High-strength, high-toughness silicon nitride sinter

A high-strength, high-toughness silicon nitride sinter prepared by:

• mixing a silicon nitride powder and a sintering additive;
• mixing 0.1 to 10% by volume, based on the amount of silicon nitride-sintering additive mixture, of elongated single crystal .beta.-silicon nitride seed particles having a larger minor diameter than the average particle diameter of said silicon nitride powder and having an aspect ratio of at least 2, into said silicon nitride-sintering additive mixture;
• shaping the resultant mixture by a means which orients said elongated single crystal .beta.-silicon nitride seed particles, in their elongated dimension, coplanar with a plane defined by the direction of movement of said means, thereby preparing a green body;
• and
• sintering said green body, thereby simultaneously densifying said green body and inducing epitaxial growth of said single crystal .beta.-silicon nitride seed particle thereby obtaining a silicon nitride sinter having a strength of not less than 1100 MPa and a fracture toughness of not less than 11 MPa m.sup.1/2.