Fig. 7. Fracture features observed by SEM: (a) Morphology of the fracture surface. Three regions: initiation region, propagation region and final fracture region are labeled in
this figure. (b) Pore at the surface act as initiation site. (c) Micro-cell on the surface act as initiation site. (d) Low magnification image of crack propagation region. (e) High
magnification image of the propagation region. (f) Morphology of dimples and plate structure.