Deformation Mechanism and Recrystallization Relationships in Galfenol Single Crystals: On the Origin of Goss and Cube Or
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tion to the stable {111}h112i orientation in Goss-oriented Fe-3 pct Si single crystal, which has been attributed to instability under deformation at reduction percentages greater than 40 pct.[14,15] The orientation distribution function (ODF) plot shown in Figure 1(c) exhibits twofold symmetry and preferred orientation in a transition process. The symmetrically equivalent orientations are (111)½112/ð111Þ[112] by onefold (F = 90 deg), (111)½1 21/ð111Þ½121 and (111)½211/ ð111Þ½211 by twofold (F = 90 deg, u1 = 90 deg). However, a weak Goss component is retained, which we expect would mostly disappear under higher thickness reduction percentages than 50 pct due to the crystal rotation.[14,16] Figure 2 shows EBSD-scanned images of the deformed surface for features of microstructure, grain configuration, and GB conditions after the crystal rotation. As expected from Figure 1, single Goss (011) grain in Figure 1(a) was mostly changed to {111} and {001} grains in Figures 2(b) and (e), where the both images were obtained by scanning different areas in the same sample. Deformation bands with red color were associated with shear band structure, exposed on the sample surface. It is well known that, at the early stages of deformation, {112}h111i twins form, activated in the two slip systems, i.e., (112)½111 and ð112Þ½111. The two twinning planes belong to the zone axis of ½110|TD which lies on the (111) and ð111Þ planes. As the deformation continues, the initial Goss (110) and twinning {112} planes rotate to the {111}h112i orientation because they are linked along the ½110|TD direction. At the same time, shear bands form symmetrically relative to the (110) plane that is inclined by 35.4 deg, perpendicular to the rolling plane.[12,14] This 35.4 deg
angle corresponds to the misorientation angle between (110) and (111) planes. The inclination angle is matched with the rotation angle of ~37 deg in Figure 1(b). When one of the twinning planes rotates by 20 deg within the deformation bands, it becomes exposed on the surface, parallel to the (001)½1 10 orientation. Further rotation is terminated upon reaching 35.4 deg at which point this rotation results in producing a deviation angle of 15.4 deg around (001)½1 10 orientation perpendicular to the rolling plane. This matches well with the observation of {001}h110i components in the rolled single crystal that have the deviation angles of ~17 deg in Figure 1(b). Decisive evidence of rotation from (011)[100] single crystal in Figure 2(a) to the {111}h112i orientation is indicated by the existence of bright areas with no boundaries in {111} grains (Figure 2(c)), corresponding to blue color in Figure 2(b). If not due to rotation, one would expect to find a lot of subgrain boundaries with low misorientation angles and boundaries caused by slip mechanisms, like the dark gray strips in Figure 2(c), present during the deformation. In Figure 2(d), we see evidence that the subgrain boundaries (red line; misorientation angles of 2 to 5 deg) and high-angle GBs (blue lin
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