Consolidation of Si3N4 by hot isostatic pressing

Silicon nitride (Si3N4) is being considered for gas turbine engine applications because present-day metallic alloys are rapidly approaching the limits of their temperature capabilities. The present investigation was undertaken to determine the feasibility of producing a sound, dense Si3N4 body without additives, using conventional gas hot-isostatic-pressing techniques and an uncommon hydraulic hot-isostatic-pressing technique. These two hot-isostatic-pressing (HIP) techniques produce much higher pressure (275-413 MN/sq m) than conventional hot-pressing techniques and have the potential of producing large bodies of desirable shapes. Evaluation was based on density measurement, microscopic examination, both optical and electron, and X-ray diffraction analysis.