Sheng Huaping, Şopu Daniel, Fellner Simon, Eckert Jürgen, Gammer Christoph
Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstraße 12, 8700 Leoben, Austria.
Technische Universität Darmstadt, Institut für Materialwissenschaft, Fachgebiet Materialmodellierung, Otto-Berndt-Straße 3, Darmstadt D-64287, Germany.
Phys Rev Lett. 2022 Jun 17;128(24):245501. doi: 10.1103/PhysRevLett.128.245501.
A deep understanding of the mechanisms controlling shear banding is of fundamental importance for improving the mechanical properties of metallic glasses. Atomistic simulations highlight the importance of nanoscale stresses and strains for shear banding, but corresponding experimental proofs are scarce due to limited characterization techniques. Here, by using precession nanodiffraction mapping in the transmission electron microscope, the atomic density and strain distribution of an individual shear band is quantitatively mapped at 2 nm resolution. We demonstrate that shear bands exhibit density alternation from the atomic scale to the submicron scale and complex strain fields exist, causing shear band segmentation and deflection. The atomic scale density alternation reveals the autocatalytic generation of shear transformation zones, while the density alternation at submicron scale results from the progressive propagation of shear band front and extends to the surrounding matrix, forming oval highly strained regions with density consistently higher (∼0.2%) than the encapsulated shear band segments. Through combination with molecular dynamic simulations, a complete picture for shear band formation and propagation is established.
深入理解控制剪切带形成的机制对于改善金属玻璃的力学性能至关重要。原子模拟突出了纳米尺度应力和应变对剪切带形成的重要性，但由于表征技术有限，相应的实验证据很少。在此，通过在透射电子显微镜中使用进动纳米衍射映射，以2纳米分辨率定量绘制了单个剪切带的原子密度和应变分布。我们证明，剪切带在从原子尺度到亚微米尺度上呈现密度交替，并且存在复杂的应变场，导致剪切带的分割和偏转。原子尺度的密度交替揭示了剪切转变区的自催化生成，而亚微米尺度的密度交替是由剪切带前沿的渐进传播引起的，并延伸到周围基体，形成密度始终比封装的剪切带段高约0.2%的椭圆形高应变区域。通过与分子动力学模拟相结合，建立了剪切带形成和传播的完整图像。
