TITANIUM MASTER ALLOY FOR TITANIUM-ALUMINUM BASED ALLOYS

Abstract

A process is disclosed for the electro-refinement of titanium aluminides to produce titanium-aluminum master alloys which process is effective even in the presence of substantial amounts of aluminum and in the presence of ten (10) or more weight percent oxygen in the material(s) to be refined. The process is likewise effective without the addition of titanium chlorides or other forms of soluble titanium to the electrolyte bath comprising halide salts of alkali metals or alkali-earth metals or a combination thereof.

Claims

1. A process for electro-refining titanium-aluminide to produce titanium-aluminum master alloys, comprising: a. placing titanium-aluminide comprising more than ten weight percent aluminum, and at least ten weight percent oxygen, into a reaction vessel, the reaction vessel configured with an anode, a cathode, and an electrolyte, the electrolyte including halide salts of alkali metals or alkali-earth metals or a combination thereof; b. heating the electrolyte to a temperature sufficient to create a molten electrolyte mixture; c. directing an electrical current from the anode through the molten electrolyte mixture to the cathode; and d. dissolving the titanium-aluminide from the anode to deposit a titanium-aluminum master alloy at the cathode; wherein the titanium-aluminum master alloy contains less than 5.0 wt % aluminum.

2. (canceled)

3. The process of claim 1 wherein the titanium-aluminide comprises 10%-25% aluminum and at least 10% oxygen by weight.

4-5. (canceled)

6. The process of claim 1 wherein the titanium-aluminum master alloy comprises about 90.0% to 99.0% titanium and about 1.0% to 10.0% aluminum by weight, wherein the weight percentage of titanium and aluminum sum to 100.0%.

7-15. (canceled)

18. The process of claim 1 wherein the temperature range in the heating step is between 550° C. and 650° C. and the titanium master alloy product is a powder.

19. The process of claim 1 wherein the temperature range in the heating step is between 650° C. and 750° C. and the titanium master alloy product is wool-like.

20. The process of claim 1 wherein the temperature range in the heating step is between 750° C. and 850° C. and the titanium master alloy product is crystalline.

21. The process of claim 1 wherein the electrical current density of the cathode is between 0.01 A/cm.sup.2 and 1.0 A/cm.sup.2.

22-24. (canceled)

25. The process of claim 1 further including the step of using a reference electrode to monitor electrical differentials wherein the electrical differential between the anode and the reference electrode is 0.2V-0.8V.

26-27. (canceled)

28. The process of claim 1 wherein the electrical differential between the anode and the cathode is 0.4V-2.0V.

29-31. (canceled)

32. The process of claim 1 comprising the further step of adjusting the distance between the anode and the cathode to prevent short circuiting of the current flow through the electrolyte between the anode and the cathode.

33. The process of claim 1 wherein the distance between the anode and the cathode is 2.0 cm-6.0 cm.

34-35. (canceled)

36. The method of claim 1 wherein the electrolyte is substantially free of added titanium chlorides or other added forms of soluble titanium.

37. The method of claim 1 further comprising, after the dissolution and deposition step, the steps of allowing the electrolyte to cool and recovering the titanium-aluminum master alloy from the reaction vessel prior to solidification of the electrolyte.

38. The method of claim 1 wherein the titanium-aluminum master alloy contains 2.5 wt. % or less aluminum.

Description

DETAILED DESCRIPTION

[0066] Reference will now be made in detail to the various embodiments of the present disclosure. The embodiments are described below to provide a more complete understanding of the components, processes and apparatuses of the present disclosure. Any examples given are intended to be illustrative, and not restrictive.

[0067] One embodiment of the present disclosure provides a method for the refining of titanium-aluminide products from titanium-bearing ores.

[0068] In the present disclosure, refining of the titanium-aluminide products is done via electrochemical refining. A titanium-aluminide product is placed in a reaction vessel having a cathode and an anode. The anode is embodied as a movable perforated basket/container made from quartz or metals that are more noble than titanium (e.g. nickel or iron) to hold the titanium aluminide to be refined. The cathode is at or near the bottom of the reaction vessel, with the anode suspended above the cathode. Having the ability to adjust the distance between the cathode and the anode provides a means of maintaining an optimum distance between the cathode and the anode throughout the refining operation. This optimum distance ranges between 1 and 6 cm. The electrical differential between the anode and the cathode is between 0.4 and 2.0 volts, and the cathode current density is between 0.01 and 1 A/cm.sup.2. During the refining process, master alloy is deposited on the cathode as dendrites. Growth of the dendrites throughout the process decreases the distance between the cathode and the anode. Thus, some adjustment in distance may be necessary to maintain current density and to avoid short circuiting the current flow. Without adjusting the anode-cathode distance throughout the process, the dendrites could touch the anode which would produce an electrical short-circuit.

