TESTING INDUCED NANOSCALE INSTABILITIES OF SECONDARY PHASES IN Si_3N_4, THE TEM APPROACH TO HIGH-TEMPERATURE MICROSTRUCTURES

摘要

The significance of dynamic microstructures in liquid-phase sintered Si_3N_4 due to the constraints of HT-testing is addressed by focusing on three Si_3N_4 materials which have been tested on a different time scale extending from several minutes to well in excess of 1000 hours. As shown by high-resolution and analytical transmission electron microscopy, HT-testing can introduce nanoscale morphological and compositional instabilities of both the amorphous and crystalline secondary phases, providing a surprisingly sensitive tool to monitor the response of Si_3N_4 materials at high temperatures, which is otherwise insufficiently described by the as-sintered microstructure.