Experimental study on the preparation of 3D printed tantalum metal powder by filament electroburst method
Release time:
2025-04-29
1 Introduction
In recent years, tantalum metal is widely used in aerospace, defense, chemical industry and other fields due to its high melting point and low vapor pressure [1]. In addition, tantalum and its alloys have been increasingly used in 3D printing of medical human implants due to its excellent biocompatibility and bone bioactivity, as well as its ability to induce bone growth and resist bacterial infection [2].
Therefore, the research application of tantalum and its alloys in 3D printing medical human implants is increasing [2].
At present, as a refractory tantalum raw material for 3D printing - metal tantalum powder, the main preparation methods are physicochemical method, plasma spheronization method, plasma rotating electrode atomization method, radio frequency plasma spheronization method [3]. A domestic company uses hydrogenation dehydrogenation method to prepare spherical/spherical tantalum powder, the obtained tantalum powder has the characteristics of concentrated particle size distribution, good fluidity, low oxygen content [4], but the preparation process is complex, tantalum powder purity is low; a foreign company adopts plasma spheronization technology to prepare spherical tantalum powder, the prepared tantalum powder is low in oxygen content [5], but the cost of the preparation is high, and the efficiency of a single spheronization is low; a domestic company adopts plasma Rotating electrode atomization method for the preparation of tantalum powder, obtaining a high degree of sphericity, high purity of spherical tantalum metal powder [6], but the method requires high-power, high-energy-consuming system, and the particle size of the prepared tantalum powder is not easy to control; a domestic research institute to use radio-frequency plasma spheroidization technology to prepare a smooth surface, good sphericity, no hollow powder spherical tantalum powder [7], but the tantalum powder particle size is not easy to control, dependent on the original powder particle size.
This paper focuses on a non-contact gas discharge type electro-explosive device, the metal powder prepared by this device has the advantages of good sphericity, less satellite powder and easy to control the particle size. By changing the initial charging voltage, tantalum wire diameter for the test, collecting the electrical signal of the circuit, combined with the waveform to analyze the mechanism, and observing the morphology of tantalum powder, statistics of tantalum powder particles particle size, and studied the relationship between different electrical parameters and energy deposition, particle size.
2 test device and method
The circuit principle of the electro-explosive preparation of metal powder device is shown in Figure 1, which is mainly composed of boosting circuit, voltage doubling rectifier circuit, isolation switch, line resistance, line inductance, energy storage capacitance and so on.
Metal wire electric explosion test process for the first explosion chamber cavity into a vacuum, then filled with argon to 0.1MPa; and then through the charging circuit to the energy storage capacitor charging, which makes the formation of a high-voltage electric field between the two electrodes; followed by the reciprocating mechanism to drive the wire wheel will be sent to the electrode between the wire; and finally the isolation switch action, the switch to penetrate the air gap, under the action of the high-voltage electric field will be the end of the electrode end of the part of the wire between the gap between the air Breakthrough, and then realize the pulse of high current into the wire to complete the electric explosion.
The use of TektronixP6015A high-voltage probe and Pearson101 Roche coil to collect voltage and current response in the process of electro-explosion, the response signal through the high-sampling rate TektronixTDS2024B digital oscilloscope acquisition and storage; and the use of SEM (scanning electron microscope) to analyze the morphological characteristics of the explosion products. NanoMeasure software statistics of metal powder particle size and distribution. The energy storage capacitance was 8.88 μF, the metal wire was tantalum wire with 99.99% purity, which is easily available in the market, the length of the air gap between the isolation switches was 2 mm, the length of the air gap between the electrodes and the metal wire was 1.8 mm, and the electrode spacing was set to 56 mm.
Deposition energy is an important indicator of the quality of the explosion in the electro-explosive process of the wire, which is calculated as the electro-explosive process of the voltage on the wire and the product of the current in the loop in the electro-explosive time period of the integral. Measured in the actual test voltage for the voltage on the wire, electrode and wire between the air gap resistance voltage and air gap inductance voltage, line resistance voltage and line inductance voltage and the sum of the voltage, namely
where u(t) is the measured voltage, ur(t) is the voltage on the metal wire, i(t) is the loop current, L is the sum of the line inductance and air gap inductance, and R is the sum of the line resistance and air gap resistance.
The air gap inductance Lδ can be obtained from the empirical formula [8], which is calculated as
where d is the length of the spark channel in cm, a and b are the radii of the spark channel and return conductor in cm, respectively, and the inductance of the spark channel in nH.
The air gap resistance Rδ can be obtained from the spark resistance calculation equation [9] proposed by Weizel and Rompe, which is calculated as
where s is the air gap spacing, p is the atmospheric pressure (0.1 MPa), and a is the gas spark constant (the gas spark constant for argon [10] is 22Pα-m2-V-2-s-1).
According to the method mentioned in the literature [11], the initial charging voltage is set to 6 kV, the short-circuit copper wire length is 56 mm, and the wire diameter is 2.5 mm, and the loop inductance is estimated to be about 0.026 μH and the resistance is about 0.008 Ω by the short-circuit current test.
