Abstract Molecular dynamics simulation is used to identify and quantify the initial plastic deformation mechanisms of gold as a model face-centered cubic (fcc) metal in the nanoindentation process. The coupling effects of crystallographic orientation and internal structural defects on the resulting load distribution at the onset of plasticity are investigated to clarify the anisotropic characteristics of material responses to crystallographic orientation. Homogenous defect nucleation is studied by correlating the indentation force-displacement curve with the instantaneous defect structure. In the absence of pre-existing defects, nanoindentation deformation is dominated by nucleation of Shockley partial dislocations regardless of crystal orientation. Various forms of dislocation propagation are observed in different crystal orientations. The elastic-plastic transition point appears later for the [111]-oriented surface than the ones for [001]-, and [011]-oriented surfaces. The relation of hardening and dislocation density shows that conventional Taylor hardening captures the plasticity after a certain amount of indentation depth in the presence of enough dislocation density. The crystal's sensitivity to the presence of internal structural faults is strongly dependent on the crystallographic orientation. Nanoindentation simulations in the presence of sessile dislocation loops in the structure show that the most significant reduction in the pop-in load happens for the [111] oriented sample. Our simulations suggest that the indentation near a defect can lead to small, subcritical events that lead to a smoother "pop- in" at the onset of plasticity. Since internal defects in materials are nearly inevitable, a defect-based model can be useful to understand the stochastic pop- in loads in nanoindentation tests.

中文翻译：

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纳米压痕过程中晶体各向异性和预先存在的缺陷对 Fcc 单晶初始塑性的影响

摘要 分子动力学模拟用于识别和量化金作为模型面心立方 (fcc) 金属在纳米压痕过程中的初始塑性变形机制。研究了结晶取向和内部结构缺陷对塑性开始时产生的载荷分布的耦合效应，以阐明材料对结晶取向响应的各向异性特征。通过将压痕力-位移曲线与瞬时缺陷结构相关联来研究均匀缺陷成核。在没有预先存在的缺陷的情况下，无论晶体取向如何，纳米压痕变形都由肖克利部分位错的成核支配。在不同的晶体取向中观察到各种形式的位错传播。[111]取向表面的弹塑性转变点比[001]-和[011]取向表面的弹塑性转变点出现得晚。硬化与位错密度的关系表明，在存在足够位错密度的情况下，常规泰勒硬化在一定量的压痕深度后捕获塑性。晶体对内部结构断层存在的敏感性很大程度上取决于晶体取向。在结构中存在固着位错环的情况下的纳米压痕模拟表明，[111] 取向的样品发生了弹出载荷的最显着降低。我们的模拟表明，缺陷附近的压痕会导致较小的亚临界事件，从而在塑性开始时导致更平滑的“弹出”。