Microstructure and Mechanical Properties of Silicon Nitride

초록

The effects of h-BN content on microstructure, mechanical properties, and machinability were investigated. The relative density of the sintered compact decreased with increasing BN content. The flexural strength also decreased with h-BN content, mainly due to lower Young’s modulus of BN compared to Si3N4. With increasing h-BN content, Si3N4/h-BN based ceramic composites revealed enhanced crack resistance (R-curve) behavior. The Vickers indentation crack paths in specimens are sinusoidal due to bridging and pull out of grains during crack propagation. The grain size of ß-Si3N4 slightly decreased with h-BN content. During end-milling and micro drilling process, monolithic Si3N4 ceramic could not be machined, due to brittle fracture. However, thrust forces measured for Si3N4/h-BN composites decreased with increasing h-BN content, showing the excellent macro and micro machinabilty.