Deformed microstructure Clause Samples

Deformed microstructure. For investigation under deformed state, TEM samples were prepared from the gauge section region of the TM state specimens. At room temperature, the deformed microstructure shows similar characteristics as those typically observed for an as-received state (Fig. 7a). However, the dislocations are mostly bowed out due to pinning at the nano-sized Y-Ti-O particles (Fig. 7b). It is evident from the Fig. 7a and b that the dislocation activity is homogeneously distributed across the whole grains. At elevated temperatures, the microstructural evolution becomes prominent with the decrease in dislocation density and the appearance of polygonal grains that replace the original lath structure (c.f. Fig. 7a and c). The temperature dependence of grain sizes is shown in Fig. 9. Interestingly, a more intense dislocation activity is noticed close to the grain boundaries in form of a dislocation pile-up (Fig. 7c). In addition, slight coarsening of M23C6 carbides was also observed. At 800°C, the M23C6 precipitate sizes close to PAGBs were in a range of around 100 to 450 nm. However, the Y-Ti-O particles appeared very stable over the whole investigated temperature range, without any change in shape or size. Fig. 8 presents TEM images in a deformed state obtained after the tensile test at 800°C. Fig. 8a shows a bright field image of an equiaxed α-Fe grain with high dislocation pile-up at the grain boundaries and dislocations that are pinned to the Y-Ti-O particles at various locations. The selected area diffraction pattern from the grain in the middle is near the α-Fe [100]-zone axis (inset Fig. 8a). The dark field image (Fig. 8b) obtained from marked (white circle) reflection 𝑔⃗ = {11̅0} reveals the dislocation structure. The partially illuminated grain displays a dark contrast near the grain boundaries and a bright contrast at the central region. These facts confirm a large localized deformation due to dislocation pile-up close to the grain boundaries. Moreover, it also 1 Z (%) = (𝑆𝑖𝑛𝑖𝑡𝑖𝑎𝑙−𝑆𝑓𝑟𝑎𝑐𝑡𝑢𝑟𝑒) × 100 𝑆𝑖𝑛𝑖𝑡𝑖𝑎𝑙 Where 𝑆𝑖𝑛𝑖𝑡𝑖𝑎𝑙 is the initial sample cross-section area and 𝑆𝑓𝑟𝑎𝑐𝑡𝑢𝑟𝑒 is the fractured cross-section area. confirms a presence of low-angle grain boundary (LAGB) (as indicated in Fig. 8a), which appears to be undergoing an annihilation process to form a coarse equiaxed grain. The M23C6 carbides are coherent and display a similar contrast, i.e., the same crystallographic orientation, with one of their neighboring grains (Fig. 8b). The pronounced dislocation bowing ar...