Abstract:The tensile fractography of polycrystalline beryllium with zero and ＞5% elongations at room temperature was systematically examined by scanning electron microscopy. The results show that the tensile fracture of polycrystalline beryllium is of flat surface and no necking. Regardless of elongations of polycrystalline beryllium, its macroscopic fractography has fibrous and radical zones, and its microscopic fractography has cleavage fracture patterns produced by cracks propagating along some specific crystallographic surfaces, together with tear ridges produced by some plastic deformation. Therefore, tensile fracture of polycrystalline beryllium is of quasi-cleavage one. In which, for the polycrystalline beryllium with ＞5% elongation, the boundaries between fibrous and radical zones in the fracture area are not clear, and radial patterns are tiny and of multiple directions. The main crack source is not obvious in the fractograph, and the fracture is caused by the confluence of multiple cracks. In contrast, for the polycrystalline beryllium with zero elongation, the boundaries between fibrous and radical zones in the fracture area are clear, and the radial patterns are coarse with one direction. The radical patterns are mainly across almost all regions of the fracture area, together with very limited fibrous zones. There is obviously main crack source, where some kinds of microstructure defects exist, and the fracture is mainly controlled by a single crack propagating. It can thus be concluded that the elongation of polycrystalline beryllium mainly arises from the microcrack nucleation stage. Microstructure defects lead microcracks to prematurely reach the critical size of crack propagation, which is the main reason responsible for the poor ductility of polycrystalline beryllium at room temperature.