Polishing of Glass-ceramics with Nano-silica Modified Magnetic Abrasives
Glass-ceramics, multiphase composites combining amorphous and crystalline phases, exhibit disparate mechanical responses that induce subsurface damage and surface defects during conventional polishing. This study fabricates magnetic abrasive particles (MAPs) via a bonding process with three variants: unmodified, hydrophilic nano-silica (20 nm) modified, and hydrophobic nano-silica (20 nm) modified. Base composition comprises iron powder (75 μm) and CeO2 abrasives (15 μm) at a 12:3 mass ratio. Polishing tests on glass-ceramics using an N-S array tool reveal that hydrophobic modified MAPs achieve the lowest surface roughness (Sa = 17 nm) and highest material removal depth (2.5 μm), compared to hydrophilic (Sa = 24 nm) and unmodified (Sa = 48 nm) MAPs. Dynamic friction coefficients measured in situ are 0.31, 0.35, and 0.42 for hydrophobic, hydrophilic, and unmodified MAPs, respectively. Surface and subsurface damage analyses show hydrophobic MAPs minimize pits, micro-cracks, and brittle fractures, while hydrophilic MAPs exhibit brittle spalling and unmodified MAPs show point defects. Wear tests confirm that nano-silica addition enhances bond strength and extends abrasive lifespan. The hydrophobic modification promotes surface hydration and formation of a lubricating silicate gel layer, reducing mechanical plowing and friction, thereby enabling high-quality surface integrity. These findings demonstrate that nano-silica modification effectively tunes MAP hydrophobicity, offering a viable route for ultra-smooth, low-damage polishing of glass-ceramics.