Molecular dynamics simulations of polycrystalline titanium mechanical properties: Grain size effect

In this study, the effect of grain size (d) on the deformation mechanism of polycrystalline titanium is investigated using molecular dynamics simulations. The temperature was 300 K, the strain rate was 5×108s−1, the loading mode was tensile, and the grain size ranged from 4.99 to 39.91 nm. The results show that, as the grain size increases, the peak stress initially increases and then decreases. The maximum peak stress occurs when the grain size d is 19.96 nm. When d is > 19.96 nm, peak stress and d follows Hall-Petch. When d is < 19.96 nm, it follows inverse Hall-Petch. The modulus of elasticity increases with increasing grain size; as the strain proceeds, the dislocation density decreases and subsequently increases, with the lowest dislocation density at the yield point. As grain size increases, dislocation density rises while the conversion rate of hexagonal close-packed (HCP) atoms decreases. In the elastic phase, the structure of each atom remains constant. In the plastic phase, when d is > 9.98 nm, the HCP structure decreases and the other structure increases; when d is < 9.98 nm, the HCP structure increases and the other structure decreases. When d is > 19.96 nm, dislocations dominate the deformation and no grain growth occurs during stretching; when d is < 19.96 nm, grain boundary sliding and grain boundary rotation dominate the deformation, and grain growth can be observed during stretching.