Technology Advances
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This issue of MRS Bulletin introduces a new department, TECHNOLOGY ADVANCES. This department provides up-to-date reports of materials developments that begin to bridge the gap between research innovation and application of advanced materials technologies. Coordinated by MRS Bulletin’s 2000 Visiting Scientist, Renée G. Ford of Renford Communications, Ltd., the articles present new developments and their progress toward appli-
cations. Opportunities for outside interaction, such as collaborations or technology licensing, are listed at the end of each article to facilitate further advancement of the technology. While it may not be possible to predict which technologies will be successful in the commercial market, the examples cited here present some paths to consider.
Magnetic Float Polishing Provides Improved Method for Finishing Advanced Ceramic Balls for Bearings At Oklahoma State University (OSU), magnetic float polishing (MFP), a technique that was initially investigated in Japan, has been further developed and combined with chemical-mechanical polishing (CMP) to polish ceramic balls. The Si3N4 balls produced by the OSU finishing technology are reported to be of sufficient quality for bearing applications, and the process has also been found to be successful for finishing balls of other advanced ceramics and glasses. Among various advanced ceramics, Si3N4, because of its high toughness, is the material of choice for ceramic bearings. A critical factor affecting the performance and reliability of advanced ceramics for hybrid bearing applications is the quality of the surface produced by polishing. Furthermore, because of their high hardness and inherent brittleness, ceramics are extremely sensitive to surface defects caused by grinding and polishing. Since fatigue failure is directly related to surface imperfections, defects must be minimized in order to achieve the required performance reliability in service. The conventional finishing of Si3N4 balls is essentially similar to the method used (V-groove lapping) for the finishing of steel balls, which involves low polishing speeds (~50 rpm), high loads (~10 N per ball), and use of a costly diamond abrasive. With MFP, the material removal rate can be high (~1 µm/min). The abrasives used are closer to the hardness of the work material, which minimizes the damage in the initial stages, and are considerably less costly than diamond abrasive. Ceria (CeO2) has been found to be the most effective abrasive for finishing Si3N4 balls, producing a damage-free surface with a surface roughness Ra of
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