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S. Takaya et alii, Frattura ed Integrità Strutturale, 34 (2015) 355-361; DOI: 10.3221/IGF-ESIS.34.39 360 Fatigue crack propagation (FCP) under the cathodic potential of -3V Fig. 7 shows the fracture surface of FCP test under the cathodic potential of -3V [7]. As shown in the figure, parallel lines are recognized on the fracture surface at Δ K =3.6MPam 1/2 . Based on the similar procedure in the preceding section, EBSD-assisted fractography was performed on the FCP fracture surface as shown in Fig.7. EBSD result in Fig.7 is showing the area with high CI values. First, it should be noted that twin band is hardly seen in this area. Secondly, Schmid factor and angle analysis results are summarized in Tab. 3, showing the calculated slip plane angle is 71.25º. The actual angle of parallel lines is 70 as shown in Fig.7. Consequently, it could concluded that the parallel lines were formed do to the operation of basal slip. It should be noted that the slip system (0001)[1-210] with the highest Schmid factor might have operated. Figure 7 : EBSD assisted fractography of FCP fracture surface. Slip plane Slip direction Schmid factor Slip angle, α Basal slip (0001) [11-20] -0.14 71.25 [2-1-10] 0.25 [1-210] 0.39 Primary twin (01-12) [01-1-1] -0.36 60.89 (10-12) [10-1-1] -0.39 -64.24 (1-102) [1-10-1] 0.29 -69.68 (0-112) [0-11-1] 0.32 76.60 (-1012) [-101-1] -0.40 37.80 (-1102) [-110-1] 0.34 24.96 Table 3 : Schmid factors and slip angles calculated in the area in Fig.7.