Process for producing metals, alloys and metal powders using reactive gas and oxygen scavenging reaction

Abstract

A process for producing metals, alloys and metal powders (62) includes providing a feed material (16); heating the feed material (16) in a melting hearth (12) into a molten metal (18); and reducing oxygen in the molten metal (18) using a reactive gas (34) in an ionized or unionized state and an oxygen scavenging reaction wherein reaction sites (30) in the molten metal (18) containing oxygen react with the reactive gas (34). A first system (10) configured to perform a process for producing metals and alloys includes a melting hearth (12) and a heat source system (36) in a melting chamber (42) configured to melt a feed material (16) into a molten metal (18) for atomization, casting or further processing. A second system (10P) configured to perform a process for producing metal powders (62) includes a foundry system (64) configured to melt a feed material (16) into a molten metal (18) and an atomization system (60) configured to atomize the molten metal (18) into a metal powder (62) comprised of metal particles (68).

Description

PROCESS FOR PRODUCING METALS, ALLOYS AND METAL POWDERS USING REACTIVE GAS AND OXYGEN SCAVENGING REACTIONCross Reference To Related Application

[0001] This application claims priority from US Provisional No. 63 / 574,311 filed 04 / 04 / 2024, which is incorporated herein by reference.Field

[0002] This disclosure relates to the production of metals, alloys and metal powders using recycled feed materials.Background

[0003] Demand for sustainable manufactured products and materials using recycled materials is on the rise. However, producing aerospace and high-performance industrial grade metals, alloys and metal powders from recycled feedstocks can be challenging. For example, contamination is one major concern when producing metal powder from recycled feed materials. Reactive metals and alloys that have a high affinity for interstitials, such as oxygen, hydrogen, nitrogen and carbon are particularly difficult to reprocess without increasing the concentration of interstitials. Reactive metals such as titanium are critical metals for national security, and recycling with low interstitials of such alloys is of paramount importance to the country’s defense and self-sustainment.

[0004] Interstitial elements are elements with a small atomic diameter that can easily enter in “interstices” of a lattice structure. Once at the interstices in the lattice structure of the metals and alloys, especially reactive metals and alloys, interstitial elements start to react to form interstitial compounds. Among the interstitial elements, oxygen has spontaneous reaction kinetics with reactive metals and alloys, for example, titanium and titanium alloys. Every newly exposed surface of such metals and alloys, for example, by machining, absorbs more oxygen and forms a titanium oxide film on the surface. This increases the total oxygen content of the metals and alloys. When recycling reactive metals into metal powders, this excess oxygen, which has been absorbed throughout the lifecycle of the component or recycled material, must be removed to specific levels to meet requirements for metal powder production.

[0005] Currently there are processes for recycling high-performance metals and alloys into powders having low interstitials. For example, prior art processes for producing metal powders often include the deoxygenation / deoxidation in solid state (DOSS) after the powder is produced, either by HDH (hydride-dihydride process), atomizing or spheroidizing. Briefly, DOSS involves a lengthy process of leaching oxygen out of the solid powder particles using highly oxidative metals such as Ca, Mg or Na and their halides. These processes can cause inpowder morphology degradation, and yield loss, during subsequent washing and rinsing process.

[0006] This disclosure discloses a process for producing metals and alloys by reducing the amount of oxygen in a molten metal using a reactive gas and an oxygen scavenging reaction. This disclosure also discloses a process for producing metal powders using a cold hearth melting system configured to perform a melting process of a molten metal, and a subsequent gas atomizing process of the molten metal into metal particles.Summary

[0007] A process for producing metals, alloys and metal powders includes the steps of providing a feed material; heating the feed material in a melting hearth into a molten metal; and reducing oxygen in the molten metal using a reactive gas in an ionized or unionized state and a single step oxygen scavenging reaction wherein reaction sites in the molten metal containing oxygen react with the reactive gas. The process can also include stirring the molten metal during the reducing step to expose additional reaction sites of the molten metal to the reactive gas. The process can also include pouring the molten metal during the reducing step to expose additional reaction sites of the molten metal to the reactive gas. The process can also include correcting a composition of the feed material during the heating step by adding additives to the molten metal in the melting hearth.

