Tensile behavior and microstructural evolution of a carbon/silicon carbide composite in simulated re-entry environments

Carbon fiber reinforced silicon carbide matrix composites with a protective coating were prepared by chemical vapor infiltration. Their tensile strength was about 240-250 MPa at room temperature, and 330-390 MPa in vacuum. Tensile behavior in a simulated re-entry environment was studied and compared with that in vacuum. The microstructural evolution on tensile fracture surfaces were investigated by scanning electron microscopy, and an oxidation damage pattern of fibers on tensile fracture surface was presented and discussed. A significant strength reduction was observed in re-entry environments due to the interaction of load, high temperature, and oxidation. The non-uniform oxidation of fibers weakened the load-carrying ability due to decreasing effective loaded area and hence strength. Finally, a minimum diameter of total fiber cluster embedded in composites is suggested about 220 μm for use under high load in re-entry environments at 1800 °C.