Abstract
It is an universal phenomenon that the dislocations are produced in metal plastic deformation, which will has a potential value in fundamental research field for metal strengthening and toughening if its evolution characteristics and laws are investigated. Therefore, this behavior of movable dislocation for metal Al is studied by atomic simulation, and the microscopic mechanism of metal strengthening and toughening are also revealed through studying the interaction between movable dislocation induced by nano-indentation and twin boundary. Furthermore, the movable dislocation features, and dislocation density, and hardness, and adhesive effect are analyzed, and the comparison between the single boundary height and the multilayer twin boundary height is conducted. It is found that the plastic deformation of aluminum mental can be dominant by coordinating the amorphous generation and hexagonal close-packed structure under high speed deformation. In the nano-indentation process, the twin boundary has two obvious effects on movable dislocation of moving changes: one is to hinder the dislocation from migrating, the other is to induce dislocation to produce a cell, which result in the dislocation entanglement and generation of cross slip, it is also the main reason why the metal has excellent mechanical properties of strengthening and toughening features. These results demonstrate that the local non-contact region on the surface of Al substrate can induce atomic mismatch spots to appear during loading, and when the distance between the twin boundary and the upper surface of the substrate decreases, the effects of dislocation winding and dislocation slip become more obvious, and the anti-adhesion effect also decreases. In addition, the twin boundary is treated as the propagation of plastic ring source in the dislocation emission process when substrate is continuously loaded. These results provide an important theoretical source for improving metal strengthening and toughening effect.
Highlights
Three dimensional physical model for single crystal aluminum and twin aluminum substrates constructed by atomic simulation method
3) (Engineering Training Center, Quzhou University, Quzhou 324000, China) ( Received 14 July 2021; revised manuscript received 14 September 2021 )
Summary
图 1 单晶 Al 和孪晶 Al 的纳米压痕三维原子物理模型 Fig. 1. Three dimensional physical model for single crystal aluminum and twin aluminum substrates constructed by atomic simulation method. 本文物理模型皆在 NVE 系综完成 牛顿方程迭代, 模拟时间步长取 1 fs[28]. 其中, 绿色原子表示面心立方结构 (FCC), 红 色原子表示密排六方结构 (HCP), 蓝色原子表示 体心立方结构 (BCC), 白色原子表示其他结构 (other), 即非晶. 在孪晶建模时, 可看出孪晶 Al 中 只有 HCP 界面结构, 表示孪晶界面存在 (见图 1(b)). 图 2 为探针下压位移 X = 10 nm 的单晶 Al 和孪晶 Al 受载变形行为, 为了解其变形特性, 采 用中心对称参数法 (CSP) 识别基底被压表面原子 失配程度. 图 3(a)—(d) 为探针下压位移 X = 10 nm 的 单晶 Al 和孪晶 Al 的上表面剪切变形特性. 此外, 观察图 3(e)—(h) 的基底内结构演化知, 单 晶 Al 塑性变形扩展程度最深, 孪晶 Al 基底的扩展 程度与孪晶界距离基底上表面距离 d 有直接关联, 且孪晶界对位错表现出明显的阻碍作用, 以致可动 位错不断塞积于孪晶界与上表面非晶界的狭窄通 道, 最后在紧密接触区形成明显的位错胞三维空间 结构, 该空间结构内存有大量位错类型. 基底高速 受载时, 应力会驱动紧密接触区产生大量非晶结构 和密排六方结构 (见图 3 和图 4 所示), 表明高速变 形情况下, 金属的非晶产生和密排六方 HCP 结构 出现会协同主导 Al 基塑性变形 出 60°和 120°, 且面心金属受载时的内部变形出现 可动位错不断产生滑移 (见图 3(e)—(h)). 另外, 面 心金属会通过此滑移方式释放受载产生的应力集 中, 起到抵抗变形作用, 以此实现金属韧性增强. 此外, 观察图 3(e)—(h) 的基底内结构演化知, 单 晶 Al 塑性变形扩展程度最深, 孪晶 Al 基底的扩展 程度与孪晶界距离基底上表面距离 d 有直接关联, 且孪晶界对位错表现出明显的阻碍作用, 以致可动 位错不断塞积于孪晶界与上表面非晶界的狭窄通 道, 最后在紧密接触区形成明显的位错胞三维空间 结构, 该空间结构内存有大量位错类型. 基底高速 受载时, 应力会驱动紧密接触区产生大量非晶结构 和密排六方结构 (见图 3 和图 4 所示), 表明高速变 形情况下, 金属的非晶产生和密排六方 HCP 结构 出现会协同主导 Al 基塑性变形
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