[0008] Exemplary feed materials include: titanium, tantalum, niobium, vanadium, hafnium, nickel, iron, and alloys of these metals, at least some of which are in recycled form. Exemplary reactive gases include hydrogen, argon, helium, carbon dioxide, carbon monoxide and nitrogen in pure forms, or as gas mixtures. During the process, the reactive gas encounters the molten metal at elevated temperatures, either during melting or atomizing, causing a reaction with oxygen or oxide compounds at reaction sites on the surface of the molten metal, or in metal particles produced during atomizing, thus removing oxygen into the reactionchamber by movement of resultant oxygen-containing compounds, such as water vapor. The process can be used to remove oxygen to acceptable levels permitting use of the metals, alloys and metal powders in industrial manufacturing processes including, but not limited to, additive manufacturing, surface cladding, and powder forging.

[0009] A first system configured to perform a process for producing metals and alloys includes a melting hearth and a heat source system in a melting chamber configured to melt a feed material into a molten metal for atomization, casting or further processing. During the process for producing metals and alloys, the reactive gases can be introduced into the melting chamber by transmitting the reactive gas through a conduit associated with the heat source onto a surface of the molten metal in the melting hearth. Alternately, the reactive gas can be injected into an atmosphere of the melting chamber using a reactive gas distribution system.

[0010] A second system configured to perform a process for producing metal powders includes a foundry system configured to melt a feed material into a molten metal and an atomization system configured to atomize the molten metal into a metal powder comprised of metal particles. During the process for producing metal powders, the reactive gas can be introduced during atomizing of the molten metal, as an atomizing gas introduced into the atomization system. The presence of the reactive gas while atomizing is advantageous, as the reactive gas encounters more surface area on the metal particles, thus accelerating the oxygen scavenging reaction. During the process for producing metal powders, the reactive gas can also be introduced into the foundry system during melting of the feed material as an ionized plasma.Brief Description of the Drawings

[0011] All of the figures are schematic in nature and may not be drawn to scale.

[0012] Figure 1A is schematic perspective view of a first system for performing a process for producing metals and alloys;

[0013] Figure IB is schematic cross-sectional view taken along section line 1B-1B of Figure 1A illustrating a melting hearth of the first system and electromagnetic stirring of a molten metal in the melting hearth;

[0014] Figure 1C is an enlarged schematic cross-sectional view taken along section line 1C of Figure IB illustrating an oxygen scavenging reaction at a reaction site on a surface of the molten metal;

[0015] Figure ID is an enlarged schematic cross-sectional view taken along section line ID- ID of Figure 1A illustrating a heat source of the first system having a reactive gas conduit;

[0016] Figure IE is an enlarged schematic view of a melting chamber of the first system illustrating a gas distribution system of the first system and pouring of molten metal from the melting hearth at different tilt angles;

[0017] Figure 2A is schematic view of a second system for performing a process for producing metal powder;

[0018] Figure 2B is an enlarged schematic cross-sectional view of a metal particle of the metal powder produced by the second system;

[0019] Figure 2C is an enlarged schematic cross-sectional view taken along section line 2C of Figure 2B illustrating an oxygen scavenging reaction at a reaction site on the metal particle; and

[0020] Figure 3 A is a flow diagram illustrating steps in a process for producing metals and alloys; and

[0021] Figure 3B is a flow diagram illustrating steps in a process for producing metal powders.Detailed Description

[0022] Referring to Figure 1 A, a first system 10 for performing a process for producing metals and alloys is illustrated schematically. The first system 10 includes a melting hearth 12 having a melting cavity 14 configured to melt a feed material 16 into a molten metal 18. The melting hearth 12 can have any geometrical peripheral configuration, such as rectangular, square or circular. The melting hearth 12 includes a pour notch 20 in flow communication with the melting cavity 14 for pouring the molten metal 18 into an atomization system to be further described, or a casting system (not shown). US Patent Nos. 9,925,591and 10,654,106, both of which are incorporated herein by reference, describe further details of the first system 10 including composition correction of the feed material using additives.

