Mechanical and dielectric properties of SiCf/NBAS composites with dip-coated La2Ti2O7 interphase

To improve the properties of SiC fiber-reinforced ceramic-matrix composites for potential use as radar-absorbing materials, La 2 Ti 2 O 7 interphase was dip-coated on the surface of the SiC fibers, and the SiC f /NBAS composites were then prepared. The pristine SiC fibers with relatively high electrical resistivity were mainly composed of amorphous Si x C y O and a small amount of β -SiC and free carbon. A weak La 2 Ti 2 O 7 interphase improved the flexural strength and toughness of the composites due to the fiber pull-out and crack deflection. The measured room-temperature complex permittivity of the composites increased, and the dielectric loss was greater than that of the pristine SiC fibers owing to the production of excess free carbon in the degradation of SiC fibers during the preparation of SiC f /NBAS composites. The excess free carbon with higher electrical conductivity was also believed to play a significant part in the increase of dielectric permittivity of the composites with the increasing heat-treatment temperatures even below 1000 °C. A dual-layer structure was designed to expand the bandwidth for microwave absorption.