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通过扫描电镜系统分析了伸长率>5%和零伸长率多晶Be室温拉伸断口形貌。发现多晶Be无论伸长率高低,拉伸断口均平整、无颈缩;断口宏观形貌分纤维区和放射区,微观形貌既有裂纹沿一定结晶学表面扩展形成的解理断裂特征,又有一定塑性变形产生的撕裂棱,属准解理断口。但是,伸长率>5%的多晶Be断口纤维区和放射区界限不清晰,放射花样细小且走向多变,断口没有明显的主裂纹源,断裂是由多个裂纹源汇合所致。而零伸长率多晶Be断口纤维区和放射区界限清晰,放射花样粗大且走向单一,并且纤维区占整个断口比例极小,放射花样则几乎遍布断口通区,断口上可见明显的主裂纹源,主裂纹源中心往往存在某种组织缺陷,断裂主要是单一裂纹扩展所致。这表明多晶Be的伸长率主要来自于裂纹形核阶段,微观组织缺陷造成裂纹过早地达到临界裂纹扩展尺寸,是导致多晶Be材室温伸长率降低的主要原因。
Scanning electron microscopy (TEM) was used to analyze the tensile fracture morphology of polycrystalline Be at room temperature with elongation> 5% and zero elongation. It is found that the tensile fracture is smooth and no necking occurs regardless of the elongation of poly Be Be. The macrostructure of the fracture surface is divided into cleavage fracture formed by the extension of a certain crystallographic surface in the fiber and radiation zones and the micro-morphology, There are some plastic deformation of the tear edge, is subject to cleavage fracture. However, the limit of the fiber zone and the radiation zone of the poly Be Be fracture with an elongation of more than 5% is not clear, and the radiation pattern is small and variable. The fracture has no obvious main crack source and the fracture is caused by the convergence of multiple crack sources. The zero elongation poly Be beam fracture zone and the radiation zone clear boundaries, radiation patterns thick and to a single, and the fiber area accounted for the entire fracture ratio is very small, radiation pattern is almost all over the fracture area, the fracture can be seen on the main crack Source and main crack source centers often have some kind of organizational defects. The fracture is mainly caused by single crack propagation. This indicates that the elongation of polycrystalline Be mainly comes from the nucleation stage of the crack. The microstructure defects cause the crack to reach the critical crack growth prematurely, which is the main cause of the decrease of the room temperature elongation of the polycrystalline Be.