ON THE NATURE OF MACHINING CRACKS IN GROUND CERAMICS: PART II, COMPARISON TO OTHER SILICON NITRIDES AND DAMAGE MAPS

ABSTRACT

The size and severity of grinding machining cracks in a sintered reaction bonded silicon nitride are compared to data for other silicon nitrides. Crack sizes follow a similar trend with grinding wheel grit size despite differences in microstructures, strengths, and fracture toughnesses. Silicon nitrides with enhanced fracture toughness actually develop deeper machining cracks than in less tough silicon nitrides. Machining damage maps for silicon nitride are presented.

Keywords:

• Grinding Cracks
• Machining Cracks
• Fractography
• Silicon Nitride
• Damage Maps

ACKNOWLEDGMENTS

The authors thank the members of the Ceramic Machining Consortium who participated in this program. We especially recognize Dr. B. Mikijelj of Ceradyne Inc., Mr. Richard Allor of Ford Motor Company, and Drs. Ron Chand and C. Guo of Chand-Kare Technical Ceramics. Partial support for this project was furnished by the U. S. Department of Energy, Office of Transportation Technologies, under contract DE-AC05–84OR21400 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. 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

¹Certain commercial materials or equipment are identified in this paper to specify adequately the experimental procedure. Such identification does not imply endorsement by the National Institute of Standards and Technology nor does it imply that these materials or equipment are necessarily the best for the purpose.

^*Manufacturer's data.

^** Consortium preliminary data References (2–8).

^‡HV denotes Vickers hardness. HK denotes Knoop hardness. The number in parenthesis is the indentation load (kgf).

^†Test method: SCF surface crack in flexure; CN chevron notched beam; SEPB, single-edge precracked beam; IS, indentation strength.

– Not available or reported.

[] Data source, reference.