Yi-Hyun Park

Influence of Grain Size on Thermal Conductivity of SiC Ceramics

SiC fiber reinforced-SiC ceramic matrix (SiCf/SiC) composites are one of the candidate structural materials for nuclear fusion reactors systems because of their low activation, mechanical property and chemical stability at high temperature. High thermal conductivity of SiCf/SiC composites is required to reduce heat load and to provide high thermal conversion efficiency. The objective of this study is to determine thermal conductivity on grain size dependence of SiC ceramics which is the matrix in composites. β-SiC powder was sintered by hot-press method. Al2O3 and Y2O3 were used as sintering additives. The grains size was grew with increase of holding time at 1900 °C. Thermal conductivity of SiC ceramics was gradually increased up to 112 W/mK. Thermal conductivity of SiC ceramics is dependent on growth of grain size due to the scattering of the phonon by the grain boundaries leads to a size-dependence.

Nondestructive Testing of NITE-SiC Ceramics for Fusion Reactor Application

Ultrasonic test (UT) method is a suitable one for examining the inherent structural defects such as pores and cracks of SiC/SiC composites. In this study, the examination sensitivity limit of UT method based on computerized tomography (C-Scan inspection) was performed by inserting an artificial defect in SiC ceramics material. The artificial defect was simulated interface defect of SiC/SiC composites. A right triangle artificial defect that has approximately 100 µm of thickness was made. The UT inspection was performed in axial and planar direction to investigate the measurement limit of width and depth. The applied transducers were focused-immersion type. The used frequencies ranges were 50 and 80 MHz. The detection limit was decided compare with results of microscope. The reflected intensity of 50% can be reliable value in detection of defects.