Effect of heat treatment on the thermal expansion of 1D C/SiC composites from room temperature to 1400 °C

1D C/PyC and 1D SiC/C/SiC composites as well as a bulk CVD SiC material were prepared. The effects of heat treatment on the thermal expansion behavior of the composites from room temperature to 1400 °C were investigated. The thermal expansion behavior of 1D C/PyC and 1D SiC/C/SiC composites depended on the thermal stress and the transition temperature of thermal stress from compressive to tensile in both the fibers and the matrix. The heat treatment affected the expansion behavior by changing the thermal stress and the transition temperature. The treatment increased the transition temperature of axial stress in 1D C/PyC from its deposition temperature to 1300 °C and then increased its longitudinal CTE above this temperature, but it had no obvious effect below this temperature. The treatment did not increase the transition temperature of axial stress in 1D SiC/C/SiC, but led to fracture of the fibers from the deposition temperature to 1300 °C. As a result, the treatment increased its longitudinal CTE below 1300 °C, but had nearly no effect on it above 1300 °C. The treatment increased the transition temperature of radical stress in 1D C/PyC from its deposition temperature up to 1300 °C, and then the transverse CTE of the composite below 1300 °C depended on that of the SiC matrix.