Formation of α‐Si 3 N 4 Solid Solutions in the System Si 3 N 4 ‐A1N‐Y 2 O 3

The subsolidus phase diagram of the quasiternary system Si 3 N 4 ‐AlN‐Y 2 O 3 was established. In this system α‐Si 3 N 4 forms a solid solution with 0.1Y 2 O 3 : 0.9 AIN. The solubility limits are represented by Y 0.33 Si 10.5 Al 1.5 O 0.5 N 15.5 and Y 0.67 Si 9 A1 3 ON 15 . At 1700°C an equilibrium exists between β‐Si 3 N 4 and this solid solution.