Extra‐Large Grains in the Silicon Nitride Ceramics Doped with Yttria and Hafnia

Abstract

Microstructural development of silicon nitride doped with Y 2 O 3 and HfO 2 was investigated to determine how extra‐large grains develop during gas pressure sintering. Grains as long as 200 µm and a few tens of micrometers wide developed at high temperatures (>2173 K) in a fine‐grained matrix containing a limited amount of liquid which had a poor propensity to spread. A small number of grains could grow quite large before their growth was halted by neighboring grains of comparable size.