Analysis of Grain Boundary Mobility in Commercially Pure Copper and Pure Nickel

1. Analysis of Grain Boundary Mobility in Commercially Pure Copperand Pure Nickel Ana Erb Advisor: Professor A. D. Rollett

2. Interests & Goals • Mobility pertains to the movement of grain boundaries, dominated by solute. • Solute present in commercial alloys affect the migration of the boundaries. • Boundary mobility controls recrystallization in alloys, which is of importance to industry.

3. Recrystallization: the formation of new, strain-free grain structure from that existing in cold worked metal. The effects of annealing on metals: (a) cold work, (b) after recovery, (c) after recrystallization, and (d) after grain growth.

4. Approach Equation for grain boundary mobility: where, V is the velocity of the boundaries, M is the mobility of the boundaries, and P is the driving pressure for migration. V M P Annealing & OIM (during recrystallization) Hardness Test Stored Energy

5. Commercially Pure Copper • Initial treatment • Anneal at 800°C for 20 hours • Roll to 30% reduction • Polish overnight on the Vibromet • Scratch sample perpendicular to the rolling direction

6. Figure on the left is after initial treatment, scratch can be seen. Figure on the right is after the second anneal (800°C for 2 hours), sample oxidized and scratch gone.

7. Commercially Pure Copper • Twin boundaries observed in copper samples. • Characterized as a 60° rotation about <111> crystal direction. • Used information from “Extracting Twins from Orientation Imaging Microscopy Scan Data,” Ryan J.Larson and Stuart I. Wright. 111 Pole Figure for Copper Sample S3  60°<111> (depicted in black)

8. Pure Nickel • Initial treatment • Anneal two samples at 1000°C for 30 minutes • Roll to 30% reduction • Electro-polish • Scratch sample perpendicular to the rolling direction • Second anneal • Anneal sample again after first OIM scan • one sample at 900°C in argon for 20 minutes • other sample at 700°C in argon for 20 minutes

9. Figure on the left is after initial treatment. The sample was then annealed at 900°C for 20 minutes in an argon tube

10. Figure on the left is after initial treatment. The sample was then annealed at 700°C for 20 minutes in an argon tube.

12. Nickel OIM Data

13. Solving For Mobility Shear Modulus

14. Calculated Mobility and Grain Boundary Diameters

15. Future Work • Take samples back to FAMU/FSU COE. • Prepare more nickel samples, now knowing what temperature range to work on. • Obtain more grain mobility data on both the commercially pure copper samples and pure nickel samples.

16. Acknowledgements • Dr. Anthony D. Rollett • Mitra Taheri • Jason Gruber • Herb Miller • Chaovoon Samuel Lim • Mohammed Haroon Alvi • Jennifer Barrow • Diego Laboy

17. Reference • Humphreys, F.J. and M. Hatherly Recrystallization and Related Annealing Phenomena. Elsevier Science Ltd. 1996. • Kalu, Peter. Recrystallization and Grain Size Determination. PowerPoint Presentation, Fall 2003. • Rollett, A.D. Grain Boundary Properties: Energy, Mobility. PowerPoint presentation, Spring 2003. • Taheri, Mitra L. In-Situ Quantification of the Solute Effect on Mobility, Character and Driving Pressure of Grain Boundaries During Recrystallization in Aluminum Alloys. Carnegie Mellon University.

18. More on Mobility Two main categories of boundary types: • Low angle grain boundaries • Migration in the LAGBs occur during recovery • High angle grain boundaries • Migration in the HAGBs occur during recrystallization • Angle refers to the angle of rotation required to coincide the two lattices.

19. Solutes & Mobility • Solutes tend to segregate to any interface and lower the free energy of the system. • For a boundary to move away from the segregated solute requires energy to be supplied. • Mobility is also strongly sensitive to boundary type. • High mobilities tend to be associated with CSL structures.

20. Coincident Site Lattice(CSL) • A CSL is when a finite fraction of lattice sites coincide between two lattices. • The reciprocal of the ratio of CSL sites to lattice sites is denoted by .