Effect of shell-layer diamond particle size in CIP@Ni–P/ND composite abrasives on surface generation during dynamic cluster magnetorheological polishing of sapphire wafers

Chemical composite plating was used to prepare CIP@Ni–P/ND core–shell magnetic composite abrasives, which were subsequently applied to the dynamic cluster magnetorheological polishing of sapphire wafers. The effects of process parameters and shell-layer diamond particle size on the processing performance were investigated, and the corresponding material removal mechanism was elucidated. The results show that the ND abrasive particles were firmly held by the Ni–P alloy matrix on the CIP surface, forming a core–shell encapsulated structure. Diamond particles with a size of 200 nm homogenized the load borne by individual particles through densification of the magnetic chains, maintained the depth of cut below the critical value for the brittle–ductile transition, and promoted a shift in material removal from brittle fracture to a shear-sliding-dominated mode, leaving only extremely shallow micro-scratches on the surface. Under optimized parameters, with a polishing-disc speed of 40 r/min, a workpiece speed of 400 r/min, and a machining gap of 1.0 mm, the surface roughness (Sa) of the sapphire wafer decreased to 0.446 nm, while the material removal rate (MRR) reached 1510.91 nm/h. This study extends the application of self-prepared CIP@Ni–P/ND abrasives to sapphire wafers and provides theoretical support and a technical pathway for efficient ultrasmooth planarization.