Sohn Sungwoo, Jung Yeonwoong, Xie Yujun, Osuji Chinedum, Schroers Jan, Cha Judy J
Department of Mechanical Engineering and Materials Science, Yale University, New Haven, Connecticut 06511, USA.
Energy Sciences Institute, Yale West Campus, West Haven, Connecticut 06516, USA.
Nat Commun. 2015 Sep 1;6:8157. doi: 10.1038/ncomms9157.
Atomistic understanding of crystallization in solids is incomplete due to the lack of appropriate materials and direct experimental tools. Metallic glasses possess simple metallic bonds and slow crystallization kinetics, making them suitable to study crystallization. Here, we investigate crystallization of metallic glass-forming liquids by in-situ heating metallic glass nanorods inside a transmission electron microscope. We unveil that the crystallization kinetics is affected by the nanorod diameter. With decreasing diameters, crystallization temperature decreases initially, exhibiting a minimum at a certain diameter, and then rapidly increases below that. This unusual crystallization kinetics is a consequence of multiple competing factors: increase in apparent viscosity, reduced nucleation probability and enhanced heterogeneous nucleation. The first two are verified by slowed grain growth and scatter in crystallization temperature with decreasing diameters. Our findings provide insight into relevant length scales in crystallization of supercooled metallic glasses, thus offering accurate processing conditions for predictable metallic glass nanomolding.
由于缺乏合适的材料和直接的实验工具，对固体结晶的原子层面理解尚不完整。金属玻璃具有简单的金属键和缓慢的结晶动力学，使其适合用于研究结晶过程。在此，我们通过在透射电子显微镜内原位加热金属玻璃纳米棒来研究金属玻璃形成液体的结晶过程。我们发现结晶动力学受纳米棒直径影响。随着直径减小，结晶温度最初降低，在某一特定直径处呈现最小值，然后在该直径以下迅速升高。这种不寻常的结晶动力学是多种竞争因素共同作用的结果：表观粘度增加、成核概率降低以及异质成核增强。前两个因素通过晶粒生长减缓以及结晶温度随直径减小而分散得到验证。我们的研究结果为过冷金属玻璃结晶中的相关长度尺度提供了见解，从而为可预测的金属玻璃纳米成型提供了精确的加工条件。
