Effect of Grinding Method on Bending Strength of Silicon Nitride

摘要

The surface of bending specimens of silicon nitride is finished by the surface grinding method or the face-grinding method. A disk-shaped or cup-shaped diamond wheel with the grit size of # 200/230 is used for grinding. The feed direction of the grinding wheel is either parallel or perpendicular to the longitudinal direction of bending specimens. The grinding flaw size is estimated from the bonding strength and the residual stress distribution near the ground surface. In the case of surface grinding. the depth of grinding flaws formed parallel to the feed direction ranges from 40 to 70 um. This grinding flaw extends outside the compressive residual stress zone, so the stress shielding effect is small. The large flaw size reduces the fracture strength. On the other hand, the depth of flaws of face-ground specimens rages from 10 to 30 um. The fracture strength after face-grinding is higher than that of lapped specimens because the flaw lies in the compression zone. The face-grinding method is recommended to minimize machining costs because finer finishing is unnecessary after face-grinding.