Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/14—Making metallic powder or suspensions thereof using physical processes using electric discharge
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/06—Metallic powder characterised by the shape of the particles
  • B22F1/065—Spherical particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy
  • H05H1/461—Microwave discharges
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/52—Generating plasma using exploding wires or spark gaps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
  • B22F2009/0824—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid with a specific atomising fluid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
  • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
  • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
  • B22F2009/0848—Melting process before atomisation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2202/00—Treatment under specific physical conditions
  • B22F2202/13—Use of plasma
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/26—Plasma torches
  • H05H1/30—Plasma torches using applied electromagnetic fields, e.g. high frequency or microwave energy

Definitions

• the present subject matter relates to advanced materials and, more particularly, to the production of metal powders for diverse applications, such as additive manufacturing for the aerospace and medical industries.
• Plasma atomization typically uses a wire as a feedstock, and a source of plasma (a.k.a. plasma torch) as atomizing agent to simultaneously melt and break-up the particles.
• a source of plasma a.k.a. plasma torch
• Using a wire provides the stability required so that the narrow plasma jets are aiming property at the wire, since the plasma jets have to melt the wire and atomize it in a single step.
• this technology currently produces the finest, most spherical and densest powders on the market In other words, the yield of powders produced in the 0-106 micron range is very high, sphericity is near perfect and gas entrapment is minimized.
• 2017/0326649-A1 which is entitled “Process and Apparatus for Producing Powder Particles by Atomization of a Feed Material in the Form of an Elongated Member* and which was published on November 16, 2017 with Boulos et al. as inventors, has reported a feed rate of 1.7 kg/h for stainless steel.
• Wire arc spray is a mature and reliable technology that Is used in the field of thermal spray to apply coating onto surfaces. It essentially consists of passing a high current through one or two wires and having an electrical arc between the two wires, or between the single wire and an electrode. Quality wire arc systems can run with near 100 % duty cycle at very high throughput (-20 to 50 kg/h). Moreover, this technology is highly energy efficient, since the arc contacts directly the wire. However, the purpose of this technology is to produce coatings and not to produce powders. Since this technology uses a cold gas to atomize the spray, it produces very irregular and angular shapes, which is not desirable for most applications.
• an apparatus for producing metallic powders from wire feedstock comprising a plasma torch and a wire adapted to be fed in the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode.
• a plasma atomization process comprising:
• an electrical arc being adapted to be transferred to the wire or wires to produce particles
• the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a wire adapted to be fed in the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode.
• the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least one wire adapted to be fed in the apparatus, the plasma torch being adapted to atomize the molten wire into particles, and a cooling chamber adapted to solidify the particles into powders, and wherein the wire is adapted to serve as a cathode in the plasma torch.
• the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least a pair of wires adapted to be fed in the apparatus, the plasma torch bang adapted to atomize the molten wires into particles, wherein one of the wires is adapted to serve as an anode, whereas the other wire is adapted to serve as a cathode.
• the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a wire adapted to be fed in the plasma torch, the
• plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode.
• the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least one wire adapted to be fed in the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein the apparatus is adapted to be cooled by a gas thereby heating up the gas, with the so heated gas being adapted to be used as the plasma gas.
• a plasma atomization process comprising:
• a plasma atomization process comprising:
• FIG. 1 and 2 are vertical cross-sectional views of an apparatus for producing metallic powders from a pair of wires, using dual wire arc plasma atomization r in accordance with an exemplary embodiment;
• Fig, 3 is a schematic elevation view of a system for producing metallic powders, which uses the apparatus shown in Figs. 1 and 2, in accordance with an exemplary embodiment, Including that of Figs. 1 and 2;
• FIG. 4 is a conceptual schematic of an electrical configuration used in accordance with an exemplary embodiment, including that of Figs. 1 and 2;
• FIG. 5 shows an example of electrical trendlines of embodiments in operation of the present disclosure, -
• Fig. 6 is a SEM image of 100 times magnification of 45-106 pm Ti64 grade 23 powder produced by the means of the embodiment of Figs. 1 and 2;
• Fig. 7 is a SEM image of 100 times magnification of 20-120 of Zirconium powder produced by the means of the embodiment of Figs. 1 and 2;
• Fig. 8 shows a typical laser diffraction powder size distribution graph for a raw powder produced by the means of at least one embodiment herein disclosed;
• FIG. 9 is a schematic vertical cross-sectional view of an apparatus for producing metallic powders from a single wire, using a plasma torch which can transfer an arc with the said single wire, in accordance with an exemplary embodiment
• FIG. 10 is a schematic vertical cross-sectionai view of an apparatus for producing metallic powders from a single wire, using a centrally fed plasma torch, in accordance with an exemplary embodiment.
