Fig. 1. TEM images of the pearlite structure in the as-patented PSW. (a) Bright-field (BF) TEM image of the ferrite/cementite lamellae. Inset is a composite SAED pattern of the two phases showing their orientation relationship is [010]c// [111]f, (101)c//($11\bar{2}$)f. (b) High resolution HAADF image of the cementite/ferrite interface which is atomically coherent. (c, d) HRTEM image of the interface and the corresponding strain map derived by GPA software. Along the interface, strain concentration only appears at the arrowed interfacial dislocation.

Fig. 2. Microstructure evolution in PSWs with progressive deformation strains. (a) BF TEM image of the pearlite lamellae in the as-rolled wire under the two-beam imaging conditions. The threading dislocations and short dislocation loops (denoted by arrows) near the interfaces are seen in ferrite layers. (b) Micrograph of the wire at ε = 0.18. The dislocations in ferrite were multiplied and the cementite layer was plastically deformed. (c) BF TEM image of the wire at a strain of 0.53. In this sample, the dislocation density in cementite layers was further increased.

Fig. 3. (a) HRTEM image of the Fe3C/Fe interfaces in the as-rolled sample. (b) IFFT image derived from (a) showing the apparent interfacial mismatch in this sample. The interfacial dislocations are denoted by arrows. (c) Strain analysis based on the image (a). The interfacial dislocations induced localized strain concentrations at the interfaces.

Fig. 4. (a) HRTEM image showing a part of cementite lattice (between the arrows) near the interface became disordered. (b) High resolution HAADF image of the interfaces in the as-rolled sample. The dark contrast and blurred lattice of the interfacial area in cementite layer are remarkable.

Fig. 5. (a) HRTEM image of a Fe3C/Fe interface in the wire at a strain of 0.18. (b) A zoom-in image of the Fe3C/Fe interface showing its undulated feature. The high-density of interfacial dislocations are marked. (c) The strain distribution derived from (b). The Fe3C part is half-transparently masked to highlight the interfacial strain which is caused by the accumulation of interfacial dislocations.

Fig. 6. (a) HRTEM micrograph of the interface structure at ε = 0.53. The FFT pattern derived from the area A and B in cementite are shown in the insets. The diffraction spots belonged to cementite as denoted in the pattern B are missing in A, suggesting the structural change of the cementite crystal. (b) Zoom-in image of a part of the interface in (a). The arrows denote the dislocation transmission across the boundary.

Fig. 7. (a) Dark-field TEM image of the sample at ε = 1.13. The SAED pattern is given in the inset. The diffraction rings as well as TEM image suggested the cementite layers are composed of nanocrystallines. (b) and (c) BF TEM images of the wire at strains of ε = 1.13 and ε = 2.45, respectively. The dislocations stored at interfaces were largely reduced and the contrast of cementite layers became uniform.

Fig. 8. (a) HRTEM image of the lamellae in the sample at ε = 2.45. The lattice of cementite became highly disordered. (b) Strain map derived from (a) indicating the interfacial strain was relaxed. No strain concentration was found along the interface.

Fig. 9. EFTEM images and analyses of the pearlite lamellae at variant drawing strains. (a), (b) and (c) are TEM images of the pearlite in PSWs at the strain of 0, 0.53 and 2.45, respectively. (d), (e) and (f) are the carbon maps acquired by EFTEM mode, corresponding to the area in (a), (b) and (c), respectively. (g), (h) and (i) are line profiles from the position “A” to “B” in (d), (e) and (f), showing the carbon content (contrast intensity) in cementite layers relative to the nearby ferrite layers. The carbon depletion in the deformed wires is remarkable.

Fig. 10. Schematic illustration of the glide dislocation in ferrite approaching the Fe3C/Fe interface with the Isaichev OR. The carbon atoms near the dislocation are allowed to be attracted by the dislocation core (green arrows). Meanwhile, the formed carbon vacancies provide addition space to accommodate the dislocation trusting-into under applied stress (red arrow).