Introduction of twins into diamond can affect the hardness of diamond, but the underlying microcosmic mechanism remains unknown. Here we have compared the mechanical properties of diamond NPs with three different models, i.e. single crystal nanopillars (SC NPs), twin crystalline nanopillars (TC NPs), and five-fold twinned nanopillars (FT NPs), with diameters from 5 to 30 nm during both tension and compression by molecular dynamics simulations. Our study reveals that the mechanical properties of diamond NPs are closely related to the models of NPs, diameters, and loading modes. The stress–strain responses present significant asymmetry during tension and compression. And the yield strength and strain for FT NPs are always higher than those of TC and SC NPs due to the effect of five-fold twin boundary. The existence of plasticity in diamond NPs is confirmed by the abundance of dislocations after yield strain. The tension–compression asymmetry is also reflected by the differences in dislocation type, dislocation evolution processes, and the fracture shape of the NPs. Moreover, the typical characteristic during tension is that stacking faults are always found following the slip of dislocations, and during compression is that dislocation networks are observed for TC and FT NPs with diameters larger than 20 nm.

在金刚石中引入孪晶会影响金刚石的硬度，但其潜在的微观机制仍不清楚。在这里，我们比较了金刚石纳米颗粒与三种不同模型的机械性能，即直径为 5 至 30 nm 的单晶纳米柱 (SC NP)、双晶纳米柱 (TC NP) 和五重孪晶纳米柱 (FT NP)通过分子动力学模拟在拉伸和压缩过程中。我们的研究表明，金刚石纳米粒子的力学性能与纳米粒子的模型、直径和加载模式密切相关。在拉伸和压缩过程中，应力-应变响应呈现出显着的不对称性。由于五重孪晶界的影响，FT NPs 的屈服强度和应变始终高于 TC 和 SC NPs。屈服应变后的大量位错证实了金刚石纳米粒子中塑性的存在。位错类型、位错演化过程和纳米颗粒断裂形状的差异也反映了拉压不对称性。此外，拉伸过程中的典型特征是位错滑移后总是出现堆垛层错，压缩过程中则观察到直径大于20 nm的TC和FT纳米粒子的位错网络。