LOW COST PROCESSING TO PRODUCE SPHERICAL TITANIUM ALLOY POWDER Ti6Al4V

[0001] The present patent application claims priority to US Patent Application No. 61 / 517,871 filed on April 27, 2011.

State of the art [0002] Powdered metals provide various application possibilities for the production of components. In particular, powdered metals are used in sintering as well as as a raw material for the melting of fast products forming products similar in shape to the final product. Ideally, powdered metals exhibit a spherical morphology that provides good flowability and packing density. Steel and many other powdered metals are widely used to produce cheap components. The possibility of producing components using powdered titanium alloys has long been sought for, which has not been widely used mainly due to the high price of powdered titanium. In 2010 and 2011, the cost of spherical powdered titanium was around 150 $ / lb. At such high prices,

[0003] The high cost of the spherical titanium powder is largely due to the high cost of the conventional machining required to produce the titanium alloy block from the spongy mold, which is then fused to form a spherical titanium powder using one of several methods. Modern titanium processing includes large-scale batch segregation operations. Typically, the production of the titanium sponge in the Koll process is carried out in large retorts allowing processing of about ten tonnes of batches over several working days adding TiCl4 to the magnesium melted in the retort and removing the resulting molten MgCl2 from the retort, then removing the MgCl2 residue for a week or longer. unreacted Mg by evaporation under vacuum. The vacuum-cleaned sponge is then fused in large-scale smelting furnaces for reactive metals where heat is supplied via an electron beam or plasma. The alloy components can then be added to the large multitone melts giving the desired alloy composition, such as Ti6Al-4V, which is then cast into bars. Often a threefold fusion is carried out to obtain a homogeneous alloy. As a result, the prices of titanium bars change quite cyclically, which also affects the high cost of spherical powdered titanium. Often a threefold fusion is carried out to obtain a homogeneous alloy. As a result, the prices of titanium bars change quite cyclically, which also affects the high cost of spherical powdered titanium. Often a threefold fusion is carried out to obtain a homogeneous alloy. As a result, the prices of titanium bars change quite cyclically, which also affects the high cost of spherical powdered titanium.

[0004] US 7,297,271 A2, CN1270864 A, US 2009/0107294 A1 and US 2007/0062332 disclose methods for preparing powdered alloys.

Summary of the Invention [0005] The present invention provides a process according to claim 1 for a low cost manufacture of a spherical titanium powder. In the invention, the titanium sponge is fed to the plasma heating system, to which the powdered alloy precursor of the desired alloying metals, e.g. aluminum and vanadium, or powdered aluminum and vanadium, can be fed separately to the plasma station, where it melts through the plasma and obtains a melt or a stream of molten homogeneous alloy, e.g. Ti-6Al-4V, continuously. The molten alloy composition is dispersed by blowing a stream of inert gas to the surface of the pool or by a stream under controlled conditions, blowing droplets of molten alloy that upon cooling gives a spherical titanium alloy, e.g. Ti-6Al-4V. Savings are significant. While the cost of the titanium sponge changes cyclically, its price in 2010-2011 was in the range of $ 3 to 10 $ / lb, and usually 1

EP 2 701 869 in the range of 4 - 6 $ / lb. The cost of operating with plasma to melt the titanium alloys in a controlled size metal pool and generate a spherical powder is approximately in the range of 1-200 / lb, which is the starting point for the production of spherical Ti-6Al-4V powder from conventional sponge springs in from 10 to 15 $ / lb, which in turn gives significant savings over conventionally produced spherical powdered titanium, the cost of which, as mentioned above, is of the order of 150 $ / lb.