• the present approach disclosed herein provides methods and apparatuses for producing metallic powders, by combining features of the above- described plasma atomization and wire arc spray technologies, including by using some of the concepts of the wire arc spray technology and adapting it to make it suitable for the production of high purity spherical powders. More specifically, the gas jet is replaced by a source of plasma and the molten wire is atomized into a cooling chamber as seen in atomization processes.
• One key consideration is powder quality. Wire arc was not developed for high quality powder production and must therefore be adapted and tuned towards powder quality.
• the current disclosure includes a control strategy that improves stability of the melting process, which will be described in more details further below.
• a source of plasma (such as one or multiple plasma torches or an electrical arc), delivers a plasma stream that can be accelerated to supersonic velocity prior or after hitting the molten stream with high momentum.
• the supersonic plasma jet source is produced via an arc plasma torch because it is widely available.
• any thermal plasma sources such as inductively-coupled and microwave plasma sources, could be used as well.
• Example 1 Dual Wire Arc Plasma Atomization (Main Embodiment)
• Fig. 1 details the specific components that make up apparatus A. These include a high flow rate plasma torch 501 and an anode integrated supersonic nozzle 505 that emits an atomizing jet onto a pair of wires 502 being fed towards an apex 508 whereupon an electrical arc is transferred from one wire to the other wire.
• This electrical current provides the energy necessary for the continuous melting of the conductive continuously fed feedstock.
• the current is passed to the wires 502 by contact tips 509 that are made of a high conductivity alloy, for example copper zirconium, which has a good wear resistance at high temperatures.
• a ceramic tip 510 provides the electrical Insulation of a water-cooled contactor 514 from the body of the reactor through a gas sheath nozzle 513 and of the torch's supersonic nozzle 505.
• the intense heat emitted by the plasma.torch 501 and the transferred arc requires the contactors to be water cooled vriiiie the contact tip itself is a replaceable consumable.
• water enters at 503 the contactor's manifold 515 at the rear and is directed towards the tip where it Is returned upwards again and out through exit 504. Electrical power is provided to the transferred arc system via the manifolds through a lug mount 511.
• Fig. 2 shows a perpendicular cut view of the apparatus A, where the high flow rate plasma torch emits an atomizing jet via the supersonic nozzle 605 at the wire apex 608.
• a sheath gas is Injected into the reactor at 602 to fill the cavity surrounding the torch's nozzle and water-cooled contactors 607.
• This sheath gas is expelled via the sheath gas nozzle 606 into the reactor surrounding the electrical arc between the wires.
• This sheath gas serves multiple purposes, such as it prevents back flow of powders and hot gases as well as aid in maintaining the arc within the supersonic plume.
• a recirculation zone around the high velocity jet where fine powders can accumulate in suspension is the primary cause of satellites in plasma-atomized powders as new droplets are projected through a cloud of fines which are thus welded to the surface.
• the diffuser 610 removes the vast majority of this occurrence, thus greatly reducing satellite formation.
• a torch receiver 611 is water-cooled as the reactor's jacket water enters from an inlet 603 at the bottom and an outlet 604 at the top.
• FIG. 3 schematically illustrates a system S adapted to produce metallic powders, and embodying either one of the apparatuses A, A' and A”, respectively, of Figs. 1-2, 9 and 10. More particularly, the system S Includes the dual-wire or single-wire plasma-based atomization apparatuses A A' or A”.
• the system S is shown specifically In Hs twin wire arc configuration A with a centrally located high flow rate plasma torch 301 and the two (2) servo driven wire feeders 302.
• An atomization zone 303 comprises of the transferred arc between the one or two wires, the sheath gas and plasma torch flow and is directed into the reactor by way of an anti-satellite diffuser 304.
• the reactor is comprised of a settling chamber 305 where spheroid ization and solidification occur, and a water-cooled jacket 306 to maintain a constant cooling rate in the chamber 305 for the powders.
• the powders are then entrained via a pneumatic conveyor 307 to a cyclonic separator 308 where the bulk powders settle in a collection canister 309.
