire length. This invention achieves efficient and low-damage preparation of ultrafine tungsten rhenium wire, significantly improving the diameter tolerance, mechanical and electrical properties of the wire.

Description

Technical Field

[0001] This invention belongs to the field of precision preparation technology of refractory metal ultrafine wires, and specifically relates to a method for preparing high-performance, high-consistency tungsten-rhenium alloy ultrafine wires for high-end equipment such as high-temperature temperature measurement, crystal growth, vacuum electronics, and ion sources. Background Technology

[0002] Tungsten rhenium wire (typically W-3Re / W-25Re, etc.) is a key material for high-temperature thermocouples, sapphire single-crystal furnace-bundled heaters, vacuum furnace heating elements, and ion source filaments due to its high melting point, stable thermoelectric properties, excellent high-temperature strength, and corrosion resistance. With the miniaturization and precision of devices, the diameter requirements for wires are becoming increasingly stringent (e.g., below φ20μm), and near-demanding requirements are being placed on the uniformity of diameter, resistance consistency, and high-temperature lifespan along the entire length of the wire.

[0003] Currently, the preparation of ultrafine tungsten rhenium wire mainly relies on the traditional multi-pass drawing combined with intermediate annealing process. This process route has fundamental bottlenecks: (1) contradiction between work hardening and annealing: small deformation per pass and frequent intermediate annealing. Small fluctuations in the annealing process (temperature, time) will lead to uneven grain size, which in turn will cause local mechanical and electrical property differences in the wire; (2) low diameter control accuracy: factors such as wire drawing die wear, vibration, and temperature fluctuations make it difficult to control the wire diameter online, resulting in poor uniformity along the entire length; (3) high wire breakage rate of ultrafine wire: as the wire diameter becomes thinner, the toughness reserve of the wire decreases, and any small defects or performance inhomogeneities in the interior will become crack sources under tensile stress, leading to wire breakage; (4) difficulty in achieving both surface quality and performance consistency: frequent annealing and pickling can easily lead to surface damage and impurity penetration. Summary of the Invention

[0004] The purpose of this invention:

[0005] To overcome the shortcomings of traditional wire drawing technology, an innovative method is provided that can achieve high uniformity, high performance and high yield in the preparation of ultrafine tungsten rhenium wire.

[0006] The technical solution adopted in this invention is as follows:

[0007] The core innovation of the preparation method of highly uniform ultrafine tungsten rhenium wire lies in the construction of a full-process precision control system that includes "bulk microstructure optimization → energy-assisted friction reduction and loss reduction → online instantaneous softening → intelligent closed-loop diameter control".

[0008] 1. Billet Pretreatment and Composite Forging: The sintered billet is pretreated using equal diameter angular extrusion (ECAP), a highly plastic deformation technique. ECAP introduces extremely high shear strain without changing the billet's cross-sectional area, effectively breaking down coarse grains to obtain an ultrafine-grained (down to submicron) microstructure and significantly increasing dislocation density. This microstructure provides excellent plasticity for subsequent drawing, allowing for larger passes. Subsequent rotary forging further densifies and homogenizes the microstructure.

[0009] 2. Ultrasonic Vibration Assisted Micro-Stretching: To reduce drawing stress and improve surface quality, axial ultrasonic vibration is applied to the wire during the drawing process. The "volume effect" of ultrasonic vibration can reduce the drawing force by 20%-40%, reducing the tensile stress on the wire and lowering the risk of wire breakage; its "surface effect" can effectively reduce friction between the wire and the die, inhibit the generation of microcracks, and improve surface finish.

[0010] 3. Pulsed Current Online Annealing: To eliminate performance fluctuations, a high-energy pulsed current is applied immediately after the wire is demolded for instantaneous annealing. The Joule heating effect of the pulsed current allows the wire to rapidly rise to near its recrystallization temperature within milliseconds, achieving efficient dynamic recovery and recrystallization, almost completely eliminating work hardening from the previous pass. Due to the extremely short heating time and narrow heat-affected zone, excessive grain growth is avoided, resulting in a fine and uniform equiaxed grain structure. This continuous "drawing-instantaneous annealing" process replaces the traditional discrete intermediate annealing, completely eliminating performance fluctuations caused by uneven batch annealing.

[0011] 4. Intelligent closed-loop control: In order to ensure diameter uniformity, an integrated laser diameter measuring instrument is used to monitor the wire diameter in real time and feed the signal back to the control system. The system automatically fine-tunes the pulling speed, ultrasonic power and pulse current parameters to form a closed-loop control, ensuring the high stability of the wire diameter along its entire length. Detailed Implementation

[0012] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0013] Unless otherwise specified, in all embodiments and comparative examples, sintered billets of tungsten-rhenium alloy (W-25Re) with a rhenium content of 25wt% were used as raw materials, with an initial diameter of Φ2.0mm.