[0069] The reaction vessel also holds an electrolyte capable of transporting titanium and aluminum ions. This electrolyte is placed in the reaction vessel and heated to subject the titanium-aluminum product to an electro-refining process. The electrolyte used during the refining operation may be a mixture of MgCl.sub.2—NaCl—suitable for a temperature range of 550° C.-650° C., KCl—NaCl— suitable for a temperature range of 650° C. to 750° C., or NaCl— suitable for a temperature range of 750° C.−850° C. The refining operation is performed under an inert atmosphere. A resistive element furnace or an induction furnace can be used to heat the electrolyte. In the present disclosure, both types of furnaces (resistive element and induction) have been used. When using an induction furnace, a molybdenum susceptor crucible was used to couple with the induction field in order to generate heat that was transmitted to the electrolyte blend. The perforated basket holding the titanium aluminides to be refined is used as the anode in the electronic circuit by connecting a lead to the positive (+) side of an electric power supply. Metal foil can be placed around the inside of the reaction vessel and used as the cathode by connecting it to the negative (−) side of the electric power supply. During operation, the titanium-aluminide is oxidized (ionized) and titanium and aluminum ions migrate to the cathode where they are reduced to form titanium master alloy crystals or a wool layer of the refined titanium-aluminum alloy product. Impurities are concentrated (left behind) in the anode basket or remain in the molten electrolyte.

[0070] Alternatively, a cathode in the form of a metal plate can be placed parallel to the bottom of the reaction vessel with the anode basket suspended above the plate. In this configuration, the optimum distance between the cathode plate and the anode basket can be maintained by moving the anode basket vertically throughout the refining operation. The cathode is connected to the negative (−) side of the power supply by the lead and the anode is connected to the positive (+) side of the power supply. The cathode to anode distance is between 2 cm and 6 cm. Other configurations for the electro-purification cell are possible as well.

[0071] Titanium-aluminides to be electro-refined can be produced by reducing titanium bearing ores with Al (e.g., by using the UTRS Process). TiO.sub.2 content in titanium bearing ore can be anywhere between 75-98% by weight. Desired composition of titanium-aluminide can be achieved by varying the TiO.sub.2: Al ratio. As an example, mixing 559 g of a Rutile ore (˜94% TiO.sub.2 content) with 232 g of Al powder and 455 g of CaF.sub.2 will produce an acceptable blend. Charging the blend into a graphite vessel, ramping the temperature at 10° C./min. (in an argon atmosphere) to 1725° C. and soaking for ˜ 15 min. will produce suitable titanium aluminide metal that can be used as feed for the electro-refining process described herein.

[0072] Titanium-aluminides to be electro-refined can also be produced by melting titanium and aluminum scrap metals according to appropriate ratios.

[0073] Samples produced from the following examples were analyzed by using Atomic Emission Spectroscopy—Direct Current Plasma (DCP—OES) for analyzing metal concentrations and Inert Gas Fusion (IGF) for analyzing oxygen concentrations. Instruments were calibrated by using NIST standards. With reference to the following Examples, the cathode deposit refers to the master alloy produced via the various methods, as outlined in each Example. The percentages of various components are in weight percent. Unless otherwise specified, the cathode deposit (alloy product) refers to a wt. % Aluminum, the balance being Titanium and if present, any unavoidable impurities.

[0074] Example 1. Titanium-aluminide used in this example was produced by melting appropriate amounts of titanium and aluminum to produce Ti-36% Al alloy. Oxygen content of this alloy was 0.2%. The alloy was cut into small pieces and 29.0 g of this material was electro-refined at a constant DC current of 1.0 A. The refining process was carried out in NaCl—KCl (44:56 wt. %) electrolyte at 750° C. Nine grams (9.0 g) of cathode deposit was harvested and contained 33 wt. % Al.

[0075] Example 2. Titanium-aluminide used in this example was produced by melting appropriate amounts of titanium and aluminum to produce a Ti-10% Al alloy. Oxygen content of this alloy was 0.2%. The alloy was cut into small pieces and 31.0 g of this material was electro-refined at a constant DC current of 1.0 A. The refining process was carried out in NaCl—KCl (44:56 wt. %) electrolyte at 750° C. 14.0 g of cathode deposit was harvested and contained 7.0% Al.

[0076] Example 3. Titanium-aluminide used in this example was produced by aluminothermic reduction of TiO.sub.2 with Al to produce a Ti-13% A1-11%0 alloy. The alloy was broken into small pieces and 31.0 g of this material was electro-refined at a constant DC current of 1.0 A. The refining process was carried out in NaCl—KCl (44:56 wt. %) electrolyte at 750° C. 18.0 g of cathode deposit was harvested and contained 2.5% Al.

