Plastic deformation of silicon nitride/boron nitride fibrous monoliths

High-temperature compressive creep of unidirectional Si3N4/BN fibrous monoliths has been investigated at 1300–1500°C in an inert atmosphere. The results were then compared to those for deformation of the Si3N4 and BN base materials. Plasticity of the fibrous monoliths was limited to very low stresses when the Si3N4 cells were oriented perpendicular to the stress axis because the BN cell boundaries failed, followed by failure of the Si3N4 cells. In the fibrous monolith in which cells were oriented parallel to the stress axis, steady-state deformation controlled by deformation of the Si3N4 cells was achieved.