Evaluating the Suitability of Glass Optical Fiber as a Toughening Agent in Silicon Composites Developed by Spark Plasma Sintering

This study explores the repurposing of waste glass optical fibers (SiO₂ fibers) by using them as toughening agents for silicon. The poor fracture toughness of silicon has precluded its development as a structural material and reinforcing it with a second phase such as glass fiber is a potential route for enhancing its toughness. In this work, the focus is checking the extent of toughening brought about by the introduction of SiO₂ fibers in the silicon matrix and understanding the reasons for the same. A composite of 79 wt.% silicon and 21 wt.% SiO₂ fiber was synthesized by spark plasma sintering at 1473 K at an applied pressure of 75 MPa. The spark plasma sintered composite possessed a relative density of 99%. The silicon matrix and SiO₂ fiber reinforcement exhibited an average hardness of 12 GPa & 7 GPa respectively. The indentation fracture toughness of the composite was observed to be 1.55 MPa.m^1/2 which is ~ 8% higher than the indentation fracture toughness of nominally pure silicon. The SiO₂ fibers were unable to provide sufficient crack deflection or crack blunting and consequently, the enhancement in toughness was marginal.