VISCOUS ENERGY-DISSIPATION AT HIGH-TEMPERATURES IN SILICON-NITRIDE

Viscous energy dissipation in a liquid phase sintered silicon nitride, and the resulting internal friction, were investigated at temperature s up to 1300 degrees C with uniaxial tension-compression, torsion pend ulum, and impulse excitation tests. The amount of internal friction, w hich is lower after heat treatment of the silicon nitride, reaches a s teady-state value only after long-term tests at high temperature. A lo w and a high (> 50 MPa) stress amplitude regime are distinguished, rev ealing the existence of different anelastic deformation mechanisms. Th e evolution of the microstructure is investigated by X-ray diffraction , analysis of scanning electron microscopy images, and high resolution and analytical transmission electron microscopy in order to relate sp ecific internal friction features to the silicon nitride microstructur e. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. Ali rights reserved.