Abstract
Due to the high density of grain boundaries (GBs), nanocrystalline metals possess superior properties, including enhanced strength, work hardening, and fatigue resistance, in comparison to their conventional counterparts. The expectation of GB migration is critical for grain coarsening and GB annihilation in these materials, significantly affecting the polycrystalline network and mechanical behavior. Here, we perform molecular dynamics (MD) simulations on gold (Au) nanocrystals containing multiple parallelly arranged GBs, with a focus on the investigation of annihilation mechanisms of low-angle grain boundaries (LAGBs). It is observed that the shear-coupled motion of LAGBs, consisting of dislocations, gives rise to their preliminary migration with the reduced separation distance between GBs. With subsequent GB motion, the LAGBs encountered with neighboring GBs, and can be annihilated by various mechanisms, including dislocations interpenetration, dislocations interaction, or dislocations absorption, depending on the specific configuration of the neighboring GB. These findings enhance our understanding of GB interactions and shed light on the controlled fabrication of high-performance nanocrystalline metals.
Highlights
We found that the deformation mechanism that governs the annihilation behavior of the low-angle grain boundaries (LAGBs) depends on the initial grain boundaries (GBs) structure
Grain lated to GB annihilation, which is often observed to occur during plastic deformation
It is revealed that LAGB kept a consistent migration rate in the early stage
Summary
Nanocrystalline materials, with a high percentage of GBs, are widely attractive for various engineering applications due to their enhanced strength and ductility with respect to their coarse-grained polycrystalline counterparts [1,2]. Strategies for improving fatigue and corrosion resistance have been proposed [5,6], these materials typically exhibit softening-induced failure, associated with dislocation exhaustion or low-angle grain boundaries (LAGBs) disappearance [1,7,8]. The softening behavior and ductility are strongly related to the deformation mechanisms. GB-mediated deformation mechanisms, such as GB sliding [9,10], GB migration [11], or grain rotation [12], are prevalent and at least partly linked with GB annihilation in metallic nanocrystalline materials [13]. A variety of studies have been focused on the mechanical response of individual GBs [14,15], the nanocrystalline networks, consisting of multiple GBs, may exhibit different kinetic behaviors [16,17], which was rarely studied. The plastic deformation behavior in polycrystals, involving cooperative motion and interactions of parallel GBs or GB junctions [18,19], plays an important role and must be taken into account in practice
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