[0014] Example 1

[0015] (1) Billet pretreatment and composite billet making:

[0016] The W-25Re alloy sintered billet was heated to 1350℃ under argon protection and held for 30 minutes. Using an equal-diameter angular extrusion die (channel angle 110°), three extrusion passes were performed along the Bc path (the billet rotated 90° around its axis after each extrusion pass), with the billet returning to its initial orientation between passes. Immediately afterward, multi-die rotary forging was performed to reduce the billet diameter from Φ2.0mm to Φ0.8mm, obtaining a coarse wire billet with fine grains and a uniform microstructure.

[0017] (2) Ultrasonic vibration-assisted micro-stretching:

[0018] The coarse filament is fed into a micro-drawing machine, with an ultrasonic vibration device installed in front of the drawing die inlet. Axial vibration at a frequency of 30kHz and an amplitude of 10μm is applied to the moving filament. A nano-hexagonal boron nitride-based lubricant (particle size ≤80nm) is continuously supplied to the drawing die. The deformation per pass is controlled at 18%, drawing the filament from Φ0.8mm to Φ0.5mm.

[0019] (3) Pulsed current online annealing:

[0020] After the filament exits the mold and before winding, it is passed through a pair of pulsed current electrodes. A pulsed current with a current density of 6000 A / mm², a pulse width of 5 ms, and a frequency of 50 Hz is applied for instantaneous Joule heating annealing.

[0021] (4) Intelligent closed-loop control:

[0022] A laser diameter gauge is used to monitor the diameter of the annealed wire in real time, with an accuracy of ±0.1μm. The diameter signal is fed back to the control system to dynamically adjust the drawing speed, ultrasonic power, and pulse current parameters.

[0023] (5) Repeated pulling:

[0024] Repeat steps (2)-(4) to perform multiple drawing passes, and finally achieve the target diameter Φ25μm.

[0025] Product diameter uniformity: Wire diameter Φ25.0±0.3μm, diameter fluctuation no greater than ±0.5μm; Room temperature mechanical properties: Tensile strength 2150MPa, elongation after fracture 15%; Resistivity consistency: Room temperature resistivity fluctuation better than ±1.2%; High temperature life: Life reaches 120 hours in static air at 1800℃, life fluctuation better than ±8%; Microstructure: Uniform and fine equiaxed recrystallized structure, average grain size 1.2μm.

[0026] Example 2

[0027] Process modification: In process (2), the ultrasonic vibration frequency is changed to 25kHz and the amplitude is changed to 8μm. The deformation per pass is adjusted to 15%.

[0028] Product diameter uniformity: Φ25.0±0.4μm, room temperature mechanical properties: tensile strength 2050MPa, elongation after fracture 16%, resistivity consistency: fluctuation better than ±1.3%, high temperature life: 115 hours at 1800℃, fluctuation better than ±9%, microstructure: average grain size 1.3μm.

[0029] Example 3

[0030] Process modification: In process (2), the ultrasonic vibration frequency is changed to 35kHz and the amplitude is changed to 12μm. The deformation per pass is adjusted to 22%.

[0031] Product diameter uniformity: Φ25.0±0.5μm, room temperature mechanical properties: tensile strength 2250MPa, elongation after fracture 13%, resistivity consistency: fluctuation better than ±1.4%, high temperature life: 110 hours at 1800℃, fluctuation better than ±10%, microstructure: average grain size 1.1μm.

[0032] Example 4

[0033] Process modification: In process (3), the pulse current density is adjusted to 4000A / mm² and the pulse width is adjusted to 8 milliseconds.

[0034] Product diameter uniformity: Φ25.0±0.3μm, room temperature mechanical properties: tensile strength 2100MPa, elongation after fracture 14%, resistivity consistency: fluctuation better than ±1.3%, high temperature life: 1800℃ life 118 hours, fluctuation better than ±9%, microstructure: average grain size 1.4μm.

[0035] Example 5

[0036] Process modification: In process (3), the pulse current density is adjusted to 8000A / mm² and the pulse width is adjusted to 3 milliseconds.

[0037] Product diameter uniformity: Φ25.0±0.4μm, room temperature mechanical properties: tensile strength 2200MPa, elongation after fracture 12%, resistivity consistency: fluctuation better than ±1.5%, high temperature life: 105 hours at 1800℃, fluctuation better than ±10%, microstructure: average grain size 1.0μm.

