Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.
Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
Proc Natl Acad Sci U S A. 2017 Dec 26;114(52):13631-13636. doi: 10.1073/pnas.1708618114. Epub 2017 Dec 11.
Molecular processes of creep in metallic glass thin films are simulated at experimental timescales using a metadynamics-based atomistic method. Space-time evolutions of the atomic strains and nonaffine atom displacements are analyzed to reveal details of the atomic-level deformation and flow processes of amorphous creep in response to stress and thermal activations. From the simulation results, resolved spatially on the nanoscale and temporally over time increments of fractions of a second, we derive a mechanistic explanation of the well-known variation of creep rate with stress. We also construct a deformation map delineating the predominant regimes of diffusional creep at low stress and high temperature and deformational creep at high stress. Our findings validate the relevance of two original models of the mechanisms of amorphous plasticity: one focusing on atomic diffusion via free volume and the other focusing on stress-induced shear deformation. These processes are found to be nonlinearly coupled through dynamically heterogeneous fluctuations that characterize the slow dynamics of systems out of equilibrium.
使用基于元动力学的原子方法，在实验时间尺度上模拟了金属玻璃薄膜的蠕变分子过程。分析原子应变和非仿射原子位移的时空演化，揭示了在应力和热激活下，非晶态蠕变的原子级变形和流动过程的细节。从模拟结果中，我们在纳米尺度上进行了空间分辨，并在几分之一秒的时间增量上进行了时间分辨，得出了对蠕变速率随应力变化的著名规律的力学解释。我们还构建了一个变形图，描绘了在低应力和高温下扩散蠕变的主要状态和在高应力下的变形蠕变。我们的发现验证了两种非晶态塑性机制的原始模型的相关性：一种侧重于通过自由体积的原子扩散，另一种侧重于应力诱导的剪切变形。这些过程通过动态异质波动非线性耦合，这些波动特征是远离平衡系统的慢动力学。
