Magnetorheological finishing with chemically modified fluids for studying material removal of single-crystal ZnS

S. Salzman; H. J. Romanofsky; Y. I. Clara; L. J. Giannechini; Garrett J. West; J. C. Lambropoulos; S. D. Jacobs

doi:10.1117/12.2028941

15 October 2013 Magnetorheological finishing with chemically modified fluids for studying material removal of single-crystal ZnS

S. Salzman, H. J. Romanofsky, Y. I. Clara, L. J. Giannechini, Garrett J. West, J. C. Lambropoulos, S. D. Jacobs

Author Affiliations +

Proceedings Volume 8884, Optifab 2013; 888407 (2013) https://doi.org/10.1117/12.2028941
Event: SPIE Optifab, 2013, Rochester, New York, United States

Abstract

Magnetorheological finishing (MRF) of polycrystalline, chemical-vapor–deposited (CVD) zinc sulfide (ZnS) and zinc selenide (ZnSe) can leave millimeter-size artifacts on the part surface. These pebble-like features come from the anisotropic mechanical and chemical properties of the ceramic material and from the CVD growth process itself. The resulting surface texture limits the use of MRF for polishing aspheric and other complex shapes using these important infrared (IR) ceramics. An investigation of the individual contributions of chemistry and mechanics to polishing of other polycrystalline ceramics has been employed in the past to overcome similar material anisotropy problems. The approach taken was to study the removal process for the different single-crystal orientations that comprise the ceramic, making adjustments to mechanics (polishing abrasive type and concentration) and polishing slurry chemistry (primarily pH) to equalize the removal rate for all crystal orientations. Polishing with the modified slurry was shown to prevent the development of surface texture. Here we present mechanical (microhardness testing) and chemical (acid etching) studies performed on the four single-crystal orientations of ZnS: 100, 110, 111, and 311. We found that the (111) plane is 35% to 55% harder and 30% to 40% more resistant to chemical etching than the other three planes. This relatively high degree of variation in these properties can help to explain the surface texture developed from MRF of the polycrystalline material. Theoretical calculations of microhardness, planar, and bond densities are presented and compared with the experimental data. Here surface characterization of these single-crystal orientations of ZnS for material removal and roughness with chemically modified MR fluids at various pH levels between pH 4 and pH 6 are presented for the first time.

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S. Salzman, H. J. Romanofsky, Y. I. Clara, L. J. Giannechini, Garrett J. West, J. C. Lambropoulos, and S. D. Jacobs "Magnetorheological finishing with chemically modified fluids for studying material removal of single-crystal ZnS ", Proc. SPIE 8884, Optifab 2013, 888407 (15 October 2013); https://doi.org/10.1117/12.2028941

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