Toughened ceramic composite materials comprising coated refractory fibers in a ceramic matrix wherein the fibers are coated with carbon and an additional coating of ceramic material and carbon mixture

摘要

A fiber reinforced ceramic composite material exhibiting high tensile strength, high fracture toughness and high-temperature oxidation resistance is produced by simultaneously depositing a thin coating layer of refractory metal carbide with fugitive carbon onto the fiber reinforcement prior to the subsequent densification with the ceramic matrix. The energy behind propagating matrix cracks in the resulting composite material are effectively dissipated by crack deflection/branching, fiber debonding and frictional slip through the relatively weak and compliant fiber coating layer. These energy release and arrest mechanisms sufficiently impede the driving force behind unstable crack propagation and render the cracks non-critical, thereby serving to blunt and/or divert propagating matrix cracks at or around the reinforcing fiber. While significantly increasing the strength and fracture toughness of the composite, the compliant refractory fiber coating system enables the composite to remain oxidatively stable when stressed at or beyond the matrix cracking stress point and subsequently exposed to temperatures above 800° C. in air.