The effect of whisker orientation in SiC whisker-reinforced Si 3N 4 ceramic matrix composites

Abstract

Si 3N 4 ceramic matrix composites reinforced by nearly unidirectionally aligned SiC whiskers have been prepared by extrusion and hot pressing. Unlike the case in traditional Si 3N 4 ceramic matrix composites reinforced by random SiC whiskers, the mechanical properties of the composites exhibit a significant dependence on whisker orientation. In the direction of whisker alignment for SiC(w)/Si 3N 4 composites, increments in bending strength and fracture toughness of 200 MPa and 3 MPa·m 1/2 are obtained respectively, compared to the values in the direction perpendicular to whisker alignment. Based on microscopic fractographic observation and micromechanics analyses, the effects of whisker orientation on toughening mechanisms are discussed. The results indicate that the whisker orientation, θ , is a decisive factor for the essential toughening mechanisms of whiskers. Only in the case of small θ and weak interface can whisker pullout occur, and whisker has maximum toughening effect. The results show that effects of whisker strengthening and toughening can be improved simultaneously through whisker oriented alignment. ©