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ABSTRACT
Machining cracks in ground sintered reaction-bonded silicon nitride (SRBSN) rods and bars were analyzed by fractographic techniques. Grinding flaw sizes were as small as 12 µm and as large as 80 µm 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.
ACKNOWLEDGMENTS
The authors thank the members of the Ceramic Machining Consortium who participated in this program. We especially recognize Dr. Biljana. Mikijelj of Ceradyne Inc., Mr. Richard Allor of Ford Motor Company, and Drs. Ron Chand and C. Guo of Chand-Kare Technical Ceramics. Support for this project was furnished by the U. S. Department of Energy, Office of Transportation Technologies, with Oak Ridge National Laboratory.
Dr. Hockin Xu and Mr. Robert Gettings assisted with earlier phases of the Consortium project and with fracture toughness testing. Dr. William Luecke kindly furnished a micrograph of the microstructure. Over the course of this multiyear project, we were privileged to work with the following enthusiastic postdoctoral and guest worker colleagues who contributed a great deal to the success of this project: Dr. Phillip Koshy, Dr. Tim Strakna, Mr. Jeffrey Swab, and Dr. Kang Xu.
Notes
—Not available or not reported.
—Not available or reported.
Note: All specimens were cut from rods, with the exception of the last two entries which were for bars out from plates.