Brennhaugen David D E, Georgarakis Konstantinos, Yokoyama Yoshihiko, Nakayama Koji S, Arnberg Lars, Aune Ragnhild E
Department of Materials Science and Engineering, NTNU, Norwegian University of Science and Technology, 7491, Trondheim, Norway.
School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, MK43 0AL, UK.
Sci Rep. 2018 Nov 5;8(1):16317. doi: 10.1038/s41598-018-34681-4.
Despite significant research efforts, the deformation and failure mechanisms of metallic glasses remain not well understood. In the absence of periodic structure, these materials typically deform in highly localized, thin shear bands at ambient and low temperatures. This process usually leads to an abrupt fracture, hindering their wider use in structural applications. The dynamics and temperature effects on the formation and operation of those shear bands have been the focus of long-standing debate. Here, we use a new experimental approach based on localized boiling of liquid nitrogen by the heat generated in the shear bands to monitor the tensile plastic deformation of a bulk metallic glass submerged in a cryogenic bath. With the "nitrogen bubbles heat sensor", we could capture the heat dissipation along the primary shear banding plane and follow the dynamics of the shear band operation. The observation of nitrogen boiling on the surface of the deforming metallic glass gives direct evidence of temperature increase in the shear bands, even at cryogenic temperatures. An acceleration in bubble nucleation towards the end of the apparent plastic deformation suggests a change from steady-state to runaway shear and premonitions the fracture, allowing us to resolve the sequence of deformation and failure events.
尽管进行了大量的研究工作，但金属玻璃的变形和失效机制仍未得到很好的理解。由于缺乏周期性结构，这些材料通常在环境温度和低温下在高度局部化的薄剪切带中发生变形。这个过程通常会导致突然断裂，阻碍它们在结构应用中的更广泛使用。剪切带形成和运行过程中的动力学及温度效应一直是长期争论的焦点。在此，我们采用一种基于剪切带中产生的热量使液氮局部沸腾的新实验方法，来监测浸没在低温浴中的块状金属玻璃的拉伸塑性变形。借助“氮气泡热传感器”，我们能够捕捉沿主剪切带平面的热耗散，并跟踪剪切带运行的动力学过程。在变形金属玻璃表面观察到氮沸腾，直接证明了即使在低温下剪切带中温度也会升高。在明显塑性变形接近尾声时气泡成核加速，表明从稳态剪切转变为失控剪切，并预示着断裂，这使我们能够解析变形和失效事件的顺序。
