Magnetic domains along shear bands in amorphous metals observed by spin-polarized scanning electron microscopy
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K. Koike Advanced Research Laboratory, Hitachi Ltd., Hatoyama, Saitama 350-03, Japan
J. C. M. Li Materials Science Program, Department of Mechanical Engineering, University of Rochester, Rochester, New York 14627 (Received 15 July 1992; accepted 14 December 1992)
A novel spin-polarized scanning electron microscope with capabilities of observing microscopic domain structures and determining in-plane magnetization directions has been used to investigate the stress-induced magnetic domains in the Fe78B13Si9 (Allied 2605-S2) metallic glass. The magnetic structure in the vicinity of shear bands that are produced near a Mode III crack has been examined. On the tensile side of bending, arrays of individual, discontinuous magnetic "islands" of similar shape and size (about 2-10 yLtm in length, 3 /mm in width, and spaced about 2 - 4 /mm apart) are uniformly distributed on one side of the shear bands. Their easy axis is about parallel to the shear bands. On the other hand, well-defined elliptical domains are found between shear bands on the compression side of bending. Their easy axes are approximately perpendicular to the shear bands. These results suggest the existence of isolated defects of similar stress fields located along the shear bands. The possibility that these defects are dislocations will be investigated next.
I. INTRODUCTION Amorphous metals such as Fe78B13Si9 (Allied 2605S2) manufactured by rapid quenching from the molten state exhibit outstanding magnetic properties. Their magnetization characteristics as well as magnetic domain structures are very sensitive to the applied stress and the residual stresses, such as resulting from the meltspinning process.1"7 While the lack of atomic long-range order in amorphous alloys may contribute to their low elastic moduli, many experiments show that their plasticdeformation behaviors resemble the crystalline materials. Localized inhomogeneous shear deformation takes place by formation and propagation of shear bands.8"10 Experimental evidences on nonuniform shear displacements along the bands, reverse shearing phenomena, etching characteristics, and the annealing effect on shear bands suggest the existence of discrete defects such as dislocations in amorphous metals.6-810"13 However, the exact mechanism is still under dispute due to the lack of direct experimental evidence. It has been suggested that since the magnetic properties and the domain structures of the Fe-based metallic glasses (normally with high positive magnetostriction) are highly stress dependent, an investigation of the microscope magnetic domain structures along shear bands may give us insights to the deformation mechanisms of such amorphous materials.14 J. Mater. Res., Vol. 8, No. 4, Apr 1993 http://journals.cambridge.org
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Among the methods of observing domain walls and domain structures, a recently developed spin-polarized scanning electron microscope (spin-SEM) has been used to investigate domain patterns in the various stress states. The spin-SEM offers important characteri
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