Thermo-mechanical process to enhance the quality of grain boundary networks

• US 8,876,990 B2
• Filed: 08/20/2009
• Issued: 11/04/2014
• Est. Priority Date: 08/20/2009
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Schuh, Christopher A., Kita, Koichi
• Primary Examiner(s): Zhu, Weiping
• Application Number:
  US12/544,568
• Publication Number:
  US 20110041964A1
• Time in Patent Office: 1,902 Days
• Field of Search: 148/525, 148/559, 148/592
• US Class Current: 148/559
• CPC Class Codes: C21D 2201/03 Amorphous or microcrystalline structure
• CPC Class Codes: C21D 7/13 by hot working
• CPC Class Codes: C21D 8/00 Modifying the physical properties by deformation combined with, or followed by, heat treatment hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02

Abstract

Methods to enhance the quality of grain boundary networks are described. The process can result in the production of a metal including a relatively large fraction of special grain boundaries (e.g., a fraction of special grain boundaries of at least about 55%).

Claims

1. A method of processing a metal, comprising:

while maintaining the metal at a temperature suitable to anneal the metal;

applying a force to strain the metal over a first period of time; and

reducing the applied force over a second period of time subsequent to the first period of time;

wherein the metal is processed to have a special grain boundary fraction of at least about 55%.

2. A method as in claim 1, further comprising, while maintaining the metal at a temperature suitable to anneal the metal, applying a second force to strain the metal over a third period of time subsequent to the first and second periods of time, and reducing the applied second force over a fourth period of time subsequent to the third period of time.

3. A method as in claim 2, wherein the first force is applied at a first temperature and the second force is applied at a second temperature, and the first and second temperatures are substantially different.

4. A method as in claim 3, wherein the first temperature is higher than the second temperature.

5. A method as in claim 2, wherein the applied force produces a cumulative engineering strain of at least about 10%.

6. A method as in claim 2, wherein the applied force produces a cumulative engineering strain of at least about 50%.

7. A method as in claim 1, further comprising additional cycles of applying force to strain the metal and reducing force.

8. A method as in claim 1, wherein the temperature is above about 0.4 T_m expressed in Kelvins.

9. A method as in claim 1, wherein the temperature at which recrystallization of the metal occurs is between about 0.4 T_m expressed in Kelvins and 0.75 T_m expressed in Kelvins.

10. A method as in claim 1, further comprising heating the metal above the temperature prior to maintaining the metal above the temperature.

11. A method as in claim 1, wherein the metal is processed to have a special grain boundary fraction of at least about 60%.

12. A method as in claim 1, wherein the metal is processed to have a special grain boundary fraction of at least about 65%.

13. A method as in claim 1, wherein the reducing step comprises reducing the applied force to zero.

14. A method as in claim 1, wherein the reducing step comprises reducing the applied force to a non-zero value.

15. A method as in claim 1, wherein the applied force produces an engineering strain of at least about 3%.

16. A method as in claim 1, wherein the applied force produces an engineering strain of at least about 10%.

17. A method as in claim 1, wherein the applied force produces a von Mises strain of at least about 3%.

18. A method as in claim 1, wherein the applied force produces a von Mises strain of at least about 10%.

19. A method as in claim 1, wherein the applied force produces a rate of strain of at least about 0.01% per second.

20. A method as in claim 1, wherein the first period of time is at least about 0.01 seconds.

21. A method as in claim 1, wherein the second period of time is at least about 0.01 seconds.

22. A method as in claim 1, wherein the metal comprises nickel.

23. A method as in claim 1, wherein the metal comprises copper.

24. A method as in claim 1, wherein the metal comprises a copper alloy, a nickel alloy, and/or a steel.

25. A method as in claim 1, wherein the metal is substantially free of oxygen.

26. A method as in claim 1, wherein the metal comprises a face-centered cubic metal with a stacking fault energy of less than about 100 mJ/m².

27. A method as in claim 1, wherein the metal is processed to have a special grain boundary fraction of at least about 55% without substantially heating the metal after the force application step.

28. A method as in claim 1, wherein the first period of time is at least about 1 second.