MECHANICAL-PROPERTIES OF HOT-PRESSED SILICON-NITRIDE WITH DIFFERENT GRAIN STRUCTURES

During hot‐pressing of α‐Si3N4 powders, the equiaxed α micro‐structure gradually transforms into a β structure characterized by needle‐shaped prismatic grains which are closely entangled and linked together. With increasing amounts of the β fraction, the bend strength, fracture toughness, and work of fracture increase significantly, then decrease as grain growth occurs. The Klc, improves by a factor of >2 and the change in γF by a factor of >4. The crack resistance to achieve the same crack velocity in materials of different β contents shows a similar trend. The dependence of the mechanical properties on the microstructure is explained by linking and pullout of the β crystals and by grain coarsening. Copyright © 1979, Wiley Blackwell. All rights reserved