[0023] The first system 10 is designed to process feed materials 16 that include at least some recycled material. Exemplary feed materials include: titanium, tantalum, niobium, vanadium, hafnium nickel, iron, and alloys of these metals. Exemplary forms for the feed materials 16 include: machining chips, scrap metal cut into chunks, out-of-specification metalpowder, and metal pucks made of recycled material. US Patent Application Serial No. 18 / 925,173, which is incorporated herein by reference, discloses a consolidator system for processing recycled materials into metal pucks.

[0024] As shown in Figure 1A, the first system 10 also includes a feeder system 22, such as a tube, channel, or conveyor, in close proximity to the melting hearth 12, configured to feed the feed material 16 into the melting cavity 14. US Patent No. 12,259,185, which is incorporated herein by reference, discloses a powder feed system.

[0025] As shown in Figure IB, the first system 10 also includes an electromagnetic stirring system 24 configured to generate one or more electromagnetic fields 26 for stirring the molten metal 18 in the melting cavity 14. As indicated by the stir flow arrows 28 the electromagnetic stirring is three dimensional, such that the molten metal 18 is stirred in x, y and z directions. As shown in Figure 1C, this stirring action exposes reaction sites 30 on a surface 32 of the molten metal 18 to a reactive gas 34. The reaction sites 30 can include oxygen in the form of metal oxides that are prevalent in recycled materials, as previously explained in the background. The reaction sites 30 can also include dissolved oxygen in the molten metal 18 that has been released by the action of heat and electromagnetic stirring. The exact oxygen scavenging reaction occurring at the reaction sites 30 will depend on the materials for the feed materials 16 and the reactive gases 34. For example, for a feed material 16 comprising Ti having reaction sites 30 comprising TiCh and the reactive gas comprising H2, an exemplary reaction would be TiCh + 2H2 = Ti + 2H2O. As another example, for dissolved O2 and the reactive gas 34 comprising H2, an exemplary reaction would be 2H2 + 02 = 2H2O.

[0026] As also shown in Figure 1A, the first system 10 also includes a heat source system 36, such as a plasma torch system, a plasma transferred arc system, an electric arc system, an induction system, a photon system, or an electron beam energy system in close proximity to the melting cavity 14 of the melting hearth 12, which is configured to heat the molten metal 18 in the melting cavity 14. The heat source system 36 can be configured to melt the feed materials 16, using melt cycles defined by energy input per weight of material and a calculated vaporization rate. As shown in Figure ID, the heat source system 36 can also include a reactive gas conduit 38 in flow communication with a reactive gas supply 40, configured to direct the reactive gas 34 onto the surface 32 (Figure 1C) of the molten metal 18 in the melting cavity 14.

[0027] The first system 10 also includes a melting chamber 42, which can comprise a sealed melting vessel 44, which is shown schematically in Figure IE. US Patent Publication No. 2023 / 0235959 Al, which is incorporated herein by reference, discloses a sealed melting chamber having a load lock system for manufacturing metal alloys and metal powder. As shown in Figure IE, the melting chamber 42 can be in flow communication with a reactive gas distribution system 46 that can include a gas supply 48, a pump 50 and one or more nozzles 52. The reactive gas distribution system 46 is configured to inject the reactive gas 34 into the melting chamber 42 at a selected temperature, pressure and flow rate. The melting chamber 42 is also configured to receive the compounds produced by the scavenging reaction. For example, a scavenged FEO compound would flow into the melting chamber 42 as water vapor.

[0028] As shown in Figure 1A, the melting hearth 12 also includes an actuator 54 in signal communication with a central processing unit (CPU) (not shown) having a linkage 56 configured to support and move the melting hearth 12 to a desired hearth tilt angle. US Patent No. 12,145,197, which is incorporated herein by reference describes further details of a melting hearth having tilting capabilities.

