Fracture characteristics Sample Clauses

Fracture characteristics. The overall view of the fracture surface after the room temperature tensile test is shown in Fig. 10a. This macro view shows the presence of distinct radial macrocracks propagating parallel to the tensile axis (i.e. along the extrusion direction). Moreover, fracture protrusions and steps are observed perpendicular to the final magistral failure (see Fig. 10b). At higher magnification (Fig. 11a), the central region exhibits mostly ductile dimples, with sizes of 0.48 ± 0.24 µm, resulting from the coalescence of microvoids that appear to nucleate from the second phase particles (like oxides and carbides). The dimpled fracture surface suggests intragranular crack growth. Nonetheless, the occurrence of some splitting-related decohesion is also observed (see marked arrows in Fig. 11a). Similar to the behavior at room temperature, the specimens tested at elevated temperatures display significant necking at failure; however, no radial cracks are observed (see Fig. 10c). At 500°C, the fracture surface forms with a shear-lip zone at the outer periphery and dimples (0.92 ± 0.24 µm) that are larger and deeper in comparison to those present at room temperature (c.f. Fig. 11a and b). The temperature dependence of dimple sizes is shown in Fig. 9. At 650°C, the fracture surface reveals two distinct mechanisms of failure. The outer peripheral region (Fig. 11c) shows a fracture surface with dimples that are large (1.56 ± 0.47 µm) and prominent (c.f. Fig. 11a-c). Conversely, the central region exhibits dimples that are not discernable and have many small particles (0.52 ± 0.17 µm) present at their walls (see inset in Fig. 11c). At 800°C, minor localized necking of the specimen is observed (Fig. 10d). The entire fracture surface manifests similar small particles (0.62 ± 0.23 µm), as observed in the central region of the 650°C specimen (Fig. 11d). The temperature dependence of particle sizes is shown in Fig. 9. Interestingly, the particle size matches the average grain sizes at 800°C. The observation of the specimen (800°C) cut along the loading/extrusion direction revealed development of microvoids and its coalescence to form cavities (Fig. 12). Fig. 10: SEM fracture surface images of the tested specimens: At 25°C, macro view (a) shows distinct radial macrocracks propagating parallel to the tensile axis, and magnified image (b) shows radial cracks along with fracture protrusion and steps perpendicular to the fracture surface. At 500°C, the macro view (c) shows a shear-lip zon...