5 Parameter analysis of Modified 316 LN Stainless steel

1. 5 Parameter analysis of Modified 316 LN Stainless steel By: Nicholas Bembridge1 Advisors: Dr Anthony Rollett2 & Dr Peter Kalu1 PhD Researchers: Mohammed Alvi2 Jason Gruber2 & Steven Downey1 (1)FAMU FSU College of Engineering (2) Carnegie Mellon University

2. Long term Goal The long term goal of this research is to examine the microstructure and texture changes caused by heat treatment of modified 316LN stainless steel. Current Goals • Examine grain boundary character distribution in M316LN stainless steel. • Determine grain size and twin density with sufficient statistical confidence.

3. Background Currently Modified 316 LN Stainless steel is used as a superconducting wire conduit in the 45 Tesla Hybrid Magnet System at the National High Magnetic Field Laboratory.

4. Heat treatment • Cu/Nb3Sn Superconductors • Cu-NB wires with thin layer of Sn Conduit Processing Annealed, Cold rolled – As Received • Cold worked • Jacket Formation (forming & welding) • Magnet coil winding • Nb3Sn reaction Heat Treatment (100hrs at 700oC) • Produces superconductor from Cu-Nb wires and Tin • Primary Selection Criteria for material use

5. Material

6. Grain Boundary Character Why do we need 5 parameters? - Describing a grain boundary requires a misorientation (3 parameters) and a normal (2 parameters). Why might the 5 parameter distributions be interesting? - This material has a high density of twins, so we would like to know if the twins are all coherent twins; also we would like to know if any other boundary types are favored “GBCD” = Grain Boundary Character Distribution

7. Experimental Procedure • As received M316LN samples were furnace annealed in argon atmosphere at 700o C for varying lengths of time and water quenched. *Received in cold rolled and annealed condition. • O.I.M. analysis done with Phillips XL-40 FEG SEM Orientation Imaging Microscope and TSL software. • Between 300x300 and 350x350 micron scan area. • 0.5 micron step size for good resolution.

8. OIM Overview • Electron diffraction gives grain orientation. • Orientations are measured point by point across the sample’s surface. 1 1 3 3 2 2

9. Results • OIM IPF Maps • Twin density data • Grain size data • Plots of GBCD for as-received, and comparison of as-received with 50 hours anneal

10. IPF Maps IPF Map Legend As Received 100 Hour Texture is weak, therefore sample suitable for GBCD analysis

11. Twin density data Typical twinned grain Typical twin

12. Grain size data

13. 300 500 450 400 600 • As Received [100] Misorientations based on [100] show low frequencies; slight bias towards {111} and {110} normals.

14. 300 400 500 200 600 • As Received [110] Peaks present for [110] misorientations at 30°, 40°, with normals between (001) and (1-11); also 60° with (-111).

15. 400 300 500 200 600 • As Received [111] All [111] misorientations favor pure twist boundaries with (111) normals; only 60°[111] shows a massive peak, corresponding to the coherent twin. Peak at (111)-50°[111] may be “leakage” from the coherent twin in (111)-60°[111].

16. [110] 600 [111] [111] 500 500 600 Comparative MRD for selected misorientations As Received 50hr [110]

17. [111] [111] 600 600 Comparison Continued As Received 50hr • Peaks occur at similar locations • Peaks have similar intensities • No change in GBCD

18. Conclusions • GBCD is similar to other low stacking fault energy fcc metals such as brass. • Negligible changes in Grain size and Twin density. • Negligible changes in texture. • Negligible changes in grain boundary character distribution as far as 50 hours. • Annealing at 7000 C has essentially no effect on the microstructure.

19. Acknowledgements • Dr. Kalu 1 • Dr. Rollett 2 • Steven Downey 1 • Mohammed Alvi 2 • Jason Gruber 2 • Herb Miller2 • TriciaBennett 2 (1)FAMU/FSU College of Engineering (2) Carnegie Mellon University

20. Any Questions?

21. Supplemental Slides

22. 50 150 200 100 MRD Plots - As Received [100]

23. 100 50 150 200 MRD Plots - As Received [110]

24. 300 400 500 450 600 • As Received [110]

25. 50 100 150 200 MRD Plots - As Received [111]

26. 400 300 450 500 600 • As Received [111]