[0029] As also shown schematically in Figure IE, the melting hearth 12 can be tilted by the actuator 54 (Figure 1 A) and linkage 56 (Figure 1 A) from any angle between 0° to 90° to pour a pour stream 58 of the molten metal 18 from the melting cavity 14. In the neutral or 0° position, the reactive gas 34 in the melting chamber 42 contacts the surface 32 of the molten metal 18 in the melting hearth 12, substantially as previously described. When the melting hearth 12 is tilted from the neutral position to pour the molten metal 18 from the melting cavity 14, the reactive gas 34 in the melting chamber 42 also contacts the pour stream 58 of the molten metal 18 flowing over the pour notch 20 (Figure 1A). This exposes additional areas of the molten metal 18 and additional reaction sites 30 (Figure 1C) to contact with the reactive gas 34. In Figure IE, for illustrative purposes the melting hearth 12 is shown at pour angles of 30°, 45°, 60° and 90°. However, in actual practice the melting hearth 12 can be tilted at any angle to provide a pour stream 58 having a uniform mass flow rate. US Patent Application Serial No. 18 / 975,113, which is incorporated herein by reference, discloses a tilting melting hearth configured to provide a pour stream having a uniform mass flow rate.

[0030] Referring to Figure 2A, a second system 10P for performing a process for producing metal powder 62 is illustrated schematically. The second system 10P includes a foundry system 64 and an atomization system 60. The foundry system 64 includes a meltinghearth 12P and a heat source system 36P configured to melt a feed material 16P into a molten metal 18P and to pour a pour stream 58P of the molten metal 18P into an atomization die 66 of the atomization system 60. The melting hearth 12P includes an electromagnetic stirring system 24P configured to electromagnetically stir the molten metal 18P substantially as previously described for electromagnetic stirring system 24 (Figure IB). The melting hearth 12P includes a pour notch 20P and has tilting capabilities substantially as previously described for the melting hearth 12. The melting hearth 12P has features substantially as described in previously cited US Patent Nos. 9,925,591, 10,654,106, and 12,145,197.

[0031] Still referring to Figure 2A, the atomization system 60 includes the atomization die 66 in flow communication with the melting hearth 12P configured to receive the pour stream 58P of molten metal 18P and produce the metal powder 62. As shown in Figure 2B, the metal powder 62 comprises a plurality of spherical metal particles 68 having a desired particle shape and particle size. As shown in Figure 2A, the atomization die 66 can include a metal body 70 having passageways for gas jets 72. The atomization die 66 also includes an orifice 74 in configured to receive the pour stream 58P of molten metal 18P. The gas jets 72, which are arranged in a circular pattern, impinge a reactive gas 34P onto the pour stream 58P of molten metal 18. The gas jets 72 all converge on the pour stream 58P of molten metal 18P within the atomization die 66 to disintegrate the pour stream 58P of molten metal 18P and generate the metal powder 62. In addition, the metal particles 68 (Figure 2B) can be formed with a desired shape (e.g., spherical) and particle size (e.g., diameter D of 1-500 pm) using techniques that are known in the art. The particles 68 (Figure 2B) cool in free-fall until reaching the bottom of an atomization tower (not shown) of the atomization system 60. The metal powder 62 can then be segregated into groups of similar particle size using gravity, screening, or cyclonic separation.

[0032] Still referring to Figure 2A, the atomization system 60 can also include a reactive gas distribution system 46P in flow communication with a reactive gas supply 48P. The reactive gas distribution system 46P can distribute the reactive gas 34P into a process chamber 76 of the atomization system 60 in selected areas thereof. For example, the reactive gas 34P can be directed onto the pour stream 58P of molten metal 18 from different directions before it enters the atomization die 66. As another alternative, the reactive gas 34 can be directed onto the metal particles 68 (Figure 2C) formed by the atomization die 66. As another alternative, the reactive gas 34P can be injected into the gas jets 72 of the atomization die 66as an atomization gas. As shown in Figure 2C, the reactive gas 34P scavenges oxygen from reaction sites 30P on the metal particles 68 substantially as previously described for reaction sites 30 (Figure 1C).

[0033] Figure 3A illustrates steps in a process for producing metals and alloys using the first system 10 (Figure 1A). Figure 3B illustrates steps in a process for producing metals and alloys using the second system 10P (Figure 2 A).

