Process for Producing Metals, Alloys and Metal Powders Using Reactive Gas and Oxygen Scavenging Reaction

This application claims priority from U.S. Provisional No. 63/574,311 filed Apr. 4, 2024, which is incorporated herein by reference.

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

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.

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.

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 in-powder morphology degradation, and yield loss, during subsequent washing and rinsing process.

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.

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.

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 reaction chamber 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.

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.

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.

Referring to, a first systemfor performing a process for producing metals and alloys is illustrated schematically. The first systemincludes a melting hearthhaving a melting cavityconfigured to melt a feed materialinto a molten metal. The melting hearthcan have any geometrical peripheral configuration, such as rectangular, square or circular. The melting hearthincludes a pour notchin flow communication with the melting cavityfor pouring the molten metalinto an atomization system to be further described, or a casting system (not shown). U.S. Pat. Nos. 9,925,591 and 10,654,106, both of which are incorporated herein by reference, describe further details of the first systemincluding composition correction of the feed material using additives.

The first systemis designed to process feed materialsthat 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 materialsinclude: machining chips, scrap metal cut into chunks, out-of-specification metal powder, and metal pucks made of recycled material. U.S. patent application Ser. No. 18/925,173, which is incorporated herein by reference, discloses a consolidator system for processing recycled materials into metal pucks.

As shown in, the first systemalso includes a feeder system, such as a tube, channel, or conveyor, in close proximity to the melting hearth, configured to feed the feed materialinto the melting cavity. U.S. Pat. No. 12,259,185, which is incorporated herein by reference, discloses a powder feed system.

As shown in, the first systemalso includes an electromagnetic stirring systemconfigured to generate one or more electromagnetic fieldsfor stirring the molten metalin the melting cavity. As indicated by the stir flow arrowsthe electromagnetic stirring is three dimensional, such that the molten metalis stirred in x, y and z directions. As shown in, this stirring action exposes reaction siteson a surfaceof the molten metalto a reactive gas. The reaction sitescan include oxygen in the form of metal oxides that are prevalent in recycled materials, as previously explained in the background. The reaction sitescan also include dissolved oxygen in the molten metalthat has been released by the action of heat and electromagnetic stirring. The exact oxygen scavenging reaction occurring at the reaction siteswill depend on the materials for the feed materialsand the reactive gases. For example, for a feed materialcomprising Ti having reaction sitescomprising TiOand the reactive gas comprising H, an exemplary reaction would be TiO+2H=Ti+2HO. As another example, for dissolved Oand the reactive gascomprising H, an exemplary reaction would be 2H+O=2HO.

As also shown in, the first systemalso includes a heat source system, 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 cavityof the melting hearth, which is configured to heat the molten metalin the melting cavity. The heat source systemcan be configured to melt the feed materials, using melt cycles defined by energy input per weight of material and a calculated vaporization rate. As shown in, the heat source systemcan also include a reactive gas conduitin flow communication with a reactive gas supply, configured to direct the reactive gasonto the surface() of the molten metalin the melting cavity.

The first systemalso includes a melting chamber, which can comprise a sealed melting vessel, which is shown schematically in. US Patent Publication No. 2023/0235959 A1, 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, the melting chambercan be in flow communication with a reactive gas distribution systemthat can include a gas supply, a pumpand one or more nozzles. The reactive gas distribution systemis configured to inject the reactive gasinto the melting chamberat a selected temperature, pressure and flow rate. The melting chamberis also configured to receive the compounds produced by the scavenging reaction. For example, a scavenged HO compound would flow into the melting chamberas water vapor.

As shown in, the melting hearthalso includes an actuatorin signal communication with a central processing unit (CPU) (not shown) having a linkageconfigured to support and move the melting hearthto a desired hearth tilt angle. U.S. Pat. No. 12,145,197, which is incorporated herein by reference describes further details of a melting hearth having tilting capabilities.

As also shown schematically in, the melting hearthcan be tilted by the actuator() and linkage() from any angle between 0° to 90° to pour a pour streamof the molten metalfrom the melting cavity. In the neutral or 0° position, the reactive gasin the melting chambercontacts the surfaceof the molten metalin the melting hearth, substantially as previously described. When the melting hearthis tilted from the neutral position to pour the molten metalfrom the melting cavity, the reactive gasin the melting chamberalso contacts the pour streamof the molten metalflowing over the pour notch(). This exposes additional areas of the molten metaland additional reaction sites() to contact with the reactive gas. In, for illustrative purposes the melting hearthis shown at pour angles of 30°, 45°, 60° and 90°. However, in actual practice the melting hearthcan be tilted at any angle to provide a pour streamhaving a uniform mass flow rate. U.S. patent application Ser. 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.