• a valve 310 is used to Isolate the canister 309 for collection during continuous operation.
• the argon is then vented from the system through a filtration unit 311 for powders too fine to settle out in the cyclonic separator 308.
• conductive materials 405 can be made of various conductive materials, such as titanium, zirconium, copper, tin, aluminum, tungsten, carbon steel, stainless steel, etc., and their alloys.
• T o ensure stability of the wire arc system for atomization, the system needs to control 2 out of 3 parameters, namely voltage, current and feed speed. These three parameters need to reach a steady state in equilibrium to be considered in continuous operation. In steady state, the distance between the wire, the length of the arc and the power become constant To reach this steady state, several configurations can be employed, such as:
• the only variable in the process is a portion of the total current, which needs to fluctuate to allow the other parameters to remain constant (degree of freedom). Therefore, the voltage-controlled power supply provides an additional current that is variable to complement what is missing to the current already provided by the current-controlled power supply to melt the proper amount of metal, so the system remains in steady state.
• Fig. 5 shows the electrical trendlines recorded for the main embodiment during operation using the electrical control strategy herein suggested. In summary, it shows that all variables are highly stable except for the current of the voltage-controlled power supply, for reasons explained above. [00067] Such stable operation, as shown in Fig. 5, allows to produce highly spherical powders, as shown in Figs. 6 and 7, for ⁇ 64 and Zirconium, respectively.
• Fig. 8 shows a typical particle-size distribution curve for powder produced using the main embodiment with the electrical control strategy herein explained.
• Example 2 Single-Wire Arc Plasma Atomization
• an apparatus A' for producing metallic powders from a conductive wire feedstock is also disclosed, wherein a wire 405 is centrally led along arrow 409 in front of a transferred plasma torch 401 equipped with a supersonic nozzle 411, where an arc 403 is formed between the wire 405, and one electrode 402.
• a wire guide 407 in front of the plasma torch 401 , the wire 405 itself can be melted very efficiently via a transferred arc.
• the remaining energy is then used to warm up an inert gas (e.g.
• argon fed via a pre-heated gas channel 404, to plasma state, which gas is then accelerated through the supersonic nozzle.411 This acceleration of the carrier gas atomizes the metal droplets further by shredding them.
• the particles then solidify into small spherical particles in a cooling chamber (as exempSfled in Fig. 3), for instance filled with an inert gas (e.g. argon).
• Reference 408 denotes a plasma plume.
• Example 3 Centrally-Fed Single Wire Arc Plasma Atomization
• a wire 110 is centrally fed along arrow 111 into a plasma torch 112, where an arc 128 is formed between the wire 110, which acts as a cathode, and one electrode (see anode 114).
• the wire 110 By inserting the conductive wire 110 through a wire guide 116 of the plasma torch 112, the wire 110 itself can be melted very efficiently via a transferred arc.
• the wire guide 116 can double as an ignition cathode.
• the remaining energy is then used to warm up an inert gas (e.g. argon), fed via a preheated gas channel 118, to plasma state, which gas is then accelerated through a supersonic nozzle 120.
• This acceleration of the carrier gas atomizes the metal droplets further by shredding them.
• the particles then solidity into small spherical particles in a cooling chamber (as exemplified in Fig. 3), for instance filled with an inert gas (e.g. argon).
• Reference 122 denotes a plasma plume.
• the embodiments described herein provide in one aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and one or two wires adapted to be fed in the apparatus, the plasma torch being adapted to atomize the molten wire into particles, and a cooling chamber adapted to solidify the particles Into powders, and wherein the wire is adapted to serve as a cathode in the plasma torch.
• the embodiment described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a pair of wires adapted to be fed in the apparatus, the plasma torch being adapted to atomize the molten wires into particles, wherein one of the wires is adapted to sen/e as an anode, whereas the other wire is adapted to serve as a cathode.
• an embodiment includes an electrical control strategy that allows for the smooth and stable operation of the said embodiment
• an apparatus for producing metallic powders from wire feedstock comprising a plasma torch and a wire adapted to be fed into the apparatus, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode of the torch.
• the embodhients described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least one wire adapted to be centrally fed inside the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode within the torch.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Chemical & Material Sciences (AREA)
• Nanotechnology (AREA)
• Electromagnetism (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Plasma Technology (AREA)
• Powder Metallurgy (AREA)

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