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Статья. Опубликована в журнале "LLE Review". – 2000. – Vol. 82 – P. 107-118.
Название на русском языке: Наноиндентирование твердости частиц, используемых при магнитореологическом полировании.Авторы: A.B. Shorey, K.M. Kwong, K.M. Johnson, S.D. Jacobs.Аннотация к статье на английском языке: A technique for nanoindentation of small, magnetic and nonmagnetic abrasive particles has been described. Most results are consistent with what has been previously reported, but some results are new. While Krell et al.28 show microhardness differences in various grinding aluminas, it is interesting to see Figure 82.65 The relative nanohardness values of the particles, glasses, and crystal that have been indented (in air) at 5-mN load on the nanoindenter. the large differences in nanohardness values of the actual commercial products used in grinding and polishing. The literature contains only Moh’s hardness data for cerium oxide abrasives. We report here, for the first time, an actual nanohardness value for individual cerium oxide abrasives. The tests and procedures described here allow for the characterization of the mechanical properties of small particles that is not possible through microindentation without sintering or using samples much larger than those normally used. This allows for the study of abrasives in forms actually used in polishing, so that full characterization of the mechanical properties of polishing materials is now possible. Furthermore, removal experiments using various combinations of magnetic and nonmagnetic abrasive particles and slurry fluid chemistries should give valuable information in the future regarding the removal mechanisms for MRF.
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NANOINDENTATION HARDNESS OF PARTICLES USED IN MAGNETORHEOLOGICAL FINISHING (MRF)
Nanoindentation Hardness of Particles Used in Magnetorheological Finishing (MRF) Introduction Classical finishing processes of optics employ precisely shaped, viscoelastic pitch or polyurethane foam–faced tools to transfer pressure and velocity through an abrasive slurry to the workpiece. Material is removed by chemical and mechanical interactions among the abrasive (typically micron- to submicron-size cerium oxide or aluminum oxide), the carrier fluid (water), and the workpiece. Magnetorheological finishing (MRF)—a new method of polishing optics—is being studied at the Center for Optics Manufacturing (COM) at the University of Rochester. This method utilizes a suspension consisting of magnetic particles [typically carbonyl iron (CI)], nonmagnetic abrasive particles, water, and stabilizing agents. Figure 82.59 shows an MR polishing machine. Rotation of the bottom wheel takes the fluid from the delivery nozzle and drives it underneath the part, where there is a strong magnetic field. Under the influence of the magnetic field, the fluid behaves like a “plastic” fluid; it is the shear stress caused by the hydrodynamic flow between the part and the rotating wheel that removes the material.1
Part
Part path
Wheel Nozzle
MR fluid ribbon
Collector Pole pieces
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Figure 82.59 Photograph of the MRF polishing process. The fluid emerges from the nozzle on the left and is carried to the right into the polishing zone under the part surface by the rotation of the wheel. The pole pieces are part of the electromagnet that provides the magnetic field that stiffens the fluid into a ribbon.
LLE Review, Volume 82
Figure 82.60 shows an example of microroughness on the surface of an initially pitch-polished fused-silica part processed without part rotation and with a nonaqueous MR fluid. With all chemistry eliminated, what remains are parallel grooves approximately 16-nm peak-to-valley and 1-nm rms,2 caused by microscratching along the directi