1999 Volume 42 Issue 4 Pages 560-567
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 bending strength and the residual stress distribution near the ground surface. In the case of surfece-grinding, the depth of grinding flaws formed parallel to the feed direction ranges from 40 to 70 μm. 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 ranges from 10 to 30 μm. 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 facegrinding.