Mechanical properties of several advanced Tyranno-SA fiber-reinforced CVI-SiC matrix composites

A recently developed SiC fiber, Tyranno-SA (2D plain-woven), was used as the reinforcement in several SiC/SiC composites. The composites were fabricated by chemical vapor infiltration (CVI) process. The mechanical properties and fracture behaviors were investigated using three-point bending test. The Tyranno-SA fiber possesses rough fiber surface with pure SiC surface chemistry, which may result in strong fiber/matrix bonding and fiber sliding resistance. Various pyrolytic carbon (PyC) and SiC/PyC interlayer coatings were applied in the composites to modify the mechanical properties of the interface. The interlayers were deposited by isothermal CVI process. The test results revealed a close PyC layer dependence of the strength of the composites. The ultimate flexural strength (UFS) increased with the increasing of the PyC layer thickness up to 100 nm, and then, kept at similar level till 200 nm. The Tyranno-SA/SiC composites exhibited relatively high proportional limit stresses due mainly to the large Young's modulus of the fiber. Fiber pullouts were observed at the fracture surfaces of all the interlayered composites. Attractive promising was exhibited on further improvement of the mechanical properties of the composites through further improvement of the interfacial properties and the matrix densification process.