Methods of forming near-net shape structures from non-stoichiometric oxides

1. A method of forming a near-net shape structure, the method comprising:

sintering a green structure exhibiting a green structure shape and comprising a stoichiometric metal oxide in a reducing atmosphere to form a structure comprising a non-stoichiometric metal oxide comprising at least one metal and less than a stoichiometric amount of oxygen; and

after sintering the green structure to form the structure comprising the non-stoichiometric metal oxide, electrochemically reducing the non-stoichiometric metal oxide in an electrochemical cell to form a near-net shape structure comprising the at least one metal and having less than about 1,500 ppm oxygen, wherein the near-net shape structure has a shape substantially corresponding to the green structure shape.

2. The method of claim 1 , wherein sintering a green structure comprising a stoichiometric metal oxide comprises exposing the stoichiometric metal oxide to an elevated temperature in the presence of a reducing gas.

3. The method of claim 2 , wherein exposing the stoichiometric: metal oxide to an elevated temperature in the presence of a reducing gas comprises exposing the stoichiometric metal oxide to the elevated temperature in the presence of hydrogen.

4. The method of claim 1 , wherein sintering a green structure comprising a stoichiometric metal oxide in a reducing atmosphere to form a structure comprising a non-stoichiometric metal oxide comprising at least one metal and less than a stoichiometric amount of oxygen comprises forming a non-stoichiometric metal oxide comprising at least one transition metal oxide.

5. The method of claim 1 , wherein sintering a green structure comprising a stoichiometric metal oxide in a reducing atmosphere to form a structure comprising a non-stoichiometric: metal oxide comprising at least one metal and less than a stoichiometric amount of oxygen comprises forming a non-stoichiometric metal oxide comprising at least one rare earth element.

6. The method of claim 1 , wherein sintering a green structure comprising a stoichiometric metal oxide in a reducing atmosphere to form a structure comprising a non-stoichiometric metal oxide comprising at least one metal and less than a stoichiometric amount of oxygen comprises forming a non-stoichiometric metal oxide comprising at least one dopant selected from the group consisting of boron, carbon, phosphorus, silicon, and aluminum.

7. The method of claim 1 , wherein electrochemically reducing the non-stoichiometric metal oxide in an electrochemical cell comprises electrochemically reducing the non-stoichiometric metal oxide in the electrochemical cell using a molten salt electrolyte comprising one or more of calcium chloride, sodium chloride, calcium bromide, and sodium bromide.

8. The method of claim 1 , wherein electrochemically reducing the non-stoichiometric metal oxide in an electrochemical cell to form a near-net shape structure comprising the at least one metal and having less than about 1,500 ppm oxygen comprises forming a near-net shape structure exhibiting magnetic properties.

9. The method of claim 1 , wherein forming a near-net shape structure comprising the at least one metal comprises forming a near-net shape structure comprising one or more of an alloy comprising dysprosium and iron, an alloy comprising terbium and iron, an alloy comprising dysprosium and nickel, and an alloy comprising neodymium and iron.

10. The method of claim 1 , wherein sintering a green structure comprising a stoichiometric metal oxide in a reducing atmosphere to form a structure comprising a non-stoichiometric metal oxide comprising at least one metal and less than a stoichiometric amount of oxygen comprises forming a non-stoichiometric metal oxide that is from about 1 percent to about 20 percent oxygen deficient relative to the stoichiometric metal oxide.

11. A method of forming a near-net shape structure, the method comprising:

forming a green structure comprising at least one stoichiometric metal oxide;

sintering the green structure in the presence of at least one reducing gas to reduce the at least one stoichiometric metal oxide of the green structure and to form a non-stoichiometric metal oxide; and

reducing the non-stoichiometric metal oxide in an electrochemical cell including a cathode comprising the non-stoichiometric metal oxide to form a structure having a near-net shape and comprising an elemental metal or a metal alloy.

12. The method of claim 11 , wherein sintering the green structure in the presence of at least one reducing gas comprises sintering the green structure in the presence of hydrogen.

13. The method of claim 11 , wherein forming a structure having a near-net shape and comprising an elemental metal or a metal alloy comprises forming a structure comprising the at least one metal and less than about 2,000 ppm oxygen.

14. The method of claim 11 , wherein forming a structure having a near-net shape and comprising an elemental metal or a metal alloy comprises forming a structure comprising at least two transition metals.

15. The method of claim 11 , wherein reducing the non-stoichiometric metal oxide in an electrochemical cell to form a structure having a near-net shape comprises forming a structure that is smaller than the green structure.

16. A method of forming a near-net shape structure, the method comprising:

forming a structure comprising an oxygen deficient non-stoichiometric metal oxide in a reducing environment, the non-stoichiometric metal oxide comprising less than a stoichiometric amount of oxygen and at least one metal, wherein the structure comprising the oxygen deficient non-stoichiometric metal oxide consists essentially of the non-stoichiometric metal oxide; and

after forming the non-stoichiometric metal oxide, electrochemically reducing the non-stoichiometric metal oxide in an electrochemical cell to form the near-net shape structure.

17. The method of claim 16 , wherein forming a structure comprising an oxygen deficient non-stoichiometric metal oxide in a reducing environment comprises forming the structure comprising the oxygen deficient non-stoichiometric metal oxide by additive manufacturing in the presence of a reducing gas.

18. The method of claim 16 , wherein forming a structure comprising an oxygen deficient non-stoichiometric metal oxide in a reducing environment comprises annealing or sintering a metal oxide in the reducing environment.

19. The method of claim 16 , further comprising, prior to forming a structure comprising an oxygen deficient non-stoichiometric metal oxide in a reducing environment, forming a metal oxide on a substrate by thermal spraying.

20. The method of claim 16 , wherein electrochemically reducing the non-stoichiometric metal oxide in an electrochemical cell to form a near-net shape structure comprises forming the near-net shape structure to have a size that is less than a size of the oxygen deficient non-stoichiometric metal oxide.

21. The method of claim 1 , wherein sintering a green structure exhibiting a green structure shape and comprising a stoichiometric metal oxide in a reducing atmosphere to form a structure comprises forming the green structure consisting essentially of the stoichiometric metal oxide.

22. The method of claim 16 , wherein electrochemically reducing the non-stoichiometric metal oxide in an electrochemical cell to form the near-net shape structure comprises applying a voltage of from about 2.5 V to about 2.9 V between a working electrode and a counter electrode of the electrochemical cell.

23. The method of claim 16 , wherein electrochemically reducing the non-stoichiometric metal oxide in an electrochemical cell to form the near-net shape structure comprises applying a voltage of from about 1.8 V to about 2.9 V between a working electrode and a counter electrode of the electrochemical cell.