[0034] Example 1 : Tests were performed using a system configured substantially as described for the second system 10P (Figure 2A). This type of system is commercially available from Applicant, Continuum Powders Corporation, Cloverdale, CA, under the trademark GREYHOUND. Also in the tests, the feed material 16P comprises recycled machine chips made of a titanium alloy (Ti6A14V). The Table 1 below shows results from several hydrogen deoxidation tests that were performed while atomizing titanium alloy (Ti6A14V). Data includes results from control samples for metal powders processed without any reactive gases. Data also include results from test samples for metal powders 62 (Figure 2A) produced using hydrogen as the reactive gas 34 (Figure 2A). In four of the five tests using hydrogen as the reactive gas 34 (Figure 2A), oxygen in the metal powders 62 (Figure 2A) produced was reduced significantly from the control samples and from the feed material 16.

[0035] Table 1

[0036] Example 2: A process in which the reactive gas 34 (Figure 1C) comprises hydrogen, carbon dioxide, or carbon monoxide mixed with a plasma process gas comprising argon, helium or a mixture of both. The reactive gas 34 (Figure 1C) can be introduced through the heat source system 36 (Figure 1A), which can be in the form of a DC Transferred- Arc plasma torch, to produce reactive gas radicals in the ionized plasma, wherein these radicals interact with the molten metal 18 (Figure 1A) at superheated temperatures in a tundish to scavenge oxygen in the molten metal 18 during melting and subsequent atomization.

[0037] Example 3 : The atomization die 66 (Figure 2A) featuring the orifice 74 (Figure 2A) at the die face having one or more discreet gas jets 72 (Figure 2A) in flow communication with a pure or mixed reactive gas source 48P (Figure 2A). Flow of the reactive gas 34P (Figure 2A) through the orifice 74 (Figure 2A) can occur continuously during a heat or can occur during primary atomization or intermittently. Introduction of the reactive gas 34P (Figure 2A) at this proximity to the atomization event allows for increased coverage of the disintegrated partially solidified metal particles 68 (Figure 2C) with the reactive gas 34P (Figure 2A). Mechanics of introduction of the reactive gas 34P (Figure 2A) at this location allow the high surface area super-heated metal to disassociate hydrogen molecules into reactive sub-species thus speeding the reaction.

[0038] Example 4: A process as specified in Example 3, in which the reactive gas 34P (Figure 2A) is introduced into the processing chamber 76 (Figure 2A) adjacent to atomization of the pour stream 58P (Figure 2A) of molten metal 18P for the purpose of scavenging oxygen in the feed materials 16P (Figure 2A) being atomized. In an illustrative embodiment, the reactive gas 34P (Figure 2A) can be injected no more than 1 inch from the periphery of the atomization die 66 (Figure 2A).

[0039] Example 5: A process as disclosed in US PatentNos. 9,925,591 and 10,654,106, that uses hydrogen for in situ composition correction allowing for deoxygenation of multiple alloys and forms, but which can be specifically applied to recycled 3D printed powder, or undersized and oversized powder from an atomization event, effectively putting out of spec powder in one end and harvesting in spec powder on the other. In this example, the feed material 16P can comprise powder placed in the melting hearth 12P (Figure 2A) by a feeding mechanism, such as described in US Patent Application Serial No. 18 / 128,438, which is melted, atomized using the reactive gas 34P (Figure 2 A) in the form of hydrogen, and then collected in a discreet process all in a sealed chamber 76 (Figure 2A).

[0040] Example 6: A process that can use the reactive gas 34P (Figure 2A) comprising hydrogen, carbon dioxide or carbon monoxide, that have a scavenging effect on oxygen in reactive metals including titanium, niobium, vanadium, hafnium when used as in accordance with the previously described processes.

[0041] Example 7: A process that allows a rapid reaction between liquid or semi solid metal droplets with the reactive gas 34P (Figure 2A) during an atomization event at atmospheric pressure.

[0042] While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and subcombinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.

