Influence of pyrolytic carbon interface thickness on microstructure and mechanical properties of SiC/SiC composites by NITE process

Unidirectional SiC/SiC composites were prepared by Nano-Infiltration and Transient Eutectic-phase (NITE) process using SiC nano-powder infiltration technique, and the effects of pyrolytic carbon (PyC) interface thickness between fibers and matrix on density, microstructural evolution and mechanical properties were characterized. SiC fibers both with and without PyC interface were employed as reinforcement and SiC nano-powder was employed for matrix formation with 12 mass% sintering additives of the total powder. The thickness of PyC layer deposited by chemical vapor deposition (CVD) process was highly-accurately controlled at about 0.25, 0.50 and 1.00 μm. Nearly full-dense SiC/SiC composites with uncoated fibers caused strong interaction between fibers and matrix, resulting in a brittle fracture behavior without fiber pull-out. Higher strength with a pseudo-ductile fracture behavior could be obtained using 0.50 μm of PyC interface thickness, where a lot of deflects and branches of the propagating cracks and fiber pull-out were observed. Induced PyC interface conditions strongly affect the density, microstructural evolution, and therefore dominate mechanical properties and fracture behaviors.