Referring to, a second systemP for performing a process for producing metal powderis illustrated schematically. The second systemP includes a foundry systemand an atomization system. The foundry systemincludes a melting hearthP and a heat source systemP configured to melt a feed materialP into a molten metalP and to pour a pour streamP of the molten metalP into an atomization dieof the atomization system. The melting hearthP includes an electromagnetic stirring systemP configured to electromagnetically stir the molten metalP substantially as previously described for electromagnetic stirring system(). The melting hearthP includes a pour notchP and has tilting capabilities substantially as previously described for the melting hearth. The melting hearthP has features substantially as described in previously cited U.S. Pat. Nos. 9,925,591, 10,654,106, and 12,145,197.

Still referring to, the atomization systemincludes the atomization diein flow communication with the melting hearthP configured to receive the pour streamP of molten metalP and produce the metal powder. As shown in, the metal powdercomprises a plurality of spherical metal particleshaving a desired particle shape and particle size. As shown in, the atomization diecan include a metal bodyhaving passageways for gas jets. The atomization diealso includes an orificein configured to receive the pour streamP of molten metalP. The gas jets, which are arranged in a circular pattern, impinge a reactive gasP onto the pour streamP of molten metal. The gas jetsall converge on the pour streamP of molten metalP within the atomization dieto disintegrate the pour streamP of molten metalP and generate the metal powder. In addition, the metal particles() can be formed with a desired shape (e.g., spherical) and particle size (e.g., diameter D of 1-500 μm) using techniques that are known in the art. The particles() cool in free-fall until reaching the bottom of an atomization tower (not shown) of the atomization system. The metal powdercan then be segregated into groups of similar particle size using gravity, screening, or cyclonic separation.

Still referring to, the atomization systemcan also include a reactive gas distribution systemP in flow communication with a reactive gas supplyP. The reactive gas distribution systemP can distribute the reactive gasP into a process chamberof the atomization systemin selected areas thereof. For example, the reactive gasP can be directed onto the pour streamP of molten metalfrom different directions before it enters the atomization die. As another alternative, the reactive gascan be directed onto the metal particles() formed by the atomization die. As another alternative, the reactive gasP can be injected into the gas jetsof the atomization dieas an atomization gas. As shown in, the reactive gasP scavenges oxygen from reaction sitesP on the metal particlessubstantially as previously described for reaction sites().

illustrates steps in a process for producing metals and alloys using the first system().illustrates steps in a process for producing metals and alloys using the second systemP ().

Example 1: Tests were performed using a system configured substantially as described for the second systemP (). This type of system is commercially available from Applicant, Continuum Powders Corporation, Cloverdale, CA, under the trademark GREYHOUND. Also in the tests, the feed materialP comprises recycled machine chips made of a titanium alloy (Ti6Al4V). The Table 1 below shows results from several hydrogen deoxidation tests that were performed while atomizing titanium alloy (Ti6Al4V). Data includes results from control samples for metal powders processed without any reactive gases. Data also include results from test samples for metal powders() produced using hydrogen as the reactive gas(). In four of the five tests using hydrogen as the reactive gas(), oxygen in the metal powders() produced was reduced significantly from the control samples and from the feed material.

Example 2: A process in which the reactive gas() comprises hydrogen, carbon dioxide, or carbon monoxide mixed with a plasma process gas comprising argon, helium or a mixture of both. The reactive gas() can be introduced through the heat source system(), 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() at superheated temperatures in a tundish to scavenge oxygen in the molten metalduring melting and subsequent atomization.

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

Example 4: A process as specified in Example 3, in which the reactive gasP () is introduced into the processing chamber() adjacent to atomization of the pour streamP () of molten metalP for the purpose of scavenging oxygen in the feed materialsP () being atomized. In an illustrative embodiment, the reactive gasP () can be injected no more than 1 inch from the periphery of the atomization die().

Example 5: A process as disclosed in U.S. Pat. Nos. 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 materialP can comprise powder placed in the melting hearthP () by a feeding mechanism, such as described in U.S. patent application Ser. No. 18/128,438, which is melted, atomized using the reactive gasP () in the form of hydrogen, and then collected in a discreet process all in a sealed chamber().

Example 6: A process that can use the reactive gasP () 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.

Example 7: A process that allows a rapid reaction between liquid or semi solid metal droplets with the reactive gasP () during an atomization event at atmospheric pressure.

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.