Atomic Analysis of Cleavage Fracture in Nickel Crystal under Tension with Transverse Constraint.
Atomic Analysis of Cleavage Fracture in Nickel Crystal under Tension with Transverse Constraint.
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横向约束张力下镍晶体解理断裂的原子分析。
DOI：
10.1299/kikaia.63.2380
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
R. Ohtani
中科院分区：
文献类型：
--
作者：
K. Yashiro;T. Kitamura;R. Ohtani
通过原子分析阐明了镍晶体解理断裂的判据，以确定微材料强度的评价方法。该分析基于使用 EAM（嵌入原子方法）势的分子动力学模拟。首先，对几种尺寸的模拟单元的镍单晶在横向变形受到约束的[001]方向受拉时进行了模拟。随着簇中原子数量 n 的增加，断裂应变的大小单调减小。当n=4时，解理断裂发生在拉伸应变e=0.263处，该应变小于根据Born分析计算出的晶格失稳临界应变e=0.304。由于各晶格的位移存在波动，当全局应变为0.263时，最大局部应变达到晶格失稳的临界应变。换句话说，活动的自由度带来了断裂应变的减少。在32lnl256中，由于转化而没有发生裂解，这超出了本研究的范围。在 ng500 中，解理从局部晶格开始，当局部应变超过晶格不稳定性时，(111) 面上的剪切变形会在局部晶格处相遇。还对具有Σ5扭曲晶界的镍在横向约束下进行了拉伸模拟。在 e=0.130 处观察到晶粒内发生剪切变形，出现晶粒解理断裂。详细观察表明，晶界处的局部应变远高于晶粒的局部应变，当达到晶格失稳时，晶界处就会发生解理断裂。因此，通过将玻恩分析的晶格不稳定性应用于局部应变，可以定量估计解理断裂的标准。
The criterion for cleavage fracture in nickel crystals was elucidated by the atomic analysis in order to determine the evaluation method of strength of micro-materials. The analysis was based on a molecular dynamics simulation using the EAM (embedded atom method) potential. First, a simulation was conducted on a nickel single crystal with several size of the simulation cell under tension along the [001] direction where the transverse deformation was constraint. As the number of atoms in a cluster, n, increases, the magnitude of strain at fracture decreases monotonically. In n=4, the cleavage fracture takes place at the tensile strain, e=0.263, which is smaller than the critical strain of lattice instability, e=0.304, calculated on the basis of the Born's analysis. Since the displacement of each lattice have fluctuation, the maximum local strain reaches the critical strain of lattice instability when the global strain is 0.263. In order words, the freedom of mobility brings about the reduction of fracture strain. In 32lnl256, the cleavage does not take place due to the transformation which is out of scope in this study. In ng500, the cleavage initiates from the local lattice where the shear deformation on (111) planes meet when the local strain exceeds the lattice instability. A tensile simulation was also carried out for a nickel with Σ5 twist grain boudaries under traverse constraint. Cleavage fracture at a grain bouudary is observed at e=0.130 with shear deformation in a grain. It is revealed from the detail observation that the local strain at grain boundaries are much higher than that of grains and the cleavage fracture at the grain boundary takes place when it reaches the lattice instability. Thus, the criterion for cleavage fracture is quantitatively estimated by applying the lattice instability of Born's analysis to the local strain.