Investigation of Grain Boundary Content on Crack Propagation Behavior of Nanocrystalline Al by Molecular Dynamics Simulation

Abstract

The nanocrystalline metal material has been an investigation hotspot due to its excellent mechanical property. The high content of grain boundaries (GBs) in microstructure is the key factor affecting its fracture behavior during service. Therefore, it is essential to investigate the effect mechanism of nanoscale GB on crack propagation. In this study, four molecular dynamics (MD) models of nanocrystalline aluminum (Al) with different GB contents are established. The results show that the high‐content GBs in polycrystals can increase the toughness and absorb energy, reducing the risk of brittle crack propagation. The presence of GB can reduce the stress concentration of the crack, and the dislocation emission from the crack tip can be absorbed by the front GB. The microstructure with high‐content GBs can actuate more plastic deformation mechanisms such as multiple slips, GB slip, and migration. The region with more GBs can induce a more even deformation of the whole microstructure by means of dislocation emission and GB migration to the region with fewer GBs. The purpose of this study is to provide a rational mechanism reference for the failure of nanocrystalline metal material.

The Effect of Impact Load on the Atomistic Scale Fracture Behavior of Nanocrystalline bcc Iron

“…In this work, a nanocrystalline bcc iron model with average grain diameter of 15 nm was developed by Voronoi method, where the crystal orientation of each grain is random, as shown in Figure 1a. The Voronoi method was shown to produce nanocrystals with grain boundary structures similar to what is expected in polycrystalline material and log-normal grain size distributions similar to what is found in experiments [14,31] and is, therefore, widely used to construct the atomistic models [14][15][16][17][18][19][20][23][24][25][26][27][28][30][31][32]34]. The developed 3 of 11 model has L X × L Y × L Z dimensional size of 60 nm × 60 nm × 30 nm and 9,197,099 iron atoms.…”

“…Nanocrack initiation and propagation were observed to preferably take place at the high-angle grain boundaries perpendicular to the stretching direction [ 29 ]. Different from the fracture behavior of nanocrystalline metals without pre-existing cracks, dislocation and twinning are generated around crack tips besides grain boundary activities during the fracture of nanocrystalline metals with pre-existing cracks [ 30 , 31 , 32 , 33 , 34 ]. With crack propagation in nanocrystalline metals, nanovoids are usually generated at grain boundaries ahead of the crack [ 33 ].…”

“…A further study by the authors showed that these nanovoids are generated by intergranular decohesion that results from the fast Intergranular crack propagation on some cross-sections, and the fracture behavior of cracked nanocrystalline metals is dominated by crack propagation instead of grain boundary activities [ 34 ]. However, the high grain boundary proportion can indeed significantly improve the fracture toughness of nanocrystalline metals [ 32 , 33 , 34 ]. This improvement was found to be attributed to the weakening of intergranular decohesion [ 34 ].…”