Atomistic processes of diffusion-induced unusual compression fracture in metallic nanocrystals

Local thickening, resulting from displacive or diffusive mechanisms individually, is frequently observed in nanoscale metals during compression. However, it is not fully understood how a coupled displacive-diffusive mechanism would mediate the compressive deformation of metallic nanocrystal. Here, by conducting <i>in situ</i> atomic-scale compression tests, we find that, instead of local thickening commonly reported thus far, abnormal thinning events consecutively occur in silver nanocrystals, where preexisting dislocations and crystal slip serve as stimuli to activate surface atom diffusion. Below a critical width, tensile-fracture-like failure occurs in the silver nanocrystals. This work sheds light on atomic-scale diffusion-mediated compressive deformation of metallic nanocrystal. <i>In situ</i> atomic-scale compression tests reveal that surface atom diffusion mediates consecutive thinning events and ultimate compression fracture in silver nanocrystals.

单独由位移机制或扩散机制所导致的局部增厚现象，在纳米金属的压缩过程中频繁被观测到。然而，耦合位移-扩散机制如何介导金属纳米晶的压缩变形，目前尚未得到充分阐明。本文通过开展原位原子尺度压缩试验，发现银纳米晶中并未出现此前普遍报道的局部增厚现象，反而接连发生异常变薄事件——预先存在的位错与晶体滑移作为触发因素，激活了表面原子扩散过程。当尺寸低于临界宽度时，银纳米晶会发生类拉伸断裂失效。本研究揭示了金属纳米晶原子尺度扩散介导的压缩变形机制。原位原子尺度压缩试验表明，表面原子扩散介导了银纳米晶中连续的变薄事件与最终的压缩断裂。