Effect of oxidation on the damping behavior of 2D C/SiC composites

A carbon fiber preform was chemical vapor infiltrated with a pyrocarbon (PyC) interphase and a SiC matrix, and then coated with a SiC outer layer by chemical vapor deposition to prepare 2D C/SiC composites with a density of 2.1 g/cm(3). The composites were oxidized at 700, 1000, 1300 degrees C for 2, 5 and 10h, respectively. The damping behavior of the oxidized composites was measured by a dynamical mechanical analyzer and the microstructural damage produced. by the oxidation was investigated by scanning electron microscopy. Results show that the damping of the composites oxidized at 700 degrees C and 1000 degrees C increases initially and then decreases with increasing oxidation time while that of the composites oxidized at 1300 degrees C is independent of the oxidation time. The damping capacity of the C/SiC composites is determined by the carbon fibers, PyC interphase, SiC matrix and their interaction. The oxidation of the composites increases the damping by weakening the interfacial bonding due to the oxidation of PyC during the initial stage of oxidation, and decreases the damping by the oxidation loss of carbon fibers and excessive damage of the PyC interphase during the latter stages of oxidation. SiO2, formed at 1300 degrees C by the oxidation of SiC fills the voids produced by carbon oxidation, which increases the dampingand compensates for the decrease of damping produced by carbon loss and excess damage of the PyC interphase.