Transparent polycrystalline yttrium aluminum garnet (YAG) ceramics have garnered an increased level of interest for high-power laser applications due to their ability to be manufactured in large sizes, and doped in relatively substantial concentrations when compared to traditional single-crystalline gain media. However, surface characteristics have a direct effect on the lasing ability of these materials, and a lack of a fundamental understanding of the polishing mechanisms of these ceramics remains a challenge for their utilization. The aim of this paper is to study the polishing characteristics of YAG ceramics using magnetic field-assisted finishing (MAF). An experimental setup was developed, through the refinement of the MAF process, for YAG ceramic workpieces. Using this equipment with diamond abrasives, the YAG ceramic surfaces were polished to sub-nanometer scale. Polishing trials with fine diamond abrasive and colloidal silica were then performed on this sub-nanometer surface and the material removal mechanisms were analyzed.
Polishing with 0–0.1 μm diameter diamond abrasive caused increasing roughness with polishing time due to the continuous cycle of relatively substantial chipping followed by minor smoothing. Polishing with colloidal silica caused valleys to widen with increased polishing time and the grain structure of the ceramic influenced the material removal.