关键词: 剪切增稠抛光, 氮化硅, 流变行为, 应力状态, 材料去除, 精密抛光

Abstract: In the investigation，the control strategy of ultra-precision machining of Si₃N₄ ceramics is analyzed on the
basis of the principle of shear thickening polishing (STP)，and the rheological behaviors of the prepared STP slurry with cubic boron nitride (CBN) abrasives are discussed． Then，the variations of the surface morphology and surface residual stress state of Si₃N₄ ceramics before and after the polishing are analyzed to reveal the polishing characteristics of STP． The results show that (1) the slurry displays a reversible shear thinning and shear thickening behavior，which meets the requirement of the slurry for processing STP; (2) the machining efficiency and surface quality of Si₃N₄ ceramics can be controlled by changing the grain size of CBN abrasives，and the theoretical values of the material removal and the surface roughness can reflect the change of experimental values; (3) the STP removal of Si₃N₄ is a continuous micro cutting process named "flexible polishing"，in which the brittle shear or the adhesive wear is employed in the initial stage of machining and the ductile removal of the microscopic plastic flow is used in the later stage; (4)when the grain size reaches nanoscale，the surface stress state of Si 3 N 4 will change from the initial residual tensile stress to the compressive stress，which means that the STP can efficiently remove the damage layer of the original surface and produce merely new small damage; (5) with the extension of the polishing time，the material removal amount of Si₃N₄ first increases quickly and then tend to increase slowly; (6) after polishing for 90 min，the material removal rate decreases from 5． 00 ～ 2． 40μm/h to 3． 24 ～ 2． 04μm/h and the surface roughness R_a reduces from 108． 9 ～111． 1 nm to 22． 0 ～10． 7nm; and (7) after polishing for 150min，R_a can be reduced to 9． 6 ～7． 2nm，which indicates that STP process achieves the precision polishing of Si 3 N 4 ceramics．

Key words: shear-thickening polishing, silicon nitride, rheological behavior, stress condition, material removal, precision polishing