An atomistic simulation on the tensile and compressive deformation mechanisms of nano-polycrystalline Ti

Abstract

In the present work, the molecular dynamics (MD) simulation is employed to investigate the tensile and compressive deformation behavior of nano-polycrystalline Ti with the mean grain size of 6.8 nm. The deformation behaviors reveal that the nano-polycrystalline Ti has different deformation mechanisms under the tension or compression. When the nano-polycrystalline Ti is applied tensile loading, the dislocation density quantification shows that there is no significant new dislocation appearing before the tensile strain reaches the failure strain (ε = 0.12). Instead, a 25° difference in the grain boundary misorientation angle between two grains was observed, which indicates that the grain boundary rotation and sliding are appeared to dominate the tensile deformation process of nano-polycrystalline Ti. When the nano-polycrystalline Ti is applied compressive loading, the compressive stress increases linearly with the increase in compressive strain before the compressive strain arrives 0.075. Once the compressive strain exceeds 0.075, the nano-polycrystalline Ti enters the plastic deformation stage. In this case, the hcp-Ti atoms near the grain boundary were firstly transformed to the bcc-Ti atoms and then the hcp-Ti atoms within the grain transforms into the bcc-Ti atoms with the increase in compressive strain, which indicates that the plastic deformation of nano-polycrystalline Ti during the compression is dominated by the phase transformation from hcp-Ti to bcc-Ti. In addition, it is found that the deformation behaviors of nano-polycrystalline Ti are sensitive to strain rate and temperature. The present work could be beneficial for the design and fabrication of nano-polycrystalline Ti alloys with excellent mechanical properties.