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.