Synthesis and characterization of the rheological behavior of MR fluid for polishing silicon wafer using double-disc chemical-assisted magneto-rheological finishing process

Double-disc chemical-assisted magneto-rheological finishing (DDCAMRF) process is a successfully developed precision material removal process that has been applied to the polishing of brittle materials viz. monocrystalline silicon wafer. The mechanism of silicon polishing using the DDCAMRF process depends mainly on the magnetorheological (MR) fluid, which behaves as a multi-point finishing tool. The MR fluid synthesized in the present work comprised of carbonyl iron powder, alumina abrasives, deionized water, and glycerol as the base fluid. The application of a magnetic field in the prepared MR fluid samples significantly affects its rheological properties, which in turn affects the quality of finished wafer surface. Therefore, the rheological, as well as magnetic properties of prepared MR fluid samples need to be studied in detail. The flow behavior of MR fluid is affected by the applied magnetic field, which therefore exhibits transition from Bingham-fluid like structure to gel-like structure. To characterize MR fluid's magnetic behavior, the M-B curve of the prepared MR fluid samples was plotted to determine the saturation magnetization using the data obtained from vibrating sample magnetometer (VSM). Rheological properties like viscosity and yield stress of the prepared MR fluid were measured by using the parallel-plate rheometer. The obtained rheological data from the rheometer was fitted using the defined constitutive equations of respective fluid models, viz. Bingham-Plastic (BP), Herschel-Bulkley (HB), and Casson's (CS), respectively. The experimental results were analyzed, and the effect of increase in temperature on viscosity and yield stress was also discussed.