Microstructure and Mechanical Properties of Silicon Nitride/h-BN Based Machinable Ceramics
The effects of h-BN content on the microstructure, mechanical properties, and machinability of Si3N4 ceramics 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 h-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 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.
Hai-Doo Kim, Hua-Tay Lin and Michael J. Hoffmann
W. S. Cho et al., "Microstructure and Mechanical Properties of Silicon Nitride/h-BN Based Machinable Ceramics", Key Engineering Materials, Vol. 287, pp. 340-345, 2005