[0006] In a further embodiment of the invention, the electrolytically produced titanium is fed to a plasma heated evaporator in an inert atmosphere or under vacuum, heated to 800-1600C, causing rapid evaporation of bound electrolyte salts that are returned to the electrolyte and the remaining titanium is fed to a plasma heated station, where additional heat is supplied to melt and obtain a titanium alloy analogously to the previously discussed sponge raw material, wherein a spherical homogeneous alloy powder is produced on a plasma heating station by injecting a stream of inert gas into the melt in a controlled manner. conditions and blowing droplets of molten alloy, which after cooling give a spherical powder of a titanium alloy. Again, the savings are significant. The estimated cost of electrolytic titanium production is about 1.5 - 2.5 $ / lb, which is the starting point for the production of spherical titanium alloy powder below 10 $ / lb. The heat source for heating the salt-electrolytic stream titanium from about 500 ° C to over 900 ° C for the purpose of rapid and pulse evaporation of the salt can be resistive, radiation, inductive, microwave or plasma. Plasma heating is typically used to spherically form liquid titanium to obtain a spherical powder. induction, microwave or plasma. Plasma heating is typically used to spherically form liquid titanium to obtain a spherical powder. induction, microwave or plasma. Plasma heating is typically used to spherically form liquid titanium to obtain a spherical powder.

[0007] In contrast to the conventional Koll process, the methods of the present invention can be carried out in a continuous mode with little segment heating. For example, in the case of vacuum pulse evaporation of the electrolytic salt residue, the amount of powdered titanium or titanium sponge with MgCl2 and Mg, which is immediately heated in the range of 10 g to 100 kg, preferably in the range of 100 g to 10 kg, which is similar amount to the amount of titanium that is plasma melted and forms a stop. In the present invention, the homogeneity of the alloy is obtained instantaneously in small alloy tanks.

[0008] In the conventional prior art sponge-making process, the vacuum evaporation, melting and mixing of the alloy and casting to the bars takes at least 20 days in the case of a ten-tonne refiner, which translates to about 1000 lb / day (454 kg / day) . In order to prepare a powdered alloy, a longer time is needed, which further reduces the unit speed of powder production. In the present invention, the pulse evaporation time of the salt and plasma melting is quite short, i.e. in only one minute, and usually no more than 10 minutes depending on the enthalpy or heat flow supplied from the plasma or other heat source. Even at lower heating rates, e.g. 10 minutes, and low material content, e.g. at 1 kg, sixty kilograms can be processed within an hour, and 1440 kg during the day, which significantly exceeds the possibilities of large-scale modern processing based on the Koll's process. In the manufacturing operation according to the present invention, the productivity can be of the order of 10 kg of processed material in three minutes, thereby allowing to produce 4800 kg per day, providing a favorable amount of material in terms of scale and economy.

Brief description of the drawings [0009] Further details and advantages of the present invention will be illustrated by the following detailed description and embodiments, in combination with the accompanying drawings, wherein:

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Figure 1 is a schematic diagram, while Figure 1a is an enlarged view illustrating a method of manufacturing a spherical titanium powder according to a first embodiment of the present invention;

Figure 2 is a schematic diagram illustrating a method of producing spherical titanium alloy particles according to a second embodiment of the present invention;

Figure 3 is a schematic diagram illustrating a method of producing spherical titanium alloy particles according to a third embodiment of the present invention;

Figure 4 is a photograph obtained by scanning electron microscopy of a titanium alloy spherical powder according to an embodiment of the present invention;

Figure 5 is a photograph obtained by scanning electron microscopy of a spherical titanium alloy powder according to a further embodiment of the present invention; and Figure 6 is a photograph obtained by scanning electron microscopy of a spherical titanium alloy powder according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to Figures 1 and 1a, in a first embodiment of the present invention, the titanium sponge 14 is supplied to a welding torch of the type 10 plasma plated arc: PTA illustrated in Figure 1 in US patent application No. 2006/0185473-A1, the content of which has not been included here as a reference. The aluminum-vanadium alloy precursor powder or alloying mixture mixture is introduced into the plasma torch from the dispenser 20 at controlled rate to give the Ti-6Al-4V alloy. On the target substrate 24, a molten pool of Ti-6Al-4V is formed, approximately one-inch and one-eighth of an inch in diameter to a quarter of an inch.

