Off-axis creep of a ceramic-matrix/continuous-ceramic-fiber composite: Experimental evaluation

摘要

The compression creep of a unidirectionally reinforced, SiC continuous fiber/calcium aluminosilicate (anorthite) glass-ceramic matrix composite was evaluated experimentally. Experiments covered the stress (−σ1) and temperature (T) ranges of 20–40 MPa and 1300–1320°C, respectively. The experiments also emphasized characterization of the rheology as a function of the angle of misorientation (ϕ) between the applied compressive load and the direction of reinforcement. For any given σ, T condition, the highest steady-state strain rate occurred for ϕ ∼ 50° (up to an order of magnitude faster than in the transverse, ϕ = 90°, case); overall composite strain in this case included a substantial contribution from displacement across the fiber-matrix interface. The data reveal that the interfacial rheology responsible for the displacement is distinctly temperature sensitive. Evaluation of the composite flow through its comparison to numerical/rheological models that scrutinize the interfacial effect implies that the interface is characterized by a non-Newtonian viscous rheology; this suggests that the interface response involves specifically the flow of the thin amorphous silica interphase that comprises a portion of the fiber-matrix interface in this material. The overall plastic response of the unidirectionally reinforced material is nevertheless rate-limited by plastic flow of the matrix and can be described by the superposition of three modes of strain, the magnitude of each being dependent specifically on ϕ.