[0077] Example 4. Titanium-aluminide used in this example was produced by aluminothermic reduction of TiO.sub.2 to produce a Ti-10% A1-13%0 alloy. The alloy was broken into small pieces and 276.0 g of this material was electro-refined at a constant DC current of 6.0 A. The refining process was carried out in NaCl—KCl (44:56 wt. %) electrolyte at 750° C. 96.0 g of cathode deposit was harvested and contained 1.1% Al.

[0078] Example 5. Titanium-aluminide used in this example was produced by aluminothermic reduction of TiO.sub.2 to produce Ti-13% A1-11%0 alloy. The alloy was broken into small pieces and 70.0 g of this material was electro-refined at a constant voltage of 0.8V. The voltage of the anode was controlled by using a titanium rod as pseudo-reference electrode. The refining process was carried out in NaCl—KCl (44:56 wt. %) electrolyte at 750° C. 25.0 g of cathode deposit was harvested and contained 2.8% Al.

[0079] Example 6. Titanium-aluminide used in this example was produced by aluminothermic reduction of TiO.sub.2 to produce Ti-15% Al alloy and electro-refined to produce a Ti-13% A1-0.7%0 alloy. This alloy had wool-like morphology. The alloy was pressed into small pieces and 40.0 g of this material was electro-refined a second time at a constant voltage of 0.8V. The voltage of the anode was controlled by using a titanium rod as pseudo-reference electrode. The refining process was carried out in NaCl—KCl (44:56 wt. %) electrolyte at 750° C. 30.0 g of cathode deposit was harvested and contained 7.5% Al.

[0080] Example 7. Titanium-aluminide used in this example was produced by melting appropriate amounts of titanium, aluminum and iron to produce Ti-10% A1-48% Fe alloy. The alloy was cut into small pieces and 29.0 g of this material was electro-refined at a constant DC current of 1.0 A. The refining process was carried out in NaCl—KCl (44:56 wt. %) electrolyte at 750° C. 9.0 g of cathode deposit was harvested and contained 17% Al and 1.6% Fe.

[0081] Example 8. Titanium-aluminide with a composition of Ti-10% A1-12%0 was electro-refined to obtain the composition of Ti-2.7% A1-1.1% O. The refined material was then once again electro-refined to obtain final product with 99.0% of Ti.

[0082] Current efficiency for the electro-refining process depends on the size of titanium-aluminide pieces. A current efficiency of 80% is achieved for the process when less than 4.0 mm pieces were used. Current efficiency is estimated as a percentage of actually harvested yield to theoretically expected yield. Theoretically expected yield is proportional to total amount of coulombs passed through the system.

[0083] Examples 3, 4, 5, and 8 demonstrate that if the precursor material contains more than 10% oxygen, a very good separation of titanium and aluminum can be achieved during the electro-refining process. The titanium master alloy products in these examples illustrate that more than 78% of the aluminum in the initial precursor material was removed. In contrast, Examples 1, 2 and 6 demonstrate that not more than 42% of the aluminum contained in the precursor material can be removed during electro-refining without the presence of a substantial amount of oxygen.

[0084] After the refining operation, the resulting refined titanium master alloy product can be further processed into a final alloy product by adding additional elements. For example, the resulting refined titanium master alloy can be ground or milled with vanadium and converted into Ti—Al—V powder.

[0085] Example 9. 56.4 g of Ti-4.6% Al master alloy mixed with 2.8 g of V—Al alloy, 0.55 g Al and melted in VAR. Resulting final alloy had a composition of Ti-6.3A1-3.8V.

[0086] The refining operation produces a refined titanium master alloy product with a finely structured, dendritic morphology. For example, the titanium master alloy product may comprise titanium crystallites that have deposited on the cathode during the electro-refining operation. The fine dendritic structure of the titanium master alloy product uniquely provides a pathway for near-net shaped parts through hydraulic compression and subsequent sintering without the aid of a binding agent. Surface area in the refined titanium-aluminum alloy product ranged between 0.1 m.sup.2/g and 2.5 m.sup.2/g.

[0087] Due to the small size and delicate nature of the refined titanium master alloy product, near-net-shaped products can be compressed for further processing. The dendritic form of the refined titanium master alloy product (titanium master alloy wool) can be compressed by using hydraulic pressure. To accomplish this, the titanium master alloy wool is placed into a compression mold of desired shape. The mold is then placed into a hydraulic press where, between 35 to 65 tons/in.sup.2 is applied. This procedure can produce near-net shaped titanium parts that can then be sintered, used as consumable electrodes in a vacuum arc remelt (VAR) process, melted or further processed depending on the product application.

[0088] While specific embodiments of the disclosure have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosure which is to be given the full breadth of the appended claims and any and all equivalents thereof.