[0038] Example 6

[0039] Process modification: In process (1), the number of equal diameter angular extrusion passes is increased to 4. The final target diameter is changed to Φ15μm.

[0040] Product diameter uniformity: Φ15.0±0.2μm, room temperature mechanical properties: tensile strength 2400MPa, elongation after fracture 10%, resistivity consistency: fluctuation better than ±1.6%, high temperature life: 95 hours at 1800℃, fluctuation better than ±10%, microstructure: average grain size 0.8μm.

[0041] Example 7

[0042] Process modification: Use W-3Re alloy with rhenium content of 3wt%. In process (2), the lubricant is changed to nano-diamond based.

[0043] Product diameter uniformity: Φ25.0±0.3μm, room temperature mechanical properties: tensile strength 1980MPa, elongation after fracture 18%, resistivity consistency: fluctuation better than ±1.2%, high temperature life: 100 hours at 1800℃, fluctuation better than ±10%, microstructure: average grain size 1.5μm.

[0044] Comparative Example 1

[0045] Process modification: The equal diameter angular extrusion pretreatment in step (1) is omitted, and the sintered billet is directly subjected to rotary forging and drawing.

[0046] Product diameter uniformity: Φ25.0±1.5μm, with severe fluctuations; room temperature mechanical properties: tensile strength 1850MPa, elongation after fracture 8%, with large performance dispersion; resistivity consistency: fluctuation rate exceeds ±5%; high temperature life: 70 hours at 1800℃, with fluctuation rate exceeding ±25%; problem: uneven billet structure, leading to difficulties in subsequent processing and poor performance consistency.

[0047] Comparative Example 2

[0048] Process modification: The ultrasonic vibration assistance in step (2) is omitted, and the traditional dry drawing method is adopted.

[0049] Product diameter uniformity: Φ25.0±0.8μm, room temperature mechanical properties: tensile strength 1950MPa, elongation after fracture 9%, high wire breakage rate, surface quality: rough surface with scratches and microcracks, resistivity consistency: fluctuation rate exceeds ±3%, problems: high pull-out force, poor surface quality, low yield.

[0050] Comparative Example 3

[0051] Process modification: The pulse current online annealing in step (3) is omitted, and traditional intermittent furnace annealing is adopted.

[0052] Product diameter uniformity: Φ25.0±1.2μm, room temperature mechanical properties: tensile strength 1900MPa, elongation after fracture 11%, large performance fluctuation, resistivity consistency: fluctuation rate exceeds ±4%, microstructure: uneven grain size, mixed crystal phenomenon exists, problem: unstable annealing process, resulting in uneven microstructure and properties.

[0053] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0054] Process or parameter changes Normal process Reduce ultrasonic vibration frequency, amplitude, and channel deformation. Improve ultrasonic vibration frequency, amplitude, and channel deformation. Reduce pulse circuit density and increase pulse width Increase pulse circuit density and reduce pulse width Increasing the number of equal diameter angular extrusion passes reduces the final target diameter. Change alloy composition and lubricant Omit equal diameter angular extrusion pretreatment Omitted ultrasonic vibration assistance Omitted pulsed current online annealing Alloy sintered billet feed rate (kg) 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 rhenium content in alloy (wt%) 25.0 25.0 25.0 25.0 25.0 25.0 3.0 25.0 25.0 25.0 Equal diameter angular extrusion passes 1~4 3 3 3 3 3 4 3 - 3 3 Mass of extruded billet (kg) 0.980 0.980 0.980 0.980 0.980 0.975 0.980 1.000 0.980 0.980 Target diameter for rotary forging (mm) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Mass of coarse wire after rotary forging (kg) 0.965 0.965 0.965 0.965 0.965 0.957 0.965 0.975 0.965 0.965 Ultrasonic vibration frequency (kHz) 20-40 30 25 35 30 30 30 30 30 - 30 Ultrasonic vibration amplitude (μm) 5~15 10 8 12 10 10 10 10 10 - 10 lubricant Nano-hexagonal boron nitride Nano-hexagonal boron nitride Nano-hexagonal boron nitride Nano-hexagonal boron nitride Nano-hexagonal boron nitride Nano-hexagonal boron nitride Nano diamond Nano-hexagonal boron nitride Nano-hexagonal boron nitride Nano-hexagonal boron nitride Deformation per pass (%) 10~25 18 15 22 18 18 18 18 18 18 18 Mass of the intermediate wire after drawing (kg) 0.936 0.941 0.926 0.936 0.931 0.909 0.938 0.897 0.907 0.921 Pulse current density (A / mm²) ≥5000 6000.0 6000.0 6000.0 4000.0 8000.0 6000.0 6000.0 6000.0 6000.0 - Pulse width (s) 1~10 5 5 5 8 3 3 5 5 5 - Weight of annealed wire (kg) 0.935 0.94 0.925 0.935 0.93 0.908 0.937 0.896 0.906 0.921 Final target diameter (μm) 10-50 25.0 25.0 25.0 25.0 25.0 15.0 25.0 25.0 25.0 25.0 Final weight of tungsten rhenium wire (kg) 0.916 0.921 0.907 0.916 0.911 0.881 0.918 0.869 0.884 0.898 Overall diameter of the filament (μm) 10-50 25.0±0.3 25.0±0.4 25.0±0.5 25.0±0.3 25.0±0.4 15.0±0.2 25.0±0.3 25.0±1.5 25.0±0.8 25.0±1.2 Diameter fluctuation (μm) ≤±0.5 ≤±0.5 ≤±0.5 ≤±0.5 ≤±0.5 ≤±0.5 ≤±0.5 ≤±0.5 serious ≤±0.8 ≤±0.2 Tensile strength at room temperature (MPa) 2150 2050 2250 2100 2200 2400 1980 1850 1950 1900 Elongation after fracture (%) 15 16 13 16 12 10 18 8 9 11 Room temperature resistivity fluctuation (%) ＜±1.5 ＜±1.2 ＜±1.3 ＜±1.4 ＜±1.3 ＜±1.5 ＜±1.6 ＜±1.2 ＜±5 ＞±3 ＞±4 High-temperature lifespan (h) 120 115 110 118 105 95 100 70 80 90 Lifetime volatility (%) ＜±10 ＜±8 ＜±9 ＜±10 ＜±9 ＜±10 ＜±10 ＜±10 ＜±25 ＜±20 ＜±15 Average grain size (μm) 1.2 1.3 1.1 1.4 1.0 0.8 1.5 Inequality 1.2 Inequality

