Evolution of solidification defects in deformation of nano-polycrystalline aluminum

Abstract

Formation of solidification defects and their evolution in uniaxial tensile deformation of solidified polycrystalline aluminum (Al) were investigated by molecular dynamics (MD) simulations. First, solidification process was simulated both isothermally and with different quench rates. At the initial stages of nucleation, coherent twin boundaries and/or fivefold twins formed depending on the quench rate or the undercooling temperature. The solidified polycrystalline Al consisted of randomly distributed grains, twin boundaries, and vacancies. Evolution of nanostructures and defects in uniaxial tensile deformation of solidified Al under different temperatures and strain rates were studied. Void formation at grain boundaries and detwinning of preexisting solidification twins and deformation twins were observed during the uniaxial deformation. It was also found that the temperature of deformation has a stronger effect than the applied strain rate on the strength of solidified samples. For solidified cases with grain sizes lower than 10 nm, the yield strength and Young’s modulus increased with increasing grain size, indicating an inverse Hall-Petch relationship. Similar to experimental data, MD simulations showed a higher yield strength for single crystal Al and a large plastic deformation for polycrystalline Al.