Realistic grain boundaries in nanocrystalline thin films

Abstract Molecular dynamics simulations were conducted to investigate the mechanical properties of nanocrystalline aluminum (Al) with grain sizes ranging from 10 to 22 nm. The grain size dependence of the elastic modulus, ultimate tensile strength, and engineering yield strength were analyzed. The experimental in-situ TEM values for modulus and strength are significantly lower than the simulated values using Voronoi tessellation. The grain boundaries (GBs) generated using traditional Voronoi tessellation are almost perfect, containing only geometrically necessary defects, which may not accurately represent the real material structures. To simulate more realistic GBs, we employed a melt–cool method to create initial polycrystalline samples and simulate more realistic GBs. In contrast to Voronoi-generated GBs, melt–cool GBs are less perfect and feature defects such as dislocations and vacancies within the grains. The grain size in the melt–cool method is controlled by the cooling rate, with faster cooling resulting in smaller grain sizes due to decreased recrystallization time. A comparison between the melt–cool and Voronoi tessellation random samples was performed. Although the melt–cool results remain higher than the experimental values, they show an apparent reduction compared to the Voronoi tessellation samples. This suggests that the more realistic grain-boundary structures produced by the melt–cool method better reflect the imperfections found in real materials, offering a closer match to experimental observations.