[0011] A stream of inert gas, e.g. argon, is passed continuously through the nozzle 26 so that it hits the surface of the molten pool 22, blowing droplets of molten melt from the pool, which in turn solidify upon cooling in the form of spherical alloy particles. The flow of inert gas from the nozzle 26 should be controlled so that the jet hits the surface of the molten pool at an angle of 45 to 180 degrees and at a rate of 10 to 1000 liters / minute, it should blow out the melt from the pool at the same rate, with which lake is formed. The molten alloy is blown out from the surface of the pool as fine droplets of substantially uniform shape, which cool almost immediately and form a substantially homogeneous alloy particle,

[0012] Optionally, the target substrate 24 may be subjected to vibrations, e.g. by ultrasound or piezoelectric vibrator 200 (Figure 1a), to aid in lifting and removing particles from the molten pool.

[0013] Alternatively, instead of initially collecting the molten alloy produced in the PTA on substrate 24, the molten melt stream can be treated with an argon gas stream to break up the titanium alloy particle stream into smaller particles that are then cooled to the spherical powder form in liquid argon.

[0014] With reference to Figure 2, according to a further embodiment of the invention, TiCl4 and Mg vapors are directed to the reaction zone 110 of the fluidized bed reactor 112, where they can react via homogeneous nucleation to give small particles, usually below one micron, which are collected in a series of cyclone separators 114 designed to collect such small particles at a flow rate of 3

EP 2 701 869 reactor gas. The small particles are recycled in the reaction zone 110 of the fluidized bed reactor where they are built up by additional deposition from TiCl4 and Mg vapors. The re-circulation is continued until the particles reach the desired size range, for example 40 microns to 300 microns. As the particles grow, they also become heavier and settle at the bottom of the reactor, from where they can be extracted by gravitational flow through the tube 116 connected to the bottom of the fluidized bed reactor, i.e. as described in previous US Patent No. 7,914,600, the content of which is not it has been included here in the form of a link.

[0015] The particles discharged are then directed to a shallow heated reservoir 118 to form a melt 120 melt bladder. As before, the argon stream 122 is passed through the melt stream, or to the surface of the metal pool to blow out the titanium alloy particles that are discharged from the reservoir 118 through the conduit 124.

[0016] With reference to Figure 3, according to still another embodiment of the invention, titanium powder is produced by reducing TiCl 4 with magnesium, as described in our co-pending patent application No. 12 / 016,859, the content of which is not included here in in the electrolysis dish according to Figure 2 of the aforementioned '859 application, in block 140. A slurry of MgCl2 slurry containing titanium powder is formed and directed to the salt evaporation system 142, where residual salts are removed by heating. The heat source may be resistive, radiation, inductive, microwave or plasma, the heating being carried out under an inert atmosphere and, if required, under reduced pressure to assist evaporation. After evaporation of the MgCl2 salt, the titanium powder obtained together with the powdered alloy metal is directed to a PTA smelting system similar to that shown in Figure 1, and illustrated generally as block 144, where a substantially uniform spherical powdered alloy is produced by blowing droplets of molten alloy from its stream from the system PTA, or as previously collected in a pool on a substrate, and as previously cooled and collected solid powder. [0017] The present invention will be further described with reference to the following non-limiting working examples: wherein a substantially homogeneous spherical powdered alloy is produced by blowing droplets of the molten alloy from its stream from the PTA system, or as previously collected in a pool on the substrate, and as previously cooled and collecting the solidified powder. [0017] The present invention will be further described with reference to the following non-limiting working examples: wherein a substantially homogeneous spherical powdered alloy is produced by blowing droplets of the molten alloy from its stream from the PTA system, or as previously collected in a pool on the substrate, and as previously cooled and collecting the solidified powder. [0017] The present invention will be further described with reference to the following non-limiting working examples:

