Silicon Oxycarbide Nanocomposite Laminates Reinforced with Carbon Nanotubes of High Degree of Alignment and Ultrahigh Packing Density

Abstract

With properties including high stiffness, high strength, low density, and high aspect ratio, carbon nanotubes (CNTs) are ideal reinforcements for ceramic matrix composites (CMCs) for enhanced strength and toughness. However, prior studies on CNT- reinforced CMCs generally showed limited mechanical and multifunctional property enhancements due to damage, random orientation, low volume fraction, and agglomeration of the introduced CNTs. In this study, we developed a bulk nanocomposite laminating process for ceramic matrix composites (BNL4CMC) to overcome such limitations and to enable the fabrication of ceramic nanocomposite laminates reinforced with highly aligned, uniformly distributed CNTs of ultrahigh packing densities (>40 vol%). Instead of direct mixing, the polymer precursors for the ceramic can be infused into horizontally aligned CNT (HA-CNT) arrays followed by curing and pyrolysis to convert the polymer matrix to ceramic while preserving the CNTs’ high degree of alignment and packing density. Silicon oxycarbide (SiOC), which possesses high modulus, high hardness, creep resistance, and good thermal/chemical stability, is selected as the matrix for this study. Using the BNL4CM approach, we successfully fabricated 4-ply HA-CNT/SiOC laminates with ultrahigh CNT packing density (> 40 vol%), uniform distribution, and nanofiber alignment. Microstructure and morphology characterizations including X-ray micro-computed tomography (X-ray μCT) and scanning electron microscopy (SEM) are used to study the evolution of HA- CNT/SiOC laminates’ microstructure during the fabrication process. Nano-indentation was performed to obtain the elastic modulus and hardness of the fabricated HA- CNT/SiOC laminates. The process-structure-property relation obtained will inform the design and manufacturing of other HA-CNT reinforced ceramic systems for enhanced mechanical and multifunctional properties.