Relationships between carbon fiber type and interfacial domain in ZrB 2 -based ceramics

Different kinds of commercial C chopped fibers were added to a ZrB2 ceramic doped with Si3N4 as sintering additive in order to study the different interfacial domains between fiber and matrix. The composites were hot-pressed at 1700°C and their final relative densities were higher than 95%. Depending on the fiber type, different interfaces formed with the matrix, resulting in different extent of fiber pullout. Fibers reacted with the additive and were surrounded by SiC and ZrC phases, weakly bonded to the fiber itself. Only high modulus fiber maintained a rounded shape and no reaction products formed around it. The fracture toughness values did not vary among the various composites, but the work of fracture notably increased for higher modulus fiber. The room-temperature strength varied from about 250 to 400 MPa and the strength in air at 1500°C decreased to 110-270 MPa depending on the interface formed around the fiber.