1. Mechanical properties of SiC fibers grown by laser-induced CVD
Principal Investigators:
A.B.Mann and M.J.Matthewson
Graduate student:
Shawn Ward
Rearrange names to be in line

2. Objective and related work
Characterization of mechanical properties of Laser-CVD SiC
Mechanical testing
Bending
Tensile
Indentation
Young’s modulus and hardness
Raman spectroscopy
Helium-ion microscopy
Chemical Vapor Infiltration SiC fibers
ORNL
SiC/SiC composites commercially available
Hi-Nicalon, SCS, SI-TUFF, Sylramic, …

3. Laser-induced CVD FreeFormFibers, LLC
Laser lattice in precursor gas for SiC
Rapid processing
Uniform fibers
Any CVD-compatible material can be made
Silicon carbide
Carbon fiber
Boron carbide

4. Raman procedure 3C, 4H, 6H polytypes have different Raman spectra
Samples were positioned upright with fracture face exposed to laser or laying on a side
Samples were fractured after mounting to ensure clean face
Optical Studies of Undoped and Doped Wide Bandgap Carbide and Nitride Semiconductors

5. Raman

6. Raman fracture face

7. Raman explained Outside of fiber Fracture face
Wide peak at 480 cm-1 indicates amorphous Si
Verifies prior SEM work on fibers
Fracture face
Split SiC TO peak at 796 cm-1
Si: Amorphous outside to crystalline inside of fiber
Heat-damaged fibers show clear 3C-SiC peaks
Carbon G and D peaks
Si-1 peak sometimes
785 vs 514 laser
785 higher volume sampled
Increased chance of sampling large SiC x-tal
514 more surface specific
Better spatial resolution

8. Nanoindentation Hysitron Triboindenter w/ Berkovich tip
Indenting outside of fiber – amorphous layer
Indent inside of sample (seen in HIM images)
Obtain Young’s modulus E, Hardness, H
Maximum values:
E: 303 GPa, H: 88 GPa
Average values:
E: 150 GPa, H: 15 GPa

9. Nanoindentation
Same load function used in both graphs – hold at MAX load present
Each curve is an indent on a separate fiber
Indents on outside of fiber
Epoxy lowers scatter in data

10. Results: Nanoindentation
NO hold at max load
No crossover
CA, JB behave similarly
Both have adhesion issues (knee on CA-512)
Outside fiber values:
Er≈80-150GPa
H≈15GPa ± 4GPa
Graph bigger

11. Microscopy

12. Microscopy

13. Future work Surface-Enhanced Raman Spectroscopy (SERS) Microtomography
Gold nanoparticles on surface of a cross-section
Enhance Raman signal of surface chemistry, rather than of phonon modes
Microtomography
Erich Schmid Institute of Materials Science, Deformation Mechanisms of Nano-Porous Hexagonal Metals, ESI,

14. Future work Two point bending One point bending
Large sample sizes possible
Dynamic test
One point bending
Small weights at fiber tips
Distance between ends measured
Weight increased and distance re-measured
From slope of resulting line and geometry, E can be calculated 14

15. Questions?