Effect of preform on thermal expansion coefficient of C/C composites

Using natural gas as precursor gas, intergrated carbon felt and 2D needle carbon felt as preforms, two kinds of C/C composites were prepared by thermal gradient chemical vapor infiltration, and both of them have a same density of 1.74 g/cm³. With help of optical microscope and scanning electronic microscope, the growth characteristic and microstructure of pyrolytic carbon matrix were observed, and thermal expansion testing machine was employed to measure their thermal expansion coefficient (CTE). The CTE of C/C composites reinforced by different preforms was studied, and the CTE difference in different direction was explained. The results show that, the CTEs of composite A and B gradually increases with increasing temperature, and the CTE in Z direction is higher than that in XY direction. When the fiber volume fraction of two composites in Z direction is near, with the fiber volume fraction in XY direction increasing, their CTEs increase in Z direction and decrease in XY direction displaying α_B-Z > α_A-Z > α_A-XY > α_B-XY. The CTE of C/C composites mainly depends on the volume fraction and arrangement of carbon fiber in preform, carbon matrix and porous distribution, and the former has decisive function.