Advanced Microstructural Characterization of Dimpled Laminated Metals

1. Dimpling: The Final Frontier It’s not just for golf balls and grandmothers anymore! Student: Jason Burbey Faculty Advisor: Professor Eric Stach

2. Outline • Background • Objective • Sample Preparation/Characterization • Sample Prep. Instruments • Work Completed • Future Work • Acknowledgements • Questions

3. Background • Professor Ravi Chandran • University of Utah • Laminated Steel and Brass • Repeated cold rolling • Continuation of previous study • Evaluated Mechanical Properties • Inverse relationship between yield strength and bilayer thickness • Yield strengths as high as 850 MPa • Why? • Microstructural characterization needed Ravichandran, K. “Nanoscale Steel-Brass Multilayer Laminates Made By Cold Rolling: Microstructure and Tensile Properties.” Scripta Materialia Vol 42: 949,951

4. Objective • Microstructural Characterization of laminates • Bright Field Images in TEM • Features of interest: • Bilayer thickness • Interlamellar structure • Dislocation density and distribution

5. Sample Preparation/Characterization • Dimple specimens to 10-15um • Ion Mill to produce very small hole in specimen • Electron Transparent • Take bright-field images of specimen using TEM

6. The Dimpler • Model 2000 Sample Prep System • Diamond Slurries and pastes • 6,3,1, .25 micron

7. The Ion Mill • Gatan Model 600 Duo-Mill • Ar+ ions directed at specimen from both sides at a set angle • Fairly time consuming

8. Transmission Electron Microscope • JEOL Model 2000FX • Uses an Ultra High Vacuum (UHV) • 10^-9 -10^-11 atm • Capable of high resolution images at high magnifications • 1,000,000X or higher • Resolution of < 3Å

9. Work completed • Dimpled metallic laminates • SS grinding wheel • Ion Mill attempt • Micarta grinding Wheel • Dimpled Ta/Si specimens • Dimpled InAs/GaP specimens

10. Metallic Laminates: SS grinding Wheel • Thicknesses varied from 90-290um • Used 3um slurry and dimpled to 20um • Not all specimens were 20um • Used optical microscope to check thickness • Re-dimpling difficult • Specimens 10-15um achieved • Ion Mill trials • Inefficient • Start Over! • Made more specimens • New dimpling progression • Used different wheel

11. Dimpling Laminates: Micarta Grinding Wheel • Micarta Wheel is flatter and thicker than the SS grinding wheel • Dimple the whole specimen surface • Used 6um slurry • Sped up dimpling progress • Much smoother surface • Very important for Ion Milling • Successful specimens created • Stopped after 1um slurry • More scratches observed with .25um paste

12. SS vs. Micarta

13. 1um slurry vs. .25um paste w/micarta wheel

14. Ta/Si Specimens • Checking phase transformation of Ta • Blue side = Si • Reflective = Ta • Use diamond scribe to cleave specimens

15. Dimple on Si side SS grinding wheel Specimens thicker than laminates 470-520um Same progression as laminates Same force exerted by grinding arm Sample Prep Problem • Destruction of specimens • Force too much • Si is fragile! • Would crack at approx. 20um

16. Solution for Ta/Si specimens • Use less force! • Progressively decrease force • Before switching slurry/paste • 3 specimens from each bulk sample ready for Ion Milling

17. In/As specimens • Thicknesses between 310-320um • Dimpled on GaP side • Used SS grinding wheel • Same dimpling progression as Ta/Si • Like butter! • It smells… • 3 specimens ready for Ion Milling

18. Future Work • Ion Mill all of the different specimens • Characterize specimens in TEM with help from Professor Stach • Publish characterization results

19. Acknowledgements • Dr. King • Professor Stach • Cheryl Waller • Vijay Rawat • Rocco Cerchiara from Fischione • Jan Eberle • MSE Dept.

20. Questions?