High-Temperature Behavior of Chemically Treated Silicon Nitride Powders

The mechanical properties of chemically treated, then sintered, Si3N4 was studied. Raw materials consisted of two types of Si3N4 produced by the nitridation of silicon. The chemical treatment involved leaching in different acids (HCl, HNO3, HF, and combinations thereof). The powders were sintered by hot isostatic pressing with 2.5% yttria, and the high‐temperature properties of the resultant materials were evaluated by the stepped‐temperature stress rupture (STSR) method (24‐h hold time at 150‐MPa stress at 1000°, 1100°, 1200°, 1300°, and 1400°C). A significant decrease in high‐temperature performance was observed for acidleached powders, especially when HF‐containing acids were used.