Claims

1. A method for preparing highly uniform ultrafine tungsten-rhenium wire, characterized in that, The process includes the following steps: (1) Pretreatment of billet and composite billet making: The sintered billet of tungsten rhenium alloy is heated to 1200-1500℃ under a protective atmosphere. It is first extruded 1-4 times through an equal diameter angular extrusion die, and then immediately subjected to multi-die rotary forging to reduce the diameter, so as to obtain a coarse wire billet with fine grains and uniform structure. (2) Ultrasonic vibration-assisted micro-stretching: The coarse wire blank is fed into the micro-stretching machine. An ultrasonic vibration device is installed in front of the drawing die inlet to apply axial vibration with a frequency of 20-40kHz and an amplitude of 5-15μm to the wire in motion; the deformation per pass is controlled at 10%-25%; (3) Pulsed current online annealing: After the wire is demolded and before it is wound, it is passed through a pair of pulsed current electrodes and instantaneously Joule heating annealed by applying a high-density (≥5000A / mm²) and short pulse width (1-10 ms) pulsed current. (4) Intelligent closed-loop control: The diameter of the annealed wire is monitored in real time by a laser diameter measuring instrument, and the diameter signal is fed back to the control system to dynamically adjust the drawing speed, ultrasonic vibration parameters and pulse current energy to maintain a constant wire diameter; (5) Repeat steps (2)-(4) to perform multiple drawing passes until the target ultra-fine diameter (e.g., 10-50 μm) is achieved.

2. The method according to claim 1, characterized in that, In process (1), the equal diameter angular extrusion uses a die with a channel angle of 90°-120°, the extrusion path is Bc path (the billet rotates 90° around its axis after each extrusion), and the extrusion temperature is 0.5-0.6 times the absolute temperature of the alloy melting point.

3. The method according to claim 1, characterized in that, In step (2), during the ultrasonic vibration-assisted micro-stretching process, an ultrafine lubricant based on nanodiamond or hexagonal boron nitride is continuously supplied into the drawing die. The lubricant particle size is ≤100nm to reduce friction and adhesive wear.

4. The method according to claim 1, characterized in that, In step (3), the pulsed current online annealing has a pulse frequency of 1-100Hz. By adjusting the pulse frequency and duty cycle, the instantaneous temperature of the wire is controlled near its recrystallization temperature (0.7-0.9Tm), so as to achieve continuous dynamic recovery and recrystallization, thereby almost completely eliminating work hardening.

5. A highly uniform ultrafine tungsten-rhenium wire prepared by the method according to any one of claims 1-4, characterized in that, Its diameter ranges from 10 to 50 μm, with a total diameter fluctuation of no more than ±0.5 μm, a room temperature resistivity fluctuation better than ±1.5%, and a creep life fluctuation better than ±10% at 1800℃.