Microstructure design and control for improvement of thermal conductivity of SiC_f/SiC composites

摘要

We focused on microstructure design and control of SiC_f/SiC composite based on our fabrication process and the simple model of thermal conductivity of the SiC_f/SiC composite, and the improvement of their thermal conductivity was investigated. Submicron-sized α-SiC with coarse a-SiC particles addition was used as the starting materials for SiC matrix layers between SiC fiber cloths because it showed higher thermal conductivity. The thermal conductivity of PCS-composite, EPD-composite and Untreated-com-posite was 18, 45 and 56 W/m K, respectively, and these values were much higher than that of the composites reported in our previous papers. Untreated composite is simply considered as a multilayered composite consisting of the SiC fiber layers with high thermal conductivity and the SiC matrix layers with high thermal conductivity. The experimental thermal conductivity of the Untreated composite well agreed with the theoretical thermal conductivity calculated by series model. Thermal conductivity of EPD-composite was lower than that of Untreated composite. In EPD-composite, the thermal conductivity of SiC fiber layers with the SiC matrix should be lower than that of SiC fibers themselves due to the SiC matrix with slightly lower thermal conductivity in SiC fiber cloths. The SiC matrix formed in SiC fiber cloths in PCS-composite was derived from PCS, and this matrix would show much lower thermal conductivity due to its low crystallinity. PCS-composite is considered as a multilayered composite consisting of the SiC fiber layers with very low thermal conductivity and the SiC matrix layers with high thermal conductivity, and thus the PCS-composite has low thermal conductivity. In this study, higher thermal conductivity of SiC_f/SiC composite was successfully achieved by EPD process and using microstructure-controlled SiC matrix and polycrystalline SiC fibers.