Texture development in Si3N4/BN fibrous monolithic ceramics

Preferred orientation was measured in Si3N4/BN fibrous monolithic ceramics using x-ray diffraction. The materials were manufactured by co-extrusion of polymer binder/ceramic blends which were subsequently pyrolized and then h ot-pressed to produced a fully dense ceramic composite. A very strong modif ied wire texture was present in the BN with the basal planes aligned parall el to the axis of extrusion due to shear-induced reorientation of the plate let-shaped BN particles during co-extrusion. Texture was also observed in t he Si3N4 and was attributed to a combination of co-extrusion and hot-pressi ng. After hot pressing, the basal planes of the rod-shaped beta-Si3N4 were observed to be preferentially aligned perpendicular to the extrusion direct ion. Measurements prior to hot-pressing revealed that a small amount (appro ximate to 5%) of beta-Si3N4 was present in the alpha-Si3N4 starting powder. Although texturing of the predominant alpha-Si3N4 did not occur during co- extrusion, significant texturing of the beta-Si3N4 was observed. During sub sequent hot-pressing, the pre-existing textured beta-Si3N4 particles appear ed to act as seeds for transformation and preferred growth of rod-shaped be ta grains parallel to the axis of extrusion. (C) 2000 Kluwer Academic Publi shers.