Example 1 [0018] A pure vaporized titanium sponge was directed to a plasma deposition system (PTA) in a heat source controlled by a numerical control system (CNC) as described in published US application 2006/0185473-A1, which was simultaneously charged with a aluminum alloy precursor powder. vanadium at controlled rate to obtain a molten pool of Ti-6Al-4V alloy. The melted lake was approximately one-inch in diameter and one-eighth to one-fourth the depth. The argon stream was continuously blown into the metal pool resulting in a spherical powder as shown in the SEM picture in Figure 4. Supplying raw materials and melting in the PTA system was performed in a continuous mode, as well as supplying a stream of argon that blew spherical particles,

Example 2 [0019] The process of Example 1 was repeated except that the metal pool obtained in the PTA system was collected on a target substrate containing an opening through which the molten titanium alloy dripped with a stream of argon gas. The melt stream was broken down into particles by a stream of argon gas, and the particles were cooled to form a spherical powder in liquid argon at the bottom of the powder trapping tank. The titanium powder produced is shown in Figure 5.

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Example 3 Powdered electrolytic titanium was obtained by treatment according to US Pat. No. 7,914,600, 7,410,562, and 7,794,580 or alternatively by adding titanium tetrachloride (TiCl4) to an electrolyte containing KCl-LiCl. Titanium powder was produced in an electrolytic system configured for continuous operation, with an initial stream at about 500 ° C containing about 15% titanium powder and 75% liquid salt. A stream of powdered electrolytic titanium-salt was pumped into a shallow tank heated inductively to about 1000 ° C. The tank had a reduced pressure of about 10 Torr, which ensured efficient evaporation of the KCl-LiCl salt in about three minutes. The remaining powdered electrolytic titanium was mixed together with powdered aluminum and vanadium in such a ratio,

Example 4 [0021] A standard Koll reaction was carried out to yield a titanium sponge. After the by-product of the remaining MgCl2 by-product remaining unreacted Mg, the sponge with residual MgCl2 and Mg was directly fed into the plasma system described in Example 3 without pre-evaporating the residual MgCl2 and Mg. The plasma melted the titanium and evaporated MgCl2 and Mg. Argon gas was blown through plasma electrodes onto the surface of the melt by blowing droplets of liquid titanium, which were cooled to give spherical titanium particles, which were in turn collected as before.

Example 5 [0022] The process of Example 4 was repeated except that a titanium sponge containing MgCl2 residues and Mg was added either Al-V alloy or separate powdered metals to form titanium alloy powder. Example 6 [0023] Titanium powder was obtained by reducing TiCl 4 with magnesium, as described in our co-pending patent application No. 12 / 016,859 to obtain a MgCl 2 stream at about 800 ° C containing about 20% titanium powder. The slurry stream was fed to the salt evaporation system described in Example 3. After evaporation of MgCl2 salt, the titanium powder together with the chromium powder and molybdenum was fed to the PTA smelting system as described in Examples 1 and 2, wherein using the treatment of Example 2 a spherical alloy powder containing Ti-5Cr-2Mo was obtained. Ti-8Al-1Mo-1V alloy particles can be obtained in a similar manner.

[0024] It will be understood that any titanium alloy composition may be made in the form of a spherical powdered alloy or alternatively as a bar with the addition of alloying elements co-fed with powdered titanium to a smelting plasma system; however, this is not within the scope of the present invention. It is also understood that the particles that react or residues that have not reacted with the molten titanium can be introduced into the spherical powder of the titanium alloy. An example of a reactive powder is titanium diboride, which reacts after giving titanium boride, aluminum nitride, which after cooling gives titanium nitride and Al3Ti, or boron carbide, which after cooling gives titanium boride and titanium carbide. Non-limiting examples of particles more stable than titanium include hafnium oxide or calcium oxide. In addition, neutral gasses other than argon may be preferred.

[0025] The above description, embodiments and examples are provided to illustrate the scope of the present invention. It is obvious that many changes are possible in the described embodiments and arrangements within the scope of the invention.