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

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, … http://www.substech.com

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

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

Raman

Raman fracture face

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

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

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

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

Microscopy  

Microscopy

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, http://esi.oeaw.ac.at/project/deformation-mechanisms-nano-porous-hexagonal-metals, 27 08 2016

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

Questions?