Elevated-temperature mechanical properties of silicon nitride/boron nitride fibrous monolithic ceramics

A unique, all-ceramic material capable of nonbrittle fracture via crack def lection and delamination has been mechanically characterized from 25 degree s through 1400 degrees C. This material, fibrous monoliths, was comprised o f unidirectionally aligned 250 mu m diameter silicon nitride cells surround ed by 10 to 20 mu m thick boron nitride cell boundaries. The average flexur e strengths of fibrous monoliths were 510 and 290 MPa for specimens tested at room temperature and 1300 degrees C, respectively. Crack deflection in t he BN cell boundaries was observed at all temperatures. Characteristic flex ural responses were observed at temperatures between 25 degrees and 1400 de grees C. Changes in the flexural response at different temperatures were at tributed to changes in the physical properties of either the silicon nitrid e cells or boron nitride cell boundary.