Issue34

S. Takaya et alii, Frattura ed Integrità Strutturale, 34 (2015) 355-361; DOI: 10.3221/IGF-ESIS.34.39 358 Figure 5 : EBSD assisted fractography; (a) Area I, (b) Area II, (c) Area III. Twining is major deformation mechanism in Mg alloy with relatively low CRSS, and generally observed as twin band in the EBSD analysis. Especially in the area “I” (Fig.5(a)), the area with high CI values is relatively large. But twin band was not recognized in this area, indicating that basal slip predominantly operated. Based on the Euler angle of the grain, Schmid factor and angle analyses were performed. As schematically seen in Fig.6, the coordinate A1, A2 and A3 in EBSD analysis was fixed against fractured CT specimen (Fig.6(a)). When the slip plane in Fig.6(b) operated, the intersection line between slip plane and A1-A2 plane (fracture surface) could be defined as a slip line. Then, the angle, α, was defined as the angle between slip line and specimen thickness direction. Plus or minus sign of α was defined as shown in Fig.6(c). The typical examples of Schmid factors and the angles calculated in the area “I” (Fig.5(a)) and “III” (Fig.5(c)) are summarized in Tabs. 1 and 2, respectively. For example, when basal slip operated in the area “I”, the calculated angle, α, is -86.74º (Tab. 1), indicating that the slip line should nearly parallel to the crack propagation direction on the fracture surface. In Fig.5(a), the lines are nearly parallel to the crack propagation direction as predicted from Euler angle. Furthermore, twining is hardly seen in the area “I”. Consequently, it could be concluded that the parallel lines in the area “I” were formed due to the operation of basal slip. It should be noted that basal slip systems (0001)[11-20] and (0001)[1- 210] have high Schmid factors, indicating that those slip systems operated. In the area “III”, the basal slip line angle, α, would be 75.73º, which corresponds well with the actual angles of parallel lines in (Fig.5(c)), namely 80º. The angles of (a) (b) (c)