Abstract: 3D-C/SiC composites with PyC interphase in different thickness were fabricated by low pressure chemical vapour infiltration （LPCVI）,and the effect of PyC interphase thickness on thermal expansion of 3D-C/SiC composites is studied. It is shown that the effect of interphase thickness on thermal expansion of 3D-C/SiC composites lies in its influence on interphase bonding strength and sliding resistance in the debonding layer. In a certain thickness range （about 70-220nm）,coefficient of thermal expansion （CTE） of the composites decreases gradually with increasing of PyC interphase thickness. Moreover,heat treatment improves the thermal stability of the composites,and influences the CTE by changing interfacial thermal stress and microstructure of the composites, and changes CTE of the composites intensively at high temperatures by changing interfacial thermal stress and microstructure of materials. However,heat treatment does not change the matrix crack sealed temperature.

Key words: 3D-C/SiC composite, interfacial thermal stress, thermal expansion, PyC interphase, CVI