Effect of crystal orientation on the size effects of nano-scale fcc metals

The present work investigates the dominant mechanisms in the plasticity of nano-sized fcc metallic samples. Molecular dynamics simulations of nanopillar compression show that plasticity always starts with the nucleation of dislocations at the free surface, and the crystal orientation affects the subsequent microstructural evolution. The Schmid factor of leading and trailing partials plays a decisive role in leading to the twinning, or slip deformation. A significant difference is observed in the strength of pillars of the same size with different orientations. The power-law equation exponent is completely dependent on the crystal orientations, and a weak or no size effect is observed in the compression of [100]- and [110]-oriented nanopillars. The observed orientation based behaviour decreases by confining the free surface.

本研究聚焦纳米级面心立方（face-centered cubic, FCC）金属样品的塑性变形主导机制展开探究。纳米柱压缩的分子动力学模拟结果显示，塑性变形始终起源于自由表面处的位错形核，且晶体取向会显著影响后续的微观结构演化过程。先导不全位错与尾随不全位错的施密特因子（Schmid factor）是决定材料发生孪生变形还是滑移变形的核心因素。尺寸相同但取向各异的纳米柱，其力学强度存在显著差异。幂律方程的指数完全由晶体取向决定；针对[100]与[110]取向的纳米柱开展压缩测试时，未观测到明显的尺寸效应，仅存在微弱尺寸效应。通过限制自由表面，上述观测到的取向依赖性行为会被削弱。