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-aluminides to produce titanium 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 of 500? C.-900? C. 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.

2. The process of claim 1 wherein the anode includes a non-consumable mesh container in which the titanium aluminide is placed, the titanium aluminide being consumable during the refining process.

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

4. The process of claim 1 wherein the titanium-aluminide comprises 15%-25% aluminum and at least 10% oxygen by weight.

5. The process of claim 1 wherein the titanium-aluminide comprises 20%-25% aluminum and at least 10% oxygen by weight.

6. The process of claim 1 wherein the titanium aluminum master alloy comprises about 99.0% titanium and about 1.0% aluminum by weight.

7. The process of claim 1 wherein the titanium aluminum master alloy comprises about 98.0% titanium and about 2.0% aluminum by weight.

8. The process of claim 1 wherein the titanium aluminum master alloy comprises about 97.0% titanium and about 3.0% aluminum by weight.

9. The process of claim 1 wherein the titanium aluminum master alloy comprises about 96.0% titanium and about 4.0% aluminum by weight.

10. The process of claim 1 wherein the titanium aluminum master alloy comprises about 95.0% titanium and about 5.0% aluminum by weight.

11. The process of claim 1 wherein the titanium aluminum master alloy comprises about 94.0% titanium and about 6.0% aluminum by weight.

12. The process of claim 1 wherein the titanium aluminum master alloy comprises about 93.0% titanium and about 7.0% aluminum by weight.

13. The process of claim 1 wherein the titanium aluminum master alloy comprises about 92.0% titanium and about 8.0% aluminum by weight.

14. The process of claim 1 wherein the titanium aluminum master alloy comprises about 91.0% titanium and about 9.0% aluminum by weight.

15. The process of claim 1 wherein the titanium aluminum master alloy comprises about 90.0% titanium and about 10.0% aluminum by weight.

16. The process of claim 1 wherein the electrolyte is substantially free of added titanium chlorides.

17. The process of claim 1 wherein the electrolyte is substantially free of added forms of soluble titanium.

18. The process of claim 1 wherein the temperature range 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 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 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 0.05 A/cm.sup.2.

22. The process of claim 1 wherein the electrical current density of the cathode is between 0.05 A/cm.sup.2 and 0.1 A/cm.sup.2.

23. The process of claim 1 wherein the electrical current density of the cathode is between 0.1 A/cm.sup.2 and 0.5 A/cm.sup.2.

24. The process of claim 1 wherein the electrical current density of the cathode is between 0.5 A/cm.sup.2 and 1.0 A/cm.sup.2.

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-0.4V.

26. 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 0.4V-0.6V.

27. 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 0.6V-0.8V.

28. The process of claim 1 wherein the electrical differential between the anode and the cathode is 0.4V-0.8V.

29. The process of claim 1 wherein the electrical differential between the anode and the cathode is 0.8V-1.2V.

30. The process of claim 1 wherein the electrical differential between the anode and the cathode is 1.2V-1.6V.

31. The process of claim 1 wherein the electrical differential between the anode and the cathode is 1.6V-2.0V.

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-4.0 cm.

34. The process of claim 1 wherein the distance between the anode and the cathode is 4.0 cm-6.0 cm.

35. A method of refining titanium aluminides into master titanium-aluminum alloys, comprising: a. placing a 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 of both; 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, said master alloy containing up to 10 wt. % aluminum.

36. The method of claim 35 wherein the electrolyte is substantially free of added titanium chlorides or other added forms of soluble titanium.

37. The method of claim 35 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 35 wherein the titanium-aluminum master alloy contains 2.5 wt. % or less aluminum.

Description

EXAMPLE 1

[0074] 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 33wt. % Al.

EXAMPLE 2

[0075] 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.

EXAMPLE 3

[0076] Titanium-aluminide used in this example was produced by aluminothermic reduction of TiO.sub.2 with Al to produce a Ti-13% A1-11% O 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.

EXAMPLE 4

[0077] Titanium-aluminide used in this example was produced by aluminothermic reduction of TiO.sub.2 to produce a Ti-10% A1-13% O 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.

EXAMPLE 5

[0078] Titanium-aluminide used in this example was produced by aluminothermic reduction of TiO.sub.2 to produce Ti-13% A1-11% O 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.

EXAMPLE 6

[0079] 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% O 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.

EXAMPLE 7

[0080] 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.

EXAMPLE 8

[0081] Titanium-aluminide with a composition of Ti-10% A1-12% O 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.

EXAMPLE 9

[0085] 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.