Since the main way of depositing energy is the Joule heat generated on the wire when it passes through the pulsed high current, the deposition energy is
where ur(t) is the voltage on the metal wire, t0 is the starting moment of the explosion, and t3 is the ending moment of the explosion.
3 test results and analysis
Typical waveform from Figure 2 tantalum wire can be seen, tantalum wire electric explosion waveform is different from the typical voltage and current waveforms of the previous wire electric explosion [12], did not appear the first rapid rise in current after the decline until zero, but a slow rise until the end of the explosion as plasma oscillations.
According to the circuit parameters and voltage and current waveform characteristics, and reference to the tungsten wire electro-explosion process [13-14], the tantalum wire electro-explosion process is divided into the following five stages, as shown in Figure 3.
0-t0 stage: isolation switch action, current breakdown isolation switch air gap and electrode air gap; t0-t1 stage: the current acts on the tantalum wire, began to deposit energy for solid-state heating; t1-t2 stage: tantalum wire for solid-state heating, its resistance changes are small, and gradually transformed from solid to liquid, at this time the tantalum wire is in the solid-liquid mixing state, the moment of t2 tantalum wire completely melted; t2-t3 stage: tantalum wire started from the liquid to the gas state. wire began to be transformed from liquid to gas, the voltage rises rapidly to promote the ionization process, the macroscopic performance of the voltage rises rapidly to the apex and then falls, this phenomenon is called the voltage collapse, also known as the breakdown process [14]; t3 moments after: t3 moments of the voltage reaches a peak, the peak point for the phase explosion point, tantalum wire in the discharge channel formed before the expansion of the gasification after the formation of the plasma in the process, the beginning of the plasma Oscillation.
3.1 The effect of changes in wire diameter on the discharge parameters
For 0.2mm, 0.3mm diameter tantalum wire electric explosion did not completely gasification, belongs to the incomplete gasification type, while 0.4mm diameter tantalum wire occurred completely gasification, belongs to the complete gasification type. 0.2mm, 0.3mm diameter tantalum wire in the voltage before the collapse, did not appear the phenomenon of sudden changes in the current, while 0.4mm diameter tantalum wire in the voltage before the collapse of the current appeared to be a sudden change, become flat and then slowly rise to the peak. rises slowly to the peak value.
Initial charging voltage of 10kV voltage and current waveforms under different filament diameters are shown in Figure 4. With the increase of tantalum wire diameter, the moment of the peak voltage of the electric explosion is delayed, the time required for the phase transition to gasification increases, the moment of the electric explosion is delayed, the specific parameters are shown in Table 1. tantalum wire diameter increased from 0.2mm to 0.4mm, the peak voltage decreased from 9.6kV to 7kV, but the current corresponding to the peak voltage is multiplied by a factor of increase, and the moment of the peak voltage is delayed from 0.94μs to 1.96μs.
This is because with the increase in tantalum wire diameter, the time required for vaporization increases, resulting in the delay in the moment of the peak voltage, which in turn makes the time required for the electric explosion increases; in the tantalum wire state is a solid state, the initial resistance is with the increase in wire diameter continues to decrease, in the tantalum wire phase change to the gaseous state in the process of the tantalum wire resistance will be increased dramatically, but the resistance of the tantalum wire with a large diameter in the gasification relative to the tantalum wire resistance is still smaller than that of the tantalum wire with a small diameter, the resistance is still smaller than that of the tantalum wire. Wire resistance is still smaller than the resistance of small diameter tantalum wire, although the wire diameter of 0.4mm tantalum wire gasification of the current required is greater than the wire diameter of 0.2mm, 0.3mm tantalum wire current required, but the peak voltage with the increase in tantalum wire diameter shows a downward trend.
3.2 Effect of initial charging voltage on deposition energy
According to the formula of heat absorbed by metal wire [15], calculate the melting energy and vaporization energy required for tantalum wire with different wire diameters. Comparing the deposition energy of tantalum wire under different wire diameters and different initial voltages, it is found that the tantalum wire with a wire diameter of 0.4 mm is completely vaporized to form a plasma to oscillate at any initial charging voltage; and for tantalum wires with wire diameters of 0.2 mm and 0.3 mm, the deposition energy is intermediate between the melting energy and the vaporization energy in this condition, that is to say, a part of tantalum wire is melted, and part of tantalum wire is vaporized, and this gas-liquid mixture is not as good as that of tantalum wire under different initial charging voltages. This gas-liquid mixture formed metallic tantalum powder after the end of the deposition energy, accompanied by a shock wave and argon gas cooled after a rapid collision.
10
Tantalum wire of different diameters in different initial charging voltage under the electro-explosive deposition energy shown in Table 2, with the initial charging voltage continues to increase, the tantalum wire on the deposition of energy also has a different degree of increase, and the wire diameter of 0.4mm tantalum wire on the deposition energy is always the diameter of 0.3mm, 0.2mm tantalum wire on the deposition of energy of a few times as much, this is because with the tantalum wire diameter increases, initial resistance is decreasing, the current passes more easily through the interior of the wire rather than the surface, and the time required for vaporization during electroexplosion increases.
