The knowledge regarding anisotropic mechanical behaviors in nanoscale body-centered cubic (bcc) metals remains obscure. Herein, we report the orientation-dependent ductility in bcc Mo nanocrystals (NCs), which exhibit poor ductility along [110] direction but possess relatively better ductility along the [001] and [112] orientations. The origin of different deformability can be traced down to the distinct deformation mechanisms: the unexpected crack nucleation and propagation induce premature fractures in [110]-oriented NCs; in contrast, deformation twinning could contribute to the enhanced ductility in [001]-oriented NCs; interestingly, we find the activation of multiple dislocation slips in [112]-oriented NCs with the highest ductility. Further molecular dynamics simulations provide deeper insights into the defect dynamics that are closely interlinked with experimental observations. Our findings advance the basic understanding of orientation-dependent mechanical properties and help to guide endeavors to architecture the microstructures of bcc metals with enhanced ductility.

关于纳米级体心立方 (bcc) 金属的各向异性机械行为的知识仍然模糊不清。在此，我们报告了 bcc Mo 纳米晶体 (NCs) 中取向相关的延展性，其沿 [110] 方向表现出较差的延展性，但沿 [001] 和 [112] 方向具有相对较好的延展性。不同变形能力的起源可以追溯到不同的变形机制：意外的裂纹形核和扩展导致 [110] 取向的 NC 过早断裂；相比之下，形变孪生有助于增强 [001] 取向 NC 的延展性；有趣的是，我们发现在具有最高延展性的 [112] 取向 NC 中激活了多个位错滑移。进一步的分子动力学模拟提供了对与实验观察密切相关的缺陷动力学的更深入了解。我们的研究结果推进了对取向相关机械性能的基本理解，并有助于指导努力构建具有增强延展性的 bcc 金属的微观结构。