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对粗晶纯Al多晶体的疲劳断口进行了扫描电镜分析,在应变控制循环形变下,晶粒粗大而延性很好的金属的疲劳断口具有某些特征:断裂源少而集中,断裂源附近裂纹呈扇形扩展,疲劳条纹为循环解理刻面,每一条纹由较宽的解理刻面和窄的解理台阶两部分组成,台阶往往由于塑性形变而钝化;在裂纹扩展第Ⅱ阶段的疲劳条纹清晰、连续,布满裂纹扩展第Ⅱ阶段的整个区域,不同水平面形成的条纹间以“麻花形”的条带连接;多处观察到沿条纹形成的二次微裂纹,有些已发展成二次宏观裂纹,并有二次疲劳条纹;在断口上可观察到解理小舌台;断口上无最后拉断的静断区,对疲劳条纹的形成机制进行了初步的探讨。
The fatigue fracture of coarse crystalline Al polycrystalline body was analyzed by scanning electron microscopy. The fatigue fracture of coarse and ductile grains with some coarse grains and ductile ductility under cyclic deformation of strain control has some characteristics: the fracture source is small but concentrated, and the fracture near the fracture source The fan-shaped extension of the fatigue stripe for the cycle cleavage facets, each of the stripes by a wide cleavage facets and narrow cleavage steps of two parts, the step is often due to plastic deformation and passivation; crack propagation in the second phase of Fatigue stripes are clear, continuous, and full of cracks propagating throughout the entire region of Stage II. Stripes formed at different levels are connected by “twisty” bands; secondary micro-cracks along the stripes are observed at various locations, some of which have developed into Secondary macrocracks and secondary fatigue streaks. Cleavage tongue plate can be observed on the fracture surface, and there is no static fracture zone on the fracture surface. The formation mechanism of fatigue streak is preliminarily discussed.