Molecular Dynamics Study On Plastic Deformation Mechanism Of HCP-Titanium Crystal

In the present work, the plastic deformation of hcp-Ti was investigated via molecular dynamic (MD) simulations, An analytic embedded atomic potential describing the interatomic interaction of hcp-Ti was used. The MD simulations were performed with the LAMMPS software.The elastic constants and the vacancy formation energy of hcp-Ti were evaluated first to identify the validity of the selected potential for hcp-Ti. The theoretical results are in good agreement with experimental findings implying that the selected potential describes the interatomic interactions in hcp-Ti properly and could be used to simulate the plastic deformations of hcp-Ti. Therefore, the tensile and shear deformations of hcp-Ti under different loading conditions at different temperatures were simulated. The main conclusions are summarized below:For the tensile deformation along the [ 0001]direction, the deformation process could be divided into four stages: the elastic, the even plastic, the necking, and the fracture stages. It was shown that the elastic deformation behaviors is independent on the deformation temperatures, while the deformation process was significantly influenced by temperature in the second stage (the plastic deformation).The plastic deformation is mainly contributed by the {1 121}< 1126>twins with the yield stress of 6.92 GPa at 77K. With the increase of the deformation temperature, cr + ar type slips were added to the deformation process. At 300K, only a few cr + ar slip systems were observed and the yield stress was reduced to 6.0 GPa. Further increasing the temperature to 773K, the cr + ar slip became the predominant body contributed to the deformation process and the yield stress decreases to 2.9 GPa.The influence of the loading orientation on the deformation process was also simulated. At 300K, the [ 0001] and the [1 010] directions are the hard and soft orientations with the yield stresses of 6.0 and 1.88 GPa, respectively.The shear deformations on the basal plane (the ( 0001)[1210] slip systems), on the prismatic planes (the (1 010)[1210] slip systems), and on the pyramidal planes (the (1 011)[1210] slip systems) were also simulated. It was found that the loading speed does not affect the elastic deformation, but does affect the plastic deformation process. The yield strength is increase with the increase of the loading speed.