Claims

WHAT IS CLAIMED IS:

1. A process for producing metals and alloys comprising: providing a feed material selected from the group of metals consisting of titanium, tantalum, niobium, vanadium, hafnium, nickel, iron and alloys thereof, with at least some the metals in recycled form; heating the feed material in a melting hearth into a molten metal; and reducing oxygen in the molten metal using a reactive gas and an oxygen scavenging reaction wherein reaction sites in the molten metal containing oxygen react with the reactive gas, the reactive gas comprising a gas selected from the group consisting of hydrogen, argon, helium, carbon dioxide, carbon monoxide and nitrogen in pure forms, or as gas mixtures.

2. The process of claim 1 further comprising stirring the molten metal during the reducing step to expose additional reaction sites of the molten metal to the reactive gas.

3. The process of claim 1 further comprising pouring the molten metal during the reducing step.

4. The process of claim 1 wherein the feed material comprises titanium and the reactive gas comprises hydrogen.

5. The process of claim 1 wherein the feed material comprises an item selected from the group consisting of machining chips, scrap metal cut into chunks, out-of-specification metal powder, and metal pucks made of recycled material.

6. The process of claim 1 further comprising providing a first system comprising a heat source system and a melting chamber for the melting hearth configured to perform the melting step and the reducing step.

7. The process of claim 6 wherein the melting hearth includes an electromagnetic stirring system and further comprising stirring the molten metal during the reducing step using the electromagnetic stirring system.

8. The process of claim 6 wherein the melting hearth includes a tilting linkage and further comprising tilting the melting hearth during the reducing step using the tilting linkage.

9. The process of claim 6 wherein the heat source system includes a conduit for injecting the reactive gas onto the molten metal as an ionized plasma.

10. The process of claim 6 wherein the heat source system includes a heat source selected from the group consisting of a plasma torch system, a plasma transferred arc system, an electric arc system, an induction system, a photon system, and an electron beam energy system.

11. A process for producing metal powders comprising: providing a feed material selected from the group of metals consisting of titanium, tantalum, niobium, vanadium, hafnium, and alloys thereof, with at least some the metals in recycled form; heating the feed material in a melting hearth into a molten metal; atomizing the molten metal; and reducing oxygen in the molten metal during the atomizing step using a reactive gas and an oxygen scavenging reaction wherein reaction sites in the molten metal containing oxygen react with the reactive gas, the reactive gas comprising a gas selected from the group consisting of hydrogen, argon, helium, carbon dioxide and carbon monoxide, in pure form, or as a gas mixture.

12. The process of claim 11 further comprising providing a second system comprising a foundry system comprising a melting chamber for the melting hearth, a heat source system configured perform the heating step, and an atomization system configured to perform the atomizing step, and introducing the reactive gas during atomizing of the molten metal as an atomizing gas.

13. The process of claim 11 further comprising directing the reactive gas onto a pour stream of the molten metal proximate to the atomization system.

14. The process of claim 11 further comprising correcting a composition of the feed material during the heating step.

15. The process of claim 11 wherein the feed material comprises an item selected from the group consisting of machining chips, scrap metal cut into chunks, out-of-specification metal powder, and metal pucks made of recycled material.

16. A system configured to perform a process for producing metal powders comprising: a feed material selected from the group consisting of titanium, tantalum, niobium, vanadium, hafnium, and alloys thereof, with at least some the metals in recycled form; a foundry system comprising a melting hearth and a heat source system configured to melt the feed material into a molten metal; an atomization system configured to atomize the molten metal into a metal powder comprised of metal particles, the atomization system comprising an atomization die having an orifice for receiving the molten metal and a plurality of gas jets; and a reactive gas supply in flow communication with the gas jets configured to inject a reactive gas through the gas jets onto the molten metal as an atomization gas, the reactive gas comprising a gas selected from the group consisting of hydrogen, argon, helium, carbon dioxide and carbon monoxide, in pure form, or as a gas mixture.

17. The system of claim 16 wherein the atomization system includes a reaction chamber in flow communication with the reactive gas supply.

18. The system of claim 16 wherein the melting hearth of the foundry system comprises a tilting melting hearth.

19. The system of claim 16 wherein the heat source system includes a heat source selected from the group consisting of a plasma torch system, a plasma transferred arc system, an electric arc system, an induction system, a photon system, and an electron beam energy system.

20. The system of claim 16 wherein the metal comprises titanium and the reactive gas comprises hydrogen.

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