Magnetic Float Polishing Processes and Materials Therefor

Abstract

A methodology for finishing of HIP'ed Si.sub.3 N.sub.4 balls from the as-received condition by magnetic fluid polishing. It involves mechanical removal of material initially using harder abrasives with respect to the work material (of different materials of progressively lower hardnesses and finer grain sizes) followed by final chemo-mechanical polishing (CMP) using preferably a softer abrasive for obtaining superior finish with minimal surface or subsurface defects, such as scratches, microcracks, or pits on the Si.sub.3 N.sub.4 balls. High material removal rates (1 .mu.m/min) with minimal subsurface damage is obtained with harder abrasives, such as B.sub.4 C or SiC (relative to Si.sub.3 N.sub.4) due to the use of a flexible support system, small polishing loads (1N/ball), and fine abrasives but high polishing speeds (compared to conventional polishing) by rapid accumulation of minute amounts of material removed by microfracture. Final polishing of the Si.sub.3 N.sub.4 balls using a softer abrasive, such as CeO.sub.2 (that chemo-mechanically react with the Si.sub.3 N.sub.4 work material) results in high quality Si.sub.3 N.sub.4 balls of bearing quality with a superior surface finish and damage-free surface.