Zhang Hao, Srolovitz David J, Douglas Jack F, Warren James A
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada T6G 2V4.
Proc Natl Acad Sci U S A. 2009 May 12;106(19):7735-40. doi: 10.1073/pnas.0900227106. Epub 2009 Apr 29.
Polycrystalline materials are composites of crystalline particles or "grains" separated by thin "amorphous" grain boundaries (GBs). Although GBs have been exhaustively investigated at low temperatures, at which these regions are relatively ordered, much less is known about them at higher temperatures, where they exhibit significant mobility and structural disorder and characterization methods are limited. The time and spatial scales accessible to molecular dynamics (MD) simulation are appropriate for investigating the dynamical and structural properties of GBs at elevated temperatures, and we exploit MD to explore basic aspects of GB dynamics as a function of temperature. It has long been hypothesized that GBs have features in common with glass-forming liquids based on the processing characteristics of polycrystalline materials. We find remarkable support for this suggestion, as evidenced by string-like collective atomic motion and transient caging of atomic motion, and a non-Arrhenius GB mobility describing the average rate of large-scale GB displacement.
多晶材料是由被薄的“非晶”晶界（GBs）分隔的晶体颗粒或“晶粒”组成的复合材料。尽管在低温下对晶界进行了详尽的研究，此时这些区域相对有序，但在较高温度下对它们的了解却少得多，在高温下它们表现出显著的迁移率和结构无序，且表征方法有限。分子动力学（MD）模拟可及的时间和空间尺度适合于研究高温下晶界的动力学和结构性质，我们利用MD来探索晶界动力学的基本方面作为温度的函数。长期以来，基于多晶材料的加工特性，人们一直假设晶界具有与玻璃形成液体共同的特征。我们发现这一观点得到了显著支持，如线状集体原子运动和原子运动的瞬态笼蔽现象，以及描述大规模晶界位移平均速率的非阿仑尼乌斯晶界迁移率所证明。
