HUANG et al:NANOSTRUCTURED Cu 1499 deformed sample was characterized by transmission electron microscopy (TEM)as well as high-resolution TEM (HRTEM).The HRTEM was carried out in a JEOL 3000 FEG electron microscope operated at 300 kV.The point-to-point resolution is about 1.8 A. TEM and HRTEM samples were prepared by jet elec- tro-polishing at room temperature.The electrolyte consists of 33%orthophosphoric acid and 67%water. To enhance the image contrast,most of the HREM images were reconstructed from Fast Fourier Trans- formation,during which the diffuse scattering from the background or inelastic scattering was filtered. DTZ 3.EXPERIMENTAL RESULTS 3.1.Microstructures and dislocations in nanostruc- tured Cu processed for 14 RCS passes Figure 3(a)is a TEM micrograph showing that individual grains were produced with sizes ranging from less than 100 nm to a few hundred nanometers, 100nm separated by high-angle grain boundaries(high-angle GBs).Most grains are heavily strained and contain high density of dislocations.The corresponding elec- tron diffraction pattern (EDP)in Fig.3(b)exhibits diffraction rings,indicating a polycrystalline struc- ture.The diffraction rings show significant 011 tex- ture.Figure 4(a)shows a TEM micrograph of a grain with a diameter of about 500 nm.A number of fine structures were observed in the interior of the grain. As pointed out by two arrowheads,an array of dislo- 3nm cations piled up along the (111)plane.Consequently, two subgrains (denoted by I and 2)with a misorien- tation of about 1 were produced(measured from the Fig.4.(a)A TEM micrograph showing fine deformation struc- tures in a grain.The numbers 1-3 denote three subgrains:the HRTEM image,not shown here).The dislocations are two arrowheads point out an array of dislocations:the four stars mostly 60 type (as shown later in Fig.4(c))and are mark a low-angle GB:the white circle marks a dislocation tan- glissible along the (111}planes. gle zone (DTZ):the white square marks a transition from DTZ A low-angle GB was also found in this grain,as to dislocation cells.(b)An HRTEM image of the low-angle GB pointed out by the four stars in (a).(c)A Fourier filtered marked by four stars in Fig.4(a).The low-angle GB HRTEM image of a 60 dislocation.A Burgers circuit was was formed by the accumulation of a number of gliss- drawn to enclose the dislocation core marked by a "T".The ile dislocations.It is not edge-on but overlapped,as electron beam and the dislocation line is parallel to [11O].and revealed by the periodic Moire Fringes.Figure 4(b) the Burgers vector b =1/2[011]or 1/2[101]. is an HRTEM image of a local region of this low- angle GB.The misorientation of the two grains is about 5.The spacing of the Moire pattern can be d=2.08 A.D is calculated to be 23.84 A.which calculated using the formula:D=d/o,where d is the agrees well with the experimental value of 24 A,as measured from Fig.4(b). lattice spacing and a is the rotation angle.For Cu. Dislocation cell structure was also observed in subgrain 3 in Fig.4(a).These cells may form individ- ual subgrains upon further plastic straining.Dislo- cation tangling was frequently observed in the interior of grains,as marked by a white circle in Fig.4(a). where the grain is heavily strained.We shall refer such a region as dislocation-tangle zone (DTZ).Fig- ure 4(c)shows a Fourier filtered HRTEM image of a 60 dislocation which was frequently observed in RCS-deformed Cu.Assuming the electron beam and the dislocation line is parallel to [110].the Burgers vector of the dislocation is determined to be 1/2[101] Fig.3.TEM micrographs showing:(a)nanostructured Cu pro- or 1/210111.which has an angle of 60(or 120)with duced by the RCS process:and (b)the corresponding EDP. respect to the dislocation line.For this reason,theHUANG et al.: NANOSTRUCTURED Cu 1499 deformed sample was characterized by transmission electron microscopy (TEM) as well as high-resolution TEM (HRTEM). The HRTEM was carried out in a JEOL 3000 FEG electron microscope operated at 300 kV. The point-to-point resolution is about 1.8 A˚ . TEM and HRTEM samples were prepared by jet elec￾tro-polishing at room temperature. The electrolyte consists of 33% orthophosphoric acid and 67% water. To enhance the image contrast, most of the HREM images were reconstructed from Fast Fourier Trans￾formation, during which the diffuse scattering from the background or inelastic scattering was filtered. 3. EXPERIMENTAL RESULTS 3.1. Microstructures and dislocations in nanostruc￾tured Cu processed for 14 RCS passes Figure 3(a) is a TEM micrograph showing that individual grains were produced with sizes ranging from less than 100 nm to a few hundred nanometers, separated by high-angle grain boundaries (high-angle GBs). Most grains are heavily strained and contain high density of dislocations. The corresponding elec￾tron diffraction pattern (EDP) in Fig. 3(b) exhibits diffraction rings, indicating a polycrystalline struc￾ture. The diffraction rings show significant 011 tex￾ture. Figure 4(a) shows a TEM micrograph of a grain with a diameter of about 500 nm. A number of fine structures were observed in the interior of the grain. As pointed out by two arrowheads, an array of dislo￾cations piled up along the (111) plane. Consequently, two subgrains (denoted by 1 and 2) with a misorien￾tation of about 1° were produced (measured from the HRTEM image, not shown here). The dislocations are mostly 60° type (as shown later in Fig. 4(c)) and are glissible along the {111} planes. A low-angle GB was also found in this grain, as marked by four stars in Fig. 4(a). The low-angle GB was formed by the accumulation of a number of gliss￾ile dislocations. It is not edge-on but overlapped, as revealed by the periodic Moire´ Fringes. Figure 4(b) is an HRTEM image of a local region of this low￾angle GB. The misorientation of the two grains is about 5°. The spacing of the Moire´ pattern can be calculated using the formula: D = d/a, where d is the lattice spacing and a is the rotation angle. For Cu, Fig. 3. TEM micrographs showing: (a) nanostructured Cu pro￾duced by the RCS process; and (b) the corresponding EDP. Fig. 4. (a) A TEM micrograph showing fine deformation struc￾tures in a grain. The numbers 1–3 denote three subgrains; the two arrowheads point out an array of dislocations; the four stars mark a low-angle GB; the white circle marks a dislocation tan￾gle zone (DTZ); the white square marks a transition from DTZ to dislocation cells. (b) An HRTEM image of the low-angle GB pointed out by the four stars in (a). (c) A Fourier filtered HRTEM image of a 60° dislocation. A Burgers circuit was drawn to enclose the dislocation core marked by a “T”. The electron beam and the dislocation line is parallel to [11¯0], and the Burgers vector b = 1/2[011] or 1/2[101]. d(111) = 2.08 A˚ . D is calculated to be 23.84 A˚ , which agrees well with the experimental value of 24 A˚ , as measured from Fig. 4(b). Dislocation cell structure was also observed in subgrain 3 in Fig. 4(a). These cells may form individ￾ual subgrains upon further plastic straining. Dislo￾cation tangling was frequently observed in the interior of grains, as marked by a white circle in Fig. 4(a), where the grain is heavily strained. We shall refer such a region as dislocation-tangle zone (DTZ). Fig￾ure 4(c) shows a Fourier filtered HRTEM image of a 60° dislocation which was frequently observed in RCS-deformed Cu. Assuming the electron beam and the dislocation line is parallel to [110], the Burgers vector of the dislocation is determined to be 1/2[101] or 1/2[011], which has an angle of 60° (or 120°) with respect to the dislocation line. For this reason, the