Fig. 11 (a) Fractured fatigue sample (3mm), (b) and (c) Cross section of
fractured fatigue sample, (d) Separation of macro morphology of fracture
surface, (e) and (f) Fatigue crack initiation region (Region 1), (g)
Fatigue crack propagation region (Region 2), (h) and (i) Complete
fracture region (Region 3)
The fractured SZ sample (2 mm) under a stress of 315 MPa is shown in
Fig. 12 (a). The cross section of the fractured sample is shown in Fig.
12 (b)-(d). The crack initiation region was indicated in Fig. 12 (c). In
Fig. 12 (d), the debonding of lamellar structure was observed. The macro
morphology of fracture surface is shown in Fig. 12 (e). Three regions,
including region 1, region 2, and region 3, were also distinguished. The
microstructure of region 1 is shown in Fig. 12 (f) and (g). The fracture
step was observed in Fig. 12 (f) and (g). Therefore, the fatigue crack
initiated in region 1. For region 2, the remarkable fatigue striation
was observed as shown in Fig. 12 (h). Therefore, the fatigue crack
propagated in region 2. The microstructure of region 3 is shown in Fig.
12 (i) and (j). The complete fracture character was observed.