JOURNAL OF MATERIALS SCIENCE 35 (2000) 3365 – 3371

Texture development in Si₃N₄/BN fibrous

monolithic ceramics

S. Y. LIENARD§, D. KOVAR

Texas Materials Institute and Department of Mechanical Engineering University of Texas at

Austin, Austin, Texas 78712, USA

E-mail: dkovar@mail.utexas.edu

R. J. MOON, K. J. BOWMAN

Department of Materials Engineering, Purdue University, West Lafayette, IN 47907, USA

J. W. HALLORAN

Department of Materials Science and Engineering, University of Michigan, Ann Arbor,

MI 48019, USA

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 hot-pressed to produced a fully dense

ceramic composite. A very strong modified wire texture was present in the BN with the

basal planes aligned parallel to the axis of extrusion due to shear-induced reorientation of

the platelet-shaped BN particles during co-extrusion. Texture was also observed in the

Si₃N₄ and was attributed to a combination of co-extrusion and hot-pressing. After hot

pressing, the basal planes of the rod-shaped b-Si₃N₄ were observed to be preferentially

aligned perpendicular to the extrusion direction. Measurements prior to hot-pressing

revealed that a small amount (5%) of b-Si₃N₄ was present in the a-Si₃N₄ starting powder.

Although texturing of the predominant a-Si₃N₄ did not occur during co-extrusion,

significant texturing of the b-Si₃N₄ was observed. During subsequent hot-pressing, the

pre-existing textured b-Si₃N₄ particles appeared to act as seeds for transformation and

preferred growth of rod-shaped b grains parallel to the axis of extrusion.© 2000 Kluwer

Academic Publishers