Reaction Synthesis and Mechanical Properties of Lu ₄ Si ₂ O ₇ N ₂

Abstract

Crystallized Lu – Si – O – N phases were believed to be the grain‐boundary ( GB ) phases that might provide Si 3 N 4 with excellent high‐temperature mechanical properties. However, little is known about the intrinsic properties, as well as the synthesis, of the Lu – Si – O – N ceramics. This work reveals the reaction paths of heating Lu 2 O 3 , SiO 2 , and Si 3 N 4 powder mixtures (with the stoichiometry of 4:0.96:1) from room temperature to 1600°C. Thereafter, dense Lu 4 Si 2 O 7 N 2 samples are synthesized by in situ reaction/hot‐pressing method, and the mechanical properties at room temperature and elevated temperatures are reported for the first time. The Lu 4 Si 2 O 7 N 2 samples show significant high‐temperature mechanical properties, such as the elastic stiffness remains 77% from room temperature to 1500°C; and bending strength keeps 93% from room temperature to 1400°C. The present results shine a light on Lu 4 Si 2 O 7 N 2 as a promising target GB phase for the optimization of high‐temperature mechanical properties of Si 3 N 4 .