On the nature of machining cracks in ground ceramics: Part I: SRBSN strengths and fractographic analysis

Machining cracks in ground sintered reaction-bonded silicon nitride (SPLBSN) rods and bars were analyzed by fractographic techniques. Grinding flaw sizes were as small as 12 mu m and as large as 80 mu m and correlated strongly with grinding direction and wheel grit size. Some grinding treatments had no deleterious effect on strength since the machining cracks were very small and fracture occurred from the material's inherent flaws. The telltale signs of machining damage may be detected with conventional low power optical microscopy using simple fractographic techniques. The telltale signs are summarized in a new series of schematic drawings which will aid pattern recognition for engineers and fractographers.