Pile-up transmission and reflection of topological defects at grain boundaries in colloidal crystals

Xin Cao,Nicola Manini,Clemens Bechinger,Andrea Vanossi,Emanuele Panizon,Erio Tosatti

doi:10.1038/s41467-020-16870-w

Abstract

Crystalline solids typically contain large amounts of defects such as dislocations and interstitials. How they travel across grain boundaries (GBs) under external stress is crucial to understand the mechanical properties of polycrystalline materials. Here, we experimentally and theoretically investigate with single-particle resolution how the atomic structure of GBs affects the dynamics of interstitial defects driven across monolayer colloidal polycrystals. Owing to the complex inherent GB structure, we observe a rich dynamical behavior of defects near GBs. Below a critical driving force defects cannot cross GBs, resulting in their accumulation near these locations. Under certain conditions, defects are reflected at GBs, leading to their enrichment at specific regions within polycrystals. The channeling of defects within samples of specifically-designed GB structures opens up the possibility to design novel materials that are able to confine the spread of damage to certain regions.

Highlights

Crystalline solids typically contain large amounts of defects such as dislocations and interstitials
The plastic deformation of crystalline materials typically takes place via the elementary flow of topological defects such as dislocations and interstitials[1,2,3,4,5]. The dynamics of such defects under external stress is of central importance for understanding the mechanical behavior of crystals. In contrast to their rapid propagation within single crystals, the motion of the defects is severely influenced by grain boundaries (GBs) in polycrystals, leading to a mechanical reinforcement of polycrystalline materials which increases with the inverse average grain size[6,7,8,9,10]
Various techniques have been developed to process materials in order to optimize their properties regarding specific technological applications. Many of these methods are based on empirical findings rather than on a detailed microscopic understanding how defects affect the material properties. This lack of knowledge is partially due to the difficulty to observe the atomistic kinetics of defects moving across GBs with single-particle resolution and in real time

Summary

Introduction

Crystalline solids typically contain large amounts of defects such as dislocations and interstitials. The dynamics of such defects under external stress is of central importance for understanding the mechanical behavior of crystals In contrast to their rapid propagation within single crystals, the motion of the defects is severely influenced by grain boundaries (GBs) in polycrystals, leading to a mechanical reinforcement of polycrystalline materials which increases with the inverse average grain size[6,7,8,9,10]. This empirically observed Hall–Petch relation has been explained with the GB-assisted accumulation of defects, which leads to an increasing yield strength[9,10]. Their confinement to specific regions of the polycrystalline sample suggests the fabrication of polycrystalline monolayers with directiondependent mechanical properties

Methods

Results

Conclusion