11
With the increasing initial charging voltage, the deposition energy on the tantalum wire with a filament diameter of 0.4 mm also increases to different degrees, and the average particle size of micron tantalum powder gradually decreases, and the initial charging voltage of 11 kV ~ 14 kV, the average particle size of micron tantalum powder does not change significantly, and stays at about 11 μm as shown in Fig. 5, while the particle size requirement of 3D printed metal powder is generally in the range of 20 μm ~ 80 μm [16]. m [16], which is a large difference from the average particle size of the desired tantalum powder.
3.3 Tantalum powder micro-morphology and particle size distribution
By observing the electron microscope photographs taken under different initial voltages of 0.4mm tantalum wire, it was found that only when the initial charging voltage was 10kV, the tantalum powder particles were spherical or spheroidal, more uniformly distributed, with smooth surfaces, good sphericity, and fewer particles with obvious defects, but with a wider range of particle size distribution, as shown in Fig. 6(a); whereas under other initial voltages, the tantalum powder particles were basically in the form of a droplet, with more flocculents around them, and the initial particle size distribution was much larger. flocculent more, it is initially judged that this flocculent is the particle size of nanometer level particles, and the agglomeration phenomenon occurs, as shown in Figure 6(b).
Observation of scanning electron microscope photographs of 0.3mm and 0.2mm tantalum wires under different initial charging voltages revealed that only micrometer tantalum powder particles with a narrower distribution can be obtained under an initial charging voltage of 10kV, as shown in Figure 7. However, 0.3mm wire diameter tantalum wire under the condition of initial charging voltage of 10kV, more satellite powder appeared, the formation of this satellite powder is because in the process of explosion, a strong shock wave will be generated, the explosion formed by the mass of the larger particles will obtain a smaller speed, the mass of the smaller particles will obtain a larger speed, in the role of the same shock wave, the particles of different masses will contact each other, the mass of the larger particles have a larger surface and cooling is slower, the smaller particles in the cooling process will therefore be attached to the surface of the larger particles, as the larger particles cooled to form a satellite sphere of powder.
13
As shown in Figure 8 is the particle size distribution of micron tantalum powder particles obtained by electroexplosion of tantalum wire with three different wire diameters at an initial charging voltage of 10 kV, it can be seen from the figure that the particle size distribution of micron tantalum powder particles prepared by tantalum wire with different wire diameters is similar to a positively skewed distribution, with the tantalum powder prepared by 0.2 mm tantalum wire concentrated in the range of 28 μm to 36 μm, and that of 0.3 mm tantalum wire concentrated in the range of 43 μm to 57 μm, and that of 0.3 mm tantalum wire concentrated in the range of 43 μm to 57 μm. between 43μm~57μm, and the tantalum powder prepared by 0.4mm tantalum wire is concentrated between 49μm~86μm. In these three cases, the distribution range of micron tantalum powder is narrower under 0.2mm conditions, and the distribution range of micron tantalum powder is wider under 0.3mm and 0.4mm conditions, but the required micron tantalum powder can also be obtained after screening.
4 Conclusion
Tests show that the gas discharge type preparation of metal powder electro-explosion device can produce relatively pure, spherical degree of good micron spherical tantalum powder particles, this method lays the foundation for the preparation of micron spherical tantalum powder.
Different wire diameter filament electro-explosion process have gone through five stages, wire diameter of 0.4mm tantalum wire in the electro-explosion process occurred in the complete gasification, while the wire diameter of 0.2mm, 0.3mm tantalum wire is not completely gasification, in the gas-liquid mixing state. In the same initial charging voltage, with the increase in tantalum wire diameter, the peak voltage of the electric explosion was a downward trend and the moment of the peak voltage delayed, the phase transition to the gasification of the time required to increase the moment of the electric explosion is delayed, the time required for the electric explosion increased. With the increasing initial charging voltage, the deposition energy on a certain wire diameter tantalum wire will have different degrees of increase, the average particle size of the prepared micron spherical tantalum powder in the gradual decrease. At an initial charging voltage of 10 kV, tantalum filaments of different filament diameters can obtain spherical micron tantalum powder with a more uniform distribution, smooth surface and good sphericity. micron tantalum powder under 0.2 mm conditions has a narrower distribution range, good sphericity, and meets the particle size requirements of micron-sized 3D printing metal powders.
Reference: Qin Jun et al: Experimental Study on Preparation of 3D Printed Tantalum Metal Powder by Silk Electroburst Method
Spherical tantalum powder prepared by Stardust Technology using RF plasma spheronization technology is characterized by high purity, low oxygen content and good fluidity. The technology melts irregular tantalum powder particles through high-temperature plasma to form a spherical shape under the action of surface tension, which effectively improves the vibrational density and mobility properties of the powder, and meets the process requirements of additive manufacturing, powder metallurgy and other fields for spherical powder. The resulting powder has a controllable particle size distribution and a high degree of sphericity, which is suitable for electronic components, high-temperature alloys, medical implants and other precision manufacturing fields. The process can reduce the introduction of impurities and improve batch stability compared with traditional methods, providing a reliable material base for high-end applications. Welcome to consult the professional staff: Manager Zheng +86 13318326187.
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